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Proposing Institution

Lehrstuhl für Aerodynamik, TU München
Project Manager

Prof. Dr.-Ing. Rainer Friedrich
Boltzmannstr. 15
86748 Garching
In numerical simulations of compressible flows two simplifications are usually common: the neglectof the bulk viscosity and the use of constant specific heats. The latter is certainly an acceptableapproximation in low temperature ranges, but not in higher temperature ranges as they arise in high-speed flight. The neglect of the bulk viscosity must lead to errors in cases where polyatomic gases are the working fluids, e.g. in diffusers and nozzles. In these the straining of fluid particles (bycompression and expansion) has a direct effect on the viscous stress tensor. Now, the flow in diffusers and nozzles of technical interest is mostly turbulent and the mean viscous stress tensor plays a role in near wall regions even at high Reynolds numbers. Besides this, the fluctuating viscous stress tensor is part of the turbulent dissipation rate tensor, which contributes to the Reynolds stress transport. Hence,the bulk viscosity should also matter in such cases. In a recent publication of M.S. Cramer (2012) it is shown that the bulk viscosity of several gases, e.g. common diatomic gases can exceed values of theshear viscosity by factors of hundred or thousand. This motivates us to perform direct numericalsimulations (DNS) of supersonic turbulent flows in plane nozzles and diffusers in order to answer thefundamental questions about the need to work with the bulk viscosity and with temperature-dependentspecific heats in high-speed turbulent flows, which are completely described by the compressibleNavier-Stokes equations.

Impressum, Conny Wendler