Simulation of supersonic flow: comparison of LES against URANS and RANS turbulence models

Abstract

This study aims to analyze the influence of different turbulence models in capturing the flow profile in supersonic nozzles as ones used in steam jet ejectors. Based on the recent experiments by T. Sriveerakul.; S. Aphornratana.; K. Chunnanond [International Journal of Thermal Sciences 46 (2007) 812-822] computations were performed using three different turbulence models, a modified RANS model (SST k-ω), a URANS model with Scale Adaptative Simulation -SAS and the large eddy simulation (LES), with three different steam jet operational conditions, the simulation results were compared with experimental data. First, SAS and SST k-ω computations were performed with three meshes with different refinement level on a mesh independency study. It was observed that SAS model was more sensitive with mesh refinement. In less refined mesh the pressure profile obtained was very close to SST k-ω results indicating that mesh refinement and time step weren't enough to activate the source term included in ω. With two other meshes a SAS convergence was observed while these meshes are refined enough to use LES. LES time average values of the variables under study on the most refined mesh were included in the comparison. Furthermore Mach number plots along the equipment center line showed the shock waves formation and the pressure profile recuperation that occurs in the diffuser. The RANS SST k-ω turbulence model results showed the smallest errors related to the experimental data.