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.