Investigation of a Variable Geometry Supersonic Diffuser

Citation

Heppe, R. Richard (1947) Investigation of a Variable Geometry Supersonic Diffuser. Engineer's thesis, California Institute of Technology. doi:10.7907/WYNA-G323. https://resolver.caltech.edu/CaltechETD:etd-10302003-162416

Abstract

A flexible second throat supersonic diffuser has been tested in the GALCIT 2-1/2 inch supersonic wind tunnel at Mach numbers of 2.60 and 3.33. The theoretical minimum area relation for starting a supersonic tunnel has been checked at the two Mach numbers, and the amount by which the height of the second throat may be reduced after the tunnel has been started was determined. Minimum compression ratios for the starting and reduced second throat conditions have been determined and compared with those previously found here and theoretically estimated by Crocco. Effect of nozzle surface roughness on supersonic flow is noted, and Schlieren photographs representing the flow in a variety of conditions are presented. A series of Schlieren photographs shows the flow in the second throat at progressively greater amounts of area reduction. The theoretical minimum second throat area relation was found to predict the second throat size for starting within 3 percent at both Mach numbers, being conservative by that amount in both cases. Only about 1/3 of the theoretically predicted reduction of second throat area after starting was realized at both Mach numbers before separation of the boundary layer broke down flow throughout the nozzle. Minimum compression ratios were reduced some 9 and 6 percent for Mach numbers 2.60 and 3.33 respectively. These decreases, though not as large as anticipated, nevertheless have the lowest compression ratios ever measured in the GALCIT tunnel, ratios less than Crocco's estimate, heretofore never realized. Transition, though not occurring by means of a normal shock wave, was found to be stable a few inches downstream of the second throat.

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