Correct Answer - Option 3 : Reynolds number
Explanation
Forces encountered in flowing fluids include those due to inertia, viscosity, pressure, gravity, surface tension and compressibility.
These forces can be written as follows:
Reynolds number (Re):
It is defined as the ratio of inertia force to viscous force.
\({\rm{Re = }}\frac{{{\rm{\rho Vl}}}}{{\rm{\mu }}}\)
Froude number (Fr):
It is defined as the ratio of inertia force to gravity force.
\({\rm{Fr = }}\frac{{\rm{V}}}{{\sqrt {{\rm{gL}}} }}\)
Weber number (We):
It is defined as the ratio of the inertia force to surface tension force.
\({\rm{We = }}\frac{{{\rm{\rho }}{{\rm{V}}^{\rm{2}}}{\rm{l}}}}{{\rm{\sigma }}}\)
Mach number (M):
It is defined as the ratio of inertia force to velocity of sound.
\({\rm{M = }}\frac{{\rm{V}}}{{\rm{c}}}{\rm{ = }}\frac{{\rm{V}}}{{\sqrt {\frac{{{\rm{dP}}}}{{{\rm{d\rho }}}}} }}\)
