Low Reynolds number flow can be a very interesting topic. Low Reynolds number flow (Re ) is also called Stokes flow. At very low Reynolds number, the Navier-Stokes equations can be greatly simplified. Fluid mechanics at human length scales, such as swimming, is generally not very low Reynolds number. Developments in microfluidics, nanotechnology, and biomimicry has increased the frequency with which engineers encounter low Reynolds flows problems. Because humans often encounter fluids at moderate of high Reynolds numbers, our intuition can deceive us. Two of the most basic results of low Reynolds flow is that it is fully reversible and independent of time.

As a refresher, the Reynolds number is the ratio of inertial to viscous forces and is given by

where is the fluid density, is the velocity, is a characteristic length such as a diameter, and is the viscosity. The Reynolds number can also be thought of as the ratio of the momentum diffusion rate to the viscous diffusion rate. At Reynolds numbers less than approximately 2000, the flow is laminar. For Reynolds numbers greater than approximately 4000, the flow is turbulent. Continue reading Low Reynolds number flow