Effects of Leading-Edge Tubercles on Hydrodynamic Characteristics at Different Reynolds Numbers

Abstract

Recently the leading edge tubercles which are believed to significantly help the whale to execute rolls and loops under water have attracted great attention as one of the passive flow control methods. Many researchers have studied the effects of the convex structure of a humpback whale on the aerodynamic performance of the blade. However, the effect of leading edge tubercles on hydrodynamic characteristics, especially in the turbulent regime, is still being investigated. The purpose of this paper is to investigate Reynolds number effects on the hydrodynamic characteristics induced by a hydrofoil with leading edge tubercles in transitional and near-turbulent regimes using computational fluid dynamic. The Reynolds numbers based on chord of transition and near-turbulent regimes are respectively 160,000 and 1,000,000. It is found that the tubercled hydrofoil has a spanwise pressure gradient at the leading edge, and the pressure gradient between the peak and trough drives the fluid to the low pressure region. Three-dimensional laminar separation bubbles (LSBs) are formed after the fluid flow over the hydrofoil. As the angle of attack increases, the separation bubbles move forward. Under small angles of attack, the pressures, spanwise velocity and normal velocity at the two Reynolds numbers are similar in the distribution, but the pressure and velocity are very different under large angles of attack. In addition, the position and shape of the LSBs are different at the two Reynolds numbers. The range of LSBs is larger at low Reynolds number, because complete turbulence at high Reynolds number inhibits flow separation. The numerical simulation results show that the influence of the leading edge tubercles on the lift and drag of the foil is different under different Reynolds numbers.