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Jan-Niklas Hau
Department of Fluid Mechanics TU Darmstadt Petersenstr. 30, 64287 Darmstadt, Germany, Graduate School CE, TU Darmstadt Dolivostrasse 15, 64293 Darmstadt, Germany

Martin Oberlack
Chair of Fluid Dynamics, Dept. Mech. Eng., TU Darmstadt, Otto-Berndt-Str. 2, 64287 Darmstadt, Germany; Center of Smart Interfaces, TU Darmstadt, Germany; GS Computational Engineering, TU Darmstadt, Germany

George Chagelishvili
Abastumani Astrophysical Observatory Ilia State University & Nodia Institute of Geophysics Tbilisi State University Tbilisi, 0160, Georgia

George Khujadze
Universitat Siegen, Chair of Fluid Mechanics Paul-Bonatz-Str. 9-11, 57068 Siegen, Germany & Abastumani Astrophysical Observatory Ilia State University, Tbilisi 0160, Georgia

Alexander Tevzadze
Faculty of Exact and Natural Sciences Javakhishvili Tbilisi State University Tbilisi 0128, Georgia


The sound generation by pure vortex mode disturbances in an two-dimensional (2D) unbounded inviscid plane Couette flow is investigated. We present results by Kelvin-mode analysis as well as numerical simulations of the Euler equations, while focusing on the dynamics in the spectral plane. Our results show a dominance of the anisotropic linear sound generation in subsonic shear flows by vortices inside the boundaries of rapid distortion theory (RDT). The linearly generated, highly directional field is comparable to the hydrodynamic field, which physical headstone is the mode coupling, induced by the non-normality in shear flow systems at moderate shear rates of the velocity. Comparisons of the classical acoustic analogy (AA) approach by Lighthill (1952) with the herein presented results identify the inability of AAs to capture the shear-induced anisotropy of the generated waves in the spectral plane.