It is important basically, when flow around bluff bodies, particularly where vortex shedding takes place, vortex formation and shedding takes place. These are some of the important non dimensional numbers. There are other numbers depending on when the flow is in a magnetic field or sometimes we call it when we call it viscous elastic fluid or even if sometimes we will call about talk about elastic fluid.
So, in such cases, there are certain other numbers which are non dimensional numbers. They play a significant role, but we will not go to those details where this basic background is. This is because of course, here are emphasize numbers, which are important to wherein environment. So, these are the things, which emphasize with this understanding about the various various forces and the various non dimensional numbers.