Abstract
In this paper we extend the Rapiddistortion theory (RDT)based model derived by Goldstein, Afsar & Leib (J. Fluid Mech., vol. 736, pp. 532569, 2013) for the sound generated by the interaction of a largeaspectratio rectangular jet with the trailing edge of a flat plate to include a more realistic upstream turbulence spectrum that possess a decorrelation (i.e. negative dip) in its spacetime structure and use results from threedimensional ReynoldsAveraged NavierStokes (RANS) solutions to determine the mean flow, turbulent kinetic energy and turbulence length & time scales. Since the interaction noise dominates the lowfrequency portion of the spectrum, we use an appropriate asymptotic approximation for the Rayleigh equation Green’s function, which enters the analysis, based on a twodimensional mean flow representation for the jet. We use the model to predict jetsurface interaction noise for a range of subsonic acoustic Mach number jets, nozzle aspect ratios, streamwise and transverse trailingedge locations and compare them with experimental data. The RANS meanflow computations are also compared with flow data for selected cases to assess their validity. We find that finite decorrelation in the turbulence spectrum increases the lowfrequency algebraic decay (the lowfrequency “rolloff”) of the acoustic spectrum with angular frequency to give a model that has a pure dipole frequency scaling. This gives better agreement with noise data compared to Goldstein et al. (2013) for Strouhal numbers less than the peak jetsurface interaction noise. For example, through sensitivity analysis we find that there is a difference of 10 dB at the lowest frequency for which data exists (relative to a model without decorrelation effects included) for the highest acoustic Mach number case. Secondly, our results for the planar flow theory provide a first estimate of the lowfrequency amplification due to the jetsurface interaction for moderate aspect ratio nozzles when RANS meanflow quantities are used appropriately. This work will hopefully add to noise prediction efforts for aircraft configurations in which the exhaust systems are tightly integrated with the airframe.
Original language  English 

Pages (fromto)  177–207 
Number of pages  30 
Journal  Journal of Sound and Vibration 
Volume  386 
Early online date  8 Oct 2016 
DOIs  
Publication status  Published  6 Jan 2017 
Keywords
 jetsurface interaction
 rapiddistortion theory
 trailing edge noise
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Profiles

Mohammed Afsar
Person: Academic