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1
Doig, Graham Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "Compressible ground effect aerodynamics." Awarded by:University of New South Wales. Mechanical & Manufacturing Engineering, 2009. http://handle.unsw.edu.au/1959.4/44696.
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The aerodynamics of bodies in compressible ground effect flowfields from low-subsonic to supersonic Mach numbers have been investigated numerically and experimentally. A study of existing literature indicated that compressible ground effect has been addressed sporadically in various contexts, without being researched in any comprehensive detail. One of the reasons for this is the difficulty involved in performing experiments which accurately simulate the flows in question with regards to ground boundary conditions. To maximise the relevance of the research to appropriate real-world scenarios, multiple bodies were examined within the confines of their own specific flow regimes. These were: an inverted T026 wing in the low-to-medium subsonic regime, a lifting RAE 2822 aerofoil and ONERA M6 wing in the transonic regime, and a NATO military projectile at supersonic Mach numbers. Two primary aims were pursued. Firstly, experimental issues surrounding compressible ground effect flows were addressed. Potential problems were found in the practice of matching incompressible Computational Fluid Dynamics (CFD) simulations to wind tunnel experiments for the inverted wing at low freestream Mach numbers (<0.3), where the inverted wing was found to experience significant compressible effects even at Mach 0.15. The approach of matching full-scale CFD simulations to scale model testing at an identical Reynolds number but higher Mach number was analysed and found to be prone to significant error. An exploration was also conducted of appropriate ways to conduct experimental tests at transonic and supersonic Mach numbers, resulting in the recommendation of a symmetry (image) method as an effective means of approximating a moving ground boundary in a small-scale blowdown wind tunnel. Issues of scale with regards to Reynolds number persisted in the transonic regime, but with careful use of CFD as a complement to experiments, discrepancies were quantified with confidence. The second primary aim was to use CFD to gain a broader understanding of the ways in which density changes in the flowfield affect the aerodynamic performance of the bodies in question, in particular when a shock wave reflects from the ground plane to interact again with the body or its wake. The numerical approach was extensively verified and validated against existing and new experimental data. The lifting aerofoil and wing were investigated over a range of mid-to-high subsonic Mach numbers (1>M???>0.5), ground clearances and angles of incidence. The presence of the ground was found to affect the critical Mach number, and the aerodynamic characteristics of the bodies across all Mach numbers and clearances proved to be highly sensitive to ground proximity, with a step change in any variable often causing a considerable change to the lift, moment and drag coefficients. At the lowest ground clearances in both two and three dimensional studies, the aerodynamic efficiency was generally found to be less than that of unbounded (no ground) flight for shock-dominated flowfields at freestream Mach numbers greater than 0.7. In the fully-supersonic regime, where shocks tend to be steady and oblique, a supersonic spinning NATO projectile travelling at Mach 2.4 was simulated at several ground clearances. The shocks produced by the body reflected from the ground plane and interacted with the far wake, the near wake, and/or the body itself depending on the ground clearance. The influence of these wave reflections on the three-dimensional flowfield, and their resultant effects on the aerodynamic coefficients, was determined. The normal and drag forces acting on the projectile increased in exponential fashion once the reflections impinged on the projectile body again one or more times (at a height/diameter ground clearance h/d<1). The pitching moment of the projectile changed sign as ground clearance was reduced, adding to the complexity of the trajectory which would ensue.
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Pande, Abhijit. "Effect of struts on aeroacoustics of axisymmetric supersonic inlets." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-07292009-090449/.
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Nikolov, Zhivko. "Effect of upstream turbulence on truck aerodynamics." Thesis, Linköpings universitet, Mekanisk värmeteori och strömningslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-138696.
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The aerodynamic team at SCANIA has discovered the need to investigate the effect of the upstream turbulence conditions on the aerodynamics of the trucks. This need comes from the fact that there are differences between the drag coefficients obtained using computational fluid dynamics (CFD) and the on-road measurements. This difference can lead to wrong predictions of fuel consumption and emissions, which can cause incorrect evaluation of design changes. In this study the problem of modeling upstream turbulence in CFD simulations is addressed together with its effect on the aerodynamics of the trucks. To achieve this, representative values of turbulence intensity and length scale were found from the work of different researchers, who performed on-road measurements for various conditions. These values were then used in a method by Jakob Mann to generate a synthetic turbulence field. This field was then used to generate time varying velocity components, added to the mean velocity at the inlet of a CFD simulation. After the implementation of the method it was discovered that the conditions at the test section of the virtual wind tunnel were representative of the on-road measurements. The results showed drag increase and wake length decrease, similar to previous studies performed on simple geometries. It also showed that the higher mixing of the flow increases the drag by surface pressure increase of forward facing surfaces and pressure decrease at the base. These conclusions may be extended to other bluff body geometries and it shows the importance of good design around gaps. The comparison between two truck geometries showed that a truck with better aerodynamics in a smooth flow shows less drag increase with introduction of upstream turbulence.
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Jones, Marvin Alan. "Mechanisms in wing-in-ground effect aerodynamics." Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343624.
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An aircraft in low-level flight experiences a large increase in lift and a marked reduction in drag, compared with flight at altitude. This phenomenon is termed the 'wing-in-ground' effect. In these circumstances a region of high pressure is created beneath the aerofoil, and a pressure difference is set up between its upper and lower surfaces. A pressure difference is not permitted at the trailing edge and therefore a mechanism must exist, which allows the pressures above and below to adjust themselves to produce a continuous pressure field in the wake. It is the study of this mechanism and its role in the aerodynamics of low-level flight that forms the basis of our investigation
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Xin, Hong. "Development and validation of a generalized ground effect model for lifting rotors." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/11880.
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Pulla, Devi Prasad. "A study of helicopter aerodynamics in ground effect." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1149869712.
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Molina, Juan. "Aerodynamics of an oscillating wing in ground effect." Thesis, University of Southampton, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.582653.
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This research intends to provide new insight into the aerodynamics of wings in ground effect under dynamic motion. This work represents a new step forward in the field of race car aerodynamics, in which steady aerodynamics are well understood. As the first comprehensive study on oscillating wings in ground effect, several modes of oscillation were studied numerically, including heaving, pitching and combined motion of an airfoil and heaving of a wing fitted with endplates. A wide range of reduced frequencies were tested for the simulations at different ride heights, which showed appreciable differences with respect to a stationary wing. The flowfield around the airfoil was obtained by solving the Reynolds-Averaged Navier- Stokes equations, while Detached Eddy Simulation was used for the wing. A dynamic mesh model was implemented to adapt the grid to the wing motion. The results showed other aerodynamic mechanisms in addition to the ground effect, namely the effective incidence and added mass. Stall can be postponed to lower ride heights by increasing the frequency of heaving, while a pitching airfoil can stall below the static stall incidence when placed close to the ground. A stability analysis showed that flutter can occur at low frequencies in heaving motion but increasing the frequency always stabilises the motion. The behaviour of the vortex formed on the inboard face of the endplate is altered by the heaving motion and has an important effect on the downforce generation. Vortex breakdown can be induced or suppressed depending on the frequency and effective incidence. At high frequencies, these vortices interact with counter-rotating trailing edge vortices to form vortex loops that transform into omega vortices in the wake. Additional experiments for a stationary wing serve to qualitatively validate and complement the reference cases.
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Wang, Yi-Ren. "The effect of wake dynamics on rotor eigenvalues in forward flight." Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/13031.
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Zarifi-Rad, Farrokh. "Effect of model cooling in periodic transonic flow." Thesis, Queen's University Belfast, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334688.
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Tyll, Jason Scott. "Concurrent Aerodynamic Shape / Cost Design Of Magnetic Levitation Vehicles Using Multidisciplinary Design Optimization Techniques." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/40514.
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A multidisciplinary design optimization (MDO) methodology is developed to link the aerodynamic shape design to the system costs for magnetically levitated (MAGLEV) vehicles. These railed vehicles can cruise at speeds approaching that of short haul aircraft and travel just inches from a guideway. They are slated for high speed intercity service of up to 500 miles in length and would compete with air shuttle services. The realization of this technology hinges upon economic viability which is the impetus for the design methodology presented here. This methodology involves models for the aerodynamics, structural weight, direct operating cost, acquisition cost, and life cycle cost and utilizes the DOT optimization software. Optimizations are performed using sequential quadratic programming for a 5 design variable problem. This problem is reformulated using 7 design variables to overcome problems due to non-smooth design space. The reformulation of the problem provides a smoother design space which is navigable by calculus based optimizers. The MDO methodology proves to be a useful tool for the design of MAGLEV vehicles. The optimizations show significant and sensible differences between designing for minimum life cycle cost and other figures of merit. The optimizations also show a need for a more sensitive acquisition cost model which is not based simply on weight engineering. As a part of the design methodology, a low-order aerodynamics model is developed for the prediction of 2-D, ground effect flow over bluff bodies. The model employs a continuous vortex sheet to model the solid surface, discrete vortices to model the shed wake, the Stratford Criterion to determine the location of the turbulent separation, and the vorticity conservation condition to determine the strength of the shed vorticity. The continuous vortex sheet better matches the mechanics of the flow than discrete singularities and therefore better predicts the ground effect flow. The predictions compare well with higher-order computational methods and experimental data. A 3-D extension to this model is investigated, although no 3-D design optimizations are performed.
NOTE: An updated copy of this ETD was added on 05/29/2013.Ph. D.
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Mahon, Stephen Alexander. "The aerodynamics of multi-element wings in ground effect." Thesis, University of Southampton, 2005. https://eprints.soton.ac.uk/47619/.
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Ehirim, Obinna Hyacinth. "Aerodynamics and performance enhancement of a ground-effect diffuser." Thesis, Cranfield University, 2018. http://dspace.lib.cranfield.ac.uk/handle/1826/13211.
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This study involved experimental and equivalent computational investigations into the automobile-type 3―D flow physics of a diffuser bluff body in ground-effect and novel passive flow-control methods applied to the diffuser flow to enhance the diffuser’s aerodynamic performance. The bluff body used in this study is an Ahmed-like body employed in an inverted position with the slanted section together with the addition of side plates along both sides forming the ramped diffuser section. The first part of the study confirmed reported observations from previous studies that the downforce generated by the diffuser in proximity to a ground plane is influenced by the peak suction at the diffuser inlet and subsequent static pressure-recovery towards the diffuser exit. Also, when the bluff body ride height is gradually reduced from high to low, the diffuser flow as indicated by its force curve and surface flow features undergoes four distinct flow regimes (types A to D). The types A and B regimes are reasonably symmetrical, made up of two low-pressure core longitudinal vortices travelling along both sides of the diffuser length and they increase downforce and drag with reducing ride height. However, below the ride heights of the type B regime, types C and D regimes are asymmetrical because of the breakdown of one vortex; consequently a significant loss in downforce and drag occurs. The second part of the study involved the use ― near the diffuser exit ― of a convex bump on the diffuser ramp surface and an inverted wing between the diffuser side plates as passive flow control devices. The modification of the diffuser geometry with these devices employed individually or in combination, induced a second-stage pressure-drop and recovery near the diffuser exit. This behaviour was due to the radial pressure gradient induced on the diffuser flow by the suction surface ii curvature of the passive devices. As a result of this aerodynamic phenomenon, the diffuser generated across the flow regimes additional downforce, and a marginal increase in drag due to the profile drag induced by the devices.
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Mahalingam, Raghavendran. "Structure of the near wake of a rotor in forward flight and its effect on surface interactions." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/11974.
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Ockfen, Alex Earle. "Viscous modeling of ground effect aerodynamics of airfoil and jet." Pullman, Wash. : Washington State University, 2008. http://www.dissertations.wsu.edu/Thesis/Fall2008/a_ockfen_112408.pdf.
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Thesis (M.S. in mechanical engineering)--Washington State University, December 2008.Title from PDF title page (viewed on Dec. 31, 2008). "School of Mechanical and Materials Engineering." Includes bibliographical references (p. 149-154).
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Cheung, Chak Wah. "Mathematical modelling of unsteady aerodynamics and its effect on dynamic response." Thesis, Queen Mary, University of London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244073.
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Phillips, Catriona. "Computational study of rotorcraft aerodynamics in ground effect and brownout." Thesis, University of Glasgow, 2010. http://theses.gla.ac.uk/1783/.
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When helicopters operate close to the ground in desert conditions, the rotor wake can entrain large amounts of dust into the flow field surrounding the aircraft. This entrainment of dust can result in the potentially dangerous condition known as brownout where the pilot loses situational awareness. Understanding the physics that governs the entrainment of dust from the ground may eventually allow the condition of brownout to be avoided completely. To enable the formation of dust clouds around helicopters to be investigated, Brown's Vorticity Transport Model~(VTM) has been enhanced to include the ability to model the entrainment of dust from the ground and the transport of this dust once in the flow field. Comparison of the predictions of the VTM with experimental results has shown the VTM to be capable of capturing the general characteristics of the dust clouds. Close examination of the formation of the dust clouds revealed that the general physics that governs the entrainment process is the same for different rotors and a universal model of this process is described. Differences in the size and density of the dust clouds that form around different rotors result from differences in the overall behaviour of the wakes that are generated. The design of a rotor can have a significant effect on the size and density of the dust cloud that is produced. The tip vortices have been identified as the main cause of the changes to the dust cloud. However, the behaviour of these tip vortices, when the rotor is operating in ground effect, is dependent on the rotor design and also on the advance ratio of the rotor. Thus, to determine the size and density of the dust cloud that would form around any particular rotor, the behaviour of the wake of that rotor must first be known.
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Zerihan, Jonathan. "An investigation into the aerodynamics of wings in ground effect." Thesis, University of Southampton, 2001. https://eprints.soton.ac.uk/426058/.
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The aerodynamics of wings in ground effect has been studied using experimental and computational methods. Wind tunnel tests were used to quantify the effect of the ground on the aerodynamic performance of a wing, with the suction surface nearest to the ground. Features of the flowfield around the wing were investigated using Laser Doppler Anemometry and Particle Image Velocimetry to map the wake at the centre of the wing, and the state of the tip vortex. Initially, a single element configuration was used, both under transition free and transition fixed conditions. The application of Gurney flaps was then examined. The experimental study was completed using a double element configuration. The performance is discussed together with the flowfield results. Wind Tunnel testing was performed at a Reynolds number of approximately 0.75x10(6) based on the chord of the double element wing. The application of a computational technique has been examined using a Reynolds averaged Navier Stokes solver. Trends in the aerodynamic performance of a single element aerofoil in ground effect were predicted well using a Spalart-Allmaras turbulence model.
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Bhattacharya, Samik Ahmed Anwar. "Effect of three dimensional forcing on the wake of a circular cylinder." Auburn, Ala, 2009. http://hdl.handle.net/10415/1852.
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Grohsmeyer, Steven P. "Numerical investigation of the effect of leading edge geometry on dynamic stall of airfoils." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA239949.
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Thesis (M.S. in Aeronautical Engineering)--Naval Postgraduate School, September 1990.Thesis Advisor(s): Ekaterinaris, John A. ; Platzer, Max. "September 1990." Description based on title screen as viewed on December 21, 2009. DTIC Identifier(s): Dynamics, leading edges, airfoils, dynamic stall, oscillating airfoil, pitching airfoil, leading edge geometry, pressure gradient, theses. Author(s) subject terms: Dynamic stall, oscillating airfoil, pitching airfoil, leading edge geometry, pressure gradient. Includes bibliographical references (p. 111-112). Also available in print.
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Westbury, Philippa Sarah. "The effect of Reynolds number and wall roughness on bursts in turbulent boundary layers." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320742.
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Pino, Romainville Francisco Adolfo. "The effect of adding multiple triangular vortex generators on the leading edge of a wing." Morgantown, W. Va. : [West Virginia University Libraries], 2005. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4405.
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Thesis (M.S.)--West Virginia University, 2005.Title from document title page. Document formatted into pages; contains xiv, 86 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 73-76).
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Ganesh, Balakrishnan. "Unsteady aerodynamics of rotorcraft at low advance ratios in ground effect." Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-03072006-145825/.
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Thesis (Ph. D.)--Aerospace Engineering, Georgia Institute of Technology, 2006.Narayanan Komerath, Committee Chair ; Lakshmi Sankar, Committee Member ; JVR Prasad, Committee Member ; Mark Costello, Committee Member ; A. Terrence Conlisk Jr., Committee Member.
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George, Sean (Sean Peter Merrill) 1973. "The effect of configurational asymmetries on projectile aerodynamics, stability, and performance." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/28193.
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Senior, Andrea Elizabeth. "The aerodynamics of a diffuser equipped bluff body in ground effect." Thesis, University of Southampton, 2002. https://eprints.soton.ac.uk/47113/.
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An investigation of the flow physics of a diffuser equipped bluff body in ground effect has been undertaken. Situated at the rear of a racing car undertray, the diffuser is an important component and the least understood part of the vehicle. Diffuser performance can change dramatically with vehicle ride height. This includes a significant loss in performance at low ride heights which can also be a serious vehicle safety issue. An increased understanding of the diffuser behaviour in ground effect is required to assist design improvements. An accurate experimental database of the flow field is necessary both to aid this understanding and also to provide information against which the continuing development of computational simulations may be assessed. The present research is two-fold; experimental and computational. Model tests were conducted on a generic 3D bluff body equipped with a fixed angle diffuser representative of current racing car diffusers. Extensive experimental tests in wind tunnels equipped with moving belts included mean forces, surface pressures, oilflow visualisation, laser doppler anemometry and particle image velocimetry. The 3D diffuser flow field has been measured for the first time and the results are used to analyse the behaviour of the diffuser in ground effect. Complementary RANS simulations provide valuable insight into the modelling requirements. It is known that the diffuser generates down-force by accelerating air underneath the model through the channel formed by the model underside and the ground. The diffuser flow is characterised by a counter rotating vortex pair. The present research presents a new understanding of the diffuser flow field and the mechanisms causing its behaviour in ground effect. It has been found that the behaviour of the vortices alters according to the model ride height and the pressure gradient inside the diffuser. Additional down-force is generated due to the low pressure zones associated with these vortices. At relatively large ground clearances, the vortices are coherent and strong with a high axial speed core. At these heights the down-force experienced by the model increases with reducing model ride height. This behaviour is terminated at lower ground clearances by the advent of a plateau in the down-force curve and the occurrence of breakdown in the vortices inside the diffuser. The vortex breakdown results in large, diffusive and weak vortices. Maximum down-force on the model occurs at the lowest ride height of this type of flow at the end of the plateau. A sharp reduction in the down-force occurs thereafter, due to the complete breakdown of one of the vortices. The resulting asymmetric flow consists of a single coherent vortex to one side of the flow and significant flow reversal at the other side. At very low ride heights the vortices are asymmetric and weak Down-force reduction is believed to occur as a result of the steep pressure gradient inside the diffuser which advances the vortex breakdown inside the diffuser upstream as the model ride height is reduced. At the point of down-force reduction one of the vortices breaks down completely. At very low ride heights the boundary layers at the model underside and at the moving ground are believed to merge to restrict flow through the diffuser inlet. The experimental database is comprehensive and provides the necessary tool for validation of computational modelling. A computational simulation of the flow at a high ride height successfully predicts force and surface pressure coefficients and the main flow features.
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Catalano, F. M. "The effect of a high thrust pusher propeller on the flow over a straight wing." Thesis, Cranfield University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385759.
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Chokani, Ndaona. "A study of the passive effect on transonic shockwave/turbulent boundary layer interactions on porous surfaces." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293606.
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Harris, Andrew Peter. "A study of the aerodynamic characteristics of a propeller and wing including the effect of ground proximity." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386686.
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Guerra, Joel Tynan. "Investigating the Effect of an Upstream Spheroid on Tandem Hydrofoils." DigitalCommons@CalPoly, 2018. https://digitalcommons.calpoly.edu/theses/1959.
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This thesis documents a series of three dimensional unsteady Reynolds Averaged Navier-Stokes CFD simulations used to investigate the influence of an upstream prolate spheroid body on tandem pitching hydrofoils. The model is validated by performing separate CFD simulations on the body and pitching hydrofoils and comparing results to existing experimental data. The simulations were run for a range of Strouhal numbers (0.2-0.5) and phase differences (0-π). Results were compared to identical simulations without an upstream body to determine how the body affects thrust generation and the unsteady flow field.
The combined time-averaged thrust increases with Strouhal number, and is highest when the foils pitch out of phase with each other. At intermediate phase differences between φ = 0 and φ = π the leading foil produces significantly more thrust than the trailing foil, peaking at φ = π/2. For St = 0.5 this difference is 21.7%.
Results indicate that adding an upstream prolate spheroid body does not significantly alter thrust results, though it does provide a small (nearly negligible) boost. Vorticity from the body is pulled downstream from the pitching foils, which interacts with the vortex generation when the vortex being generated is of the same sign as the body vorticity. This body vorticity does not affect the vorticity magnitude of the downstream vortex pairs.
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Cai, Jielong. "Changes in Propeller Performance Due to Ground and Partial Ground Proximity." University of Dayton / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1588164898961792.
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Mankowski, Oliver Andrew. "The wind tunnel simulation and effect of turbulent air flow on automotive aerodynamics." Thesis, Durham University, 2013. http://etheses.dur.ac.uk/10558/.
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This thesis presents the research completed to design, commission and evaluate a turbulence generation system for Durham University’s 2m wind tunnel and the development of a method to simulate on road turbulence and measure its effects on a vehicle. The objective was to develop a test approach for simulating and analysing a vehicle’s response to unsteady airflows. This approach focussed on simulating the overlap of the range of turbulence frequencies which exist both at significant energy in the on road environment and the frequencies at which a significant vehicle response is seen. The frequency range where both conditions exist was seen to be between 1 – 10Hz. Confirmation of this transient frequency range was through the use of an admittance technique developed in this thesis which compares unsteady effects to quasi-steady effects. The technique was also developed to account for the component of unsteady pressure self excitedness that exists, effectively the noise component in an admittance analysis. The approach concluded with the operation of a new turbulence generation system (TGS), which simulates the wind characteristics experienced by vehicles as they move through the on road wind environment. The design was informed both by previous works and an on road investigation of environment and vehicle response. An on road study consisting of 8,800-seconds of on road measurements was completed to record incoming flow velocities and passenger sideglass static pressures (a region noted in studies to show a notable response to yawed flow). The on road environment was shown to have significant energy in the 0.1 10Hz range (reduced frequency K = 0.1 10 for a vehicle driving at highway speeds). Yaw angles ranged between ±20o, but with the vast majority within ±6o. Correspondingly, the turbulence intensity range was 0.5 15%, but with the majority below 8%. The challenges of generating turbulent length scales in the order of size of a vehicle’s length, whilst also at reasonable turbulent intensities were assessed to be beyond the capability of a passive device. Through a series of iterative CFD tests, an active “lift based” TGS was designed, based around two oscillating yaw aerofoils, which also encompassed additional inlet and outlets controlled by shutter panels. These ensured that the jet shear layer did not interact with the test model and helped to achieve higher peak yaw angles and good flow uniformity. A full aerodynamic design of the TGS was completed from the CFD studies, from which a high level mechanical design was specified including target aerofoil displacement and acceleration rates, control system requirements and the linkage design. The construction and installation of the TGS was undertaken by an external contractor. Due to its numerous configurable control parameters, a significant commissioning project was required and completed to determine the system’s optimum configuration. The system is capable of operating up to 10Hz at ±10o flow yaw angle and in a programmed arbitrary mode. The system also has the capability to generate pitch and longitudinal turbulence effects (Cooper et al (1989)). A 40% scaled model of the vehicle studied on the road was placed into the wind tunnel and a range of cases were generated including wind conditions previously recorded on road. The results showed that the technique of using both a roof mounted probe and the TGS system are able to take on road flow conditions and accurately recreate their effects on vehicles in a wind tunnel. Multiple aspects of the work (on road, CFD and wind tunnel) showed that below K = 0.3 pressure fluctuations behaved in a quasi steady manner. Admittance greater than unity was observed near the A pillar, but admittance was generally below unity and reduced progressively for K > 1. Self excitedness was seen to decrease in unsteady tests (in comparison to quasi steady) tests in the A pillar region, but increase between unsteady to quasi steady tests in the mirror wake region.
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Heyder-Bruckner, Jacques. "The aerodynamics of an inverted wing and a rotating wheel in ground effect." Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/207263/.
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This study investigates the aerodynamics of nil inverted wing in ground effect, a race car wheel and the interaction between the two components, using numerical and experimental methods. The wheels were located behind the wing at flU overlap and gap of 20mm, and the wing ride height. iu the vertical direction was the primary variable. Models of 50% scale were used , giving a Reynolds number of 5.8 x 105 based on the wing chord . The Detached-Eddy Simulation model was validated against wind tunnel measurements including PIV, surface pressures and forces , where it was found to outperform a Reynolds averaged Navier-Stokes approach which used the Spalart-Allmaras turbulence model. It accurately predicted the wing vortex breakdown at low ride heights, which is of the bubble type with a spiralling tail, and the wake of the wheel. A mesh sensitivity study revealed that a finer mesh increased the amount of structures captured with the DES model, improving its accuracy.
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Schreiber, Charla W. "Effect of span variation on the performance of a cross flow fan." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Jun%5FScheiber.pdf.
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Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, June 2006.Thesis Advisor(s): Garth V. Hobson, Knox T. Millsaps. "June 2006." Includes bibliographical references (p. 47). Also available in print.
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Diasinos, Sammy Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "The aerodynamic interaction of a rotating wheel and a downforce producing wing in ground effect." Awarded by:University of New South Wales. Mechanical & Manufacturing Engineering, 2009. http://handle.unsw.edu.au/1959.4/44516.
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The performance of current open wheeler race cars depends heavily on the effectiveness of the aerodynamic package of which the front wing and wheels make a significant contribution. Previous investigations have focused on the aerodynamic characteristics of each of these bodies in isolation. Investigations that have considered both working in unison have conflictingly reported that the wheel presence aids or hinders the wing???s performance while the wheel???s aerodynamic performance has been neglected. In order to obtain a more thorough understanding of the interaction of a wing and wheel, experimental results were used to validate a computational model used to investigate a wing and wheel in isolation and in combination. The combined wing and wheel investigation demonstrated that three main interactions can occur, depending on the selection of wing span, angle of attack and height used, while the wheel width and track were found to have little influence. The three interacting states differ in the path that the main and secondary wing vortices take around the wheel and the subsequent variation in the combined wake structure. In general, the wing in the presence of the wheel reduced the wing???s ability to generate downforce by up to 45% due to the high pressure regions generated forward of the wheel. This was also found to alleviate the adverse pressure gradients experienced by the wing, and also reduce the drag by up to 70%. For this reason, the downforce loss phenomenon was observed to occur at a height 0.08c to 0.32c lower in comparison to the same wing in isolation, dependant on the wing span. Wheel lift and drag values were also observed to reduce in the presence of a wing by up to 65% and 38% respectively due to the influence of the wing???s flow structures have on the wake of the wheel. As a result,it was shown that the combined wing and wheel downforce and drag optima differed by up to 75% and 25% respectively to those which would be estimated if the two bodies were investigated individually and the results summed highlighting the importance of investigating these two bodies in unison.
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Adhynugraha, Muhammad Ilham. "Longitudinal dynamics of wing in ground effect craft in waves." Thesis, Cranfield University, 2017. http://dspace.lib.cranfield.ac.uk/handle/1826/13095.
Full textAbstract:
An assessment of the longitudinal motion of a hybrid configuration called the aerodynamically alleviated marine vehicle (AAMV) with the presence of waves, is demonstrated in the thesis. The development of this type of vehicle requires a mathematical framework to characterise its dynamics with the influence of external forces due to the waves’ motion. An overview of the effect of waves towards the models of dynamics developed for wing in ground effect (WIGE) craft and high-speed marine vehicles (planing craft) is carried out. However, the overview only leads to a finding that the longitudinal stability of a lifting surface over wavy ground effect is not entirely established. Taking this fact into account, the analysis of the model is proposed for a WIGE craft configuration. A simplification is adopted considering heave motion only in the modelling of oscillation. The simplification is made to thoroughly capture the effect of oscillation toward dynamic stability of the vehicle. To support the model verification, a numerical simulation followed by a semi-empirical design method was adopted to produce aerodynamic data, both in two-dimensional and three-dimensional domains, respectively. The results show that the combination of underpinning parameters, i.e. ride height, frequency and amplitude of oscillation, remarkably influence the aerodynamics. The characteristics in aerodynamics affect the production of stability derivatives and eventually stability behaviour of the chosen configuration. Some patterns in the results are identified but there also some data that show the peculiarity. Thus further investigation is needed.
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Setrakian, A. A. S. "The effect of rectangular obstacles on the diffusion of a wall jet." Thesis, Edinburgh Napier University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233908.
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Barker, Brian W. "Effect of Adaptive Tabs on Drag of a Square-Base Bluff Body." DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1295.
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This thesis involves the experimental wind tunnel testing of a 0.127m by 0.127m square-base bluff body to test the effectiveness of trailing edge tabulations to reduce drag in the Cal Poly 0.912m by 1.219 m low-speed wind tunnel. To accomplish this, the boundary layer was first measured on the trailing edge of the model for the three speeds at 10, 20, and 30 m/s, with Re = 8.3e4, 1.6e5 and 2.5e5 respectively, without the tabs. Three different tests were performed to determine the effectiveness of the tabs. These tests included base pressure measurements, total drag force measurements and hotwire velocity fluctuation measurements. These tests were repeated with tabs on the model’s trailing edge at the three different tab heights and without tabs at all three test speeds.
The base pressure measurements showed a decrease in average base pressure with the addition of tabs which signifies an increase in drag. The total drag measurements confirmed this by showing that the overall force increases with the addition of the tabs. The hotwire tests further confirm this by showing that the vortex is present for every configuration tested.
This thesis showed that the addition of tabs was unsuccessful in reducing the effects of the vortex shedding for a square-base bluff body. The addition of low, medium, and high tabs to the square base of the bluff body all showed an increase in vortex strength and overall drag. Further study is required to determine if drag savings are feasible for tabs all around the square base of the bluff body and at different locations.
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Sawyer, Scott R. "Experimental Investigation of Drag Reduction by Trailing Edge Tabs on a Square Based Bluff Body in Ground Effect." DigitalCommons@CalPoly, 2015. https://digitalcommons.calpoly.edu/theses/1414.
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This thesis presents an experimental investigation of drag reduction devices on a bluff body in ground effect. It has previously been shown that the addition of end-plate tabs to a rectangular based bluff body with an aspect ratio of 4 is effective in eliminating vortex shedding and reducing drag for low Reynolds number flows. In the present study a square based bluff body, both with and without tabs, will be tested under the same conditions, except this time operating within proximity to a ground plane in order to mimic the properties of bounded aerodynamics that would be present for a body in ground effect.
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Kuya, Yuichi. "Aerodynamics and multi-fidelity surrogate modelling of an inverted wing with vortex generators in ground effect." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/73331/.
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A study of an inverted single-element wing with vortex denerators in ground effect is presented. Counter-rotating and co-rotating rectangular-vane type vortex generators with different device heights are studied on the suction surface of the wing. The primary application of this study is a front wing of race cars. This study comprises three main elements: 1) experimental study, 2) computational study and 3) multi-fidelity surrogate modelling. An experimental testing is performed in a wind tunnel equipped with a moving belt rig, studying time-averaged and unsteady aerodynamic characteristics. The experimental work performed shows that a use of vortex generators, notably of the counter-rotating sub-boundary layer vortex generator type, can be effective at controlling flow separation, with a resultant improvement in downforce within relatively low drag penalty. The results also reveal fundamental vortex characteristics for flow separation control. A computational study is performed by three-dimensional Reynolds-averaged Navier-Stokes steady simulations with the Spalart-Allmaras turbulence model. The computations are validated against the experimental results so as to provide confidence, with the validation exhibiting close agreement with the experimental results. The computational results complement the experimental results by highlighting the flow physics of how vortex generators can help control flow separation on an inverted wing in ground effect and how critical vortex generator type and size are for its effectiveness. An application of a force-based vortex generator source term model is also examined. A multi-fidelity surrogate modelling approach working with co-kriging regression and statistical techniques is presented, unsing the experimental and computational data sets. This approach exhibits an efficient improvement of surrogate models, compared to conventional surrogate models. Surrogate models of sectional downforce of an inverted wing with counter-rotating sub-boundary layer vortex generators in ground effect are constructed as a response of the ride height and incidence.
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Wood, Daniel. "The effect of rear geometry changes on the notchback flow field." Thesis, Loughborough University, 2015. https://dspace.lboro.ac.uk/2134/18889.
Full textAbstract:
An experimental investigation into the form of the notchback wake topology, its temporal behaviour, and how this changes with the underlying geometry has been undertaken to further understanding of this flow regime pertaining to a popular automotive body type. Whilst this work has been performed at model scale on a simplified body a sufficiently complex design of backlight header and trailing pillar have been utilised. Thereby allowing the systematic study of the wake structure of a family of production representative geometries to be undertaken enabling the flow topology across bodies with parameters representative of vehicles produced from the 1960s to the present day to be investigated. Body force measurements showed both drag and rear lift to increase with backlight angle in a manner which was largely expected due to these designs being representative of older production notchback vehicles. Manufacturers knowledge and understanding of how drag changes with this parameter, combined with on going shape optimisation studies, have led to the shallower backlight angles common to modern designs. Detailed flow field measurements were subsequently used to determine the form and temporal behaviour of the flow topologies responsible for this force behaviour. Across the range of geometries tested, the in-notch structures were shown to undergo significant variation, both their time-averaged form and time-variant behaviour changing. Common to all configurations were the presence of a pair of strong trailing vortex structures which flanked the edges of the backlight and bootdeck. However, flow in the centre of the backlight underwent the greatest variation. This region was shown to develop from a largely attached form at shallower backlight angles before developing into an increasingly strong hairpin like structure. As backlight angle increased further the topology ultimately took a highly asymmetric form. With these changes of the flow topology also came changes of the temporal behaviour which revealed vortex shedding, flow structure oscillation and the switching of bi-stable structures as backlight angle increased. It is hoped that in thoroughly understanding the range of notchback flow topologies typically generated by production vehicles that this work will form the vital foundation upon which future investigations looking to reduced drag can be based.
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Al-Maaitah, Ayman Adnan. "Effect of suction and cooling on the stability of subsonic and supersonic boundary layers." Diss., Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/54481.
Full textAbstract:
An investigation is conducted into the effect of cooling and suction on the stability of subsonic flows over two-dimensional roughness elements and supersonic flows over flat plates. First, the effect of wall cooling on the two-dimensional linear stability of subsonic flows over two-dimensional surface imperfections is investigated. Results are presented for flows over smooth humps and backward-facing steps with Mach numbers up to 0.8. The results show that, whereas cooling decreases the viscous instability, it increases the shear-layer instability and hence it increases the growth rates in the separation region. The coexistence of more than one instability mechanism makes a certain degree of wall cooling most effective. For the Mach numbers 0.5 and 0.8, the optimum wall temperatures are about 80% and 60% of the adiabatic wall temperature, respectively. Increasing the Mach number decreases the effectiveness of cooling slightly and reduces the optimum wall temperature.
Second, the effect of suction on the stability of compressible flows over backward-facing steps is investigated. Mach numbers up to 0.8 are considered. As expected, suction considerably reduces the separation region. The results show that continuous suction stabilizes the flow outside the separation bubble, as expected, but it destabilizes the flow inside it. Nevertheless, the overall N factor decreases as the suction level increases. This is due to the considerable reduction in the separation bubble. For the same suction flow rate, properly distributed suction strips are more effective in stabilizing the flow than continuous-suction distributions. Furthermore, the size of the separation bubble, and hence its effect on the instability, can be considerably reduced by placing strips with high suction velocities in the separation region
Third, the effect of suction on the stability of supersonic and hypersonic boundary layers is investigated. Calculations are performed for non-similar and self-similar boundary layers. The variation of the maximum growth rate with Mach number at low levels of suction is different from that at high levels of suction. This is due to the coexistence of viscous and inviscid instability mechanisms in supersonic and hypersonic boundary layers. Suction is more effective in stabilizing the viscous instability, and hence it is more effective at low Mach numbers. Although suction decreases the maximum growth rate of second-mode waves, small levels of suction increase the growth rates of disturbances having certain frequencies. On the other hand, first-mode waves are stabilized by suction at all frequencies. Constant-suction distributions considerably move the critical Reynolds numbers of second-mode waves to higher values while the critical Reynolds numbers of first-mode waves are not sensitive to suction.Ph. D.
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Dunn, Dwain Iain. "The effect of endwall contouring on the unsteady flow through a turbine rotor." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/95940.
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Thesis (PhD) -- Stellenbosch University, 2014.ENGLISH ABSTRACT: With increasing environmental concerns and the drive for a greener economy comes an increased desire to improve turbine engine fuel efficiency and reduce emissions. Unfortunately weight reduction techniques used increase the blade loading, which in turn increases the losses. Non-axisymmetric endwall contouring is one of several techniques being investigated to reduce loss in a turbine. An investigation at Durham University produced a non-axisymmetric endwall design for a linear cascade. An adaption of the most promising endwall was investigated in an annular rotating test rig at the CSIR using steady state instrumentation. The current investigation extends those investigations into the unsteady time domain. Previous investigations found that a generic rotor endwall contour improved efficiency by controlling the endwall secondary flow vortex system in both a linear cascade and an annular 1½ stage rotating test turbine. The current research was aimed at determining if there were any unsteady effects introduced by the contoured endwall. The approach was unique in that it investigated the unsteady effects of an endwall contour originally designed for a linear cascade both experimentally and numerically at three incidence angles (positive, zero and negative to represent increased load, design load and decreased load respectively), the results of which are openly available. Unsteady experimental hotfilm results showed that the endwall contour made the velocity profile more radially uniform by reducing the strength of the endwall secondary flow vortex system. The fluctuations in the velocity were also reduced producing a more temporally uniform velocity profile. The FFT magnitude of the velocity at the blade passing frequency below midspan was also reduced. It was found that the reduction in the endwall secondary flow vortex system due to the contour increased with increasing loading. Numerical results showed that the oscillations in the flow were small and did not penetrate the boundary layer. The contoured rotor was forward and aft loaded when compared to the annular rotor, resulting in a weaker cross passage pressure gradient which allowed the endwall secondary flow vortex system to be less tightly wrapped. Numerical results did not show a significant difference in the oscillations observed in the annular and contoured rotor. A new objective function for use in the endwall optimisation process was proposed that acts as a proxy for efficiency, but is less prone to uncertainty in the results. When used on the current results it shows the same trend as efficiency. It remains to be used to design an endwall for full validation.
AFRIKAANSE OPSOMMING: Met ’n toenemende omgewingsbesorgdheid en die strewe na ’n groener ekonomie kom ’n toenemende behoefte om turbine enjin brandstofdoeltreffendheid te verbeter en vrystellings te verlaag. Ongelukkig het gewigsbesparingstegnieke wat gebruik is die lemlading verhoog, wat op sy beurt die verliese verhoog. Nie-assimmetriese endwandprofilering is een van verskeie tegnieke wat ondersoek word om verliese in ’n turbine te verminder. ’n Ondersoek by die Universiteit van Durham het ’n nie-assimmetriese endwandontwerp vir ’n lineêre kaskade gelewer. ’n Aanpassing van die mees belowende endwand is in ’n annulêre roterende toetsopstelling by die WNNR getoets, deur gebruik te maak van bestendige toestand instrumentasie. Die huidige ondersoek brei daardie ondersoeke uit na die nie-bestendige verwysingsraamwerk . Vorige ondersoeke het bevind dat die generiese rotor endwandprofiel doeltreffendheid verbeter as gevolg van die beheer van die endwand sekondêre vloei draaikolkstelsel in beide ’n lineêre kaskade sowel as ’n annulêre 1½ stadium roterende toetsturbine. Die huidige navorsing was daarop gemik om vas te stel of die endwandprofiel enige onbestendige effekte tot gevolg gehad het. Die benadering was uniek in die sin dat dit die onbestendige effekte ondersoek het van ’n endwandprofiel wat oorspronklik ontwerp is vir ’n lineêre kaskade beide eksperimenteel en numeries op drie invalsshoeke (positief, nul en negatief om onderskeidelik verhoogde lading, ontwerplading en verlaagde lading te verteenwoordig), waarvan die resultate algemeen beskikbaar is. Onbestendige eksperimentele warmfilm resultate het getoon dat die endwandprofiel die snelheidsprofiel meer radiaal uniform gemaak het deur die vermindering van die sterkte van die endwand sekondêre vloei werwelstelsel. Die skommelinge in die snelheid is ook verminder wat ’n meer tyduniforme snelheidsprofiel gelewer het. Die FFT (Fast Fourier Transform) grootte van die snelheid van die lem verbygaan frekwensie onder lem midbestek het ook verminder. Daar was bevind dat die vermindering in die endwand sekondêre vloei draaikolkstelsel as gevolg van die endwandprofiel toeneem met toenemende lading. Numeriese resultate het getoon dat die ossilasie in die vloei klein was en nie die grenslaag binnegedring het nie. Die rotor met gevormde wand het ’n voor- en agterlading gehad in vergelyking met die rotor met annulêre wand, wat tot ’n laer drukgradient dwarsop die vloeirigting gelei het, die endwand sekondêre vloei draaikolkstelsel minder beperk het. Numeriese resultate het nie ’n beduidende verskil in die ossilasies tussen die annulêre en gevormde rotorwand getoon nie. ’n Nuwe doelwitfunksie vir gebruik in die endwand optimersproses is voorgestel wat dien as ’n plaasvervanger vir doeltreffendheid, maar minder geneig is tot onsekerheid in die resultate. Wanneer dit gebruik word op die huidige resultate toon dit dieselfde tendens as doeltreffendheid. Dit moet nog gebruik word in die ontwerp van ’n endwand vir volledige bevestiging.
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Walter, Daniel James, and Daniel james walter@gmail com. "Study of aerofoils at high angle of attack in ground effect." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080110.145138.
Full textAbstract:
Aerodynamic devices, such as wings, are used in higher levels of motorsport (Formula-1 etc.) to increase the contact force between the road and tyres (i.e. to generate downforce). This in turn increases the performance envelope of the race car. However the extra downforce increases aerodynamic drag which (apart from when braking) is generally detrimental to lap-times. The drag acts to slow the vehicle, and hinders the effect of available drive power and reduces fuel economy. Wings, in automotive use, are not constrained by the same parameters as aircraft, and thus higher angles of attack can be safely reached, although at a higher cost in drag. Variable geometry aerodynamic devices have been used in many forms of motorsport in the past offering the ability to change the relative values of downforce and drag. These have invariably been banned, generally due to safety reasons. The use of active aerodynamics is currently legal in both Formula SAE (engineering compet ition for university students to design, build and race an open-wheel race car) and production vehicles. A number of passenger car companies are beginning to incorporate active aerodynamic devices in their designs. In this research the effect of ground proximity on the lift, drag and moment coefficients of inverted, two-dimensional aerofoils was investigated. The purpose of the study was to examine the effect ground proximity on aerofoils post stall, in an effort to evaluate the use of active aerodynamics to increase the performance of a race car. The aerofoils were tested at angles of attack ranging from 0° - 135°. The tests were performed at a Reynolds number of 2.16 x 105 based on chord length. Forces were calculated via the use of pressure taps along the centreline of the aerofoils. The RMIT Industrial Wind Tunnel (IWT) was used for the testing. Normally 3m wide and 2m high, an extra contraction was installed and the section was reduced to form a width of 295mm. The wing was mounted between walls to simulate 2-D flow. The IWT was chosen as it would allow enough height to reduce blockage effect caused by the aerofoils when at high angles of incidence. The walls of the tunnel were pressure tapped to allow monitoring of the pressure gradient along the tunnel. The results show a delay in the stall of the aerofoils tested with reduced ground clearance. Two of the aerofoils tested showed a decrease in Cl with decreasing ground clearance; the third showed an increase. The Cd of the aerofoils post-stall decreased with reduced ground clearance. Decreasing ground clearance was found to reduce pitch moment variation of the aerofoils with varied angle of attack. The results were used in a simulation of a typical Formula SAE race car.
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Llewelyn-Davies, D. I. T. P. "The use of the College of Aeronautics Whirling Arm facility to determine the effect of flow curvature on the aerodynamic characteristics of an ogive-cylinder body." Thesis, Cranfield University, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382145.
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Soso, Michael D. "An investigation into the aerodynamics of a wing in ground effect in generic racing car wake flows." Thesis, University of Southampton, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.417986.
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Abraham, Santosh. "Aerodynamic Performance of High Turning Airfoils and the Effect of Endwall Contouring on Turbine Performance." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/77196.
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Gas turbine companies are always focused on reducing capital costs and increasing overall efficiency. There are numerous advantages in reducing the number of airfoils per stage in the turbine section. While increased airfoil loading offers great advantages like low cost and weight, they also result in increased aerodynamic losses and associated issues. The strength of secondary flows is influenced by the upstream boundary layer thickness as well as the overall flow turning angle through the blade row. Secondary flows result in stagnation pressure loss which accounts for a considerable portion of the total stagnation pressure loss occurring in a turbine passage. A turbine designer strives to minimize these aerodynamic losses through design changes and geometrical effects. Performance of airfoils with varying loading levels and turning angles at transonic flow conditions are investigated in this study. The pressure difference between the pressure side and suction side of an airfoil gives an indication of the loading level of that airfoil. Secondary loss generation and the 3D flow near the endwalls of turbine blades are studied in detail. Detailed aerodynamic loss measurements, both in the pitchwise as well as spanwise directions, are conducted at 0.1 axial chord and 1.0 axial chord locations downstream of the trailing edge. Static pressure measurements on the airfoil surface and endwall pressure measurements were carried out in addition to downstream loss measurements. The application of endwall contouring to reduce secondary losses is investigated to try and understand when contouring can be beneficial. A detailed study was conducted on the effectiveness of endwall contouring on two different blades with varying airfoil spacing. Heat transfer experiments on the endwall were also conducted to determine the effect of endwall contouring on surface heat transfer distributions. Heat transfer behavior has significant effect on the cooling flow needs and associated aerodynamic problems of coolant-mainstream mixing.
One of the primary objectives of this study is to provide data under transonic conditions that can be used to confirm/refine loss predictions for the effect of various Mach numbers and gas turning. The cascade exit Mach numbers were varied within a range from 0.6 to 1.1. A published experimental study on the effect of end wall contouring on such high turning blades at high exit Mach numbers is not available in open literature. Hence, the need to understand the parametric effects of endwall contouring on aerodynamic and heat transfer performance under these conditions.Ph. D.
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Geyman, Matthew Kenneth. "Wing/Wall Aerodynamic Interactions in Free Flying, Maneuvering MAVs." University of Dayton / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1335113432.
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Sulaeman, Erwin. "Effect of Compressive Force on Aeroelastic Stability of a Strut-Braced Wing." Diss., Virginia Tech, 2001. http://hdl.handle.net/10919/26421.
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Recent investigations of a strut-braced wing (SBW) aircraft show that, at high positive load factors, a large tensile force in the strut leads to a considerable compressive axial force in the inner wing, resulting in a reduced bending stiffness and even buckling of the wing. Studying the influence of this compressive force on the structural response of SBW is thus of paramount importance in the early stage of SBW design.
The purpose of the this research is to investigate the effect of compressive force on aeroelastic stability of the SBW using efficient structural finite element and aerodynamic lifting surface methods. A procedure is developed to generate wing stiffness distribution for detailed and simplified wing models and to include the compressive force effect in the SBW aeroelastic analysis. A sensitivity study is performed to generate response surface equations for the wing flutter speed as functions of several design variables. These aeroelastic procedures and response surface equations provide a valuable tool and trend data to study the unconventional nature of SBW.
In order to estimate the effect of the compressive force, the inner part of the wing structure is modeled as a beam-column. A structural finite element method is developed based on an analytical stiffness matrix formulation of a non-uniform beam element with arbitrary polynomial variations in the cross section. By using this formulation, the number of elements to model the wing structure can be reduced without degrading the accuracy.
The unsteady aerodynamic prediction is based on a discrete element lifting surface method. The present formulation improves the accuracy of existing lifting surface methods by implementing a more rigorous treatment on the aerodynamic kernel integration. The singularity of the kernel function is isolated by implementing an exact expansion series to solve an incomplete cylindrical function problem. A hybrid doublet lattice/doublet point scheme is devised to reduce the computational time.
SBW aircraft selected for the present study is the fuselage-mounted engine configuration. The results indicate that the detrimental effect of the compressive force to the wing buckling and flutter speed is significant if the wing-strut junction is placed near the wing tip.Ph. D.
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Rinehart, Christopher S. "Aerodynamic forces induced by controlled transitory flow on a body of revolution." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42830.
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The aerodynamic forces and moments on an axisymmetric body of revolution are
controlled in a low-speed wind tunnel by induced local flow attachment. Control is
effected by an array of aft-facing synthetic jets emanating from narrow, azimuthally
segmented slots embedded within an axisymmetric backward facing step. The actuation
results in a localized, segmented vectoring of the separated base flow along a rear Coanda
surface and induced asymmetric aerodynamic forces and moments. The observed effects
are investigated in both quasi-steady and transient states, with emphasis on parametric
dependence. It is shown that the magnitude of the effected forces can be substantially
increased by slight variations of the Coanda surface geometry. Force and velocity
measurements are used to elucidate the mechanisms by which the synthetic jets produce
asymmetric aerodynamic forces and moments, demonstrating a novel method to steer
axisymmetric bodies during flight.
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Thake, Michael Patrick Jr. "Investigation of a Laminar Airfoil with Flow Control and the Effect of Reynolds Number." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1292962211.
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Viswanath, Kamal. "Effect of frontal gusts and stroke deviation in forward flapping flight and deconstructing the aerodynamics of a fruit bat." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/50825.
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This dissertation broadly seeks to understand the effect different kinematic parameters, external forces, and dynamic wing conformation have on the fluid dynamics of flapping flight. The primary motivation is to better grasp the fundamental fluid phenomena driving efficient flapping flight in the Reynolds number regime of birds, bats, and man made fliers of similar scale. The CFD solver (GenIDLEST) used is a Navier-Stokes solver in a finite volume formulation on non-staggered structured multiblock meshes. It has the capability for both body-fitted moving grid simulations and Immersed Boundary Method (IBM) for simulating complex bodies moving within a fluid.To that purpose we investigate the response of a rigid flapping thin surface planar wing in forward flight, at Re=10,000, subjected to frontal gusts. Gusts are a common ecological hazard for flapping fliers, especially in crowded environments. Among the various temporal and spatial scales of gust possible, we look at the phasing and duration of very large spatial scale gusts and their impact on the unsteady fluid dynamics of flapping within a single flapping cycle. The gust is characterized by a step function with time scale much smaller than the flapping time period. Having the advantage of prescribing the motion, as well as the timing and duration of the gust, this allowed the observation of the effect of angle of attack (AOA) and wing rotation on the evolution of the Leading Edge Vortex (LEV) and, hence the instantaneous lift and thrust profiles, by varying the parameters. During the downstroke, frontal gusts accelerated the flow development resulting in early separation of existing LEVs and formation of new ones on the wing surface which influenced the force generation by increasing the lift and thrust. These phenomena underscored the importance of the unsteady vortex structures as the primary force generators in flapping flight.The effect of the gust is observed to be diminished when it occurs during rapid supination of the wing. Unlike the influence of the vortices during the downstroke, the upstroke primarily reacted to effective AOA changes.
A key characteristic of the kinematics of fliers in nature is stroke deviation. We investigate this phenomenon using a similar framework as above on a rigid thin surface flat-plate flapping wing in forward flight. Stroke deviation happens due to a variety of factors including wing flexion, wing lateral translation, and wing area change and here we investigate the different stroke deviation trajectories. Various trajectories were analyzed to assess the different capabilities that such kinematics might offer. The instantaneous lift and thrust profiles were observed to be influenced by a combination of the Leading Edge Vortex (LEV) and the Trailing Edge Vortex (TEV) structures existing in the flow at any given time. As an index of the cost of performance across all cases, the power requirements for the different cases, based on the fluid torques, are analyzed. Anti-clockwise figure-of-eight-cycle deviation is shown to be very complex with high power costs while having better performance. The clockwise elliptic-cycle held promise in being utilized as a viable stroke deviation trajectory for forward flight over the base non stroke deviation case.
Armed with insight gained from these simple flapping structures, we are able to conduct the analysis of the flapping flight data obtained on a fruit bat. Understanding the full complexity of bat flight and the ways in which bat flight differs from that of other vertebrate flight requires attention to the intricate functional mechanics and architecture of the wings and the resulting unsteady transient mechanisms of the flow around the wings. We extract the detailed kinematic motion of the bat wing from the recorded data and then simulate the bat wing motion in the CFD framework for a range of Reynolds numbers. The Strouhal number calculated from the data is high indicating that the flow physics is dominated by the oscillatory motion. From the data the bat exhibits fine control of its mechanics by actively varying wing camber, wing area, torsional rotation of the wing, forward and backward translational sweep of the wing, and wing conformation to dictate the fluid dynamics. As is common in flapping flight, the primary force generation is through the attached unsteady vortices on the wing surface. This force output is modulated by the bat through varying wing camber and the wing area. Proper orthogonal decomposition of the wing kinematics is undertaken to compile a simpler set of kinematic modes that can approximate the orignial motion used by the fruit bat. These modes are then analyzed based on aerodynamic performance and power cost for more efficient flight. Understanding the physics of these modes will help us use them as prescribed kinematics for mechanical flappers as well as improve upon them from nature.
Ph. D.