Progress in the observation and modeling of turbulent multi-phase flows

Multi-phase flows of environmental import involve the interactions of solid, gas, and/or liquid phases. In the last decades, important advances have taken place in the observation and modeling of multi-phase flows. New accurate instruments to measure the air concentration in air-water flows and to analyse the motion of solid particles in water and gas; new theories to address the interactions of the diverse turbulence scales of the flow; and more powerful computers have all allowed researchers to study multi-phase flows from previously unexplored points of view. In Nature, multi-phase flows are mostly turbulent and, therefore, they are extremely complicated, with a broad range of relevant length and time scales [1]. For example, the time scales range from less than 1ms for the turbulence dissipation in a small stream to about 24 h and 50min for a tidal cycle in coastal zones (Fig. 1), and to more than 50 years for the currents controlling the balances between oxygen and carbon dioxide. Several recent papers have remarked that the difficulties in understanding multi-phase flows stem from two basic facts: the phases do not distribute uniformly, and the small-scale interactions may have profound effects on large-scale behaviours. These difficulties become important for the prediction of the behaviour of flows in many environmentalproblems and applications. The aim of this Special Issue is to present a group of papers that: (a) summarize thestate-of-the-art in the knowledge about multi-phase flows in environmental applications; (b)report recent results of research (of experimental, numerical and/or theoretical nature) on environmental multi-phase flows; and (c) suggest novel pathways of analysis in the area

Numerical simulation of rectangular dropshafts using a volume-of-fluid (VoF) technique

This paper focuses on the implementation, validation and exploitation of a vertical dropshaft flow operation using the commercial VOF-based Computational Fluid Dynamics (CFD) code, FLOW-3D®. Using the experimental data of Chanson (2002), the package was used to simulate the flow patterns in a rectangular dropshaft with plunge-flow pattern. Both k−epsilon and k−epsilon RNG turbulence closures were tested and the computed hydraulic parameters were found to be in good agreement with the experimental observations. The results demonstrate that the CFD modeling of rectangular plunge-flow dropshaft hydraulics is viable and useful to evaluate the hydraulic parameters of fundamental importance when modeling collection systems in one dimension

Numerical Simulation of Turbulent Free Surface Flow Around a Circular Cylinder

Mini-Symposium: CFD in the Nearfield of Structure

Temporal evolution of jet induced scour depth in cohesionless granular beds and the phenomenological theory of turbulence

In this work, we investigate the temporal evolution of the jet-driven scour depth in a pothole lying on a cohesionless granular bed by using diverse approaches. First, we present new experiments which encompass cases with jet angles ranging from 45° to 90° from the horizontal, several initial water depths, and different particle sizes, supplementing experiments developed recently by the last two authors. In particular, we address relatively large angles, mostly absent in previous analyses. Our results initially confirm the existence of two very different stages in the scour process, essentially overlooked in datasets used to obtain the traditional formulas—developing and developed phases; they then provide unprecedented evidence of the very distinct behavior at 90°, characterized by a step-wise behavior. Second, after revisiting the rationale of a theory for the equilibrium condition developed elsewhere by the first author and a collaborator, we employ the existing and new datasets to determine the multiplicative constants embedded in the equilibrium scour formulas. Third, we present a novel theory for the temporal evolution of the scour depth during the developed phase (but with good prediction capabilities in the developing phase as well). By invoking the conservation of mass of sediment in the pothole, in addition to the energy conservation within the pothole and the phenomenological theory of turbulence, we obtain ordinary differential equations which we solve by numerical means. We validate the theory using our new and other datasets. Finally, we provide interesting interpretations of the scour process by using the results of the theory

Soil Pollution Prevention and Remediation

1DICATECh, Polytechnic University of Bari, Via Orabona 4, 70125 Bari, Italy 2Department of Civil and Environmental Engineering, University of California, Davis, 3105 Ghausi Hall, One Shields Avenue, Davis, CA 95616, USA 3School of Environmental Engineering, Technical University of Crete, 73100 Chania, Greece 4Dipartimento di Ingegneria Strutturale, Edile e Geotecnica, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino, Ital

Numerical simulation of spheres moving and colliding close to bed streams, with a complete characterization of turbulence

River morphodynamics and sediment transportMechanics of sediment transpor

Soil Pollution Prevention and Remediation

Constructed wetland application

Drought and the Sacramento-San Joaquin Delta, 2012–2016: Environmental Review and Lessons

This paper reviews environmental management and the use of science in the Sacramento–San Joaquin Delta during California’s 2012–2016 drought. The review is based on available reports and data, and guided by discussions with 27 agency staff, stake-holders, and researchers. Key management actions for the drought are discussed relative to four major drought water management priorities stated by water managers: support public health and safety, control saltwater intrusion, preserve cold water in Shasta Reservoir, and maintain minimum protections for endangered species. Despite some success in streamlining communication through interagency task forces, conflicting management mandates sometimes led to confusion about priorities and actions during the drought (i.e., water delivery, the environment, etc.). This report highlights several lessons and offers suggestions to improve management for future droughts. Recommendations include use of pre-drought warnings, timely drought declarations, improved transparency and useful documentation, better scientific preparation, development of a Delta drought management plan (including preparing for salinity barriers), and improved water accounting. Finally, better environmental outcomes occur when resources are applied to improving habitat and bolstering populations of native species during inter-drought periods, well before stressful conditions occur.

Three-dimensional Hydrodynamic Modeling of Density Currents in the Chicago River, Illinois (HES 68)

Metropolitan Water Reclamation District of Greater Chicagounpublishednot peer reviewe

Hydraulic Model Study of a Canoe Chute for Low-head Dams in Illinois (HES 63)

Illinois Department of Natural Resources, Office of Water Resources (IDNR WR009820 S98-284)unpublishednot peer reviewe