Hydraulics & Fluid Mechanics
The normal stress is same in all directions at a point in a fluid

only when the fluid is incompressible and has zero viscosity
When there is no motion of one fluid layer relative to an adjacent layer
only when the fluid is frictionless
irrespective of the motion of one fluid layer relative to an adjacent layer

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Hydraulics & Fluid Mechanics
True one-dimensional flow occurs when

the magnitude and direction of the velocity do not change from point to point in the fluid
the direction and magnitude of the veiocity at all points are identical
the fluid particles move in plane or parallel planes and the streamline pat-terns are identical in each plane
the velocity of successive fluid par-ticles, at any point, is the same at suc-cessive periods of time

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