I need to analyse an airfoil fitted with a oscillating Gurney flap at the trailing edge (on the pressure surface). The airfoil is fixed pitch, whilst the flap oscillates linearly up and down (from zero length i.e. NO FLAP, to 1.5% chord length) with time. The flap has no thickness for simplicity. What is the best way to approach this problem? At first a DEFINE_CG_MOTION UDF was considered for rigid body motion, however this would result in the flap oscillating across BOTH the pressure AND suction surface of the airfoil (as the flap retracts from the pressure surface, it is deployed in the suction surface, and vice versa… i do not want this! I want the flap to oscillate on the pressure surface ONLY). Would it be easier to model the flaps linear oscillation as the flap growing and shrinking with time? If so, what is the method?

Thank you in advance for your time and expertise

N.B. this is a 2D problem