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The in-cabin sound pressure level response of a vehicle in yawed wind conditions can differ significantly between the smooth flow conditions of the aeroacoustic wind tunnel and the higher turbulence, transient flow conditions experienced on the road. Previous research has shown that under low turbulence conditions there is close agreement between the variation with yaw of in-cabin sound pressure level on the road and in the wind tunnel. However, under transient conditions, sound pressure levels on the road were found to show a smaller increase due to yaw than predicted by the wind tunnel, specifically near the leeward sideglass region. The research presented here investigates the links between transient flow and aeroacoustics. The effect of small geometry changes upon the aeroacoustic response of the vehicle has been investigated.

A vehicle driving on the road experiences unsteady flow conditions which are not generally reproduced in the development environment. This paper investigates the potential importance of this difference to aeroacoustics and hence to occupant perception and proposes a methodology to enable better ranking of designs by taking account of wind noise modulation. Two approaches of reproducing the effects of unsteady wind on aeroacoustics were investigated: an active wind tunnel Turbulence Generation System (TGS) and a quasi-steady approach based on measurements at a series of fixed yaw angles. A number of tools were used to investigate the onset flow and its impacts, including roof-mounted probe, acoustic heads and surface microphones. External noise measurements help to reveal the response of separate exterior noise sources to yaw.

Sports Utility Vehicles (SUVs) typically have a blunt rear end shape (for design and practicality), however this is not beneficial for aerodynamic drag. Drag can be reduced by a number of passive and active methods such as tapering and blowing into the base. In an effort to combine these effects and to reduce the drag of a visually square geometry slots have been introduced in the upper side and roof trailing edges of a squareback geometry, to take air from the freestream and passively injects it into the base of the vehicle to effectively create a tapered body. This investigation has been conducted in the Loughborough University’s Large Wind Tunnel with the ¼ scale generic SUV model. The basic aerodynamic effect of a range of body tapers and straight slots have been assessed for 0° yaw. This includes force and pressure measurements for most configurations.

Two methods of passive flow control were investigated to determine their effectiveness in reducing aerodynamic drag on large Sports Utility Vehicles (SUVs). Passive means of flow control were selected since all active methods require the input of additional energy (e.g., pressurized fluids or electrical energy). The selected methods were base bleed and the use of a rear cavity, and various combinations of these were experimentally tested in full-scale wind tunnels with and without a moving belt/rotating wheel assembly. Aerodynamic drag reduction was accomplished by restructuring the low-pressure wake directly behind the vehicle. External cavity depths ranging from d/h=0.17 to 0.83 were used, while body cavity depths ranged from d/h=0 to 0.83, where the depth of the cavity d is non-dimensionalized by the height h of the base area.

The Range Rover Evoque is a compact luxury SUV, first introduced by Land Rover in 2012. Almost 800,000 units of the first-generation vehicle were sold. This paper explores some of the challenges entailed in developing the next generation of this successful product, maintaining key design cues while at the same time improving its aerodynamic efficiency. A development approach is outlined that made use of both numerical simulation and full-scale moving ground wind tunnel testing. A drag coefficient of 0.32 was obtained for the best derivative by paying particular attention to: the integration of active grille shutters; the front bumper and tyre package; brake cooling; underfloor design; wake control strategy; and detail optimization. This approach delivered the most aerodynamic Range Rover at the time of its introduction. The impact of these design changes on the aerodynamic flow field and consequently drag is highlighted.

Numerical simulation of aerodynamics for vehicle development is used to meet a wide range of performance targets, including aerodynamic drag for fuel efficiency, cooling flow rates, and aerodynamic lift for vehicle handling. The aerodynamic flow field can also be used to compute the advection of small particles such as water droplets, dust, dirt, sand, etc., released into the flow domain, including the effects of mass, gravity, and the forces acting on the particles by the airflow. Previous efforts in this topic have considered the water sprays ejected by rotating wheels when driving on a wet road. The road spray carries dirt particles and can obscure the side and rear glazing. In this study, road sprays are considered in which the effects of additional water droplets resulting from splashing and dripping of particles from the wheel house and rear under body are added to help understand the patterns of dirt film accumulation on the side glass and rear glass.

Government regulations and consumer needs are driving automotive manufacturers to reduce vehicle energy consumption. However, this forms part of a complex landscape of regulation and customer needs. For instance, when reducing aerodynamic drag or vehicle weight for efficiency other important factors must be taken into account. This is seen in vehicle bonnet design. The bonnet is a large unsupported structure that is exposed to very high and often fluctuating aerodynamic loads, due to travelling in the wake of other vehicles. When travelling at high speed and in close proximity to other vehicles this unsteady aerodynamic loading can force the bonnet structure to vibrate, so-called “bonnet flutter”. A bonnet which is stiff enough to not flutter may be either too heavy for efficiency or insufficiently compliant to meet pedestrian safety requirements. On the other hand, a bonnet which flutters may be structurally compromised or undermine customer perceptions of vehicle quality.

Testing real-time vehicular systems challenges the tester to design test cases for concurrent and sequential input events, emulating unexpected user and usage profiles. The vehicle response should be robust to unexpected user actions. Sequence Covering Arrays (SCA) offer an approach which can emulate such unexpected user actions by generating an optimized set of test vectors which cover all possible t-way sequences of events. The objective of this research was to find an efficient nonfunctional sequence testing (NFST) strategy for testing the robustness of real-time automotive embedded systems measured by their ability to recover (prove-out test) after applying sequences of user and usage patterns generated by combinatorial test algorithms, considered as “noisy” inputs. The method was validated with a case study of an automotive embedded system tested at Hardware-In-the-Loop (HIL) level. The random sequences were able to alter the system functionality observed at the prove-out test.

Many modern vehicles have blunt rear end geometries for design aesthetics and practicality; however, such vehicles are potentially high drag. The application of tapering; typically applied to an entire edge of the base of the geometry is widely reported as a means of reducing drag, but in many cases, this is not practical on real vehicles. In this study side tapers are applied to only part of the side edge of a simplified automotive geometry, to show the effects of practical implementations of tapers. The paper reports on a parametric study undertaken in Loughborough University’s Large Wind Tunnel with the ¼ scale Windsor model equipped with wheels. The aerodynamic effect of implementing partial side edge tapers is assessed from a full height taper to a 25% taper in both an upper and lower body configuration. These were investigated using force and moment coefficients, pressure measurements and planar particle image velocimetry (PIV).

A novel semi-analytical solution has been developed for the calculation of the static and dynamic response of an off road tire interacting with a deformable terrain, which utilizes soil parameters independent of the size of the contact patch (size-independent). The models involved in the solution presented, can be categorized in rigid and/or pneumatic tires, with or without tread pattern. After a concise literature review of related methods, a detailed presentation of the semi-analytical solution is presented, along with assumptions and limitations. A flowchart is provided, showing the main steps of the numerical implementation, and various test cases have been examined, characterized in terms of vertical load, tire dimensions, soil properties, deformability of the tire, and tread pattern. It has been found that the proposed model can qualitatively capture the response of a rolling wheel on deformable terrain.

Water accumulating on a vehicle's wind screen, driven over the A-pillar by a combination of aerodynamic forces and the action of the windscreen wipers, can be a significant impediment to driver vision. Surface water film, or streams, persisting in key vision areas of the side glass can impair the drivers' ability to see clearly through to the door mirror, and laterally onto junctions. Common countermeasures include: water management channels and hydrophobic glass coatings. Water management channels have both design and wind noise implications. Hydrophobic coatings entail significant cost. In order to manage this design optimisation issue a water film and wiper effect model has been developed in collaboration with Jaguar Land Rover, extending the capabilities of the PowerFLOW CFD software. This is complimented by a wind-tunnel based test method for development and validation. The paper presents the progress made to date.

Little research has been done on spray characteristics of 2,5-dimethylfuran (DMF), since the breakthrough in its production method as an alternative fuel candidate. In this paper, the spray characteristics of pure fuels (DMF, Isooctane) and DMF-Isooctane blends under different ambient pressures (1 bar, 3 bar and 7 bar) and injection pressures (50 bar, 100 bar and 150 bar) were studied using Phase Doppler Particle Analyzer (PDPA) and high speed imaging. Droplet velocity, size distribution, spray angle and penetration of sprays were examined. Based on the results, DMF had larger SMD and penetration length than isooctane. The surface tension of fuel strongly influenced spray characteristics. Increasing the surface tension by 26 % resulted in 12 % increase in SMD. Higher ambient pressure increased the drag force, but SMD was not influenced by the increased drag force. However, the increased ambient pressure reduced the injection velocity and We number resulting in higher SMD.

Short tapered sections on the trailing edge of the roof, underside and sides of a vehicle are a common feature of the aerodynamic optimization process and are known to have a significant effect on the base pressure and thereby the vehicle drag. In this paper the effects of such high aspect ratio chamfers on the time-dependent base pressure are investigated. Short tapered surfaces, with a chord approximately equal to 4% of the overall model length, were applied to the trailing edges of a simplified passenger car model (the Windsor Body) and base pressure studied via an array of surface pressure tappings. Two sets of configurations were tested. In the first case, a chamfer was applied only to the top or bottom trailing edge. A combination of taper angles was also considered. In the second case, the chamfer was applied to the side edges of the model base, leaving the horizontal trailing edges squared.

Simulations are presented which fully couple both the aerodynamics and cooling flow for a model of a fully engineered production saloon car (Jaguar XJ) with a two-tier cooling pack. This allows for the investigation of the overall aerodynamic impact of the under-hood cooling flow, which is difficult to predict experimentally. The simulations use a 100 million-element mesh, surface wrapped and solved to convergence using a commercially available RANS solver (STARCCM+). The methodology employs representative boundary conditions, such as rotating wheels and a moving ground plane. A review is provided of the effect of cooling flows on the vehicle aerodynamics, compared to published data, which suggest cooling flow accounts for 26 drag counts (0.026 Cd). Further, a sensitivity analysis of the pressure drop curves used in the porous media model of the heat exchangers is made, allowing for an initial understanding of the effect on the overall aerodynamics.

Historically vehicle aerodynamic development has focused on testing under idealised conditions; maintaining measurement repeatability and precision in the assessment of design changes. However, the on-road environment is far from ideal: natural wind is unsteady, roadside obstacles provide additional flow disturbance, as does the presence of other vehicles. On-road measurements indicate that turbulence with amplitudes up to 10% of vehicle speed and dominant length scales spanning typical vehicle sizes (1-10 m) occurs frequently. These non-uniform flow conditions may change vehicle aerodynamic behaviour by interfering with separated turbulent flow structures and increasing local turbulence levels. Incremental improvements made to drag and lift during vehicle development may also be affected by this non-ideal flow environment. On-road measurements show that the shape of the observed turbulence spectrum can be generalised, enabling the definition of representative wind conditions.

In order to specify a brake system that will have robust performance over the entire range of expected vehicle drive cycles it is vital that it has sufficient thermal inertia and dissipation to ensure that component temperatures are kept within acceptable limits. This paper presents a high fidelity CAE (computer aided engineering) technique for predicting the temperature of the front brake and the surrounding suspension components whilst installed on vehicle. To define the boundary conditions the process utilizes a coupled unsteady CFD (computational fluid dynamics) and thermal solver to accurately predict the convective heat transfer coefficients across a range of vehicle speeds. A 1-D model is used to predict the brake energy inputs as well as the vehicle speed-time curves during the drive cycle based on key vehicle parameters including wide-open-throttle performance, drive train losses, rolling resistance, aerodynamic drag etc.

The vehicle dynamics control systems are traditionally based upon utilizing wheel brakes as actuators. However, there has been recently strong interest in the automotive industry for introduction of other vehicle dynamics actuators, in order to improve the overall vehicle stability, responsiveness, and agility features. This paper considers various actuators such as active rear and central differentials and active front and rear steering, and proposes design of related yaw rate control systems. Different control subsystems such as reference model, feedback and feedforward control, allocation algorithm, and time-varying controller limit are discussed. The designed control systems are verified and compared by computer simulation for double lane change and slalom maneuvers.

Cooling drag, typically known as the difference in drag coefficient between open and closed cooling configurations, has traditionally proven to be a difficult flow phenomenon to predict using computational fluid dynamics. It was seen as an academic yardstick before the advent of grille shutter systems. However, their introduction has increased the need to accurately predict the drag of a vehicle in a variety of different cooling configurations during vehicle development. This currently represents one of the greatest predictive challenges to the automotive industry due to being the net effect of many flow field changes around the vehicle. A comprehensive study is presented in the paper to discuss the notion of defining cooling drag as a number and to explore its effect on three automotive models with different cooling drag deltas using the commercial CFD solvers; STARCCM+ and Exa PowerFLOW.

This paper presents a methodology for simulating Fluid Structure Interaction (FSI) for a typical vehicle bonnet (hood) under a range of onset flow conditions. The hood was chosen for this study, as it is one of the panels most prone to vibration; particularly given the trend to make vehicle panels lighter. Among the worst-case scenarios for inducing vibration is a panel being subjected to turbulent flow from vehicle wakes, and the sudden peak loads caused by emerging from a vehicle wake. This last case is typical of a passing manoeuvre, with the vehicle suddenly transitioning from being immersed in the wake of the leading vehicle, to being fully exposed to the free-stream flow. The transient flowfield was simulated for a range of onset flow conditions that could potentially be experienced on the open road, which may cause substantial vibration of susceptible vehicle panels.

The pressure on the base of a vehicle is a major contributor to the aerodynamic drag of all practical vehicle geometries, and for some vehicles, such as an SUV, it is particularly important because it can account for up to 50% of the overall drag. Understanding the mechanisms that influence the base pressure and developing our simulation tools to ensure that base pressure is accurately predicted are essential requirements for the vehicle design and engineering process. This paper reports an experimental study to investigate the base pressure on a specifically designed generic SUV model. The results from ¼ scale wind tunnel tests include force and moment data, surface pressures over the base region and particle image velocimetry (PIV) in the wake. Results are presented for the vehicle in different ride height, underfloor roughness and wheel configurations and the paper includes some description of the experimental errors. Some initial CFD simulations are also reported.