inviskøs

Inviskös, or inviscid in English, describes a fluid whose viscosity is so small that viscous forces can be neglected for the purpose of analysis. The term is an idealization used in fluid dynamics and aerodynamics to simplify the governing equations of motion. Real fluids always possess some viscosity, but the inviscid assumption remains a common starting point in theory and computation.

The motion of an inviscid fluid is described by the Euler equations, which arise from the Navier–Stokes equations with zero viscosity. Under this assumption, viscous shear stresses are ignored, and along a streamline Bernoulli’s principle can apply for steady, incompressible flow. When combined with incompressibility, potential-flow theory often provides analytic insights for simple geometries.

Applications of inviscid models include external aerodynamics at high Reynolds numbers, where the flow away from solid surfaces can be approximated as inviscid, and various problems in hydrodynamics and atmospheric science. In computational fluid dynamics, inviscid or panel-method approaches estimate pressure distributions and global flow features, typically used in conjunction with boundary-layer models to account for near-surface effects.

Limitations are inherent in the inviscid assumption. It fails near solid boundaries where viscous boundary layers form, in regions with significant shear or turbulence, and where viscous dissipation matters for energy budgets. As a result, inviscid solutions are often treated as first approximations or combined with viscous models in hybrid or multi-region methods to capture both exterior and near-wall behavior.