Journal of Hydraulic Engineering

This article aims to provide a comprehensive appraisal on the current status of three-dimensional (3D) numerical modeling of local scour around instream hydraulic structures. Many computer models have been developed or are in development to simulate riverbed morphology. Local scour, however, is a special category that requires in general a 3D model based on some averaged/filtered form of the Navier-Stokes (NS) equations and a 3D sediment transport model. Only limited number of 3D scour codes are available for practical usage; there is also a lack of literature on the limitations of the models in capturing the scour-producing flow and the sediment transport solvers embedded within. For 3D local scour modeling, the main intrinsic uncertainty lies primarily in the sediment part. In this article, the basic theory and the state of the art of current 3D local scour models are reviewed, focusing primarily on the sediment solver, and future research needs are discussed.

This paper proposes a modification to a previous shock tracking–capturing approach used for simulating transient flows in stormwater systems. Based on the Godunov-type finite-volume (FV) method, this modified approach uses two governing equations for free-surface and pressurized flows discretized. The free-surface flow is simulated using an explicit FV method. However, the pressurized flow is discretized on one control volume and simulated using an implicit FV method. Different examples will be solved to examine the abilities of the proposed modified approach. The examples are pressurized and partially pressurized flows, including the water hammer, the pipe-filling bore advancement, and air pocket entrapment problems. The partially pressurized flow following air pocket entrapment is analyzed under different conditions including various ranges of driving pressure, air and water lengths, as well as dry-bed and with and without air-release conditions. It will be shown that the proposed modification can result in improving the overestimated peak values and the underestimated attenuation of pressure distribution. In addition, it will be shown that the proposed modified approach exhibits less oscillatory behavior, particularly in simulating pipe-filling bore advancement.

The effluents produced by reverse osmosis desalination plants are usually disposed under the surface of the sea as inclined negatively buoyant jets (INBJ), to achieve the highest mixing rate. Bed slope in the local environment is one of the contributing factors in the behavior of INBJs. The aim of the present study is to utilize large eddy simulation (LES) to study the effects of the bed slope on the dilution and spreading of INBJs with 30°, 45°, and 60° nozzle angles. In this regard, five down slopes, 0°, 5°, 10°, 15°, and 20° were considered for the bed, and the mixing and geometrical properties of INBJs were studied in both jet plume and spreading layer regions. Present simulations show that the increase in the bed slope for all the three nozzle angles favorably increases the dilution of the INBJs at return point, concentration buildup point (CBP), impact point, and on the bed. For a 20° increase in the bed slope, the relative increase in the dilution at CBP of 30°, 45°, and 60° INBJs is calculated as 167.75%, 81.13%, and 107.43%, respectively. Also, the centerline dilution is the highest for the 60° nozzle angle at each bed inclination. The distribution of the mean concentration on the bed shows that an increase in the nozzle and bed inclination results in a significant decrease in the mean concentration and the area in which the effluent alters the ambient water quality. Present results suggest that the INBJs should be discharged into the ambient water in sloped environments, and the nozzle angle of 60° is preferred to 30° and 45° regardless of the bed inclination.

A spillway is a conveyance structure designed to pass flood waters. The construction of steps down the steep chute may contribute to some energy dissipation, in turn reducing the size of the downstream energy dissipator. A unique opportunity for field observations was provided at the Hinze Dam Stage 3 (Gold Coast, Australia) between 2013 and 2021. Detailed observations were conducted for six overflow discharges within $20.9{\mathrm{m}}^3/\mathrm{s}<\mathrm{Q}<334{\mathrm{m}}^3/\mathrm{s}$ with Q the volume discharge, corresponding to dimensionless discharges $0.44<{\mathrm{d}}_{\mathrm{c}}/\mathrm{h}<2.82$ with $d_c$the critical depth and h the step height and Reynolds numbers ranging from $0.68\times {10}^7$ to $10.8\times {10}^7$. Some uniquely novel aspects of the research included a series of systematic observations of a full-scale prototype stepped spillway, operating with a relatively wide range of unit discharges $1.71{\mathrm{m}}^2/\mathrm{s}<\mathrm{q}<27.3{\mathrm{m}}^2/\mathrm{s}$ with q the unit discharge. The observations provided new information on the basic hydraulic flow patterns, inception of free-surface aeration, and surface velocity field. Overall, the current study detailed some unique insights into the mechanisms leading to air entrainment in skimming flows in high-velocity prototype stepped spillways. While surface velocity measurements were achieved, the limitations are discussed and future enhancements are proposed.

A major challenge of prototype air-water flow measurement is the limited endurance of fragile phase-detection needle sensors in a high-momentum flow with risks of debris damage and particulate erosion. In the present study, a thick-tip conductivity probe is manufactured with sturdier needle sensors than the commonly used laboratory-sized probes. The large sensor tip had low chance to pierce small air bubbles and water droplets, leading to deterioration in the signal output quality, which prevents derivation of basic air-water flow properties using the conventional signal processing technique. To extract valid phase information from the low-quality signal, calibration experiments were conducted in laboratory with reference to a regular-sized probe, to explore a proper signal processing method for the thick-tip probe. The method was validated, and the thick-tip probe was deployed in a field hydraulic jump measurement, allowing for access to the air-water flow characteristics of the prototype D-type jump with a Reynolds number of ${1.88\times 10}^6$. Despite the effort of signal calibration and compensation, the use of the thick-tip probe does not guarantee accurate bubble size measurement and requires higher sampling frequencies. Therefore, probes with fine sensor tips are still preferable in prototype measurement.