Direct Numerical Simulation of a BZT Dense Gas Compressible Shear Layer

by Aurélien Vadrot, Christophe Corre & Alexis Giauque
Laboratoire de Mécanique des Fluides et d’Acoustique (LMFA) – CNRS: UMR 5509, Ecole Centrale de Lyon, Ecully, France

The peculiar thermodynamic properties of dense gases make them of primary interest to the industrial community working on heat recovery and transfer. In the vicinity of the critical point the sound speed drops significantly in dense gases, which leads to a strong increase of compressibility effects. The use of such gases raises modelling issues when numerically designing ORC turbines since the turbulent flows at stake include both significant compressibility effects and potential differences with respect to perfect gases because of the aforementioned uncommon thermodynamic properties – in particular, for BZT gases, the occurrence of an inversion zone in which the fundamental derivative of thermodynamics becomes negative.

Direct Numerical Simulation (DNS) is the favored tool to better understand the development of turbulence in BZT dense gas flows and provide both guidelines and validation databases for the subsequent development of subgrid models to be used for Large Eddy Simulation or statistical models to close the RANS equations. DNS of dense gases has been used in few previous works for flow configurations such as freely decaying and forced Homogeneous Isotropic Turbulence and turbulent channel flow. The present study is devoted to the DNS of a time-developing BZT dense gas compressible shear layer. While homogeneous isotropic turbulence may be seen as reflecting the turbulent behaviour in a turbine inter-blade, the shear layer development provides insight into the turbulence characteristics in the blade’s wake.

www.aero.polimi.it