Enhancement of OWC Wells turbine efficiency and performance using riblets covered blades, a numerical study

•The micrometer protrusions similar to shark skin (riblet) were added to the Well turbine blades to increase the efficiency and enhance the operating range.•Riblet covered blades cause 18.36% and 16.82% increase in the torque and efficiency respectively.•Decrease of separated boundary layer for riblet covered Wells turbine at high flow coefficients leads to an increase in the operating range of the turbine.•Riblet covered surfaces plays an important role in increasing the trust coefficient.•Riblet covered surfaces in the blade tip area improves the pressure distribution on the blade and increases the average efficiency. Oscillating water column (OWC) is one of the first devices used for wave energy conversion. This wave absorber converts pneumatic energy to mechanical energy through a Wells turbine. In this paper, the micrometer protrusions similar to shark skin (riblet) were added to the Wells turbine blades to investigate its effect on the improvement of the device performance as well as its efficiency. The flow interaction with Wells turbine was modeled using Star CCM+ software. In this process, the structured grid was used throughout the study domain. The numerical modeling results show that for high flow coefficients, applying riblet on the blade surface results in an increase in the thrust coefficient and a decrease in the blade suction surface pressure. The proposed design significantly improves the pressure distribution around the blade and the separation point, as well as the efficiency of the turbine within the computational range. Another benefit of riblets is the delay and reduction of separation at the tip of the blade. In addition, there is an increase of 18.4% in the torque coefficient and 16.8% in the efficiency of the riblet covered blades in deep fatigue conditions. Furthermore, the results show that in computational range, the Wells turbine demonstrates 2.3% increase in efficiency.