Assessment of URANS and LES Methods in Predicting Wake Shed Behind a Vertical Axis Wind Turbine

TL;DR

This study compares URANS and LES computational methods in predicting wake shed behind a vertical axis wind turbine, using high-fidelity simulations and POD analysis to evaluate flow structures and model accuracy.

Contribution

It provides a comprehensive comparison of RANS and LES methods for VAWT wake prediction, including POD analysis to interpret flow structures and model performance.

Findings

LES captures flow dynamics more accurately than RANS.

POD analysis reveals key flow structures and scales.

Model performance varies with TSR conditions.

Abstract

In order to shed light on the Vertical-Axis Wind Turbines (VAWT) wake characteristics, in this paper we present high-fidelity CFD simulations of the flow around an exemplary H-shaped VAWT turbine, and we propose to apply Proper Orthogonal Decomposition (POD) to the computed flow field in the near wake of the rotor. The turbine under consideration was widely studied in previous experimental and computational investigations. In the first part of the study, multiple Reynolds-Averaged Navier-Stokes (RANS) simulations were performed at the Tip Speed Ratio (TSR) of peak power coefficient, to select the most accurate turbulence model with respect to available data. In the following step, further RANS numerical simulations were performed at different TSRs to compare the power coefficient against experimental data. Then, Large Eddy Simulation (LES) was applied for multiple TSR conditions. The spatial and temporal POD modes along with modal energy for the RANS and LES results were extracted, and the performance of the turbulence models was assessed. Also, an interpretation of the POD modes with respect to the flow structures was given to highlight the most significant time and length scales of the predictions considering the different dynamical levels of approximations of the computational models.