add standard nondimensional groups in fluids

uni/mmme/2xxx/2047_thermodynamics_and_fluid_dynamics/dimensional_analysis.md

@@ -120,4 +120,44 @@ where $M$, $L$, and $T$ are units of mass, length, and time respectively.
 The two equations results in some simple simultaneous equations to solve to find the
 coefficients $a$, $b$, $c$, $d$, $e$, $f$.
 
+# Standard Nondimensional Groups in Fluids
+
+This is not an exhaustive list.
+
+## Reynolds Number
+
+$$\text{Re} = \frac{\rho U L}{\mu}$$
+
+Represents ratio of intertial forces over viscous forces.
+Important in all viscous flows.
+
+## Froude Number
+
+$$\text{Fr} = \frac{U^2}{gL}$$
+
+Represents ratio of inerital forces over gravitational forces.
+Important in flows with interfaces (e.g. gas-liquid).
+
+## Weber Number
+
+$$\text{We} = \frac{rho U^2 L}{\sigma}$$
+
+where $\sigma$ is the surface tension coeffecient.
+
+Represents ratio of inertial to capillary forces.
+Important to flows with strong surface tension effects (e.g. droplets,
+bubbles, jets)
+
+## Strouhal Number
+
+$$\text{St} = \frac{fL}{U}$$
+
+where $f$ is frequency.
+
+Important in flows with velocity oscillations.
+
+## Mach Number
+
+$$\text{Ma} = \frac U a$$
+