We are developing a high-fidelity model of a full scale generic airbreathing hypersonic flight vehicle, (CSULA-GHV), with an integrated airframe-propulsion system configuration resembling an actual test vehicle. The CSULA-GHV is specifically designed to study the unique challenges associated with modeling and control of airbreathing hypersonic vehicles. The model is developed to investigate and quantify the couplings between aerodynamics, propulsion system, structural dynamics and control system. The configuration and dimensions are developed based on 2-D compressible flow theory, and a set of mission requirements broadly accepted for a hypersonic cruise vehicle intended for both space access and military applications. The model has the conventional control surfaces and variable inlet geometry. Analytical aerodynamic calculations are conducted assuming a cruising condition of Mach 10 at an altitude of 100 km. The 2-D oblique shock theory is used to predict shock wave angles, pressure on the frontal surface, and Mach number at the engine inlet. The scramjet engine is simply modeled by a 1-D compressible flow with heating, which predicts the flow rate of hydrogen fuel required for a chosen design Mach number at the engine exit. The exit flow is modeled by 2-D expansion wave theory, which can be used to predict the pressure on the rear surface. Resultant aerodynamic forces, total lift and drag, and engine thrust are then estimated by summation of these pressure forces and momentum change of the airflow. The unique aspect of this study is the multidisciplinary simulations of the vehicle dynamics in conjunction with the theory which enables quantification of the couplings. These couplings are broadly ignored in models used for control system design in the past.
Computational Fluid Dynamics (CFD) simulations are conducted using FLUENT, a CFD code capable of simulating compressible flow coupled with combustion. Hydrogen fuel is injected from the upper surface of the scramjet as a boundary condition in this CFD model.
The full scale vehicle will experience significant aeroelastic effects. Structural vibration will cause mass flow spillage and off-design engine operations when the frontal shock wave misses the lip of the engine inlet. To account for this effect a finite element structural model is constructed for extraction of fundamental frequencies and modes.
Copyright © 2004 Multidisciplinary Flight Dynamics & Control Laboratory
Cal State University, Los Angeles