Evaluation of RANS-based turbulence models for isothermal flow in a realistic can-type gas turbine combustor application

TL;DR

This study evaluates various RANS turbulence models for simulating isothermal flow in a gas turbine combustor, highlighting their strengths and limitations in predicting complex swirling flows.

Contribution

It provides a comparative assessment of standard two-equation models and LPS-RSM for confined swirling flows in combustors, emphasizing the need for more advanced models.

Findings

SST k-omega model was most accurate among two-equation models.

LPS-RSM showed some promise but had significant discrepancies.

Isotropic turbulence assumptions limit model accuracy in swirling flows.

Abstract

The present study assesses RANS-based turbulence models to simulate isothermal flow in a combustor representing a constituent can combustor of can-annular configuration used in jet engines. Two-equation models (standard $k-\epsilon$, realizable $k-\epsilon$, standard $k-\omega$, SST $k-\omega$), and Linear Pressure Strain - Reynolds Stress Model (LPS-RSM), are assessed by comparing their predictions of mean axial and transverse velocity, turbulent kinetic energy, and shear stress with the experimental data at the primary and dilution hole planes in combustor. While the two-equation models generally have failed to predict the confined swirling flow at both positions accurately, the SST $k-\omega$ model yielded the most accurate, followed by standard $k-\omega$ and realizable $k-\epsilon$ models. The discrepancies between the computational and experimental results could be attributed to the isotropic turbulence assumptions, which, however, are invalid for confined swirling flows. Further, the two-equation model formulations cannot capture the intricacies of vortex flow and its interaction with the surroundings in confined swirling flows. LPS-RSM, which considers turbulence anisotropy, showed some promise, although overpredicted results follow the trend with experimental values at the primary holes plane. However, at dilution holes plane, the model overpredicted the velocity field and underestimated turbulence field, including turbulent kinetic energy and shear stress. These observed discrepancies can be ascribed to the pressure-strain correlation in the LPS-RSM, which assumes the pressure is a linear function of the strain-rate tensor. However, for complex flows, this linear assumption is quite simplistic. Hence, this study suggests that more advanced turbulence models such as non-LPS-RSM are needed to accurately predict the confined swirling flow in combustors.