LES and DNS of Turbulent Flows in Weakly Compressible Condition

Flow field of low Mach number (e.g. M <0.3) is usually simulated by the incompressible flow scheme due to the severe limitation of time-increment in the compressible flow scheme. In this work, we propose a modification to the usual incompressible scheme, based on the elliptic equation for pressure, to improve the accuracy for turbulent flows considering weak compressibility. Two examples will be shown to validate our method. (1) LES (Large-Eddy Simulation) was conducted for turbulent flow around NACA0012 airfoil. Particular attention was focused on the influence of compressibility, despite the low Mach number range. In addition, new subgrid scale model of one-equation type using dynamic procedure was compared with traditional Smagorinsky model. Our method successfully reproduced the separation bubble near the leading edge, resulted in the improvement in the intensity of pressure fluctuation. (2) DNS (Direct Numerical Simulation) of turbulent flow in a plane channel is carried out, taking wall temperature difference into account. As a result of the density fluctuation in near-wall eddies, asymmetric profiles are observed in turbulence statistics. By the 4-quadrant analysis of turbulent shear stress, it is found that the ejection events in the vicinity of the walls are particularly affected by the density variation.