Numerical Simulations of the Near-Field Region of Film Cooling Jets Under High Free Stream Turbulence: Application of RANS and Hybrid URANS/Large Eddy Simulation Models

Abstract

This paper investigates the flow field and thermal characteristics in the near-field region of film cooling jets through numerical simulations using Reynolds-averaged Navier–Stokes (RANS) and hybrid unsteady RANS (URANS)/large eddy simulation (LES) models. Detailed simulations of flow and thermal fields of a single-row of film cooling cylindrical holes with 30 deg inline injection on a flat plate are obtained for low (M = 0.5) and high (M = 1.5) blowing ratios under high free stream turbulence (FST) (10%). The realizable k‐ε model is used within the RANS framework and a realizable k‐ε-based detached eddy simulation (DES) is used as a hybrid URANS/LES model. Both models are used together with the two-layer zonal model for near-wall simulations. Steady and time-averaged unsteady film cooling effectiveness obtained using these models are compared with available experimental data. It is shown that hybrid URANS/LES models (DES in the present paper) predict more mixing both in the wall-normal and spanwise directions compared to RANS models, while unsteady asymmetric vortical structures of the flow can also be captured. The turbulent heat flux components predicted by the DES model are higher than those obtained by the RANS simulations, resulting in enhanced turbulent heat transfer between the jet and mainstream, and consequently better predictions of the effectiveness. Nevertheless, there still exist some discrepancies between numerical results and experimental data. Furthermore, the unsteady physics of jet and crossflow interactions and the jet lift-off under high FST is studied using the present DES results.