The goal of this investigation is to develop high performance Vertical Axis Wind Turbines (hereafter VAWT) for clean energy supply systems. For this purpose, we attempted to simulate flow around a VAWT with Large Eddy Simulation (LES). Since the angles of attack of VAWT are widely changed during the rotor rotation, large scale separation and interaction between the turbulent wakes are occurred [1]-[3]. Therefore, unsteady and high accuracy simulation is necessary to simulate flow around a VAWT. LES with a sliding mesh technique was utilised to solve the complicated flow around the VAWT. The numerical results show the large separation occurred and unsteady aerodynamic forces were observed in the wake of VAWT. The time ratio of negative torque generated after rotor rotation time was small at a tip-speed ratio (TSR) of 3. Therefore, the maximum power coefficient can be obtained at a TSR of 3. In the case of high TSRs, the predicted results were in good agreement with that of momentum theory. However, the discrepancies among torque coefficient between the results of LES and momentum theory were large at low tip-speed ratios. The discrepancy seems to occur with the effect of dynamic stall. The study revealed that the LES is a suitable method to estimate the performance of VAWT.
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