Transition in a separation bubble

Abstract

In the interest of being able to predict separating-reattaching flows, it is necessary to have an accurate model of transition in separation bubbles. An experimental investigation of the process of turbulence development in a separation bubble shows that transition occurs within the separated shear layer. A comparison of simultaneous velocity traces from probes separated in the lateral direction suggests that Kelvin-Helmholtz waves, which originate in the laminar shear layer, do not break down to turbulence simultaneously spanwise when they proceed to agglomerate. The streamwise development of intermittency in this region, can be characterized by turbulent spot theory with a high dimensionless spot production rate. Moreover, the progression of intermittency along the centerline of the shear layer is similar to that in attached boundary layer transition. The transverse development of intermittency is also remarkably similar to that in attached boundary layers. The parameters obtained from these measurements agree with correlations which were previously deduced from turbulence intensity measurements.