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1
Tulapurkara, E. G. "Turbulence models for the computation of flow past airplanes". Progress in Aerospace Sciences 33, n. 1-2 (gennaio 1997): 71–165. http://dx.doi.org/10.1016/s0376-0421(96)00002-4.
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Bäuerle, N., O. Engelhardt-Funke e M. Kolonko. "ROUTING OF AIRPLANES TO TWO RUNWAYS: MONOTONICITY OF OPTIMAL CONTROLS". Probability in the Engineering and Informational Sciences 18, n. 4 (ottobre 2004): 533–60. http://dx.doi.org/10.1017/s0269964804184088.
Testo completoAbstract (sommario):
We consider the problem of routing incoming airplanes to two runways of an airport. Due to air turbulence, the necessary separation time between two successive landing operations depends on the type of airplane. When viewed as a queuing problem, this means that we have dependent service times. The aim is to minimize the waiting times of aircrafts. We consider here a model in which arrivals form a stochastic process and the decision-maker does not know anything about future arrivals. We formulate this as a problem of stochastic dynamic programming and investigate the monotonicity of optimal routing strategies with respect to the workload of the runways, for example. We show that an optimal strategy is monotone (i.e., of switching type) only in a restricted case where decisions depend on the state of the runways only and not on the type of the arriving aircraft. Surprisingly, in the more realistic case where this type is also known to the decision-maker, monotonicity need not hold.
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Hariyadi, Setyo, Sutardi Sutardi, Wawan Aries Widodo e Bambang Juni Pitoyo. "Comparative Study of Forward Wingtip Fence and Rearward Wingtip Fence on Wing Airfoil Eppler E562". Journal of Energy, Mechanical, Material, and Manufacturing Engineering 5, n. 1 (31 maggio 2020): 25. http://dx.doi.org/10.22219/jemmme.v5i1.11968.
Testo completoAbstract (sommario):
The perfect wing is a dream that many airplanes has manufactured have been striving to achieve since the beginning of the airplane design. There are some aspect that most influence in aircraft design lift, drag, thrust, and weight. The combination of these aspects leads to a decrease in fuel consumption, which reduces pollution in our atmosphere and increase in economic revenue. One way to improve aircraft performance is to modify the tip of the wing geometry, which has become a common sight on today’s airplanes. With computational programs, the effects on drag due to wingtip devices can be previewed. This research was done numerically by using turbulence model k-ω SST. Reynolds number in this research was 2,34 x 10 4 with angle of attacks are 0o, 2o, 4o, 6o, 8o, 10o, 12o, 15o, 17o and 19o. The model specimen is wing airfoil Eppler 562 with winglets. Two types of wingtips are used: forward and rearward wingtip fence. From this study, it was found that wingtip fence reduced the strength of vorticity magnitude on the x axis compared to plain wings. The leakage of fluid flow effect at the leading edge corner of the wingtip, giving pressure gradient and slightly shifting towards the trailing edge. this occurs in the plain wing and rearward wingtip fence but does not occur in the forward wingtip fence..
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Aqilah, Farah, Mazharul Islam, Franjo Juretic, Joel Guerrero, David Wood e Farid Nasir Ani. "STUDY OF MESH QUALITY IMPROVEMENT FOR CFD ANALYSIS OF AN AIRFOIL". IIUM Engineering Journal 19, n. 2 (1 dicembre 2018): 203–12. http://dx.doi.org/10.31436/iiumej.v19i2.905.
Testo completoAbstract (sommario):
ABSTRACT: Airfoils generate lift in engineering applications such as for airplanes, wind turbines, automotive spoilers, etc. For accurate CFD analysis of airfoils, the quality of the mesh is of paramount importance, especially when dealing with turbulent flows commonly encountered in real life applications. Currently there are different tools that are available to improve the quality of the mesh required for CFD studies. This paper describes a study to assess the significant of the quality of the mesh on CFD analyses of NACA 23012 airfoil by using selected open source tools. The turbulence is modeled using the well-known k-ω Shear Stress Transport model. For validation, results have been compared with experimental datasets which were obtained from “TAG Stuttgart #1†tunnel.
ABSTRAK: Sayap pesawat dapat menghasilkan daya angkat dalam aplikasi kejuruteraan seperti kapal terbang, turbin angin, spoiler automotif, dan sebagainya. Kualiti pada jaringan adalah amat penting bagi mendapatkan analisa CFD yang tepat pada sayap pesawat, terutamanya apabila berhadapan situasi aliran turbulen sebenar. Pada masa ini terdapat pelbagai perisian bagi meningkatkan mutu jaringan dalam kajian CFD. Kertas kerja ini membentangkan satu kajian bagi menilai kepentingan kualiti jaringan pada analisis CFD bagi sayap pesawat NACA 23012 dengan menggunakan sumber terpilih perisian terbuka. Model turbulen dibangunkan mengguna pakai model k-ω Shear Stress Transport (SST) yang terkenal. Bagi pengesahan, keputusan uji kaji telah dibandingkan dengan set data yang diperoleh dari terowong "TAG Stuttgart #1â€."
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Majka, Andrzej. "Flight Loads of Mini UAV". Solid State Phenomena 198 (marzo 2013): 194–99. http://dx.doi.org/10.4028/www.scientific.net/ssp.198.194.
Testo completoAbstract (sommario):
Designing and building of the unmanned aircraft, especially light and ultra light vehicles, is mainly performed using the experience gained when constructing the flying models. There have not been uniform principles of building and exploiting of the mini and micro UAV (Unmanned Aerial Vehicle) in the form of regulations similar to those for manned airplanes. The unmanned vehicles of these classes in terms of their abilities and attractive price are more frequently exploited using the same air area as manned airplanes performing missions over the inhabited areas. An urgent necessity arises to work out the norms of flight suitability of the mini and micro unmanned aerial vehicles. The work contains the analysis of suitability of the current aviation regulations to determine the requirements for the mini unmanned vehicles. The work concentrates on the phenomenon of determining the symmetrical loads from the maneuvers and the turbulence atmosphere. The result of this analysis is the Limit Maneuver Envelope, Limit Gust Envelope and Limit Combined Envelope for mini UAV. The analyzed flight states allowed selecting the so called design cases which can become a basis for determining the norms of loading of mini unmanned aerial vehicles which can constitute the beginning of the regulations for building of the unmanned aerial vehicles of this class.
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Xu, Xin, Da Wei Liu, De Hua Chen e Yuan Jing Wang. "Numerical Investigation on Shock-Induced Separation Structure of Supercritical Airfoil". Advanced Materials Research 756-759 (settembre 2013): 4502–5. http://dx.doi.org/10.4028/www.scientific.net/amr.756-759.4502.
Testo completoAbstract (sommario):
The supercritical airfoil has been widely applied to large airplanes for sake of high aerodynamic efficiency. But at transonic speeds, the complicated shock-induced separation on the upper surface of supercritical airfoil will change the aerodynamic characteristics. The transonic flows over a typical supercritical airfoil CH were numerically investigated in this paper, in order to analyses different shock-induced separation structure. The two-dimensional Navier-Stokes equations were solved with structure grids by utilizing the S-A turbulence model. The computation attack angles of CH airfoil varied from 0oto 4o, Mach numbers varied from 0.74 to 0.82 while Reynolds numbers varied from 3×106to 50×106per airfoil chord. It is shown that with the attack angle increases, the separation bubble occurred on the upper surface first, then the trailing-edge separation occurred, the trailing-edge would separate totally at last. The different separation structure would result in different pressure coefficient distribution and boundary layer thickness.
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Łapka, Piotr, Marije Bakker, Piotr Furmański e Hans van Tongeren. "Comparison of 1D and 3D thermal models of the nacelle ventilation system in a small airplane". Aircraft Engineering and Aerospace Technology 90, n. 1 (2 gennaio 2018): 114–25. http://dx.doi.org/10.1108/aeat-09-2015-0204.
Testo completoAbstract (sommario):
Purpose Insight in the temperature distribution on the internal and external surface of the nacelle is of great importance during the design phase of an aircraft. However, detailed information is not always needed. In a preliminary project stage or during parametric optimization, short analysis times are often more crucial than high accuracy. In such cases, the global insight in the temperature levels suffices to gain understanding of the relevance and influence of certain parameters. Nevertheless, estimating the maximum temperature for the most adverse conditions should also be done before a prototype is built. Therefore, this study aims to present and compare a simplified and an advanced methodology for the analysis of engine bay cooling and ventilation systems as well as heat transfer in the nacelle in a small airplane equipped with a turboprop engine in the tractor arrangement. Design/methodology/approach Both approaches included conductive, convective and radiative heat transfer in the engine bay of the small airplane I-23 as well as heat conduction in the nacelle made of material with anisotropic thermal conductivity. The one-dimensional (1D) model assumed that the nacelle with the air flow and engine was represented by a lumped thermal model in which heat was exchanged between the different lumped segments (the nodes) and the flowing air and engine. The three-dimensional (3D) model was based on the continuous control volume approach for heat, fluid flow and thermal radiation as well as on realizable k-ε turbulence model. Both models used commercial software. Findings The temperature distribution at the internal and external surface of the top nacelle was calculated. The 1D model predicted a temperature per node (per segment) while the 3D model was able to determine its values accurately and find the location of hot spots. Considering the complex geometry of the engine bay and nacelle and the assumed simplification, the obtained 1D and 3D results agreed quite well. Practical implications Both models will help in the development of new ventilation and cooling systems of the engine bay and nacelle as well as in the selection of materials for parts of the top cowling in the newly redesigned airplane I-23 equipped with a turboprop engine. In addition, the methodology presented in this paper might be applied in the development of other airplanes. Originality/value The 1D and 3D models of complex heat transfer inside the engine bay and in the nacelle of the newly re-designed airplane I-23 were elaborated and compared.
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Aylor, Donald E., Matthew T. Boehm e Elson J. Shields. "Quantifying Aerial Concentrations of Maize Pollen in the Atmospheric Surface Layer Using Remote-Piloted Airplanes and Lagrangian Stochastic Modeling". Journal of Applied Meteorology and Climatology 45, n. 7 (1 luglio 2006): 1003–15. http://dx.doi.org/10.1175/jam2381.1.
Testo completoAbstract (sommario):
Abstract The extensive adoption of genetically modified crops has led to a need to understand better the dispersal of pollen in the atmosphere because of the potential for unwanted movement of genetic traits via pollen flow in the environment. The aerial dispersal of maize pollen was studied by comparing the results of a Lagrangian stochastic (LS) model with pollen concentration measurements made over cornfields using a combination of tower-based rotorod samplers and airborne radio-controlled remote-piloted vehicles (RPVs) outfitted with remotely operated pollen samplers. The comparison between model and measurements was conducted in two steps. In the first step, the LS model was used in combination with the rotorod samplers to estimate the pollen release rate Q for each sampling period. In the second step, a modeled value for the concentration Cmodel, corresponding to each RPV measured value Cmeasure, was calculated by simulating the RPV flight path through the LS model pollen plume corresponding to the atmospheric conditions, field geometry, wind direction, and source strength. The geometric mean and geometric standard deviation of the ratio Cmodel/Cmeasure over all of the sampling periods, except those determined to be upwind of the field, were 1.42 and 4.53, respectively, and the lognormal distribution corresponding to these values was found to fit closely the PDF of Cmodel/Cmeasure. Model output was sensitive to the turbulence parameters, with a factor-of-100 difference in the average value of Cmodel over the range of values encountered during the experiment. In comparison with this large potential variability, it is concluded that the average factor of 1.4 between Cmodel and Cmeasure found here indicates that the LS model is capable of accurately predicting, on average, concentrations over a range of atmospheric conditions.
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Bruce Ralphin Rose, J., e Gr Jinu. "Gust Induced Aerodynamic Force Prediction on a Transport Wing Using Quasi-Steady Approximation". International Journal of Computational Methods 12, n. 06 (dicembre 2015): 1550034. http://dx.doi.org/10.1142/s0219876215500346.
Testo completoAbstract (sommario):
The atmospheric wind turbulence over a specified time period has a strong influence on the airplane performance characteristics. Forecasting of this unsteady aerodynamic phenomenon is complex one for designing the control systems to ensure the structural safety. A novel approach is developed to assess the influence of a gust structure on the aerodynamic coefficients of an airplane. The load factor enhancement because of the discrete gust is also quantified to ensure the safety margin. The Kussner’s function is used to determine the time varying increment of gust-dependent lift produced on an airplane wing entering a sharp-edged gust. A most general gust shape is assumed for the present study with quasi-steady approximation. The turbulent viscosity across the chord wise positions are quantified to calculate the velocity fluctuations because of eddies. Determining the gust influence on the fundamental lift and drag characteristics of a commercial airplane is focused in the present investigation. It is accomplished with the help of Wagner’s function in the time domain for the gust response-dependent lift. The outcome of the numerical simulation process is fully verified using the theoretical and experimental results. Solution convergence is attained for a range of input conditions and it shows that the proposed methodology is competent to assess the gust response for various airplane systems design.
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Ma, Tielin, Zhihua Wei, Haibing Chen e Xiangsheng Wang. "Simulation of the dynamic retrieval process of a towed target system under towing airplane’s wake and atmospheric turbulence". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 234, n. 9 (2 aprile 2020): 1518–30. http://dx.doi.org/10.1177/0954410020916292.
Testo completoAbstract (sommario):
This paper studies the dynamic retrieval process of a towed target system under perturbation by simulating the reel-in operation under the towing airplane’s wake and atmospheric turbulence. To settle the computational problem of cable tension, the constant-length method is proposed to transform this variable-mass problem into a constant-length problem based on a mass-spring model that discretizes the cable. A three-dimensional atmospheric turbulence field is built using a recursive function to model the complex perturbation field along the cable. A horseshoe vortex model is adopted to simulate the towing airplane’s wake. Simulation analysis shows that both the reel-in speed and turbulence significantly affect the retrieval deviation, whereas the airplane’s wake has little influence. The reel-in speed should be chosen in concert with the turbulence intensity to achieve a high retrieval success rate. Moreover, a higher reel-in speed is preferred to maintain cable strain and smoothen the process when the retrieval tolerance is satisfied.
11
Trevino, George. "Airplane flight through wind-shear turbulence". Journal of Aircraft 23, n. 9 (settembre 1986): 733–35. http://dx.doi.org/10.2514/3.45372.
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Antolovic, Dorea, e Davor Franjkovic. "Calculation of Airplane Wake Turbulence Re-Categorisation Effects". Transportation Research Procedia 51 (2020): 179–89. http://dx.doi.org/10.1016/j.trpro.2020.11.020.
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Brostow, Witold, Haley E. Hagg Lobland, Taruna Reddy, Ram P. Singh e Leslie White. "Lowering mechanical degradation of drag reducers in turbulent flow". Journal of Materials Research 22, n. 1 (gennaio 2007): 56–60. http://dx.doi.org/10.1557/jmr.2007.0003.
Testo completoAbstract (sommario):
Drag reduction (DR) agents are used in several ppm concentrations to accelerate significantly the flow through conduits in oil pipelines, oil well operations, flood water disposal, fire fighting, field irrigation, transport of suspensions and slurries, sewage systems, water heating and cooling systems, airplane tank filling, marine systems, and also in biomedical systems including blood flow. The drag reduction agents are typically high molecular mass polymers; in industrial applications they undergo mechanical degradation in turbulent flow. We provide an equation that describes quantitatively the degradation, thus predicting drag reduction as a function of time and of the concentration of the drag reduction agent. We report how grafting a polymer on the backbone of a different polymer affects the drag reduction efficacy. Our grafted polymer undergoes degradation by flow turbulence more slowly and also provides high levels of drag reduction efficacy at much lower concentrations than homopolymers do.
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Yang, Shi-Bin, Li-Bao Wang e Dan Xu. "Computational analysis on actuator failures of flexible aircraft". International Journal of Computational Materials Science and Engineering 07, n. 01n02 (giugno 2018): 1850014. http://dx.doi.org/10.1142/s2047684118500148.
Testo completoAbstract (sommario):
A coupled model of aeroservoelasticity and hydraulic actuator used for failure simulation is presented. The mathematical model composites rigid-body modes, elastic modes, control surface modes, unsteady aerodynamic forces and failure models (jam, loss of control (LOC), oscillatory failure, and hydraulic fluid leakage). A clear framework of coupling method of airplane aeroelastic equation and control surface dynamic equation is provided to study the impacts of surface failures on rigid-elastic motion of airplane. The coupled model is shown to be effective in evaluation of gust response in both discrete gust and continuous turbulence conditions compared with results obtained from the 3-order simplified actuator. Examples of gust load alleviation (GLA) system with LOC of ailerons are given. Results show that total loss of function of GLA system is caused by the LOC. With continuous turbulence excitation, the failure loads is several times larger than that without GLA system.
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Poirion, F. "Response of an airplane to non-Gaussian atmospheric turbulence". Journal of Aircraft 28, n. 9 (settembre 1991): 579–83. http://dx.doi.org/10.2514/3.46067.
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Alapetite, Alexandre, Emilie Møllenbach, Anders Stockmarr e Katsumi Minakata. "A Rollercoaster to Model Touch Interactions during Turbulence". Advances in Human-Computer Interaction 2018 (18 ottobre 2018): 1–16. http://dx.doi.org/10.1155/2018/2698635.
Testo completoAbstract (sommario):
We contribute to a project introducing the use of a large single touch-screen as a concept for future airplane cockpits. Human-machine interaction in this new type of cockpit must be optimised to cope with the different types of normal use as well as during moments of turbulence (which can occur during flights varying degrees of severity). We propose an original experimental setup for reproducing turbulence (not limited to aviation) based on a touch-screen mounted on a rollercoaster. Participants had to repeatedly solve three basic touch interactions: a single click, a one-finger drag-and-drop, and a zoom operation involving a 2-finger pinching gesture. The completion times of the different tasks as well as the number of unnecessary interactions with the screen constitute the collected user data. We also propose a data analysis and statistical method to combine user performance with observed turbulence, including acceleration and jerk along the different axes. We then report some of the implications of severe turbulence on touch interaction and make recommendations as to how this can be accommodated in future design solutions.
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Serokhvostov, Sergey. "MAXIMIZATION OF FLIGHT TIME FOR AIRPLANES WITH ELECTRICAL DRIVE BY POWERPLANT OPTIMIZATION". Aviation 11, n. 2 (31 marzo 2007): 37–40. http://dx.doi.org/10.3846/16487788.2007.9635959.
Testo completoAbstract (sommario):
In this paper, the problem of maximizing the flight time of an airplane with an electrical power plant (AEP) by the optimization of the mass of the accumulator in cases of fixed and non‐fixed airframe is considered. Variants of high (turbulent flow) and low (laminar flow) Reynolds numbers are taken into account. Dependence of flight time on airplane parameters is obtained. The behaviour of flight time as a function of accumulator mass near the maximum is also investigated. A comparison between the results obtained and the data for the existing AEP is made. On the basis of the results obtained, the influence of aircraft parameters on flight time is analyzed.
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Proskurnikov, Anton V., e Oleg N. Granichin. "Evolution of clusters in large-scale dynamical networks". Cybernetics and Physics, Volume 7, 2018, Number 3 (30 novembre 2018): 102–29. http://dx.doi.org/10.35470/2226-4116-2018-7-3-102-129.
Testo completoAbstract (sommario):
Recent tremendous progress in electronics, complexity theory and network science provides new opportunities for intellectual control of complex large-scale systems operating in turbulent environment via networks of interconnected miniature devices, serving as actuators, sensors and data processors. Actual dynamics of the resulting control systems are too sophisticated to be examined controlled by traditional methods, which primarily deal with ordinary differential equations. However, their complexity can be dramatically reduced by fast processes, organizing the elementary units of the system (called agents) into relatively small number of clusters. The clusters emerge and deteriorate in response to changes in the environment, and the processes of their formation and destruction are very short in time. During the periods of the clusters’ existence, the system’s dynamics is essentially low-dimensional due to synchronization between the agents in each cluster. An enormously complicated system is thus reduced to a finite-dimensional model with time-varying structure of the state vector. The low-dimensionality of the reduced model allows to control it by using classical methods, e.g. model-predictive or adaptive control. This philosophy of complex systems control is illustrated on an experimental setup, called the “airplane with feathers”. The wings of this airplane are equipped with arrays of microsensors, microcomputers, and microactuators (“feathers”). The feathers self-organize into clusters by using a multi-agent consensus protocol; the aim of this coordination is to reduce the perturbing forces, affecting the airplane in a turbulent flow.
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Alaoui-Sosse, Sara, Pierre Durand, Patrice Medina, Philippe Pastor, Marie Lothon e Iuri Cernov. "OVLI-TA: An Unmanned Aerial System for Measuring Profiles and Turbulence in the Atmospheric Boundary Layer". Sensors 19, n. 3 (30 gennaio 2019): 581. http://dx.doi.org/10.3390/s19030581.
Testo completoAbstract (sommario):
In recent years, we developed a small, unmanned aerial system (UAS) called OVLI-TA (Objet Volant Leger Instrumenté–Turbulence Atmosphérique) dedicated to atmospheric boundary layer research, in Toulouse (France). The device has a wingspan of 2.60 m and weighed 3.5 kg, including payload. It was essentially developed to investigate turbulence in a way complementary to other existing measurement systems, such as instrumented towers/masts. OVLI-TA’s instrumental package includes a 5-hole probe on the nose of the airplane to measure attack and sideslip angles, a Pitot probe to measure static pressure, a fast inertial measurement unit, a GPS receiver, as well as temperature and moisture sensors in specific housings. In addition, the Pixhawk autopilot is used for autonomous flights. OVLI-TA is capable of profiling wind speed, wind direction, temperature, and humidity up to 1 km altitude, in addition to measuring turbulence. After wind tunnel calibrations, flight tests were conducted in March 2016 in Lannemezan (France), where there is a 60-m tower equipped with turbulence sensors. In July 2016, OVLI-TA participated in the international project DACCIWA (Dynamics-Aerosol-Chemistry-Clouds Interactions in West Africa), in Benin. Comparisons of the OVLI-TA observations with both the 60 m tower measurements and the radiosonde profiles showed good agreement for the mean values of wind, temperature, humidity, and turbulence parameters. Moreover, it validated the capacity of the drone to sample wind fluctuations up to a frequency of around 10 Hz, which corresponds to a spatial resolution of the order of 1 m.
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Crawford, Timothy L., e Ronald J. Dobosy. "A sensitive fast-response probe to measure turbulence and heat flux from any airplane". Boundary-Layer Meteorology 59, n. 3 (maggio 1992): 257–78. http://dx.doi.org/10.1007/bf00119816.
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Фомичов, Петро Олександрович, Тетяна Сергіївна Бойко e Олександр Олександрович Севостьянов. "Метод расчета усталостного повреждения регулярных зон крыла самолета при случайном нагружении на этапах типового полета". Aerospace technic and technology, n. 3 (27 maggio 2021): 13–23. http://dx.doi.org/10.32620/aktt.2021.3.02.
Testo completoAbstract (sommario):
In accordance with the airworthiness standards, the aircraft structure must be operationally survivable, it means that structure must be able to remain efficiency in the presence of admissible damage. But, accumulating above than a certain level, damages cause fatigue failure of the structure, in the form of micro- and submicrocracks, thus reducing its strength characteristics. Currently, several approaches have been formed to ensure the safety of an aircraft structures in terms of strength. One of them is ensuring a safe resource (safe durability). This principle implies that during the specified service life of the product, no damage will occur in it, reducing the strength below the permissible level. The aircraft resource is limited “from above” by the durability of the regular zones of airframe. Therefore, predicting the durability of an aircraft wing structure at the design stage is a fundamental engineering problem to ensure its safety and economic efficiency. At the same time, the first step in dealing with aircraft fatigue damage at the design stage is the collection and assessment of the operational loads of the analog aircraft. However, at the design stage of a new aircraft model, obtaining such data is not always possible. Therefore, the purpose of this article is to develop a method for calculating fatigue damage at the stage of cracking and assessing the durability of regular zones of a transport aircraft wing, taking into account the conditions of its operation. The tasks to be solved are: to isolate the factors that determine the durability of the aircraft at flying in turbulent air; to take into account the asymmetry of loads and accumulated damage that occurs at each stage during the entire flight of the aircraft; to determine the aircraft's resource depending on the profile of a typical flight. The method is based on a standardized atmospheric turbulence model, typical flight profiles, fatigue characteristics of materials, the hypothesis of linear summation of damages and calculation based on nominal stresses. As result, comparison between the calculated integral repeatability of overloads and equivalent bending moments with the results of processing flight test data showed good agreements. Conclusions. The scientific novelty of the work lies in the fact that a method for calculating the fatigue damage of the regular wing zones, taking into account the expected flight profile of the aircraft was developed. This means that the proposed method makes it possible to carry out a preliminary assessment of the resource when designing an airplane without using data on the operational loads of an analogue airplane, and also estimate the residual resource of the airplane during its operation.
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MORARU, Laurentiu, e Marius STOIA-DJESKA. "Notes Regarding the Dynamics of an Airplane subjected to Vertical Gusts". INCAS BULLETIN 12, n. 1 (1 marzo 2020): 127–34. http://dx.doi.org/10.13111/2066-8201.2020.12.1.12.
Testo completoAbstract (sommario):
The behavior of the aircraft within turbulent atmosphere is a key aspect of design. Many books and articles deal with this topic. The current paper presents studies related to predicting the responses of aircraft flying through vertical gusts. The equations describing the dynamics of the longitudinal channel of the airplane are written to include the effect of the vertical wind. The paper includes comparisons of results provided by non-linear and linearized equations of motion.
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Si, Chao Wei, Guo Wei Han, Jin Ning, Wei Wei Zhong e Fu Hua Yang. "Design of a MEMS Resonant Wind Sensor on Airplane Wing". Key Engineering Materials 562-565 (luglio 2013): 436–40. http://dx.doi.org/10.4028/www.scientific.net/kem.562-565.436.
Testo completoAbstract (sommario):
A new kind of wind sensor made up of MEMS resonators is designed in the paper capable of sensing the lift, the resistance and the turbulence of airplane wings by mounting on the surface. The designed wind sensor is made up of four MEMS wind pressure gauges fixed around a square wind resistance block which used to block the wind to change the wind pressure on the surface, and the change of wind pressure is detected by MEMS wind pressure gauges to reveal the air condition on the surface of the airplane wings. As known, a MEMS resonator is a second-order resonant system whose damping factor is mainly dependent on the air pressure, and the characteristic is often used to detecting the airtightness of a sealed chamber for the damping factor is sensitive under high vacuum, while a MEMS resonator with the damping factor sensitive at atmospheric pressure is designed in this paper for sensing wind pressure change, and the MEMS resonator is manufactured on SOI substrates with deep reactive ion etching technology. Also relations between the wind pressure change and the wind speed around a block at atmosphere is revealed by finite element simulation. Compared to traditional wind sensors such as anemometers and Venturi tubes, the designed MEMS wind sensor with a very small size is suitable to mount on different zones of a wing with a large amount to monitor the air condition and have less influence on air flow.
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ZHU, CHENGXIANG, BIN FU, ZHIGUO SUN e CHUNLING ZHU. "3D ICE ACCRETION SIMULATION FOR COMPLEX CONFIGURATION BASING ON IMPROVED MESSINGER MODEL". International Journal of Modern Physics: Conference Series 19 (gennaio 2012): 341–50. http://dx.doi.org/10.1142/s2010194512008938.
Testo completoAbstract (sommario):
Ice accretion on 3D complex configuration is studied by numerical method. The flow field is obtained by using Fluent 6.0 with S-A turbulence model, droplet trajectories and impingement characteristics are obtained using the Eulerian approach, ice shape is calculated basing on the improved Messinger model with a new runback distribution scheme. Using the method presented in this paper, ice accretion on NACA0012 is computed, and the results are in good agreement with the available experiment data. It shows preliminarily that the improved method described in this paper is feasible. Meanwhile, ice accretion on a four-element airplane is studied. According to the analysis of the calculated result, it illustrates that using the method presented in the paper can correctly simulate the ice accretion on 3D complex configuration.
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Reichstein, Torben, Alois Peter Schaffarczyk, Christoph Dollinger, Nicolas Balaresque, Erich Schülein, Clemens Jauch e Andreas Fischer. "Investigation of Laminar–Turbulent Transition on a Rotating Wind-Turbine Blade of Multimegawatt Class with Thermography and Microphone Array". Energies 12, n. 11 (1 giugno 2019): 2102. http://dx.doi.org/10.3390/en12112102.
Testo completoAbstract (sommario):
Knowledge about laminar–turbulent transition on operating multi megawatt wind turbine (WT) blades needs sophisticated equipment like hot films or microphone arrays. Contrarily, thermographic pictures can easily be taken from the ground, and temperature differences indicate different states of the boundary layer. Accuracy, however, is still an open question, so that an aerodynamic glove, known from experimental research on airplanes, was used to classify the boundary-layer state of a 2 megawatt WT blade operating in the northern part of Schleswig-Holstein, Germany. State-of-the-art equipment for measuring static surface pressure was used for monitoring lift distribution. To distinguish the laminar and turbulent parts of the boundary layer (suction side only), 48 microphones were applied together with ground-based thermographic cameras from two teams. Additionally, an optical camera mounted on the hub was used to survey vibrations. During start-up (SU) (from 0 to 9 rpm), extended but irregularly shaped regions of a laminar-boundary layer were observed that had the same extension measured both with microphones and thermography. When an approximately constant rotor rotation (9 rpm corresponding to approximately 6 m/s wind speed) was achieved, flow transition was visible at the expected position of 40% chord length on the rotor blade, which was fouled with dense turbulent wedges, and an almost complete turbulent state on the glove was detected. In all observations, quantitative determination of flow-transition positions from thermography and microphones agreed well within their accuracy of less than 1%.
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Blay-Carreras, E., D. Pino, A. Van de Boer, O. De Coster, C. Darbieu, O. Hartogensis, F. Lohou, M. Lothon, H. Pietersen e J. Vilà-Guerau de Arellano. "Role of the residual layer and large-scale subsidence on the development and evolution of the convective boundary layer". Atmospheric Chemistry and Physics Discussions 13, n. 12 (2 dicembre 2013): 31527–62. http://dx.doi.org/10.5194/acpd-13-31527-2013.
Testo completoAbstract (sommario):
Abstract. Observations, mixed-layer theory and the Dutch Large-Eddy Simulation model (DALES) are used to analyze the dynamics of the boundary layer during an intensive operational period (1 July 2011) of the Boundary Layer Late Afternoon and Sunset Turbulence campaign. Continuous measurements made by remote sensing and in situ instruments in combination with radio soundings, and measurements done by remotely piloted airplane systems and two aircrafts probed the vertical structure and the temporal evolution of the boundary layer during the campaign. The initial vertical profiles of potential temperature, specific humidity and wind, and the temporal evolution of the surface heat and moisture fluxes prescribed in the numerical simulations are inspired by some of these observations. The research focuses on the role played by the residual layer during the morning transition and by the large-scale subsidence on the evolution of the boundary layer. By using DALES, we show the importance of the dynamics of the boundary layer during the previous night in the development of the boundary layer at the morning. DALES numerical experiments including the residual layer are capable to model the observed sudden increase of the boundary-layer depth during the morning transition and the subsequent evolution of the boundary layer. The simulation shows a large increase of the entrainment buoyancy heat flux when the residual layer is incorporated into the mixed layer. We also examine how the inclusion of the residual layer above a shallow convective boundary layer modifies the turbulent kinetic energy budget. Large-scale subsidence mainly acts when the boundary layer is fully developed and, for the studied day, it is necessary to be considered to reproduce the afternoon observations. Additionally, we investigate how carbon dioxide (CO2) mixing ratio stored the previous night in the residual layer plays a fundamental role in the evolution of the CO2 mixing ratio during the following day.
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LINDBORG, ERIK. "Can the atmospheric kinetic energy spectrum be explained by two-dimensional turbulence?" Journal of Fluid Mechanics 388 (10 giugno 1999): 259–88. http://dx.doi.org/10.1017/s0022112099004851.
Testo completoAbstract (sommario):
The statistical features of turbulence can be studied either through spectral quantities, such as the kinetic energy spectrum, or through structure functions, which are statistical moments of the difference between velocities at two points separated by a variable distance. In this paper structure function relations for two-dimensional turbulence are derived and compared with calculations based on wind data from 5754 airplane flights, reported in the MOZAIC data set. For the third-order structure function two relations are derived, showing that this function is generally positive in the two-dimensional case, contrary to the three-dimensional case. In the energy inertial range the third-order structure function grows linearly with separation distance and in the enstrophy inertial range it grows cubically with separation distance. A Fourier analysis shows that the linear growth is a reflection of a constant negative spectral energy flux, and the cubic growth is a reflection of a constant positive spectral enstrophy flux. Various relations between second-order structure functions and spectral quantities are also derived. The measured second-order structure functions can be divided into two different types of terms, one of the form r2/3, giving a k−5/3-range and another, including a logarithmic dependence, giving a k−3-range in the energy spectrum. The structure functions agree better with the two-dimensional isotropic relation for larger separations than for smaller separations. The flatness factor is found to grow very fast for separations of the order of some kilometres. The third-order structure function is accurately measured in the interval [30, 300] km and is found to be positive. The average enstrophy flux is measured as Πω≈1.8×10−13 s−3 and the constant in the k−3-law is measured as [Kscr ]≈0.19. It is argued that the k−3-range can be explained by two-dimensional turbulence and can be interpreted as an enstrophy inertial range, while the k−5/3-range can probably not be explained by two-dimensional turbulence and should not be interpreted as a two-dimensional energy inertial range.
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Granichin, O. N., e T. A. Khantuleva. "Adapting wing elements (“feathers”) of an airplane in a turbulent flow with a multiagent protocol". Automation and Remote Control 78, n. 10 (ottobre 2017): 1867–82. http://dx.doi.org/10.1134/s0005117917100101.
Testo completo
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Luce, Hubert, Lakshmi Kantha, Hiroyuki Hashiguchi, Abhiram Doddi, Dale Lawrence e Masanori Yabuki. "On the Relationship between the TKE Dissipation Rate and the Temperature Structure Function Parameter in the Convective Boundary Layer". Journal of the Atmospheric Sciences 77, n. 7 (1 luglio 2020): 2311–26. http://dx.doi.org/10.1175/jas-d-19-0274.1.
Testo completoAbstract (sommario):
AbstractUnder stably stratified conditions, the dissipation rate ε of turbulence kinetic energy (TKE) is related to the structure function parameter for temperature , through the buoyancy frequency and the so-called mixing efficiency. A similar relationship does not exist for convective turbulence. In this paper, we propose an analytical expression relating ε and in the convective boundary layer (CBL), by taking into account the effects of nonlocal heat transport under convective conditions using the Deardorff countergradient model. Measurements using unmanned aerial vehicles (UAVs) equipped with high-frequency response sensors to measure velocity and temperature fluctuations obtained during the two field campaigns conducted at Shigaraki MU observatory in June 2016 and 2017 are used to test this relationship between ε and in the CBL. The selection of CBL cases for analysis was aided by auxiliary measurements from additional sensors (mainly radars), and these are described. Comparison with earlier results in the literature suggests that the proposed relationship works, if the countergradient term γD in the Deardorff model, which is proportional to the ratio of the variances of potential temperature θ and vertical velocity w, is evaluated from in situ (airplane and UAV) observational data, but fails if evaluated from large-eddy simulation (LES) results. This appears to be caused by the tendency of the variance of θ in the upper part of the CBL and at the bottom of the entrainment zone to be underestimated by LES relative to in situ measurements from UAVs and aircraft. We discuss this anomaly and explore reasons for it.
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Unterstrasser, S., R. Paoli, I. Sölch, C. Kühnlein e T. Gerz. "Dimension of aircraft exhaust plumes at cruise conditions: effect of wake vortices". Atmospheric Chemistry and Physics Discussions 13, n. 11 (18 novembre 2013): 30039–96. http://dx.doi.org/10.5194/acpd-13-30039-2013.
Testo completoAbstract (sommario):
Abstract. The dispersion of aircraft emissions during the vortex phase is studied, for the first time using a 3-D LES model with Lagrangian particle tracking. The simulations start with a fully rolled-up vortex pair of a type B747/A340 airplane and the tracer centred around the vortex cores. The tracer dilution and plume extent is studied for a variety of ambient and aircraft parameters until aircraft-induced effects have deceased. For typical upper tropospheric conditions, the impact of stratification is more dominant compared to turbulence intensity or vertical wind shear. Moreover, the sensitivity to the initial tracer distribution was found to be weak. Along the transversal direction the tracer concentrations can be well approximated by a Gaussian distribution, along the vertical a superposition of three Gaussian distributions is adequate. For the studied parameter range the vertical plume expansion ranges from 400 m to 550 m and cross-sectional area from 4.0×104 m2 to 6.0×104 m2 after six minutes. For validation, selected simulations were compared to an alternative LES model and to in-situ NO-measurements.
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Unterstrasser, S., R. Paoli, I. Sölch, C. Kühnlein e T. Gerz. "Dimension of aircraft exhaust plumes at cruise conditions: effect of wake vortices". Atmospheric Chemistry and Physics 14, n. 5 (14 marzo 2014): 2713–33. http://dx.doi.org/10.5194/acp-14-2713-2014.
Testo completoAbstract (sommario):
Abstract. The dispersion of aircraft emissions during the vortex phase is studied using a 3-D LES model with Lagrangian particle tracking. The simulations start with a fully rolled-up vortex pair of a type B747/A340 airplane and the tracer centred around the vortex cores. The tracer dilution and plume extent is studied for a variety of ambient and aircraft parameters until aircraft-induced effects have ceased. For typical upper tropospheric conditions, the impact of stratification is more dominant compared to turbulence intensity or vertical wind shear. Moreover, the sensitivity to the initial tracer distribution was found to be weak. Along the transverse direction, the tracer concentrations can be well approximated by a Gaussian distribution, along the vertical a superposition of three Gaussian distributions is adequate. For the studied parameter range, the vertical plume expansion ranges from 400 m to 550 m and cross-sectional area from 4.0 × 104 m2 to 6 × 104 m2 after six minutes. For validation, selected simulations were compared to an alternative LES model and to in-situ NO-measurements.
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Ayudia, Siti Aisyah, Artoto Arkundato e Lutfi Rohman. "Study of Vortex Generator Effect on Airfoil Aerodynamics Using the Computational Fluids Dynamics Method". Computational And Experimental Research In Materials And Renewable Energy 3, n. 2 (24 novembre 2020): 23. http://dx.doi.org/10.19184/cerimre.v3i2.23547.
Testo completoAbstract (sommario):
The lift force is one of the important factors in supporting the aircraft flying capabilities. The airplane has a section called the aircraft wing. In particular, the wing section of aircraft is called the airfoil. One of the efforts to increase the lift force is to make the flow of air fluid at the top of the airfoil more turbulent. Turbulent flow can attract momentum from the boundary layer, the result of this momentum transfer has energy that is more resistant to the adverse pressure gradient which can trigger the flow separation. Efforts that can be made to reduce separation flow and increase lift force are the addition of a turbulent generator on the upper surface of the airfoil, one type of turbulent generator is a vortex generator, a vortex generator can accelerate the transition from the laminar boundary layer to the turbulent boundary layer. This study was conducted with the aim of knowing the effect of the vortex generator on the aerodynamics of NACA-4412 using the computational fluid dynamics method. The main thing that will be investigated is the effect of the straight type vortex generator application on the lift coefficient, by comparing the plain airfoil and airfoil that has been applied to the vortex generator to vary the angle of attack. The variation of the angles of attack are 0º, 5º, 10º, 15º and the placement of the vortex generator is 24% of the leading edge. The results obtained that the lift coefficient changes with increasing angle of attack and the application of a vortex generator to an airfoil can increase the lift coefficient than a plain airfoil. The optimum increase in lift coefficient is at the angle of attack of 5º as much as 13%.
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Mahdal, Miroslav, Josef Dobeš e Milada Kozubková. "Measurement of Aerodynamic and Acoustic Quantities Describing Flow around a Body Placed in a Wind Tunnel". Measurement Science Review 19, n. 1 (1 febbraio 2019): 20–28. http://dx.doi.org/10.2478/msr-2019-0004.
Testo completoAbstract (sommario):
Abstract Aerodynamically generated noise affects passenger comfort in cars, high-speed trains, and airplanes, and thus, automobile manufacturers aim for its reduction. Investigation methods of noise and vibration sources can be divided into two groups, i.e. experimental research and mathematical research. Recently, owing to the increase in computing power, research in aerodynamically generated noise (aero-acoustics) is beginning to use modern methods such as computational fluid dynamics or fluid-structure interaction. The mathematical model of turbulent flow is given by the system of partial differential equations, its solution is ambiguous and thus requires verification by physical experiment. The results of numerical methods are affected by the boundary conditions of high quality gained from the actual experiment. This article describes an application of complex measurement methodology in the aerodynamic and acoustic (vibro-acoustic) fields. The first part of the paper is focused on the specification of the experimental equipment, i.e. the wind tunnel, which was significantly upgraded in order to obtain the relevant aerodynamics and vibro-acoustics data. The paper presents specific results from the measurement of the aerodynamic and vibro-acoustic fields.
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Jimenez, Pedro, Piotr Lichota, Daniel Agudelo e Krzysztof Rogowski. "Experimental Validation of Total Energy Control System for UAVs". Energies 13, n. 1 (18 dicembre 2019): 14. http://dx.doi.org/10.3390/en13010014.
Testo completoAbstract (sommario):
This paper presents an analysis of a Total Energy Control System (TECS) introduced by Lambregts to control unmanned aerial vehicle (UAV) velocity and altitude by using the total energy distribution. Furthermore, an extended Kalman filter (EKF) approach was used to predict aircraft response in terms of angular rates and linear acceleration during a test flight campaign. From both approaches, state equations were obtained to model the aircraft using Matlab-Simulink. From an aerodynamic study, airplane characteristics were obtained in terms of non-dimensional derivatives and compared to those obtained from the experimental methods. It was determined that TECS approach was very accurate; however, disturbance errors could be decreased by adjusting some model parameters. On the other hand, it was difficult to obtain a real estimation from the EKF method due to the presence of turbulence during flight and the relatively low inertia of the scale model. Dynamic characteristics were validated using a low-cost inertial sensor that cab be easily integrated in UAV platforms. The gathered data can be used to predict model characteristics by integrating the information into flight simulators for future design development.
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Lekic, Nikola, Jonathan Sheu, Hayley Ennis, Nathan Lebwohl e Motasem Al-Maaieh. "Why you should wear your seatbelt on an airplane: Burst fracture of the atlas (jefferson fracture) due to in-flight turbulence". Journal of Orthopaedics 17 (gennaio 2020): 78–82. http://dx.doi.org/10.1016/j.jor.2019.06.019.
Testo completo
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Regmi, Ram P. "Aviation Hazards in the Sky over Thada as Revealed by Meso-scale Meteorological Modeling". Journal of Institute of Science and Technology 19, n. 2 (9 novembre 2015): 65–70. http://dx.doi.org/10.3126/jist.v19i2.13854.
Testo completoAbstract (sommario):
The airplane of Nepal Army in-route to Kathmandu Airport from Nepalgunj lost its communication with the air traffic control room from the sky of Thada of Arghakhachi District. The plane was found with breath taking crashing over the Bowang high mountain area of Baglung District. The weather pattern over the area has been numerically reconstructed with the application of Weather Research and Forecasting (WRF) model initialized with NCEP FNL meteorological and USGS land use and terrain elevation data to examined the effect of prevailing weather pattern. The reconstructed weather pattern show that the atmosphere over Thada and associated areas capture an adverse condition for aviation activities, as it appears highly turbulent and is intense subsidence prone. A detail long-term investigation usefully complemented with field observation may provide better understanding and for improved flight safety.Journal of Institute of Science and Technology, 2014, 19(2): 65-70
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Seredyn, Tomasz, Adam Dziubiński e Piotr Jaśkowski. "CFD Analysis of the Fluid Particles Distribution by Means of Aviation Technique". Transactions on Aerospace Research 2018, n. 1 (1 marzo 2018): 67–97. http://dx.doi.org/10.2478/tar-2018-0006.
Testo completoAbstract (sommario):
Abstract The article describes a computational study, using CFD models, of droplet spray dispersal in the wake of a ‘Turbo Kruk’ airplane up to 500 m downstream. The CFD Reynolds-averaged Navier-Stokes (RANS) models use a Lagrangian (droplet phase) and Eulerian (fluid phase) procedure to predict the droplet trajectories trough the turbulent aircraft wake. The methods described in the work have the potential to improve current models for aerial spraying and will help in the development of new spraying procedures. In this study, the CFD models are used to describe the phenomenon of sprays released from atomizers mounted on the plane. A parametric study of the aircraft model examines the effects of crosswind on the aircraft’s vortex structures and the resulting droplet trajectories. The study shows, that such influence is underestimated in the current models. A comparison of the present results to AGDISP predictions is provided.
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D’Oriano, Vera, Raffaele Savino e Michele Visone. "Aerothermodynamic study of a small hypersonic plane". Aircraft Engineering and Aerospace Technology 90, n. 2 (5 marzo 2018): 471–80. http://dx.doi.org/10.1108/aeat-06-2015-0151.
Testo completoAbstract (sommario):
Purpose This paper aims to present an aerothermodynamic analysis of a new concept of a small hypersonic airplane. Aerodynamics characteristics for different flow conditions encountered during the missions are analyzed. The effects of elevons deflection for pitch control and of the presence of engines on aerodynamic performances are also investigated for different flight conditions. The effects of boundary layer laminar–turbulent transition on aerodynamic heating are studied to preliminarily identify proper materials that can sustain the hypersonic phase. Design/methodology/approach Aerodynamic characteristics are predicted by means of the semi-empirical aerodynamic prediction code Missile DATCOM and computational fluid dynamics simulations. Computational fluid dynamics analysis is also performed to investigate aerodynamic heating phenomenon. Findings Major discrepancies between the results offered by the two methods have been registered in transonic regime, whereas in subsonic and super-hypersonic conditions, Missile DATCOM confirms to be a suitable tool for preliminary design steps. The results of the analysis show that for the identification of the materials that can sustain the hypersonic phase, the turbulent solution must be taken into account. Carbon fiber reinforced ceramics composite materials seem particularly well suited for the nose, wing and vertical tail leasing edges and control surfaces, while titanium alloys could be used for the rest of the vehicle surface. Originality/value This new concept of vehicle is designed both for point-to-point medium range hypersonic transportation and long duration suborbital space tourism missions, by integrating available technologies developed for aeronautical and space systems.
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Chatterjee, Amlan Chatterjee. "Dynamic Flight Routing Using Internet of Things Framework". INTERNATIONAL JOURNAL OF COMPUTERS & TECHNOLOGY 20 (22 giugno 2020): 65–80. http://dx.doi.org/10.24297/ijct.v20i.8771.
Testo completoAbstract (sommario):
With increased demand of quicker travel, both for passengers and cargo, there has been major advancements in commercial airlines and number of flights have increased significantly over the last few years. Novel challenges have been introduced due to the rising number of flights in the areas of safety, route planning and maintenance. In addition, for commercial flights, the surge in the number of passengers have also exposed avenues for improving the quality of flight travel, from entering the airport premises to leaving the same at the destination. Although there are many areas of flight and airport operations that can benefit from leveraging technological advancements, choosing safe flight path and making dynamic modifications to it is the critical aspect that needs to be addressed. Comprehending available information to adhere to the provided route and also avoiding known areas of air turbulence, adds to the financial benefit of the commercial airline as well as the safety of the airplane and the passengers are ensured. In this paper, the various aspects of improving the flight routing by providing dynamic intelligent path options to ensure adherence to the provided flight path possible is studied; options for improving the flight safety and turbulence avoidance, which benefits both the passengers and the aircraft are also explored. In addition, keeping aircraft away from conflict zones or war zones, and also from areas of natural disaster, like erupting volcanic ash or forest fires is relevant. Although these issues have been studied before, most of the techniques depend heavily on infrastructure that is on the ground. The basic model requires constant communication with an air traffic control tower, that would provide updates and changes to the flight path as necessary. This leads to some of these methods being unusable on flights operating on oceanic routes and away from the communication zone of the devices placed on land masses. Therefore, in this paper an Internet of Things based framework is proposed to address and handle the above mentioned issues. The framework is structured on the communication model of information exchange among aircraft within the range, as well as taking advantage of ground infrastructure if there is a possible network link to the same. A number of algorithms are proposed for dynamic intelligent routing of flights as well as detection and avoidance of air turbulence. The implementations of the proposed algorithms show improvements ranging from 10% to 30% in the methods as compared to using the infrastructure based conventional techniques.
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John, Michael O., Dominik Obrist e Leonhard Kleiser. "Secondary instability and subcritical transition of the leading-edge boundary layer". Journal of Fluid Mechanics 792 (4 marzo 2016): 682–711. http://dx.doi.org/10.1017/jfm.2016.117.
Testo completoAbstract (sommario):
The leading-edge boundary layer (LEBL) in the front part of swept airplane wings is prone to three-dimensional subcritical instability, which may lead to bypass transition. The resulting increase of airplane drag and fuel consumption implies a negative environmental impact. In the present paper, we present a temporal biglobal secondary stability analysis (SSA) and direct numerical simulations (DNS) of this flow to investigate a subcritical transition mechanism. The LEBL is modelled by the swept Hiemenz boundary layer (SHBL), with and without wall suction. We introduce a pair of steady, counter-rotating, streamwise vortices next to the attachment line as a generic primary disturbance. This generates a high-speed streak, which evolves slowly in the streamwise direction. The SSA predicts that this flow is unstable to secondary, time-dependent perturbations. We report the upper branch of the secondary neutral curve and describe numerous eigenmodes located inside the shear layers surrounding the primary high-speed streak and the vortices. We find secondary flow instability at Reynolds numbers as low as$Re\approx 175$, i.e. far below the linear critical Reynolds number$Re_{crit}\approx 583$of the SHBL. This secondary modal instability is confirmed by our three-dimensional DNS. Furthermore, these simulations show that the modes may grow until nonlinear processes lead to breakdown to turbulent flow for Reynolds numbers above$Re_{tr}\approx 250$. The three-dimensional mode shapes, growth rates, and the frequency dependence of the secondary eigenmodes found by SSA and the DNS results are in close agreement with each other. The transition Reynolds number$Re_{tr}\approx 250$at zero suction and its increase with wall suction closely coincide with experimental and numerical results from the literature. We conclude that the secondary instability and the transition scenario presented in this paper may serve as a possible explanation for the well-known subcritical transition observed in the leading-edge boundary layer.
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Regmi, Ram P. "Aviation Hazards Over the Jomsom Airport of Nepal as Revealed by Numerical Simulation of Local Flows". Journal of Institute of Science and Technology 19, n. 1 (8 novembre 2015): 111–20. http://dx.doi.org/10.3126/jist.v19i1.13836.
Testo completoAbstract (sommario):
Jomsom Airport of Nepal is considered to be one of the world’s most extreme airports. The frequency of aircraft crashing along the Kali Gandaki River Valley and over the Jomsom Airport is very high. Pre-monsoon time local flow characteristics over the Kali Gandaki Valley has been studied to understand the meteorological hazards for aviation activities along the valley and over the Jomsom Airport with the application of the WRF Modeling System initialized with NCEP meteorological, USGS 24 categories land use, and 30 second terrain data. Four days long simulation was carried out for the period of 15 May 0000 UTC to 19 May 0000 UTC, 2012 to capture the 16 May 2012 incidence of light aircraft crashing in the late morning time of the day. The study revealed that there are enough grounds to believe that the crashing of the plane resulted due to the adverse local flow system prevailing over the Jomsom Airport area during the period. The significant subsidence from the relatively strong boundary layer wind aloft, the ground level opposite wind and the low-level turbulence might have leaded the airplane to crash just after its takeoff from the runway. The local flow system over the Kali Gandaki Valley makes afternoon time flights over the Jomsom Airport almost impossible and the narrow slot of time during morning time is also not free from difficult situation. Journal of Institute of Science and Technology, 2014, 19(1): 111-120
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Gatti, Davide, e Maurizio Quadrio. "Reynolds-number dependence of turbulent skin-friction drag reduction induced by spanwise forcing". Journal of Fluid Mechanics 802 (5 agosto 2016): 553–82. http://dx.doi.org/10.1017/jfm.2016.485.
Testo completoAbstract (sommario):
This paper examines how increasing the value of the Reynolds number $Re$ affects the ability of spanwise-forcing techniques to yield turbulent skin-friction drag reduction. The considered forcing is based on the streamwise-travelling waves of spanwise-wall velocity (Quadrio et al., J. Fluid Mech., vol. 627, 2009, pp. 161–178). The study builds upon an extensive drag-reduction database created via direct numerical simulation of a turbulent channel flow for two fivefold separated values of $Re$, namely $Re_{\unicode[STIX]{x1D70F}}=200$ and $Re_{\unicode[STIX]{x1D70F}}=1000$. The sheer size of the database, which for the first time systematically addresses the amplitude of the forcing, allows a comprehensive view of the drag-reducing characteristics of the travelling waves, and enables a detailed description of the changes occurring when $Re$ increases. The effect of using a viscous scaling based on the friction velocity of either the non-controlled flow or the drag-reduced flow is described. In analogy with other wall-based drag-reduction techniques, like riblets for example, the performance of the travelling waves is well described by a vertical shift of the logarithmic portion of the mean streamwise velocity profile. Except when $Re$ is very low, this shift remains constant with $Re$, at odds with the percentage reduction of the friction coefficient, which is known to present a mild, logarithmic decline. Our new data agree with the available literature, which is however mostly based on low-$Re$ information and hence predicts a quick drop of maximum drag reduction with $Re$. The present study supports a more optimistic scenario, where for an airplane at flight Reynolds numbers a drag reduction of nearly 30 % would still be possible thanks to the travelling waves.
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Vellinga, Olaf S., Ronald J. Dobosy, Edward J. Dumas, Beniamino Gioli, Jan A. Elbers e Ronald W. A. Hutjes. "Calibration and Quality Assurance of Flux Observations from a Small Research Aircraft*". Journal of Atmospheric and Oceanic Technology 30, n. 2 (1 febbraio 2013): 161–81. http://dx.doi.org/10.1175/jtech-d-11-00138.1.
Testo completoAbstract (sommario):
Abstract Small environmental research aircraft (ERA) are becoming more common for detailed studies of air–surface interactions. The Sky Arrow 650 ERA, used by multiple groups, is designed to minimize the complexity of high-precision airborne turbulent wind measurement. Its relative wind probe, of a nine-port design, is furthermore used with several other airplanes. This paper gives an overview of 1) calibration of the model that converts the probe’s raw measurements to meteorological quantities; 2) quality control and assurance (QC–QA) in postprocessing of these quantities to compute fluxes; and 3) sensitivity of fluxes to errors in calibration parameters. The model, an adapted version of standard models of potential flow and aerodynamic upwash, is calibrated using an integrated method to derive a globally optimum set of parameters from in-flight maneuvers. Methods of QC–QA from the tower flux community are adopted for use with airborne flux data to provide more objective selection criteria for large datasets. Last, measurements taken from a standard operational flight are used to show fluxes to be most sensitive to calibration parameters that directly affect the vertical wind component. In another test with the same data, varying all calibration parameters simultaneously by ±10% of their optimum values, the model computes a response in the fluxes smaller than 10%, though a larger response may occur if only a subset of parameters is perturbed. A MATLAB toolbox has been developed that facilitates the procedures presented here.
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Efimtsov, B. M., e L. A. Lazarev. "The possibility of reducing the noise produced in an airplane cabin by the turbulent boundary layer by varying the fuselage stiffening set with its mass being invariant". Acoustical Physics 61, n. 5 (settembre 2015): 580–84. http://dx.doi.org/10.1134/s1063771015040041.
Testo completo
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Weibring, Petter, Dirk Richter, James G. Walega, Alan Fried, Joshua DiGangi, Hannah Halliday, Yonghoon Choi et al. "Autonomous airborne mid-infrared spectrometer for high-precision measurements of ethane during the NASA ACT-America studies". Atmospheric Measurement Techniques 13, n. 11 (17 novembre 2020): 6095–112. http://dx.doi.org/10.5194/amt-13-6095-2020.
Testo completoAbstract (sommario):
Abstract. An airborne trace gas sensor based on mid-infrared technology is presented for fast (1 s) and high-precision ethane measurements during the Atmospheric Carbon and Transport-America (ACT-America) study. The ACT-America campaign is a multiyear effort to better understand and quantify sources and sinks for the two major greenhouse gases carbon dioxide and methane. Simultaneous airborne ethane and methane measurements provide one method by which sources of methane can be identified and quantified. The instrument described herein was operated on NASA's B200 King Air airplane spanning five separate field deployments. As this platform has limited payload capabilities, considerable effort was devoted to minimizing instrument weight and size without sacrificing airborne ethane measurement performance. This paper describes the numerous features designed to achieve these goals. Two of the key instrument features that were realized were autonomous instrument control with no onboard operator and the implementation of direct absorption spectroscopy based on fundamental first principles. We present airborne measurement performance for ethane based upon the precisions of zero air background measurements and ambient precision during quiescent stable periods. The airborne performance was improved with each successive deployment phase, and we summarize the major upgraded design features to achieve these improvements. During the fourth deployment phase in the spring of 2018, the instrument achieved 1 s (1σ) airborne ethane precisions reproducibly in the 30–40 parts per trillion by volume (pptv) range in both the boundary layer and the less turbulent free troposphere. This performance is among some of the best reported to date for fast (1 Hz) airborne ethane measurements. In both the laboratory conditions and at times during calm and level airborne operation, these precisions were as low as 15–20 pptv.
46
Baghi, R., P. Durand, C. Jambert, C. Jarnot, C. Delon, D. Serça, N. Striebig, M. Ferlicoq e P. Keravec. "A new disjunct eddy-covariance system for BVOC flux measurements – validation on CO<sub>2</sub> and H<sub>2</sub>O fluxes". Atmospheric Measurement Techniques Discussions 5, n. 3 (13 giugno 2012): 4157–93. http://dx.doi.org/10.5194/amtd-5-4157-2012.
Testo completoAbstract (sommario):
Abstract. The disjunct eddy covariance (DEC) method is an interesting alternative to the conventional eddy covariance (EC) method, because it allows the estimation of turbulent fluxes of species for which fast sensors are not available. A new disjunct sampling system (called MEDEE) was developed and validated. This system was built with chemically inert materials. Air samples are grabbed quickly and alternately in two cylindrical reservoirs, whose internal pressures are regulated by a moving piston. It was designed to be operated either on ground or aboard an airplane (the French ATR-42 research aircraft). It is also compatible with most analysers since it transfers the air samples at a regulated pressure. For validating the system, DEC and EC measurements of CO2 and latent heat fluxes were performed concurrently during a field campaign. EC fluxes were first compared to simulated DEC (SDEC) fluxes and then to actual DEC fluxes. The EC fluxes were in agreement with both the simulated and actual DEC fluxes. The EC fluxes compare well to SDEC fluxes (R2 = 0.92 and 0.68 for latent heat and CO2 fluxes, respectively) and to actual DEC fluxes (R2 = 0.91 and 0.67 for latent heat and CO2 fluxes, respectively), in spite of low fluxes experienced during the campaign. This good agreement between the two techniques demonstrates that MEDEE is suitable for DEC measurements and highlights the DEC method as a reliable alternative to EC for slower sensors. A first field campaign focused on biogenic volatile organic compound (BVOC) emissions was done to measure isoprene fluxes above a downy oak (Quercus Pubescens) forest in the southeast of France. The measured emission rates were in good agreement with the values reported in earlier studies. Further analysis will be conducted from ground-based and airborne campaigns in the forthcoming years.
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Lex, Elina. "Sounding out Place and Cultural Memory in <i>Tempelhofer: Human Scale</i>". Abstracts of the ICA 1 (15 luglio 2019): 1–2. http://dx.doi.org/10.5194/ica-abs-1-212-2019.
Testo completoAbstract (sommario):
<p><strong>Abstract.</strong> With the increase of sonic life in digital spaces, new platforms for the exhibition of sound are emerging; from multisensory web interfaces, open access databases, apps for playing with sound, to experimental locative and geo-located pieces. From iPods, mobile phones, and noise cancelling headphones, new technological tools are constantly remediating how we listen and relate to the sonic spaces around us. The collaboration between digital humanities, sound studies, locative media and cartography holds many possibilities for challenging silent and text-centric cultures of communication into rich multi-sensory experiences that accommodate diverse knowledges and abilities. By thinking through new modes for staging cultural memory and presenting ephemera like sound, digital mapping tools can facilitate alternative forms of sensory relationships to the social and physical spaces around us.</p><p><i>Tempelhofer: Human Scale</i> is a web-based and locative sound mapping project based in Berlin’s Tempelhofer Feld. What was once an airport, military base, and monument of Nazi Germany, the grounds have only recently been transformed into a public park, recreation area, and event space; a blank slate for human potential. On the north side, a Shaolin Temple lies just opposite a mini golf course made up of 18 interactive sculptures designed by local artists. DIY garden communities make up another corner. Recreational activities such as cycling, Segway clubs, and kite flying roam in and around the empty airport runways. A “grillplatz” barbeque area accommodates hundreds of families and youth, emitting thick clouds of smoke that mirror, in a historical juxtaposition, the airplane exhaust of a once operating airport. Bearing the aroma of a new Berlin, Tempelhofer Feld now embodies a melting pot of different foods, activities, and cultures coming into sensory contact. In the shadows of the massive airport structure lies a refugee camp, producing complex questions around heritage, conservation, and the politics of public space.</p><p>Tempelhofer Feld is a space that is highly politicized with its own contentious history and questions of preservation. Originally designed as a cornerstone for Hitler’s “world capital,” the airport sought to “crystalize claims of racial supremacy and world domination through architecture” (Parsloe 2017). Locating a refugee camp on this site not only creates complex associations between past and present but it also illuminates the tensions around living conditions on a site upheld by many strict heritage and conservation bylaws. Tempelhofer Feld is Europe’s largest protected historical monument, meaning complex tensions around preservation/conservation and development/change are consistently playing out. To explore these tensions, my project utilizes mapping technologies to trace how new emerging ephemeral activities are interacting with place, along with its complex politics, preserved history, and cultural memory. These ephemeral activities emerging out of the public spaces of the park produce fascinating tensions between the vital idealism of Berlin’s present and the turbulent history of its recent past. Recycled and reactive spaces like Tempelhofer Feld display the complex tensions between the re-adaptive and ephemeral nature of the park against its permanent state of preservation and commemoration of history. It underscores how charged public spaces in the city can be: “how should Berliners remember the past in a way that will most intelligently inform how they will move forward into the future?” (Malamud 2013).</p><p>The series of sound recordings focus on the quiet, intimate, and ephemeral scale of human activity – from walking, jogging, barbequing, lounging, kite-flying, socializing, gardening. These different sound activities are placed as destinations on a map that can be explored on a web interface as well as through geo-located points when walking through the park. To recreate the locative experience of the park on the web interface, sound clips are set against photographs of the different landscapes of the airport; expansive, barren, and sometimes empty of human activity. The intimacy of these sounds set against the open landscapes is meant to invert a space originally designed for technical infrastructure, transportation, and nationalist domination – a scale in which the individual human body often becomes erased. The question of scale is central to these explorations: how can sound on the intimate human scale be used to invert the scale of a massive airport/urban park? How does sound, with its embodied/sensory functions, invert questions around remote sensing that goes into mapping satellite imagery? What aspects of human sensory experience are erased or go unnoticed through remote, vision-based satellite and mapping technologies?</p><p>Soundscapes embody the complex relationship between human and environment in a complex system of information exchange. To the World Soundscape Project, soundwalking is a method for deep listening and participation in our everyday soundscapes: it involves “not simply a passive monitoring, but an active mental and physical participation in the ongoing composition forever being created” (Truax 1974, 38). This idea that the soundscape is not only something we passively listen to but something we also actively engage in and contribute to is central to the interactivity of this project. Sound can be activated through the user’s touch (on the web, through the mouse and in person, through their location). Different sound nodes can be activated simultaneously, building up a more complex and layered soundscape. By interacting with these different sounds, the user can acoustically design and recompose the soundscape around them, contributing to a greater sense of spatial and aural awareness.</p><p>The ephemeral nature of these activities/happenings is also emphasized through sound’s own elusive materiality, intangibility, and ephemerality. How the temporal and ephemerality of sound can be used as an archival tool to map out the contingent and ephemeral nature of memory is an essential question to this project. In Mark Smith’s theorization of sonic geographies, he states, “if we listen to it, the landscape is not so much a static topography that can be mapped and drawn, [but] a fluid and changing surface that transforms as it is enveloped by different sounds” (Bull and Back 2016, 11). The sonic geography of Tempelhofer Feld therefore represents its transformative and constantly evolving surface. While urban spaces (and its associated cartographic technologies) have dominantly been understood as visual spectacles, sound mapping foregrounds the vital role that sound plays in understanding the everyday cultural, political, and physical spaces around us.</p>
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Brunton, Steven L., e Bernd R. Noack. "Closed-Loop Turbulence Control: Progress and Challenges". Applied Mechanics Reviews 67, n. 5 (26 agosto 2015). http://dx.doi.org/10.1115/1.4031175.
Testo completoAbstract (sommario):
Closed-loop turbulence control is a critical enabler of aerodynamic drag reduction, lift increase, mixing enhancement, and noise reduction. Current and future applications have epic proportion: cars, trucks, trains, airplanes, wind turbines, medical devices, combustion, chemical reactors, just to name a few. Methods to adaptively adjust open-loop parameters are continually improving toward shorter response times. However, control design for in-time response is challenged by strong nonlinearity, high-dimensionality, and time-delays. Recent advances in the field of model identification and system reduction, coupled with advances in control theory (robust, adaptive, and nonlinear) are driving significant progress in adaptive and in-time closed-loop control of fluid turbulence. In this review, we provide an overview of critical theoretical developments, highlighted by compelling experimental success stories. We also point to challenging open problems and propose potentially disruptive technologies of machine learning and compressive sensing.
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"Deep stall: the turbulent story of Boeing commercial airplanes". Choice Reviews Online 43, n. 08 (1 aprile 2006): 43–4629. http://dx.doi.org/10.5860/choice.43-4629.
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Antonova, Anna, Mykola Kulyk e Ivan Lastivka. "MODELING OF AN AIRPLANE WING MOMENTS INDUCED BY ATMOSPHERIC TURBULENCE". Proceedings of National Aviation University 59, n. 2 (4 luglio 2014). http://dx.doi.org/10.18372/2306-1472.59.6790.
Testo completo