Three-dimensional velocity measurements in annular diffuser segments including the effects of upstream strut wakes

Experiments were performed to provide 3D velocity data for CFD validation on the flow in two annular diffuser segments with straight inner walls and angled outer walls. The sensitivity of these flows to inlet condition perturbations was also examined. One of the diffusers was designed to operate far from separation for unperturbed inlet conditions. The other had the same length and inlet shape as the first diffuser but a larger expansion ratio, chosen to place it along the line of first appreciable stall. Each diffuser was connected to two different inlets, one containing a fully-developed channel flow, the other containing wakes from a row of struts. Three-component velocity measurements were taken on the flow in each inlet/diffuser combination using Magnetic Resonance Velocimetry. The less aggressive diffuser did not stall while the larger-angle diffuser showed very small regions of reversed flow both with and without the wake disturbances. By the end of both diffusers, turbulence had damped out all secondary flows generated by the struts, but the larger diffuser exhibited increased streamwise velocity nonuniformity due to the struts.