Ring vanes were recognized as being beneficial for increasing pressure recovery and reducing stall in wide-angled diffusers. Augmentation devices can also reduce swirl-induced flow distortion. A three-point ring vane was inserted into a short annular diffuser with a length-to-inlet-height ratio of 14.5 and area ratio of 4. Numerical optimization studies were completed using the realizable k-ε turbulence model at zero and 12 deg inlet swirl that established a preferential location of the ring vane leading edge. Parametric computational fluid dynamics studies evaluated the influence of the dominant variables — overall length and angle — at 0 to 12 deg inlet swirl. Performance was dependent on the ability of the ring vane to reduce outer wall stall without swirl or the central toroidal recirculation zone with swirl and the ring vane wake. Shorter vanes angled towards the centre reduced back pressure with no swirl whereas longer outward-angled vanes were preferred with 12 deg swirl.

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