Anströmung

Anströmung is a term used in German fluid dynamics to denote the incident or approach flow that encounters a surface, boundary, or inlet. It describes the undisturbed upstream fluid velocity and state that set the inbound conditions for the local flow around objects such as wings, ducts, turbines, or vehicles. The concept is often discussed in contrast to the surrounding or downstream flow fields and to the flow inside a device or channel.

In practice, anströmung is characterized by the velocity vector relative to the surface, its direction, speed, as well as the fluid’s density, temperature, and turbulence intensity. Engineers study the anströmung to predict pressure distributions, lift, drag, and heat transfer. In aerodynamics, the angle and magnitude of the anströmung influence boundary-layer development, potential flow, and separation phenomena. In turbomachinery and inlet design, controlling the anströmung helps achieve a more uniform, efficient flow entering a component, reducing losses and improving performance.

In meteorology and building physics, anströmung describes how external wind or air enters openings, interacts with structures, and affects ventilation, comfort, and energy performance. The term is primarily used in German-language literature; in English-language texts it is often translated as incident flow or approach flow, depending on context. When discussing the local flow field, anströmung serves as a key boundary-condition descriptor alongside free-stream conditions and the surrounding flow.