Tadakazu Tanino

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

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 (

A Study on the Direction of Crack Propagation at Damaged Parts of Hot Dip Galvanizing Bath

At start-up operation of hot dip galvanizing baths to galvanize steel products, several leakage accidents of liquid zinc due to the damage at the vicinity of welded parts between side and bottom plates have been reported. Among these accidents, it is found that transferred liquid zinc solidified in the bath heated inadequately. In another paper, the authors investigate stress levels and directions at corners of the bath to clarify the cause of the damage applying unsteady heat conduction analysis, elastic and elastic-plastic analysis for solidified zinc inside of the bath as mechanical approaches. However, they have not studied the direction of the crack, that is, it starts from the vicinity of a welded part at the bottom plate and propagates downward vertically or 45 degrees toward outside of side plate, then changes its direction to be parallel to the bottom plate. This paper investigates the cause of the direction change of crack, which propagates downward then horizontally, at the corner of the bottom plate from mechanical and material aspects.