Drag & Lift Notes | Study Mechanical Engineering SSC JE (Technical) - Mechanical Engineering

DRAG AND LIFT

• The component of the force parallel to the direction of flow is called the drag & normal component is called the lift. 
• Friction drag - when flow occurs past a flat surface at zero incidence, the fluid exerts a drag-force on the surface known as friction drag which is in downstream direction. 
• Pressure drag - when flow occurs past a surface which is not everywhere parallel to the fluid stream a drag force results on account of difference of pressure over the body surface, known as pressure drag. 
• Stream lined body has friction drag only whereas Bluff body has pressure drag only 
• Total drag on the sphere is about one-third of the drag for the disc. 
• Coefficient of drag and lift

 Flow at very small Reynolds number is known as the creeping motion  Boundary Layer Parameters in Laminar Conditions

Boundary Layer thickness (d) =

Displacement thickness (d*) =

Momentum thickness (q) =

Local friction drag coefficient Cd* =

Average friction drag coefficient Cd =
 

Shear stress to =

•  Boundary Layer Parameters in Turbulent Conditions

• The drag which depends upon profile and orientation of the airfoil, known as profile drag, whereas drag which depends upon the airfoil plan form & is induced by the lift force is known as induced force. 
• The phenomenon of lift produced by imposing circulation over a uniform fluid steam is known as Magnus effect.