Sound Generation in Plane Couette Flow: A Failure of Lighthill’s Analogy
The linearmechanism of acoustic wave generation by initially pure vortex perturbations embedded in a two-dimensional, inviscid and unboundedCouette flow is investigated by Kelvin-mode analysis and direct numerical simulations (DNS). Our results show a misleading representation of the linear sources of aerodynamic sound generation by Lighthill’s acoustic analogy approach, not taking the strong anisotropy of the linear generation of acoustic waves by pure vortex mode perturbations in non-normal shear flow systems into account. DNS confirm the importance of linear sound production in the range of validity of rapid distortion theory (RDT), herein being superior compared to the nonlinear mechanism despite the common opinion.
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