Influence of Surface Irregularities on Hydrodynamic Instabilities in Couette-Taylor Flow

Abstract

In this work, we propose an experimental study of roughness effect on hydrodynamic instabilities’ Couette-Taylor flow. During experiments, the inner cylinder rotates at a given angular velocity and the outer cylinder is maintained fix. The main objective of the study is to highlight the geometric parameters’ effect on the flow. We mainly focused our attention on the effect of the wall roughness parameter on the appearance instabilities in the studied configuration (delay or advance in its appearance). For this purpose, a qualitative study was performed using Kalliroscope particles to visualize the instabilities. Then, we applied polarography to different types of roughness as a quantitative study. Hence, the possibility to characterize the flow regimes of the first instabilities (TVF, WVF, MWVF, and TN). The experiments have shown that surface irregularities, have an effect on the appearance of the first instabilities, which depend on the size and nature of the roughness. In fact, the surface roughness not only increases the friction on the wall, but it also greatly influences the transport of the mass and momentum in a given flow regime. The flow, therefore, undergoes more friction when the inner cylinder (in rotation) has a rough surface. This friction slows the velocity of the fluid particles; which delays the onset of instability. The movement of the particles will therefore, be dampened by the irregularities at the level of the rough surface. Moreover, the results also proved that as soon as the Couette-Taylor cells are established, the roughness is no longer a particle motion damper, but on the contrary, it promotes the continuation of the disturbance of the flow. The flow becomes then less slowdown in the hollow of the surface irregularities; which leads to less friction. For higher Taylor numbers, the study showed a faster transition from one regime to another.