I come from a pure mathematics background, so I have very limited physics knowledge. I'm currently working out the non-dimensional form for the Navier-Stokes equations and have some questions. Where do the reference values come from? Is this something people measure it for each type of fluid and tabulate it somewhere? (So are they in a text book or do people measure it experimentally in "real life" problems?)

Someone once told me that the reference value for density is often taken from water, but this may be wrong, or I remembered incorrectly.

I need a short sentence to say what these are and where do they come from.


The reference values come from the physical system you are modeling, i.e. oil in a pipeline will have the density, viscosity of oil, diameter of the pipe and the cross-sectional velocity as reference values. Often the exact physical situation doesn't matter as long as you keep your dimensionless numbers constant (geometric and dynamic similarity)

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