Taylor-Couette flow with periodically corotated and counterrotated cylinders

The stability of Taylor-Couette flow is studied as a function of the angular velocities of the inner and outer cylinders, Ω₁ and Ω₂={ε}Ω₁ cos({ω}t), respectively. Contrary to the theoretical prediction, outer cylinder modulation stabilizes the flow. The critical Reynolds number, Re1c, is a function of the dimensionless frequency, {γ}=({ω}d²/2{ν})1/2, where d is the gap size and {ν} is the kinematic viscosity, and a monotonically increasing function of {ε} over the range examined: 0.3{≤}{ε}{≤}2.0. At larger {ε} stabilization is spectacular, Re1c reaching a value nearly double the value for stationary outer cylinder.