Effects of torsional stiffness on hydrodynamic performance of an oscillating and passive pitching trapezoidal panel

In this work, a three dimensional hinged oscillating and passive pitching torsional spring model is proposed. The oscillatory motion is prescribed at the leading edge while the pitching motion is the result of interaction of hydrodynamics, moment of inertia and torsional spring torque. The unsteady hydrodynamics of the trapezoidal panel (AR=2.025) and flow fields are simulated by an in-house immersed-boundary-method based direct numerical simulation (DNS) solver. The oscillation amplitude is 0.4 chord length while the reduced frequency k=0.4 and the Reynold number is set to 500. The Cauchy number is changed to study the effects of torsional stiffness on the hydrodynamics of the panel. Results show that the panel generates a simple-harmonic pitching motion and generates the maximum time averaged thrust when Ch=0.07 and a pair of reversed trailing edge vortices are shown to be generated in each circle. When Ch number is closed to 0.17, the panel has the best propulsion economy.