Thermal Control for Hypersonic Vehicle Propulsion

This paper describes some of the key features and conclusion of a preliminary thermal control system design for the National Aero-Space Plane (NASP). The cooling of the airframe and propulsion system is achieved by pumping cold fuel through a network of heat exchangers prior to combustion. Simultaneously, the controller must provide the proper total flow for thrust generation, and must optimize the turbomachinery operating point within the turbomachinery operating constraints. For this problem, we find that efficient use of fuel cooling throughout the vehicle's operating envelope requires modulating the flow splits within the network as the flight condition changes. This modulation cannot be accomplished through scheduling alone if off-nominal heat loads and valve failures are to be tolerated. Local control of panel temperature provides some tolerance, but it is not sufficient. A hierarchical controller consisting of a central control algorithm to coordinate the local controllers as well as the turbomachinery control provides large tolerance to off-nominal heat loads and valve failures. Dynamic reponse predictions based on a high-fidelity nonlinear simulation are presented.