The important dimensionless numbers in fluid mechanics are
1. Reynold’s number
2. Froude’s number
3. Weber’s number
4. Euler’s number
5. Mach’s number or Cauchy’s number
Reynold’s number: Reynold’s number is the ratio of inertia force to the viscous force.
Froude’s number: Froude’s number is the ratio of inertia force to the gravity force.
Weber’s number: Weber’s number is the ratio of inertia force to the surface tension force.
Euler’s number: Euler’s number is the ratio of inertia force to the pressure force.
Mach’s number or Cauchy’s number: Mach’s number or Cauchy’s number is the ratio of inertia force to the elastic force.