Using inflexion points to stabilize boundary layers

Abstract eng:
We propose strategies for modifying a basic velocity profile so as to make it more stable. It is found that small modifications can produce very large increases in the critical Reynolds number for linear instability. What is especially surprising is that these stabilizing modifications create inflexion points in the profile. Our usual understanding of boundary layer stability suggests that introducing an inflexion point will be destabilizing, as it will create an inviscid instability. We use Orr-Sommerfeld calculations to show that while this destabilization does indeed take place at very large Reynolds numbers, there can be a simultaneous strong stabilization at lower Reynolds numbers. Recognising that some inflexional profiles can be very stable opens up possibilities for new stabilization strategies for transition delay.

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