Effect of passive flow control on the aerodynamic performance, entropy generation and aeroacoustic noise of axial turbines for wave energy extractor

Wells turbine is the simplest type of an axial flow self-rectifying air turbine that can be used in conjunction with Oscillating Water Column (OWC) system in the extraction of ocean wave energy. It has been noticed that this turbine is subjected to early stall. As a consequence, several attempts for improving the energy extraction performance of Wells turbine within the stall regime have been investigated. One of these attempts was using an inclined slot as a passive flow control to obtain a delayed stall. In the following study, the impact of varying the angle for the slot on the performance of Wells turbine in the stall regime was investigated. Furthermore, the first law of thermodynamics and the entropy analysis has been used to examine the effect of the slot angle on the entropy generation features around the turbine blade. Moreover, Investigation of slot angle effect on the aerodynamics noise emission from Wells turbine airfoil during the normal operation and the stall regime is covered in this study. The blade of turbine with optimum angle of slot was investigated using the OWC based on actual data from the Egyptian Northern Coast. It was found that the optimum slot angle is 10° clockwise which results in 3% improvement in the torque coefficient before the stall and 15% after the stall as compared to the 0° slot. Otherwise, it gives a lower global entropy generation rate than the 0° slot by 4% before the stall and 3% after the stall. Furthermore, using airfoil of blade turbine with a slot resulted in a reduction of aeroacoustic noise by −21.2% at the stall regime under oscillating flow conditions. © 2018 Elsevier Ltd