Some Effects on Conical Diffuser Performance of Preceding Normal Shock Boundary-Layer Interaction

Abstract
Experimental results are presented for the variation of the static pressure rise coefficient Cp, the transformation efficiency η the total pressure loss coefficient CL and the outlet kinetic energy coefficient ɛ2 with the Mach number and the effective throat length for subsonic conical diffusers with total expansion angles of 5°, 12° and 20° and an overall area ratio of 10:1. The junction between the parallel entry pipe and the diffuser cone is sharp and the diffuser inlet conditions are evaluated from measurements on a plane 1°5 diameters upstream of the diffuser's sharp transition. The shock Mach number was varied from 1°05 to 1°25 whilst the diffuser inlet Reynolds number varied between 9°0 × 105 and 1°22 × 106. A comparison of the results with those of diffusers preceded by wholly subsonic flow in the entry pipe shows the beneficial effect of interaction, the most significant gains being with the lowest angle diffuser.

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