The Euler number (Eu), in Physics, is a dimensionless number used in fluid flow calculations. It expresses the relationship between a local pressure drop e.g. over a restriction and the kinetic energy per volume, and is used to characterize losses in the flow, where a perfect friction-less flow corresponds to an Euler number of 0. The inverse of the Euler number is referred to as the Ruark Number with the symbol Ru.
It is defined as `E_u = (rho_"u"-rho_"d")/(rho*V^2)` , where:
The definition and formula for Euler number was taken from Wikipedia (https://en.wikipedia.org/wiki/Euler_number_(physics)).