Határrétegelmélet

Határrétegelmélet, which translates to "boundary layer theory" in English, is a fundamental concept in fluid dynamics. It describes the thin layer of fluid close to a solid surface where viscous effects are significant. Outside this layer, the fluid flow can often be treated as inviscid, meaning viscosity is negligible.

The theory was pioneered by Ludwig Prandtl in 1904. He proposed that for high Reynolds number flows, the bulk of the fluid behaves as if it were inviscid, but a thin layer adjacent to the surface experiences significant shear stress due to viscosity. Within this boundary layer, the fluid velocity changes rapidly from zero at the surface (due to the no-slip condition) to the free-stream velocity further away.

The properties of the boundary layer depend on whether the flow within it is laminar or turbulent. Laminar boundary layers are characterized by smooth, ordered fluid motion, while turbulent boundary layers exhibit chaotic, irregular motion with increased mixing and momentum transfer. The transition from laminar to turbulent flow is a critical aspect of boundary layer behavior.

Understanding boundary layers is crucial for analyzing phenomena such as drag on an object, heat transfer between a fluid and a surface, and the design of aerodynamic and hydrodynamic systems. It allows for simplifications in complex fluid flow problems by separating the flow into two distinct regions with different governing equations.