Le Fang

Non-equilibrium turbulent phenomena in transitional channel flows

ABSTRACTNon-equilibrium turbulent flows were considerably investigated in recent years, but most studies are restricted in grid-generated turbulence. In the present contribution we show by large-eddy simulation (LES), that there exists a weakly non-equilibrium turbulence region before the beginning of the full-developed turbulence. Both the dissipation coefficient and the skewness of longitudinal velocity gradient are used as characteristic non-equilibrium quantities, illustrating that the non-equilibrium turbulence region in channel flow is weakly similar to previous studies in grid-generated turbulence. The observation of non-equilibrium turbulence region in transitional channel flow is also expected to inspire future improvement of turbulence models.

A Local Regrouping Method in the 2D SPH Simulation

The distortion of particles distribution is a defect that usually leads to numerical instability in the traditional SPH method. In this contribution, we introduce a novel local regrouping method to solve this problem. The basic idea is to keep the particles undeformed by regrouping, dividing or combining the deformed particles. We succeed to simulate the Taylor-Green vortex in 2D with this method, and demonstrate the effectiveness of this method.

Modification of Spalart-Allmaras Turbulence Model for Predicting S825 Airfoil Aerodynamic Performance

In this paper, a 2-D numerical simulation of the wind turbine S825 airfoil is conducted with Spalart-Allmaras (SA) turbulence model at different attack angles. By comparing with experimental data, a novel method of modifying SA model is proposed. The key parameter in SA turbulence model is set with different values in the non-separating region and separating region divided by separating point respectively. This method improves the predictive accuracy of SA turbulence model when the airfoil works at stall conditions.