Aerodynamic Force and Flow Structures of Two Airfoils in Flapping   Motions
  Aerodynamic force and flow structures of two airfoils in tandem configuration performing flapping motions are studied, using the method of solving the Navier-Stokes equations in moving overset grids. Three typical phase differences between the fore- and aft-airfoil flapping cycles are considered. 
Shi Long Lan and Mao Sun