230
P. Liu
H 0
C
C
C
C
Fig. 3.57 Water hammer fluctuation process of gradual closing of water diversion
pipeline valve
reservoir
Surge shaft
Water hammer wave
propagation
Pressure piping
Hydraulic
turbine
H
z
3-3
0
0
Wake channel
1-1
2-2
Fig. 3.58 Water hammer fluctuation process of gradual closing of turbine guide
vane of hydropower station
From the physical essence, the unsteady flow in pressure pipeline is a kind
of physical phenomenon of disturbance wave propagation in the pipeline.
Wherever the wave goes, it will cause the hydraulic elements of the original steady flow state to change obviously with time. Because there is no free
surface in the pressurized pipe, the water hammer phenomenon will cause
the change in density and the elastic deformation of the pipe wall in addition
to the change in velocity and pressure. From the mechanical particle of view,
the oscillating flow of water in the pipeline mainly propagates in the form of
gravity wave, and the inertial force and gravity play the main role in the flow
process. In the water hammer phenomenon, the unsteady flow in the pipeline
propagates in the form of pressure wave (elastic wave), and the inertial force
and elastic force play the main role.