Predicting the Unstart of Scramjet Engine Air Intakes through CFD Simulation

Abstract

Scramjet is an air breathing engine in which the combustion takes in a supersonic air stream by generating high pressure. Wedge shaped strut plays a major role in the scramjet engine to mix and compress air at high speeds, igniting the air fuel mixture and sustaining the flame. But the geometric profile of wedge in which the air gets blocked partially or completely is unanswered. Therefore, the effect of blockage on intake characteristics is investigated in this present study. Numerical investigations are carried out using ANSYS Fluent at Mach 5 to study the changes in static pressure, stagnation pressure, temperature and mass flow rate for different percentage of blockage which is varied from 10% to 45%. Unstart-free air intake for scramjet engine is ensured by keeping the percentage blockage of fuel injection struts between 10% and 35%. The Mach number at supersonic regime until 35% of blockage turns suddenly into subsonic conditions afterwards for further increase in blockage percentage. Moreover, as the blockage is further increased beyond 35%, bow shock is observed ahead of the cowl and the flow through the intake is subsonic, thereby indicating ‘unstart’ intake. Based on this geometry in air intake, smooth gas dynamic compression or ramming effect is obtained up to 35% of blockage.