It has recently been shown by Heenan and Morrison (1998a,b) that buffet due to separated flow downstream of a backward-facing step can be attenuated more or less completely by use of a permeable reattachment surface vented to an airtight plenum.With an impermeable surface,the global unsteadiness is driven by the feedback from thereattachment point of pressure and vorticity fluctuations towards the step.Their work also suggests that a permeable surface immediately downstream of separation also affects the pressure field.
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