CFD Modeling of a Pitching Airfoil for the Estimation of the Performance Curve in an H‐Rotor Vertical Axis Wind Turbine

Abstract

In this work, the performance curve of a straight‐bladed vertical axis wind turbine (VAWT) is estimated through a CFD two‐dimensional modeling of a single airfoil under unsteady pitching motion. A typical URANS approach, with a k‐ω SST turbulence model and UDF functionalities, has been employed to simulate a fixed airfoil under variable inlet conditions. Induction factors are previously computed using a simple stream tube model (SSTM) in an iterative process. Frequencies and amplitudes of the pitching motion are modified to simulate the operative range of tip‐speed ratios (TSRs) for the wind turbine. The obtained results have been compared with experimental curves of a 0.5 solidity turbine measured in a wind tunnel. The experimental results of the wind‐tunnel turbine provide a maximum Cp value of 0.22 at a TSR = 3.1, while the numerical procedure estimates a value of 0.33, also at TSR = 3.1. Despite of the discrepancy, due to the 2D assumptions in the simulation, the procedure makes reliable and more accurate estimations than traditional analytical models with steady coefficients. This alternative methodology significantly reduces the computational cost. Moreover, these nonrotating simulations allow more robust and practical routines that can be easily implemented in optimization algorithms for the design of VAWTs.