Povolny, John H.
An investigation has been conducted to determine the increase in the useful ranges of flight conditions that may be obtained with a given jet-engine research facility when the choked nozzle technique or the exhaust jet diffuser, or both, are employed. This report described these two methods, presents the considerations involved in their application, and gives typical results of their use as well as confirmation of the accuracy of data obtained by utilization of these techniques. The validity and accuracy of the choked nozzle technique and the associated area-pressure-differential thrust correction term were substantiated by turbojet-engine and exhaust-nozzle performance data covering a range of nzzle pressure ratios up to about 10. It was demonstrated by calculations for a typical turbojet engine installed in a typical altitude test facility that a considerable increase in the range of flight conditions that can be investigated may be obtained by use of the choked nozzle technique. It was also demonstrated that the range of facility exhaust pressures or exhauster flows may be increased by use of the exhaust jet diffuser.
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