Advances in Modeling the Aeroacoustic Coupling of Supersonic Dual Impinging Jets

Speaker: Spencer Stahl, aerospace engineering student

Abstract:
Vertical Take-Off and Landing (VTOL) maneuvers are subject to unfavorable conditions for the aircraft, flight deck, and nearby personnel. Such problems include, unsteady aerodynamic loading, aeroacoustic structural response, hot-gas ingestion, ground degradation, and harmful sound levels. Many of these adverse conditions manifest from the impingement of supersonic jet exhausts that establish an aeroacoustic resonance between the aircraft and the ground. The associated feedback mechanism has warranted study of single impinging jets (SIJ) in isolation. However, the additional jet found in VTOL propulsion, introduces flow features that modulate the feedback dynamics in each jet. In these dual impinging jet (DIJ) configurations, a turbulent fountain-flow is generated between the jets, resulting in unsteady upwash forces under the aircraft and hydrodynamic coupling of the jets. In addition, acoustic coupling ambiguously increases the resonance across the DIJ system at different heights. Large Eddy Simulations (LES), in conjunction with experimental observation, are used to advance the understanding of the anomalous coupling phenomenon. Differences between SIJ, identical DIJ, and mixed DIJ systems are studied across the transonic regime at moderate nozzle-to-ground impingement heights. Mixed DIJs have different operating conditions in each jet, inducing greater fountain-flow shear-layer interactions for the weaker jet, further affecting resonance characteristics. A combination of physics-based and newly developed data-driven decompositions are applied to the LES solutions. Mechanistic descriptions that relate fountain-flow shear-layer interactions, unique DIJ global impingement modes, and the transfer of acoustic and hydrodynamic energies through the receptivity and impingement processes are elucidated. The effects of DIJ coupling renders established SIJ models insufficient at predicting the complete acoustic profile over a range of heights. Insights from the decomposed LES are used to extend the SIJ model by accounting for DIJ acoustic coupling, successfully predicting the modulation of impinging tones and the height of peak sound levels.

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Committee Members
Professor Datta Gaitonde
Mechanical and Aerospace Engineering Lian Duan
Professor Jen-Ping Chen
Dr. David Gonzalez