Types of Drag

بسم الله الرّحمن الرّحیم

بسم الله الرّحمن الرّحیم

Aerodynamic Drag (1)

Types of Drag

Lift is in nature an inviscid phenomenon, however the drag is a viscous phenomenon. 

The airfoil design in xfoil MDES is such that it preserves the lift. Hence, L/D is increased  by decrease of drag. 

Drag types:

Vortex (Induced) drag (named after Prof. Veldhuis)

Interference drag

Viscous drag

Pressure

Skin Friction: pressusre loss

Bubbles/Separation/

Skin friction

Viscosity

∂u/∂y

Wave drag

For a problem, only viscous drag exists. To reduce viscous drag, laminar flow has lower friction, viscosity and ∂u/∂y but not separation. 

Therefore to decrease viscous drag, we want laminar flow and we want it attached (since laminar flow separates easily). Therefore, to decrease viscous drag, we should delay transition and we should prevent bubbles and separation.