ChokedFlowEffekte

Choked flow, also known as sonic flow or critical flow, is a fluid dynamics phenomenon that occurs when the velocity of a fluid reaches the speed of sound in that medium. This typically happens in a convergent-divergent nozzle when the pressure ratio across the nozzle is sufficiently large. When choked flow is achieved, the mass flow rate through the nozzle becomes independent of the downstream pressure. Further decreases in downstream pressure will not increase the mass flow rate.

The effect is a consequence of the compressibility of the fluid. In a converging nozzle, as the fluid accelerates, its density decreases. At the throat of the nozzle, where the area is smallest, the fluid velocity reaches sonic speed (Mach 1). Beyond the throat, in the diverging section, if the pressure ratio is high enough, the fluid continues to expand and accelerate to supersonic speeds (Mach > 1). If the downstream pressure is too high, the flow will remain subsonic throughout the nozzle, and the mass flow rate will still be dependent on downstream pressure.

Choked flow is a critical concept in the design of supersonic wind tunnels, rocket engines, and various other fluidic devices. Understanding and controlling choked flow conditions are essential for achieving desired performance characteristics and ensuring operational stability. The mass flow rate at choked conditions is a function of the upstream stagnation conditions (temperature and pressure) and the properties of the fluid.