Journal of Hydraulic Engineering

Wall shear stress modification in self-aerated flows has been observed in boundary layer–type flows mainly in the form of drag reduction. Due to its complexity, drag reduction has predominantly been studied using experimental techniques and empirical analyses, whereas the development of conceptual approaches is limited. In this study, two-phase open-channel flow equations with variable density are revisited and bottom air concentration is identified as a key parameter for drag reduction in air-water flows. The application of this new theory to smooth and stepped chute flows is introduced, and implications for the determination of friction factors are discussed. A modified version of the Manning-Strickler formula is proposed to model friction factors across a wide range of roughness and bottom air concentration levels.

The flow in every meandering channel with a specific sinuosity has its own convective pattern. However, most of the previous numerical works did not take this nature as an essential aspect when validating their computed flows, and even some typical works turned out to fail to capture the correct convective patterns of meandering flows. In this paper, a numerical model is established on the basis of the three-dimensional continuity and Reynolds-averaged Navier-Stokes (RANS) equations and used to simulate two representative laboratory tests where the channels had different sinuosities and the flows manifested different convective patterns. The agreement between the computed and measured flow characteristics for both tests demonstrates that the present model can capture the correct convective patterns of meandering flows for various sinuosities. The reasons are inferred as the use of the $k\text{-}\epsilon$ turbulence model to determine the eddy viscosity throughout almost the whole flow depth and the use of the antisymmetrically identical condition at the inlet and outlet boundaries of a meander loop.

This paper explores flood-induced hydrodynamic and debris impact forces on masonry arch bridges using the numerical method smoothed particle hydrodynamics (SPH). Masonry arch bridges make up a significant proportion of the bridge stock in many parts of the world, including the UK and US. Although the masonry arch is a durable bridge form, those spanning watercourses can be vulnerable to the effects of flooding. Where fast flood flows impinge on the bridge superstructure, highly transient behavior is observed, which can lead to violent interactions, especially where debris is carried by the flow. This paper investigates flood-induced impact pressures on a typical single-span masonry arch bridge subject to hydrodynamic action and discrete floating debris. Different debris orientations relative to the bridge span are considered. Results revealed that the presence of the debris can lead to impact pressures an order of magnitude greater than the hydrodynamic conditions alone. Furthermore, the influence of debris orientation at impact was significant, with the 90° orientation resulting in higher peak impact pressures with shorter impact duration compared with the 0°.

Aeration occurs in many natural and human-made flows and must be considered in engineering design. In water infrastructure, air–water flows can be violent and of very high velocity. To date, most fundamental research and engineering design guidelines involving air–water flows have been based upon laboratory scale measurements with limited validation at prototype scale with larger Reynolds numbers. Herein, unique measurements were conducted in high-velocity air–water flows in the tunnel chute of the 225-m-high Luzzone arch Dam in Switzerland. For each of the two test series, an array of 16 double-tip conductivity probes was installed in the circular tunnel chute of 3 m diameter and slope of $\approx 37°$ measuring void fraction, bubble count rate, interfacial velocity, and droplet sizes for four different discharges of up to $15.9{\mathrm{m}}^3/\mathrm{s}$ corresponding to Reynolds numbers of up to $2.4\times {10}^7$ and mean flow velocities of up to $38\mathrm{m}/\mathrm{s}$. Void fraction and interfacial velocity distributions, as well as design parameters such as depth-averaged void fractions and flow resistance, compared well with previous laboratory studies and empirical equations. The droplet chord sizes exhibited scale effects, and care must be taken if air–water mass transfer and droplet momentum exchange processes are assessed at the laboratory scale.

Rectangular piano key weirs (RPKW) have been introduced as an innovative type of labyrinth weir with a smaller footprint and high hydraulic performance. To date, limited attention has been paid to PKWs with other planforms. In this study, experiments and numerical simulations were conducted to investigate and compare the discharge capacity of unsymmetrical trapezoidal piano key weirs (TPKW) and classical rectangular PKWs with varying inlet/outlet key width ratios. Results indicate that, even if all other parameters are held constant, the discharge capacity of a trapezoidal PKW can still be further improved by up to 10% through optimizing the key width ratio. Relative to RPKWs, TPKWs were proven to be more efficient, especially for high relative heads because of the larger outlet cross section, and less efficient for low relative heads due to the relative lack of total crest length. For the specific geometric configurations considered in this study, the optimal range of key width ratio for TPKW and RPKW is likely to be within 1.30 to 1.57 and 1.50 to 1.77, respectively. At the end of this study, a new PKW configuration is introduced, which combines the advantages of both geometries (rectangular and trapezoidal) and improves the overall weir efficiency up to 8%.

The Sidoardjo Mud Volcano in East Java, Indonesia, started on May 29, 2006. The average daily discharge of the mud volcano is $\mathrm{50,000}{\mathrm{m}}^3/\mathrm{day}$, with a 35% average concentration of sand, silt, and clay. Since 2017, the finer fractions have been diverted to the Madura Strait through the Porong River. The Ginonjo Outlet serves as a point source with a constant discharge of $45{\mathrm{m}}^3/\mathrm{s}$ and an average sediment concentration of $\mathrm{57,000}\mathrm{mg}/\mathrm{L}$. The settling and transport of fine sediments were studied through field measurements at 106 cross sections over 16 km of the Porong River. At low flow, maximum concentrations decreased from 4,200 to $90\mathrm{mg}/\mathrm{L}$ in the study reach. The two-dimensional mixing and settling model with flocculation resulted in better agreement with the observed data than did models without flocculation. Flocculation tests showed an increase in settling velocity from 0.013 to $0.028\mathrm{mm}/\mathrm{s}$. Flocculation affected settling of approximately 38% of the total sediment load. The fractions coarser than 92 μm settled within the first 4 km from the point source.

Accumulation of floating woody debris at flow control structures can result in reduced discharge efficiency. Labyrinth weirs may be more likely to catch debris on the crest than other weirs due to their ability to pass large discharges with relatively small heads. Therefore, prompted from field data at Lake Brazos Dam, a laboratory-scale hydraulic model study was performed to evaluate the floating woody debris blocking sensitivity of labyrinth weirs in channel and reservoir applications, including arced labyrinth weirs. Experimental test results noted debris entrapment locations on the crest and that debris blockage probability is primarily a function of trunk diameter and upstream head. Debris accumulation tests indicated that lower heads are more sensitive to debris blockage than higher heads. Specifically, for smaller flow depths the initial or reference head (without debris) increased by up to 17% with debris, while at higher reference heads the head increase due to debris was approximately 7% or less.

Numerical simulation of undular hydraulic jumps, which occur at an inflow Froude number slightly above unity, remain an important and enigmatic challenge in hydraulic engineering. In this study, a systematic assessment of the two-dimensional (2D) Reynolds averaged Navier Stokes–volume of fluid (RANS-VOF) equations coupled with the $k–\omega$ shear stress transport (SST) turbulence model was carried out for the simulation of undular jumps. The modeling strategies adopted for obtaining a stable undular jump profile are highlighted in this paper. The correlation between turbulence intensity at the jump toe and jump characteristics is also demonstrated. Comparison of laboratory observations with results obtained from experiments conducted under different discharge, approach Froude number, and inflow conditions demonstrated that the proposed 2D RANS model can accurately reproduce the key free-surface characteristics corresponding to undular jumps. The model was capable of reproducing the velocity and pressure fields with greater accuracy than the depth-averaged model. The model was also successful in reproducing the bottom recirculation region below the first wave crest for undular jumps with partially developed boundary layer at the jump toe. The proposed 2D RANS-VOF computational fluid dynamics (CFD) model coupled with the k–ω SST turbulence closure equation is, therefore, recommended as an efficient tool for hydraulic computations, especially for the simulation of weak undular jumps.