væskestrømningshastigheder

Fluid flow, or væskestrømning, refers to the motion of liquids and gases as they respond to pressure differences, gravity, and interactions with boundaries. It is described by the conservation laws of mass, momentum and energy, and is modeled with equations that can be solved analytically in simple cases or numerically for complex geometries. The fundamental framework includes the continuity equation, which expresses conservation of mass, and the Navier–Stokes equations, which express conservation of momentum for viscous fluids. For many liquids at moderate speeds the flow can be treated as incompressible, meaning density is approximately constant.

Flow regimes are commonly classified by the Reynolds number, Re = ρvL/μ, which compares inertial to viscous forces. Low-Re flows tend to be laminar and orderly, while high-Re flows become turbulent with chaotic fluctuations. Classic results include Poiseuille flow, describing steady laminar flow in a circular pipe, and Bernoulli’s principle for inviscid, steady flow along a streamline. Boundary layers describe the region near solid surfaces where viscous effects are significant.

Practical analysis relies on both analytical solutions for simplified geometries and numerical methods such as computational fluid dynamics (CFD) for complex domains. Experimental techniques, including flow visualization, hot-wire anemometry, and particle image velocimetry, provide velocity fields and flow rates. Common applications span engineering systems (piping, HVAC, and propulsion), aerodynamics, and physiological flows such as blood movement in vessels.

Understanding fluid flow enables efficient design, prediction of transport processes, and insight into natural phenomena where fluids interact with forces and boundaries.