Experimental investigation of flow-induced vibration of a pitch-plunge NACA 0015 airfoil under deep dynamic stall

The flow-induced vibration of a NACA 0015 airfoil model with pitch and plunge degrees of freedom is investigated in a high-speed wind tunnel using motion sensors, pressure sensors on the airfoil surface and synchronized high-speed Schlieren visualizations of the unsteady flow field at Reynolds numbers Re=180000-570000. Compared to other studies, the model has considerably smaller dimensions (with a chord length of 59.5 mm) and operates at higher flow velocities (from 37 to 125 m/s). With a relatively low pitch to plunge natural frequency ratio and zero initial incidence angle, the model is highly susceptible to deep dynamic stall instability with the peak-to-peak pitch amplitude reaching up to 90°. The limit cycle response of the system as a function of freestream flow velocity is reported in detail, together with synchronized Schlieren visualizations of the flow field revealing the boundary layer behavior during dynamic stall. With increasing inflow velocity, the plunge amplitude increases dramatically, accompanied also by slight rise in the frequency of oscillation and decrease of the phase lag between pitch and plunge. The pitch amplitude has a maximum at 62 m/s and further decreases with increasing flow velocities.