Numerical and experimental turbulence studies on shallow open channel flows

YesBased on the previous studies, the shallow water equations (SWEs) model was proven to be insufficient to consider the flow turbulence due to its simplified Reynolds-averaged form. In this study, the k-ε model was used to improve the ability of the SWEs model to capture the flow turbulence. In terms of the numerical source terms modelling, the combined k-ε SWEs model was improved by a recently proposed surface gradient upwind method (SGUM) to facilitate the extra turbulent kinetic energy (TKE) source terms in the simulation. The laboratory experiments on both the smooth and rough bed flows were also conducted under the uniform and non-uniform flow conditions for the validation of the proposed numerical model. The numerical simulations were compared to the measured data in the flow velocity, TKE and power spectrum. In the power spectrum comparisons, a well-studied Kolmogorov’s rule was also employed to complement both the numerical and experimental results and to demonstrate that the energy cascade trend was well-held by the investigated flows.The Major State Basic Research Development Program (973 program) of China (Grant Number 2013CB036402). Open Fund from the State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, China (Grant Number SKLH-OF-1103)

Discontinuous galerkin flood model formulation: Luxury or necessity?

The finite volume Godunov-type flood model formulation is the most comprehensive amongst those currently employed for flood risk modeling. The local Discontinuous Galerkin method constitutes a more complex, rigorous, and extended local Godunov-type formulation. However, the practical merit associated with such an increase in the level of complexity of the formulation is yet to be decided. This work makes the case for a second-order Runge-Kutta Discontinuous Galerkin (RKDG2) formulation and contrasts it with the equivalently accurate finite volume (MUSCL) formulation, both of which solve the Shallow Water Equations (SWE) in two space dimensions. The numerical complexity of both formulations are presented and their capabilities are explored for wide-ranging diagnostic and real-scale tests, incorporating all challenging features relevant to flood inundation modeling. Our findings reveal that the extra complexity associated with the RKDG2 model pays off by providing higher-quality solution behavior on very coarse meshes and improved velocity predictions. The practical implication of this is that improved accuracy for flood modeling simulations will result when terrain data are limited or of a low resolution. © 2014. American Geophysical Union

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

The effect of lateral channel contraction on dam break flows: Laboratory experiment

This paper presents an investigation of dam break flow in a channel with lateral contraction. An experiment was carried out in a laboratory flume by instantaneous removal of a plate. The problem was studied in a smooth prismatic channel of rectangular cross-section over horizontal dry bed. At a certain distance downstream from the dam location, two symmetrical triangular-shaped lateral sidewall obstacles were installed to generate converging-diverging channel reach. Thus, it points out the abrupt variation of topography in floodplain for practical applications. Adopted measuring technique, digital image processing, detected the flood wave propagation quite well thereby synchronous recording of the flow through the entire channel with three cameras. The continuous free surface profiles and stage hydrographs were obtained without disturbing the flow. The experimental data were compared with the results of RANS-based numerical simulation. Comparisons between measured and computed results show good agreement. © 2012 Elsevier B.V.MMF2007BAP6This work was partly supported by Cukurova University Research Fund under Project No.: MMF2007BAP6. This support is gratefully acknowledged

Dam-break flows during initial stage using SWE and RANS approaches

Experimental and numerical results relating to dam-break flows are compared. Dam-break waves were generated by the quasi-instantaneous removal of a plate in a smooth prismatic channel of rectangular cross-section over horizontal dry and wet beds. The laboratory experiments were conducted to determine the initial stages of the free surface profiles using digital image processing. The flow characteristics were detected by applying an adequate, simple and economical measuring technique. The experimental results were compared with the results of a commercially available CFD program, solving the Reynolds-averaged Navier-Stokes (RANS) equations with the k- turbulence model involving the shallow-water equations. Measured and computed free surface profiles during the initial dam-break stages indicate that although both models predict the dam-break flow with a reasonable accuracy, the agreement using the RANS model is better. © 2010 International Association for Hydro-Environment Engineering and Research

Investigation of dam-break induced shock waves impact on a vertical wall

In the present study, experimental tests and VOF-based CFD simulations concerning impact of dam-break induced shock waves on a vertical wall at downstream end were investigated. New laboratory experiments were carried out in a rectangular flume with a smooth horizontal wet bed for two different tailwater levels. Image processing was used for flow measurement and time evolutions of water levels were determined effectively by means of synchronous recorded video images of the flow. This study scrutinized formation and travelling of negative wave towards upstream direction, which was resulted from the reflection of flood wave against downstream end wall. In numerical simulation, two distinct approaches available in FLOW-3D were used: Reynolds- averaged Navier-Stokes equations (RANS) with the k-? turbulence model and the Shallow Water Equations (SWEs). The measured results were then compared with those of numerical simulations and reasonable agreements were achieved. General agreement between laboratory measurements and RANS solution was better than that of SWE. © 2015 Elsevier B.V

Dam-break flow in the presence of obstacle: Experiment and CFD simulation

The aim of this paper is to present an experimental and numerical investigation of dam-break flow over initially dry bed with a bottom obstacle. This test case highlights not only the bottom slope effects but also those of abrupt change in channel topography. Dam-break flow was applied in a smooth prismatic channel of rectangular cross-section over a trapezoidal bottom sill on the downstream bed. The present study scrutinized the formation and propagation of negative bore behind the sill. The flow was numerically simulated by the VOF-based commercially available CFD program, Flow-3D, solving the Reynolds Averaged Navier Stokes equations with the k-? turbulence model (RANS) and the Shallow Water Equations (SWE). To validate CFD models an experiment was carried out. Using an advanced measuring technique, digital image processing, the flow was recorded simply through the glass walls of channel; thus, continuous free surface profiles were acquired synchronously with three cameras along the channel. The adopted measuring technique is non-intrusive and yields accurate and valuable results without flow disturbances. Comparison of the computed results with experimental data shows that RANS model reproduces the flow under investigation with reasonable accuracy while simple SWE model indicates some discrepancies particularly in predicting the negative wave propagation.MMF2007BAP6This work was partly supported by Cukurova University Research Fund under project no: MMF2007BAP6. This support is gratefully acknowledged

Investigation of dam-break flow over abruptly contracting channel with trapezoidal-shaped lateral obstacles

The present paper aims to investigate the dam-break flow over dry channel with an abrupt contracting part in certain downstream section. A new experiment was carried out in a smooth-prismatic channel with rectangular cross section and horizontal bed. A digital imaging technique was adopted for flow measurement and thus flood wave propagation was sensitively obtained. Synchronous filmed images of the dam-break flow were nonintrusively acquired with three cameras, through glass sidewalls of the channel. Free surface profiles and time evolution of water levels were derived directly from the recorded video images using virtual wave probe without disturbing the flow. Furthermore, the present study highlights the formation and propagation of the negative bore due to abruptly contracting channel. The measured results were compared with the numerical solution of Reynolds averaged Navier-Stokes (RANS) equations with k-turbulence model and good agreement was achieved. New experimental data can be useful for scientific community to validate numerical models. © 2012 American Society of Mechanical Engineers