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SUMMARY:Oblique transition in separated high-speed flows - Mihailo Jovanov
 ic (University of Southern California)
DTSTART:20220328T123000Z
DTEND:20220328T130000Z
UID:TALK171122@talks.cam.ac.uk
DESCRIPTION:We utilize resolvent and weakly nonlinear analyses in combinat
 ion with direct numerical simulations (DNS) to identify mechanisms for obl
 ique transition in a Mach 5 flow over an adiabatic slender double-wedge. E
 ven though the laminar separated flow is globally stable\, resolvent analy
 sis demonstrates significant amplification of unsteady external disturbanc
 es. These disturbances are introduced upstream of the separation zone and 
 they lead to the appearance of oblique waves further downstream. We demons
 trate that large amplification of oblique waves arises from interactions o
 f the fluctuation shear stress with streamline curvature of the laminar ba
 se flow in the separated shear layer. This is in contrast to the attached 
 boundary layers\, where no such mechanism exists. We also use a weakly non
 linear analysis to show that the resolvent operator associated with linear
 ization around the laminar base flow governs the evolution of steady reatt
 achment streaks that arise from quadratic interactions of unsteady oblique
  waves. These quadratic interactions generate vortical excitations in the 
 reattaching shear layer which lead to the formation of streaks in the reci
 rculation zone and their subsequent amplification\, breakdown\, and transi
 tion to turbulence downstream. Our analysis of the energy budget shows tha
 t deceleration of the base flow near reattachment is primarily responsible
  for amplification of steady streaks. Finally\, we employ DNS to examine l
 atter stages of transition and demonstrate the predictive power of input-o
 utput framework in uncovering triggering mechanisms for oblique transition
  in separated high-speed boundary layer flows.\nJoint work with: Anubhav D
 wivedi and G. S. Sidharth
LOCATION:Seminar Room 1\, Newton Institute
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