Turbulence Model Comparison for Compressors SST vs k-ω vs RSM

Turbulence modeling plays a vital role in compressor simulations by enabling accurate prediction of complex flow phenomena. These phenomena, including strong pressure gradients, boundary-layer separation, and rotational effects, pose significant challenges for numerical simulations. To address these complexities, various turbulence models have been developed, each offering unique advantages and limitations. The choice of turbulence model, such as the Shear Stress Transport (SST) K-omega, Standard K-omega, and Reynolds Stress Model (RSM), significantly affects the accuracy, numerical stability, and computational cost of the simulation. Selecting the most suitable model is crucial to achieving reliable results while minimizing computational resources.

The SST K-Omega turbulence model, also known as the Shear Stress Transport model, is widely regarded as an industry standard for turbomachinery and compressors. This model effectively combines the near-wall accuracy of the K-Omega model with the free-stream independence of the K-Epsilon model. The resulting hybrid approach enables excellent predictions of flow separation under adverse pressure gradients. As a result, the SST K-Omega model is well-suited for addressing complex compressor flows. Its reliability in predicting compressor performance and capturing separation in diffusers has made it a preferred choice in industry applications. However, its accuracy can be limited in highly curved flows unless curvature corrections are applied.

The Standard K-Omega turbulence model is widely used in computational fluid dynamics for its ability to accurately capture near-wall boundary layer flow. This model is notable for its improved performance in the viscous sublayer, yielding more accurate results than the K-Epsilon model without the need for complex damping functions. The Standard K-Omega model is particularly well-suited for capturing fluid flow behavior in regions with significant near-wall interactions. However, its application is often limited by extreme sensitivity to inlet boundary conditions, which can lead to instability and inaccuracy in complex or rapidly changing flows. In compressor simulations, the Standard K-Omega model has largely been superseded by the SST K-Omega model due to stability concerns. Despite its limitations, the Standard K-Omega model remains a widely utilized tool in turbulence modeling.

The Reynolds Stress Model (RSM) is a turbulence modeling approach that delivers high-fidelity simulations of complex, highly swirling, or rotating flows, making it an attractive choice for applications that require detailed flow-field analysis. By directly solving the Reynolds stress transport equations, RSM relaxes the isotropic eddy-viscosity assumption commonly used in K-Omega models, allowing for a more accurate capture of turbulence anisotropy in rotating impellers. This, in turn, enables the model to effectively simulate the intricate flow dynamics present in such applications. However, the increased accuracy of RSM comes at a high computational cost, requiring up to 7 equations to be solved, which can lead to convergence issues and reduced numerical stability.