A synthetic forcing to trigger laminar-turbulent transition in parallel wall bounded flows via receptivity
Résumé
Research on laminar-turbulent transition of wall-bounded parallel flows has usually focused
on controlled scenarios where transition is triggered by perturbations having simple shapes
and spectra. These disturbances strongly differ from the environmental noise usually
present in experimental setups or industrial applications, where uncontrolled transition is
usually observed. In this paper a new method is proposed to trigger uncontrolled transition
to turbulence in wall-bounded parallel flows exploiting the receptivity of the flow to a
volume forcing.
Using some concepts provided by linear stability and sensitivity analysis, such as the
resolvent, we propose a method for constructing a volume forcing capable of inducing
stochastic velocity perturbations with a prescribed energy level, eventually leading to
laminar-turbulent transition as a response of the system to external noise.
The method has been tested in a channel flow configuration, using direct numerical
simulations of the fully nonlinear Navier-Stokes equations in the presence of the volume
forcing constructed on the basis of optimal forcing functions. Subcritical transition to
turbulence induced by the prescribed forcing has been investigated and compared to
other transition scenarios, where deterministic perturbations are imposed for obtaining
a turbulent flow. Finally, the fully developed turbulent flows induced by the proposed
method has been analysed, showing that low-order statistics and energy balance equations
are practically unaffected by the continuous synthetic forcing.
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