Effect of free stream turbulence on the topology of laminar separation bubble on a sphere. (10th October 2022)

• Record Type: Journal Article
• Authors: Desai, Aditya; Mittal, Sanjay
• Is Part Of: Journal of fluid mechanics. Volume 948(2022)
• Publication Date: 2022-10-10
• Subjects: intermittency -- turbulent transition -- wakes; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2022.696
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract: Abstract : The topology of a laminar separation bubble (LSB) on a sphere in the critical regime is investigated via experiments at five turbulent intensities: $T_u=0.06\, \%$, $0.42\, \%$, $0.71\, \%$, $1.00\, \%$ and $1.36\, \%$ . The drag crisis occurs at a lower $Re$ and becomes gradual with increasing $T_u$ . 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 $Re$ . This azimuthal expansion of the LSB is accompanied by intermittency for a small range of $Re$ . 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 $Re$ in the critical regime, some of its fragments relocate to alternate locations. Moderate increase in $T_u$ ( $0.42\, \% \leq T_u \leq 0.71\, \%$ ) leads to rich dynamics with several intermittent flow states. However, fewer intermittent states are observed beyond a certain $T_u$ ( ${\geq }1.00\, \%$ ).