Investigation of Tabs in Short Annular Diffusers With Swirling Flow

Abstract

Square tabs were placed on the base of an ellipsoidal center-body (CB) in short annular diffusers. Tests were conducted in subsonic swirling flow with an inlet Reynolds number of 1 × 105. The tabs, with a projected height equivalent to the boundary layer thickness, reduced the outlet distortion and incurred a pressure penalty in the three smaller diffusers whose designs were not expected to stall. The largest area ratio (AR = 6.18) diffuser improved back pressure coefficient 4.6% with four tabs that blocked 4.7% of the inlet cross section over its bare diffuser but was 42% lower than that obtained by the AR = 2.73 diffuser with no tabs. Computational fluid dynamics (CFD) was useful for capturing relevant flow features that corroborated with experimental data and literature. Tabs oriented normal to the diffuser axis were less effective at influencing the flow as swirl angle increased but similar elongated wakes oriented with the flow direction were observed at all simulated swirl angles. The CFD either predicted equivalent performance due to the over-prediction associated with diffusion equaling the under-prediction associated with vorticity or over-predicted performance.