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The Use Of Acoustic Scale Models For Investigating Near Field Noise Of Jet And Rocket Engines

Report Number: WADD TR 61-178
Author: Morgan, Walter V.
Author: Young, Kenneth J.
Author: Sutherland, L. C.
Corporate Author: The Acoustics Group, Aero-Space Division, Boeing Airplane Company
Laboratory: Flight Dynamics Laboratory
Date of Publication: 1961-04
Pages: 100
Contract: AF 33(616)-6834
Project: 1370
Task: 13786
AD Number: AD0268576

Analytical and experimental studies have been made to examine the feasibility of using acoustic scale models for near field noise investigations. Analyses show that the important characteristics of noise generation, propagation, and measurement can be scaled. A relatively few deviations from this involve small errors which are generally negligible in the near field. The most straightforward model is seen to be one which duplicates the gas flow parameters of the full scale engine. The validity of such models has been demonstrated by a series of tests for a wide variety of nozzle exit conditions, from turbojet through rocket exhausts, and whether in a free field or in the presence of objects which interfere with the flow, such as shaped nozzles and flame deflectors. It is further determined both analytically and experimentally that models, in certain cases, may be simplified without impairing the results of a scaled test. Considerations in simplifying a model include: reduction of the nozzle size; absence or presence of reflecting surfaces; use of fewer than the full scale number of engines; and use of a substitute gas which is different from and at a lower temperature than that in the full scale engine.

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