Accurate Stall Prediction for Thick Airfoil by Delayed Detached-Eddy Simulations

Abstract

The continuous increase in wind turbine blade length raises a serious question about how to effectively reduce the blade mass. As one of the solutions, recently, some wind turbine manufacturers are moving towards longer blades with thicker airfoils. As most of the numerical simulation experiences are based on thin airfoils, the present paper focused on airfoils with thickness to chord ratios of 30% and specifically focused on the influence of spanwise length on the numerical results. Airfoils with a spanwise length of 0.1 to 5 chords were simulated utilizing the Delayed Detached-Eddy Simulations (DDES) approach. One of the important objectives was to identify the necessary grid resolution and configuration while still maintaining accuracy under a deep stall situation. It was found that the spanwise length of the computational domain had a crucial influence on the prediction of lift and drag. At a stall angle of attack, the aerodynamic force could not be accurately predicted when the airfoil span was reduced to 0.3 chords, even with a high grid density. The periodicity of the spanwise flow was clearly visible when the airfoil span was extended to 5 chords.

Investigating 3-D Flow Characteristics of Wind Turbine Airfoils using Delayed Detached Eddy Simulations at High Reynolds Numbers

“…The investigation included discussions on grid independence, boundary conditions, time integration, and grid spacing. Sun et al [10] focused on accurate stall prediction for a thick wind turbine airfoil and the effect of span length in capturing the 3D turbulent nature of flow over the airfoil. This was achieved by solving Shear Stress Transport (SST) based Delayed Detached Eddy Simulation (DDES) equations in an O-type computational domain.…”