Abstract
In this paper we continue efforts aimed at modeling jet noise using selfconsistent analytical approaches within the generalized acoustic analogy (GAA) formulation. The GAA equations show that the farfield pressure fluctuation is given by a convolution product between a propagator tensor that depends on the (true) nonparallel jet mean flow and a generalized fluctuating stress tensor that is a stationary random function of time and includes the usual fluctuating Reynolds’ stress tensor as well as enthalpy fluctuation components. Here, we focus on approximating the propagator tensor by determining an appropriate asymptotic solution to the adjoint vector Green’s function that it depends on by using an asymptotic approach at all frequencies of interest for jet noise prediction. The Green’s function is then rationally approximated by a composite formula in which the GSA (GoldsteinSescuAfsar, J. Fluid Mech., vol. 695, pp. 199234, 2012) nonparallel flow Green’s function asymptotic solution is used at low frequencies and the O(1) frequency parallel flow Green’s function is used for all frequencies thereafter. The former solution uses the fact that nonparallelism will have a leading order effect on the Green’s function everywhere in the jet under a distinguished scaling in which the jet spread rate is of the same order as the Strouhal number for a slowlydiverging mean flow expansion. Since this solution, however, is expected to apply up to the peak frequency, the latter O(1) frequency Green’s function in a parallel flow must be used at frequencies thereafter.
We investigate the predictive capability of the composite Green’s function for the prediction of supersonic axisymmetric round jets at fixed jet Mach number of 1.5 and two different temperature ratios (isothermal & heated) using Largeeddy simulation data. Our results show that, in the first instance, excellent jet noise predictions are obtained using the nonparallel flow asymptotic approach, remarkably, up to a Strouhal number of 0.5. This is true for both heated and unheated jets. Furthermore, we develop the analytical approach required to extend this solution by appropriate asymptotic approximation to O(1) frequencies.
Original language  English 

Pages  117 
Number of pages  17 
DOIs  
Publication status  Published  20 Jun 2017 
Event  23rd AIAA/CEAS Aeroacoustics Conference  Denver, Colorado, United States Duration: 5 Jun 2017 → 9 Jun 2017 
Conference
Conference  23rd AIAA/CEAS Aeroacoustics Conference 

Country  United States 
City  Denver, Colorado 
Period  5/06/17 → 9/06/17 
Keywords
 aeroacoustics
 aerospace
 generalized acoustic analogy
 GAA
 jet noise
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Profiles

Mohammed Afsar
Person: Academic