External-Compression Supersonic Inlet Free from Violent Buzz

摘要

To greatly improve the supersonic inlet stability at low cost of structural weight and complexity, a novel buzz suppression strategy based on fixed-geometry air bleed is developed. It is designed to have plenty of narrow flush slots that are widely distributed along the compression surface. Using the natural pressure gradient varying with the terminal shock position, it is capable of creating self-adaptive bypass flow removal upstream of the internal duct. A strong stabilizing effect can be thus automatically produced on the subcritical flowfield by eliminating shock-induced separation and discharging excessively captured airflow. Simultaneously, the undesired air leakage at the critical regime can be naturally restricted to prevent a prohibitive performance penalty during normal operation. To verify the effectiveness, an external-compression inlet model is specially designed and carefully tested at freestream Mach numbers of 2.0 and 2.5 with an almost full exit throttle range considered (0-99.1%). Results indicate that the subcritical stable-flow range is remarkably extended from a throttle threshold of 53.7% to that of 86.4% and 73.7%, respectively, after the usage of the proposed bleed method. Moreover, intense flow instability is totally eliminated, even when the duct exit is almost closed. Further analysis reveals that the bleed flow rate at the near-critical state is not beyond 1% of the inlet flow rate for both freestream conditions. It actually causes no obvious loss of the inlet flow rate. Also, the following total pressure drop and drag increase are below 0.4%. Additionally, the observed unique buzz flow implies that the buzz origin is not necessarily limited to the two known sources, as opposed to the long-established understanding.