Doctor of Philosophy (PhD)
Civil and Environmental Engineering and Construction
First Committee Member
Second Committee Member
Third Committee Member
Fourth Committee Member
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To avoid disrupting the flow in flood control channels with lateral drainage pipes, or impact channel capacity, confluences are constructed at small angles (Maximum 30○). These small angles are costly to construct, since they require more real estate than greater angles.
By performing several laboratory experiments in the Fluid Dynamics Laboratory of the University of Nevada, Las Vegas (UNLV) and utilizing a numerical model (FLOW-3D), this study investigated the impact of submerged lateral drainage pipe discharges into rectangular open channels, on flow topology in the confluence hydrodynamics zone (CHZ). This was done across a range of channel widths, flow rates, Froude numbers, junction angles, inlet pipe diameters, and lateral flows, to main channel flow ratios. The flow topology information in channel confluences with lateral drainage pipes is necessary to determine the channel wall heights required to contain flows in the vicinity of laterals.
The experiments were conducted in two different flume configurations with different widths of 16” and 24”, and three junction angles of 30°, 45°, and 90°. They had lateral flow to the main channel flow ratios of 2.5% and 5% for the wide channel configuration, and 2.5%, 5%, and 7.5% for the narrow channel configuration, as well as different Froude numbers from 0.7 (sub-critical) to 3.27 (super-critical). The experimental results showed that, as the junction angle and the lateral flow proportions increased, the maximum water height ratios in the channel also increased.
Furthermore, the simulations were performed on three different channel widths of 10’, 25’, 50’, with three initial water heights in the channel of 4’, 7’, 10’. They included three junction angles of 30°, 45°, 90° and three lateral pipe diameters of 1.5’, 3’, 5.’ The lateral flow to main channel flow ratios were 2.5%, 5.0%, 10% (based on the flow rates in the 10’ channel, in order not to exceed a maximum flow velocity of 50 ft/s in the pipe), as well as three Froude numbers of 0.8, 1.2, 2.0.
Several zones were identified in the open channel confluences that were simulated: (1) a zone of flow stagnation near the upstream junction corner; (2) a zone of flow deflection; (3) a zone of negative pressure; (4) a flow separation zone below the downstream junction corner; (5) the water level drawdown immediately downstream of the junction; (6) the maximum water height; and, (7) a flow recovery zone in the downstream of the channel. The simulation results showed that the junction angle and momentum ratios were the main factors impacting the shape of these zones, and consequently, the flow topology in the CHZ.
Moreover, it was observed that as the two flows merged in the confluence, the flow rate and velocity in the channel and pipe, along with the junction angle, were the main factors impacting maximum water height in the CHZ. Therefore, as the product of the mass flow rate and velocity is the momentum, and as the perpendicular component of the momentum through the lateral pipe impacts the flow characteristics in the channel, (QV + qv(cosθ))/(qv(sinθ)) was related to the relative increase in the channel’s water height (H/H0), to develop conservative design curves.
The results showed that flow structure and water surface variations in the CHZ were highly influenced by the junction angle, as well as the momentum ratios of the channel flow and pipe flow ((QV + qv(cosθ))/(qv(sinθ))). Moreover, it was observed that as the (QV + qv(cosθ))/(qv(sinθ)) increased, H/H0 in the channel decreased. Among almost all scenarios, in the cases that the value of (QV + qv(cosθ))/(qv(sinθ)) was greater than 500, the channel’s maximum increase in water height was 20%. Similarly, in cases in which (QV + qv(cosθ))/(qv(sinθ)) was greater than 1,000, the channel’s maximum increase in water height was 10%. This implies that the (QV + qv(cosθ))/(qv(sinθ)) values of 500 and 1,000 can be considered as critical numbers in designing open channel confluences with lateral drainage pipes.
Finally, the results were used to develop conservative design curves for channel confluences with lateral drainage pipes. The developed design curves can be used to analyze water surface elevation variations in different channel and pipe configurations and flow conditions to determine the channel wall heights required to contain flows in the vicinity of laterals.
Channel and pipe confluence; Confluence hydrodynamics zone; Flood control channel; Open channel flow
Civil Engineering | Hydraulic Engineering
University of Nevada, Las Vegas
Nazari-Sharabian, Mohammad, "A Hybrid Experimental-Numerical Study on the Flow Topology in the Confluence Hydrodynamics Zone of an Open Channel with Lateral Drainage Pipe Discharge" (2020). UNLV Theses, Dissertations, Professional Papers, and Capstones. 3934.
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