Flow separation and subsequent reattachment exert an important influence on the mechanism of heat transfer. In some cases, they have a harmful effect such as uneven heat loading in thermal equipment, but in others, they produce a beneficial effect like heat transfer enhancement point. Thus, in engineering practice, it is quite essential to understand the basic mechanism of heat transfer in separating and reattaching flows. A backward-facing step is one of the most fundamental geometries where the flow separation and reattachment occur. Flow past a backward-facing step has a variety of engineering applications such as energy system equipment, electronic cooling, cooling of nuclear reactors, cooling of turbine blades, combustion chambers, environmental control systems, and many other devices.