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Laminar and turbulent flow

  1. Aug 13, 2009 #1
    Hi, guys, i tried to read the definitions of laminar and turbulent flowon some of the website, but had difficult time understanding them. I am wondering if you guys can explain the above terms in more plain words?
  2. jcsd
  3. Aug 13, 2009 #2
    What specifically don't you understand?
  4. Aug 13, 2009 #3


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    Staff: Mentor

    Have you ever seen the flame and smoke of a candle flow straight and steady upwards, then suddenly get turbulent? That's laminar and turbulent flow.
  5. Aug 14, 2009 #4

    Jano L.

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    Gold Member

    I think there is no exact mathematical definition of laminar/turbulent flow.

    Roughly speaking, laminar flow is such a flow, in which water particles follow streamlines that vary only slowly compared to the velocity of water. Turbulent flow is such a flow where fluid particles does not follow any steady streamlines (imagine smoke 0,5 m above the cigarette).

    Practically, the fluid is in the laminar regime because its viscosity damps every instability of the flow. Instable flow with a lot of whirlpools require a lot of mechanical energy, which gets converted into heat by friction. Turbulent regime can start when the fluid velocity is so high that it can supply this energy. But this transition into instable flow depends on the geometry, kind of surface of the container and so on, so there is no simple sharp transition condition.
  6. Aug 14, 2009 #5
  7. Aug 14, 2009 #6
    They often visualize laminar flow in a way that a group of streamlines (trajectories of fluid particles) trace out a tube-shaped region of space; that region has cross section area A; particles pass by that cross section with velocity v; the volume flow rate (cubic meters per second) is the product Av; if the fluid is incompressible (which liquids are) then Av is constant all along the tube-shaped region (the property known as continuity). You can say that only if you don't have turbulence. With turbulence the particle velocities would be all scrambled up.
  8. Aug 14, 2009 #7


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    Laminar flow follows a smooth path. The velocity of the fluid at any point is constant. Above certain critical speeds the flow becomes turbulent where it is irregular and characterised by small whirlpool regions.

    Like russ has mentioned. if you look at a candle that has recently been blown out, you will notice the smoke particles are smooth and then at a certain height make whirlpool like formations.
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