Predicting unsteady heat-fluid interaction features and nonlinear acoustic behaviors in standing-wave thermoacoustic engines using unsteady RANS, LES and hybrid URANS/LES methods

Abstract

The study presented in this paper aims to simulate a standing-wave thermoacoustic engine (SWTAE) system by capturing its nonlinear thermoacoustic features with three-dimensional (3D) unsteady Reynolds-Averaged Navier-Stokes (URANS) and hybrid URANS/LES (Large Eddy Simulation) models such as Detached-Eddy Simulations (DES) and Stress-blended Eddy Simulation (SBES) models. For comparison, LES is also conducted as a reference case to examine the turbulence model effect on capturing the nonlinear features of heat-driven acoustics in the SWTAE system. The 3D model is validated against numerical results available in the literature, along with mesh- and time-independence studies. The comparison studies show that the computation time required for modeling SWTAE using SBES and DES is 28.4% and 36.5% less than LES, respectively. It is also shown that the prediction of the acoustic power of SWTAE using URANS is about 21.0% lower than that using LES, while the results from SBES and DES are in relatively good agreement with LES. Comparative studies of nonlinear hydrodynamics in the flow fields show that the results from SBES are closer to LES than DES, which can be attributed to the SBES model providing a faster transition to an explicit LES model outside the wall boundary layer. Furthermore, the heat transfer characteristics are compared by analyzing heat leaks and transversal heat flux, and it is found that the URANS model overestimates the heat transfer characteristics, while the results of the other three models are smaller than those obtained by URANS. In conclusion, the SBES model has great potential to be applied in simulating thermoacoustic nonlinear and flow behaviors of SWTAEs. It has the attractive features of delivering relatively accurate predictions and a significant reduction in computational times and costs compared to LES.