ABSTRACT
The fluid that we deal with in this unit is a viscous fluid, so the velocity of fluid flow becomes zero at the solid surface. The consequence of this no-slip condition is that flow velocity changes from zero at the wall to the free-stream value sufficiently far away from the wall surface. This thin layer is called the boundary layer, an important concept in fluid dynamics, which explains how the fluid forces are generated. So, in Section 1.3, we learn the basic behaviour of boundary layers to be able to estimate the viscous drag acting on the solid surface.
The boundary layers over solid bodies behave differently depending on their shape. For example, the drag force acting on sports cars is much less than that on pickup trucks, where the boundary layer is separated from the body surface of vehicle creating a strong flow disturbance. In Section 1.4 we study the streamlining strategy to reduce the drag force of immersed bodies. We also discuss how the drag of immersed bodies is affected by the Reynolds number as well as the wall roughness.
