Total drag is made up of form drag (also referred to as pressure drag) and residuary drag. Residuary drag is what is left over from the total drag after the form drag has been subtracted, i.e. the wake drag and the skin friction drag.
Figure 1 shows how form drag is effected by the streamlined shape of the body. For a flat blocky shape, the form drag will be high and for a streamlined low-profile body, the form drag will be minimized. The separation of of the fluid creates turbulence and results in pockets of low and high pressure that leave a wake behind the body, thus the term pressure drag. The pressure drag opposes forward motion and is a component of the total drag.
Figure 1: Form Drag (Also Called Pressure Drag)
Figure 2 shows the tremendous wake generated behind the Seawolf class submarine. This wake is in essence "wasted" energy that the ship generates. This wasted energy was not used to propel the submarine forward, but rather to generate waves. The photo taken from the website: http://www.fas.org/man/dod-101/sys/ship/cwolf02m.jpg
Figure 2: Wake
Drag
Figure 3 depicts the drag due to skin friction. This the "stickiness" of the surface of the vessel or a function of its ability to prevent the fluid from freely flowing over the surface.
Figure 3: Skin Friction
Figure 4 shows a depiction of the external fluid flow across a flat plate. Polymer ejectant has been shown to be most effective when ejected between the buffer zone and the viscous sublayer. Ejectors prior to the Cortana Fluidics Ejector typically ejected polymer out above the buffer zone and into the turbulent boundary layer where the polymer has little to no benefit until much further downstream where the turbulence may bring a portion of the ejectant back into the effective zone.
