Tuesday, December 16, 2008

Convective and Local Acceleration

Convective acceleration is defined as the rate of change of velocity due to the change of position of fluid particles in a fluid flow.

Local acceleration or Temporal acceleration is defined as the rate of change of velocity with respect to time at a given point in a flow field.

18 comments:

  1. can anyone give an example... i really need it...

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    1. an example of convective is the airflow under a jetplane wing flying 31,000 feet above the sahara desert with a humidity equal to 112%

      Sorry for the slow reply, will get back to you regarding local :)

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  2. Convection flow is due advection and diffusion, and Navier-Stokes equation include only advection (there is no term including thermal flow). So "convective flow" should be named "advective flux".

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  3. thanks, can any give me example of local acceleration

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  7. is thr any equation to define convective acceleration

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  9. can tou plz give the counter example of LOCAL AND CONVECTIVE acceleration

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  10. acceleration is defined as the rate of change of velocity. This rate of change with respect to the position or displacement is said to be the convective acceleration. Local acceleration is the differential with respect to time

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  11. This comment has been removed by the author.

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  12. Here is what I think is an easier example of convective versus local acceleration.

    First, visualize flow in a river, in steady-state, i.e., flow rate is not changing with time. If there is a smooth contraction, this is the river narrows, then water will have to start going faster and faster through that contraction, in order to maintain continuity (conservation of mass: for a constant and uniform flow rate Q, V must increase when the cross-sectional area of flow A decreases, so that Q = V A is maintained).

    If you stay put at one point (or cross-section) in the river, nothing will change with time, as you are in steady-state (it is a "time-independent" flow), so that the local acceleration at that point, dV/dt, is zero (should be symbols for partial derivative...). On the other hand, if you were floating down the river in a raft, you would be clearly accelerating as you enter that contraction! (or else, there would be no fun in doing white water sports, right?) That is the convective acceleration: as you move with the flow, in this case on your raft, there is an acceleration in the downstream direction. Mathematically, this acceleration is Vx dVx/dx (again, partial derivatives), where x is the downstream direction.

    Let us consider a more general case: same river, same reach, same contraction, but this time there is a flood wave coming, so that the flow rate Q is increasing with time. Because Q is increasing, the velocity Vx at any fixed point will increase with time, i.e., local acceleration will not be zero as in the previous case... The explanation for convective acceleration would still be the same.

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