Numerical Investigations on Optimal Tip Speed Ratio of Wind Turbines Using BEM and CFD
AbstractAn optimum Horizontal Axis Wind Turbine (HAWT) geometry can be generated by comparing the power efficiency of different Tip Speed Ratios (TSR). The properties that generate the optimum geometry are sorted as choosing the right airfoil varying along the blade, blade width, twist angle and the Design Tip Speed Ratio (DTSR). The blade length and twist angle can be determined with the DTSR. The study chooses three different DTSR values 6, 7 and 8 for the investigation, since in literature, some researchers advice to choose between 5-10 and some others 6-8 [14] [15]. According to the three DTSR and chosen three standard airfoils (NACA 64-415, RISØ-A1-21, NREL S809), nine different HAWT geometries are generated. The chord length and twist angle of the nine geometries are calculated based on the Schmitz theory. For the theoretical calculation of the rotor power efficiency, an algorithm is programmed in MATLAB®, based on the Blade Element Momentum (BEM) theory. Also, the nine HAWT dimensions are integrated to a Computer Aided Design (CAD) code for the numerical calculation of the power efficiency by ANSYS® Fluent Computational Fluid Dynamics (CFD) computer package simulation program based on the Finite Element Method (FEM). The results found in both BEM and CFD are interpreted. How to determine the right geometry dimensions that generate the highest power efficiency is presented