Journal of Hydraulic Engineering

Over the years, large eddy simulation (LES) has emerged as a tool to study problems in fluid mechanics characterized by complex physics and geometry. Among these, attention has been paid to studying problems of relevance in hydraulics and environmental fluid mechanics. For many years, LES has been used as an underresolved, or coarse, direct numerical simulation (DNS) where the scales unrepresented by the grid are modeled by means of a sub-grid-scale model, designed to drain energy from the resolved scales of motion. This method, although limited in applicability because of its computational cost, has allowed exploitation of the physics of a class of idealized flow fields of importance in hydraulic engineering. This study reports on investigations into processes of interest to hydraulic engineering. Some significant examples of such studies, together with relevant research from the literature, are given. Specifically, a description of literature related to turbulence in presence of longitudinal bars and local scours, studies of irregular roughness present in hydraulic applications, studies of Lagrangian and Eulerian dispersion processes, and studies of gravity currents is given. Although unable to give an answer to real-scale problems in hydraulic engineering, such studies allow unveiling of the physics behind phenomena present in hydraulics and, on the other hand, allow improved parametrization to be used in reduced-order models. The study is concluded with the author’s point of view on the importance of LES in hydraulic engineering in the upcoming future.

An experimental approach to examine the instabilities present on free surfaces of non-Newtonian fluid flow occurring in inclined channels is presented. When these flows occur in favorable conditions of inclination and discharge, it is observed that the propagation of instabilities can evolve into a specific type of wave, known as roll waves. The experimental apparatus developed allows simulation of stabilized roll waves in many scenarios for Newtonian and non-Newtonian rheology fluids, thereby constituting a highly useful approach for the understanding and control of roll waves. The fluid test for the non-Newtonian case used a gel rheometrically representative of the muddy material presented in natural disasters, such as mudflows. A low-cost, high-performance, and nonintrusive level measurement system (ultrasonic transducer) is proposed. A comparison between the experimental results obtained and a one-dimensional (1D) mathematical model exhibited good amplitude and wave-period estimations.

In hydraulic engineering, it is common to find geometric transitions where a channel is not prismatic. Among these geometric transitions, constrictions and obstructions are channel reaches in which a cross-section contraction is followed by an expansion. These nonprismatic reaches are significant because they induce rapid variations of the flow conditions. In the literature, the characteristics of the geometric transitions have been well studied for the case of the steady-state flow, but less attention has been dedicated to the unsteady flow conditions. The present paper focuses on the exact solution of the dam-break problem in horizontal frictionless channels where constrictions and obstructions are present. In order to find this solution, the geometric transition is assumed to be short with respect to the channel length, and a stationary solution of the shallow water equations is used to describe the flow through the nonprismatic reach. The mathematical analysis, carried out with the elementary theory of the nonlinear hyperbolic systems of partial differential equations, shows that the dam-break solution always exists and that it is unique for the given initial conditions and geometric characteristics of the problem. The one-dimensional mathematical model proves to be successful in capturing the main characteristics of the flow immediately outside the geometric transition, in comparison with a two-dimensional numerical model. The exact solution is then used to reproduce a set of experimental dam-break results, showing that the one-dimensional mathematical theory agrees with the laboratory data when the flow conditions through the constriction are smooth. The exact solutions presented here allow the construction of a class of benchmarks for the one-dimensional numerical models that simulate the flow propagation in channels with internal boundary conditions.

This paper experimentally studies the hydraulic characteristics of arced weirs located in a reservoir. The accuracy and ability of the response surface methodology (RSM), especially central composite design (CCD), to describe the hydraulic performance of this type of weir is validated using experimental data. The discharge coefficient of arced weirs is presented as a function of headwater ratio ($H_o/P$) and magnification ratio ($L/W$) using both traditional and response surface methodologies. The results indicate that like the traditional methodology, RSM-CCD introduces an acceptable model to determine the discharge coefficient of the arced weirs, but it requires a much lower number of experiments. The results show that the discharge coefficient of an arced weir decreases by increasing $H_o/P$ and $L/W$ [or arc angle ($\mathrm{\Theta }$)]. In addition, compared to a linear weir, the efficiency of an arced weir can increase up to 50%. Finally, based on the experimental results, a method is introduced for designing the in-reservoir arced weirs.

Aging embankment dams are commonly plagued with insufficient spillway capacity. To provide increased spillway capacity, stepped chutes are frequently applied as an overtopping protection system for embankment dams. Stepped chutes with sufficient length develop aerated flow. The aeration and flow turbulence can create a significant amount of splash over the stepped chute training wall if not appropriately accounted for in the design. Recommendations for stepped chute training wall height requirements are available in the literature with little to no supporting data available. Researchers at the USDA-Agricultural Research Service (ARS) Hydraulic Engineering Research Unit (HERU) in Stillwater, Oklahoma, conducted a series of tests in a near prototype scale stepped chute facility to quantify the maximum splash height, $y_{sp}$, expected from aerated flow and to provide design recommendations for training wall height necessary to minimize erosive splash over the wall. Data indicate the maximum $y_{sp}$ ranged between 1.1 and 3.7 times the critical flow depth ($d_c$) and between 2.3 and 5.5 times the bulked flow depth ($y_{90}$). For $0.035\le h/d_c<0.4$, the minimum training wall height required above the step edge downstream of the free-surface inception point, $y_{sw}$, is $1.4y_{90}$. For $0.4\le h/d_c\le 1.1$, $y_{sw}$ normalized by $y_{90}$ follows a simple power function of $h/d_c$. According to the data, an increase of $y_{sw}$ to approximately $2.0y_{90}$ may be needed. These minimum training wall height requirements are recommended for use in skimming flow conditions (i.e., $0.035\le h/d_c\le 1.1$) for nonconverging stepped chutes with slopes ranging 10–30°.

In the study of mechanics of sediment transport, settling velocity is one of the important parameters because it is needed to solve the governing equations. It has been established that the presence of particles in the flow reduces the settling velocity of a particle, and this phenomenon is commonly known as hindered settling. The clear water settling and hindered settling of a particle are mathematically connected by a concentration function and a term in the power of concentration function, which is known as the exponent of reduction of settling velocity. Based on several turbulent features, a number of experimental and theoretical investigations have been carried out to formulate deterministic mathematical models on the exponent of reduction of settling velocity. However, a probabilistic study to formulate such models is still lacking in the literature. The present study therefore focuses on the modeling of exponent of reduction of settling velocity in a sediment-laden flow probabilistically, which is explored using the concept of entropy theory. The model is shown to be a function of particle Reynolds number, volumetric concentration, and relative mass density of sediment particles through the inclusion of these parameters in a hypothesized cumulative distribution function. The authors tested the model using experimental data from the literature and also compared these data with those of existing models. Relative percentage error between the observed and computed values of all the models shows the better prediction accuracy of this model in comparison to the others.

Compacted-soil embankment approaches to bridge abutments commonly fail during abutment scour. This paper presents flume observations on scour at bridge abutments with embankment approaches formed of weak, or weakened, compacted soil. The failure modes described in this paper add to modes reported by prior studies and are at one extreme of a range of failure modes insofar that abutment failure is attributable to erosion and washout of a relatively weak or weakened approach rather than the scour of the floodplain near the abutment toe. A prominent observation was that the local flow field around an abutment column, where it adjoined the approach, plays a significant role in eroding the embankment. One experiment with a riprap-protected, spill-through abutment led to the result of scour perched up in the partially eroded compacted-soil approach around an abutment column. The embankment approaches tested were larger than those used in flumes presented heretofore.