Drag & Lift | Mechanical Engineering SSC JE (Technical) PDF Download

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

Drag & Lift | Mechanical Engineering SSC JE (Technical)
Drag & Lift | Mechanical Engineering SSC JE (Technical)

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

Boundary Layer thickness (d) =
Drag & Lift | Mechanical Engineering SSC JE (Technical)

Displacement thickness (d*) =
Drag & Lift | Mechanical Engineering SSC JE (Technical)

Momentum thickness (q) =
Drag & Lift | Mechanical Engineering SSC JE (Technical)

Local friction drag coefficient Cd* =
Drag & Lift | Mechanical Engineering SSC JE (Technical)

Average friction drag coefficient Cd =
 

Shear stress to =
Drag & Lift | Mechanical Engineering SSC JE (Technical)

 

  •  Boundary Layer Parameters in Turbulent Conditions

Drag & Lift | Mechanical Engineering SSC JE (Technical)

Drag & Lift | Mechanical Engineering SSC JE (Technical)
Drag & Lift | Mechanical Engineering SSC JE (Technical)

  • 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.
The document Drag & Lift | Mechanical Engineering SSC JE (Technical) is a part of the Mechanical Engineering Course Mechanical Engineering SSC JE (Technical).
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FAQs on Drag & Lift - Mechanical Engineering SSC JE (Technical)

1. What is drag in mechanical engineering?
Drag in mechanical engineering refers to the resistance force experienced by an object moving through a fluid, such as air or water. It acts in the opposite direction to the object's motion and is caused by the interaction between the object and the fluid. Drag can significantly affect the performance and efficiency of vehicles, aircraft, and other mechanical systems.
2. How is drag force calculated?
The drag force can be calculated using the drag equation, which is given by the formula: Drag force = 0.5 * (fluid density) * (velocity squared) * (drag coefficient) * (reference area) Here, the fluid density represents the density of the fluid through which the object is moving, the velocity is the speed of the object relative to the fluid, the drag coefficient is a dimensionless value that depends on the shape and surface properties of the object, and the reference area is a characteristic area of the object perpendicular to the flow direction.
3. What factors affect drag?
Several factors affect drag, including the shape and surface roughness of the object, the velocity of the object relative to the fluid, the fluid density, and the viscosity of the fluid. Additionally, the presence of boundary layers, turbulence, and the interaction between different flow regions can also influence the drag force experienced by an object.
4. How does lift work in mechanical engineering?
In mechanical engineering, lift refers to the upward force generated by the motion of an object through a fluid, typically air. Lift is mainly associated with the aerodynamics of wings, rotors, and other lifting surfaces. It is generated due to the difference in pressure between the upper and lower surfaces of the object, resulting in an upward force that opposes the object's weight.
5. How is lift force calculated?
The lift force can be calculated using the lift equation, which is given by the formula: Lift force = 0.5 * (fluid density) * (velocity squared) * (lift coefficient) * (reference area) Here, the fluid density represents the density of the fluid, the velocity is the speed of the object relative to the fluid, the lift coefficient is a dimensionless value that depends on the shape and angle of attack of the object, and the reference area is a characteristic area of the object perpendicular to the flow direction.
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