Connection between vortex structures and the center of pressure in unsteady separated flow over pitching swept wings

We analyze the stability characteristics of elastically mounted rigid swept wings using previously acquired measurements (Zhu et al. JFM, 2023). The NACA0012 wings featured sweep angles of 0°, 10°, and 20°, and experienced large amplitude sinusoidal pitching instabilities below a critical torsional spring stiffness. The time-varying location of the center of pressure (CP) is calculated from the measured forces and moments. Although there is little change in the CP in the cross-chord direction, the spanwise position shows considerable movement, and its trajectory varies with sweep angle due to the changing strength and evolution of the leading edge and tip vortices. The Force Moment Partitioning Method (FMPM) is applied to time-resolved stereo PIV measurements, and used to disentangle contributions due to wing kinematics, vortex and viscous phenomena as well as the different roles of the leading edge and tip vortices.