Effect of non-parallel mean flow on the acoustic spectrum of heated supersonic jets : explanation of 'jet quietening'
Afsar, M. Z. and Sescu, A. and Sassanis, V. (2019) Effect of non-parallel mean flow on the acoustic spectrum of heated supersonic jets : explanation of 'jet quietening'. Physics of Fluids B. ISSN 2163-503X (https://doi.org/10.1063/1.5117231)
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Abstract
Noise measurements of heated axisymmetric jets at fixed supersonic acoustic Mach number indicate that the acoustic spectrum reduces when the temperature ratio increases. The 'spectral quietening' effect has been observed both experimentally and computationally using Large Eddy Simulations (LES). It was explained by Afsar et al. (M. Z. Afsar and M. E. Goldstein & A. M. Fagan AIAAJ., Vol. 49, p. 2522, 2011) through the cancellation introduced by enthalpy flux/momentum flux coupling term using the generalized acoustic analogy formulation. But the parallel flow assumption is known to give inaccurate predictions at high jet speeds. In this paper we therefore extend the non-parallel flow asymptotic theory of Goldstein et al. (M. E. Goldstein, A. Sescu & M. Z. Afsar, J. Fluid Mech., Vol. 695, p. 199, 2012) for the vector Green’s function of the adjoint linearized Euler equations (ALEE) in the analogy. Using a steady Reynolds Averaged Navier Stokes (RANS) calculation for the jet mean flow, we find that the coupling term propagator is positive-definite and asymptotically sub-dominant at low frequencies corresponding to the peak jet noise when non-parallel flow effects are taken into account and self-consistent approximations for the turbulence structure are made. The validity of the non-parallel flow-based acoustic analogy model is assessed at various observation angles by computing the overall sound pressure level (OASPL) and use this to suggest a more rational explanation of the quietening effect. In general, our noise predictions are in very good agreement with acoustic data beyond the peak frequency.
ORCID iDs
Afsar, M. Z. ORCID: https://orcid.org/0000-0002-7417-2089, Sescu, A. and Sassanis, V.;-
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Item type: Article ID code: 69942 Dates: DateEvent16 October 2019Published16 October 2019Published Online21 September 2019AcceptedSubjects: Technology > Motor vehicles. Aeronautics. Astronautics
Science > PhysicsDepartment: Strategic Research Themes > Ocean, Air and Space
Faculty of Engineering > Mechanical and Aerospace EngineeringDepositing user: Pure Administrator Date deposited: 24 Sep 2019 15:23 Last modified: 03 Sep 2024 12:13 URI: https://strathprints.strath.ac.uk/id/eprint/69942