Three diffuser sets (N/W1, held constant in each set) were built and tested for performance and flow regime over a range of total area ratios, AR, which yielded unstalled and stalled flows. At each AR and N/W1, a simple class of convex-inward (trumpet-shaped), straight, and convex-outward (bell-shaped) wall shapes were tested. It is concluded that there is little advantage to be gained by contouring the walls of two-dimensional diffusers. A corollary result shows that the performance prediction method of reference [1] gives good results for unstalled diffusers.

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A procedure for the design of two-dimensional, curved diffusers is developed and evaluated through comparisons with flow regime and performance data. As input to the method, the inner and outer-wall potential-flow pressure distributions are specified as combinations of straight-wall diffuser pressure distributions. The diffuser shape is calculated using the method of Stanitz. In Part II criteria are established for choosing desirable inner and outer-wall pressure distributions. These criteria are based on systematic performance and flow regime tests carried out on curved diffusers with inner-wall length to throat width ratios between 4 and 10, area ratios between 1.5 and 2.1, and turning angles between 30 and 90 deg. The procedure yields diffusers of higher performance than circular-arc center-line diffusers.

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