Fluid MechanicsMechanical Engineering

Velocity Potential Function

Function of Velocity Potential

It is defined as a scalar function of space and time such that its negative derivative along any direction gives the component of velocity along that direction.

Derivative

Remember:

  • Negative sign implies flow always occurs in the direction of decreasing potential.
  • Velocity potential function exists only for irrotational flow and potential flow.
  • If velocity potential function satisfies the Laplace equation, then it also satisfies continuity equation and hence the flow is possible.

Flow Through Pipes

Friction Loss/Darcy Weisbach Equation

Darcy Weisbach equation.

Darcy Weisbach equation

Laminar Flow Through Circular Pipe (Hagen-Poiseuille Flow)

Shear stress (τ) distribution

Shear stress

The negative sign on x  ∂p/∂x indicates decrease in pressure in the direction of flow. The pressure must decrease because pressure force is the only means available to compensate for resistance to the flow, the potential and kinetic energy remain constant.

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