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This article is concerned with the numerical study and modelling of twoaspects the formation of laminar holes in transitional turbulence of planeCouette flow (PCF). On the one hand, we consider quenches: sudden decreases ofthe Reynolds number R which force the formation of holes. The Reynolds numberis decreased from featureless turbulence to the range of existence of theoblique laminar-turbulent bands [Rg;Rt]. The successive stages of the quenchare studied by means of visualisations and measurements of kinetic energy andturbulent fraction. The behaviour of the kinetic energy is explained using akinetic energy budget: it shows that viscosity causes quasi modal decay untillift-up equals it and creates a new balance. Moreover, the budget confirms thatthe physical mechanisms at play are independent of the way the quench isperformed. On the other hand we consider the natural formation of laminar holesin the bands, near Rg. The Direct Numerical simulations (DNS) show that holesin the turbulent bands provide a mechanism for the fragmented bands regime andorientation fluctuations near Rg. Moreover the analysis of the fluctuations ofkinetic energy toward low values demonstrates that the disappearance ofturbulence in the bands can be described within the framework of LargeDeviations. A Large Deviation function is extracted from the ProbabilityDensity Function of the kinetic energy.

Mechanical and statistical study of the laminar hole formation in transitional plane Couette flow