Couette flow refers to viscous flow between two parallel surfaces. The most common example of such flows is flow between two parallel plate or between two concentric cylinders (in most viscometers or journal bearings). The primary driving factor for these flows is 'shear'. For example, in the case of two parallel plates, when the top plate is moving with a constant velocity V, it induces motion to the fluid layer just adjacent to it (because of no-slip condition). This fluid layer sticking to the plate therefore has a velocity = V. In the similar manner, this fluid layer pulls its adjacent fluid layer and this process continues. This is commonly referred to as a shear driven flow. In such cases, the velocity profile between the two parallel plates is linear.