Inviscid flow

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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 . 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

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.

[edit] 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.

[edit] See also

• Viscosity
• Fluid dynamics
• Stokes flow, in which the viscous forces are much greater than inertial forces.