Numerical investigation of flat-plate film cooling using Very-Large Eddy Simulation method

Abstract

Film cooling is an important cooling method to protect the hot components in aero-engines and it is a classical research topic for decades. However, accurate simulation of the film cooling is still challenging. The present study aims to study film cooling with a newly developed Very-Large Eddy Simulation (VLES) method. State-of-the-art turbulence modelling methods are also included for comprehensive comparisons of film cooling simulations, i.e., VLES and DES (Detached Eddy Simulation) of hybrid RANS-LES method and the classical LES (Large Eddy Simulation) method are applied. Numerical simulations are performed for a single row film cooling benchmark test case (Sinha et al., 1991), in which the turbulence intensity of the freestream flow is about 0.2%, at two density ratios and two blowing ratios, corresponding to four momentum flux ratios. The results predicted by different turbulence methods are compared in detail, including the film cooling effectiveness, the velocity flow fields, as well as the relevant turbulent flow structures. The predicted results are also compared with available experimental data. It is found that for the three cases with low momentum flux ratios (smaller than 0.3), the three turbulence methods produce quite different results, while for the case with higher momentum flux ratio of 0.5, the differences between the results of three turbulence methods become less significant. Overall, the present VLES method performs best among the three selected methods, and its predictions agree well with the experimental data. While for the DES method, it severely delays the Kelvin-Helmholtz instability of the turbulence mixing process in film cooling and thus fails to accurately predict the cooling effectiveness at low momentum flux ratio. The study demonstrates the potentials of the newly developed VLES method for accurate prediction of complex film cooling problems.