Numerical investigation of the natural transition in flat-plate boundary layers on superhydrophobic surfaces considering the influence of the leading edge region

The natural transition in flat-plate boundary layers on superhydrophobic surfaces is studied while considering the influence of the leading edge region. A method for calculating basic laminar flow on superhydrophobic surfaces while considering the influence of the leading edge region is proposed, which accurately obtains the flow field in the whole computational domain from the leading edge region to the downstream region with acceptable computational load. The results obtained by this method are compared to those ignoring the influence of the leading edge region, such that this influence can be seen. The influence decreases the thickness of the laminar boundary layers on superhydrophobic surfaces and increases the slip velocity on the wall. The linear stability of the boundary layers is also analyzed. The influence of the leading edge region delays the critical location of flow instability on superhydrophobic surfaces and narrows the unstable zone. The eN method is used to predict the transition locations. The influence of the leading edge region further delays the transition location, and the transition delay effect becomes stronger as the slip length or the oncoming flow velocity increases. Furthermore, a method for predicting the spectrum of wall fluctuating pressure in the laminar flow region over underwater vehicles is proposed. At the downstream region, the amplitude of the wall fluctuating pressure increases and the frequency range decreases. Superhydrophobic surfaces suppress the wall fluctuating pressure, and the influence of the leading edge region enhances this suppression effect.