Note on the Simple Ram-Air Intake Preceded by Normal Shock in Supersonic Flight

Abstract

This note considers the performance of a simple ram-air intake at supersonic flight speeds. The intake is preceded by a normal shock after which the flow is diffused at subsonic velocities. Exact expressions are developed for the ram pressure ratio and the ram efficiency as functions of the flight Mach Number and the diffuser efficiency. In addition, a simple, approximate equation is developed for the ram pressure ratio a t flight Mach Numbers greater than 2.0. The conclusions of this analysis are: (1) For flight Mach Numbers greater than. 2.0, the ram pressure ratio varies approximately with the square of the Mach Number; (2) for a diffuser efficiency of 1.0, the minimum ram efficiency is 0.76; (3) for very high flight Mach Numbers, the ram efficiency becomes asymptotic to 1.0; and (4) for diffuser efficiencies less than 1.0, the ram efficiency is improved by normal shock compression at low flight Mach Numbers.