Browsing by Author "Saddington, A. J."
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Item Open Access Aerodynamic problems of urban UAV operations(2011-09-09) Kittiyoungkun, S; Saddington, A. J.; Knowles, KevinUnmanned Air Vehicles, UAVs are designed to operate without any onboard controllers. Consequently, they are considered to operate in a wide range of applications. Missions in undesirable conditions such as bad weather and/or highly unsteady gustiness could cause an unsuccessful operation. In many ways, aerodynamics is a key feature in the performance of UAVs such as influencing deformation vehicle, guidance and control. Two aspects of this research are, therefore, to understand flying conditions of UAVs in an urban environment and how the flying performance is affected by such conditions. The first objective relies on understanding air flow behaviour in the lower part of the urban environment which has the most important role on the response of UAVs. The second objective will be to look at the characteristics of a three-dimensional airfoil when it encounters an unsteady sinusoidal gust at different oscillation frequencies and freestream velocities. As the first step of the studies on the aerodynamic problem of UAV operations in the lower part of an atmospheric boundary layer in an urban environment, the boundary layer thickness in a suitable wind tunnel facility were the first experimental results obtained. Experimental measurements of the mean velocity profile in a turbulent boundary layer were investigated for three different floor roughness conditions as well as a smooth wall condition. As a result, three different boundary layer thicknesses were then classified depending on the wall surface roughness and a combination with turbulence generators providing a maximum thickness of 280 mm at the centre of the tunnel test section. However,the experimental investigations into the turbulent boundary layer over a rough wall have shown that the boundary layer thickness is dependent on the surface roughness and is different from that obtained under the smooth wall condition. An experimental study into a simulated urban flow regime was then carried out after the measurement of the boundary layer. Wind tunnel experiments on the airflow around a single and twin buildings including an investigation of the airflow between the gap of the buildings were obtained. Wind in the lower part of the atmospheric boundary layer is more a micro-scale problem which increases or decreases the wind speed induced by buildings nearby. The studies have found some strong concentrated vortices caused by the flow separation essentially independent of the nature of the upstream flow and usually as a direct result of the building geometry and orientation. As the measurement location increased further downstream from the back of the buildings, the concentrated vortices were found to be weak and disappeared into the wake region. Finally, an experiment was conducted using a sinusoidal gust generator to describe the effects of wind oscillation parameters such as oscillation amplitude, oscillation frequency and reduced frequency under static and dynamic conditions. An evaluation was made of the onset of dynamic stall due to rapid changes in angle of attack during an unsteady pitch motion. The NACA 23012 wing profile was tested at a fixed angle of attack condition with varying oscillation flow parameters. Results demonstrate that those parameters influence the dynamic stall and hysteresis loop based on lift coefficient and angle of attackItem Open Access Aerodynamics and performance enhancement of a ground-effect diffuser(2018-04) Ehirim, O H; Knowles, Kevin; Saddington, A. J.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.Item Open Access Aerodynamics of a convex bump on a ground-effect diffuser(Journal of Fluids Engineering, 2018-04-19) Ehirim, Obinna; Knowles, Kevin; Saddington, A. J.; Finnis, Mark V.A ground-effect diffuser is an upward-sloping section of the underbody of a racing car that enhances aerodynamic performance by increasing the downforce, thus improving tire grip. The downforce generated by a diffuser can be increased by geometric modifications that facilitate passive flow control. Here we modified a bluff body equipped with a 17° diffuser ramp surface (the baseline/plane diffuser) to introduce a convex bump near the end of the ramp surface. The flow features, force and surface pressure measurements determined in wind-tunnel experiments agreed with previous studies but the bump favorably altered the overall diffuser pressure recovery curve by increasing the flow velocity near the diffuser exit. This resulted in a static pressure drop near the diffuser exit followed by an increase to freestream static pressure, thus increasing the downforce across most of the ride heights we tested. We observed a maximum 4.9% increase in downforce when the modified diffuser was compared to the plane diffuser. The downforce increment declined as the ride height was gradually reduced to the low-downforce diffuser flow regime.Item Open Access Comparison of passive flow control methods for a cavity in transonic flow(AIAA, 2016-03-21) Saddington, A. J.; Thangamani, Varun; Knowles, KevinAcomparative study of different passive control techniques was conducted on a cavity with a length of 320mmwith length-to-depth and length-to-width ratios of five and two, respectively. The tests were conducted at a freestream Mach number of 0.71. Both leading-edge and trailing-edge modifications were included in the studies. Results from surface pressure measurements showed that leading-edge control techniques were more effective at suppressing cavity tone amplitudes than trailing-edge modifications.Asquare-tooth spoiler showed the greatest reduction in tonal amplitude (8.8 dB); however, a sawtooth spoiler showed the greatest reduction in overall sound pressure level (8.13 dB). Velocity measurements inside the cavity were made using particle image velocimetry for the clean cavity and the cavity with sawtooth spoilers. The results showed a reduction in momentum exchange between the freestream flow and the cavity when spoilers were used. This is proposed to be the main reason for the reduced tonal amplitudes.Item Open Access Computational investigation of cavity flow control using a passive device(Royal Aeronautical Society, 2012-12-31T00:00:00Z) Khanal, B.; Knowles, Kevin; Saddington, A. J.In this paper, the results of computational studies on the unsteady flow features in threedimensional empty cavities and cavities with a representative store are presented. Flow simulations with a turbulence model based on a hybrid method, which behaves as a standard Reynolds-averaged Navier-Stokes (RANS) model within the attached boundary layer and as a Large-Eddy Simulation LES Sub-Grid Scale model in the rest of the flow (commonly known as Detached-Eddy Simulation [DES]) are used in this study. The time-mean flow study showed the presence of three-dimensional effects inside the cavities. The mean flowfield visualisation also clearly showed the presence of a pair of 'tornado-like' vortices in the upstream half of the cavity which merge to a single, large recirculation further downstream. Visualisation for the cavity-with-store case revealed that the mean flowfield was effectively divided into two halves with signifiant reduction of the spanwise flow across the cavity width. In the unsteady flow study, near-field acoustic spectra were computed for the empty cavity and cavity-with-store cases. Study of unsteady pressure spectra for the cavitywith- store case found the presence of many peaks and the corresponding mode frequencies were found to agree well with the Rossiter modes. The blockage effect of store and strut on the spanwise flow is thought to have reduced the interaction, and subsequent non-linear coupling, between the Rossiter modes. This may be the reason for the co-existence of multiple modes without the coupling among them.Item Open Access Computational study of cavity flowfield at transonic speeds(2009-12-31T00:00:00Z) Khanal, B.; Knowles, Kevin; Saddington, A. J.In this paper, the results of a computational study on the unsteady flow features in three-dimensional empty cavities and a cavity with a store are presented. Flow simulations with a turbulence model based on a hybrid method, which behaves as a standard RANS model within the attached boundary layer and as a LES Sub-Grid Scale model in the rest of the flow, including the separated regions, are used in this study. The time-mean flow study showed the existence of spanwise flow in the 3D cavity. In the unsteady flow study, computed near- field acoustic spectra were for empty cavity as well as cavity-withstore cases. Unsteady results from an empty cavity case are compared with experimental data and the frequency of the dominant mode is in good agreement with the experiment. Study of unsteady pressure spectra for the cavity-with-store case found the presence of many peaks and the corresponding mode frequencies were found to agree well with the Rossiter modes. The mean flowfield visualisation for the cavity-with-store case clearly showed that the mean flowfield was effectively divided into two halves with signifiant reduction of the spanwise flow across the cavity width. This blockage effect of store and strut on the spanwise flow is thought to have reduced the interaction, and subsequent non-linear coupling between, the Rossiter modes. This may be the reason for the coexistence of multiple modes without the coupling among them.Item Open Access Controlling unsteady cavity flows using internal structures(La Societe Savante de L'Aeronautique et de L'Espace, 2017-03-29) Knowles, Kevin; Bacci, David; Saddington, A. J.; Newby, B; Taylor, N JWe report experimental measurements and preliminary analysis on a series of geometric modifications to a rectangular cavity, aimed at alleviating the severity of the aeroacoustic environment. The cavity had a length-to-depth ratio of 5 and a width-to-depth ratio of 1, and featured a simplified representation of a generic missile on the centre line. The modifications consisted of full width and depth ribs or “collars” with a cutout for the missile. Collars could be fitted at various combinations of locations in the cavity and were either straight (i.e. perpendicular to the cavity centre line), leaned or yawed. The cavity flowfield was characterised by surface pressure measurements along the ceiling. Judging from the available measurements the presence of collars modified the mean pressure distribution, and appeared to reduce the acoustic tones and generally lower the broadband noise.Item Open Access Determining the extent to which simulation can be used to train RAF pilots to fly and fight the Eurofighter Typhoon(2017-06-19) Allsop, A J; Knowles, Kevin; Saddington, A. J.This research examines the extent to which simulation can be used to train pilots of the Royal Air Force to fly and fight the Eurofighter Typhoon, and is the culmination of a series of trials over a period of 4 years. The approach was threefold, firstly examining the performance of students trained entirely on the Operational Conversion Unit’s full syllabus in the simulator and then tested against their peers on each of the four phases in live flight, secondly investigating the cultural acceptance levels of the present Typhoon pilots and lastly using lessons learnt to generate and test a syllabus to train Typhoon pilots to Mult Role Combat Ready in 40% of the present time. It was found that increasing the proportion of synthetics from the lowest Live Synthetic Balance (LSB) of 75:25 used on the front-line meets a cultural and resource barrier at 50:50. This did not represent the maximum LSB achievable however with the heavily synthetic Multi-Role Syllabus reaching an LSB of 21:79 with successful completion of the end of course test. Cultural acceptance of the simulator had correlations with the squadron a pilot was assigned to, the manner in which the simulators were programmed for use and the experience level of the pilot. No evidence was found within the sample to suggest age had an effect. Recommendations on minimum proportions of live and synthetic training was mapped for each of the required tasks and comparisons of these were made across complexity levels. Resource savings found by the generating and testing a Multi Role Combat Ready syllabus that recognised and incorporated all the strengths, weaknesses and lessons identified in the previous trials generated a saving of approximately 9 months and 100 Typhoon live flying hours per student, equivalent to approximately 1300 man maintenance hours that could be reinvested into personnel in the form of leave, adventurous training or development.Item Open Access The effects of scaling and high subsonic cavity flow and control(2014-08-15) Thangamani, Varun; Saddington, A. J.; Knowles, KevinThe effects of scaling a cavity with respect to a fixed incoming boundary layer thickness on its flow dynamics and control was studied experimentally. Three cavity models with constant length-to-depth ratio of 5 and length-to-width ratio of 2 and with corresponding linear dimensions in the ratio 0.5 : 1 : 2 were tested at freestream Mach number 0.71. Additionally, the 0.5 and 1 scale models were tested at freestream Mach number of 0.85. The experiments involved timeaveraged pressure measurements, unsteady pressure measurements, and PIV measurements. Time-averaged pressure measurements made at the floor were used to study the ’flow-type’ of the cavities. Unsteady pressure measurements were used to study the acoustic characteristics of the cavity. The cavity length-to-boundary layer thickness ratios tested were 10, 20 and 40. The Cp distribution on the clean cavities indicated a change in the cavity flowtype with change in the cavity scale. Varying the L/δ from 10 to 40 changed the cavity flow-type from open to transitional. Analysis of the frequency spectra of the cavity revealed an increase in tonal amplitudes and OASPL with increasing L/δ . The PIV measurements indicated that this could be caused by an increase in energy exchange between the freestream and the cavity. The velocity magnitudes inside the cavities were found to increase with increase in L/δ . A comparative study of different passive control methods on the largest cavity showed that leading-edge spoilers were superior in cavity tone suppression. Of these, the effectiveness of a sawtooth spoiler on the three cavities of different scales was tested. The results showed that while the spoiler was effective in eliminating tones and suppression of noise for the smaller cavities, it was unable to eliminate the tones completely for the largest cavity. To find the correct method for scaling the spoilers with the cavity dimensions, different spoiler heights were tested on the three cavities. The results showed that the cavity noise suppression for a given cavity attains saturation level at a particular spoiler height, called the critical spoiler height. An increase in spoiler height beyond the critical spoiler height was found to have no effect on the noise suppression. It is also found that this critical spoiler height can be scaled with the length of the cavity (for given L/D, M and spoiler profile) irrespective of the boundary layer thickness.Item Open Access Effects of scaling on high subsonic cavity flow oscillations and control(AIAA, 2014-02-28) Thangamani, Varun; Knowles, Kevin; Saddington, A. J.The effects of scaling on cavity oscillations and control have been studied by measuring the unsteady pressure on the floor of three cavities of different scales. The cavities have a length-to-depth ratio of 5 and a length-to-width ratio of 2, and the corresponding linear dimensions are in the ratio0.5∶1∶2. The experiments were conducted with clean cavities and cavities fitted with leading-edge sawtooth spoilers so as to study the influence of scaling on clean cavities as well as the effectiveness of the passive control method on different sized cavities. The results showed significant variation of certain spectral characteristics of the clean cavities. The control effectiveness of the spoilers also showed variations with a change in scale of the model. It is recommended that, before implementing a passive control device for practical applications, the device should be tested in the possible range of cavity length-to-boundary-layer-thickness ratio (L/δ) that can be experienced in actual flight.Item Open Access An efficiently parallelized high-order aeroacoustics solver using a characteristic-based multi-block interface treatment and optimized compact finite differencing(MDPI, 2017-05-28) Khanal, B; Saddington, A. J.; Knowles, KevinThis paper presents the development of a fourth-order finite difference computational aeroacoustics solver. The solver works with a structured multi-block grid domain strategy, and it has been parallelized efficiently by using an interface treatment based on the method of characteristics. More importantly, it extends the characteristic boundary condition developments of previous researchers by introducing a characteristic-based treatment at the multi-block interfaces. In addition, most characteristic methods do not satisfy Pfaff’s condition, which is a requirement for any mathematical relation to be valid. A mathematically-consistent and valid method is used in this work to derive the characteristic interface conditions. Furthermore, a robust and efficient approach for the matching of turbulence quantities at the multi-block interfaces is developed. Finally, the implementation of grid metric relations to minimise grid-induced errors has been adopted. The code was validated against a number of benchmark cases, which demonstrated its accuracy and robustness across a range of problem typesItem Open Access Engineering maintenance decision-making with unsupported judgement under operational constraints(Elsevier, 2022-05-10) Green, Richard N.; McNaught, Ken R.; Saddington, A. J.In operational engineering maintenance situations, limitations on time, resource or the information available often inhibit rigorous analysis on complex decision problems. Decision-makers who are compelled to act in such circumstances, may be informed by some level of analysis if available, or else may have to rely on their unsupported judgement. This paper presents three engineering risk decision-making case studies across a 20 year span from the rail, aerospace, and military aviation contexts, highlighting the fallibilities of using unsupported judgements in an unstructured manner. To help situate this type of decision situation, we provide a descriptive model of the decision space which extends an existing description from the discipline of decision analysis. Furthermore, to help make and describe the distinction between unsupported and supported thinking, we provide another descriptive model, this time drawing parallels with the distinction made between Type 1 and Type 2 reasoning. This model is an extension of the default-interventionist model from cognitive psychology. The paper concludes that there is a pressing need to provide some form of support to engineering decision-makers facing operational decisions under severe time pressure. While the ultimate aim must be to improve the quality of decision-making, improved transparency is an important additional benefit. Increased emphasis on decision justification and self-awareness are suggested as potential ways of improving this situation. A further contribution of this paper is to identify and strengthen linkages between safety science and two other relevant disciplines, decision analysis and psychology. Such linkages make it easier to communicate across traditional disciplinary boundaries and may provide opportunities for interdisciplinary learning or suggest future directions for collaborative research.Item Open Access Hypersurface normalised gain-scheduled controller for a non-linear 6-DOF fast jet(Elsevier, 2020-07-25) Hamilton, Jordan; Galvão Wall, David; Saddington, A. J.; Economou, John T.This paper describes a novel approach for improving the dynamic response of a bank-to-turn autopilot for a non-linear six degree-of-freedom (6-DoF) aircraft model. The autopilot consists of a series of gain-scheduled (GS) proportional, integral and derivative (PID) controllers that govern the aircraft's angular velocities for roll, pitch and yaw. The controller gains have been optimised for localised trim points and applied continuously to the controllers using linear interpolation to form a hypersurface. Our novel solution has been achieved by implementing a set of scheduled gains for near-zero reference signals and integrating this with a set of gains that are normalised to the reference signal. The proposed approach has been compared to conventional gain scheduling techniques using a series of step input simulated manoeuvres, applied individually to the roll and pitch controllers. The results show improved rise and fall times, steady state errors, as well as reduced controller effortItem Open Access Laser doppler anemometry measurements in the near-wake of an isolated formula one wheel(Springer Science Business Media, 2007-05-01T00:00:00Z) Saddington, A. J.; Knowles, R. D.; Knowles, KevinAn experimental investigation was conducted to identify the main structures in the near wake of an isolated Formula One wheel rotating in ground contact. A 50 percent-scale isolated wheel assembly, geometrically similar to the configuration mounted on a Formula One racing car, was tested in a closed-return three-quarter open-jet wind tunnel. The test Reynolds number, based on wheel diameter was 6.8 × 105. Using laser doppler anemometry, three velocity components were measured with a total of 1966 data points across four planes and within one diameter downstream of the wheel axis. Based on analysis of these data, the main characteristics of the near-wake of an isolated wheel rotating in ground contact are presented. A revised model of the trailing vortex system induced in the wake of such a wheel is proposed, which clarifies the contradictory ones published in the literature to dateItem Open Access Multi-mode electric actuator dynamic modelling for missile fin control(MDPI, 2017-06-14) Gurav, Bhimashankar; Economou, John T.; Saddington, A. J.; Knowles, KevinLinear first/second order fin direct current (DC) actuator model approximations for missile applications are currently limited to angular position and angular velocity state variables. Furthermore, existing literature with detailed DC motor models is decoupled from the application of interest: tail controller missile lateral acceleration (LATAX) performance. This paper aims to integrate a generic DC fin actuator model with dual-mode feedforward and feedback control for tail-controlled missiles in conjunction with the autopilot system design. Moreover, the characteristics of the actuator torque information in relation to the aerodynamic fin loading for given missile trim velocities are also provided. The novelty of this paper is the integration of the missile LATAX autopilot states and actuator states including the motor torque, position and angular velocity. The advantage of such an approach is the parametric analysis and suitability of the fin actuator in relation to the missile lateral acceleration dynamic behaviourItem Open Access Mutual Interference Between Jets and Intakes in STOVL Aircraft(2009-10-28T17:36:52Z) Saddington, A. J.; Knowles, Kevin; Matthews, RonDuring wind tunnel testing of jet-lift, short take-off and vertical landing (STOVL) aircraft it is usual to simulate the jet efflux but not the intake flows. The intakes, which are commonly faired over or are unpowered, are generally tested in separate wind tunnel experiments. The forces acting on the wind tunnel model are determined by the linear addition of the forces obtained from the two separate tests. There is some doubt as to whether this is a valid approach. A systematic experimental investigation was, therefore, conducted to determine the magnitude of any jet/intake interference effects on a generic jet-lift STOVL aircraft in transitional flight, out of ground effect. Comparisons made between separate and simultaneous jet and intake testing concluded that a mutual jet/intake interference effect does exist. The existence of this interference means that the aerodynamic wing lift loss in transitional flight deduced from isolated jet and intake testing is less than the lift loss obtained from simultaneous jet and intake testing. The experimental research was supplemented by some simplified computational fluid dynamics (CFD) studies of elements of the flow-field about the aircraft using the k-e turbulence model. The numerical modelling enabled aspects of the flow-field around the aircraft to be visualised which could not easily be done using the experimental apparatus. It is a requirement of the Eng]) programme that part of this thesis must address a management topic linked to the research. In this case the management aspects of wind tunnel project work were examined. A scenario was developed which established a requirement for a large-scale, low-speed wind tunnel with a Reynolds number capability of 20 million. A study was performed on the decision-making process and investment appraisal methods used in the procurement of such a wind tunnel.Item Open Access A new systems engineering structured assurance methodology for complex systems(Elsevier, 2018-11-24) Farnell, G. P.; Saddington, A. J.; Lacey, Laura J.As technology advances, systems behaviour becomes more difficult to predict and control, resulting in a lack of systems assurance across the supply chain. Here we describe a structured approach to address the assurance of complex systems developed and operated within highly regulated environments. The new approach is based on a methodology that can address both new and legacy systems, and influences system intervention. We propose an enterprise approach by observing the importance of all organisational contributions to a safe working system throughout the intended project life cycle. This research was catalysed by the need to address the certification of the F-35B stealth fighter for UK operations from 2012 onwards. We offer a pragmatic strategy to achieve systems control by adopting a holistic approach to systems engineering while promoting the development of an enabling environment that can determine system threats and enable appropriate controls. We propose a systematic coordination process to minimise the potential for ‘organisational drift’. This holistic approach to systems engineering and assurance is defined as ‘systems engineering structured assurance’. The methodology provides a confidence assessment for a particular product or system while remaining agnostic to regulatory constraints. The diligent completion of the methodology increases systems confidence and informs the regulatory environment.Item Open Access On the Characteristics of a Twin-Jet STOVL Fountain(2015-03-03) Saddington, A. J.; Knowles, Kevin; Cabrita, P. M.The interaction of multiple jets with the ground is of great importance for the design and operation of short take-off, vertical landing aircraft. The fountain upwash flow, generated by the impingement of two axisymmetric, compressible, turbulent jets onto a ground plane was studied using laser-based particle image velocimetry and laser Doppler velocimetry. Measurements were made with nozzle pressure ratios of between 1.05 and 4, nozzle height-to-diameter ratios of between 2.4 and 8.4, nozzle splay angles of between 15 degrees and a nozzle spacing-to-diameter ratio of seven. The effect of varying these parameters on the fountain velocity decay, spreading rate and momentum flux ratio are discussed. Mean fountain upwash velocity profiles were found to be self-similar for all test conditions. A distinct frequency of fountain oscillation was identified but only at a nozzle height of 4.4 diameters.Item Open Access On the near wake of a Formula One front wheel(Professional Engineering Publishing, 2013-12-31T00:00:00Z) Knowles, R. D.; Saddington, A. J.; Knowles, KevinVelocity measurements were made in the near wake of the front wheel of a Formula One car using a laser Doppler anemometer. Tests were carried out on a 50% scale in a closed-return three-quarter open-jet wind tunnel. Three configurations were investigated to determine the effect of both the car and an external wheel support strut on the wheel wake. In each of the configurations the test Reynolds number, based on the wheel diameter, was 6.8 × 105. Three components of the velocity were measured at two planes less than than 1.0D(whereDis the wheel diameter) downstream of the wheel axis. These data were used to visualise the extent of the wake, the flow structures present and also the streamwise turbulence intensity. The presence of the car was found to alter significantly the structure of the wheel wake when compared with an isolated wheel. In addition, the external support strut was found to have less impact in the presence of the car than previous isolated wheel studies have suggested. No previous such studies appear to have been published in the open literature.Item Open Access On the near-wake of a ground-effect diffuser with passive flow control(Springer Verlag, 2019-02-08) Ehirim, Obinna; Knowles, Kevin; Saddington, A. J.; Finnis, Mark V.; Lawson, Nicholas J.A ground-effect diffuser is an upwardly-inclined section of an automobile’s underbody which increases aerodynamic performance by generating downforce. To understand the diffuser flow physics (force behaviour, surface and off-surface flow features), we established the near-wake (within one vehicle width of the base) velocity profiles and flow structures of an automotive ground-effect diffuser using a bluff body with a 17 degree slanted section forming the plane diffuser ramp surface (baseline geometry), and endplates extending along both sides of the ramp. Wind tunnel experiments were conducted at a Reynolds number of 1.8 million based on the bluff body length, and laser Doppler velocimetry was used to measure two-dimensional velocity components on three planes of the diffuser near-wake. We also measured the velocity field in the near-wake of diffusers with modified geometry (with an inverted wing or a convex bump) as passive flow control devices. The near-wake velocity profiles indicated that the passive flow control methods increased the diffuser flow velocity and that the longitudinal vortices along the diffuser determined the shape of the flow structures in the near-wake of the diffuser bluff body