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''Inviscid flow'' is a fluid flow where viscous (friction) forces are small in comparison to inertial forces, i.e. a flow with a Reynolds number $Re\; gg\; 1$. The assumption that viscous forces are negligible can be used to simplify the Navier-Stokes equations to the Euler equations.
In the case of incompressible flow, the Euler equations governing inviscid flow are:
:$$
holeft(
rac{partial}{partial t}+{old u}cdot
abla
ight){old u}+
abla p=0

:$$
abla cdot mathbf{u} = 0
which, in the stationary case, can be solved using potential flow theory. More generally, Bernoulli's equation can be used to analyse certain time-dependent compressible and incompressible flows.

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Problems with the inviscid flow model

See also

Problems with the inviscid flow model

While throughout much of a flow the effect of viscosity may be small, a number of factors make the assumption of negligible viscosity invalid in many cases. Viscosity often cannot be neglected near boundaries because the no-slip condition can generate a region of large strain rate (a boundary layer) which enhances the effect of even a small amount of viscosity. Turbulence is also observed in some high Reynolds number flows, and is a process through which energy transferred to decreasingly small scales of motion until it is dissipated by viscosity.

See also

★ Viscosity

★ Fluid dynamics

★ Stokes flow, in which the viscous forces are much greater than inertial forces.