Realfluid

Realfluid is a term used in physics and engineering to refer to real fluids in contrast to idealized or simplified fluid models. Real fluids possess properties such as viscosity and thermal conductivity, and their density can vary with pressure and temperature. They may also exhibit surface tension and phase changes, and many fluids show non-Newtonian behavior where viscosity depends on shear rate.

In fluid dynamics, real-fluid behavior is described by the Navier–Stokes equations together with appropriate constitutive relations that specify how stress relates to strain and other conditions. Viscosity leads to energy dissipation and shear stresses, while compressibility becomes important for gases at high speeds or large pressure variations. Non-Newtonian fluids add further complexity, with viscosity depending on shear rate, time, or history. Surface tension and multiphase interactions influence interfacial flows and phase transitions.

Real-fluid modeling is essential across many fields, including aerospace, hydraulics, chemical processing, and climate science. It contrasts with ideal-fluid models, which assume inviscid, incompressible, and often single-phase flow for analytical tractability, but may yield inaccuracies near boundaries or under conditions where viscous or compressible effects are significant. Real-fluid analyses therefore rely on experimental data and computational methods to capture true flow behavior.

Common real fluids include water, air under standard conditions, oils, and liquid metals. Because their properties depend on temperature, pressure, and composition, real-fluid calculations often require empirical data or equation-of-state models and, in many cases, numerical simulation through computational fluid dynamics.