Function euler_number 

pub fn euler_number(delta_p: f64, rho: f64, v: f64) -> f64

Euler number: Eu = ΔP / (ρ·v²).

Ratio of pressure forces to inertial forces.

• delta_p — pressure drop [Pa].
• rho — fluid density [kg/m³].
• v — characteristic velocity [m/s].