Extended Synthetic Turbulence Inflow Generator within a Hybrid LES–URANS Methodology for the Prediction of Non–Equilibrium Wall–Bounded Flows

Abstract

The objective of the present paper is the fusion of a proper synthetic turbulence inflow generator with an unified hybrid LES–URANS method. The hybrid approach relies on an explicit algebraic Reynolds stress model within the unsteady Reynolds–averaged Navier–Stoks (URANS) mode. To extend the application area of the hybrid method, the digital filter concept by Klein et al. (J. Comp. Phys. 186, 652–665, 2003) is employed. Due to the application of the inflow generator within the hybrid simulation, an additional formulation for the modeled turbulent kinetic energy is necessary to ensure a reasonable inflow profile for this quantity. The required integral time scale and the two integral length scales are presently determined based on pre–simulations applying periodic boundary conditions but can also rely on other sources such as experimental data. With the aid of these integral scales and reference profiles of the mean velocity and the Reynolds stress tensor instantaneous inflow velocity profiles are generated. The integral scales are evaluated for the plane channel flow (Re t = 590) as well as the periodic hill flow (Re b = 10,595). The generated inflow data are used for these test cases and extensively evaluated. Besides the analysis of the adaptation length for both benchmarks, the mean profiles of the velocity as well as selected second–order moments of the simulations applying the synthetic inflow profiles are compared with reference data and results of hybrid simulations applying periodic boundary conditions. Furthermore, the influence of the grid resolution is analyzed.