LOW-REYNOLDS-NUMBER INSTABILITY OF THE LAMINAR FLOW BETWEEN WAVY WALLS
Instability of a viscous incompressible flow in a channel with wavy walls is investigated theoretically, numerically and experimentally. Linear stability analysis shows that appropriately chosen wall waviness leads to flow destabilization at surprisingly low Reynolds numbers. The unstable mode of disturbances forms a vortex array, which travels downstream. The remarkable feature is that the most destabilizing waviness does not introduce any additional flow resistance. The outcome of the stability analysis are consistent with the result of direct numerical simulation obtained using CFD finite volume package FLUENT (Ansys Inc.). Preliminary experimental data gained for a channel with appropriately corrugated wall seem to confirm these predictions.
Thermohydraulic transport characteristics in wavy microchannel under pulsating inlet flow condition
The numerical investigation on developing unsteady laminar fluid flow and heat transfer inside a 2D wavy microchannel, due to sinusoidal varying velocity component at inlet is done. The thermohydraulic flow was developing while the microchannel walls were kept at constant uniform temperature. The transient solution of 2DNavier-Stokes equation was attained using the SIMPLE algorithm with the momentum interpolation technique. The deionized water is used as working fluid and Reynolds number ranging from 0.1 to 100. The simulation results reports, mainly the heat transfer and pressure drop for wavy microchannel are compared with straight microchannelby keeping the cross sectional area same. By comparing with steady flow in wavy channel it was seen that imposed sinusoidal velocity at inlet can improved performance in terms of heat transfer at different amplitude (0.2, 0.5, 0.8) and frequency (1, 5, 10) while keeping the friction factor within tolerable limits.
Two-dimensional instability of flow in a rough channel
Linear stability of a two-dimensional flow in a channel with distributed surface roughness is considered. The structure of the disturbance field is related to the structure of the roughness when the ratio of the respective wave numbers is rational; they are not related if this ratio is irrational. It is shown that the stability problem is not unique in the former case but unique in the latter. It is found that disturbances in the form of traveling waves are destabilized by the presence of the roughness. A very good approximation of the critical Reynolds numbers can be found using only the dominant Fourier mode to represent roughness geometry.