Effect of Secondary Injection on the Characteristics of a Supersonic Parallel Diffuser

Abstract

This paper reports further progress in evaluating the performance of the supersonic parallel diffuser incorporating a sudden entry enlargement which provides for the injection of secondary fluid. The effects of introducing proportions up to 10 per cent of the primary flow in a two-dimensional diffuser are illustrated by schlieren photographs of the flow patterns and by measurements of the local wall static pressure and heat transfer distributions. The normal and oblique shock regimes (corresponding respectively to the unstarted and started conditions) are modified by the strengthening of the weak shock system generated at the primary nozzle mouth. Optimum overall static pressure recovery is reduced by the admission of secondary fluid, though the conditions under which it is achieved remain unchanged unless forced injection is used. The local heat transfer no longer follows the static pressure distribution and in the unstarted diffuser large peaks occur near mid-length. Over an intermediate range of Reynolds number the mean heat transfer is greater than that without secondary flow but otherwise it is less.