Review of supersonic boundary layer instability and transition models (original) (raw)

2012

Extensive research has been carried out to study the stability and transition of incompressible boundary layers, but the compressible counterpart has not received adequate attention. The effect of compressibi lity on the structure of boundary layer needs study. The present effort is to study the stability behaviour of the supersonic and hypersonic boundary layers in the presence of adverse pressure gradients and free stream turbulence. Compressible boundary layers have dominantly 2-D instabilities of Tollmein3chlichting (TS) waves in the early transition, which couple with subharmonics in resonance and nonresonance mechani sms . Dominant transttton structures are the A and hairpin vortices (3-D) in staggered (peak-valley) type and commonly occurring with large amplitudes or in aligned pattern when growth rate is supressed by external forcing, implicitly (complaint coatings) or explicitly (suction, favourable pressure gradients, cooling, etc. ). The aim of the present study is to see...

Instability wave–streak interactions in a supersonic boundary layer

Journal of Fluid Mechanics, 2017

The interaction of stationary streaks undergoing non-modal growth with modally unstable instability waves in a supersonic flat-plate boundary-layer flow is studied using numerical computations. For incompressible flows, previous studies have shown that boundary-layer modulation due to streaks below a threshold amplitude level can stabilize the Tollmien–Schlichting instability waves, resulting in a delay in the onset of laminar–turbulent transition. In the supersonic regime, the most-amplified linear waves become three-dimensional, corresponding to oblique, first-mode waves. This change in the character of dominant instabilities leads to an important change in the transition process, which is now dominated by oblique breakdown via nonlinear interactions between pairs of first-mode waves that propagate at equal but opposite angles with respect to the free stream. Because the oblique breakdown process is characterized by a strong amplification of stationary streamwise streaks, artifici...

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