Unsteady Viscous Flow Analysis around Horizontal Axist Wind Turbine Rotor using Vortex and Panel Methods

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This project has been proceeded to establish a basis of numerical calculation tool for analyzing incompressible viscous flow fields around rotor blades of horizontal axis wind turbines, adopting a vortex method along with a panel method (boundary element method) within the period of 1997 and 1998 of academic years. The vortex method is one of the powerful tool for the analysis of high Reynolds number, unsteady and outer flows. The final objective of the project is to estimate three dimensional flow nature in the vicinity of the rotor blade including the flow separation near the blade root, which has been difficult for the existing prediction models to describe.At the beginning of the project, the flow around two dimensional airfoil section (MELO 12 ; designed by Mechanical Engineering Laboratory of MITI) was analyzed applying mainly the third level model of the vortex method. In this model the vortices from the surface of the body are treated as the vortex sheets and the vortex blobs at a certain distance from the surface. Compared with the calculation by the second level model of the vortex method, the third level model consumes longer calculation time and provides larger instability of the flow fields because of larger number of vortices introduced for the calculation.Effects of discretizing method of the blade surface into panels as well as panel number on the calculated results were examined carefully especially near the trailing edge, applying to the airfoil sections of MELO12 and symmetric Joukowski. As a result, a small thickness artificially given at the trailing edge can improve the convergency of the calculation and provide more realistic results.