  This paper deals with the investigation of flow field due to clap and fling
mechanism using immersed boundary coupled with lattice Boltzmann method. The
lattice Boltzmann method (LBM), an alternative to Navier Stokes solver, is used
because of its simplicity and computational efficiency in solving complex
moving boundary problems. Benchmark problems are simulated to validate the
code, which is then used for simulating flow over two elliptic wing of aspect
ratio 5 performing clap and fling flapping motion for different flow parameters
such as Reynolds number (Re = 75,100,150), advance ratio (J = 10E-3,10E-2,2)
and frequency (f = 0.05Hz,0.25Hz). Numerical simulation is able to capture
typical low Reynolds number unsteady phenomena such as, 'wake vortex wing
interaction', 'Kramer effect' and 'delayed stall'. The results are both
qualitatively and quantitatively consistent with experimental observation. The
parametric study involving different combinations of Re, f and J depict
distinctly different aerodynamic performances providing physical insights into
the flow physics. It is observed that a combination of low f, low J and high Re
flow results in better aerodynamic performance. Pronounced lift enhancement via
leading edge vortices are obtained in unsteady regime (J<1) compared to
quasi-steady regime (J>1). The role of leading edge vortices in enhancing lift
are investigated by studying the size and strength of these vortices for
different flow conditions. For a given Re, the magnitude of maximum lift
coefficient decreases with increasing f irrespective of the value of J; while
the same is enhanced with the increasing Re.
