Numerical Investigation of an Air-Air Ejector with Diffuser for use in Gas Turbine Exhaust Systems

摘要

An ejector is a simple device used to drive a secondary air flow of cool ambient air using the momentum of a primary air flow. Gas turbine ejector exhaust systems are commonly used to pump engine enclosure ventilation air or provide exhaust cooling. Reduction in plume temperature is particularly desirable for military aircraft to avoid detection from infra-red guided missiles. This review evaluates the capability of Reynolds-averaged Navier-Stokes computational fluid dynamics on short cylindrical air-air ejectors whose primary jet flow has Reynolds number Re_D_1 = 2.0·10~6 and Mach number M_1 = 0.23. Three numerical studies were performed using the realizable k-e turbulence model: (1) rounded secondary inlets, (2) ejector length, and (3) diffuser divergence angle. Results for the area ratio two mixing tubes show that increasing the radius of the rounded inlet, lengthening the ejector to at least seven mixing tube diameters, and specifying a divergence angle of 10° on an area ratio two diffuser give an exhaust system with the best pumping, pressure recovery, and mixing. Diffuser pressure coefficient was compared against experimental results and was over-predicted in excess of 22% due to the implementation of an isotropic turbulence model.