Capturing downstream wake of a marine current turbine by URANS and SST-IDDES

Unsteady Reynolds-Averaged Navier-Stokes (URANS) and SST-based improved delayed detached eddy simulation (SST-IDDES) are used to compare the performance, flow field characteristics, and downstream turbine installation distance of a Marine Current Turbine (MCT). The flow domain is discretized with unstructured tetrahedral mesh using the Fluent 2020R1 meshing tool, sliding mesh method used for turbine rotation. The governing equation's convergence conditions are set to 10(-5). Second-order backward Euler and central differencing schemes are utilized for temporal and spatial discretization. It is found that power and torque coefficients predicted by both models match well with the available experimental data. The URANS model predicts relatively lesser transient properties than the IDDES model due to its isotropic character. Because of its anisotropic nature, the SST-based IDDES model predicts higher turbulence intensity. For both models, the tip vortex diffused near wake (3D) region, whereas the hub vortex diffused at 18D in URANS and 16.5D in SST-IDDES, supporting the assessment of downstream turbine installation distance. The percentage difference of power coefficient for both models is 2%, and the thrust coefficient is 1% at the optimum TSR (= 3.8). It is demonstrated that the SST-IDDES model is regarded as a reliable model to analyze the wake characteristics of marine current turbines.

Automated summary

In this study, the performance, flow field characteristics, and downstream turbine installation distance of a Marine Current Turbine (MCT) are compared using Unsteady Reynolds-Averaged Navier-Stokes (URANS) and SST-based improved delayed detached eddy simulation (SST-IDDES) models. Both models accurately predict the power and torque coefficients compared to experimental data. The URANS model shows less transient properties due to its isotropic character, while the SST-IDDES model predicts higher turbulence intensity due to its anisotropic nature. The results demonstrate that the SST-IDDES model is a reliable tool for analyzing the wake characteristics of marine current turbines.