TRANSITION IN A SEPARATION BUBBLE

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 influence de velopment in a separation bubble shows that transition occurs within t he separated shear layer. A comparison of simultaneous velocity traces from probes separated in the lateral direction suggests that Kelvin-H elmholtz waves, which originate in the laminar shear layer, do not bre ak down to turbulence simultaneously across their span when region pro ceed to agglomerate. The streamwise development of intermittency in th is region can Its characterized by turbulent spat theory with a high d imensionless spot production rate. Moreover the progression of intermi ttency along the centerline of the shear layer is similar to that in a ttached boundary layer transition. The transverse development of inter mittency is also remarkably similar to that in attached boundary layer s, The parameters obtained from these measurements agree with correlat ions previously deduced from turbulence intensity measurements.