BLOODHOUND Design   Engine Intake Design   Wheel Design   Nose Design   Base Drag   Winglet Design   Vehicle Sensitivity Analysis

 

During the initial design studies, considerable concerns were expressed about the high drag levels that the CFD simulations were predicting. These concerns were so great that the team began wondering if the current jet/rocket combination would be sufficient to get a car up to a speed of 1000mph. With the car being regarded as an assembly of discrete sections, a major advantage of CFD studies is that it is possible analyse precisely how much each section contributes to the aerodynamic forces acting on the vehicle. It became standard procedure to produce, along with the overall values for the lift, drag and lateral forces acting on the vehicle, information indicating the longitudinal, vertical and lateral forces on each section.

 

This process immediately highlighted that almost a third of the total vehicle drag was produced by the base area of the vehicle, i.e. the rearward facing surfaces at the tail. As the air that has been compressed and accelerated around the sides of the car suddenly reaches the tail, it is allowed to expand and to form a low pressure unstable wake behind the car. The low pressure effectively sucks the car backwards and the phenomenon is referred to as base drag. One of the tasks set to the design team was, therefore, to achieve the best possible tapering of the rear of BLOODHOUND SSC to minimise the base area and, hence, the base drag.

A consideration that could still influence the exact shape and positioning of the rear wheels, is the high speed pressure field generated by the fairings and its interaction with the main body of the vehicle. The flow surrounding the fairings consists of a pressurisation behind the bow shock followed by a low pressure expansion field. It will be beneficial to attempt to prevent the expansion field from interacting with the base of the vehicle, as this will supplement the suction effect of the base drag phenomenon.

 BLOODHOUND Design   Engine Intake Design   Wheel Design   Nose Design   Base Drag   Winglet Design   Vehicle Sensitivity Analysis