Validation of Unsteady Reynolds-Averaged Navier-Stokes Simulations on Three-Dimensional Flapping Wings

A combined experimental and computational study is presented for a wing segment undergoing a combined pitching, plunging, and rolling motion at Reynolds number of 100,000, where transition takes place along laminar separation bubbles. The numerical simulation approach addresses unsteady Reynolds-averaged Navier-Stokes solutions and covers three-dimensional transition prediction for unsteady mean flows. The numerical simulations are validated using high-resolution, phase-locked stereoscopic particle image velocimetry for a three-dimensional flapping case with a reduced frequency of k = 0.25. The flow reveals strong unsteadiness resulting in moving laminar separation bubbles, whose spatial extensions are varying in the spanwise direction. The experimental results are well captured by the numerical simulations performed in this study. Because of the vortex structure in the wake of the wing segment, the three-dimensional aerodynamics cannot be reproduced as a spanwise sequence of two-dimensional results.