Force and flow structures of a wing performing flapping motion at low Reynolds number (Q5956704)

The authors study aerodynamic forces and flow structures of a wing performing a simplified flapping motion that emulates the wing motion of small insects in normal howering flight. The governing Navier-Stokes equations are solved numerically. When the wing rotation axis is at 0.25 chord position and wing rotation is symmetrical with respect to stroke reversal, the numerical results show large peaks in \(C_L\) and \(C_D\) near the end of a stroke for the wing rotation. However, the wing rotation generates a vortical structure which induces strong downward velocity, reducing the lift production in the early part of the following stroke. When the rotation axis is moved rearward to the middle-chord position, the lift and drag peaks become smaller due to the wing rotation. In this case, the results show that the wing rotation generates a vortical structure that tends to prevent the relative motion between positive and negative vorticities, and reduces the lift production in the early part of the following stroke, which results in a smaller average \(C_L\).