Geoscience Reference
In-Depth Information
features of the stepped drop structures for the effective design of the river
environmental works must be necessary.
The present study deals with the oxygen transfer by the air entrainment
by the flow characteristics at the stepped drop structure. Hydraulic analysis
on the oxygen transfer by the nappe flow and the skimming flow, and
the relationships of the oxygen transfer to the hydraulic parameters were
presented through the hydraulic experiments.
2. Flow Characteristics and Oxygen Transfer
Stepped drop structures may be characterized by two types of flows: nappe
flow and skimming flow shown in Fig. 1.
1
At low flow rates and for relatively large step height, nappe flow occurs.
The water bounces from one step onto the next one. Dominant flow features
include, at each drop, an enclosed air cavity, a free-falling jet, a nappe
impact and a subsequent hydraulic jump on the downstream step. Energy
Hydraulic
jump
Supercritical
flow
Subcritical
flow
d
c
Free-falling nappe
Nappe flow with
hydraulic jump
h
air pocket
stagnation point
V
V
d
d
Flow
recirculation
Flow
recirculation
Skimming flow on
steep-slope channel
Skimming flow on flat-slope channel
Fig. 1.
Sketch of the nappe and skimming flow.
