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