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The effect of the upstream wake of a Formula 1 car on a following vehicle has been investigated using experimental and computational methods. Multiple vehicle studies in conventional length wind tunnels pose challenges in achieving a realistic vehicle separation and the use of a short axial length wake generator provides an advantage here. Aerodynamic downforce and drag were seen to reduce, with greater force reductions experienced at shorter axial spacings. With lateral offsets, downforce recovers at a greater rate than drag, returning to the level for a vehicle in isolation for offsets greater than half a car width. The effect of the wake was investigated in CFD using multiple vehicle simulations and non-uniform inlet boundary conditions to recreate the wake. Results closely matched those for a full two-vehicle simulation provided the inlet condition included unsteady components of the onset wake.

It is well known that in motorsport the wake from an upstream vehicle can be detrimental to the handling characteristics of a following vehicle, in particular in formulae with high levels of downforce. Previous investigations have been performed to characterize the wake from an open wheel race car and its effect on a following car, either through the use of multiple vehicles or purpose-built wake generators. This study investigates how the wake of an upstream race car impacts the aerodynamic performance of a following car in a close-following scenario. Wakes are imposed on the inlet of a CFD simulation and wake parameters (eg: velocity deficit, trailing vorticity) are directly manipulated to investigate their individual impacts on the following vehicle. The approach provides a useful alternative to the simulation of multi-vehicle cases but a better simulation could be achieved by including wake unsteadiness from the upstream vehicle.

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.

This paper outlines the creation of a facility for simulating on-road transients in a model scale, ¾ open jet, wind tunnel. Aerodynamic transients experienced on-road can be important in relation to a number of attributes including vehicle handling and aeroacoustics. The objective is to develop vehicles which are robust to the range of conditions that they will experience. In general it is cross wind transients that are of greatest significance for road vehicles. On-road transients include a range of length scales but the most important scales are in the in the 2-20 vehicle length range where there are significant levels of unsteadiness experienced, the admittance is likely to be high, and the reduced frequencies are in a band where a dynamic test is required to correctly determine vehicle response.

On-road, a vehicle experiences unsteady flow conditions due to turbulence in the natural wind, moving through the unsteady wakes of other road vehicles and travelling through the stationary wakes generated by roadside obstacles. Separated flow structures in the sideglass region of a vehicle are particularly sensitive to unsteadiness in the onset flow. These regions are also areas where strong aeroacoustic effects can exist, in a region close to the passengers of a vehicle. The resulting aeroacoustic response to unsteadiness can lead to fluctuations and modulation at frequencies that a passenger is particularly sensitive towards. Results presented by this paper combine on-road measurement campaigns using instrumented vehicles in a range of different wind environments and aeroacoustic wind tunnel tests.

A vehicle on the road encounters an unsteady flow due to turbulence in the natural wind, unsteady wakes of other vehicles and as a result of traversing through the stationary wakes of roadside obstacles. Unsteady effects occurring in the sideglass region of a vehicle are particularly relevant to wind noise. This is a region close to the driver and dominated by separated flow structures from the A-pillar and door mirrors, which are sensitive to unsteadiness in the onset flow. Since the sideglass region is of particular aeroacoustic importance, the paper seeks to determine what impact these unsteady effects have on the sources of aeroacoustic noise as measured inside the passenger compartment, in addition to the flow structures in this region. Data presented were obtained during on-road measurement campaigns using two instrumented vehicles, as well as from aeroacoustic wind tunnel tests.

Competitive aerodynamic performance of a Formula One car relies upon total understanding of the downstream wake of exposed rotating wheels. Sensitivities to the downstream vortices and low stagnation-pressure regions lead to subtle design decisions in bargeboards, side-pods and the leading edge of the highly sensitive floor region. A significant proportion of an F1 aerodynamicist's time is spent dealing with front wheel wake structures and indeed much of the front wing is developed to provide pressure gradients and vortex structures to control this wake. Wind tunnel testing of scaled deformable tyres has become a common occurrence in F1 in recent years although there is a significant lack of available literature, academic or otherwise. Due to high vertical loads experienced by a grand prix car and the relatively high levels of camber used for mechanical advantage, the use of a rigid tyre is no longer considered suitable for the accurate simulation of an F1 wheel wake.

Various techniques to reduce the aerodynamic drag of bluff bodies through the mechanism of base pressure recovery have been investigated. These include, for example, boat-tailing, base cavities and base bleed. In this study an Ahmed body in squareback configuration is modified to include a base cavity of variable depth, which can be ventilated by slots. The investigation is conducted in freestream and in ground proximity. It is shown that, with a plain cavity, the overall body drag is reduced for a wide range of cavity depths, but a distinct minimum drag condition is obtained. On adding ventilation slots a comparable drag reduction is achieved but at a greatly reduced cavity depth. Pressure data in the cavity is used to determine the base drag component and shows that the device drag component is significant. Modifications of the slot geometry to reduce this drag component and the effects of slot distribution are investigated.

A vehicle on the road encounters an unsteady flow due to turbulence in the natural wind, due to the unsteady wakes of other vehicles and as a result of traversing through the stationary wakes of roadside obstacles. There is increasing concern about potential differences between the steady flow conditions used for development and the transient conditions that occur on the road. This paper seeks to determine if measurements made under steady state conditions can be used to predict the aerodynamic behaviour of a vehicle on road in a gusty environment. The project has included measurements in two full size wind tunnels, including using the Pininfarina TGS, steady-state and transient inlet simulations in Exa Powerflow, and a campaign of testing on-road and on-track. The particular focus of this paper is on steady wind tunnel measurements and on-road tests, representing the most established development environment and the environment experienced by the customer, respectively.

For open wheel race cars the front wheel flow and the interaction of its wake with downstream components is of significant importance. Considerable effort goes into the design of front wing end plates, barge boards and underfloor components in order to manage the front wheel flow. In this study a 50% scale Formula One front wheel assembly has been tested in the Durham University 2m₂ open jet wind tunnel to evaluate the effect of through-hub flow on its cooling drag and flow structures. Varying the amount of through-hub flow gave rise to a negative cooling drag trend whereby increasing the flow through the hub resulted in a decrease in drag. This observation has been explained both qualitatively and quantitatively by inlet spillage drag. Lower than optimum airflows through the brake scoop result in undesirable separation at the inside edge and hence, an increase in drag (reversing the cooling drag trend).

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 on the road encounters an unsteady flow due to turbulence in the natural wind, the unsteady wakes from other vehicles and as a result of traversing through the stationary wakes of road side obstacles. There is increasing concern about potential differences in aerodynamic behaviour measured in steady flow wind tunnel conditions and that which occurs for vehicles on the road. It is possible to introduce turbulence into the wind tunnel environment (e.g. by developing active turbulence generators) but on-road turbulence is wide ranging in terms of both its intensity and frequency and it would be beneficial to better understand what aspects of the turbulence are of greatest importance to the aerodynamic performance of vehicles. There has been significant recent work on the characterisation of turbulent airflow relevant to road vehicles. The simulation of this time-varying airflow is now becoming possible in wind tunnels and in CFD.

At higher speeds aerodynamic noise tends to dominate the overall noise inside the passenger compartment. Large-scale turbulent conditions experienced on the road can generate different noise characteristics from those under steady-state conditions experienced in an acoustic wind tunnel. The objective of this research is to assess the relationship between on-road flow conditions and the sound pressure level in the cabin. This research, covering links between the unsteady airflow around the vehicle and aeroacoustic effects, is a natural progression from previous aerodynamic studies. On-road testing was undertaken using a current production vehicle equipped with a mobile data logging system. Testing was carried out on major roads at typical highway speeds, where wind noise is very significant. Of particular interest are high-yaw conditions, which can lead to a blustering phenomenon.

It is well documented that the aerodynamic downforce that is developed by a NASCAR race car is degraded when closely following another car. This may lead to handling imbalance and a reduced overtaking capability. Although wind tunnel studies have been performed to investigate this race situation those investigations have frequently been compromised in order to accommodate two or more test vehicles or models within the confines of the wind tunnel's working section. This study addresses that issue by using a very short, bluff body to create an accurate representation of the wake flow from the leading car in order to maximize the test length available to the test model.

It is well documented that the aerodynamic performance of an open wheel race car is degraded when closely following another car. The greatest performance loss is usually experienced by the front-mounted wing leading to reduced aerodynamic downforce, handling imbalance and a reduced overtaking capability. Although previous wind tunnel studies have been performed to investigate this race situation the model scales have generally been compromised in order to achieve representative separation between the two test vehicles within the confines of the wind tunnel working section and particularly within the limited length of the moving ground plane. This study addresses that issue by using a very short, bluff body to create an accurate representation of the wake flow from the leading car in order to provide additional, effective test length ahead of the instrumented model.

There is increasing concern about potential differences in aerodynamic behavior measured in steady flow wind tunnel conditions and that which occurs for vehicles on the road. As tools become available for better simulation of on road conditions there is a growing practical value in understanding what range of conditions are important to simulate. Surface pressures measured on the sideglass of a European hatchback vehicle in the MIRA full scale wind tunnel are compared with those measured on-road. The on-road data corresponds to relatively calm, low yaw conditions and the time averaged pressure distributions on-road and in the wind tunnel at zero yaw were very similar. Variations in instantaneous aerodynamic yaw angle produces fluctuations in surface pressures but the sensitivity of instantaneous pressures to yaw angle was lower for the on-road measurements compared with steady state wind tunnel tests.

The aerodynamic development and evaluation of passenger vehicles is almost universally performed in the controlled, low turbulence environment of a wind tunnel or under similarly idealized conditions using CFD. This environment is substantially different from that which is experienced on-road due to the effects of atmospheric winds and the wake flows from other road vehicles. The scope of this work is to establish, with regard to surface pressures, if a low turbulence wind tunnel evaluation of passenger cars yields results which accurately reproduce on-road data or whether a more complete simulation of the real world is required. The test vehicle was a Rover 214, a typical European mid-sized hatchback. Data were obtained from both the MIRA full-scale wind tunnel and on the road using the same vehicle and instrumentation. The on-road data were gathered under various atmospheric wind conditions.

Detailed flow-field data have been acquired using experimental and computational techniques in the wake of a 40% full-scale exposed wheel. The experimental investigation focused on taking discrete single-point measurements in the wake using a pneumatic 5-hole pressure probe. A wake integral method was used to compute the total drag force acting on the wheel. The computational aspects of the investigation used the commercially available Fluent 6.0 CFD package. A tetrahedral volume mesh was used to discretise the flow domain and the k-ε turbulence model was used for all calculations. The boundary conditions were set according to the experiment. As the tire rotates the work done on its surface shear layer leads to increased velocities and compression immediately ahead of the contact patch which results in pressure coefficients in excess of unity. This leads to an outflow from this high pressure zone; an effect that is known as jetting. The reverse effect occurs behind the contact patch.

Rally cars are frequently operated at high speeds on loose road surfaces and significant slip angles are achieved when cornering. A wind tunnel test procedure is presented which allows those slip angles to be accommodated whilst maintaining contact between the tires and the wind tunnel's moving ground plane. It is shown that as the slip angle is increased both the drag and lift increase whilst the centre of pressure moves rearwards. Simulations are presented which evaluate the effect of those aerodynamic changes upon the overall performance of the car over a rally stage.

Detailed flow-field measurements in the wake of a 40 percent full-scale exposed wheel have been obtained using particle image velocimetry (PIV). Additional data have been acquired in the form of surface static pressure measurements acquired using the Durham University radio telemetry system. The results presented in this paper compare and contrast, both quantitatively and qualitatively, the physical differences that exist with respect to the flow structures of rotating and non-rotating wheels. Some of the ‘special’ features of the flow-field postulated by Fackrell, such as the ‘jetting’ phenomenon, have been revisited, examined and revised based on the surface static pressure and PIV data presented in this paper. The experimental observation of a flow mechanism is presented in terms of the rear jetting after the line of contact, and the effects of this have been considered and analyzed.