Turbulence in Microchannels

Abstract

Fluid mechanics in small channels, i.e. channels of micrometer size, is dominated by surface effects and often exhibits striking differences of flow characteristics when compared with macro scale. One of important microfluidic problems is flow destabilization and occurrence laminar- turbulent transition. In this paper we describe our experimental and numerical attempts to understand growth of flow instabilities and development of turbulent structures in small channels. In the first configuration flow of water through 1mm long and 0.4mm high microchannel formed between two planes is investigated varying Reynolds number from 1000 to 6770. Fluorescent traces are used for flow visualization and microPIV acquisition of temporary velocity fields. The microPIV data are used to evaluate turbulent flow characteristics. Our experimental study shows that destabilization of flow in such a micro-channel does not necessarily occurs when it is usually expected. Nearly laminar flow structure is present within the channel even for the highest investigated flow Reynolds number. These findings are confirmed by numerical simulation performed using finite volume code. On the other hand it appears possible to achieve unstable flow pattern even for quite low Reynolds number flow regime by proper modification of the channel walls. In the second experimental and numerical study we demonstrate that appropriately chosen wall waviness of the micro-channel may lead to flow destabilization already at quite low flow Reynolds number (~100).