Shock-buffet analysis on a supercritical airfoil with a pitching degree of freedom

Abstract

The interaction between the transonic flow around a spring mounted OAT15A airfoil model and the resulting pitching motion of the model were investigated with the goal of understanding the dynamics of the occurring phenomena. The experiments were performed at a free-stream Mach number of 0.74, a Reynolds number of Re c= 3.1 × 10 6, and a mean angle of attack of 5. 8 ∘. A periodic pitch motion with an amplitude of the angle of attack of ±0.9∘ was observed for these flow conditions. The dominant structural frequency of the airfoil’s pitch motion was adjusted to be in the range of the natural buffet frequency of the flow with inhibited pitching motion of the model. The structural motion locks into the frequency of the shock buffet with the pitching degree of freedom at a dominant frequency of 115.5 Hz. Velocity field measurements by means of high repetition rate particle image velocimetry (PIV) were used to capture the motion of the shock and to determine the state of the boundary layer flow for the different phases of the model motion. The PIV results with high temporal resolution allow the detailed observation of the evolution of the different phases of the buffet cycle. Mean values and statistical quantities, spectra and space-time correlations were determined from the measurement data to analyze the flow effects. It was possible to estimate the convection velocity of turbulent structures in the detached boundary layer. Graphical abstract: [Figure not available: see fulltext.]