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Measure Flow Rates in Open Channel such as Flumes and Irrigation Ditches. Figure 3.20 (p. 124) Rectangular, sharp-crested weir geometry. Figure 3.21 (p. 126) Representation of the energy line and the hydraulic grade line. HGL vs. EGL. • For stationary bodies such as reservoirs or lakes, EGL
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Measure Flow Rates in Open Channel such as Flumes and Irrigation Ditches
Figure 3.20 (p. 124) Rectangular, sharp-crested weir geometry.
Figure 3.21 (p. 126) Representation of the energy line and the hydraulic grade line.
HGL vs. EGL • For stationary bodies such as reservoirs or lakes, EGL and HGL coincide with the free surface of the liquid. • EGL is always a distance V2/2g about the HGL. The two lines converges when velocity decreases and diverges when velocity increases. • Mechanical energy loss due to frictional effects causes the EGL and HGL to slope downward in the direction of flow.
The energy line and hydraulic grade line for flow from a tank, (b) discharge from a reservoir through a diffuser, (c) idealized Bernoulli type flow
Fluid Kinematics • Fluid Kinematics deals with describing the motion of fluids without necessarily considering the forces and moments that cause the motion. • Lagrangian description (following a fluid particle) • Eulerian description (flow field)
Lagrangian Description With a small number of objects, such as billiard Balls on a pool table, individual objects can be tracked. Newton’s laws are used to obtain the momentum and kinetic energy exchanged
Difficulties with Lagrangian Description • Fluid particles can not be easily defined or identified as fluid particles move around • Fluid is a continuum, interactions between particles are not easy to describe • Fluid parcels continuously deform as they move • Nevertheless, many practical applications of involving tracking a passive scalars in a flow, rarefied gas dynamics calculations concerning of reentry of a spaceship into the earth’s atmosphere, development of flow measurement based on particle imaging.