# Taylor number

For the flow between two concentric cylinders with radii $R_1$ and $R_2$, rotating at $\Omega_1$ and $\Omega_2$, the Taylor number is defined as,
$Ta = \frac{\mbox{Centrifugal Force}}{\mbox{Viscous Force}} = 4 \left( \frac{\Omega_1 R_1^2 - \Omega_2 R_2^2}{R_2^2 - R_1^2}\right) \; \frac{\Omega_1 d^4}{\nu}$
where $d =$ gap width between the cylinders and $\nu =$ the dynamic viscosity.