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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Characterization of Upstream Effects Due to High Blockage in the AFRL Vertical Wind Tunnel

Sholtis, Paul M. 30 May 2019 (has links)
No description available.
22

Design of a Model for Low Speed Wind Tunnel Testing

Doulas, Alex, Peter, Love January 2023 (has links)
As technology for manufacturing small scale prototypes of aeroplanes has become cheaper and more easily viable, the process of Rapid Prototyping has become more common. Rapid Prototyping allows for the fundamental aerodynamic qualities of a geometric body to be tested in a wind tunnel using a small scale prototype. This means smaller prototypes of aircraft can be manufactured more rapidly and at a lower cost, allowing for more extensive testing of a design’s final aerodynamic qualities before any actual full-size production. In order to gain a better insight in the behaviours of the full-sized aircraft itself, a downscaled version of the KTH project UAV ALPHA has been deigned for testing in a low speed wind tunnel. The design will be used in further testing to help confirm simulations and estimations done on the ALPHA of its aerodynamic performance.
23

Development of Methods for Improved Data Integrity and Efficient Testing of Wind Tunnel Models for Dynamic Test Conditions in Unsteady and Nonlinear Flight Regimes

Heim, Eugene Henry DeWendt 05 February 2004 (has links)
Today's high performance aircraft are operating in expanded flight envelopes, often maneuvering at high angular rates at high angles-of-attack, even above maximum lift. Current aerodynamic models are inadequate in predicting flight characteristics in the expanded envelope, such as rapid aircraft departures and other unusual motions. Unsteady flows of aircraft are of real concern. The ability to accurately measure aerodynamic loads directly impacts the ability to accurately model and predict flight. Current wind tunnel testing techniques do not adequately address the data fidelity of a test point under the influence of fluctuating loads and moments. Additionally, forced oscillation test techniques, one of the primary tools used to develop dynamic models, do not currently provide estimates of the uncertainty of the results during an oscillation cycle. Further, in testing models across a range of flight conditions, there are frequently parts of the envelope which are well behaved and require few data points to arrive at a sound answer, and other parts of the envelope where the responses are much more active and require a large sample of data to arrive at an answer with statistical significance. Currently, test methods do not factor changes of flow physics into data acquisition schemes, so in many cases data are obtained over more iterations than required, or insufficient data may be obtained to determine a valid estimate. Methods of providing a measure of data integrity for static and forced oscillation test techniques are presented with examples. A method for optimizing required forced oscillation cycles based on decay of uncertainty gradients and balance tolerances is also presented. / Master of Science
24

Mechanical Design,Analysis, andManufacturing of Wind Tunnel Modeland support structure

Ghika, Sara Annika January 2021 (has links)
This volume covers the phases from design to manufacturing of a wind tunnel testsupport structure for a conceptual blended wingbodyUAV designed by KTH GreenRaven Project students. The innovative aircraft design demonstrates sustainabilitywithin aviation by utilizing a hybrid electricfuelcell propulsion system. The windtunnel test to be conducted at Bristol University will produce data to evaluate theaerodynamic properties of the model for design verification. The wind tunnel modelis a smallscaled1.5mspanmodel supported by struts that change the pitch andyaw angles during testing. An external force balance provided by Bristol Universitymeasures the loads and moments experienced by the model. The main requirementsfor the structure are to withstand the aerodynamic loads imposed by the model andto change the model’s orientation while maintaining wind speed during the test. Themaximum aerodynamic loads were provided in a matrix, the largest of which was usedas the load condition for the support equating to a 512N lift at 14◦ AOA. Trade studieswere conducted to determine the mechanisms to satisfy the requirements while stayingwithin budget. The chosen design for the support structure includes a circular baseplate constrained by a locking ring with positioning pins to change the yaw angle. Themain strut is mounted at the the center of the circular base plate. A hinge bracketat the top of the strut interfaces with another hinge bracket within the model viaa clevis pin. An electric linear actuator mounted downstream of the main strut isused to vary the pitch angle, with the center of rotation at the clevis pin. Once thedesign was finalized, finite element analysis was done to verify the structural stabilityof the design. The FEA results were compared to EulerBernoulliapproximations fordeflection. Manufacturing of the components was outsourcedwhile assembly andprogramming of the actuator was done inhouse. / Det här examensarbetet är en del av ett projekt som omfattar processen från designtill tillverkning av en vindstunnelstödstruktur för en konceptuell UAV av typenflygande vinge, designad av KTH Green Raven Projectstudenter.Den innovativaflygplanskonstruktionen visar hållbarhet inom flygindustrin genom att användahybridbränsleceller som framdrivningssystem. Vindtunneltest som genomförs vidBristol University kommer att producera data för att utvärdera de aerodynamiskaegenskaperna hos modellen för verifiering av designen. Vindtunnelmodellen är ennedskalad modell på 1,5 m som stöds av stag som ändrar anfallsochgirvinklarnaunder testningen. En extern mätsond från Bristol University mäter de krafter ochmoment som modellen utsätts för. De viktigaste kraven för konstruktionen är attmotstå de aerodynamiska lasterna som modellen påför och att ändra modellensorientering samtidigt som vindhastigheten bibehålls under testet. De maximalaaerodynamiska belastningarna tillhandahölls i en matris; varav den största användessom lastfall för stödet motsvarande en 512N lyftkraft vid 14◦ anfallsvinkel. Jämförandestudier genomfördes för att bestämma mekanismerna för att uppfylla kraven samtidigtsom de låg inom budgeten. Den valda konstruktionen för stödkonstruktionenbestår av en cirkulär basplatta som fixeras med hjälp av en låsring, och som harpositioneringsstift för att ändra girvinkeln. En huvudstång är monterad i mitten avbasplattan upp till ett gångjärnsfäste i modellen. Bakom detta sitter ett linjärt ställdonsom dras ut och skjuts ihop för att ändra modellens attityd med rotationscentrum viddet övre fästet på huvudstaget. När designen slutfördes gjordes en finit elementanalysför att verifiera dess strukturella stabilitet. FEAresultatenjämfördes med EulerBernoulliuppskattningarför utböjning. Tillverkningen av komponenterna överlätstill extern part, medan monteringen och programmeringen av ställdonet gjordesinternt.
25

Investigating Forward Flight Multirotor Wind Tunnel Testing in a 3-By 4-Foot Wind Tunnel

Danis, Reed 01 June 2018 (has links) (PDF)
Investigation of complex multirotor aerodynamic phenomena via wind tunnel experimentation is becoming extremely important with the rapid progress in advanced distributed propulsion VTOL concepts. Much of this experimentation is being performed in large, highly advanced tunnels. However, the proliferation of this class of vehicles extends to small aircraft used by small businesses, universities, and hobbyists without ready access to this level of test facility. Therefore, there is a need to investigate whether multirotor vehicles can be adequately tested in smaller wind tunnel facilities. A test rig for a 2.82-pound quadcopter was developed to perform powered testing in the Cal Poly Aerospace Department’s Low Speed Wind Tunnel, equipped with a 3-foot tall by 4-foot wide test section. The results were compared to data from similar tests performed in the U.S. Army 7-by 10-ft Wind Tunnel at NASA Ames. The two data sets did not show close agreement in absolute terms but demonstrated similar trends. Due to measurement uncertainties, the contribution of wind tunnel interference effects to this discrepancy in measurements was not able to be properly quantified, but is likely a major contributor. Flow visualization results demonstrated that tunnel interference effects can likely be minimized by testing at high tunnel speeds with the vehicle pitched 10-degrees or more downward. Suggestions towards avoiding the pitfalls inherent to multirotor wind tunnel testing are provided. Additionally, a modified form of the conventional lift-to-drag ratio is presented as a metric of electric multirotor aerodynamic efficiency.
26

Experimental Investigation of Active Wingtip Vortex Control Using Synthetic Jet Actuators

Sudak, Peter J 01 August 2014 (has links) (PDF)
An experiment was performed in the Cal Poly Mechanical Engineering 2x2 ft wind tunnel to quantify the effect of spanwise synthetic jet actuation (SJA) on the drag of a NACA 0015 semispan wing. The wing, which was designed and manufactured for this experiment, has an aspect ratio of 4.20, a span of 0.427 m (16.813”), and is built around an internal array of piezoelectric actuators, which work in series to create a synthetic jet that emanates from the wingtip in the spanwise direction. Direct lift and drag measurements were taken at a Reynolds Number of 100,000 and 200,000 using a load cell/slider mechanism to quantify the effect of actuation on the lift and drag. It was found that the piezoelectric disks used in the synthetic jet actuators cause structural vibrations that have a significant effect on the aerodynamics of the NACA 0015 model. The experiment was performed in a way as to isolate the effect of vibration from the effect of the synthetic jet on the lift and drag. Lift and drag data was supported with pressure readings from 60 pressure ports distributed in rows along the span of the wing. Oil droplet flow visualization was also performed to understand the effect of SJA near the wingtip. The synthetic jet and vibration had effects on the drag. The synthetic jet with vibration decreased the drag only slightly while vibration alone could decrease drag significantly from 11.3% at α = 4° to 23.4% at α = 10° and Re = 100,000. The lift was slightly increased with a slight increase due to the jet and showed a slight increase due to vibration. Two complete rows of pressure ports at 2y/b = 37.5% and 85.1% showed changes in lift due to actuation as well. The synthetic jet increased the lift near the wingtip at 2y/b = 85.1% and had little to no effect inboard at the 37.5% location, hence, the synthetic jet changes the lift distribution on the wing. Oil flow visualization was used to support this claim. Without actuation, the footprint of the tip vortex was present on the upper surface of the wing. With actuation on, the footprint disappeared suggesting the vortex was pushed off the wingtip by the jet. It is possible that the increased lift with actuation can be caused by the vortex being pushed outboard.
27

Evaluation and performance prediction of a wind turbine blade

Pierce, Warrick Tait 03 1900 (has links)
Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2009. / The aerodynamic performance of an existing wind turbine blade optimised for low wind speed conditions is investigated. The aerodynamic characteristics of four span locations are determined from surface pressure measurements and wake surveys with a traversed five-hole probe performed in a low speed wind tunnel for chord Reynolds numbers ranging from 360,000 - 640,000. Two-dimensional modelling of the wind tunnel tests is performed with the commercial computational fluid dynamics code FLUENT. The predictive accuracies of five eddy-viscosity turbulence models are compared. The computational results are compared to each other and experimental data. It is found that agreement between computational and experimental results varies with turbulence model. For lower Reynolds numbers, the Transitional-SST turbulence model accurately predicted the presence of laminar separation bubbles and was found to be superior to the fully turbulent models considered. This highlighted the importance of transitional modelling at lower Reynolds numbers. With increasing angles of attack the bubbles were found to move towards the leading edge and decrease in length. This was validated with experimental data. For the tip blade section, computations implementing the k-ε realizable turbulence model best predicted experimental data. The two-dimensional panel method code, XFOIL, was found to be optimistic with significantly higher lift-to-drag ratios than measured. Three-dimensional modelling of the rotating wind turbine rotor is performed with the commercial computational fluid dynamics code NUMECA. The Coefficient of Power (Cp) predicted varies from 0.440 to 0.565 depending on the turbulence model. Sectional airfoil characteristics are extracted from these computations and compared to two-dimensional airfoil characteristics. Separation was found to be suppressed for the rotating case. A lower limit of 0.481 for Cp is proposed based on the experimental data. / Centre for Renewable and Sustainable Energy Studies
28

Prediction and validation of the aerodynamic effects of simulated battle damage on aircraft wings

Pickhaver, T. W. January 2014 (has links)
Aerodynamic analysis is an important area of survivability studies. There is a desire to be able to predict the aerodynamic effects of a given damage scenario on an aircraft wing with minimal wind tunnel testing or computational simulations. Due to the limited nature of previous studies, this has not generally been possible. The original contribution of this thesis is a predictive technique developed to estimate the aerodynamic effects of a simulated battle damage hole on an aircraft wing, resulting from a range of attack directions. This technique was successfully validated against experimental data. Testing under two-dimensional conditions was undertaken on a NASA LS(1)-0417MOD aerofoil at a Reynolds number of 500,000. This project simulates the effect of attack direction by varying the offset between upper and lower surface damage holes in both chordwise and spanwise directions. Damage was modelled using circular holes. Lift, drag and pitching moment coefficients were measured and supplemented with surface flow visualisation and surface pressure measurements. Coefficient increments, defined as the difference between the damage cases and a datum undamaged case were used to quantify the effects of the damage, with the performance qualified in terms of weak and strong jets. Weak jets were found to have little effect on the flow and aerodynamic properties, while strong jets caused significant disruption. The effects increased in magnitude with hole size, incidence and proximity of the upper surface hole to the pressure peak. Spanwise offset on the holes had little effect on the jet strength but introduced asymmetry into the surface flow. This effect was found to be due to the behaviour of the flow within the cavity. Three-dimensional testing was undertaken at a Reynolds number of 1,000,000 on a half wing model in order to investigate any changes in the aerodynamic characteristics of the damage when applied to a more representative aircraft wing. The higher Reynolds number exploited the larger wind tunnel working section and provided a value more representative of typical unmanned aerial vehicles. As the damage was moved towards the tip its effects were lessened and the transition from weak jet to strong jet delayed. Spanwise pressure variation from the tip also introduced asymmetry into the jet s surface flow features. Plotting coefficient increments for all attack directions against the pressure coefficient difference between upper and lower surfaces from an undamaged wing, across the equivalent damage hole region highlighted significant trends, which were used as the basis of a predictive technique for a range of hole sizes and attack directions. The validity of the technique was assessed by predicting a previously untested damage case and comparing it against subsequent wind tunnel tests. The results from this validation proved encouraging.
29

Aerodynamic parameter identification for an unmanned aerial vehicle

Padayachee, Kreelan January 2016 (has links)
A dissertation submitted to the Faculty of Engineering and the Built Environment, School of Mechanical, Industrial and Aeronautical Engineering, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg, May 2016 / The present work describes the practical implementation of systems identification techniques to the development of a linear aerodynamic model for a small low-cost UAV equipped with a basic navigational and inertial measurement systems. The assessment of the applicability of the techniques were based on determining whether adequate aerodynamic models could be developed to aid in the reduction of wind tunnel testing when characterising new UAVs. The identification process consisted of postulating a model structure, flight test manoeuvre design, data reconstruction, aerodynamic parameter estimation, and model validation. The estimators that were used for the post-flight identification were the output error maximum likelihood method and an iterated extended Kalman filter with a global smoother. SIDPAC and FVSysID systems identification toolboxes were utilised and modified where appropriate. The instrumentation system on board the UAV consisted of three-axis accelerometers and gyroscopes, a three-axis vector magnetometer and GPS tracking while data was logged at 25 Hz. The angle of attack and angle of sideslip were not measured directly and were estimated using tailored data reconstruction methods. Adequate time domain lateral model correlation with flight data was achieved for the cruise flight condition. Adequacy was assessed against Theil’s inequality coefficients and Theil’s covariance. It was found that the simplified estimation algorithms based on the linearized equations of motion yielded the most promising model matches. Due to the high correlation between the pitch damping derivatives, the longitudinal analysis did not yield valid model parameter estimates. Even though the accuracy of the resulting models was below initial expectations, the detailed data compatibility analysis provided valuable insight into estimator limitations, instrumentation requirements and test procedures for systems identification on low-cost UAVs. / MT2016
30

Influência da asa em gaivota nos coeficientes aerodinâmicos de uma aeronave / Influence of gull wing on the aerodynamic coefficients of an airplane

Barbosa, Átila Antunes França 02 September 2015 (has links)
Desde o início da década de 2010, o aumento do preço do combustível de aviação e a pressão da sociedade para redução da emissão de gases nocivos ao meio ambiente, junto com a necessidade de redução de ruído durante as fases de decolagem e pouso, levaram as companhias aéreas a buscar aeronaves mais eficientes. Para suprir essa demanda, os fabricantes de aviões comerciais solucionaram esse problema através do uso de motores de maior desempenho, que apresentam maior diâmetro que motores de gerações passadas. Desse modo, foi necessário projetar asas com maior diedro na região da raiz, possibilitando a instalação desses novos motores, e diedro menor após a seção do motor, adotando assim a solução de asa em gaivota. O presente trabalho visa analisar o impacto de diferentes tipos de asas em gaivota nos coeficientes aerodinâmicos de uma aeronave de configuração comercial típica. Para tanto, foi realizada uma revisão bibliográfica dos estudos envolvendo asas em gaivota. Numa primeira fase foi feito um estudo analítico das características aerodinâmicas de alguns modelos de aeronaves com asa em gaivota, e em uma segunda fase, foram empregadas ferramentas computacionais para analisar seus comportamentos aerodinâmicos. Posteriormente, em uma terceira fase, esses modelos foram ensaiados no túnel de vento do LAE (Laboratório de Aerodinâmica da EESC/USP), e os resultados das três fases foram comparados. / Since the beginning of the 2010s, the increasing price of aviation fuel and the pressure of society to reduce the emission of harmful gases into the environment, coupled with the need of noise reduction during the takeoff and landing, induce carrier companies to look for more efficient airplanes. To furnish this demand, the airplane manufacturers solved the problem using high performance engines, which present a larger diameter than the engines from previous generations. Thereby, it was necessary to project wing with higher dihedral on the root portion, enabling the installation of these new engines, and a lower dihedral after the engine section, thus adopting a gull wing solution. This research project aims at analyzing the impact of different types of gull wing on the aerodynamic coefficients of a typical commercial configuration airplane. For this purpose, a bibliographic review about the studies related to gull wings was performed. In a first phase, an analytical analysis of the aerodynamic characteristics of some airplane model with gull wings was done, and in a second phase, computational programs was used to study their aerodynamic behavior. Later, in a third phase, these models were tested in the wind tunnel of LAE (Laboratory of Aerodynamics of EESC/USP), and the results from the three phases were compared.

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