Laajennushyötysuhde

Laajennushyötysuhde, often translated as expansion ratio, is a term used in fluid dynamics and engineering to describe the ratio of the exit area to the inlet area of a device designed to expand a fluid. This device is typically a nozzle or a diffuser. For a nozzle, the fluid's velocity increases as it expands, and the expansion ratio is crucial in determining the final velocity and pressure of the exiting fluid. A larger expansion ratio generally leads to a greater velocity increase and a more significant pressure drop.

In the context of rocket engines, the expansion ratio of the nozzle is a critical design parameter. It is optimized to match the ambient pressure at the altitude where the rocket is expected to operate most of its mission. For sea-level operation, a smaller expansion ratio is preferred to avoid over-expansion, where the exhaust pressure drops below ambient pressure, leading to flow separation and reduced thrust. Conversely, for vacuum operation, a very large expansion ratio is desirable to maximize thrust by allowing the exhaust gases to expand as much as possible.

Diffusers, which perform the opposite function of nozzles by slowing down a fluid and increasing its pressure, also have an expansion ratio. Here, the ratio of the exit area to the inlet area is important for efficiently converting kinetic energy into potential energy. The concept of expansion ratio is fundamental to understanding and designing systems involving fluid flow and energy conversion.