To see the other types of publications on this topic, follow the link: Low wind speed threshold.
Dissertations / Theses on the topic 'Low wind speed threshold'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 43 dissertations / theses for your research on the topic 'Low wind speed threshold.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Draper, David W. "Wind Scatterometry with Improved Ambiguity Selection and Rain Modeling." BYU ScholarsArchive, 2003. https://scholarsarchive.byu.edu/etd/117.
Full textAbstract:
Although generally accurate, the quality of SeaWinds on QuikSCAT scatterometer ocean vector winds is compromised by certain natural phenomena and retrieval algorithm limitations. This dissertation addresses three main contributers to scatterometer estimate error: poor ambiguity selection, estimate uncertainty at low wind speeds, and rain corruption. A quality assurance (QA) analysis performed on SeaWinds data suggests that about 5% of SeaWinds data contain ambiguity selection errors and that scatterometer estimation error is correlated with low wind speeds and rain events. Ambiguity selection errors are partly due to the "nudging" step (initialization from outside data). A sophisticated new non-nudging ambiguity selection approach produces generally more consistent wind than the nudging method in moderate wind conditions. The non-nudging method selects 93% of the same ambiguities as the nudged data, validating both techniques, and indicating that ambiguity selection can be accomplished without nudging. Variability at low wind speeds is analyzed using tower-mounted scatterometer data. According to theory, below a threshold wind speed, the wind fails to generate the surface roughness necessary for wind measurement. A simple analysis suggests the existence of the threshold in much of the tower-mounted scatterometer data. However, the backscatter does not "go to zero" beneath the threshold in an uncontrolled environment as theory suggests, but rather has a mean drop and higher variability below the threshold. Rain is the largest weather-related contributer to scatterometer error, affecting approximately 4% to 10% of SeaWinds data. A simple model formed via comparison of co-located TRMM PR and SeaWinds measurements characterizes the average effect of rain on SeaWinds backscatter. The model is generally accurate to within 3 dB over the tropics. The rain/wind backscatter model is used to simultaneously retrieve wind and rain from SeaWinds measurements. The simultaneous wind/rain (SWR) estimation procedure can improve wind estimates during rain, while providing a scatterometer-based rain rate estimate. SWR also affords improved rain flagging for low to moderate rain rates. QuikSCAT-retrieved rain rates correlate well with TRMM PR instantaneous measurements and TMI monthly rain averages. SeaWinds rain measurements can be used to supplement data from other rain-measuring instruments, filling spatial and temporal gaps in coverage.
2
Harvey, Scott A. "Low-speed wind tunnel flow quality determination." Thesis, Monterey, California. Naval Postgraduate School, 2011. http://hdl.handle.net/10945/5584.
Full textAbstract:
Approved for public release; distribution is unlimited.lected points. Incorporated instrumentation includes pressure transducers attached to a pitot-static tube, wall static pressure taps, and a pressure rake; a hotwire anemometry system, and a linear traverse system. These were integrated with a data acquisition (DAQ) processor with analog to digital conversion and digital I/O boards, and controlled using in-house developed LabVIEW software. Testing showed a maximum axial velocity of 38 m/s, which is 84% of the tunnel?s rated speed. The 2-D flow uniformity was within ±7% by pressure rake, and ±3% with a turbulence intensity ?0.11% at full speed using a CTA, affirming the tunnel?s viability as a demonstration platform. Spectral density plots in the boundary layer exhibit typical behavior of fully developed equilibrium turbulent flow with an intertial sub-range present. Future testing of a flat-plate wake for drag modification is planned.
3
Feldman, Michael A. "Efficient Low-Speed Flight in a Wind Field." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/36527.
Full textAbstract:
A new software tool was needed for flight planning of a high altitude, low speed unmanned aerial vehicle which would be flying in winds close to the actual airspeed of the vehicle. An energy modeled NLP formulation was used to obtain results for a variety of missions and wind profiles. The energy constraint derived included terms due to the wind field and the performance index was a weighted combination of the amount of fuel used and the final time. With no emphasis on time and with no winds the vehicle was found to fly at maximum lift to drag velocity, Vmd. When flying in tail winds the velocity was less than Vmd, while flying in head winds the velocity was higher than Vmd. A family of solutions was found with varying times of flight and varying fuel amounts consumed which will aid the operator in choosing a flight plan depending on a desired landing time. At certain parts of the flight, the turning terms in the energy constraint equation were found to be significant. An analysis of a simpler vertical plane cruise optimal control problem was used to explain some of the characteristics of the vertical plane NLP results.Master of Science
4
Sangpanich, Umarin. "Optimization of wind-solar energy systems using low wind speed turbines to improve rural electrification." Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=18944.
Full textAbstract:
Electricity is significant in improving the quality of life for people in rural and remote areas in developing countries. There are two main options for Rural Electrification (RE), namely grid extension and stand-alone systems. The governments and developers face the challenges of their limitations, namely technical, economic and environmental effects of each RE choice. This thesis intends to improve RE by focusing on renewable energy technologies, namely Wind Turbine (WT) and Photovoltaic (PV) systems. They have been developed and applied to RE because they are simple and environmentally friendly. They can be installed as separate units and they are sustainable alternative energy solutions. Installation, cost and performance are crucial issues of WT and PV applications, and are based on the terrain and climate where the renewable are installed. The efficiency of WTs and PV modules has increased, while their cost has declined continuously. However, a PV system still has installatio n costs around two times more expensive per watt than WTs. Most WTs using current technology can be financially worthwhile for high wind speed areas, having wind speeds greater than 6.4 m/s at 10 m hub height, but most rural areas have wind speeds of less than 6 m/s at the same height. Therefore, Low Wind Speed Turbines (LWSTs) have evolved, by increasing rotor diameter and while maintaining similar generator capacity. This is to reduce Levelized Cost of Energy (LCOE) for WTs in low wind speed areas. This thesis proposes simple cost models, namely the Sum-component cost model and the Total-cost model in order to calculate the LCOE of LWSTs. In addition, novel aspects of this thesis are that the optimization processes of stand-alone hybrid WT-PV systems and hybrid WT-PV systems using batteries at peak demand in remote area power systems provide simple, fast and flexible methods, by applying Multi-objective Evolutionary Algorithm (MOEA). The MOEA can analyze complex objective problems a nd provide an accurate multi-objective method. Results from relevant case studies show that the cost models and the optimization processes proposed are novel and are valuable tools for analysis and design, including the approaches for improving the system reliability and for estimating the Initial Capital Cost (ICC) of WTs having different rated wind speeds. The proposed algorithms are generic and can be utilized for other energy planning problems.
5
Wise, John Nathaniel. "Optimization of a low speed wind turbine using support vector regression." Thesis, Stellenbosch : University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/2737.
Full textAbstract:
Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009.NUMERICAL design optimization provides a powerful tool that assists designers in improving their products. Design optimization automatically modifies important design parameters to obtain the best product that satisfies all the design requirements. This thesis explores the use of Support Vector Regression (SVR) and demonstrates its usefulness in the numerical optimization of a low-speed wind turbine for the power coe cient, Cp. The optimization design problem is the three-dimensional optimization of a wind turbine blade by making use of four two-dimensional radial stations. The candidate airfoils at these stations are selected from the 4-digit NACA range. A metamodel of the lift and drag coe cients of the NACA 4-digit series is created with SVR by using training points evaluated with XFOIL software. These SVR approximations are used in conjunction with the Blade Element Momentum theory to calculate and optimize the Cp value for the entire blade. The high accuracy attained with the SVR metamodels makes it a viable alternative to using XFOIL directly, as it has the advantages of being faster and easier to couple with the optimizer. The technique developed allows the optimization procedure the freedom to select profiles, angles of attack and chord length from the 4-digit NACA series to find an optimal Cp value. As a result of every radial blade station consisting of a NACA 4-digit series, the same lift and drag metamodels are used for each station. This technique also makes it simple to evaluate the entire blade as one set of design variables. The thesis contains a detailed description of the design and optimization problem, the implementation of the SVR algorithm, the creation of the lift and drag metamodels with SVR and an alternative methodology, the BEM theory and a summary of the results.
6
Joseph, Liselle AnnMarie. "Transition Detection for Low Speed Wind Tunnel Testing Using Infrared Thermography." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/78145.
Full textAbstract:
Transition is an important phenomenon in large scale, commercial, wind tunnel testing at low speeds because it is an excellent indicator of an airfoil performance. It is difficult to estimate transition through numerical techniques because of the complex nature of viscous flow. Therefore experimental techniques can be essential. Over the transition region the rate of heat transfer shows significant increases which can be detected using infrared thermography. This technique has been used predominantly at high speeds, on small models made of insulated materials, and for short test runs. Large scale testing has not been widely undertaken because the high sensitivity of transition to external factors makes it difficult to detect.
The present study records the process undertaken to develop, implement and validate a transition detection system for continual use in the Virginia Tech Stability Wind Tunnel: a low speed, commercial wind tunnel where large, aluminium models are tested. The final system developed comprises of two high resolution FLIR A655sc infrared cameras; four 63.5-mm diameter circular windows; aluminium models covered in 0.8-mm silicone rubber insulation and a top layer of ConTact© paper; and a series of 25.4-mm wide rubber silicone fiberglass insulated heaters mounted inside the model and controlled externally by experimenters. This system produces images or videos of the model and the associated transition location, which is later extracted through image processing methods to give a final transition location in percentage chord.
The system was validated using two DU96-W-180 airfoils of different chord lengths in the Virginia Tech Stability Wind Tunnel, each tested two months apart. The system proved to be robust and efficient, while not affecting the airfoil performance or any other system in use in the wind tunnel. Transition results produced by the system were compared to measurements obtained from pressure data and stethoscope tests as well as the numerical predictions of XFOIL. The transition results from all four methods showed excellent agreement with each other for the two models, for at least two Reynolds numbers and for several angles of attack on both suction and pressure side of the model. The agreement of data obtained under such different conditions and at different times suggests that the infrared thermography system efficiently and accurately detects transition for large aluminium models at low speeds.Master of Science
7
Copland, Christopher M. "The generation of transverse and longitudinal vortices in low speed wind tunnels." Thesis, University of Glasgow, 1997. http://theses.gla.ac.uk/2543/.
Full textAbstract:
The present study documents an experimental and numerical investigation into the feasibility of generating longitudinal and transverse vortices in low speed wind tunnels. The longitudinal vortex system is that of a co-rotating vortex pair which, if substituted for a classical single tip vortex, may produce a beneficial modification to Blade Vortex Interaction. The transverse vortex mimics the tip vortex of a typical helicopter rotor and may be used to assess its effect when interacting with other aerofoils or fuselage components. Experiments have been conducted to investigate the flow field associated with two co-rotating vortices which represent the idealised vortex system associated with a novel rotor blade tip platform - the Westland Helicopters Vane Tip. These vortices were generated by two rectangular NACA 0015 half wings positioned upstream of the working section of a low speed wind tunnel. Hot-wire measurements were conducted downstream of the generators using x-wire probes to document the strength, position and size of the vortices. A numerical model was utilised to provide an accurate means of determining vortex strength, position and size. Finally, the model was successfully extended to consider the rotation of the vortex system. The transverse vortex was generated by a rotating blade placed in the contraction of a low speed wind tunnel. A numerical model was utilised in the conceptual design of the experimental facility to model the flow through the settling chamber, contraction, working section and diffuser. This numerical model consisted of a three dimensional source panel method, used to calculate the constrained flow through the low speed tunnel, and a free wake model representing the wake generated by the vortex generator. Convection of the wake was determined by superposition of the undisturbed tunnel velocity and the induced velocity components from the wake itself. Results, obtained via a parametric analysis, illustrate the relationship between the geometry of the wake and basic physical design parameters. On this basis, two possible operational strategies for the upstream rotor are examined with reference to development of the experimental facility. It is concluded that, while a short duration finite rotor traverse may be the optimum vortex generation strategy, a continuous running rotor is a more cost effective and viable option.
8
Wang, Yuchen. "Blade Design of Vertical Axis Wind Turbine at Low Tip-speed-ratios." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1524224348317784.
Full text
9
Cedrun, Mark E. "Low-speed wind tunnel testing of the NPS/NASA Ames Mach 6 optimized waverider." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA283585.
Full textAbstract:
Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, June 1994.Thesis advisor(s): Conrad F. Newberry, Jeffrey V. Bowles. "June 1994." Includes bibliographical references. Also available online.
10
Blandford, Adam. "ImPressOne A pressure display and acquisition program for the low speed wind tunnel at DSTO." Fishermans Bend,Victoria : Defence Science and Technology Organisation, 2005. http://hdl.handle.net/1947/4681.
Full text
11
Broughton, Benjamin Albert. "Low speed wind tunnel testing and data correction methods for aircraft models in ground effect." Diss., University of Pretoria, 1999. http://hdl.handle.net/2263/24292.
Full textAbstract:
In this thesis, techniques for testing aircraft models in ground effect in a low speed wind tunnel are investigated. Although these types of tests have been done before, the current study is unique in that forces are measured with an overhead balance instead of an internal balance. This has the advantage that the types of models that are difficult to mount on a sting with an internal balance, can often be mounted with a strut protruding from the top of the model. Positioning a sting-mounted model close to the ground at a high angle-of-attack is also usually difficult if not impossible. Finally, drag measurements are often more accurate when measured with an overhead balance rather than with an internal sting-type balance. The disadvantages associated with this method of testing are identified and solutions suggested. These include accurate moment transfers and correcting for support tares and interference. The thesis also investigates general procedures associated with ground effect testing such as proper boundary corrections and the necessity of a rolling floor. A simplified preliminary test series was performed in order to identify shortcomings in the existing equipment and procedures. This series is explained in Chapter 2. Chapter 4 and 5 describe changes made to the existing equipment following this test series. These include a novel telescopic fairing to shroud the mounting strut and an internal pitching mechanism. The correction techniques and general theory are summarised in Chapter 3. The author concludes in Chapter 6 that with the application of the techniques described in this thesis, the test engineer should be able to obtain accurate and reliable data from most aircraft configurations. Additional suggestions for testing models in ground effect are also given in this chapter. Finally, a few shortcomings that still need to be investigated are mentioned at the end of Chapter 6. AFRIKAANS : Hierdie verhandeling ondersoek tegnieke om vliegtuigmodelle in grondeffek in 'n laespoed-windtonnel te toets. Alhoewel hierdie tipe van toetse al voorheen gedoen is, is die huidige studie uniek deurdat 'n oorhoofse balans eerder as 'n interne balans gebruik word. Die voordeel hiervan is dat modelle wat moeilik op 'n naald- of "sting"-balans monteer kan word, baie keer makliker monteer kan word met 'n stang wat deur die bokant van die model steek. Posisioneering van 'n naald-gemonteerde model naby aan die vloer van die tonnel by hoe invalshoeke is gewoonlik ook baie moeilik indien nie onmoontlik nie. Laastens is sleurkrag-metings wat met 'n oorhoofse balans gemeet is gewoonlik meer akkuraat as sleurkrag-metings wat met 'n interne naald-tipe balans gedoen is. Die nadele wat met hierdie toetsmetode geassosieer kan word, word geïdentifiseer en moontlike oplossing word voorgestel. Hierdie sluit die berekening in van akkurate moment-transformasies en monteersleureffekte en -steurings. Die verhandeling ondersoek ook algemene prosedures wat met grondeffektoetse geassosieer kan word, byvoorbeeld akkurate wandkorreksies en die nodigheid van die rolvloer. 'n Vereenvoudigde vooraf-toetsreeks was uitgevoer om moontlike tekortkominge in die bestaande toerusting en prosedures te identifiseer. Hierdie toetsreeks word in Hoofstuk 2 bespreek. Hoofstuk 4 en 5 verduidelik die veranderinge wat aan die bestaande toerusting gemaak is na aanleidng van hierdie toetsreeks. Hierdie veranderinge sluit 'n teleskopiese windskerm in om die monteerstang te isoleer van die wind, sowel as 'n interne heimeganisme om die invalshoek van die model te verstel. Die korreksieprosedures en algemene teorie word in Hoofstuk 3 opgesom. Die outeur se gevolgtekking in Hoofstuk 6 stel dat die toetsingenieur, met behulp van die gebruik van die tegnieke in hierdie verhandeling beskryf, in staat behoort te wees om betroubare metings te kan neem van meeste vliegtuigkonfigurasies. Verdere voorstelle vir die toets van modelle in grondeffek word ook in hierdie hoofstuk gemaak. Uiteindelik word 'n paar tekortkominge genoem wat moontlik in 'n toekomstige studie ondersoek kan word.Dissertation (MEng)--University of Pretoria, 1999.
Mechanical and Aeronautical Engineering
unrestricted
12
Agbali, Francis Akumabi. "DESIGN AND TESTING OF A WIND ENERGY HARNESSING SYSTEM FOR FORCED CONVECTIVE DRYING OF GRAIN IN LOW WIND SPEED, WARM AND HUMID CLIMATES." UKnowledge, 2019. https://uknowledge.uky.edu/bae_etds/66.
Full textAbstract:
Forced convective drying using a wind turbine mechanically connected to a ventilation fan was hypothesized for low cost and rapid grain drying in developing countries. The idea was tested using an expandable wind turbine blade system with variable pitch, at low wind speeds in a wind tunnel. The design was based on empirical and theoretical models embedded in a graphical user interface (GUI) created to estimate airflow-power requirements for drying ear corn. Output airflow (0.0016 - 0.0052 m3kg-1s-1) increased within the study wind speed range (2.0 - 5.5 m/s). System efficiency peak (8.6%) was observed at 3.5 m/s wind speed. Flow resistance was overcome up to 1m fill depth in 0.5 m x 0.5 m wide drying bin. Drying study at different airflow rates (no forced convection, 0.002 m3kg-1s-1 and 0.008 m3kg-1s-1) were conducted in a controlled environment at 35oC and 45% relative humidity with mean drying time; 40.3, 37.9 and 22.9 h respectively, that reduced with increasing airflow while drying the ear corn from 22% to 15% moisture content. The overall result supports the hypothesis that the wind convection system increased grain drying rates and should be further developed.
13
Harman, John E. "Feasibility and optimum design study of a low speed wind turbine rotor system for underground communication power." Morgantown, W. Va. : [West Virginia University Libraries], 2008. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=5688.
Full textAbstract:
Thesis (M.S.)--West Virginia University, 2008.Title from document title page. Document formatted into pages; contains ix, 85 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 58-59).
14
Horton, Damien. "Development of an Infrared Thermography System to Measure Boundary Layer Transition in a Low Speed Wind Tunnel Testing Environment." DigitalCommons@CalPoly, 2021. https://digitalcommons.calpoly.edu/theses/2287.
Full textAbstract:
The use of infrared thermography for boundary layer detection was evaluated for use in the Cal Poly Low Speed Wind Tunnel (LSWT) and recommendations for the successful use of this technique were developed. In cooperation with Joby Aviation, an infinite wing model was designed, manufactured and tested for use in the LSWT. The wing was designed around a custom airfoil profile specific for this project, where the nearly-flat pressure gradient at a zero pitch angle would delay the chordwise onset of boundary layer transition. Steady-state, RANS numerical simulations predicted the onset of transition to occur at 0.75 x/c for the design Reynolds Number condition of 6.25x105. The wing was manufactured from 3D printed aluminum, with a wall thickness of 0.125 inches and a chord length of 13.78 inches. Two central rows of static pressure taps were used, each with 12 functional chordwise locations. The taps were able to generate strong correlation to the numerically predicted pressure coefficient distribution.
The use of an infrared camera visualized and confirmed the presence of boundary layer transition at the chordline location anticipated by the early simulations. To do so, the model was pre-heated such that the differential cooling properties of laminar and turbulent flow would generate a clear temperature gradient on the surface correlating to boundary layer transition. Adjustment of the model’s pitch angle demonstrated a change in the onset location of boundary layer transition during the infrared testing. The change of onset location was seen to move forward along the chordline as the aerodynamic angle of attack was increased. Testing with a Preston Tube system allowed for the interpolation of local skin friction coefficient values at each static tap location. Application of both laminar and turbulent empirical assumptions, when compared to numerical expectations, allowed for the qualitative assessment of boundary layer transition onset. Overall, the wing model developed for this research proved capable of producing quality and repetitive results for the experimental goals it was designed to meet. The model will next be used in continued tests which will further explore the use of infrared thermography.
15
Ross, Ian Jonathan. "Wind Tunnel Blockage Corrections: An Application to Vertical-Axis Wind Turbines." University of Dayton / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1271306622.
Full text
16
Jöckel, Stephan [Verfasser]. "Calculation of Different Generator Systems for Wind Turbines with Particular Reference to Low-Speed Permanent-Magnet Machines / Stephan Jöckel." Aachen : Shaker, 2003. http://d-nb.info/1172611629/34.
Full text
17
Yan, Minghan. "Time-domain and harmonic balance turbulent Navier-Stokes analysis of wind turbine aerodynamics using a fully coupled low-speed preconditioned multigrid solver." Thesis, Lancaster University, 2015. http://eprints.lancs.ac.uk/76968/.
Full textAbstract:
The research work reported in this thesis stems from the development of an accurate and computationally efficient Reynolds-Averaged Navier-Stokes (RANS) research code, with a particular emphasis on the steady and unsteady aerodynamics analysis of complex low speed turbulent flows. Such turbulent flow problems include horizontal axis wind turbine (HAWT) and vertical axis wind turbine (VAWT) operating at design and off-design conditions. On the algorithmic side, the main contribution of this research is the successful development of a rigorous novel approach to low-speed preconditioning (LSP) for the multigrid fully coupled integration of the steady, time-domain and harmonic balance RANS equations coupled to the two-equation shear stress transport (SST) turbulence model. The design of the LSP implementation is such that each part of the code affected by LSP can be validated individually against the baseline solver by suitably specifying one numerical input parameter of the LSP-enhanced code. The thesis has investigated several important issues on modelling and numerical aspects which are seldom thoroughly analysed in the computational fluid dynamics problems of the type presented herein. The first and most important modelling issue is the necessity of applying the low speed preconditioning to both RANS and SST equations and maintaining the turbulent kinetic energy in the definition of the total energy, which, to the best knowledge of author, has never been seen in any published literature so far. Based on the results obtained in the analysis of the vertical axis wind turbine application, we have demonstrated that by preconditioning the SST turbulence equations, one can significantly improve the convergence rate; and keeping the turbulence kinetic energy in the total energy has a great positive effect on the solution accuracy. The other modelling issue to be analysed is the sensitivity of the flow solution to the farfield boundary conditions, particularly for low speed problems. The analyses reported in the thesis highlight that with a small size of the computational domain, the preconditioned farfield boundary conditions are crucial to improve the solution accuracy. As for the numerical aspects, we analyse the impact of using the relative velocity to build the preconditioning parameter on the flow solutions of an unsteady moving-grid problem. The presented results demonstrate that taking into account the grid motion in building the preconditioning parameter can achieve a noticeable enhancement of the solution accuracy. On the other hand, the nonlinear frequency-domain harmonic balance approach is a fairly new technology to solve the unsteady RANS equations, which yields significant reduction of the run-time required to achieve periodic flows with respect to the conventional time-domain approach. And the implementation of the LSP approach into the turbulent harmonic balance RANS and SST formulations is another main novelty presented herein, which is also the first published research work on this aspect. The newly developed low speed turbulent flow predictive capabilities are comprehensively validated in a wide range of tests varying from subsonic flow with slight compressibility to user-defined extremely low speed incompressible flows. The solutions of our research code with LSP technology are compared with experiment data, theoretical solutions and numerical solutions of the state-of-the-art CFD research code and commercial package. The main computational results of this research consist of the analyses of HAWT and VAWT applications. The first one is a comparative analysis of 30% and 93.5% blade sections of a VESTAS multi-megawatt HAWT working in various regimes. The steady, time-domain and frequency-domain results obtained with the LSP solver are used to analyse in great detail the steady and unsteady aerodynamic characteristics in those regimes. The main motivation is to highlight the predictive capabilities and the numerical robustness of the LSP-enhanced turbulent steady, time-domain and frequency domain flow solvers for realistic complex and even more challenging problems, to quantify the effects of flow compressibility on the steady and yawed wind-induced unsteady aerodynamics in the tip region of a 82-m HAWT blade in rated operating condition, and to assess the computational benefits achieved by using the harmonic balance method rather than the conventional time-domain method. The second application is the comparative aerodynamic analyses of the NREL 5MW HAWT working in the inviscid steady flow condition. The main motivation of this analysis is to further demonstrate the predictive capabilities of the LSP solver to simulate the threedimensional wind turbine flows. The last application is the time-domain turbulent flow analysis of the VAWT to the aim of demonstrating the accuracy enhancement of the LSP solver for this particular problem, the necessity of applying the full preconditioning strategy, the important effect of the turbulent kinetic energy on the solution accuracy and the proper implementation of the preconditioning parameter required for an accurate numerical solution to an unsteady moving grid low-speed problem.
18
Krøvel, Øystein. "Design of Large Permanent Magnetized Synchronous Electric Machines : Low Speed, High Torque Machiines - Gererator for Diriect Driven Wind Turbine- Motor for Rim Driven Thruster." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elkraftteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-12417.
Full textAbstract:
This work presents the design of two prototype permanent magnetized electric machines for two different applications where large permanent magnet machines might be used. Existing technology have been used as the fundament for new design and adapted to new applications, contributing, hopefully, to the development of better and more environmental friendly energy conversion. The first application presented is represented with a prototype made in cooperation with the industry in which a PM-motor is integrated into a propeller unit. Both because of the industrial connection, and the integration between the PM-motor and the propeller, the choices made for the PM-motor are conservative trying to reduce the risk. The direct rim driven thruster prototype includes a surface mounted radial flux permanent magnet machine (SM RFPM) with fractional slot winding with a q around 1. Other engineering features were introduced to make the integration of propeller and motor feasible, but without the PM-machine the thruster would not have reached the performance demand. An important part of the project was to show that the SM RFPM enables this solution, providing high performance with a large air gap. The prototype has been tested in sea, under harsh conditions, and even though the magnets have been exposed directly to sea water and been visible corroded, the electric motor still performs well within the specifications. The second application is represented with a prototype PM-generator for wind turbines. This is an example of a new, very low speed high torque machine. The generator is built to test phenomena regarding concentrated coils, and as opposed to the first application, being a pure academic university project, its success is not connected to its performance, but with the prototype’s ability to expose the phenomena in question. The prototype, or laboratory model, of the generator for direct driven wind turbines features SM RFPM with concentrated coils (CC). An opportunity to push the limits for the design was given, and taken, choosing a relative high frequency and open slots to investigate the consequences of large reluctance variations in the air gap and distorted MMF. The main purpose of the PM generator is to explore a very low speed machine with high pole number and concentrated coils with coils wound around every other tooth. The study leading to the design included a discussion of scaling of the prototype from the full size generator, which parameters to keep, which to stress and which to forget. An investigation of the winding layout and winding factors included building a smaller table model for testing of different winding configurations, was also an important part of the work. Though the prototype has its flaws, or experimental setbacks, it successfully enhances the characteristic of the low speed, high pole number and slot geometry focusing on the harmonic content of the MMF and the consequences for the losses and reactance.
19
Blanco, Mark Richard. "Design and Qualification of a Boundary-Layer Wind Tunnel for Modern CFD Validation Experiments." Youngstown State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1559237473563483.
Full text
20
Dickel, Jacob Allen. "Design Optimization of a Non-Axisymmetric Endwall Contour for a High-Lift Low Pressure Turbine Blade." Wright State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=wright1534980581177159.
Full text
21
Cejpek, Ondřej. "Návrh a realizace aerodynamického tunelu pro rozstřikovací trysky." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2020. http://www.nusl.cz/ntk/nusl-417116.
Full textAbstract:
Pracovní podmínky atomizérů v reálných operacích v průmyslu a zemědělství se liší od podmínek laboratorních, ve kterých jsou atomizéry testovány. Částečné přiblížení k realističtějším podmínkám nám může poskytnout použití větrného tunelu. Větrný tunel se používá k simulaci okolního proudění. Studium spreje ve větrném tunelu nám poskytne realističtější představu o chování spreje. Tato diplomová práce se zabývá návrhem malého, nízko rychlostního větrného tunelu pro experimenty s tlakovými vířivými tryskami s obtokem v příčném a podélném proudění. Existuje mnoho typů větrných tunelů, ale jako nejvhodnější typ byl zvolen otevřený, výtlačný větrný tunel s uzavřenou testovací sekcí. Výhodou jsou jeho kompaktní rozměry, ochrana částí tunelu před kapičkami spreje a poměrně jednoduchý návrh. Konstrukce větrného tunelu se skládá z několika částí, každá část je zkonstruována tak, aby bylo dosaženo co nejlepší kvality proudu v testovací sekci. Sprej je zkoumán pomocí optických metod Fázové Dopplerovské anemometrie (PDA), Laserové Dopplerovské anemometrie (LDA), Integrální laserová anemometrie (PIV) a pomocí vysokorychlostního záznamu. Tyto optické metody kladou speciální požadavky na konstrukci tunelu, především na konstrukci testovací sekce, která musí umožňovat optický přístup ke spreji a musí být pro tyto měřící techniky uzpůsobena. Rychlost v testovací sekci se pohybuje v rozmezí 0 až 40 m/s s intenzitou turbulence pod 0,7 %. V závěru práce je ukázka vizualizace spreje, v příčném proudění, pomocí vysokorychlostní kamery. Okolní proudění mění rozpadovou vzdálenost spreje, úhel kužele spreje i jeho tvar. Dochází k vymývání menších kapek, které jsou unášeny okolním proudem.
22
Samad-Suhaeb, Mujahid. "Aerodynamics of battle damaged finite aspect ratio wings." Thesis, Loughborough University, 2005. https://dspace.lboro.ac.uk/2134/10736.
Full textAbstract:
When an aircraft is aerodynamically or structurally damaged in battle, it may not able to complete the mission and the damage may cause its loss. The subject of aircraft battle survivability is one of critical concern to many disciplines, whether military or civil. This thesis considered and focused on Computational Fluid Dynamics [CFD] predictions and experimental investigations into the effects of simulated battle damage on the low-speed aerodynamics of a fmite aspect ratio wing. Results showed that in two-dimensional [2d] and three-dimensional [3D] CFD simulations, Fluent's® models work reasonably well in predicting jets flow structures, pressure distributions, and pressure-coefficient Cp's contours but not for aerodynamic coefficients. The consequences were therefore that CFD prediction was poor on aerodynamic-coefficients increments. The prediction of Cp's achieved good agreement upstream and near the damage hole, but showed poor agreement at downstream of the hole. For the flow structure visualisation, at both weak and strong jet incidences, the solver always predicted pressure-distribution-coefficient lower at upstream and higher at downstream. The results showed relatively good agreement for the case of transitional and strong jet incidences but slightly poor for weak jet incidences. From the experimental results of Finite Wing, the increments for Aspect-ratio, AR6, AR8 and ARIO showed that as damage moves out towards the tip, aerodynamic-coefficients increments i.e. lift-loss and drag-rise decreased, and pitching-moment-coefficient increment indicated a more positive value at all incidence ranges and at all aspect ratios. Increasing the incidence resulted in greater magnitudes of lift-loss and drag-rise for all damage locations and aspect ratios. At the weak jet incidence 4° for AR8 and in all of the three damage locations, the main characteristics of the weak-jet were illustrated clearly. The increments were relatively small. Whilst at 8°, the flow structure was characterised as transitional to stronger-jet. In Finite Wing tests and for all damage locations, there was always a flow structure asymmetry. This was believed to be due to gravity, surface imperfection, and or genuine feature. An 'early strong jet' that indicated in Finite Wing-AR8 at 'transitional' incidence of 8°, also indicated in twodimensional results but at the weak-jet incidence of 4°. For the application of 2d data to AR6, AR8, and ARIO, an assessment of 2d force results led to the analysis that the tests in the AAE's Low Turbulence Tunnel for 2d were under-predicting the damage effects at low incidence, and over-predicting at high incidences. This suggested therefore that Irwin's 2d results could not be used immediately to predict three-dimensional.
23
Memon, Muhammad Omar. "Wingtip Vortices and Free Shear Layer Interaction in the Vicinity of Maximum Lift to Drag Ratio Lift Condition." University of Dayton / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1492701624726378.
Full text
24
Pinto, Mauro Sérgio Silva. "ESPECIFICAÇÕES DE PROJETO PARA MEDIÇÃO DE VELOCIDADE DE VENTO UTILIZANDO ANEMÔMETRO ULTRASÔNICO COM O MÉTODO DE DIFERENÇA DE FASE." Universidade Federal do Maranhão, 2006. http://tedebc.ufma.br:8080/jspui/handle/tede/457.
Full textAbstract:
Made available in DSpace on 2016-08-17T14:53:14Z (GMT). No. of bitstreams: 1
Mauro Sergio Silva Pinto.pdf: 649420 bytes, checksum: 2659c3409645c14d4672fc5713698782 (MD5)
Previous issue date: 2006-10-27The time of flight method for determining the wind speed using ultrasonic transducers is presented in this work. The techniques of phase difference and threshold detection for determining the time of flight are presented. A more detailed study of the phase difference technique is carried out in order to determine the design specifications using this method with respect to the noise sensitivity, dependence of the measurement range with the medium temperature and measurement resolution. A design specification example is presented in order to illustrate the proposed procedures.
Apresenta-se neste trabalho o método do tempo de trânsito para determinação da velocidade do vento utilizando transdutores ultra-sônicos. Apresentam-se as técnicas da diferença de fase e detecção de limiar para determinação do tempo de trânsito deste método. Um estudo mais aprofundado é realizado para o método da diferença de fase de forma a determinar as especificações de projeto usando esse método, com relação à sensibilidade ao ruído, dependência da faixa de medição com temperatura do meio e resolução de medição. Um exemplo de especificação de projeto é apresentado de forma a ilustrar os procedimentos desenvolvidos.
25
Human, Jacobus Daniel. "Design of a shrouded wind turbine for low wind speeds / Jacobus Daniel Human." Thesis, 2014. http://hdl.handle.net/10394/15291.
Full textAbstract:
The use of renewable energy is promoted worldwide to be less dependent on fossil fuels and
nuclear energy. Therefore research in the field is driven to increase efficiency of renewable energy
systems.
This study aimed to develop a wind turbine for low wind speeds in South Africa. Although
there is a greater tendency to use solar panels because of the local weather conditions, there are
some practical implications that have put the use of solar panels in certain areas to an end. The
biggest problem is panel theft. Also, in some parts of the country the weather is more suitable to
apply wind turbines.
Thus, this study focused on the design of a new concept to improve wind turbines to be appropriate
for the low wind speeds in South Africa. The concept involves the implementation of a
concentrator and diffuser to a wind turbine, to increase the power coefficient. Although the wind
turbine was not tested for starting speeds, the implementation of the shroud should contribute to
improved starting of the wind turbine at lower wind speeds.
The configuration were not manufactured, but simulated with the use of a program to obtain
the power production of the wind turbine over a range of wind speeds. These values were compared
to measured results of a open wind turbine developed for South Africa.
The most important matter at hand when dealing with a shrouded wind turbine is to determine
if the overall diameter or the blade diameter of the turbine should be the point of reference. As
the wind turbine is situated in a shroud that has a larger diameter than the turbine blades, some
researchers believe that the overall diameter should be used to calculate the efficiency.
Theory was revised to determine the available energy in the shroud after initial calculations
showed that the power coefficients should have been higher than the open wind turbine with the
same total diameter. A new equation was derived to predict the available energy in a shroud.
The benefits of shrouded wind turbines are fully discussed in the dissertation content.MSc (Mechanical Engineering), North-West University, Potchefstroom Campus, 2015
26
Ortega, Mirna Monserrat Machado, and 瑪安妮. "Research and Development of Low Start Wind Speed and High Efficiency Vertical Axis Wind Turbine." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/98602295187338224371.
Full textAbstract:
碩士崑山科技大學
機械工程研究所
98
There are many types of Vertical Axis Wind Turbines (VAWT), the Wollongong design, originally conceived in Australia is a very interesting type, because it presents a gear mechanism with a high potential for commercial application. Theoretically there are many options of gear configurations, and the relationship between the number of teeth of each gear (Gear Ratio = G) has an essential impact on the function of the Wollongong turbine. In order to establish the most suitable G for the construction of the turbine, a Numerical Analysis was carried out. Through this analysis it could be concluded that a G= -1/2 would be the best option to obtain an acceptable performance, which means a larger amount of positive work. Once the best Gear Ratio was defined and could be substantiated by a Numerical Analysis, the Experimental Tests were the next step. First, a Savonius turbine was acquired which included a device to measure the voltage; this equipment was used for both turbines, in order to compare them under similar conditions. Some improvements were done to the Savonius VAWT; this consisted in the adaptation of pair of bearings to reduce the oscillatory movement, hence the efficiency would be higher. When the Savonius VAWT was in optimal conditions, the construction of the Wollongong VAWT was done through CAD and Rapid Prototyping (3D Printing) technology. The most important consideration regarding to the Wollongong turbine, beside the gear configuration, was that the measure equipment of the Savonius turbine will have to be adapted into this one. Finally both turbines were compared, and the results revealed that the Wollongong VAWT was much more efficient than the Savonius VAWT, which indicates high potential for commercial application.
27
Chen, Hsin-Pin, and 陳信賓. "Research and Test of Low Speed and Turbulence Closed Wind Tunnel." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/50599902283305782181.
Full text
28
Kuo-Hsien, Hsu, and 許國賢. "Characterization of a Low-Speed Wind Tunnel With Variable Thermal and Turbulent Properties." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/10941189636448923413.
Full textAbstract:
碩士國立交通大學
機械工程系
89
ABSTRACT An open-air vertical, circular wind tunnel has been constructed to generate the nearly uniform high- and low- turbulence flow field at various temperatures, which is capable of producing free stream with mean velocities of 0.5~2m/s, turbulence intensities of 1.5~24.7%, and temperature of 300~900K. Turbulence environments are controlled by the different sizes of the turbulent generating disk. Laser Doppler Velocimeter is used to characterize the turbulence properties of the wind tunnel, including the mean streamwise velocity, turbulent intensity, probability density function and energy power spectrum. Integral length scale and Komogorov microscale are computed using Taylor hypothesis and assuming isotropic turbulence theory, respectively. A relatively homogeneous region about 20 mm in the middle of the tunnel exit is identified, which is wide enough for future droplet experiments.
29
Lin, Tung-Liang, and 林棟梁. "The Investigqtions Of The Support System Effects On Low Speed Wind Tunnel Testing." Thesis, 1992. http://ndltd.ncl.edu.tw/handle/40810473516346305105.
Full textAbstract:
碩士逢甲大學
機械工程研究所
80
This thesis is aimed to study the effects of the support system to the results of the force tests using the NASA TP 1803 model in a low speed wind tunnel. In a series of tests in the water and wind tunnel, we investigate the influence of the support system to the vortex breakdown of the model aircraft, and study the effects of the sting shape on the characteristics of the flow flied.The results are therefore to help us to find a correct way to modify the shape of the stings to minimize the flow field disturbances caused by the support system. The test results show that: (1) The longer stings produce less flow disturbances if the stings have similar shapes are compared. (2) The disturbances caused by the straight stings are smaller than that by the offset stings and bend sting, (3) The strut has little significance in determining the breakdown position of the strake and forebody vortex, (4) Different stings have large influence on the transverse stability measurments for the NASA TP 1803 model tested.
30
McPhee, Adam D. "The Development of a Research Technique for Low Speed Aeroacoustics." Thesis, 2008. http://hdl.handle.net/10012/4276.
Full textAbstract:
The aerodynamic sound generated by wind turbines was identified as a growing concern within the industry. Prior to performing wind turbine aeroacoustic research, however, a technique suitable for studying low speed airfoils needed to be designed, serving as the primary research objective. A review of aeroacoustic theory and literature indicated that low speed flows are best studied using experimental methods, leading to the design of a near field pressure measurement technique. To facilitate the near field pressure measurements, a custom piezoelectric sensor was developed, exhibiting a pressure and frequency range of approximately 67 to 140[dB], and 100 to 10000[Hz], respectively. As a secondary research objective, a series of experiments were performed to validate the designed technique. The experiments were performed in a non-anechoic wind tunnel using a cylindrical test specimen. Using the near field pressure measurements, as well as a simple far field measurement, the sources of aerodynamic sound were effectively resolved. The Strouhal numbers corresponding to the contributing flow structures were generally within 1.5[%] of correlation based predictions. The near field pressures were consistently 10 to 15[dB] higher than the far field, quantifying the benefit of the near field technique. The method was also effective in detecting the decreasing coherence of the aeroacoustic sources with increasing Reynolds number. A minor deficiency was observed in which the ability to localize aeroacoustic sources was impeded, however, the cylinder experiments were particularly vulnerable to such a deficiency. Although the near field pressure measurements were shown to be effective in characterizing the aeroacoustic sources, a number of recommendations are presented to further improve the flexibility and measurement uncertainty of the experimental technique.
31
Hello and 吳祖仁. "Analysis of Model Oscillations at High Angles of Attack in Low Speed Wind Tunnel Testing." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/11610211268526788416.
Full text
32
CHEN, DENG-FU, and 陳登發. "The investigations of model wake blockage corrections in A. R. L. low speed wind tunnel." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/67582073278890424536.
Full text
33
Jheng-JieWang and 王政傑. "Calibrations of an Open-Circuit Low Speed Wind Tunnel and the Study of Aerodynamic Performance of a Cross-Axis Wind Turbine." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/ps7nqj.
Full text
34
Chiang, Yun-yu, and 蔣昀祐. "A Study on Simulating the Atmospheric Boundary Layer Formation in Small Low Speed Wind Tunnel - Take Wind Tunnel in CYUT as an example." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/01371503964218027149.
Full textAbstract:
碩士朝陽科技大學
建築及都市設計研究所
99
Wind tunnel laboratory in Architecture Department of CYUT is arranged for simulating the wind field in urban environment and building surroundings for research and experiments. It is planned to offer reference for site and buildings location arrangement when under design and planning. To do the urban design, architectural design, green design, structure, disaster prevention, building physical condition and equipment design, wind tunnel experiment practice is important for students to understand the wind field changing in the environment by using model simulation. It is helpful to realize the actual situation in the environment to do the urban planning and building design. Main in research is to establish the simulating atmospheric boundary layer in wind tunnel according to the different site conditions. The wind field will be affected by various site localities like seashore, plain, suburb, and urban type of terrain to form different shape of atmospheric boundary layer. Passive devices such as spires, barriers, and roughness elements were implemented in the tunnel for the simulations. We try to use different size of passive devices and spacing to generate our exclusive atmospheric boundary layer in our low speed, small size wind tunnel. These results will be judged to correct the drift or partly drift from the theory profile line of the atmospheric boundary layer by changing the size and spacing of passive devices. Finally, we will have a suitable atmospheric boundary layer which fit the theory profile line as the achievement. These wind profile will be suitable for the experiment and relevant researches. The purposes of this research are trying to can build up our wind tunnel experiment simulation abilities effectiveness and efficiency in order to help students to understand the wind effects in the environment and promote cooperation of academic circle and the field. Also these will help us to construct the data base for offering references to other researches.
35
Wong, Samuel Heng Hsin. "A Parallel Adaptive-mesh Method for Predicting Flows Through Vertical Axis Wind Turbines." Thesis, 2011. http://hdl.handle.net/1807/29648.
Full textAbstract:
Significant progress has been made towards developing an effective solution method for predicting low-speed flows through vertical-axis wind turbines. A Godunov-type finite-volume scheme has been developed for the solution of the Euler equations in two-dimensions on a multi-block mesh. The proposed algorithm features a parallel block-based adaptive mesh refinement scheme and a mesh adjustment procedure to enable straightforward meshing of irregular solid boundaries. A low-Mach-Number preconditioner is used in conjunction with a dual timestepping scheme to reduce the computational costs of simulating low-speed unsteady flows. A second-order backwards differencing time-marching scheme is used for the outer physicaltime discretization, and an explicit optimally-smoothing multi-stage time-stepping scheme with multigrid acceleration is used for the inner pseudo-time loop. Results are presented for various low-speed flows that demonstrate the suitability of the algorithms for wind turbine flows. Additional theory and discussion are also presented for extension of the schemes to the full Navier-Stokes equations.
36
Sargent, Christopher L. "The influence of helicopter tail shape on drag An aerodynamic study using a low speed wind tunnel." Thesis, 1985. http://hdl.handle.net/10945/21379.
Full text
37
Chang, Chin-Feng, and 張金鋒. "Design and Implementation of a Vertical-axis Wind Power Generator with Low Stated Speed and Power Measurement." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/30178675575696449044.
Full textAbstract:
碩士國立高雄應用科技大學
電機工程系博碩士班
96
Abstract In this thesis, we investigate a system of the vertical-axis external rotor wind power generator that includes low speed start, direct dirve without increment gear box, low noise and high effective power. From the results that further design a power plant measurement for the characteristic torgue-speed curve etc. On a wind power generator system consisting of a lift hybrid wind turbine, external rotor ac synchronous benerator and load, we proposed operating methods with matlab simulation model to design the generator system. The contribution of this thesis is to provide a solution of future products for the chips of ______ and local wind power generator systems. We can also apply this methods external rotor ac pm motor to the motor.
38
Lanspeary, Peter V. "Establishing very low speed, disturbance-free flow for anemometry in turbulent boundary layers." 1998. http://hdl.handle.net/2440/37931.
Full textAbstract:
This document addresses problems encountered when establishing the very low air-flow speeds required for experimental investigations of the mechanisms of low-Reynolds-number boundary-layer turbulence. Small-scale motions in the near-wall region are important features of turbulent boundary-layer dynamics, and, if these features are to be resolved by measurements in air with conventionally-sized hot-wire probes, a well-behaved canonical turbulent boundary layer must be developed at free stream flow speeds no higher than 4 m/s. However, at such low speeds, the turbulent boundary layers developed on the walls of a wind tunnel are very susceptible to perturbation by non-turbulent time-dependent flow structures which originate upstream from the test section in the laminar flow at the inlet and in the contraction. Four different non-turbulent flow structures have been identified. The first is a result of quasi-two-dimensional separation of the laminar boundary-layer from the surfaces of the wind-tunnel contraction. Potential flow simulations show that susceptibility to this form of separation is reduced by increasing the degree of axisymmetry in the cross-section geometry and by decreasing the streamwise curvature of the concave surfaces. The second source of time-dependence in the laminar boundary-layer flow is an array of weak streamwise vortices produced by Goertler instability. The Goertler vortices can be removed by boundary-layer suction at the contraction exit. The third form of flow perturbation, revealed by visualisation experiments with streamers, is a weak large-scale forced-vortex swirl produced by random spatial fluctuations of temperature at the wind-tunnel inlet. This can be prevented by thorough mixing of the inlet flow; for example, a centrifugal blower installed at the inlet reduces the amplitude of temperature nonuniformity by a factor of about forty and so prevents buoyancy-driven swirl. When subjected to weak pressure gradients near the start of a wind-tunnel contraction, Goertler vortices in laminar wall layers can develop into three-dimensional separations with strong counter-rotating trailing vortices. These trailing vortices are the fourth source of unsteady flow in the test-section. They can be suppressed by a series of appropriately located screens which remove the low-speed-streak precursors of the three-dimensional separations. Elimination of the above four contaminating secondary flows permits the development of a steady uniform downstream flow and well-behaved turbulent wall layers. Measurements of velocity in the turbulent boundary layer of the test-section have been obtained by hot-wire anemometry. When a hot-wire probe is located within the viscous sublayer, heat transfer from the hot-wire filament to the wall produces significant errors in the measurements of both the mean and the fluctuating velocity components. This error is known as wall-proximity effect and two successful methods are developed for removing it from the hot-wire signal. The first method is based on the observation that, if all experimental parameters except flow speed and distance from the wall are fixed, the velocity error may be expressed nondimensionally as a function of only one parameter, in the form DeltaU^+=f(y^+). The second method, which also accommodates the effect of changing the hot-wire overheat ratio, is based on a dimensional analyis of heat transfer to the wall. Velocity measurements in the turbulent boundary layer at the mid-plane of a nearly square test-section duct have established that, when the boundary-layer thickness is less than one quarter of the duct height, mean-velocity characteristics are indistinguishable from those of a two-dimensional flat-plate boundary layer. In thicker mid-plane boundary layers, the mean-velocity characteristics are affected by stress-induced secondary flow and by lateral constriction of the boundary-layer wake region. A significant difference between flat-plate and duct boundary layers is also observed in momentum-balance calculations. The momentum-integral equation for a duct requires definitions of momentumd and displacement thickness which are different from those given for flat-plate boundary layers. Momentum-thickness growth rates predicted by the momentum-integral equation for a duct agree closely with measurements of the newly defined duct momentum thickness. Such agreement cannot be obtained in terms of standard flat-plate momentum thickness. In duct boundary layers with Reynolds numbers Re_theta between 400 and 2600, similarity in the wake-region distributions of streamwise turbulence statistics has been obtained by normalising distance from the wall with the flat-plate momentum thickness, theta_2. This result indicates that, in contrast with the mean velocity characteristics, the structure of mid-plane turbulence does not depend on the proportion of duct cross-section occupied by boundary layers and is essentially the same as in a flat-plate boundary layer. For Reynolds numbers less than 400, both wall-region and wake-region similarity fail because near-wall turbulence events interact strongly with the free stream flow and because large scale turbulence motions are directly influenced by the wall. In these conditions, which exist in both duct and flat-plate turbulent boundary layers, there is no distinct near-wall or wake region, and the behaviour of turbulence throughout the boundary layer depends on both wall variables and on outer region variables simultaneously.Thesis (Ph.D.)--School of Mechanical Engineering, 1998.
39
Cheng, Tsai-Wen, and 鄭採文. "A Low-power High-speed 8-bit Pipelining CLA Design Using Dual Threshold Voltage Domino Logic and Low-cost Digital I/Q Separator for DVB-T." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/15732239599200597417.
Full textAbstract:
碩士國立中山大學
電機工程學系研究所
94
This thesis includes two topics. One is a low-power high-speed 8-bit pipelining CLA design using dual threshold voltage (dual- Vth) domino logic. The other is a low-cost digital I/Q separator for DVB-T receivers. A high speed and low power 8-bit CLA using dual- Vth domino logic blocks arranged in a PLA-like style with pipelining is presented. According to parallely precharge and sequentially evaluate in a cascaded set of domino logic blocks, transistors in the precharge part and the evaluation part of dual- Vth domino logic are, respectively, replaced by high Vth transistors to reduce subthreshold leakage current through OFF transistors, and low Vth transistors. Moreover, an nMOS transistor is inserted in the precharge phase of the output inverter such that the two-phase dual- Vth domino logic can be properly applied in a pipeline structure. Consequently, the proposed design keeps the advantage of high speed while attaining the effect of low power dissipation. A low-cost digital I/Q separator is presented in the second part of this thesis. Using digital I/Q separator in place of the traditional analog I/Q separator guarantees the design conquer gain and phase mismatch problems between the I and Q channels. The proposed design can berealized by inverters and shifters such that the goal of low cost can be achieved.
40
Shyu, Lih-Shyng, and 徐力行. "Investigation of the Model Wake Blockage Effects at High Angles of Attack in a Low-Speed Wind Tunnel." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/34117933436987184457.
Full textAbstract:
博士國立中興大學
機械工程學系所
96
Excellent maneuverability at high angle of attack flight is important objectives in the future fighter design. When a jet fighter operates at high angles of attack the resulting aerodynamics can be highly nonlinear because of the complicated flow field around the configuration, including unsteady boundary layer, vortex generating, translating, developing / bursting, post stall departures, spin and so on, in addition to their mutual interaction. To improve the fidelity of measured aerodynamic characteristics at high angle of attack for modern jet fighters, the model wake blockage effect is examined in this paper. The wake blockage effect in the 2.2×3.1 meters low speed wind tunnel is investigated experimentally by analyzing the drag and wall pressure measurements. Circular flat plates in different sizes are used to simulate a test model at high angles of attack. The present analysis results in simple formulas for the corrections of model wake blockage effect. To verify the present correction formula, the NASA TP-1803 model is force-tested in the tunnel. The present corrected test data agree very well with the NASA TP data. It is suggested to use NASA TP-1803 as the standard model to confirm the correction of test data in the tunnel annual instrumental calibration and maintenance.
41
Wang, Chien-Yu, and 王健宇. "Image Processing and Temperature Correction of Pressure-Sensitive Paint for Airofoil Surface Pressure Measurement in Low Speed Wind Tunnel." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/9n7ca7.
Full text
42
Chang, Wei-Lin, and 張維霖. "The Analyses of Scooter Fuel Spray Impingement Characteristics on a Heated Flat Plate inside the Low Speed Wind Tunnel." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/54498143347010457667.
Full textAbstract:
碩士國立雲林科技大學
機械工程系碩士班
97
This research studies the spray phenomena. A low speed wind tunnel is assembled for observing the spray impingement on a heated meal plate in order to simulate the spray characteristics in the air intake system. The experimental parameters include the fuel injection pressure, the spray impinging angle, the metal plate’s temperature, and the wind tunnel speed. A set of spray conditions are set by fixing the above four parameters for simulating the real engine spray conditions`. This study tests the spray impingement on the plate. The set up parameters include the spray injection pressure, the plate temperature, the spray impingement angle, and the crosswind speed. The spray leaves the nozzle with a spiral shape. When the fuel jet starts to breakup into small droplets the spray angle decreases. If the injection pressure is increased the spray impingement rebounding is enhanced and the liquid film is clearly formed on the impinging site (The Flooded Mode). When the metal plate is heated to 130~180 oC the liquid film starts to boil and disappear quickly (The Dry Mode). When the temperature is reached beyond 180 oC the liquid film separates from the metal plate de to fast evaporation occurs between the liquid and metal layers (The Boiling Mode). If the impinging angle increases from 15 to 45 the spray rebounding phenomena If the plate is heated the downstream rebounding jet flow has higher film boiling effect then the upstream liquid jet flow. The experimental observations suggest that the liquid film range first increases than decreases if the metal plate is heated up. The higher the impinging angle the wider range of rebounding jet appears along the downstream jet flow. If the experimental is set to have fixed 2.5 bar injection pressure and 18 degree impinging angle, the higher crosswind the less liquid film can be left on the metal plate. However, when the metal plate is heated up beyond 130 oC the film boiling mode phenomena will keep the liquid film longer on the metal plate.
43
Wang, Jang Jong, and 王政忠. "Hydraulic System and Controller Design for The Innovated Supporting System of High-Angle-Attack Testing in Low Speed Wind Tunnel/AIDC." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/13847891211780309843.
Full text