Formdraget

Formdraget, or form drag, is the component of drag that arises from the shape of an object moving through a fluid. It results from how the flow is displaced around the body, leading to pressure differences between the front and the rear as the flow separates and a wake forms. This pressure drag is the main contributor to formdraget, in contrast to skin-friction drag, which comes from viscous shear on the surface.

In fluid dynamics, total drag D is commonly expressed as D = ½ ρ v^2 A Cd, where ρ is fluid density, v is speed, A is a reference area, and Cd is the drag coefficient. Cd can be conceptually split into components such as form drag (Cd_form) and friction drag (Cd_fric). Formdraget is strongly influenced by shape and flow conditions, including Reynolds number and Mach number, as well as the presence and size of wakes.

Blunt or bluff bodies with abrupt fronts and large rear wakes produce larger form drag than streamlined shapes, which delay separation and minimize wake size. The rear geometry, leading-edge sharpness, and surface transitions all affect the extent of flow separation.

Strategies to reduce formdraget include streamlining the silhouette, tapering the rear, using rounded noses and slender tails, smoothing surface transitions, and controlling boundary-layer separation. In some cases, devices such as vortex generators may delay separation and reduce overall drag.

Applications span automotive, aeronautical, and maritime design, where minimizing form drag improves efficiency, performance, and fuel consumption. Formdraget remains a central consideration in optimizing shapes for subsonic, transonic, and supersonic regimes.