Performance of straight-walled annular diffusers with swirling flow

Performance data are presented for eight annular diffuser families, a family being defined by the inner and outer cone angles and the inlet hub-tip ratio. These results include profiles of velocity and total pressure across the inlet and outlet lanes as well as overall pressure recovery coefficients. Diffuser outer cone angles range from 10 degrees to 60 degrees and inner cone angles from 59 degrees to -19 degrees. Swirl angles were varied from 0 degrees up to 44 degrees. Each diffuser family was tested over a range of lengths and swirl angles resulting in over ninety different tests. A procedure for extending the non-swirling definition of effectiveness to swirling flows is presented and used to evaluate a limiting swirl angle for separation for free-vortex-type inlet swirl. Comparisons are made to several measured values of flow separation. Some experimental diffusers exhibited a violently unsteady hub stall which apparently consisted of rotating reverse flow regions.