By-Pass Transition in Microchannels under EDL Effect

The effect of the electric double layer (EDL) on the bypass transition mechanism in the linear evolution stage is explored through direct numerical simulations. An initial perturbation velocity field consisting of a pair of counter-rotating vortices is introduced in Poiseuille and EDL flows and the time-space evolution of the perturbed field is analysed for short times at half the critical Reynolds numbers (3000 for Poiseuille and 300 for EDL). The wall normal and spanwise perturbation velocities development are both quantitatively and qualitatively similar in macro and micro flows. The streamwise velocity, which is initially zero and set up by the generation of the wall normal vorticity is twice larger under the EDL effect. Both flows develop inclined strong streamwise shear layers. Overall is the close similarity of the disturbance evolution showing that the three dimensional linear mechanism in EDL flow lead to the structures that are at least as strong as in Poiseuille flow.