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1
Süer, Assiye. "LES Simulation of Hot-wire Anemometers." Thesis, Luleå tekniska universitet, Institutionen för system- och rymdteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-62264.
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Hot wire anemometers have been used in several wind velocity sensors deployed in Mars. They are based in keeping the temperature of a surface at a constant value, above the ambient. This is done by means of a heater controlled with an electronic system. The cooling rate of each point at the sensor surface can be used to calculate the wind velocity and direction. However, due to turbulent fluctuations, the cooling rate is not constant even in the case of constant velocity. Moreover, RANS simulations cannot estimate such fluctuations as they only provide an estimation of the averaged flow field. The goal of this work has been to estimate such fluctuations and the e↵ect they might have on the sensor readings. To do so, the turbulent cooling rate (Nusselt number) of a sensor with a generic shape, under the typical conditions to be find in Mars, has been simulated using high performance LES (Large Eddy Simulation) simulations and compared with RANS and URANS simulations.
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Seidu, Iddrisu. "Analytical and Numerical Validation of Nozzle Spray Measurement Data Obtained from a Newly Developed Production System." Cleveland State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=csu1446504762.
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Búran, Martin. "Žárový anemometr." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2019. http://www.nusl.cz/ntk/nusl-399575.
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The project deals with the effect of the airflow and temperature on the gold wirebond due to possible application in hot-wire anemometry. Theoretical fundamentals of wirebonding and hot-air anemometry are included in the text. From the area of anemometry, there is also a detailed description of measurement principles, areas of application and measuring instruments. The practical part of the text deals with design of the experimental sensor for hot-wire anemometry with use of the gold wirebond, including also the verification of the sensor's properties.
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Camano, Schettini Edith Beatriz. "Étude expérimentale des jets coaxiaux avec différences de densité." Grenoble INPG, 1996. http://www.theses.fr/1996INPG0066.
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Les jets coaxiaux ont plusieurs applications pratiques, principalement dans le domaine de la combustion, et particulierement pour les injecteurs de moteurs de fusees, ou l'oxygene liquide (lourd et a faible vitesse) est injecte dans la buse centrale, et l'hydrogene gazeux (tres leger et tres rapide) est injecte dans la buse annulaire. Afin de nous rapprocher de ce type d'ecoulement, nous avons mene des recherches sur les jets coaxiaux, monophasiques, isothermes, avec fortes differences de densite. Les gaz utilises ont ete de l'air, de l'helium et du sf#6. Nous avons mis au point une instrumentation adaptee aux ecoulements heterogenes, basee sur la thermo-anemometrie. Une sonde dite de sillage nous a permis d'identifier les regions de recirculation. Les champs de densite ont ete obtenus avec une sonde de type aspirante. Les parametres les plus importants, pour ce type de jet, sont le rapport de vitesse, r#v, et le rapport de densite, s, qui ont ete regroupes dans le rapport des flux de quantite de mouvement, m. Les jets coaxiaux presentent deux regimes d'ecoulements bien definis: l'un recirculant et l'autre de cone potentiel, qui peuvent etre distingues a partir d'une valeur critique de ce parametre, m#c, pour chaque couple de gaz. M#c vaut 40 a 50 pour l'ensemble des gaz utilises, sauf pour le couple helium-sf#6, pour laquelle m#c 80 - 100. Une bulle de recirculation se developpe avec une frontiere aval pratiquement independante de m (0,9 a 1,2 d#i suivant les differents cas etudies) et une frontiere amont qui remonte vers la buse lorsque m augmente. Les resultats concernant la longueur du cone potentiel se regroupent assez bien en fonction de m, mais il subsiste une legere influence de la densite ; un raccourcissement est constate lorsque le gaz injecte dans la buse annulaire est plus leger que le gaz du jet central. Contrairement a la tendance prevue, le couple helium-sf#6 donne un entrainement plus faible que pour les autres gaz
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Neumeister, William D. "Hot-Wire Anemometer for the Boundary Layer Data System." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/830.
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Hot-wire anemometry has been routinely employed for laboratory measurements of turbulence for decades. This thesis presents a hot-wire anemometer suitable for use with the Boundary Layer Data System (BLDS). BLDS provides a unique platform for in- flight measurements because of its small, self-contained, robust design and flexible architecture. Addition of a hot-wire anemometer would provide BLDS with a sensor that could directly measure flow velocity fluctuations caused by turbulence. Hot-wires are commonly operated in constant-temperature mode for high frequency response, but require a carefully tuned bridge. The constant-voltage anemometer (CVA) uses a simple op-amp circuit to improve frequency response over constant-current operation. Due to its balance between ease of operation and performance, a CVA system built for this project was tested with a 3.8 micron diameter, platinum-coated tungsten probe. The CVA was calibrated in a steady jet and a power-law curve fit accurately represented the calibration data. The CVA successfully measured velocity fluctuations in a turbulent jet, as well as in laminar and tripped turbulent boundary layers over a flat plate in a 110 MPH wind tunnel. CVA frequency response was investigated using a thermal/electrical model, controlled oscillation in a steady flow, and with a square wave test; these three methods showed agreement. The CVA is selected for integration with BLDS.
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Soudani, Azeddine. "Application des réseaux de neurones aux mesures simultanées en écoulement turbulent." Grenoble INPG, 1996. http://www.theses.fr/1996INPG0180.
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Une nouvelle methode pour le depouillement des etalonnages des sondes thermo-anemometriques a fil et film chauds, est employee pour les mesures simultanees de vitesses et de densite dans un ecoulement turbulent. La methode est fondee sur une application specifique des reseaux de neurones. Il s'agit de reseaux du type perceptron multicouches ayant pour regle d'apprentissage, l'algorithme de la retropogation d'erreur. Cette methode auto-adaptative a ete appliquee aux etalonnages de deux types de sonde. Elle donne une meilleure precision sur la reduction des etalonnages que les methodes classiques d'ajustement utilisant les regressions polynomiales. Les resultats obtenus par ce type de reseaux de neurones, pour le depouillement des mesures doubles simultanees, sont tres satisfaisants. Les comparaisons effectuees montre que la methode semble plus precise que celles utilisees habituellement. Les effets des differences de densite importantes, sur la structure fine de la turbulence parietale sont etudies a partir des donnees experimentales, obtenues dans une soufflerie a recirculation. Ces differences de densite, dans la couche limite, sont produites par injection tangentielle d'air ou d'helium dans un melange air-helium. Les resultats d'analyse des donnees experimentales des fluctuations de vitesse et de densite montrent que, le developpement spatio-temporel du flux massique turbulent longitudinal est fortement lie aux gradients de densite. La structure fine du flux massique turbulent ne depend pas implicitement de la difference de densite mais plutot de ses gradients. L'analyse conditionnelle dans les quadrants montre que l'injection d'helium, dans la couche limite, engendre des ejections plus violentes que dans le cas d'une injection d'air. Ce resultat est confirme par l'analyse statistique qui revele la contribution importante des ejections au flux massique turbulent
7
Lazzarini, Lorenzo. "Numerical modeling of a hot-wire anemometer in turbulent flows." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/17957/.
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The present thesis deals with the numerical modeling of an hot wire anemometer inside a turbulent channel flow at Re_tau=180 with heat transfer. There are two main approaches when studying turbulence: one could follow an experimental path or a numerical approach could be pursued. Experiments showed some issues when measuring turbulence with hot wire anemometry, spatial and temporal filtering are two examples of such problems. In the present work, numerical simulations were performed in order to validate a code that model a hot-wire probe inside a turbulent channel flow.
Direct Numerical Simulation (DNS) solved through a spectral code were used to build such model, due to their high level of precision and resolution. A validation process was performed starting from Kim & Moin experience and Kasagi studies related to DNS of channel flow with passive scalar. Following this path we implement inside our code a line source of heat mimicking the hot-wire behaviour. While simulations were running we collected statistics in order to know the values regarding turbulence fluctuations throughout the entire channel.
We obtained a new data-set coming from DNS and spectral element method with not only just a passive scalar but a precise implementation of an hot-wire probe.
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Beirutty, Mohammad Hussein. "Development of a hot-wire measurement technique for moderate intensity three-dimensional flows /." Thesis, Connect to this title online; UW restricted, 1987. http://hdl.handle.net/1773/7074.
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Lanspeary, Peter V. "Establishing very low speed, disturbance-free flow for anemometry in turbulent boundary layers." Title page, contents and summary only, 1997. http://web4.library.adelaide.edu.au/theses/09PH/09phl295.pdf.
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Thesis (Ph. D.)--University of Adelaide, Dept. of Mechanical Engineering, 1998?System requirements for accompanying computer disks: IBM-compatible computer. Other requirements: Fortran and/or C Compiler. Includes bibliographical references (p. 315-330).
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Dinsdale, Steven. "The development and application of hot-wire anemometry to I.C. engines." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305748.
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Li, Hon Yee. "Constant Voltage Hot-Wire Anemometry for the Boundary Layer Data System." DigitalCommons@CalPoly, 2013. https://digitalcommons.calpoly.edu/theses/1105.
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To continue the development of the Boundary Layer Data System (BLDS), a constant voltage hot-wire anemometer (CVA) is implemented into the BLDS for flight-testing. The hot-wire anemometer was chosen as an alternative to the traditional pressure probe because of the ability to measure both average velocity and fluctuating velocity within the boundary layer. Previous work done on the benchtop has led to the design of miniaturization, flight-capable hardware for the BLDS. The next step in the development of the BLDS – CVA calls for quantifying the accuracy of the boundary layer measurements measured by the CVA system. To do this, numerous turbulent boundary layer velocity and fluctuating velocity profiles were taken on a flat-plate at various speeds within the Cal Poly 2x2 wind tunnel with both the traditional pressure probe and the CVA. These test resulted showed agreement between the hot-wire and pressure probe data. Once this was completed the new CVA hardware was tested along with the new software that was written for the BLDS – CVA. In addition, due to the limited memory space onboard the BLDS – CVA, an approximation had to be developed to convert the average voltage data from the BLDS – CVA to the average velocity data due to the non-linear calibration function. The approximation developed was able to match the exact values from a traditional calibration. Lastly, due to the inability to perform a laboratory calibration of the hot-wire at altitude, where the conditions differ significantly from the ground conditions, a new procedure for hot-wire calibration was developed. The method developed was validated through wind tunnel testing and a computer thermal/electric model. With the completion of this work, the BLDS – CVA is ready for flight-testing.
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Ondore, Faustin Alloise. "An experimental and numerical investigation of turbulent flows in a square duct with 90deg bend." Thesis, Brunel University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286693.
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Whitney, Christopher Francis. "Heat transfer characteristics of slot jet impingement." Thesis, Nottingham Trent University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320599.
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Watson, Michael. "Measurements using a triaxial hot-wire anemometer in channnels containing helically ribbed pins." Thesis, Open University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328249.
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Canter, Caleb A. "Hot-Wire Anemometer Measurements of Atmospheric Surface Layer Turbulence via Unmanned Aerial Vehicle." UKnowledge, 2019. https://uknowledge.uky.edu/me_etds/139.
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An instrumented unmanned aerial vehicle (UAV) was developed and employed to observe the full range of turbulent motions that exist within the inertial subrange of atmospheric surface layer turbulence. The UAV was host to a suite of pressure, temperature, humidity, and wind sensors which provide the necessary data to calculate the variety of turbulent statistics that characterize the flow. Flight experiments were performed with this aircraft, consisting of a large square pattern at an altitude of 100 m above ground level. In order to capture the largest turbulent scales it was necessary to maximize the size of the square pattern. The smallest turbulent scales, on the other hand, were measured through the use of a fast response constant temperature hot wire anemometer. The results demonstrates that the UAV system is capable of directly measuring the full inertial subrange of the atmospheric surface layer with high resolution and allowing for the turbulence dissipation rate to be calculated directly.
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Saez, Manuel. "Contribution à l'étude expérimentale de la convection mixte." Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10197.
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Les travaux presentes dans cette these concernent plusieurs aspects d'un programme experimental dont l'objectif est de fournir des donnees pour la validation et l'aide au developpement des modeles de turbulence dans les codes de calculs thermohydrauliques, pour des situations d'etudes allant de la convection forcee a la convection naturelle (nombre de reynolds : 10#3 a 6. 10#4 et nombre de richardson : 10#-#4 a 1). La configuration etudiee est celle d'un ecoulement ascendant d'air entre deux parois verticales a temperatures differentes. Dans le premier chapitre, nous avons extrait de la bibliographie les donnees disponibles pour les ecoulements en canal plan et en couches limites. Le second chapitre presente les caracteristiques de l'installation et du banc d'etalonnage ainsi que la methode de positionnement des sondes pour atteindre la precision de l'ordre du centieme de millimetre requise en paroi. Le troisieme chapitre presente les techniques de mesure mises en uvre ainsi que les developpements apportes a certaines techniques experimentales. Les lois classiques de refroidissement d'un fil chaud sont verifiees jusqu'a des vitesses de quelques centimetres par seconde. En prealable aux resultats de convection forcee et mixte, nous presentons une methode que nous avons developpee pour permettre la realisation de mesures tres proches de la paroi. Notre procedure de correction des mesures est elaboree grace a une evaluation numerique de l'erreur basee sur une modelisation thermohydraulique. Les mesures en convection forcee ont permis de retrouver les lois de paroi. En convection mixte, les profils moyens de vitesse et de temperature, obtenus avec une sonde a fil chaud simple, montrent nettement l'effet des forces de volume sur le champ de vitesses. Concernant les lois de paroi en convection mixte, une piste proposee consiste a trouver des lois algebriques qui prennent en compte les effets des forces de volume, a partir de la base de donnees issue de notre experience en convection mixte. La recherche de l'existence de lois de paroi en situation de convection mixte montre que les representations des profils dimensionnels de vitesse et de temperature moyenne peut se faire suivant des lois du meme type que celles de convection forcee avec des constantes d'integration qui sont des fonctions lineaires du nombre de richardson.
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Alex, Alvisi, and Perez Adalberto. "Analysis of wall-mounted hot-wire probes." Thesis, KTH, Strömningsmekanik och Teknisk Akustik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-289564.
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Flush-mounted cavity hot-wire probes have been around since two decades, but have typically not been applied as often compared to the traditional wall hot-wires mounted several wire diameters above the surface. While the latter suffer from heat conduction from the hot wire to the substrate in particular when used in air flows, the former is belived to significantly enhance the frequency response of the sensor. The recent work using a cavity hotwire by Gubian et al. (2019) came to the surprising conclusion that the magnitute of the fluctuating wall-shear stress τ+w,rms reaches an asymptotic value of 0.44 beyond the friction Reynolds number Re τ ∼ 600. In an effort to explain this result, which is at odds with the majority of the literature, the present work combines direct numerical simulations (DNS) of a turbulent channel flow with a cavity modelled using the immersed boundary method, as well as an experimental replication of the study of Gubian et al. in a turbulent boundary layer to explain how the contradicting results could have been obtained. It is shown that the measurements of the mentioned study can be replicated qualitatively as a result of measurement problems. We will present why cavity hot-wire probes should neither be used for quantitative nor qualitative measurements of wall-bounded flows, and that several experimental short-comings can interact to sometimes falsely yield seemingly correct results.
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Li, Datian. "Visualisaton of dynamic flow processes using a novel pulsed multi-element hot-wire anemometer." Thesis, Robert Gordon University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282866.
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Murphy, Ryan. "Development of an Autonomous Single-Point Calibration for a Constant Voltage Hot-Wire Anemometer." DigitalCommons@CalPoly, 2015. https://digitalcommons.calpoly.edu/theses/1357.
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Traditionally, the measurement of turbulence has been conducted using hot-wire anemometry. This thesis presents the implementation of a constant voltage hot-wire anemometer for use with the Boundary Layer Data System (BLDS). A hot-wire calibration apparatus has been developed that is capable of operation inside a vacuum chamber and flow speeds up to 50 m/s. Hot-wires operated with a constant-voltage anemometer (CVA) were calibrated at absolute static pressures down to 26 kPa. A thermal/electrical model for a hot-wire and the CVA circuit successfully predicted the measured CVA output voltage trend at reduced pressure environments; however, better results were obtained when the Nusselt number was increased. A calibration approach that required only one measured flow speed was developed to allow autonomous calibrations of a CVA hot-wire. The single-point calibration approach was evaluated through comparison with the experimental data from the vacuum chamber over a range of 14-50 m/s and at pressures from 26 to 100 kPa. The thermal-electrical model was used to make predictions of CVA output voltage and the corresponding flow speed for conditions that could not be replicated within a laboratory. The first set of predictions were made for conditions from 7.5 to 100 kPa, at a constant temperature of 25⁰C, within a flight speed range of 40 to 150 m/s. Single-point calibrations were developed from these predictions. Additionally, the thermal-electrical model was used to predict hot-wire response for a change in temperature of 25⁰C at 26 kPa and the single-point calibration developed for the pressure range 7.5 to 100 kPa was tested for its ability to adjust. The temperature variation at a single pressure of 26 kPa proved that the single-point function was capable of adapting to off-standard temperatures with the largest deviations of +/- 7% in the mid-range velocities. With a temperature drop, the deviations were below 5%. The second set of thermal-electrical predictions involved conditions for altitude from 0 to 18 km at flow speeds from 40 to 150 m/s. A single-point calibration was developed for altitude conditions. Furthermore, to test the single-point calibration the thermal-electrical model was used to predict hot-re response for a temperature variation of 25⁰C at 18 km. The single-point calibration developed for altitude proved that it was capable of adjusting to a temperature variation of 25⁰C with maximum deviations of about 5% at mid-range velocities. It is proposed that the single-point calibration approach could be employed for CVA measurements with the Boundary Layer Data System (BLDS) to allow hot-wire data to be acquired autonomously during flight tests.
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Woyciekoski, Marcos Leandro. "Estudo do fenômeno da biestabilidade em cilindros finitos com média razão de aspecto." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/182270.
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Este trabalho apresenta um estudo experimental a respeito do fenômeno da biestabilidade em cilindros finitos com média razão de aspecto. Na biestabilidade, há uma esteira estreita a jusante de um dos cilindros e uma esteira larga a jusante do outro. Pode estar presente em muitas situações práticas da engenharia dependendo da distância entre os cilindros. Em cilindros finitos ainda é pouco compreendida e explorada. Para compreender o mecanismo do desprendimento de vórtices, são estudados o escoamento em torno de um único cilindro finito, com cilindros de diâmetros entre 25 e 60 mm e razão de aspecto entre 1 e 4 e após, o escoamento em torno de dois cilindros finitos dispostos lado a lado, com cilindros de diâmetros entre 25 e 32 mm e razão de aspecto entre 3 e 4. A técnica experimental aplicada consiste na medição das flutuações de velocidade em canal aerodinâmico, utilizando a técnica de anemometria de fio quente e na visualização do escoamento no mesmo canal, mantendo os parâmetros, utilizando gelo seco e laser. Além disso, foi realizada a visualização do escoamento em canal hidráulico com as mesmas dimensões do canal aerodinâmico, utilizando injeção de tinta através de agulhas. Para o estudo foram utilizados Re=2,00×104 para um cilindro finito e 3,86×103 ≤ Re ≤ 4,81×104 para cilindros finitos dispostos lado a lado. Os dados medidos em canal aerodinâmico são tratados através de ferramentas estatísticas, espectrais e de ondaletas, e os resultados das visualizações do escoamento são apresentados por meio de imagens obtidas das filmagens realizadas com uma câmera digital. Além disso, os vídeos são tratados com softwares de edição de vídeo e com ferramentas estatísticas. Os resultados confirmam a existência do fenômeno da biestabilidade para dois cilindros finitos dispostos lado a lado, que é um dos objetivos do estudo, nas três posições estudadas. A técnica de visualização de escoamento reforça a interpretação dos resultados obtidos através da técnica de anemometria de fio quente. Neste trabalho é considerada a existência de três escoamentos concomitantes: o escoamento ascendente, caracterizado pela estrutura de vórtices na base; o escoamento descendente, caracterizado pela estrutura de vórtices no topo; e o aqui chamado escoamento principal, caracterizado pelo desprendimento de vórtices a meia altura dos cilindros.This work presents an experimental study on the bistability phenomenon in finite cylinders with a mid-aspect ratio. In the bistability phenomenon the flow to form two wakes behind the cylinders, a large wake behind a cylinder and a narrow wake after another. It can be present in many practical engineering situations depending on the distance between the cylinders. In finite cylinders, it is still poorly understood and explored. To understand the vortex shedding mechanism are studied the flow in a single finite cylinder with diameters between 25 and 60 mm and aspect ratio between 1 and 4 is studied. After that, the flow of two finite cylinders placed side by side with cylinders of diameters between 25 and 32 mm and aspect ratio between 3 and 4 was studied. The experimental technique of hot wire anemometry in aerodynamic channel is applied in the measurement of velocity fluctuations of the flow. The flow visualization was performed on the same aerodynamic channel, keeping the parameters, through using dry ice and laser. In addition, flow visualization is performed on the hydraulic channel with the same dimensions of the aerodynamic channel using ink injection through needles. All images are captured with a camera digital. For the study, Re=2.00×104 for a finite cylinder and 3.86×103 ≤ Re ≤ 4.81×104 for finite cylinders arranged side by side were used. The data measured in aerodynamic channel are treated through statistics, spectral and wavelet tools and the videos are treated through video editing software and with statistical tools. The results show the existence of two different levels of mean velocity in time series, corresponding to two flow modes confirming the phenomenon of bistability for two finite cylinders placed side by side, which is one of the objectives of the study. The flow visualization technique strengthens the interpretation of the results obtained through the hot wire anemometer technique. In this work the existence of three concomitant flows is considered: the upwash flow, characterized by the vortex structure in the base; the downwash flow, characterized by the vortex structure at the top; and the so-called main flow, characterized by the vortex shedding at half height of the cylinders.
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Harper, Ronald Jett. "A measurement system for turbulence properties in a three- dimensional flow using a data logger." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/53074.
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An analysis is presented for hot wire/film anemometer measurement of mean velocities and turbulent stresses in a three dimensional flow field with a predominant flow direction. The experimental data can be taken with an automated traverse under the control of a digital data acquisition system which has been modified for this particular application.Master of Science
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Odemark, Ylva. "Wakes behind wind turbines - Studies on tip vortex evolution and stability." Licentiate thesis, KTH, Mekanik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-93806.
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The increased fatigue loads and decreased power output of a wind turbine placed in the wake of another turbine is a well-known problem when building new wind power farms. In order to better estimate the total power output of a wind power farm, knowledge about the development and stability of wind turbine wakes is crucial. In the present thesis, the wake behind a small-scale model turbine was investigated experimentally in a wind tunnel. The velocity in the wake was measured with hot-wire anemometry, for different free stream velocities and tip speed ratios. To characterize the behaviour of the model turbine, the power output, thrust force and rotational frequency of the model were also measured. These results were then compared to calculations using the Blade Element Momentum (BEM) method. New turbine blades for the model was constructed using the same method, in order to get an estimate of the distribution of the lift and drag forces along the blades. This information is needed for comparisons with certain numerical simulations, which however remains to be performed.By placing the turbine at different heights in a turbulent boundary layer, the effects of forest turbulence on wind turbine outputs (power and thrust) could also be investigated.The evolution of the tip vortices shed from the turbine blades was studied by performing velocity measurements around the location of the tip vortex breakdown. The vortices' receptivity to disturbances was then studied by introducing a disturbance in the form of two pulsed jets, located in the rear part of the nacelle. In order to introduce a well-defined disturbance and perform phase-locked measurements, a new experimental setup was constructed and successfully tested for two different disturbance frequencies. The mean streamwise velocity and the streamwise turbulence intensity was found to scale well with the free stream velocity and the spreading of the wake was found to be proportional to the square root of the downstream distance. The comparison for power and thrust between measurements and BEM calculations showed good agreement in some cases but worse agreement when the pitch angle of the blades was small.The velocity measurements showed that the tip vortices can be susceptible to disturbances and an earlier breakdown could be detected. However, more measurements need to be made to fully investigate the dependance on disturbance frequency and amplitude.QC 20120504
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Lenz, Birgit [Verfasser]. "Experimental Investigation of Fluctuations in Supersonic Boundary Layers via Hot-Wire Anemometry / Birgit Lenz." München : Verlag Dr. Hut, 2010. http://d-nb.info/1009095536/34.
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Rettew, A. Louisa. "The use of hot-wire anemometry in studying supersonic slot injection into a supersonic flow." Thesis, Virginia Tech, 1988. http://hdl.handle.net/10919/44083.
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Tangential supersonic slot injection (M = 1.7) of air into a supersonic air stream (M = 2.91) was studied with a dual hot wire probe. This probe was used to simultaneously determine total temperature and mass flux. Mean profiles across the entire flow field at three axial stations (x/h = 4, 10, 20) were obtained, as well as the temperature and mass flux turbulence intensities. The probe can be used anywhere except at locations where features of the flow are smaller than the separation between the wires (0.18 mm). The calibration of the probe can be repeated with less than a three percent change in calculated Nusselt number. The hot wire probe can also be tuned to obtain a high frequency response. The interaction of a shock wave, caused by a wedge placed on the upper tunnel wall, with the mixing region was investigated. Little change in the mean profiles was observed, but there was a significant increase in turbulence levels.Master of Science
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Laurantzon, Fredrik. "Flow Measuring Techniques in Steady and Pulsating Compressible Flows." Licentiate thesis, KTH, Mekanik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-26344.
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This thesis deals with flow measuring techniques applied on steady and pulsatingflows. Specifically, it is focused on gas flows where density changes canbe significant, i.e. compressible flows. In such flows only the mass flow ratehas a significance and not the volume flow rate since the latter depends onthe pressure. The motivation for the present study is found in the use of flowmeters for various purposes in the gas exchange system for internal combustionengines. Applications can be found for instance regarding measurements of airflow to the engine, or measurements of the amount of exhaust gas recirculation.However the scope of thesis is wider than this, since the thesis aims toinvestigate the response of flow meters to pulsating flows. The study is mainlyexperimental, but it also includes an introduction and discussion of several inindustry, common flow measuring techniques.The flow meters were studied using a newly developed flow rig, designedfor measurement of steady and pulsating air flow of mass flow rates and pulsefrequencies typically found in the gas exchange system of cars and smallertrucks. Flow rates are up to about 200 g/s and pulsation frequencies from 0 Hz(i.e. steady flow) up to 80 Hz. The study included the following flow meters:hot-film mass flow meter, venturi flowmeter, Pitot tube, vortex flowmeter andturbine flowmeter. The performance of these meters were evaluated at bothsteady and pulsating conditions. Furthermore, the flow under both steady andpulsating conditions were characterized by means of a resistance-wire basedmass flow meter, with the ability to perform time resolved measurements ofboth the mass flux ρu, and the stagnation temperature T0.Experiments shows that, for certain flow meters, a quasi-steady assumptionis fairly well justified at pulsating flow conditions. This means that thefundamental equations describing the steady flow, for each instant of time,is applicable also in the pulsating flow. In the set-up, back-flow occurred atcertain pulse frequencies, which can result in highly inaccurate output fromcertain flow meters, depending on the measurement principle. For the purposeof finding means to determine when back flow prevails, LDV measurementswere also carried out. These measurements were compared with measurementsusing a vortex flow meter together with a new signal processing technique basedon wavelet analysis. The comparison showed that this technique may have apotential to measure pulsating flow rates accurately.Descriptors: Flow measuring, compressible flow, steady flow, pulsating flow,hot-wire anemometry, cold-wire anemometry.QC 20101208
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Muthanna, Chittiappa. "The Effects of Free Stream Turbulence on the Flow Field through a Compressor Cascade." Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/28753.
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The flow through a compressor cascade with tip leakage has been studied experimentally. The cascade of GE rotor B section blades had an inlet angle of 65.1º, a stagger angle of 56.9º, and a solidity of 1.08. The final turning angle of the cascade was 11.8º. This compressor configuration was representative of the core compressor of an aircraft engine. The cascade was operated with a tip gap of 1.65%, and operated at a Reynolds number based on the chord length (0.254 m) of 388,000. Measurements were made at 8 axial locations to reveal the structure of the flow as it evolved through the cascade. Measurements were also made to reveal the effects of grid generated turbulence on this flow. The data set is unique in that not only does it give a comparison of elevated free stream turbulence effects, but also documents the developing flow through the blade row of a compressor cascade with tip leakage.
Measurements were made at a total of 8 locations 0.8, 0.23 axial chords upstream and 0, 0.27, 0.48, 0.77, 0.98, and 1.26 axial chords downstream of the leading edge of the blade row for both inflow turbulence cases. The measurements revealed the formation and development of the tip leakage vortex within the passage. The tip leakage vortex becomes apparent at approximately X/ca= 0.27 and dominated much of the endwall flow. The tip leakage vortex is characterized by high streamwise velocity deficits, high vorticity and high turbulence kinetic energy levels. The result showed that between 0.77 and 0.98 axial chords downstream of the leading edge, the vortex structure and behavior changes.
The effects of grid generated turbulence were also documented. The results revealed significant effects on the flow field. The results showed a 4% decrease in the blade loading and a 20% reduction in the vorticity levels within tip leakage vortex. There was also a shift in the vortex path, showing a shift close to the suction side with grid generated turbulence, indicating the strength of the vortex was decreased. Circulation calculations showed this reduction, and also indicated that the tip leakage vortex increased in size by about 30%. The results revealed that overall, the turbulence kinetic energy levels in the tip leakage vortex were increased, with the most drastic change occurring at X/ca= 0.77.Ph. D.
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Sigfrids, Timmy. "Hot wire and PIV studies of transonic turbulent wall-bounded flows." Licentiate thesis, KTH, Mechanics, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1577.
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The compressible turbulent boundary layer developing over atwo-dimensional bump which leads to a supersonic pocket with aterminating shock wave has been studied. The measurements havebeen made with hot-wire anemometry and Particle ImageVelocimetry (PIV).
A method to calibrate hot-wire probes in compressible ow hasbeen developed which take into account not only the ow velocitybut also the inuence of the Mach number, stagnation temperatureand uid density. The calibration unit consists of a small jetow facility, where the temperature can be varied. The hot wiresare calibrated in the potential core of the free jet. The jetemanates in a container where the static pressure can becontrolled, and thereby the gas density. The calibration methodwas verfied in the at plate zero pressure gradient turbulentboundary layer in front of the bump at three different Machnumbers, namely 0.3, 0.5 and 0.7. The profiles were alsomeasured at different static pressures in order to see theinuence of varying density. Good agreement between the profilesmeasured at different pressures, as well as with the standardlogarithmic profile was obtained.
The PIV measurements of the boundary layer ow in front ofthe 2D bump showed good agreement with the velocity profilesmeasured with hotwire anemometry. The shock wave boundary layerinteraction was investigated for an inlet Mach number of 0.69.A lambda shock wave was seen on the downstream side of thebump. The velocity on both sides of the shock wave as measuredwith the PIV was in good agreement with theory. The shock wavewas found to cause boundary layer separation, which was seen asa rapid growth of the boundary layer thickness downstream theshock. However, no back ow was seen in the PIV-data, probablybecause the seeding did not give enough particles in theseparated region. The PIV data also showed that the shock wavewas oscillating, i.e. it was moving approximately 5 mm back andforth. This distance corresponds to about five boundary layerthicknesses in terms of the boundary layer upstream theshock.
Descriptors:Fluid mechanics, compressible ow,turbulence, boundary layer, hot-wire anemometry, PIV, shockwave boundary layer interaction, shape factor.
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Kalpakli, Athanasia. "Experimental study of turbulent flows through pipe bends." Licentiate thesis, KTH, Linné Flow Center, FLOW, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-93316.
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This thesis deals with turbulent flows in 90 degree curved pipes of circular cross-section. The flow cases investigated experimentally are turbulent flow with and without an additional motion, swirling or pulsating, superposed on the primary flow. The aim is to investigate these complex flows in detail both in terms of statistical quantities as well as vortical structures that are apparent when curvature is present. Such a flow field can contain strong secondary flow in a plane normal to the main flow direction as well as reverse flow. The motivation of the study has mainly been the presence of highly pulsating turbulent flow through complex geometries, including sharp bends, in the gas exchange system of Internal Combustion Engines (ICE). On the other hand, the industrial relevance and importance of the other type of flows were not underestimated. The geometry used was curved pipes of different curvature ratios, mounted at the exit of straight pipe sections which constituted the inflow conditions. Two experimental set ups have been used. In the first one, fully developed turbulent flow with a well defined inflow condition was fed into the pipe bend. A swirling motion could be applied in order to study the interaction between the swirl and the secondary flow induced by the bend itself. In the second set up a highly pulsating flow (up to 40 Hz) was achieved by rotating a valve located at a short distance upstream from the measurement site. In this case engine-like conditions were examined, where the turbulent flow into the bend is non-developed and the pipe bend is sharp. In addition to flow measurements, the effect of non-ideal flow conditions on the performance of a turbocharger was investigated. Three different experimental techniques were employed to study the flow field. Time-resolved stereoscopic particle image velocimetry was used in order to visualize but also quantify the secondary motions at different downstream stations from the pipe bend while combined hot-/cold-wire anemometry was used for statistical analysis. Laser Doppler velocimetry was mainly employed for validation of the aforementioned experimental methods. The three-dimensional flow field depicting varying vortical patterns has been captured under turbulent steady, swirling and pulsating flow conditions, for parameter values for which experimental evidence has been missing in literature.QC 20120425
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Laurantzon, Fredrik. "Flow measurements related to gas exchange applications." Doctoral thesis, KTH, Strömningsfysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-94133.
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This thesis deals with flow measuring techniques applied to steady and pulsating gas flows relevant to gas exchange systems for internal combustion engines. Gas flows in such environments are complex, i.e. they are inhomogeneous, three-dimensional, unsteady, non-isothermal and exhibit significant density changes. While a variety of flow metering devices are available and have been devised for such flow conditions, the performance of these flow metersis to a large extent undocumented when a strongly pulsatile motion is superposed on the already complex flow field. Nonetheless, gas flow meters are commonly applied in such environments, e.g. in the measurement of the air flow to the engine or the amount of exhaust gas recirculation. The aim of the present thesis is therefore to understand and assess, and if possible to improve the performance of various flow meters under highly pulsatile conditions as well as demonstrating the use of a new type of flow meter for measurements of the pulsating mass flow upstream and downstream the turbine of a turbocharger. The thesis can be subdivided into three parts. The first one assesses the flow quality of a newly developed flow rig, designed for measurements of steady and pulsating air flow at flow rates and pulse frequencies typically found in the gas exchange system of cars and smaller trucks. Flow rates and pulsation frequencies achieved and measured range up to about 200 g/s and 80 Hz, respectively. The time-resolved mass flux and stagnation temperature under both steady and pulsating conditions were characterized by means of a combined hot/cold-wire probe which is part of a newly developed automated measurement module. This rig and measurement module were used to create a unique data base with well-defined boundary conditions to be used for the validation of numerical simulations, but in particular, to assess the performance of various flow meters. In the second part a novel vortex flow meter that can measure the timedependent flow rate using wavelet analysis has been invented, verified and extensively tested under various industrially relevant conditions. The newly developed technique was used to provide unique turbine maps under pulsatile conditions through time-resolved and simultaneous measurements of mass flow, temperature and pressure upstream and downstream the turbine. Results confirm that the quasi-steady assumption is invalid for the turbine considered as a whole. In the third and last part of the thesis, two basic fundamental questions that arose during the course of hot/cold-wire measurements in the aforementioned high speed flows have been addressed, namely to assess which temperature a cold-wire measures or to which a hot-wire is exposed to in high speed flows as well as whether the hot-wire measures the product of velocity and density or total density. Hot/cold-wire measurements in a nozzle have been performed to test various hypothesis and results show that the recovery temperature as well as the product of velocity and stagnation density are measured.QC 20120510
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Fornero, Agustin Matias. "Design, calculation and simulation of a wind tunnel for calibration of hot wire probes." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16225/.
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Desing, simulation and calculation of a wind tunnel used for calibration of hot wire probes. Involves the selection and calculation of the components of the wind tunnel, with special look in the convergent, where a few options where simulated and tested to find the best one.
Then, a model is proposed along with options for the fan of the wind tunnel.
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Örlü, Ramis. "Experimental study of passive scalar mixing in swirling jet flows." Licentiate thesis, KTH, Mechanics, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4142.
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Despite its importance in various industrial applications there is still a lack of experimental studies on the dynamic and thermal field of swirling jets in the near-field region. The present study is an attempt to close this lack and provide new insights on the effect of rotation on the turbulent mixing of a passive scalar, on turbulence (joint) statistics as well as the turbulence structure.
Swirl is known to increase the spreading of free turbulent jets and hence to entrain more ambient fluid. Contrary to previous experiments, which leave traces of the swirl generating method especially in the near-field, the swirl was imparted by discharging a slightly heated air flow from an axially rotating and thermally insulated pipe (6 m long, diameter 60 mm). This gives well-defined axisymmetric streamwise and azimuthal velocity distributions as well as a well-defined temperature profile at the jet outlet. The experiments were performed at a Reynolds number of 24000 and a swirl number (ratio between the angular velocity of the pipe wall and the bulk velocity in the pipe) of 0.5.
By means of a specially designed combined X-wire and cold-wire probe it was possible to simultaneously acquire the instantaneous axial and azimuthal velocity components as well as the temperature and compensate the former against temperature variations. The comparison of the swirling and non-swirling cases clearly indicates a modification of the turbulence structure to that effect that the swirling jet spreads and mixes faster than its non-swirling counterpart. It is also shown that the streamwise velocity and temperature fluctuations are highly correlated and that the addition of swirl drastically increases the streamwise passive scalar flux in the near field.
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Bennett, Matthew James. "Investigation of the flow characteristics in the spark initiation region of SI engines using hot wire and laser doppler anemometry." Thesis, Coventry University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328948.
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Powers, Alex D. "A Study of Constant Voltage Anemometry Frequency Response." DigitalCommons@CalPoly, 2016. https://digitalcommons.calpoly.edu/theses/1570.
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The development of the constant voltage anemometer (CVA) for the boundary layer data system (BLDS) has been motivated by a need for the explicit autonomous measurement of velocity fluctuations in the boundary layer. The frequency response of a sensor operated by CVA has been studied analytically and experimentally. The thermal lag of the sensor is quantified by a time constant, MCVA. When the time constant is decreased, the half-amplitude cut-off frequency, fCVA, is increased, thereby decreasing the amount of attenuation during measurements. In this thesis, three main approaches have been outlined in theory and tested experimentally to determine the feasibility and effectiveness of implementing them with CVA to limit attenuation: operation at higher Vw, implementation of software compensation, and utilization of smaller diameter sensors. Operation of CVA at higher voltage results in little improvement in frequency response but is accompanied by increased danger of wire burnout. However, sensors do need to be operated at high wire voltages to be more sensitive to velocity fluctuations and less sensitive to temperature fluctuations, without reaching a temperature high enough for wire burnout. Software compensation of the CVA output has been shown not to be useful for measurements with BLDS. The electrical noise present in the CVA measurement system is amplified by the correction algorithm and creates measurements that are not representative of the fluctuations being measured. Decreasing sensor diameter leads to a significant decrease of MCVA and therefore increase of fCVA. Under similar operating conditions, a 2.5 micron diameter sensor showed less roll off in the frequency spectra (measured higher turbulence intensities) than a 3.8 micron diameter sensor for tests in both a turbulent jet and in a turbulent boundary layer. Smaller sensors are more fragile and have been shown to have a decrease in sensitivity as compared to larger sensors; however, for some applications, the increase in frequency response may be worth the trade-off with fragility and sensitivity.
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Davies, Luca. "Studio e realizzazione di un sistema di calibrazione per anemometri in galleria del vento." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/12914/.
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Il presente elaborato propone un metodo di calibrazione alle basse velocità degli anemometri a filo caldo utilizzati nella galleria del vento presente al C.I.C.Lo.P.E. (Center for International Cooperation in Long Pipe Experiments) dell'Università di Bologna, potenzialmente estendibile ad applicazioni più generali.
In seguito ad un'analisi teorica approfondita della fattibilità di una calibrazione alle basse velocità, si è dimensionato e realizzato un prototipo in P.V.C. a geometria convergente-divergente, ritenuto in grado di produrre un flusso uniforme in uscita tale da garantire una soluzione al problema della calibrazione all'interno della test-section della galleria. Completata la fabbricazione del componente si è condotta un'analisi sperimentale, con l'ausilio del C.A.T. (Coaxial Air Tunnel) presente nell'hangar della Scuola di Ingegneria, sede di Forlì, del flusso generato internamente al divergente del calibratore.
Nonostante si sia rilevata, mediante lo studio sperimentale condotto, una non perfetta uniformità del flusso uscente dal componente, i risultati riscontrati hanno permesso di inquadrare approcci e soluzioni atti ad un'ottimizzazione del calibratore, lasciando ampio margine di miglioramento ai fini della calibrazione alle basse velocità mediante il metodo descritto.
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Imayama, Shintaro. "Studies of the rotating-disk boundary-layer flow." Doctoral thesis, KTH, Strömningsfysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-158973.
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The rotating-disk boundary layer is not only a simpler model for the study of cross-flow instability than swept-wing boundary layers but also a useful simplification of many industrial-flow applications where rotating configurations are present. For the rotating disk, it has been suggested that a local absolute instability, leading to a global instability, is responsible for the small variation in the observed laminar-turbulent transition Reynolds number however the exact nature of the transition is still not fully understood. This thesis aims to clarify certain aspects of the transition process. Furthermore, the thesis considers the turbulent rotating-disk boundary layer, as an example of a class of three-dimensional turbulent boundary-layer flows. The rotating-disk boundary layer has been investigated in an experimental apparatus designed for low vibration levels and with a polished glass disk that gave a smooth surface. The apparatus provided a low-disturbance environment and velocity measurements of the azimuthal component were made with a single hot-wire probe. A new way to present data in the form of a probability density function (PDF) map of the azimuthal fluctuation velocity, which gives clear insights into the laminar-turbulent transition region, has been proposed. Measurements performed with various disk-edge conditions and edge Reynolds numbers showed that neither of these conditions a↵ect the transition process significantly, and the Reynolds number for the onset of transition was observed to be highly reproducible. Laminar-turbulent transition for a ‘clean’ disk was compared with that for a disk with roughness elements located upstream of the critical Reynolds number for absolute instability. This showed that, even with minute surface roughness elements, strong convectively unstable stationary disturbances were excited. In this case, breakdown of the flow occurred before reaching the absolutely unstable region, i.e. through a convectively unstable route. For the rough disk, the breakdown location was shown to depend on the amplitude of individual stationary vortices. In contrast, for the smooth (clean-disk) condition, the amplitude of the stationary vortices did not fix the breakdown location, which instead was fixed by a well-defined Reynolds number. Furthermore, for the clean-disk case, travelling disturbances have been observed at the onset of nonlinearity, and the associated disturbance profile is in good agreement with the eigenfunction of the critical absolute instability. Finally, the turbulent boundary layer on the rotating disk has been investigated. The azimuthal friction velocity was directly measured from the azimuthal velocity profile in the viscous sublayer and the velocity statistics, normalized by the inner scale, are presented. The characteristics of this three-dimensional turbulent boundary-layer flow have been compared with those for the two-dimensional flow over a flat plate and close to the wall they are found to be quite similar but with rather large differences in the outer region.QC 20150119
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Kraft, Wayne Neal. "Simultaneous and instantaneous measurement of velocity and density in rayleigh-taylor mixing layers." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2772.
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Silveira, Rodrigo Santiago. "Estudo experimental do efeito da razão de bloqueio em canal aerodinâmico sobre o Número de Strouhal e o fenômeno da biestabilidade no escoamento em cilindros." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2011. http://hdl.handle.net/10183/29399.
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Este trabalho apresenta um estudo experimental do efeito da razão de bloqueio em um canal aerodinâmico no Número de Strouhal e o fenômeno da biestabilidade. É estudado o escoamento turbulento sobre um cilindro e também sobre dois cilindros dispostos lado a lado, onde fez-se uso de cilindros de vários diâmetros a fim de variar a razão de bloqueio no canal. Dois tipos de espaçamento entre os tubos são estudados. A técnica experimental consiste na medição de flutuações de velocidades em um canal aerodinâmico utilizando a técnica de anemometria de fio quente. Os dados obtidos da medição no canal aerodinâmico são tratados com o uso de ferramentas estatísticas, espectrais e de ondaletas. Para um cilindro, os resultados confirmam o aumento do número de Strouhal com o aumento da razão de bloqueio, na faixa do número de Reynolds utilizada. Razões de bloqueio mais baixas podem acarretar diminuição do número de Strouhal, também em função do número de Reynolds. Os resultados confirmam a existência do fenômeno da biestabilidade no escoamento sobre dois cilindros dispostos lado a lado, assim como a influência da razão de bloqueio sobre o fenômeno, sendo mais predominante em um dos espaçamentos estudados. Para razões de bloqueio altas, o fenômeno da biestabilidade pode não ocorrer ou pouco ocorre. Para razões de bloqueio mais baixas podemos ter também a não ocorrência do fenômeno em função das dimensões dos tubos serem mais reduzidas, fazendo com que a captação do fenômeno também seja reduzida.This paper presents an experimental study of the effect of blockage ratio in a aerodynamic channel on Strouhal number and the bistability phenomenon. It studied the turbulent flow around a single cylinder and also on two cylinders arranged side-by-side, where use has been made of cylinders of various diameters to vary the blockage ratio of the channel. Two types of pitch to diameter ratio are studied. The experimental technique consists of measuring velocity fluctuations in aerodynamic channel using the technique of hot-wire anemometry. The data obtained from measuring the aerodynamic channel are treated with the use of statistical tools, spectral and wavelet analysis. For a single cylinder, the results confirm the increase of the Strouhal number with increasing blockage ratio in the range of Reynolds number used. Lower blockage ratio can cause a decrease of the Strouhal number, also a function of Reynolds number. The results confirm the existence of the bistability phenomenon in the flow on two cylinders arranged side-by-side, as well as the influence of blockage ratio on the phenomenon, being more predominant in one of the row spacings. For higher blockage ratios, the bistability phenomenon may not occur or occurs shortly. For lower blockage ratio, due to the smaller dimensions of the tubes the phenomenon may not occur on the capture of the phenomenon is also reduced with the present experimental technique.
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Varela, Dolir Jose Climaco. "Análise experimental do escoamento transversal turbulento sobre dois cilindros paralelos fixos, com liberdade oscilatória e rotacional." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/178285.
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Este trabalho apresentada um estudo experimental do fenômeno de biestabilidade que ocorre na geometria simplificada de dois tubos dispostos lado a lado submetidos a um escoamento cruzado turbulento. Na análise consideram-se a condição de tubos fixos e com um grau de liberdade (rotacional), submetidos a diferentes números de Reynolds. A técnica experimental consiste na medição de flutuações de velocidade do escoamento através da anemometria de fio quente em canal aerodinâmico, na avaliação dos esforços do escoamento sobre os tubos com o uso de uma célula de carga e na visualização dos efeitos do fenômeno biestável sobre os tubos livres para rotacionar. Os dados obtidos da medição no canal são tratados com o uso de ferramentas estatísticas, espectrais e de ondaletas. Os resultados das visualizações do escoamento são apresentados através de imagens obtidas das filmagens realizadas com uma câmera digital. A investigação experimental consiste de ensaios de cilindros rígidos elasticamente montados e pivotados na base e posteriormente liberados para oscilar e/ou rotacionar em um eixo central aos dois tubos, submetidos ao escoamento perpendicular permanente de ar no canal Nos resultados experimentais observam-se a presença da biestabilidade e nota-se o comportamento não simultâneo deste fenômeno ao longo dos cilindros. A formação assimétrica das esteiras também é estudada e atribuída à interação entre os vórtices das esteiras, já que, inicialmente, o desprendimento dos vórtices atrás dos cilindros é simétrico. Na avaliação dos esforços por extensiometria, as etapas de condicionamento e aquisição do sinal foram elaboradas e os resultados de deformação mecânica apresentaram similaridade com o fenômeno observado na anemometria experimental. Para um número de Reynolds de 27635 encontrou-se uma força de 26,1 mN com um torque desenvolvido na célula de carga de 84,95Nmm. A técnica de visualização do fenômeno empregada corrobora a interpretação dos resultados obtidos através da técnica de anemometria de fio quente e extensiometria em canal aerodinâmico.This paper presents an experimental study of the bistability phenomenon that occurs in the simplified geometry of two tubes arranged side by side submitted to a turbulent cross flow. In the analysis we consider the condition of fixed tubes and with a degree of freedom (rotational), submitted to different Reynolds numbers. The experimental technique consists in the measurement of velocity fluctuations through the aerodynamic channel with the hot wire anemometry technique, the evaluation of the stresses of the flow on the tubes with the use of a load cell and the visualization of the effects of the bistable phenomenon on the tubes free to rotate. The data obtained from the measurement in the channel are treated with the use of statistical, spectral and wavelet tools. The results of the flow visualizations are presented through images obtained with a high speed digital camera. The experimental investigation consists of tests of rigid cylinders mounted elastically and pivoted at the base and later released to oscillate and / or to rotate in a central axis to the two tubes, submitted to the flow of air in the channel In the experimental results we observe the presence of bistability and note the non-simultaneous behavior of the phenomenon along the cylinders. The asymmetric formation of the wakes is also studied and attributed to the interaction between the vortices from wakes behind the cylinders, since, initially, the wake detachments is symmetrical. In the evaluation of the forces by means of the extensiometry technique, the steps of conditioning and acquisition of the signal were elaborated and the results of mechanical deformation presented similarity with the phenomenon observed in the experimental anemometry. For a Reynolds number of 27635 a force of 26.1 mN was found with a torque developed in the load cell of 84.95 Nmm. The technique used for the visualization of the phenomenon corroborates the interpretation of the results obtained through hot wire anemometry and extensiometry in aerodynamic channel.
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Casadei, Francesco. "Experimental investigation of the flow behind a probe rake: a similarity analysis for high speed applications." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/4887/.
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Estejab, Bahareh. "AN INVESTIGATION OF THE REYNOLDS NUMBER DEPENDENCE OF THE NEAR-WALL PEAK IN CANONICAL WALL BOUNDED TURBULENT CHANNEL FLOW." UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_theses/144.
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An experimental investigation into fully developed high aspect ratio channels was undertaken. A review of the literature reveals that there is a need for accurate measurement of the inner peak value of streamwise turbulence intensity despite the large number of studies already completed. The scattered data on this subject could be attributed either to insufficient channel size (aspect ratio or length) or to hot-wire spatial filtering.
A new, high quality, channel flow facility was designed and constructed, considering the most recent geometric limitation provided in the literature. To obtain accurate results, data were acquired using hot-wire probes with constant viscous-scale sensing length and were corrected using the most recent correction formula proposed by Smits et al. (2011). The results show dependence of inner peak value on Reynolds number in channels flow - its magnitude increasing with increasing Reynolds number.
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Eguti, Carlos César Aparecido. "Desenvolvimento de um circuito eletrônico experimental de anemômetro de fio quente /." Ilha Solteira : [s.n.], 2005. http://hdl.handle.net/11449/88878.
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Orientador: Edson Del Rio VieiraBanca: Sérgio Said Mansur
Banca: Marcello Augusto F. de Medeiros
Resumo: Anemômetros de fio quente são sensíveis instrumentos capazes de medir variações de velocidade nos mais diversos tipos de escoamentos, sejam eles gasosos ou líquidos. Um delicado filamento metálico é aquecido por uma corrente elétrica a qual gera calor por efeito Joule e transfere parte dessa energia para o escoamento incidente, sendo esta troca de calor proporcional a velocidade do fluído, definindo assim o princípio básico de funcionamento da anemometria de fio quente. Quando este filamento é montado num circuito tipo ponte de Wheatstone, pode-se relacionar a troca de calor no filamento através da variação de sua resistência elétrica fazendo o uso de circuitos eletrônicos especiais. Este trabalho aborda os conceitos básicos da anemometria de fio quente, seus circuitos de controle principais e seus modos de operação, mostrando diferentes métodos para calibração de sondas de fio quente em escoamentos gasosos, além de apresentar uma metodologia completa para construção de um sistema básico de anemômetro de fio quente de temperatura constante. Dois dispositivos foram construídos e testados sendo avaliados quanto ao seu funcionamento e sua resposta em freqüência.
Abstract: Hot wire anemometers are sensitive instruments capable of measuring fluctuation of speed in many fluid flows, gaseous or liquid. A delicate metallic filament is heated by an electric current (Joule effect) and cooled by incident flow, this heat exchange is proportional of the fluid speed, defining the basic phenomenon of hot-wire anemometry. When this filament is mounted on an arm of Wheatstone bridge, the heat lost by the filament can be related its electric resistance when special electronic circuits are used. This work presents the concepts of hot-wire anemometry, its main control circuits and its operation mode, showing the basic methods for hot wire calibration with gaseous flows, besides presenting a complete methodology for construction of a basic constant temperature hot-wire anemometer system, based on the tests of two experimental circuits which are evaluated by electronic tests and its frequency response.
Mestre
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Paula, Alexandre Vagtinski de. "Determinação de parâmetros que caracterizam o fenômeno da biestabilidade em escoamentos turbulentos." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2013. http://hdl.handle.net/10183/72928.
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Este trabalho apresenta um estudo acerca dos principais parâmetros que caracterizam o fenômeno da biestabilidade em dois tubos dispostos lado a lado submetidos a escoamento cruzado turbulento. A técnica experimental da anemometria de fio quente em canal aerodinâmico é aplicada na medição das flutuações de velocidade do escoamento após os tubos. As séries temporais obtidas são utilizadas como dados de entrada para determinação das funções densidade de probabilidade (PDF) usando um modelo de mistura finita, de acordo com uma função t de Student assimétrica e com o auxílio do método de Monte Carlo. Transformadas de ondaletas discretas e contínuas são aplicadas na filtragem das séries temporais para determinadas bandas de frequências e na análise do conteúdo de energia destes sinais. Através de conceitos de sistemas caóticos, é realizada a reconstrução do atrator do problema pelo método dos atrasos temporais, a partir das séries experimentais de velocidade, permitindo a determinação da dimensão de imersão e o cálculo do maior expoente de Lyapunov. Os resultados mostram a existência de dois patamares distintos de velocidade média nas séries temporais, correspondentes aos dois modos do escoamento, cada qual com números de Strouhal e funções densidade de probabilidade distintas. Uma análise conjunta das componentes axial e transversal do escoamento e suas PDF indicam as regiões no plano de medições onde o fenômeno se manifesta, sendo que reconstruções da trajetória filtrada das séries temporais para determinadas bandas de frequências apresentam características caóticodeterminísticas. O maior expoente de Lyapunov das séries experimentais é positivo, o que é um indício de comportamento caótico.This work presents a study of the main parameters that characterize the phenomenon of bistability in two tubes placed side by side submitted to turbulent crossflow. The experimental technique of hot wire anemometry in aerodynamic channel is applied in the measurement of velocity fluctuations of the flow after the tubes. The time series obtained are used as input data for determining the probability density functions (PDF) using a finite mixture model, according to an asymmetric Student t function and with the aid of a Monte Carlo method. Wavelet transforms are applied in discrete and continuous filtering of time series for certain frequency bands and in the analysis of the energy content of these signals. By means of chaotic systems concepts, the attractor reconstruction of the problem is performed using the method of time delays from the experimental series of velocity, allowing the determination of the embedding dimension and calculating the largest Lyapunov exponent. The results show the existence of two different levels of mean velocity in time series, corresponding to two flow modes, each one with different Strouhal numbers and probability density functions. A joint analysis of axial and transverse components of flow and its PDF indicate the regions in the measurement plan where the phenomenon is manifested, and reconstructions of the trajectory of the filtered time series for certain frequency bands have chaotic-deterministic characteristics. The largest Lyapunov exponent of experimental series is positive, which is an indication of chaotic behavior.
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Nabhani, Nader. "Hot-wire anemometry study of confined turbulent swirling flow : development of a hot-wire technique for measurement in confined turbulent swirling flow and an investigation of the effect of inlet flow rate and geometrical conditions on the velocity field." Thesis, University of Bradford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.256901.
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Ležovič, Tomáš. "Experimentální analýza proudu vzduchu z ofukovače osobního vozu s využitím žárového anemometru a návrh hodnocení kvality ofukovače." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2011. http://www.nusl.cz/ntk/nusl-229643.
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The master’s thesis deals with air flow in the interior of automobile Škoda Octavia. The attention is focused only at a side ventilating outlet. Author’s effort was to propose the appropriate criteria for evaluation and assessment of ventilating outlet quality and elaborate the methodology of measurement for these criteria. Then follows the application of the methodology and measurement of velocity field of air flow from the outlet by the method of hot wire anemometry. The thesis also contains comparison of the results with the results attained by the smoke visualization.
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Wisda, David Martin. "Noise from a Rotor Ingesting Inhomogeneous Turbulence." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/52986.
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On-blade hot wire anemometry measurements as well as far field sound measurements at several receiving angles have been previously made for a rotor partially embedded in a boundary layer. The inflow distortion effect on the rotor angle of attack distribution was determined directly from the on-blade measurements, and was found to minimally affect the angle of attack at the blade tips and lower the angle attack in the rotor disk plane as the radial location moves towards the hub. A narrow, sharp increase in angle of attack as the rotor blades approached the wall was also observed, indicating blade interaction with flow reversal. The haystacking pattern, or spectral humps that appear at multiples of the blade passage frequency, was studied for a wide range of advance ratios. At high advance ratios, evidence of vortex shedding from the blade trailing edges was observed. For low advance ratios, the haystacks narrowed, became more symmetric and increased in number. A method of determining the average acoustic signature of an eddy passage through a rotor was developed from time delay aligning multiple microphone signals and eddy passages detected using the continuous wavelet transform. It was found that the eddy passage signatures were similar to a cosine wave with a Gaussian window. It was also found that normalized timescales obtained directly from the eddy passage signatures remained somewhat constant with advance ratio, but increases slightly for fixed free stream velocities with increasing rotor RPM. For advance ratios less than 0.6, the eddy passage signatures were dominated by a tonal component due to rotor ingestion of misaligned flow caused by a boundary layer separation at the wall. This indicates that flow reversal known as the Pirouette Effect is interacting with the rotor blades.Master of Science
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Farsimadan, Ehsaan. "A study of the turbulent wake of an airfoil in an air stream with a 90° curvature using hot-wire anemometry and large eddy simulation." Thesis, Brunel University, 2008. http://bura.brunel.ac.uk/handle/2438/3612.
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The broad aim of the work presented in this thesis is to investigate the wake of an airfoil under the combined effects of streamwise curvature and pressure gradient. This was accomplished by an experimental investigation using hot-wire anemometry and large eddy simulation (LES). The wake was generated by placing a NACA 0012 airfoil in a uniform stream of air, which is then subjected to an abrupt 90o curvature created by a duct bend. The experimental work was conducted in a subsonic open-return type wind tunnel. The test section measured 457 mm × 457 mm in cross-section and consisted of a 90o bend with radius-to-height ratio of 1.17. The symmetrical airfoil was of chord length (c) 150 mm, and its trailing edge was located one chord length upstream of the bend entry. The effects of airfoil angle of attack and mainstream velocity on the mean velocity and turbulence quantities of the near-wake were examined. In addition, the mean velocity and turbulence intensity profiles of the boundary layer on the upper surface of the airfoil were measured. In the numerical investigation, the three-dimensional, incompressible turbulent flow in the duct was computed using the finite volume method. The effect of modelling parameters, namely, grid resolution and sub-grid scale (SGS) model were studied. Three different sub-grid scale models were employed, namely, the classical Smagorinsky, its dynamic variant (DSMG) and the dynamic kinetic energy transport. The effect of grid resolution was assessed by conducting simulations with the DSMG model on three different grids. The first two grids incorporated the full spanwise extent of the duct (3c), and the third grid comprised a reduced spanwise segment (0.5c) with periodic conditions set in the spanwise direction. A bounded central differencing scheme was employed for the discretization of the convection terms. The temporal discretization was by a second-order implicit method that incorporated a forward difference approximation. The performance of LES in depicting the experimental flow was assessed and compared with the results predicted by the Reynolds Stress Model. The experimental profiles at zero angle of attack revealed the differing effects of curvature on the mean and turbulence quantities in the inner-side and outer-side of the wake. The spanwise distributions of mean velocity and turbulence intensity, in the near-wake, indicated variations with identifiable peaks and troughs which corresponded to the presence of streamwise vortices in the wake. The spanwise variations were larger on the inner side of the wake and significantly reduced on the outer side. The results showed that close to the trailing edge, the dominant effect on the wake was from the airfoil boundary layer, whereas one chord length downstream of the trailing edge, it was the effect of curvature and pressure gradient from the duct which was dominant. The results from the numerical study showed the advantages of LES over Reynolds-averaged Navier-Stokes methods in predicting separation on the convex wall of the bend on relatively coarse grids, but also shortcomings in the prediction of the wake parameters. The dynamic variants of the SGS models were more accurate in predicting the flow in the wake. On a considerably finer grid with near-wall airfoil grid spacings of Δx+ < 80, Δy+ < 0.5, and 20 < Δz+ < 50, LES resulted in much improved comparisons with the experimental data. The improved prediction of the wake parameters was attributed to the improved simulation of the boundary layers on the upper surface of the airfoil. However, the effect of the reduced spanwise extent resulted in a lack of prediction of separation on the convex wall of the duct.
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Millican, Anthony J. "Bio-Inspired Trailing Edge Noise Control: Acoustic and Flow Measurements." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/78376.
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Trailing edge noise control is an important problem associated mainly with wind turbines. As turbulence in the air flows over a wind turbine blade, it impacts the trailing edge and scatters, producing noise. Traditional methods of noise control involve modifying the physical trailing edge, or the scattering efficiency. Recently, inspired by the downy covering of owl feathers, researchers developed treatments that can be applied to the trailing edge to significantly reduce trailing edge noise. It was hypothesized that the noise reduction was due to manipulating the incoming turbulence, rather than the physical trailing edge itself, representing a new method of noise control. However, only acoustic measurements were reported, meaning the associated flow physics were still unknown. This thesis describes a comprehensive wall jet experiment to measure the flow effects near the bio-inspired treatments, termed “finlets” and “rails,” and relate those flow effects to the noise reduction. This was done using far-field microphones, a single hot-wire probe, and surface pressure fluctuation microphones. The far-field noise results showed that each treatment successfully reduced the noise, by up to 7 dB in some cases. The surface pressure measurements showed that the spanwise coherence was slightly reduced when the treatments were applied to the trailing edge. The velocity measurements clearly established the presence of a shear layer near the top of the treatments. As a whole, the dataset led to the shear-sheltering hypothesis: the bio-inspired treatments are effective based on reducing the spanwise pressure correlation and by sheltering the trailing edge from turbulent structures with the shear layer they create.Master of Science
This thesis describes a project aimed at developing a technology inspired by the silent flight of owls, with the end goal of using this technology to reduce the noise generated by wind turbines. Specifically, the phenomenon known as "trailing edge noise" is the primary source of wind turbine noise, and is the noise source of interest here. It occurs when air turbulence (which can be thought of as unsteady air fluctuations) crashes into the rear (trailing) edge of wind turbine blades, scattering and producing noise. Typically, methods of reducing this noise source involve changing the shape of the trailing edge; this may not always be practical for existing wind turbines. Recently, inspired by the downy covering of owl feathers, researchers developed treatments that can be applied directly to the trailing edge, significantly reducing trailing edge noise. This bio-inspired concept was verified with numerous acoustic measurements. Based on those measurements, researchers hypothesized that the noise reduction was achieved by manipulating the incoming turbulence before it scattered off the trailing edge, rather than by changing the existing wind turbine blade, representing a new method of trailing edge noise control. However, as only acoustic measurements (not flow measurements) were reported, the changes in turbulence could not be examined. With the above motivation in mind, this thesis describes a comprehensive wind tunnel experiment to measure the changes in the aerodynamics and turbulence near the bio-inspired treatments, and relate those changes to the reduction in trailing edge noise. This was done using a hot-wire probe to measure the aerodynamics, as well as microphones to measure the radiated noise and surface pressure fluctuations. As a whole, the experimental results led to the shear-sheltering hypothesis: the bio-inspired treatments are effective based on the creation of a shear layer (a thin region between areas with different air speeds) which shelters the trailing edge from some turbulence, as well as by de-correlating surface pressure fluctuations along the trailing edge.
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Kledy, Michel. "Développement d'une méthode de mesure des champs de vitesse et de température liquide en écoulement diphasique bouillant en conditions réacteurs ou simulantes." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAI035.
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Ce travail de thèse constitue une contribution à la caractérisation des écoulements diphasiques bouillants convectifs à haute pression rencontrés dans les réacteurs à eau sous pression (REP) ou dans des conditions simulantes.La première partie présente un modèle bi-dimensionnel permettant de décrire le développement d'un écoulement bouillant dans une conduite circulaire (régime à bulle). La modélisation proposée est basée sur les équations locales stationnaires du mélange homogène fermées à l'aide d'un modèle de relaxation thermodynamique. Une confrontation des résultats avec les données expérimentales issues de la banque de donnée DEBORA a ensuite montré que si le modèle était capable de rendre compte de manière satisfaisante des résultats expérimentaux, les mécanismes de transport radiaux de la turbulence ainsi que de la vapeur étaient encore mal modélisés.La seconde partie de l'étude traite du développement de la thermo-anémométrie dans l'installation expérimentale DEBORA, afin de mesurer de manière colocalisée les champs de vitesse et de température liquide ainsi que le taux de vide en écoulement diphasique bouillant. La procédure expérimentale repose sur l'utilisation de sondes anémométriques classiques (sonde à film DANTEC@ 70 µm de diamètre, sonde à fil 2.5µm de 2.5 de diamètre) fonctionnant successivement à différentes surchauffes et pilotées à l'aide d'un anémomètre à courant constant. Des mesures ont d'abord été réalisées en écoulement monophasique chauffé, puis une procédure de discrimination phasique a été développée et a permis de fournir des premières mesures en écoulement bouillant. Ces dernières ont alors été comparées aux résultats du modèleThis study is a contribution to the comprehension of high pressure boiling flows relative to PWR.The first part exposes a two-dimensional unsteady state model in order to predict the development of a boiling flow in a circular pipe. The local mixture balanced equations are used with a relaxation model to close the vapor production rate (local homogeneous relaxation model). The results obtained from the comparison with the data bank DEBORA reveal a good qualitative agreement. Nerveless, the model is currently unable to correctly describe radial transports of turbulence and vapor fraction from the heated wall to the center of the pipe.The second part deals with the use of hot wire anemometry in experimental loop DEBORA to provide radial distributions of mean liquid velocity, mean liquid temperature and void fraction in a boiling flow. Classical hot wire probes are used (DANTEC@ hot film and hot wire probes) and are driven at different overheats using a constant current anemometer. Some measurements are first performed in single phase heated flows. Then, a phase identification procedure is developed, and some boiling flow measurements are obtained and compared with the model
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Lavička, Jiří. "Senzor měření rychlosti proudění vzduchu v elektrickém stroji." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2018. http://www.nusl.cz/ntk/nusl-378712.
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This thesis consists of description of design and construction of device for measuring air velocity created in it´s practical part. In introduction is mentioned basic theoretical information related to given problem, in the next chapters is descripted design and construction of measuring device along with description of calibration proces. At the end is placed chapter about testing the final device.
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Imayama, Shintaro. "Experimental study of the rotating-disk boundary-layer flow." Licentiate thesis, KTH, Mekanik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-95147.
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Rotating-disk flow has been investigated not only as a simple model of cross flow instability to compare with swept-wing flow but also for industrial flow applications with rotating configurations. However the exact nature of laminar-turbulent transi- tion on the rotating-disk flow is still major problem and further research is required for it to be fully understood, in particular, the laminar-turbulent transition process with absolute instability. In addition the studies of the rotating-disk turbulent boundary- layer flow are inadequate to understand the physics of three-dimensional turbulent boundary-layer flow. In present thesis, a rotating-rotating disk boundary-layer flow has been inves- tigated experimentally using hot-wire anemometry. A glass disk with a flat surface has been prepared to archieve low disturbance rotating-disk environment. Azimuthal velocity measurements using a hot-wire probe have been taken for various conditions. To get a better insight into the laminar-turbulent transition region, a new way to describe the process is proposed using the probability density function (PDF) map of azimuthal fluctuation velocity. The effect of the edge of the disk on the laminar-turbulent transition process has been investigated. The disturbance growth of azimuthal fluctuation velocity as a function of Reynolds number has a similar trend irrespective of the various edge conditions. The behaviour of secondary instability and turbulent breakdown has been in- vestigated. It has been found that the kinked azimuthal velocity associated with secondary instability just before turbulent breakdown became less apparent at a cer- tain wall normal heights. Furthermore the turbulent breakdown of the stationary mode seems not to be triggered by its amplitude, however, depend on the appearance of the travelling secondary instability. Finally, the turbulent boundary layer on a rotating disk has been investigated. An azimuthal friction velocity has been directly measured from the azimuthal velocity profile in the viscous sub-layer. The turbulent statistics normalized by the inner and outer sclaes are presented.QC 20120529