Perfect fluid

[citation needed] Real fluids are "sticky" and contain (and conduct) heat.

Perfect fluids are idealized models in which these possibilities are ignored.

Specifically, perfect fluids have no shear stresses, viscosity, or heat conduction.

A quark–gluon plasma[1] and graphene are examples of nearly perfect fluids that could be studied in a laboratory.

[2] In classical mechanics, ideal fluids are described by Euler equations.

Ideal fluids produce no drag according to d'Alembert's paradox.

In space-positive metric signature tensor notation, the stress–energy tensor of a perfect fluid can be written in the form where U is the 4-velocity vector field of the fluid and where

This takes on a particularly simple form in the rest frame where

Perfect fluids are used in general relativity to model idealized distributions of matter, such as the interior of a star or an isotropic universe.

In general relativity, the expression for the stress–energy tensor of a perfect fluid is written as where