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enter image description here Laminar flow is a streamlined steady flow with a uniform gradient of velocity across the diameter of the pipe. I am familiar with the elementary treatment of laminar flow, like basic velocity profile, shear stresses etc. But my question is:-

The velocity of the fluid particles at the edges is zero while it is maximum at the centre. This means, that in a specified interval of time, the centre bulges out more than the progress of the surrounding regions, while the fluid at the edges will remain stationary. Then, with passage of time, the centre should continue to bulge out relative to the rest of the flowing fluid, causing a very steep spike in the middle of the cylindrical flow. Does this really happen? It seems very counterintuitive and against everyday observations, if the centre does bulge out creating a steep "pyramidal" (parabolic, to be rigourous) shape of the leading surface. Also, after a definite bulge, should not gravity effects distort the shape?

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    $\begingroup$ If you're familiar with the basic velocity profile and the way to calculate it then you know that the parabolic velocity profile is in fact the steady state situation, so the profile doesn't bulge out more. What you might be confusing here is that fluid parcels in the center go faster than average and thus indeed get farther and farther ahead of the slower fluid parcels closer to the walls, but that doesn't disturb the flow profile. It is, by the way, the reason for the well-known Taylor-Aris dispersion $\endgroup$ – Michiel Feb 10 '14 at 18:07
  • $\begingroup$ As for gravity: if the fluid density is the same everywhere (which it is for a single-phase incompressible laminar flow) then gravity plays no role $\endgroup$ – Michiel Feb 10 '14 at 18:19

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