Numerical study on the hydrodynamic lubrication performance improvement of bio-inspired peregrine falcon wing-shaped microtexture

Bio-inspired surface microtexture has been adopted in mechanical systems for its advanced lubrication performance. In this study, we discerned the aerodynamic characteristics of different parts of the peregrine falcon's wing, summarized the influence of its distinctive shape on the fluid flow, and, based on simplified geometries and the bionic concept, designed a novel wing-shaped microtexture to enhance lubrication performance in friction pairs. Its shape was simplified by the following parameters: area ratio S-p, dimensionless depth h*, and orientation angle alpha. Using a multiphase flow model, we investigated the effect of the above geometrical parameters on the lubrication performance of the wing-shaped microtexture by numerical simulation. The corresponding geometrical parameters of the wing-shaped microtexture to achieve optimum lubrication performance were: S-p = 30%/h*=1.75/alpha = 0 degrees. The wing-shaped microtexture's friction coefficient(COF) corresponded to a reduction of 18.8% and 20.7%, respectively, compared to the triangle and rectangular microtexture, which had the best lubrication performance for existing applications. The results showed that the wing-shaped microtexture enhanced the lubrication performance for three reasons: 1. The biomimetic leading edge created more negative pressure and cavitation zones; 2. The interference between positive and negative pressure zones was effectively mitigated; 3. The sharp design of the biomimetic trailing edge and tail wing concentrated the positive pressure zone while increasing its area. Two double-layer composite wing-shaped microtextures were further introduced to maximize friction reduction. The impact of inner-outer layer area ratio S-p* and inner-outer depth ratio h* on the lubrication performance was investigated. Their simulation results revealed that the optimal geometric parameters for the composite microtextures were S-p*=6.3%/hp*=3.0 and S-p*=12.7%/hp*=2.0, respectively. The configurations led to additional COF reductions of 7.6% and 10.56% compared to the single-layer wing-shaped microtexture. These insights offer valuable guidance for reducing friction and wear in mechanical systems.