Experimental investigations into the aerodynamic development relevant to a world rally car

Abstract

Initial wind tunnel Appropriate testing techniques required for developing the aerodynamics of a rally cai- have been investigated. tests concentrated on boundary layer reproduction and ground plane simulation and a variable length splitter plate was designed and manufactured to generate four boundary layers of different thicknesses. A scaled wing model was then introduced to the flow and LDA, PIV, oil flow visualisations and surface static pressure measurements were The flow beneath the wing was found to be affected then undertaken. considerably by the presence of the boundary layer. As the boundary layer thickness was increased, the under-wing pressure was observed to increase, hence resulting in decreased suction. the LDA results indicated a modification to the wake profile. Furthermore, In addition to the boundary layer research, an experimental investigation into the effects of testing with yaw has been undertaken. This involved comparative studies between testing statically, where time averaged force and pressure data was recorded at discrete yaw angles, and dynamically where data is continuously and synchronously collected while the model moves thiough a prescribed yawing motion. This work was undertaken using two models, the first of which was representative of a rally car rear wing with a variable number of removable vertical fences. The second model was a complete, 35% scale, rally car model. The cai' tests were undertaken using two discrete methods. The model was initially yawed together with the overhead balance. A new in-car yaw mechanism was subsequently designed and constructed which allowed the model to yaw in isolation from the balance and mounting hardware. Force and surface pressure data was then recorded from the overhead balance while simultaneously and dynamically yawing the model. The rear wing results indicated that a diminished return was obtained by adding more than three vertical fences along the length of the wing. Although the suction acting on the wing was observed to continue to increase as more fences were added, this reduction in pressure was not observed in the downforce figures produced. The results for the car model showed a clear difference in force and static pressure magnitudes during the motion between the dynamic and static cases, producing a hysteretic 'loop' which encircles the static values. The 'ramp and hold' data also provided evidence for a distinct lag and hysteresis in the model forces when moved dynamically.

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