Wind tunnel test to investigate transition to turbulence on wind turbine airfoil

Abstract

The choice of the airfoils with excellent aerodynamics characteristics is an essential step in the design of wind turbine blade in order to obtain optimal performances. Wind tunnel test to investigate transition to turbulence on wind turbine airfoil was performed in the Universiti Teknologi Malaysia Low Speed Tunnel. Aerodynamic characteristics of a NACA 64(4)-421 airfoil in a two-dimensional setup, such as lift, drag and pressure coefficients were measured for two main cases. In the first case, tests were carried out on a clean airfoil (no turbulator) and in the second case, three configurations with three different positions of turbulator at x=10%, 20% and 50% of chord were tested. A Steady-state, two-dimensional CFD calculations were also carried out for the airfoil in same scale as experimental test using commercial CFD code, Ansys FLUENT 14. The surface coordinates of the experimental airfoil model were measured by coordinate measurement machine (CMM) and optimized in ICEM CFD software included in the Ansys package to create the related geometry and mesh. All experimental and numerical analysis were performed at velocities of V=22, 33, 45, 56, 61 m/s and at angle of attacks ranges between -6? to +30?. For the simulation, a minimum of 85000 grids was used to get a grid independent solution. To simulate the transition phenomena, K-?-SST turbulent model was used. Different types of mesh were analyzed in detail by comparing agreement between the simulated aerodynamic characteristics with experimental results. There are good agreement between experimental results and numerical results by using K-?-SST model. Both lift coefficient and pressure coefficient in experimental and numerical studies have good agreement with each other but it is not true for drag coefficients. Also according to different meshes, we found that a mesh with unit zone which contains K-?-SST model is the best model according to the convergence speed and accuracy. The effects of turbulator used in the experiment was not significant. In conclusion the study is partly successful.