Application of Reynolds Stress Model Using Direct Modeling and Actuator Disk Approaches for a Small-Scale Wind Turbine

Abstract

The Reynolds Stress Model (RSM) has been avoided for turbulence closure in CFD simulations of wind turbines, largely due to the computational expense and the high potential for numerical instability. The advantage of using RSM is having access to shear stresses that are not available from two-equation RANS-based closure models like k-e and k-w. Access to the shear stresses will aide in the understanding of how the blade design will affect the wake, particularly in the near-wake region. In this research, the RSM turbulence model has been successfully applied in simulating a three-bladed small-scale wind turbine through a direct-model approach and an actuator disk approach. In the direct-model method, the turbine blades were discretized within a rotating subdomain and in the actuator disk method, the turbine blades were modeled as a rotating disk using the Virtual Disk model available in Star CCM+. The transient Rigid Body Motion (RBM) simulation was able to accurately predict velocity deficit and tip vortices that compared well with hot-wire measurements and high speed images. The actuator disk method is more practical in simulating wind farms due to the simplified mesh and requires accurate information for lift and drag coefficients. Experimental results showed interaction between the tower and rotating blades can create significant turbulence in the wake. Experiments with multiple turbines showed how each turbine contributed to the velocity deficit and total turbulence intensity. For the experimental blade design, the velocity deficit recovered and turbulence intensity had dissipated within three rotor diameters.