Modeling of subsonic flow through a compact offset inlet diffuser

Abstract

This paper presents a comparison of computational and experimental results that were obtained during an investigation of compressible flow through a compact, highly offset diffuser. Entrance values for the Mach number and the Reynolds number were 0.341 and 5.75(10)5, respectively. Strong curvature of the diffuser centerline produced extensive separation along one wall, which resulted in an exhaust flow with highly complex crossflow patterns and spatial nonuniformities. Our objective was to evaluate the use of an existing thin-layer Navier-Stokes code (ARC3D) to predict effects of diffuser shape and inlet flow properties on pressure recovery and exit flow quality. Comparisons are shown between computed and measured flow velocity components and wall pressure distributions. Agreement was satisfactory except in regions of separated flow. The Baldwin-Lomax algebraic turbulence model used in the code does not appear to represent adequately this complex separated region. We present preliminary results of computations made with a one-half-equation turbulence model, which accounts for some of the history effects in computing the turbulence length scale. The computed results show that the details of the axial velocity distribution in the separated flow region were quite different for the two turbulence models, but other features of the flow, such as the static pressure distributions, were only slightly affected.