This study is devoted to the experimental analysis of the stratorotational instability (SRI). This instability affects the classical cylindrical Couette flow when the fluid is stably stratified in the axial direction. In agreement with recent theoretical and numerical analyses, we describe for the first time in detail the destabilization of the stratified flow below the Rayleigh line (i.e., the...

We consider the effect of surface mass flux and forced axial flow on the boundary-layer flows over rotating spheres, with a view to establishing flow-control mechanisms for rotating flows of engineering significance. A theoretical study is presented which considers the onset of convective instability modes (both stationary and travelling relative to the rotating surface) and local absolute inst...

This paper gives a pedagogic review of the envelope formalism for excitation of zonal flows by nonlinear interactions of plasma drift waves or Rossby waves, described equivalently by the Hasegawa–Mima (HM) equation or the quasigeostrophic barotropic potential vorticity equation, respectively. In the plasma case a modified form of the HM equation, which takes into account suppression of the magn...

Laboratory experiments and numerical computations are conducted for plane channel flow with a streamwise-periodic array of cylinders. Well-ordered, globally stable flow states emerge from primary and secondary instabilities, in contrast with other wall-bounded shear flows, where instability generally leads directly to turbulence. A two-dimensional flow resembling TolhnienSchlichting waves arise...

The effect of equilibrium velocity shear on the resistive tearing instability has been systematically studied, using the boundary layer approach. Both the "constant-f/!" tearing mode, which has a growth rate that scales as S -3/5, and the "nonconstant-f/!" tearing mode [a' (as) -1/3» 1], which has a growth rate that scales as S -1/3, are analyzed in the presence of flow. Here S is the usual rat...

This work is devoted to the study of the stability of Hagen–Poiseuille flow or pipe flow. The analysis is focused on the streak breakdown process by which two-dimensional streamwise-independent finite amplitude perturbations transiently modulate the basic flow leading to a profile that contains saddle points and is linearly unstable with respect to very small streamwise-dependent perturbations....

It has been known that there is a viscoelastic instability in the channel flow past a cylinder at high Deborah (De) number. Some of our numerical simulations and a boundary layer analysis indicated that this instability is related to the shear flow in the gap between the cylinder and the channel walls in our previous work. The critical condition for instability initiation may be related to an i...

Direct numerical simulation (DNS) is performed to examine laminar to turbulent transition due to high-frequency secondary instability of stationary crossflow vortices in a subsonic swept-wing boundary layer for a realistic natural-laminar-flow airfoil configuration. The secondary instability is introduced via inflow forcing and the mode selected for forcing corresponds to the most amplified sec...

We present a method to prove nonlinear instability of solitary waves in dispersive models. Two examples are analyzed: we prove the nonlinear long time instability of the KdV solitary wave (with respect to periodic transverse perturbations) under a KP-I flow and the transverse nonlinear instability of solitary waves for the cubic nonlinear Schrödinger equation.

It is found that magnetic field has a stabilization effect whereas the sheared flow has a destabilization effect on the RT instability in the presence of sharp interface. RT instability only occurs in the long wave region and can be completely suppressed if the stabilizing effect of magnetic field dominates. The RT instability increases with wave number and flow shear, and acts much like a Kelv...