Stokes number

The Stokes number St ( by: George Gabriel Stokes ) is the dimensionless parameter, which indicates the importance of the inertia of a particle ( dust particle, droplet, bubble) for its movement in a moving fluid (gas or liquid). It is defined as the ratio of the characteristic time at which the velocity of the particle velocity of the surrounding fluid by friction fits, the characteristic time in which the fluid itself changes due to external influences its speed.

For St << 1, the particles of the local flow follows.

In situations where the Stokes number is used, the particles ( viscous dissipation ) are usually so small that the frictional force between particles and fluid is proportional to the drift speed. Then is well defined as the damping time constant with which a drift velocity, caused due to unexpected loss decays exponentially.

Oscillating the fluid in a sound field, then the inverse value of the angular frequency. The fluid is accelerated through a nozzle ( application impactor ), decelerated by a diffuser (Application sampling) or deviates from a fiber ( filtration), then added, wherein the diameter of the opening or of the fiber, and the flow velocity.

• Code ( Fluid Mechanics )