Flow-Field Complexity and Design Estimation of Pier-Scour Depth: Sixty Years since Laursen and Toch
Abstracts:This paper, written to celebrate the 60th anniversary of the Journal of Hydraulic Engineering, presents a structured, contemporary approach to scour-depth estimation that matches design method practicality to pier flow-field complexity. The approach involves a mix of semiempirical formulation, advanced experimentation aided by new instruments, and computational fluid dynamics (CFD). Highly useful for understanding complex pier flow fields, CFD holds patent promise for substantial use in design estimation of scour depth. Presently, however, CFD’s limited ability to simulate erosion and scour at a pier foundation hampers CFD’s practicality for design estimation of pier-scour depth. The writers reflect back 60 years when Laursen and Toch’s milestone publication provided major insights into pier scour, and when the hot-film anemometer first became available for investigating complex flow fields. Sixty years ago, pier flow fields were thought too complex to measure, or even visualize. The writers indicate where, today, further research into pier flow fields would benefit design estimation of scour depth.
Simple Modification of Manning-Strickler Formula for Large-Scale Roughness
Abstracts:Large-scale roughness renders the flow resistance underestimated with the Manning-Strickler (MS) formula. This can be corrected simply by considering the roughness-induced flow constriction. Two modified MS formulas have been therefore derived for pipe and open-channel flows, respectively. They are applicable for small- to large-scale roughness. Without making any adjustment of the constants involved, both formulas are successfully validated by experimental data, particularly for flows significantly affected by the large-scale roughness.
Experimental Quantification of Contaminant Ingress into a Buried Leaking Pipe during Transient Events
Abstracts:It has been hypothesized that negative pressures caused by transients within water distribution systems may result in ingress of contaminated groundwater through leaks and hence pose a risk to public health. This paper presents results of contaminant ingress experiments from a novel laboratory facility at The University of Sheffield. An engineered leak surrounded by porous media was subjected to pressure transients resulting from the rapid closure of an upstream valve. It has been shown that a pollutant originating externally was drawn in and transported to the end of the pipe loop. This paper thus presents the first fully representative results proving the occurrence and hence, risk to potable water quality of contaminant ingress.
Complementary Methods for Determining the Sedimentation and Flushing in a Reservoir
Abstracts:This study analyzes the changes expected in the Paute River in Ecuador as a result of the future construction of the Paute-Cardenillo Dam (owned by Celec Ep-Hidropaute). The project must remain in use throughout its projected useful life. For this reason, the operational rules at the reservoir need to consider sedimentation effects. Four complementary methods are used to study the sediment transport and flushing. Empirical formulas and one-dimentional (1D) simulations are used to estimate sedimentation in the reservoir. Two-dimensional simulations allow the analysis of a 72-h flushing operation in the reservoir. Three-dimensional simulations show the detail of the sediment transport through bottom outlets, where the effect of increasing the roughness due to the sediment transport in the bottom outlets is considered. The results demonstrate the utility of crossing different methods to achieve adequate resolution in the calculation of sedimentation and flushing operation in reservoirs.
Method to Estimate Complete Curves of Hydraulic Pumps through the Polymorphism of Existing Curves
Abstracts:Modeling of hydraulic machines is fundamental in steady and unsteady analysis. The simulations carried out in different scenarios will define the need for protection devices or other mechanisms that ensure the operational safety of the installation with minimum investment. In addition, the employment of pumps operating as turbines (PATs) for small hydropower plants are very common. PATs are also being considered for use in water supply networks for pressure control and energy generation. In this case, modeling the reverse rotation is necessary to evaluate project feasibility. This study proposes a method to predict the complete curves of pumps using only their normal operation data and curves of other machines with similar specific speed. The complete curves are modeled as a trigonometric series, where the coefficients are fitted using the particle swarm optimization (PSO) technique. The results are compared with laboratory tests and a simulation of a pump shutdown is made to verify the differences using the modeled curve and a similar one.
What Controls the Transition from Confined to Unconfined Flow? Analysis of Hydraulics in a Coastal River Delta
Abstracts:Recent field work at the Wax Lake Delta (WLD) in coastal Louisiana indicates lateral outflow from channels to islands upstream of the receiving basin; in this region of the delta the flow transitions from confined to unconfined (i.e., from a uniform discharge profile to a nonuniform discharge profile). The hydraulics of this transition zone and the controls exerted by vegetation, topography, and river discharge fluctuations are analyzed in this work. The shallow water equations are numerically solved in two model domains: an idealized channel-island complex and the full domain of the WLD. In both domains, a significant fraction of the river discharge flows laterally from the channels to deltaic islands before reaching the receiving basin. Vegetation roughness within the delta islands significantly impacts the fraction and rate of lateral outflow from the channel, while river discharge fluctuations have a limited effect, due to the backwater control on the subcritical flow. The presence of vegetation in the islands tends to increase velocities within the channel, except in the region upstream of significant lateral outflow, where the velocity increases with decreasing vegetation roughness due to the lowered water level that reduces the flow cross-section. The topography establishes a lateral water surface gradient between the channel and the islands even with low vegetation roughness, which drives lateral flow. A velocity spreading angle is used to mark the transition from confined to unconfined flow; the angle generally increases up to the onset of unconfined flow and then decreases as the flow approaches the receiving basin and the flow in the island tends to align with that of the channel. The lateral outflow from the primary channels influences the hydraulics of the flow throughout the backwater length. The transition between confined and unconfined flow in coastal river deltas has a significant impact on the flow hydraulics and the resulting transport dynamics of solids and solutes.
Using an Improved Jet-Erosion Test to Study the Influence of Soil Parameters on the Erosion of a Silty Soil
Abstracts:A new jet-erosion test device has been developed to measure the erosion volume of soils under laboratory conditions. This device allows the determination of a complete erosion profile in addition to the depth of erosion below the jet. Jet-erosion tests using this new device were carried out on a silty soil to study the influence of the compaction dry density and water content on the erosion volume, critical shear stress (), linear erodibility coefficient (), and volumetric erodibility coefficient (). The results of these tests showed the major roles played by the compaction dry density and suction, and the important effects of the soil fabric and permeability on the penetration of water into the soil sample. An inverse relationship was observed between the volumetric erodibility coefficient and critical shear stress, which allowed an estimate of as a function of . The relationships between and , and between and , are quasi-parallel lines with smaller values of . Using the volumetric erodibility coefficient () rather than the usual linear erodibility coefficient () may lead to better prediction of erosion in hydraulic works because this coefficient is more-directly related to the loss of soil that must be quantified in practice.
Realistic Modeling of Leakage and Intrusion Flows through Leak Openings in Pipes
Abstracts:The hydraulics of leakage and intrusion flows through leak openings in pipes is complicated by variations in the leak areas owing to changes in pressure. This paper argues that the pressure–area relationship can reasonably be assumed to be a linear function, and a modified orifice equation is proposed for more realistic modeling of leakage and intrusion flows. The properties of the modified orifice equation are explored for different classes of leak openings. The implications for the current practice of using a power equation to model leakage and intrusion flows are then investigated. A mathematical proof is proposed for an equation linking the parameters of the modified orifice and power equations using the concept of a dimensionless leakage number. The leakage exponent of a given leak opening is shown to generally not be constant with variations in pressure and to approach infinity when the leakage number approaches a value of minus one. Significant modeling errors may result if the power equation is extrapolated beyond its calibration pressure range or at high exponent values. It is concluded that the modified orifice equation and leakage number provide a more realistic description of leakage and intrusion flows, and it is recommended that this approach be adopted in modeling studies.
Extended Theory of Hydraulic Hysteresis in Open-Channel Flow
Abstracts:The occurrence of hysteresis in a supercritical, open-channel flow approaching an obstacle has been recognized and investigated both experimentally and theoretically over the last few decades. However, the available theory and experimental investigations in the literature do not include the case when subcritical flow, controlled from downstream, can establish across the obstacle. The present work fills this gap by proposing a new theory that includes this occurrence and shows that two different steady flow states can establish for the same obstacle geometry and flow conditions—one with supercritical to subcritical transition far downstream from the obstacle, and the other with supercritical to subcritical transition far upstream from the obstacle. The proposed, more general theory includes the existing theory as a special case. Finally, two specific examples are illustrated and discussed, i.e., the case of flow over a raised bed hump, and the case of flow through a channel contraction.
Ring Diffuser to Dispense Antifoulants at Seawater Intakes
Abstracts:Traditional applications of chemicals to flows in water and wastewater plants are aimed at the flow itself, across its full cross section. However, at seawater intakes the need is to apply antifoulant chemicals not to the whole flow, but just around the inside wall of the intake pipe, as close to its entrance as possible. This desktop study combines the distribution hydraulics of multiport diffusers with an established design for a streamlined pipe entrance. The resulting design is of a ring diffuser incorporated within a streamlined entrance to a seawater intake pipe to provide uniform and well-positioned dosage of an antifoulant chemical stream all around the interior wall of the pipe, for effective and economical dosant application. Streamlining also minimizes head loss at the intake.