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TURBULENCE PHYSICS OF COMPRESSIBLE BOUNDARY LAYERS

Maher Lagha
Mechanical and Aerospace Department University of California, Los Angeles 420 Westwood Plaza, Los Angeles CA 90095-1597, USA

John Kim
Mechanical and Aerospace Department University of California, Los Angeles 420 Westwood Plaza, Los Angeles CA 90095-1597, USA

Jeff Eldredge
Mechanical and Aerospace Department University of California, Los Angeles 420 Westwood Plaza, Los Angeles CA 90095-1597, USA

Xiaolin Zhong
Mechanical and Aerospace Department University of California, Los Angeles 420 Westwood Plaza, Los Angeles CA 90095-1597, USA

Abstrakt

Compressible turbulent boundary layers with free-stream Mach number ranging from 2.5 up to 20 are analyzed by means of direct numerical simulation of the Navier−Stokes equations. The fluid is assumed to be an ideal gas with constant specific heats. The simulation generates its inflow condition using a rescaling-recycling method. The main objective is to study effects of Mach number on turbulence statistics and near-wall turbulence structures. The present study shows that the main turbulence statistics can be correctly described as variable-density extensions of incompressible results. The study also shows that turbulence in the near-wall region can be sustained without turbulence in the outer region, proving the existence of a local cycle within the near-wall region. Physics of near-wall turbulence is investigated in a simplified model flow, where the coherent part of turbulence is separated from the rest by a Galerkin projection. It is shown that the near-wall region is populated by crescent-shaped vortical structures, which are associated with regions with positive Reynolds stress production.