Viscous-inviscid interaction technique for prediction of aerodynamic characteristics of HAWT blade S809 airfoil

Abstract

Predicting the HAWT blades loads accurately is one of the most important parts in the wind turbine aerodynamics calculation, and is based on an accurate evaluation of the aerodynamic coefficients and of the upstream velocity field. However, these aerodynamic loads estimations remain a complicated task to perform due to the complex nature of the flow around the blades, and to their cyclical fluctuations, which can be a significant source of fatigue and vibration, resulting from the yaw, stall or turbulent conditions where the HAWT operate mostly. The main aim of the present paper is to develop a sophisticated computational model that can predict aerodynamic coefficients without using great amounts of computer time. This model is based on a strong viscous-inviscid interaction technique using the blowing velocity concept. The inviscid air flow around S809 is modeled using the potential theory of arbitrary wing sections and Prandtl-Glauert compressibility correction, the 2-D pressure potential coefficients calculations for any orientation and Reynolds number, were made. Whereas the viscous part is modeled by using the Von Karman momentum integral equation, which is resolved according to the flow regime, laminar or turbulent, the onset of flow transition governed by the viscous effects was determined by using Michel's criterion, and the boundary layer separation point location is determined from the shape factor by using Head's criterion. The numerical results of aerodynamic characteristics of HAWT blade S809 airfoil have been benchmarked against experiments for different angle of attack and Reynolds numbers, and generally a good agreement is obtained.

A novel technique for the calculation of post-stall aerodynamic coefficients for S809 airfoil

“…For the potential flow formulation, the potential theory of wing sections is implemented in previous works by the authors [13,14] and deals with the determination of the velocity distribution around airfoil,…”

“…So, the boundary layers modelling is required. For this purpose, authors used the momentum integral equation [14], ( )…”

“…Separate formulations for the external potential flow and the viscous boundary layer are mixed interactively to afford a composite solution to the entire flow field (Figure .2). For this purpose, the strong interaction method [14] which employs the blowing velocity concept as an interacting agent is adopted. This blowing velocity distribution is used as a boundary condition in the inviscid method in order to include the effects of boundary layer in the potential flow solutions.…”

“…In previous works [13,14], authors showed how to mathematically reproduce the aerodynamic coefficients for the S809 airfoil in the pre-stall region using an interacted viscous-inviscid approach. For this approach, the major assumption suggests that the flow can be separated in two sectors: within the boundary layer where the fluid is treated as viscous and outer this layer where the flow is treated as potential [15].…”