Exploration of Stall Dynamics on a High-Speed CRM wing

The sensitivity of the flowfield and the resulting loads / moments are examined on a 4% scale, half-span, high-speed version of the Common Research Model (CRM-HS). A range of Reynolds numbers and angles of attack were examined using a combination of tuft flow-visualization and Particle Image Velocimetry (PIV) in the 8 ft by 12 ft Kirsten Wind Tunnel (KWT) at the University of Washington. The tufts showed a leading edge-tip stall at every tested condition, with separation delayed to higher angle of attack at higher Reynolds numbers (𝑅𝑒). Approximate Reynolds number independence was observed for 𝑅𝑒𝑐 > 10^6, based on mean aerodynamic chord. The separation point drifts towards the root for larger angles of attack at the same 𝑅𝑒𝑐 condition. PIV data reveals a thickening of the separated shear layer and the formation of reversed flow with consequent vortical structures in the downstream region at higher angle of attack. Exploration of spanwise Proper Orthogonal Decomposition (POD) modes reveals a mode pair that appears to produce a strong, large-scale spanwise vortical motion that resembles size and topology of mean stall cells. In summary, a highly dynamic reversed flow region and spanwise periodicity are observed which is poorly represented by the mean flow.