An experimental investigation of the subsonic stall flutter

This paper reports on experimental investigations of the subsonic stall flutter of a wing in a wind tunnel.
Stall flutter (also know as Dynamic Stall) is a LCO phenomenon occurring when all or part of the flow over
a wing separates and re-attaches at least once during a full oscillation period. In order to investigate the
aeroelastic effects of the nonlinearity introduced by the boundary layer growth and flow separation and the
ensuing stall-induced LCO, a wind tunnel model of a wing undergoing stall flutter is designed, built and
tested. The model is a rectangular wing with constant cross-section free to move in the pitch and plunge
directions, restrained by torsional and linear springs respectively. The motion of the wing is measured using
laser displacement probes. Two types of stall flutter are observed and measured: 1. Non-symmetric stall
flutter, where the flow separates over one side of the wing only, and 2. Symmetric stall flutter, where the flow
separates over both sides of the wing (deep stall). The bifurcation behaviour of the wing is very complex and
both types of LCO can be observed during a single response history.