Inviscid flow

In fluid dynamics, inviscid flow is the flow of fluid that is not viscous. The principles of inviscid flow can also be applied to the flow of fluids of low viscosity in regions of the flow field where it is known there is little viscous activity.

The Reynolds number of inviscid flow approaches infinity as the viscosity approaches zero. Where viscous forces are non-existent the Navier–Stokes equations can be simplified to a form known as the Euler equations. This simplified equation is derived by considering an inviscid fluid. Using the Euler equation, many fluid dynamics problems involving low viscosity are easily solved; however, the assumption of negligible viscosity is not valid in the region of the flow field near a solid boundary (the boundary layer) or, more generally in regions with large velocity gradients which are evidently accompanied by viscous forces.

The flow of a superfluid is inviscid.