Journal of Hydraulic Engineering

The effects of relative density difference on the dilution and height of vertical negative buoyant jets were investigated experimentally. These effects, which are related to fluid density, occurred in addition to the buoyancy effects commonly parameterized by the densimetric Froude number. The density effects have generally been ignored in previous investigations and in practice on the basis of Boussinesq’s approximation. The density effects could, however, be relevant in connection to hypersaline discharges from desalination plants and dense discharges from oil and potash mining industries. A series of seven upward fountain experiments were performed in the laboratory to carry out this investigation. The flow was turbulent, the relative density difference varied from 0.0014 to 0.064, and the densimetric Froude number varied from 2.13 to 15.7. The results showed that an increase in the relative density difference reduced both the minimum return dilution and maximum height of the fountains. The observed maximum reduction in dilution was 48%, and the maximum reduction of height was 19%. The results also demonstrated that upward fountains are dynamically similar to downward fountains.

Pools and riffles are common morphological features in rivers that are frequently used but poorly specified analogs in restoration design. Here, straight two-dimensional (2D) bedforms are conceptualized as perturbations and flow recovery is measured in a laboratory flume with an array of ultrasonic Doppler velocity profilers (UDVPs). The objectives are to (1) assess the variation of skin friction, turbulent stresses, and total stress; (2) assess the role of topographical feedback on flow recovery; and (3) compare flow recovery in isolated and bedforms in series. The results show that the total shear stress and near-bed turbulence greatly exceed the skin friction in decelerating flow and the pool and that hydrodynamic recovery tends to occur at length scales similar to geophysical scales despite potential negative feedback from the bed. Repeating short bedforms can push the flow to a more turbulent and laterally concentrated equilibrium condition. Implications for sediment entrainment thresholds, existing models of riffle-pool hydrodynamics, and the stability of constructed riffle pools are discussed.

This paper presents an intrinsic approach to estimate air entrainment rates due to intake vortices based on large-scale laboratory measurements. Quasi-continuous measurements of the amount of entrained air were conducted using a sophisticated de-aeration system. The data analysis of 34 experimental runs resulted in a parameter fit describing the air entrainment rates at horizontal intakes. Additionally, a prediction band is given that provides a handle to inspect probability aspects. Furthermore, an approach to determine the critical intake submergence is presented. These guidelines enable hydraulic design engineers to estimate both the amount of entrained air and the critical intake submergence at horizontal intakes, so that the efficiency and safety of pressurized waterway systems is further increased.

An experimental campaign including measurement of pressure drops and velocity profiles was conducted on the pressurized flow in a commercial corrugated pipe. The results show that the empirical graphs suggested by Morris in the fifties may produce inaccurate assessments of the friction factor, in particular, for low Reynolds numbers. The experimental data was then reproduced by means of a numerical model with the large eddy simulation (LES) technique. The friction factor behavior for low and relatively high Reynolds numbers was thus investigated. The numerical simulations were in good agreement with the experimental results, showing the LES suitability to predict the effect of the pipe wall corrugation on the mean flow in a range of Reynolds numbers typical of engineering applications. To provide a quantitative evaluation of the numerical model, the Nash–Sutcliffe model efficiency coefficient $E$ and the root mean square error (RMSE) were calculated, demonstrating the goodness of the numerical results. The LES model was also used to investigate the effect of the wall corrugation on the turbulence. Although the inner-layer was dramatically affected by the corrugation, a collapse of the mean velocity profile was evident in the outer-layer. In the wall region, the coherent pattern of the turbulent structures appeared to be quite disaggregated in the streamwise direction, even though they preserved the alternating arrangement of positive and negative values. Overall, both qualitative and quantitative analysis revealed that, for the range of investigated values, the streak and vortical structures were independent of the Reynolds number.

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.

Explicit formulas for the times of arrival of the leading and trailing edges of a contaminant cloud are developed from a one-dimensional advection-dispersion model of transport. These times—defined as the times at which the concentration is some fraction $\alpha$ of the peak concentration—can be determined easily with iterations using a spreadsheet or other software, but this approach becomes time-consuming if many calculations are needed. Also, solutions to the transient storage zone model and its relatives can be made more efficient by identifying the arrival times of the edges of a contaminant cloud. The expressions for the arrival times depend only the fraction $\alpha$ and the Péclet number $\mathsf{P}$. For $0.01<\alpha <0.1$, the formula for the time of arrival of the leading edge is within 7% for $\mathsf{P}>1$ and 1% for $\mathsf{P}>20$, and the expression for the time of arrival of the trailing edge is within 10–20% for $\mathsf{P}=1$ and less than 1% for $\mathsf{P}>6$. Despite the criticisms of the advection-dispersion model for transport in real waterways, the formulas based on it predict the arrival times at least as well as previously proposed formulas, as long as the mean velocity over the river reach can be estimated.