Journal of Hydraulic Engineering

The $-1$ power region of the turbulence spectrum is a constant energy region responsible for energy production. However, its scaling and their implications are underreported. Experiment results show that the production region comprises 42% of turbulence kinetic energy for open-channel flows over fine gravel and very coarse gravel beds. Energy of the production region scales similarly for these gravel bed types, and enables its prediction using logarithmic and exponential equations. Similarity scaling is evidenced for the production region’s low and high wavenumber boundaries, defined as the macroturbulence and bursting wavenumbers. The macroturbulence and bursting wavenumbers have similar functions, suggesting that the production region is controlled by the same phenomena across its extent. These results are contrary to those of previous research, in which low and high wavenumber boundaries were hypothesized to be scaled by outer and inner scales, respectively. The authors introduce the macroturbulence streampower, which is derived using the energy similarity and macroturbulence wavenumber. The macroturbulence streampower is distributed across the flow depth, is dependent on roughness element, and agrees with Bagnold’s streampower near the channel half-height.

This paper focuses on air–water interactions during pipe filling. The air–water mixed flow is related to a mobile hydraulic jump in the horizontal pipe section. The trapped water–air front at the crown of the pipe bridge determines the upstream boundary conditions for the stratified flow, suppressed hydraulic jump, and slug flow regions in the horizontal pipe section. The velocity field, the water level, and the pressure were measured at different stages of the transitional flow process. A full-scale two-phase computational fluid dynamics model, with two-equation eddy viscosity turbulence to account for small scales of motion, was used to predict the air pocket dynamics. The paper suggests that in the case of a frozen upstream water–air front, the formation of a hydraulic jump downstream can be explained by long-wave-type instability, which is confirmed by the free-surface supercritical flow Froude number condition. The hydraulic jump that merges stratified flow and slug flow is characterized by the speed of the surge wave, which is determined by the pressure, cross-sectional area of water flow, and density changes. A mixing efficiency parameter was introduced to explain the dissipation of turbulent energy due to the air–water mixing front of the suppressed hydraulic jump.

The design criteria of submerged vane fields used to control the transfer of sediments into lateral channel diversions have been mostly based on suggestions of some fundamental studies on vane fields aiming to protect riverbanks against erosion. Indeed, although there are studies that investigate the effect of some characteristic parameters of submerged vanes on the desilting of lateral diversions (prevention or reduction of lateral sediment ingestion), they do not adequately cover all pertinent parameters and their significant ranges. In view of the gap of knowledge resulting from this incomplete parametric coverage, an investigation comprising 26 experiments was conducted. It investigated the effects of geometrical vane parameters and specific water discharge ratios on the desilting efficiency of submerged vane fields and on the bed morphology around a 90° lateral water diversion. The vanes displayed skew angles between 10° and 50°, and their heights were 0.2 to 0.4 times the approach flow depth. The distance from the channel bank to the inner vane row and the streamwise distance between vane arrays were, respectively, 0.7 to 1.5 and 2.0 to 3.0 times the approach flow depth. The specific water discharge ratio, $q_R$, varied between 0.1 and 0.3, and the number of vane rows was 6 and 3. The skew angle and the specific water discharge ratio were the most effective parameters on desilting, whereas the others had a small effect within the experimental limits of this study. The optimal desilting efficiency, $\approx 94\%$, was achieved when the skew angle was equal to 45° and $q_R$ was kept in the range of 0.1 to 0.2.

In the present work, the effects of particles on the flow patterns in settling tanks are studied with a computational fluid dynamics (CFD) model with various nondrag forces. The CFD model is validated with radial velocity measured with ultrasonic velocity profiler and concentration profiles for a lab-scale settling tank and industrial settling tank. The effects of lift, turbulent dispersion, and particle-fluid interaction forces are investigated on the flow patterns. The effects of particle characteristics are also studied on the separation. It was observed that instead of monodispersed particles, particle size distribution should be incorporated in the CFD model for better prediction of the concentration profiles. The forces acting on the particle shift the recirculation pattern in the settling tank. Different particles with the same Archimedes number exhibited different flow patterns. Similar flow patterns and separation efficiency is predicted for different particles with similar terminal settling velocity.

Artificial step-pool sequences have long been used in river restoration projects worldwide for channel stabilization and ecological improvement. However, previously used design methods for artificial step-pools are problematic in that the designed sequences may not fulfil restoration objectives and fail. We propose a new design framework consisting of five modules based on the morphological evolution, energy dissipation, hydraulics, and stability of step-pools. This new framework focuses on individual units instead of a reach or subreaches as done in previous approaches, allowing for greater design flexibility. A detailed description of the new unit-scale design framework is presented in this paper with step-by-step procedures and recommended criteria for design evaluation. The new framework is then applied to three mountain streams to evaluate existing artificial and natural step-pool sequences. Finally, advantages and limitations of the framework and insights for restoration of mountain streams are reviewed.

To understand the dynamics of vigorous gas jets in underwater gas blowouts, we present a laboratory experiment and data analysis to quantify key physical properties of gas jets horizontally discharged through a single nozzle. This study focuses on the sonic regime of the gas jets (the nominal Mach number from 0.8 to 3.34) and quantifies the jet-to-plume transition through observations of jet penetration length, expansion angle, and trajectory of the jets. Jet penetration is found to be scaled with a modified Froude number accounting for the parameters of real gas (density, pressure, and velocity) in the choked sonic flow. The surfacing fountain profiles are measured to connect water surface observation with the source dynamics through a nondimensional scaling using the densimetric Froude number defined at the release point. A robust $-3/5$ power-law scaling with a modified Weber number is found to well characterize the median bubble diameter for the bubble breakup process in the sonic gas jets.

Pipe wall condition assessment is critical for targeted maintenance and failure prevention in water distribution systems. This paper proposes a spatially distributed pipeline condition assessment technique using persistent hydraulic transient waves of a small magnitude (microtransient waves), with a focus on the detection and reconstruction of extended and irregular pipe wall anomalies (e.g., nonuniform blockages and internal or external corrosion that is distributed along a short extent of the pipe). For an extended and irregular anomaly, a pipe’s response to any incident waves will be complex and impose challenges in interpretation. To identify the complex response patterns, an optimization technique has been developed using a differential evolution algorithm to separate the directional impulse response functions (IRFs) and then to differentiate the anomaly-induced response in a directional IRF from noise. A layer-peeling method is then applied to the directional IRF to reconstruct the pipe impedances, which are related to the localized wave speed and pipe wall thickness. Numerical verifications have been conducted on a pipe with a deteriorated section that is assumed to have a constant internal diameter but varying wave speeds along its length (simulating a section with nonuniform external corrosion and wall thinning). The results show that the nonuniformly deteriorated section can be successfully detected and accurately reconstructed using the techniques proposed in this paper.

The purpose of this study was to illustrate the relationship between methods that utilize the damping of fluid transients and approaches based on frequency response diagrams and to discuss the two methods for both leak and burst detection. Although both methods are based on the Fourier transform of the signal, they have different signal processing approaches. This study revealed the mathematical relationship between the two methods for both leak and burst problems. The mathematical relationship between the two methods was verified numerically and experimentally. In addition, the two methods were compared from the perspectives of input signal bandwidth, problem type, low sampling rate capability, robustness, and real-time data monitoring capability. The applicability of the two methods with regard to these aspects is discussed herein.

Aerators are applied to provide air entrainment and cavitation erosion protections for high-speed flows. By traditional chute aerators in high-head bottom tunnels, it is difficult to maintain effective aeration protection for low-Froude-number and small-slope conditions. The present study explores a wedge aerator design at the bottom outlet, and detailed experimental data on the aeration cavity and the entrained air diffusion were obtained to assess the aeration protection performance. The wedge aerator separates the water flow from the bottom outlet into an upper free jet and a lower flow layer, creating a middle aeration cavity. The flowing lower layer can enhance the aeration cavity stability, ensuring the cross-sectional air diffusion generation downstream due to the flow collision interactions. The flow Froude number and vertical location are the main parameters affecting the air entrainment coefficient, cross-sectional air concentration distribution, and sufficient concentrations close to the chute floor. Optimized wedge aerators are proposed, indicating that the flow interior separation is an effective hydraulic design for bottom outlets in hydraulic engineering.