Transient disturbances in shear flows
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In the previous chapters, a far-field (asymptotic) response of shear flows to modal disturbances was considered. In this chapter, we concentrate on the response in the near-field of the disturbance source. As we know, the classical analysis of linear stability treats the disturbances as sets of separate modes of the linearized Navier–Stokes equations. However, the approach does not take into account the fact that these equations are not self-adjoint, i.e., the modes are not orthogonal. This may give rise to strong transient effects pronounced in the source near-field. It has been proven experimentally that transient phenomena close to the disturbance source can be drastic for the downstream transition to turbulence, even if the disturbances are asymptotically stable.
KeywordsFree Stream Turbulence Transient Growth Turbulent Spot Optimal Perturbation Disturbance Velocity
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