Investigation of cowl vent slots for supercritical stability enhancement in dual-mode ramjet inlets

Abstract

T HE supercritical stability margin of inward-turning scoop inlets applicable to dual-mode ramjet engines has been greatly enhanced by the incorporation of a series of cowl vent slots just downstream of the inlet throat. Data has been obtained over a range of Mach number, angle of attack, and roll angle, using two single-module inlet models. A data base has been established to characterize the effect of varying available slot spill area on the stable operating range of the inlet and on the maximum inlet air capture and pressure recovery. IntroductionA particularly attractive cycle for hypersonic air-breathing propulsion systems is the dual-mode ramjet, which operates in a subsonic combustion mode at low supersonic Mach numbers and transitions smoothly to a supersonic combustion mode of operation as the flight Mach number increases. An experimental program has been completed in which the performance of cowl vent slots for use in improving the supercritical stability margin in dual-mode ramjet inlets was demonstrated. Tests have been conducted between Mach 3 and 6 using two singlescoop inlet models consistent with a multiple inward-turning scoop (MITS) inlet concept.The MITS inlet concept incorporates four "scramjet" scoops, located around a vehicle periphery, each of which captures a portion of the required engine airflow and compresses the captured air by turning it inward toward the vehicle centerline. Furthermore, the internal inlet ducting wraps the flow captured by the four scoops such that at the combustor exit a completely annular stream is delivered. These inlets are designed to operate in a dual mode in that the internal ducting downstream of the inlet throat also serves as an isolator duct for stabilization of the inlet precombustion shock system. 1 The performance payoff possible with the use of controlled inlet bypass becomes especially beneficial for a dual-mode engine operating with a multimodule inlet feeding a common combustor. When the vehicle is operating at angle of attack the leeward modules are in a less favorable flowfield and are operating at a significantly reduced performance level. Typically, the maximum thrust level attainable corresponds to the