Effect of free stream turbulence on the topology of laminar separation bubble on a sphere

Abstract

The topology of a laminar separation bubble (LSB) on a sphere in the critical regime is investigated via experiments at five turbulent intensities:, and. The drag crisis occurs at a lower and becomes gradual with increasing. The flow is devoid of the LSB at the onset of the critical regime. It forms on a small part of the sphere and not at all azimuthal locations, early in the critical regime. The LSB forms at more azimuthal locations with increasing. This azimuthal expansion of the LSB is accompanied by intermittency for a small range of. Towards the end of the critical regime, an axisymmetric LSB forms on the sphere at all time instants. A model is proposed to estimate the azimuthal extent and distribution of the LSB from the mean force coefficients of a flow state. The model predicts that the LSB forms as multiple segments for a large part of the critical regime. During the spatial growth of the LSB with in the critical regime, some of its fragments relocate to alternate locations. Moderate increase in leads to rich dynamics with several intermittent flow states. However, fewer intermittent states are observed beyond a certain.