# Value of the Reynolds Number in constant velocity flows

Consider a fluid flowing such that all the particles have same velocity, what will be the Reynolds Number for such a flow?

We know that Reynolds number,

$$Re=\frac{inertia \,forces}{viscous \,forces}$$

in a fluid.

In a flow in which the particles have same velocities there will be no viscous forces acting on the fluid particles. Also, (and I'm not sure of this) since the particles have same velocities there will be no inertia forces too, because there is no acceleration. Then, from the definition of Reynolds Number, $$Re = \frac{0}{0}$$, which is not defined.

So what actually is the Reynolds number of a flow with constant velocity?

• That is probably why Reynolds numbers are calculated using a characteristic length. Mar 10 at 14:17

From all of the above, we can draw the conclusion that Renolds Number will always be a real number, or "zero" if $$V = 0$$.