Short annular diffuser systems consisting of a conical expansion section with negative wall angles and a solid (full outer diameter) diffusing section were tested experimentally at several inlet swirl angles of 0–40°. Tests analyzed were completed over a range of inlet Reynolds number of Ret = 0.9–2.2 × 105 and considered fully turbulent. Performance — back pressure coefficient, outlet velocity uniformity, and total pressure loss — were appreciably depreciated for inlet swirl number larger than 0.7 and the average 10° curved vane swirler out-performed its straight vaned equivalent. Three centre bodies with length half that of the diffuser and different curvatures were manufactured. Similar performance was achieved but each centre body provided marginal improvements to a particular objective. Most notably, the centre body that gave an initial flow expansion angle of 14° resulted in 1–4% lower back pressure than the other two whose expansion angles were 12° and 16°.

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