A multi-point correlation analysis of a crossflow-dominated boundary layer

Proper orthogonal decomposition (POD) is used to analyze experimental signals from multi-point measurements in transitional flow over a 45° swept wing. The data used in this analysis include single-component surface shear-stress and two-component velocity measurements. The data were obtained from two separate experiments in a highly threedimensional flow with crossflow-dominated transition occurring near x/c = 0.52. Streamwise surface shear-stress measurements were acquired through transition to turbulence. Velocity measurements were obtained across the span at constant chord locations just before and after transition. The POD solution produces energy-based modes which statistically determine the spatial evolution of the flow field across the span and through transition. The shear-stress results from the POD demonstrate the organization of energy in the Streamwise flow evolution through transition. The solution of the POD from the crossflow surface shear stress data captures the crossflow vortex wavelength which is also more directly captured when applied to the velocity measurements. The POD also reveals that the coherent structures present in the turbulent regime are a direct remnant of the instability mechanisms. These results reflect physical events in the flow which may provide valuable information to understanding the transition mechanisms and in developing flow control strategies.