Pulsed Injection Flow Control for Throttling in Supersonic Nozzles - A Computational Fluid Dynamics Based Performance Correlation (Preprint)

摘要

A vehicle propelled by an engine with a variable geometry nozzle allows the nozzle expansion ratio to vary with altitude and flight condition, thereby optimizing vehicle performance. Rockets are examples of vehicles with high nozzle pressure ratios (NPRs), which operate over a large altitude range. Active flow control offers a method of reducing the effective aerodynamic throat of a rocket nozzle in a geometrically fixed structure. Throttling the mass flow rate through the nozzle throat controls the effective throat area, subsequently controlling the effective expansion ratio of the overall nozzle. This paper presents findings from the Pulsed Injection for Rocket Flow Control Technology (PIRFCT) program, which was funded by the Defense Advanced Research Projects Agency (DARPA), and managed by the Air Force Research Laboratory (AFRL). PIRFCT evaluated potential gains in the overall performance of a rocket using active flow control at the throat for throttling. Lockheed Martin Aeronautics Company used Computational Fluid Dynamics (CFD) to simulate a high NPR rocket nozzle with active flow control. Simulations were performed with steady and pulsed flow control jets which were oriented near the throat and directed upstream at a 45-degree angle against the primary flow, and various injection conditions were modeled. All simulations were performed with the perfect gas assumption with the specific heat ratio (gamma) held constant at the value corresponding to the throat temperature. However, during the course of the program, a correlation was developed which predicts the reduction in discharge coefficient as a function of time-averaged mass flux, momentum flux and energy flux. The correlation was very general and was valid for steady and pulsed cases of various conditions.