On the origin of the inflectional instability of a laminar separation bubble

摘要: This is an experimental and theoretical Study of a laminar separation bubble the associated linear stability mechanisms. Experiments were performed over flat plate kept in wind tunnel, with imposed pressure gradient typical aerofoil that would involve bubble. The was characterized by measurement surface-pressure distribution streamwise velocity using hot-wire anemometry. Single component anemometry also used for detailed study transition dynamics. It foundthat so-called dead-air region front portion corresponded to small disturbance amplitudes, amplitude reaching maximum value close reattachment point. An exponential growth rate seen upstream mean height bubble, this indicative instability mechanism at work. infinitesimal impulsively introduced into boundary layer location, wave packet tracked (in ensemble-averaged sense) while it getting advected downstream. found be convective nature. Linear analyses (both Orr-Sommerfeld Rayleigh calculations) profiles, starting from attached adverse-pressure-gradient all way up separation-bubble (i.e. end which evolution could expected). conclusion present work primary inflectional nature, its origin can traced back location. In other words, inviscid separated shear should logically as extension layer. modifies traditional view pegs detached Outside Kelvin-Helmholtz mechanism. We contendthat only when has moved considerably away wall (and happens near maximum-height location bubble), description paradigm, scaling principles, Could become relevant. propose new most amplified frequency wall-bounded terms inflection-point vorticity thickness show universal.