A lattice Boltzmann framework for analysis of ‘clap and fling’ motion of finite thickness membranes

Abstract

In the past two decades, the lattice Boltzmann method (LBM) has offered itself as an alternative framework compared to the Navier Stokes simulations. However, the applicability of this method to simulate moving boundary problems has not received sufficient attention. The present study primarily focuses on developing and employing the halfway bounceback LBM to analyse the flow dynamics associated with the flapping motion of finite-thickness wings. A two-dimensional numerical model for one and two-winged ‘clap and fling’ stroke has been developed to study the aerodynamic performance of insect flight. The influence of kinematic parameters such as the percentage overlap between translational and rotational phase , the separation between two wings and different Reynolds numbers Re on lift generation has been studied and presented here. In addition, the time-dependent behaviour of the leading and trailing edge vortices and their role on lift generation in clap and fling type kinematics has been identified. Based on simulation data, regression analysis was carried out to express the mean lift coefficient as a function of the varied parameters. Results show that overlap ratio is the most influential parameter in enhancing lift. With increase in separation , the reduction in drag is far more dominant than the decrease in lift. With an increase in Re (which ranges between 8 and 128), the mean drag coefficient decreases monotonously, whereas the mean lift coefficient decreases to a minimum and increases thereafter. This behaviour of lift generation at higher Re was characterised by the ‘wing-wake interaction’ mechanism which was absent at low Re.