CFD Simulations to Investigate the Drag Reduction Performance of Shark Skin Inspired Riblet Structure

Initially, people think the smallest skin friction happens on the planar surface until riblet structure is first discovered on the surface of shark skin in the late 1960s, which proves to have a drag reduction performance experimentally. However, the mechanism behind the physical phenomenon is not clear even though pretty a large amount of efforts have been devoted in the past several decades. The aim of this project is to employ CFD to explore the physics of the riblet structure. And the mesh plan of the cross section is shown in figure 1.

Figure 1. Mesh plan of cross section.

A fully developed turbulent channel flow is employed in this research to investigate the performance of 3D riblet structure. RANS has been applied to investigate this structure and a drag reduction of 2% percentage has been obtained. Afterwards, a more accurate method of LES has been under research to give a more detailed description of the near wall region environment.

Figure 2. Wall shear stress of the riblet surface (left) and flat plate (right).

Part of the mechanism of riblet drag reduction could be seen from figure 2, that the shear stress of the flat plate is large compared to that of the rib surface except the tip region. Also, the simulations have been carried out under the velocity range from 0.7m/s to 5.6 m/s, and are compared to the experimental results of Reidy (1987) and NASA Langley wind tunnel test results.

Figure 3 shows the vorticity in the streamwise direction which indicates the physics of the riblet drag reduction by changing the turbulent boundary layer structure. In the future, more LES cases will be carried out to see a more detailed and accurate result. Figure 3. Stream-wise vorticity in the longitudinal section.

For more information about the project contact Yansheng Zhang (yansheng.zhang.100@strath.ac.uk) or Osman Turan (o.turan@strath.ac.uk), Professor at the Department of Naval Architecture, Ocean and Marine Engineering at the University of Strathclyde.