Fluiddynamikens

Fluiddynamikens, or fluid dynamics, is the branch of physics and engineering that studies the motion of fluids and the forces acting on them. It covers how fluids move, how pressure and velocity fields develop, and how momentum, energy, and mass are transferred within and between fluid regions. The field applies to liquids and gases in a wide range of contexts, from microscopic flows in microfluidic devices to planetary atmospheres and ocean currents.

Governing equations: The motion of fluids is described by conservation of mass (the continuity equation), conservation of momentum (the Navier–Stokes equations for viscous fluids; Euler equations for inviscid flow), and often energy conservation. Incompressible flow assumes density variation is negligible; compressible flow accounts for density changes, important at high speeds or temperature variations. Viscosity introduces internal friction and leads to boundary layers and potential turbulence.

Key concepts: Turbulence and laminar flow, characterized by Reynolds number. Boundary layers develop near solid surfaces. Vorticity and circulation describe rotational motion. Potential flow analyzes irrotational flows using simplifying assumptions. Dimensional analysis and nondimensional numbers help compare systems.

Methods: Analytic solutions exist for simple cases (steady, inviscid, one-dimensional). Numerical simulation with computational fluid dynamics (CFD) solves complex flows. Experimental techniques include wind tunnels, dye or particle visualization, hot-wire anemometry, and particle image velocimetry (PIV).

Applications: Fluid dynamics informs aerospace engineering, automotive design, civil and environmental engineering, energy technology, meteorology, oceanography, and industrial processing.

History: Early insights emerged in fluid motion studies by Bernoulli and Euler. Navier and Stokes formulated the set of equations widely used today. The field has grown with experimental and computational tools, enabling advances in design and understanding of natural phenomena.