Simulation of cartesian cut-cell technique for modeling turbulent flow in asymmetric diffusers using various turbulence models

Abstract

The process of accurately predicting the behavior of the separated turbulent flow requires extraordinary efforts, whether it is choosing the appropriate computational mesh or using the appropriate turbulence model for that. The present study introduces a comparative numerical investigation for predicting the behavior of turbulent-separated flow in asymmetric diffusers. Numerical simulation using a finite volume approach of incompressible Reynolds Averaged Navier Stokes equations (RANS) with three turbulence models (Standard k−ε, Chen-kim, and modified Chen-kim) is here performed in a self-developed FORTRAN code. The treatment of asymmetric diffusers poses challenges due to the complex flow behavior and geometry. To address this, a developed cartesian cut-cell technique is employed, which provides compatibility with solid boundaries and efficiently handles complex geometries This developed cut-cell technique is checked to treat its ability to predict complex turbulent flow with the presence of strong pressure gradient for correctness and convergence, as well as testing the proposed turbulence-models performance. So, verifications are performed by comparing the present computational results of asymmetric-diffuser flow characteristics with available experimental and LES data. The proposed models reveal acceptable agreements in most cases, especially the modified Chen-kim model, which shows a great match with the experimental and LES results for all flow characteristics. The standard k-ε model fails to predict the flow-separation well in most comparisons. Extended computational studies are also introduced to investigate the effects of diffuser cant angles (4 to 15°) and area ratio (2.4 to 7) on the diffuser flow behavior using the successfully modified Chen-kim turbulence model. The parametric study reveals that these two factors strongly affect the diffuser performance, where the pressure recovery, skin friction coefficients, and separation bubble size are provided.