Numerical study on drag reduction and wake modification for the flows over a hydrofoil in presence of surface heterogeneity

Abstract

In this article, direct numerical simulations of flow around NACA0012 hydrofoil with superhydrophobic surface (SHS) is presented. Surface heterogeneity takes into account by periodic no-slip and shear-free grates on the surface. The study is conducted for a range of 0 o − 25 o degree angles of attack and at fixed Reynolds number ( Re ) 1000. SHS leads to effective Navier slip on the hydrofoil surface and corresponding changes in velocity profile. Bubble separation delays for higher gas-fraction ( G.F ), and minimizes the vortex shedding effects. As a result, flow remains two-dimensional (2D) for higher angles of attack as compared to flow over three-dimensional (3D) hydrofoil with no-slip boundary. Both the drag reduction and enhancement of lift force are observed. Maximum lift are observed at α = 13 o , while the drag force continues to decrease with the gradual increase in angle of attack and patterned micro-grates fraction. Mode C with smaller wavelength is observed at α = 15 o . Furthermore, increase in gas-fraction leads to increase in slip length which thickens the boundary layer and mimics the vorticity implies drag reduction. Thus, replacement of the no-slip surfaces by superhydrophobic surfaces can be treated as a promising drag reduction technology.