Pressure And Velocity Fields Decomposition Around A Flapping Wing

Abstract

In the present work, the velocity and pressure fields around a flapping airfoil in pitching/heaving sinusoidal motion are decomposed in modes in the wing-fixed reference frame. This approach is aimed at assessing the contribution of the fluid structures forming on the wing surface to the aerodynamic forces. The velocity field used for this work have been obtained through Particle Image Velocity experiments at a chord-based Reynolds number of 3600 and a Strouhal number equal to 0.2. The pressure field has been reconstructed from the phase-average velocity fields using a finite-differences Poisson solver. Finally, the velocity and pressure fields have been interpolated on a wing-fixed domain and decomposed using Proper Orthogonal Decomposition and Quadratic Stochastic Estimation to account for the quadratic relation between velocity and pressure. The decomposition identified vortical flow structures over the wing which model the evolution of bound vorticity, as well as leading edge and trailing edge vortices, over the wing. These modes contribute linearly to the chord-normal force by interacting with the constant free stream contained in the time average, as well as quadratically to the chord-wise force.