Influence of Reynolds Number and Scale on Performance Evaluation of Lift-type Vertical Axis Wind Turbine by Scale-model Wind Tunnel Tests

Abstract

Abstract For Lift-type Vertical Axis Wind Turbine (VAWT), it is difficult to evaluate the performance through the scale-model wind tunnel tests, because of the scale effect relating to Reynolds number. However, it is beneficial to figure out the critical value of Reynolds number or minimum size of the Lift-type VAWT, when designing this type of micro wind turbine. Therefore, in this study, the performance of several scale-models of Lift-type VAWT (Reynolds number : 1.5x10 4 to 4.6x10 4 ) was investigated. As a result, the Reynolds number effect depends on the blade chord rather than the inlet velocity. In addition, there was a transition point of the Reynolds number to change the dominant driving force from Drag to Lift. Keywords : Vertical Axis Wind Turbine, Wind tunnel, Reynolds number, Performance, Scale effect. 1. Introduction and background Lift-type Vertical Axis Wind Turbine (VAWT) has difficulty of performance evaluation with scale-model wind tunnel tests, because of the scale effect depending on Reynolds number, and there is cost problem in field test with actual size Lift-type VAWT to evaluate several blade shapes or the size and setting angle of blade for performance improvement. If possible, it is useful to evaluate the performance of Lift-type VAWT with scale-model wind tunnel tests and these results can help us to investigate the possibility of Lift-type VAWT as micro wind turbine. However there were few reports [1][2][3] for the performance evaluation of Lift-type VAWT with scale-model wind tunnel tests and almost only the data of field test for actual size Lift-type VAWT [4] that is same type we are investigating in field test [5] were reported. For the reasons mentioned in the above, in this study, several scale-models of Lift-type VAWT were investigated for the performance with changing the pitch angle, blade chord length and blade shape as the experimental parameter of Lift-type VAWT. In performance test, low speed wind tunnel of blow down type was used and the diameter of scale-model of Lift-type VAWT was 1/7 to 1/10 compared with the one for field test [5] mentioned before. The data acquired from the performance tests were evaluated with Reynolds number (