The transitional from laminar to turbulent flow depends on geometry, surface roughness, flow velocity, surface temperature, and type of fluid. However, Osborne Reynolds discovered that the flow regime mainly depends on the ratio of inertial forces to viscous forces. This ratio is what we called as Reynolds number. At small or moderate Reynolds numbers the viscous forces are large enough to suppress theses fluctuations and to keep the fluid “in line”. Thus, the flow is streamlined and in ordered motion. However, at large Reynolds numbers, the inertial forces, which are proportional to the fluid density and the square of the fluid velocity, are large relative to the viscous force. As the results, the viscous force cannot prevent the random and rapid fluctuations of the fluid. Thus, the flow will be in disordered motion.