Evaluation of Some Recent Jet Noise Reduction Concepts
COMBUSTION RESEARCH AND FLOW TECHNOLOGY INC DUBLIN PA
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This paper discusses RANS based numerical simulations of a 110th scale over-expanded supersonic plume resembling that of an F-18 aircraft with chevrons used as passive noise reduction devices. Three variant designs of the chevrons mounted in specified azimuthal arrangements around the baseline nozzle exit are evaluated. A major effect of the chevrons is to amplify the Mach disc size and move it closer to the nozzle exit. For these over-expanded exhausts, the chevrons must extend sufficiently deep into the plume core stream to reduce jet noise levels. Results from our simulations are in nominal accord with the experimental observations primarily noise measurements as ascertained by examining the flow structure, and via using jet noise prediction codes. Evaluation of the thrust loss produced by these devices is found to be minimal except for the one chevron configuration that provided maximum noise reduction. Our studies indicate that noise reduction devices which work for laboratory model jets may have to be revised to have them work for the real engine due to complexities in the internal mixing which cannot be replicated at laboratory scale. We discuss issues related to these differences and with real aircraft effects such as plumeplume interactions and installation effects, and we present a complete aircraftdual engine plume simulation using innovative multi-element unstructured gridding.
- Attack and Fighter Aircraft