Interactive Effects of Wind Tunnel Sidewalls on Flow Structures around 2D Airfoil Model

This paper presents the effect of wind tunnel sidewalls on the wind turbine airfoils with experimental and numerical methods. The test is carried out in a low-speed wind tunnel at Re=2.62×105. Pressures acting on the airfoil surface are measured by a multiport pressure device. And, the oil flow visualization technique is used to investigate the flow field characteristics of the airfoil surface. Then, a numerical simulation was conducted with the measurement results. As a result, it is clarified the flow structures on the airfoil surface depend strongly on the angles of attack and the sidewalls. At small angles of attack, the three-dimensional separation caused by the interaction between the sidewall boundary layer and the airfoil boundary layer is very small, and only appears near the junction of the airfoil model and the sidewall. This corner separation becomes large with the increase of the angle of attack. At the middle part of the testing model, the boundary layer flow evolves into three-dimensional separation, i.e., stall cell, when the separation develops to an appreciate extent. The stall phenomenon will further spread from the center line to sidewalls with the increase of the angle of attack; and then, its development will be limited by the sidewall boundary layer separation. Comparably, the simulation shows that the sidewall make the pressure coefficient Cpdecrease, and proper boundary condition can maintain two-dimensional flow at large angles of attack by eliminating the influence of corner vortices.