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 [Formula: see text] 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 [Formula: see text], 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 [Formula: see text]. 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.

Passive Drag Reduction Technologies

“…Several studies proved SHS as a promising DR technology. SHSs alter the critical Reynolds number as well [45]. Fig.…”

“…(Left) schematic diagram of velocity gradient over SHS, (right) normalized slip velocity with gas‐fraction defined by ( L–w )/ L for flow past a NACA0012 having periodic slip and no‐slip surface 45.…”

“…A detailed numerical study of NACA0012 for different angles of attack was conducted by Kouser et al. 45, 69. The superhydrophobic surface was modeled by considering the slip/no‐slip (gas fractions) boundary condition on the surface of NACA0012 as illustrated in Fig.…”