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The no-slip condition is an empirical assumption that has been useful in modelling many macroscopic experiments. It was one of three alternatives that were the subject of contention in the 19th century, with the other two being the stagnant-layer (a thin layer of stationary fluid on which the rest of the fluid flows) and the partial slip (a finite relative velocity between solid and fluid ...
The pressure gradient does not enter into the problem. The initial, no-slip condition on the wall is (,) = , (,) =, and the second boundary condition is due to the fact that the motion at = is not felt at infinity. The flow is only due to the motion of the plate, there is no imposed pressure gradient.
Showing wall boundary condition. The most common boundary that comes upon in confined fluid flow problems is the wall of the conduit. The appropriate requirement is called the no-slip boundary condition, wherein the normal component of velocity is fixed at zero, and the tangential component is set equal to the velocity of the wall. [1]
The derivation of Stokes' law, which is used to calculate the drag force on small particles, assumes a no-slip condition which is no longer correct at high Knudsen numbers. The Cunningham slip correction factor allows predicting the drag force on a particle moving a fluid with Knudsen number between the continuum regime and free molecular flow.
Displacement thickness is an alternative definition stating that the boundary layer represents a deficit in mass flow compared to inviscid flow with slip at the wall. It is the distance by which the wall would have to be displaced in the inviscid case to give the same total mass flow as the viscous case.
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These conditions are used when we don’t know the exact details of flow distribution but boundary values of pressure are known For example: external flows around objects, internal flows with multiple outlets, buoyancy-driven flows, free surface flows, etc. The pressure corrections are taken zero at the nodes.
A schematic diagram of the Blasius flow profile. The streamwise velocity component () / is shown, as a function of the similarity variable .. Using scaling arguments, Ludwig Prandtl [1] argued that about half of the terms in the Navier-Stokes equations are negligible in boundary layer flows (except in a small region near the leading edge of the plate).