A fixed-geometry diffuser system was tested in an arc-heated, hypersonic, open-jet wind tunnel. facility at Mach numbers between 14 and 18 and Reynolds numbers (based on nozzle exit diameter) between 8,900 and 25,000. Tests were conducted both with an empty test section and with conical models in the flow. Test variables included test section open-jet length, diffuser second-throat length, and diffuser inlet geometry. Diffuser efficiency improved with increased diffuser secondthroat length,

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... increasing Reynolds number, and with the addition of conical models into the flow. Changes in open-jet length and diffuser inlet geometry had no appreciable effect on diffuser efficiency with an empty test section. A streamlined model support strut produced marked improvement in diffuser efficiency over a blunt support strut. I