High-speed Flow in A Channel
As a flow in a channel becomes supersonic, one significant change takes place. The conservation of mass flow rate leads one to expect that contracting the flow channel would increase the flow speed (i.e. making the channel narrower results in faster air flow) and at subsonic speeds this holds true. However, once the flow becomes supersonic, the relationship of flow area and speed is reversed: expanding the channel actually increases the speed.
The obvious result is that in order to accelerate a flow to supersonic, one needs a convergent-divergent nozzle, where the converging section accelerates the flow to sonic speeds, and the diverging section continues the acceleration. Such nozzles are called de Laval nozzles and in extreme cases they are able to reach hypersonic speeds (Mach 13 (9,896 mph; 15,926 km/h) at 20°C).
An aircraft Machmeter or electronic flight information system (EFIS) can display Mach number derived from stagnation pressure (pitot tube) and static pressure.
Read more about this topic: Mach Number
Famous quotes containing the words flow and/or channel:
“The current of our thoughts made as sudden bends as the river, which was continually opening new prospects to the east or south, but we are aware that rivers flow most rapidly and shallowest at these points.”
—Henry David Thoreau (1817–1862)
“Children belong in families, which, ideally, serve as a sanctuary and a cushion from the world at large. Parents belong to society and are a part of that greater world. Sometimes parents are a channel to the larger society, sometimes they are a shield from it. Ideally they act as filters, guiding their children and teaching them to avoid the tempting trash.”
—Louise Hart (20th century)