Numerical Research of the Effect of Surface Biomimetic Features on the Efficiency of Tidal Turbine Blades

Wenxian Yang,Theodoros Alexandridis,Wenye Tian

doi:10.3390/en11041014

Abstract

Horizontal-axis axial flow tidal current turbine is regularly used to exploit the kinematic energy in tidal currents. However, the scaling up of tidal current turbine is very difficult. This is because strong tidal current only exists in the underwater region close to water surface, which implies that scaling up by enlarging rotor size is not always applicable to tidal current turbines. Hence, scaling up by improving the energy capture efficiency of the tidal turbine blade becomes a plausible choice. For this reason, apart from the numerous researches based on conventional aerodynamic and hydrodynamic theories, improving efficiency by biomimetic method is attracting increasing interest in recent years. It has been proved that leading-edge tubercles have positive contribution to improving the efficiency of tidal turbine blade. However, leading-edge tubercles can be made on blade only in the manufacturing process, as the post-production of them is quite difficult. Thus, how to improve the energy capture efficiency of the existing blades becomes a challenging issue. To address this issue, numerical research of the effect of surface biomimetic features on blade efficiency is conducted in this paper. For the sake of simplicity, surface bumps are investigated in this preliminary research in order to obtain a basic understanding of the effect of surface biomimetic features. In the research, the influences of surface bumps on blade surface pressure and the ratio of lift to drag forces are investigated in different bump array scenarios and at different tidal current speeds and the angles of attack. The calculation results have shown that surface bumps do improve the ratio of lift to drag forces of the blade in spite of their array arrangement, the angle of attack and tidal current speed. This suggests that the energy capture efficiency of both new and existing blades can be further improved if appropriate biomimetic features are deployed on the blade surfaces.

Highlights

Due to the periodic motion of the moon and sun relative to the earth, regular movements of the oceans and seas are formed
It is noticed that the contributions of the surface bumps to the FL /FD and T are different in different scenarios, i.e., improving the ratio of FL /FD by 0.2~1.6% and improving torque T by 0.3~2.6%. This suggests that the contribution of the bumps can be further improved through optimizing their array arrangement on the surface of the blade
The research is focused on investigating the influences of the surface biomimetic features on the blade surface pressure and the ratio of the lift to drag forces acting on the blade under different combination conditions of bump array arrangement, angle of attack, and tidal current speed

Summary

Introduction

Due to the periodic motion of the moon and sun relative to the earth, regular movements of the oceans and seas are formed. The kinematic energy of tidal current will decrease gradually with the increase of the underwater distance due to the gradually reduced tidal current speed [5] This means that once the capacity of a tidal turbine is raised up to a certain value, further scaling up of it by size enlarging approach will become very difficult. The positive contribution of the leading-edge tubercles to improving the energy capture efficiency of the blade has been validated in many numerical and experimental researches [13,14,15].

Numerical Model of the Biomimetic Blade

Computational

Numerical Calculations

10. Torque

Conclusions