Stokes flow, named after Stokes' approach to viscous fluid flow, is the mathematical model in which the Reynolds number is so low that it is presumed to be zero.

What happens when Reynolds number is 0?

However, if we put the viscosity as 0 in the equation of Reynold's no, it will result in infinity which suggests fluid to be fully turbulent (i.e Re>4000) which then doesn't support fluid to be ideal.

Can a Reynolds number less than 100?

When flows have a high enough Reynolds number to be fully turbulent the momentum mixing induced by the turbulence often leads to a mean flow with an effective Reynolds number that is less than 100, well within the range of resolvable scales.