Hydraulics and Fluid Mechanics in ME
The hammer blow in pipes occurs when

There is excessive leakage in the pipe
The pipe bursts under high pressure of fluid
The flow of fluid through the pipe is gradually brought to rest by closing of the valve
The flow of fluid through the pipe is suddenly brought to rest by closing of the valve

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Hydraulics and Fluid Mechanics in ME
Mach number is significant in

full immersion or completely enclosed flow, as with pipes, aircraft wings, nozzles etc
all of fhe above
simultaneous motion through two fluids where there is a surface of dis-continuity, gravity force, and wave making effects, as with ship’s hulls
supersonics, as with projectiles and jet propulsion

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