Scour around a mono-pile foundation of a horizontal axis tidal stream turbine under steady current

Abstract

Seabed scour induced by a pile-supported horizontal axis tidal stream turbine is likely to cause structural instability. Therefore, it's significant to gain an insight into scour process around a tidal stream turbine to make energy harness from tidal stream commercially viable. This study experimentally investigates seabed scour around a horizontal axis tidal stream turbine with a mono-pile foundation. Results of the analyses indicate that the existence of a spinning rotor amplifies scour process around the pile due to flow acceleration between blade tip and seabed. Flow intensity and tip clearance play an important role in effecting the scour process around the turbine model. The scour depth generally increases with increasing of flow intensity and decreasing of tip clearance. When the flow intensity increases or the tip clearance decreases to a certain value, the depth or size of scour hole could increase greatly if the velocity of accelerated flow exceeds the critical velocity of sediment materials. Compared with flow intensity and tip clearance, the impact of distance between rotor and pile seems to be minor. Based on experimental results, empirical equations are proposed for predicting the size of scour holes around the pile foundation of the turbine model.