Browsing by Author "Garry, Kevin P."
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Item Open Access Active Aerodynamic Control of Heavy Goods Vehicles(Cranfield University, 2013-04) Barden, Jason; Garry, Kevin P.; Whidborne, James F.Most heavy goods vehicles in service today are fitted with add-on aerodynamic devices. The most common of which is the cab-mounted roof deflector. Such devices provide appreciable drag savings, however, they are often not optimised for the trailer. When a wind yaw angle is present, their savings also diminish as the yaw angle increases. The work conducted within this thesis investigated the possibility of using an adjustable deflector for active flow control. The optimum deflector height for a given trailer height was initially investigated using wind tunnel testing. The variation of this optimum with yaw angle and container separation was then investigated. From the results a 3D look-up table was generated. A control scheme was proposed that used the 3D look-up table requiring only three measurable inputs. The three inputs required were: the wind yaw angle, the container height and the container separation. A pressure differential located on the deflector was found to linearly relate to the wind yaw angle. This relationship allowed on-road measurement of the wind yaw angle and therefore enabled the development of a prototype controller. Extensive on-road testing and unsteady computational simulation were conducted. The results obtained indicated a mean yaw angle magnitude of around 5 perturbed by four fundamental low frequencies. These frequencies were identified in the runs conducted over the test period and an average frequency established. Higher frequency disturbances were attributed to the wakes of leading heavy goods vehicles and were filtered by a suitably chosen numerical filter. Finally, an estimation of the efficiency of the active device was made using a combination of simulation and full scale testing. From the results obtained, an optimised deflector generated an average drag reduction of 7.4%. An estimated additional drag reduction of 1.9% over the optimised deflector was predicted through use of an active system.Item Open Access Aerodynamic and performance characteristics of a passive leading edge Kruger flap at low Reynolds numbers(Royal Aeronautical Society, 2012-07-31T00:00:00Z) Moraris, Vassilis Michael; Lawson, Nicholas J.; Garry, Kevin P.An experimental and numerical study was performed on a Clark Y aerofoil with a 10% chord leading edge Kruger flap to examine its aerodynamic performance at Reynolds numbers of 0.6 × 106, 1 × 106, and 1.6 × 106, to help to identify the forces and moments acting on a basic configuration. A detailed comparison of the numerical and experimental data is presented in this paper. The leading edge flap was effective at high angles of attack with an increase in CL of up to 18% over a conventional no flap configuration and delayed separation by up to 3°. The moments around the Kruger flap rotation point were calculated from the numerical analysis as an initial stage in the design of a UAV passive flap system and they are also presented in the paItem Open Access The aerodynamic characteristics of automobile wheels - CFD prediction and wind tunnel experiment(Cranfield University, 1999-09) Axon, Lee; Garry, Kevin P.When analyzing the aerodynamic characteristics of a road vehicle, the flow around the basic body shape is complicated by the presence of the rotating wheels. Even though on most vehicles the wheels are partially shrouded their effect on the flowfield is still considerable. Despite this, very little is understood about the flow around a rotating wheel. This thesis describes the development of a validated steady state Reynolds Averaged Navier-Stokes CFD model to investigate the flow around automobile wheels. As all the previous investigations into the aerodynamic characteristics of wheel flows had been experimental, preliminary computational studies were performed. The basis of these was the 2D circular cylinder. The effects of cylinder rotation and ground proximity were modelled, and strategies for boundary conditions and mesh topology were developed. This work was extended into 3D with the modelling of an isolated wheel, both rotating and stationary. Using existing experimental data for validation, an extensive investigation into the effects of solver numerics, symmetry planes, turbulence models, and the method of turbulent closure was performed. An optimum solver configuration was developed which comprised of the RNG k-E turbulence model with full boundary layer closure. It was accurately predicted that the rotating wheel generates less lift and drag than the equivalent stationary wheel. A number of postulated experimental flow features were captured in the final solutions. Using a parallel experimental study to provide further validation data, the CFD model was extended to incorporate an asymmetric shroud containing a wheelhouse cavity. The influence of the rotation of the wheel, the geometry of the shroud, and the thickness of the stationary groundplane boundary layer were investigated. The rotating wheel now produced more drag than the equivalent stationary wheel. Reductions in wheel drag were found with a reduction in the ride height of the shroud, and with the addition of spoilers to the lower front edge of the shroud. Increasing the stationary groundplane boundary layer thickness also reduced the wheel drag. The effects of these changes on the wheel surface pressure distributions are presented.Item Open Access Analysis and prediction of the low speed flow over a highly swept wing(2000-11) Shires, Andrew; Garry, Kevin P.; Fulker, J. L.A combined experimental and theoretical study is described of the low speed flow over a highly swept and cambered wing that simulates the flow features of a transonic manoeuvre condition. The thesis is divided into two parts: Part I examines the research objectives from a customer perspective, with background information on the project history and funding sources. Since the research is aimed at improving the aerodynamic performance of low observable configurations, stealth technologies are discussed and their implications for combat aircraft wing flows. The management chapter of the thesis then discusses the influences affecting the decision making process for the acquisition of weapon systems in the UK. Part II describes the design of a highly swept and cambered wing that generates strong adverse pressure gradients near the trailing edge, leading to three-dimensional separations in this region. Using surface flow visualisation the nature of these flows is defined, indicating how the position of a separated streamline moves forward with increasing angle of incidence. These observations are confirmed by flow predictions using the SAUNA Computational Fluid Dynamics (CFD) method that solves the Reynolds Averaged Navier-Stokes equations, employing a two-equation turbulence model. The mechanism of the flow separation is also predicted using CFD, indicating that a separated stream surface reattaches at the wing trailing edge, forming a ‘tunnel’ of separated flow. To the authors knowledge this represents the first time that the main physical features of such a complex three-dimensional separated flow has been modelled using a CFD method. From an evaluation of the CFD methods employed, a design process has been proposed by which a wing designer can determine if wing flows over similar configurations remain attached. Additionally, the velocity magnitudes within parts of the separated shear layers and the wake are obtained using an optical non-intrusive measurement technique and give good agreement with the theory. -Item Open Access Comparison of the far-field aerodynamic wake development for three DrivAer model configurations using a cost-effective RANS simulation(Society of Automotive Engineers, 2017-03-28) Soares, Renan F.; Garry, Kevin P.; Holt, Jennifer C.The flow field and body aerodynamic loads on the DrivAer reference model have been extensively investigated since its introduction in 2012. However, there is a relative lack of information relating to the models wake development resulting from the different rear-body configurations, particularly in the far-field.Given current interest in the aerodynamic interaction between two or more vehicles, the results from a preliminary CFD study are presented to address the development of the wake from the Fastback, Notchback, and Estateback DrivAer configurations. The primary focus is on the differences in the far-field wake and simulations are assessed in the range up to three vehicle lengths downstream, at Reynolds and Mach numbers of 5.2×106 and 0.13, respectively.Wake development is modelled using the results from a Reynolds-Averaged Navier-Stokes (RANS) simulation within a computational mesh having nominally 1.0×107 cells. This approach was chosen to reflect a simple, cost-effective solution, using an industry-standard CFD solver. Each vehicle configuration has a smooth underbody, with exterior rear-view mirrors. The computational modelling includes a ground simulation set, and all simulations are for zero freestream yaw angle. A mesh sensitivity study was undertaken and the simulation validated against published experimental data for the body pressure distribution and aerodynamic drag.Critical assessment of the results highlights the benefits of focussed mesh refinement and specific numerical strategies for optimum performance of the CFD solver. Comparison of the far-field aerodynamic wake for the three model configurations exhibits significant differences in both extent and structure within the wake region up to three vehicle lengths downstream of the base. Total pressure loss coefficient is used as the primary aerodynamic parameter for analysis. The study is an element of a larger programme related to vehicle wake simulation and strategies are identified for possible wake modelling using simplified, computationally and experimentally efficient, shapes.Item Open Access The control of trailing edge separation on highly swept wings using vortex generators(Cranfield University, 1998-10) Broadley, Jonathan I.; Garry, Kevin P.The results from a series of low speed wind tunnel tests on two half model highly swept wings (a symmetrical aerofoil section and a highly cambered aerofail section) are presented in order to examine the trailing edge flow separation mechanism and its development with wing sweep between 30' and 60'. The tests involved surface oil flow visualisation, smoke flow visualisation, surface static pressure and force balance measurements at streamwise chord Reynolds numbers from 1.5 x 105 to 5.2 x 106 and Mach number from 0.09 to 0.17. These results are used to assess two viscous-inviscid interaction CFD methods (BVGK and VFP) and two boundary layer methods (TAPERBL and WAKELAG) used to predict the flow over the highly cambered wing. A parametric study using cropped delta vane vortex generators in a co-rotating array was conducted on the 40' swept wing to investigate the effect of vane chordwise position, vane orientation, vane height relative to the boundary layer thickness and vane spacing on the prevention of the trailing edge separation. The performance of these flow control devices is assessed in terms of changes in; the wing surface flowfield, lift curve slope and the lift-dependant drag factor. In addition comparisons are made between the clean wing and flow control wing measured pressure distributions. The results and analysis show that the performance of the vortex generators is improved when the height of the vortex generator is approximately equal to that of the local boundary layer thickness and when the vane angular deflection to the local upstream flow direction is between 14' and 21'. The performance is also seen to depend on the vanes position ahead of separation and on the adverse pressure gradient to be restored and may also depend on a vane spacing made non-dimensional on the wing normal chord rather than the vane height. Similar performance improvements are observed with the wing swept to 50' using the positioning guidelines from this optimisation study. The performance of concave slats, canted cropped delta vanes, 'bent'wires and sub-boundary layer wires as vortex generating devices are seen to be not as effective as upright cropped delta vane vortex generators. To assist in the interpretation of the parametric vortex generator study a low speed wind tunnel technique is developed using shear stress sensitive liquid crystals to investigate the downstream development of vortices from cropped delta vane vortex generators. The results show that -- i) submerged vortices have less influence on the surface flow with downstream distance than vortices closer to the edge of the boundary layer, and ii) the primary increase in skin ffiction arises in the flow adjacent to the upflow side of the vortex. This area increases with vortex size. The results from this research programme are finally shown to be applicable in two market areas. The first is as a performance improvement on current highly swept winged military aircraft and the second is as flight controls on future aircraft from making the vortex generating devices active. The possible customers in these two areas are identified and marketing strategies developed for each case.Item Open Access Crosswind aerodynamics of sports utility vehicles(Cranfield University, 1999-11) Chadwick, Andrew; Garry, Kevin P.Crosswind gusts have a continuous influence on the ride and handling of road vehicles. At low speeds the effect is negligible but as both car and wind speeds increase there is a reduction in refinement, ride quality is degraded and it becomes tiring to drive. Future environmental legislation concerning the reduction of carbon dioxide emissions will lead to a lighter road vehicle and a corresponding increase in crosswind sensitivity. The aerodynamicist's approach to understanding the fluid flow around a vehicle when subjected to a crosswind has conventionally been through steady state model tests where aerodynamic force and moment data are taken for different yaw angles. The accuracy of this data has previously been questioned because of a lack of simulation of the transient nature of the crosswind gust. Additionally, although force and moment data can tell the aerodynamicist which are the principle loads influencing a vehicles response in a crosswind, they fail to identify the specific regions on the vehicle that contribute to these aerodynamic loads. This can only be achieved by pressure mapping the model surface and although such a technique has been employed during steady state tests, no research has been presented with the correct modeling of the transient crosswind gust. To gain an initial understanding of the complex time dependent and separated flow fields around bluff vehicles, such as sports utility vehicles, when subjected to a crosswind, aerodynamic force, moment and surface pressure data of simple geometric shapes has been collected on the Cranfield crosswind track facility. Steady state data has been obtained from conventional wind tunnel tests and compared with the transient data. Unique pressure animations identify the growth and collapse of vortices on the leeward face as the primary transient characteristic and which produce peak aerodynamic yawing moments up to double that seen in the steady state.Item Open Access The effect of an end plate boundary layer on half delta wing flows at low Reynolds number.(2000-08) Alkhozam, Abdullah M; Garry, Kevin P.An experimental investigation has been carried out to study and understand the influence of an end plate boundary layer on half delta wing models at low Reynolds Number. The programme involved measurements in two facilities: a vertical water tunnel which was used for flow visualisation studies and a conventional closed working section wind tunnel for both flow visualisation and surface static pressure measurements. In both facilities dynamic and steady state or static measurements were made on half delta wing models with 55° and 70° sweep and varying thickness/chord ratio under the influence of a number of artificially generated end plate boundary layers. In both facilities, of all model configurations tested, for both dynamic and static test conditions, vortex burst was seen to move upstream, inboard and away from the wing surface as the angle of attack is increased and vortex core trajectory is seen to move towards the wing root, which is consistent with the findings of previous researchers. Vortex breakdown position is seen to move upstream, inboard toward the wing root and away from the wing surface as the end plate boundary layer thickness is increased. This is attributed to the influence of the interaction between the horseshoe vortex and the half delta wing leading edge vortex as a result of changes in the wall boundary layer thickness. In terms of vortex core trajectory, increases in end plate boundary layer thickness are seen to displace the vortex core towards the wing root. During dynamic tests an increase in wall boundary layer thickness is seen to suppress the hysteric behaviour of the vortex trajectory. Surface static pressure measurements at Reynolds Number of 479,000, during both static and dynamic tests, make it possible to see that the influence of changes in wall boundary layer thickness are small, often insignificant, at (x/c) locations greater than 0.45. This is consistent with an increase in wall boundary layer thickness promoting earlier vortex breakdown. Correlation between smoke flow visualisation (of both vortex breakdown and trajectory) and surface static pressure measurements, using the half-width of the suction peak as a parameter, was good. Differences between vortex characteristics in the water tunnel and wind tunnel were consistent with the influence of Reynolds Number.Item Open Access Examination of three candidate technologies for high-lift devices on an aircraft wing(Cranfield University, 2005-12) Knepper, Angela Marie; Garry, Kevin P.A research programme was initiated to examine three candidate high-lift technologies, which would, if implemented, simplify the mechanical complexity of the multiple component trailing-edge devices traditionally employed on civil transport aircraft. Experimental studies were undertaken with the aim of examining each technology in terms of its potential to favourably influence boundary layer development and improve the aerodynamic characteristics of a high-lift configuration. Preliminary studies of triangular serrated geometries, at the trailing edge of a modified flat plate, highlighted that the ability of the serrations to favourably influence the flow field development over an aft positioned single slotted flap was critically dependent upon the flap lap/gap and deflection angle. Under the test conditions, the serrations were most effective at low flap deflection angles, particularly serrations with a length corresponding to 13% flap chord. Extending these studies to a representative high-lift configuration significantly limited the range of flap laps/gaps and deflection angles over which the serrations were favourable. Furthermore, oil flow visualisation provided evidence of wake structures emanating from serration vertices, corroborating earlier hypotheses and suggesting the flow mechanism by which serrations favourably influenced boundary layer development over the upper surface of the downstream flap. Experiments indicated that when optimised, blowing tangentially from a slot at the trailing edge of the main element over the upper surface of a flap within a three-element high-lift configuration, provided a highly effective means of preventing boundary layer separation and increasing lift. This was corroborated by oil flow visualisation and computational simulations. Maintaining the same momentum coefficient and blowing through discrete orifices at the trailing edge of the main element, proved highly favourable, heightening the increment in lift in comparison to the corresponding tangential slot blowing configuration. Hence, the mass flow rate could be reduced in comparison to the tangential slot blowing configuration, without compromising the aerodynamic performance.Item Open Access Experimental evaluation of a passive flow-control device for a tiltrotor aircraft(2022-11-28) Proenca, Anderson R.; Prince, Simon A.; Banks-Davies, Lynton; Garry, Kevin P.This work presents a preliminary investigation into tiltrotor propeller/nacelle/wing flows, and the flow breakdowns that can lead to the phenomenon of whirl flutter. Static blade measurements were performed, results suggesting that tubercles have the potential to provide an increase in performance for the baseline blade design. A small-scale propeller rig (0.7 m swept diameter) has been designed, manufactured, and commissioned at Cranfield’s 8x6 Wind Tunnel. This new rig operates well under static and up to wind speeds of at least 30 m/s. The effect of blade pitch angle (0 to 10◦ ) and propeller rotational speed (0 to 3000 rpm) have been investigated successfully. Forces measured on the wing set at angles of attack within the range 0 to 22◦ indicate the well-established effects due to propeller slipstream. Overall, the propeller wake flow slightly decreases the lift generated by the wing model, whilst also delaying stall. Pressure taps and accelerometers mounted on the wing and propeller nacelle effectively captured the slipstream effects, blade passing frequency, and flow separation regions. Finally, blades containing tubercle-shaped vortex generators were mounted to the propeller rig. Preliminary test results for the tubercle blades are reported in the paper. Overall, effects due to the propeller slipstream are dominant on forces, pressure distribution and vibration of the wing model. At the current stage of this ongoing investigation, it is not possible to conclude whether the tubercles provide any benefit to either the propeller or wing aerodynamic efficiencies. The rig is being equipped to measure propeller thrust and torque. Flow field investigation will also be carried out in future campaigns.Item Open Access Extremum seeking control for truck drag reduction(2018-11-01) Papageorgiou, Georgios; Barden, Jason; Whidborne, James F.; Garry, Kevin P.The aerodynamic drag on a heavy truck tractor and semi-trailer combination can be reduced by means of a wind deflector installed on the roof of the tractor cab. The drag reduction is dependent upon the height and shape of the deflector. A variable height deflector has been constructed and tested in a wind-tunnel and on-road. In this paper, an extremum-seeking control scheme is proposed to adjust on-line the deflector height to minimize the aerodynamic drag. The effectiveness of the scheme is evaluated by simulation and its practicality is evaluated.Item Open Access Hypersonic interference aerothermodynamics(2009-10) Estruch-Samper, David; Lawson, Nicholas J.; Garry, Kevin P.When a vehicle travels at hypersonic speeds during launch, cruise or atmospheric re-entry it is subject to extremely high surface flow temperatures. As well as on the vehicle forebody, extreme heating can take place close to surface protuberances which are almost impossible to avoid in a real flight vehicle. These disturbances interfere with the freestream flow and result in complex viscous interactions which induce a local heat flux augmentation that can become detrimental to the integrity of the vehicle. A greater understanding of these flow phenomena is required. This thesis develops the understanding of the behaviour of the flow around surface protuberances in hypersonic vehicles and presents an engineering approach to predict the location and magnitude of the highest heat transfer rates in their vicinity. To this end, an experimental investigation was performed in a gun tunnel at freestream Mach numbers of 8.2 and 12.3 and Reynolds numbers ranging from Reoo/m=3.35xl0 ⁶ to Reꚙ /m=9.35xl0 ⁶. The effects of protuberance geometry, boundary layer state, freestream Reynolds number and freestream Mach number were assessed. Further understanding of the flowfield was obtained through oil-dot visualisations and highspeed schlieren videos taken at frame rates of up to 50 kHz. Results show the local interference interaction is strongly three-dimensional and is dominated by the incipient separation angle induced by the protuberance. In subcritical interactions - in which the incoming boundary layer remains unseparated upstream of the protuberance - the highest heating occurs adjacent to the device. In supercritical interactions - in which the incoming boundary layer is fully separated ahead of the protuberance - the highest heating generally occurs on the surface just upstream of it. An exception is for low-deflection protuberances under low-Reynolds freestream flow conditions in which case the heat flux to the side is greater.Item Open Access Hypersonic interference heating in the vicinity of surface protuberances(Springer Science Business Media, 2010-09-30T00:00:00Z) Estruch-Samper, David; MacManus, David G.; Stollery, J. L.; Lawson, Nicholas J.; Garry, Kevin P.The understanding of the behaviour of the flow around surface protuberances in hypersonic vehicles is developed and an engineering approach to predict the location and magnitude of the highest heat transfer rates in their vicinity is presented. To this end, an experimental investigation was performed in a hypersonic facility at freestream Mach numbers of 8.2 and 12.3 and Reynolds numbers ranging from Re (a)/m = 3.35 x 10(6) to Re (a)/m = 9.35 x 10(6). The effects of protuberance geometry, boundary layer state, freestream Reynolds number and freestream Mach numbers were assessed based on thin-film heat transfer measurements. Further understanding of the flowfield was obtained through oil-dot visualizations and high-speed schlieren videos. The local interference interaction was shown to be strongly 3-D and to be dominated by the incipient separation angle induced by the protuberance. In interactions in which the incoming boundary layer remains unseparated upstream of the protuberance, the highest heating occurs adjacent to the device. In interactions in which the incoming boundary layer is fully separated ahead of the protuberance, the highest heating generally occurs on the surface just upstream of it except for low-deflection protuberances under low Reynolds freestream flow conditions in which case the heat flux to the side is greater.Item Open Access The impact of inlet flow conditions on the aerodynamic performance of a NACA submerged intake for ground vehicle applications(Professional Engineering Publishing, 2013-10-31T00:00:00Z) Holt, Jennifer C.; Garry, Kevin P.Results are presented following a series of experimental measurements on a submerged NACA type intake orientated between ±30 degrees yaw to the free stream in an atmospheric boundary layer wind tunnel at a unit Reynolds number of nominally 1 x 106. The intake was subjected to a range of upstream wall boundary layer conditions and the intake mass flow (as measured by an orifice plate) was monitored to assess aerodynamic performance. The mass flow data is supported by qualitative flow visualisation within the duct, using a smoke filament illuminated in a laser light sheet in order to gain insight into the flow physics. Intake performance, expressed in terms of a non-dimensional flow momentum coefficient, is seen to degrade with both: (i) intake orientation to the free stream - changes of nominally 40% are seen for the angle range tested and (ii) increase in upstream boundary layer displacement thickness - changes of nominally 30% are seen for the range tested. This data is presented as a graphical carpet plot, it is intended that this be used as a guide to performance prediction in non-aeronautical applications where there are often significant changes in both local flow direction and boundary layer thickness. Flow visualisation studies show that the intake performance degradation with yaw angle can be attributed to a progressive change in the vortex- pair structure within the intake as the local flow angle is increased. An increase in both lateral separation and size of the respective vortex cores is considered to act so as to reduce the magnitude of the induced inflow into the intake.Item Open Access Investigation into aero-hydrodynamic surfaces for wing-in-ground effect vehicle design.(Cranfield University, 2020-12) James, Daniel; Hart, Phil; Garry, Kevin P.This project focuses on developing the required knowledge and engineering data to be applied in the preliminary design of a Wing-in-Ground Effect vehicle. Three concurrent work programmes are carried out, covering experimental testing of a novel hull design, computational analysis of three wing profiles operating in ground effect, and an experimental programme to validate an unusual profile using an unconventional technique. This work is intended to produce a reliable database of 2D aerodynamic coefficients by establishing a robust methodology for numerical solution. A detailed range of heights above ground and angles of attack have been included, and the methodology can be easily applied to additional profiles in the future. A model wing was constructed and towed near the bottom of a water tank to replicate the physics and flow patterns of a wing immersed in an incompressible fluid moving over static ground. The selected profile was included in the computational work and the results of the two methods were compared. A hull model was designed and built, then towed at high speed to assess its potential performance in the take-off phase of WIG operation. As a radiussed-chined slender hull, it would also be suitable for waterborne operation at modest speed, leading to the possibility for a dual-purpose vehicle comfortable in air or water. Finally, a parametric geometry tool was developed to explore the design space and assess feasibility of various configurations. Relationships between primary components have been derived to allow sizing and positioning with corresponding powering estimates, to generate WIG conceptual designs.Item Open Access Investigation of the aerodynamic characteristics of a lifting body in ground proximity(American Institute of Aeronautics and Astronautics, 2016-07-31) Holt, Jennifer C.; Garry, Kevin P.; Smith, TonyThe use of cambered hull shapes in the next generation of lighter-than-air vehicles to enhance aerodynamic performance, together with optimized take-off manoeuvre profiles, will require a more detailed understanding of ground proximity effects for such aircraft. A series of sub-scale wind tunnel tests at Re = 1.4 x 106 on a 6:1 prolate spheroid are used to identify potential changes in aerodynamic lift, drag and pitching moment coefficients that are likely to be experienced on the vehicle hull in isolation when in close ground proximity. The experimental data is supported by a preliminary assessment of surface pressure changes using a high order panel method (PANAIR) and RANS CFD simulations to assess the flow structure. The effect of ground proximity, most evident when non-dimensional ground clearance (h/c) < 0.3, is to reduce lift coefficient, increase drag coefficient and increase the body pitching moment coefficient.Item Open Access An investigation of the flow characteristics in the bootdeck region of a scale model notchback saloon vehicle(Professional Engineering Publishing, 2007-06-30T00:00:00Z) Lawson, Nicholas J.; Garry, Kevin P.; Faucompret, N.The results of an experimental investigation of the bootdeck flow structure of a 36 per cent scale model notchback car are presented together with a general review of advanced laser diagnostic techniques suitable for large-scale wind tunnel flow measurement. The tests were used to characterize the flow behaviour over the Reynolds number range 0.74 x 10(6)-4.93 x 10(6) in the Cranfield University 2.4 m x 1.8 m wind tunnel. The experiments involved flow visualization, rear bootdeck and backlight three-dimensional stereoscopic particle image velocimetry (PIV) measurements, and mean static and unsteady static pressure measurements. Initial results from the flow visualization suggested flow asymmetries originating in the backlight region that were sensitive to the Reynolds number. The PIV data and static pressure data, however, showed little or no sensitivity of flow to Reynolds number with consistent flow structure and levels of unsteadiness from the backlight to the rear bootdeck region. At this stage no definitive reasons can be given for the discrepancies between the flow visualization and the other data, although the flow visualization data were particularly difficult to interpret near the backlight, and the near-wake structure may be bi-stable in this Reynolds number range. More detailed three-dimensional stereoscopic, time-resolved PIV flow data are now planned to quantify conclusively the correct flow structure and its sensitivities.Item Open Access Jetstream 31 national flying laboratory: Lift and drag measurement and modelling(Elsevier, 2016-11-09) Lawson, Nicholas J.; Jacques, H.; Gautrey, James E.; Cooke, Alastair K.; Holt, Jennifer C.; Garry, Kevin P.Lift and drag flight test data is presented from the National Flying Laboratory Centre, Jetstream 31 aircraft. The aircraft has been modified as a flying classroom for completing flight test training courses, for engineering degree accreditation. The straight and level flight test data is compared to data from 10% and 17% scale wind tunnel models, a Reynolds Averaged Navier Stokes steady-state computational fluid dynamics model and an empirical model. Estimated standard errors in the flight test data are ±2.4%±2.4% in lift coefficient, ±2.7%±2.7% in drag coefficient. The flight test data also shows the aircraft to have a maximum lift to drag ratio of 10.5 at Mach 0.32, a zero lift drag coefficient of 0.0376 and an induced drag correction factor of 0.0607. When comparing the characteristics from the other models, the best overall comparison with the flight test data, in terms of lift coefficient, was with the empirical model. For the drag comparisons, all the models under predicted levels of drag by up to 43% when compared to the flight test data, with the best overall match between the flight test data and the 10% scale wind tunnel model. These discrepancies were attributed to various factors including zero lift drag Reynolds number effects, omission of a propeller system and surface excrescences on the models, as well as surface finish differences.Item Open Access Lateral aerodynamic characteristics of motor vehicles in transient crosswinds(Cranfield University, 1994-07) Cairns, Robert Stuart; Garry, Kevin P.Motor car crosswind stability can be adversely affected by reductions in both vehicle mass and drag coefficient. As these are two likely results of future developments the importance of research into vehicle aerodynamic stability is set to increase, moreover, there is evidence that transient effects will be the critical. An experimental facility has been designed and constructed and tests have been carried out to investigate the implications of simulating dynamic flow-fields. Vehicle models of approximately 1/6th scale have been propelled along a test track, in the laboratory, to pass through a simulated crosswind gust of variable resultant yaw angle. Force and moment measurements have shown the aerodynamic inputs to be highly repeatable, though the technique has been restricted somewhat by the presence of mechanical "noise". Additional dynamic yaw experiments were conducted on a bluff-body model mounted in the College of Aeronautics' Oscillatory Facility. In some ways this technique is not as realistic as the Crosswind Track in its simulation of the full scale flow, however, despite its simplicity valuable aerodynamic data was derived from this test. Quasi-static tests have also been conducted and demonstrate that for certain model configurations a clearly defined yaw angle range exists where two different wake flow-structures are possible. At any given yaw angle, the dominant structure is determined by the flowfield history - essentially the direction in which the model is moved. This causes hysteresis in the forces and moments generated. In such a situation the flow is referred to as being bi¬stable. Both track and dynamic yaw tests indicate that the bi-stable flow phenomenon, witnessed in quasi-static experiments, can influence the dynamic forces and moments measured on a model. The flow structures associated with bi-stability are viscous-dominated and the slow development of viscous loads can be an important feature. It is possible that various vehicle configurations could induce bi-stable flow. If such flow behaviour is apparent then quasi-static forces and moment measurements will not provide an adequate engineering estimate of the transient aerodynamic loads. In this event it is imperative that the automotive engineer conducts investigations into the vehicle's dynamic performance.Item Open Access Measurement of shock wave unsteadiness using a high-speed schlieren system and digital image processing(American Institute of Physics, 2008-12) Estruch-Samper, David; Lawson, Nicholas J.; MacManus, David G.; Garry, Kevin P.; Stollery, J. L.A new method to measure shock wave unsteadiness is presented. Time-resolved visualizations of the flow field under investigation are obtained using a high-speed schlieren optical system and the motion of the shock wave is determined by means of digital image processing. Information on the shock’s unsteadiness is subsequently derived with Fourier analysis. A sample study on shock unsteadiness in a shock-wave/turbulent boundary-layer interaction with separation is included. The method presented enables a measure of shock unsteadiness at locations in the imaged flow field not accessible by intrusive methods.