The Effect of Backpressure on the Transition to Subsonic Flow in the Diffuser of a Supersonic Air Intake

The paper presents the results of a numerical study of the transition from supersonic to subsonic flow in the diffuser of a supersonic ramjet air intake with a change in the backpressure in the combustion chamber (with channel throttling). Two variants of an axisymmetric diffuser with large angles are investigated (angle opening: Theta = 10 degrees, and Theta = 90 degrees). Obtained flow patterns are depending on the geometric parameters of the diffuser and on the degree of channel throttling. The flow in the diffuser with a Theta = 10 degrees, diffuser with the opening Theta = 90 degrees, on of a pseudo-shock and the separation zones in the boundary layer. The effect of back pressure on the transition characteristics (total pressure loss, static pressure increase, transition zone length, etc.) is analyzed. Despite the fundamental difference in flow regimes, the flow characteristics over a length of more than 8-10 calibers are the same. It is shown that when a diffuser with large opening angles is used, a change in the total backpressure more than 3 times in the combustion chamber does not effect on the flow in the throat and, consequently, on the flow in the air intake.