Thanks in advance, can someone explain Steady,Non steady, Uniform and Non Uniform flow and provide some example for each.


The steady state refers to any phenomenon that is independent of time. Mathematically it means:

$$\frac{\partial v}{\partial t} =0$$.

Here is an example:

Consider a fixed point in the atmosphere and an observer on an airplane moving with constant velocity then he sees the flow as steady the flow doesn't change as the observer approaches the point, however if the observe change his coordinate system, for instance an observer somewhere on the earth which is not moving, observes an unsteady flow pattern, or the flow pattern at the fixed point changes as the airplane approaches that point.

So the concept is not absolute it is coordinate dependent. Whenever an object moves through a fluid with a constant velocity, the flow field may be transformed from an unsteady flow to a steady flow by selecting a coordinate system that is fixed with respect to the moving object.

Uniform flow doend't accelerate or delay . Mathematically:

$$\frac{\partial v}{\partial s}= 0 $$.

Think about the rotational flow in your sink, it's nonuniform flow.

  • 1
    $\begingroup$ Regarding the sink - spiral vortex tank beginning at 4:20. Quibble - uniform flow doesn't have to be straight. You can have uniform flow in a pipe that has bends. It's really the speed (scalar), not the velocity (vector) that has to be constant. $\endgroup$
    – Phil Sweet
    Dec 5 '18 at 0:43
  • $\begingroup$ @PhilSweet great stuff btw, that's true, by sink i mean the flow that accelerates as a simple experiment that OP can perform at home, but right there are some subtle details in definitions, thank you for mention it. $\endgroup$ Dec 5 '18 at 7:14
  • $\begingroup$ But why cant the relative velocity of air with respect to airplane change with time? Or are you assuming it to be constant.(I couldnt understand your example please explain) $\endgroup$
    – user17332
    Dec 5 '18 at 10:21
  • $\begingroup$ @Mohan i edited the answer, hopefully it clearers the confusion. $\endgroup$ Dec 5 '18 at 11:18

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