A significant change that has been made to the BLOODHOUND SSC during the initial design phase is the transition from a twin to a single engine intake. This shift in concept took place after detailed CFD simulations of flow through the proposed twin duct configuration indicated that a symmetric mass flow distribution was not easily achievable. The predicted level of non-smoothness was deemed to be unacceptable for the EJ200 engine and the design team decided to switch to a single intake configuration with its intake positioned above thecockpit canopy.

 

A parametric study was performed to determine the effects of intake sizing, offset ratio (essentially, the degree of turning in the duct) and inlet aspect ratio (intake shape), on the duct flow. This indicated that offset ratio was the dominant factor controlling flow quality through the duct, measured in terms of pressure distortion, swirl and flow stability. Set limits for pressure distortion and swirl for the EJ200 were known and this helped fix the maximum offset ratio at 0.23 i.e. one metre of axial displacement along the duct equates to 0.23m of vertical displacement. This placed a fundamental constraint on the packaging of the rest of the vehicle, as it forced a limit on the relative position of the top of the cockpit canopy and jet engine.

 

The external flow around the vehicle and the internal duct flow are closely coupled. In fact, the geometry of the nose and cockpit canopy are of fundamental importance in terms of efficiently delivering the air supply to the EJ200. The shape of the cockpit canopy and intake are specifically designed such that, at supersonic speeds, a two-shock system is established ahead of the duct. This decelerates the flow to the subsonic condition necessary for the intake duct, whilst minimising losses in total energy and hence maximising engine performance. The final shape of the duct face was defined to ensure a smooth moulding with the cockpit canopy. This configuration minimises the extent of the total pressure variations across the duct face generated by the upstream shock system and, therefore, minimises the level of distortion transmitted through the duct to the engine.

 

With these factors determined, the final stage in the design of the duct system was to fix the intake size. Any supersonic intake system with fixed geometry is optimised for a specific design speed. If the intake size is either too small, or too large, for a given speed and throttle setting, the flow through the duct is inefficient, resulting in a loss of net thrust. Of course, the very nature of the runs that BLOODHOUND SSC will undertake means that it will never move steadily at any particular speed. Therefore, the job of choosing the intake size became a problem that ultimately rested with Ron Ayers and his performance predicting program, using data from the CFD simulations, and this resulted in a selected intake of size 0.35m². This choice means that BLOODHOUND SSC gains a little extra performance at lower speeds, as it is accelerated towards the point where the rocket will be switched on, at the expense of jet thrust at the top of the speed range, where the rocket is providing supplementary thrust.

 

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