scholarly journals DAM BREAK WAVE, TIDAL BORE, IN-RIVER TSUNAMI SURGE: WHAT THE HELL?

2020 ◽  
pp. 14
Author(s):  
Hubert Chanson
Keyword(s):  
Current Knowledge ◽  
Leading Edge ◽  
Air Entrainment ◽  
Dam Break ◽  
Cfd Modelling ◽  
Dam Breaks ◽  
Physical Experiments ◽  
Tidal Bores ◽  
2004 Tsunami ◽  
Physical Analogy

Flood waves resulting from dam breaks have been responsible for numerous losses of life through centuries. Both the 26 December 2004 tsunami and 11 March 2011 Tohoku catastrophes were human tragedies of international significance. An important point is the physical analogy between dam break waves travelling downstream, tidal bores progressing deep inland, in-river tsunami propagating upstream, as well rejection surges in hydropower canals. The leading edge is a hydrodynamic shock, with a marked discontinuity in free-surface elevation and velocity and pressure fields, and a tri-phase flow with three distinct flowing phases, i.e. liquid (water), solid (sediment) and gas (air). Seminal features of bores and surges include a net mass flux, the breaking in shallow waters, and the intense turbulence at the front associated with massive sedimentary processes and air entrainment in the breaking roller. In this keynote talk, physical experiments, numerical CFD modelling and field observations are presented and compared. Current knowledge gaps are discussed. Ultimately it is argued that the 'solitary wave' analogy is not directly relevant to model the unsteady turbulent mixing of in-river tsunami surges, tidal bores and dam break waves.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/SQaPoSj2lP4

NUMERICAL SIMULATION OF DAM BREAK BY ADAPTIVE STENCIL DIFFUSE INTERFACE METHOD

2009 ◽  
Vol 23 (03) ◽  
pp. 293-296 ◽  
Author(s):  
L. DING ◽  
C. SHU ◽  
N. ZHAO
Keyword(s):  
Numerical Simulation ◽  
Adaptive Algorithm ◽  
Leading Edge ◽  
Dam Break ◽  
Experimental Results ◽  
Diffuse Interface ◽  
Fine Scale ◽  
Experiment Data ◽  
Interface Behavior

This paper presents the application of an adaptive stencil diffuse interface method to the simulation of dam break problem. The adaptive stencil diffuse interface method is the combination of the diffuse interface method and a stencil adaptive algorithm, where the diffuse interface method is used as the solver, and the adaptive stencil refinement scheme is applied to improve the resolution around the interface so that the fine-scale interface behavior can be captured. In this paper, we use this method to simulate the dam break problem, study the dam height and leading edge position, and compare our results with the experiment data available in the literature. It is shown that the results using the adaptive stencil diffuse interface method agree very well with the experimental results.

scholarly journals Scaling for lobe and cleft patterns in particle-laden gravity currents

2013 ◽  
Vol 20 (1) ◽  
pp. 121-130 ◽  
Author(s):  
A. Jackson ◽  
B. Turnbull ◽  
R. Munro
Keyword(s):  
Granular Material ◽  
Froude Number ◽  
Particle Diameter ◽  
Granular Flows ◽  
Leading Edge ◽  
Air Entrainment ◽  
Gravity Currents ◽  
Laboratory Scale ◽  
Scale Model ◽  
Snow Avalanches

Abstract. Lobe and cleft patterns are frequently observed at the leading edge of gravity currents, including non-Boussinesq particle-laden currents such as powder snow avalanches. Despite the importance of the instability in driving air entrainment, little is known about its origin or the mechanisms behind its development. In this paper we seek to gain a better understanding of these mechanisms from a laboratory scale model of powder snow avalanches using lightweight granular material. The instability mechanisms in these flows appear to be a combination of those found in both homogeneous Boussinesq gravity currents and unsuspended granular flows, with the size of the granular particles playing a central role in determining the wavelength of the lobe and cleft pattern. When scaled by particle diameter a relationship between the Froude number and the wavelength of the lobe and cleft pattern is found, where the wavelength increases monotonically with the Froude number.

CFD modelling of near-field dam break flow

2019 ◽  
pp. 47-60
Author(s):  
S. Esmaeeli Mohsenabadi ◽  
M. Mohammadian ◽  
I. Nistor ◽  
H. Kheirkhah Gildeh
Keyword(s):  
Near Field ◽  
Dam Break ◽  
Cfd Modelling ◽  
Dam Break Flow

scholarly journals Experimental Research on the Dam-Break Mechanisms of the Jiadanwan Landslide Dam Triggered by the Wenchuan Earthquake in China

2013 ◽  
Vol 2013 ◽  
pp. 1-13 ◽  
Author(s):  
Fu-gang Xu ◽  
Xing-guo Yang ◽  
Jia-wen Zhou ◽  
Ming-hui Hao
Keyword(s):  
Wenchuan Earthquake ◽  
Discharge Channel ◽  
Landslide Dam ◽  
Dam Break ◽  
Experimental Results ◽  
Dam Breaks ◽  
The Wenchuan Earthquake ◽  
Large Numbers ◽  
Dam Management ◽  
Break Process

Dam breaks of landslide dams are always accompanied by large numbers of casualties, a large loss of property, and negative influences on the downstream ecology and environment. This study uses the Jiadanwan landslide dam, created by the Wenchuan earthquake, as a case study example. Several laboratory experiments are carried out to analyse the dam-break mechanism of the landslide dam. The different factors that impact the dam-break process include upstream flow, the boulder effect, dam size, and channel discharge. The development of the discharge channel and the failure of the landslide dam are monitored by digital video and still cameras. Experimental results show that the upstream inflow and the dam size are the main factors that impact the dam-break process. An excavated discharge channel, especially a trapezoidal discharge channel, has a positive effect on reducing peak flow. The depth of the discharge channel also has a significant impact on the dam-break process. The experimental results are significant for landslide dam management and flood disaster prevention and mitigation.

scholarly journals A 2D HLL-based weakly coupled model for transient flows on mobile beds

2020 ◽  
Vol 22 (5) ◽  
pp. 1351-1369
Author(s):  
Robin Meurice ◽  
Sandra Soares-Frazão
Keyword(s):  
Numerical Models ◽  
Morphological Evolution ◽  
Coupled Model ◽  
Dam Break ◽  
Water Levels ◽  
Test Cases ◽  
Transient Flows ◽  
Dam Breaks ◽  
Weakly Coupled ◽  
High Interaction

Abstract We propose a finite-volume model that aims at improving the ability of 2D numerical models to accurately predict the morphological evolution of sandy beds when subjected to transient flows like dam-breaks. This model solves shallow water and Exner equations with a weakly coupled approach while the fluxes at the interfaces of the cells are calculated thanks to a lateralized HLLC flux scheme. Besides describing the model, we ran it for four different test cases: a steady flow on an inclined bed leading to aggradation or degradation, a dam-break leading to high interaction between the flow and the bed, a dam-break with a symmetrical enlargement close to the gate and a dam-break in a channel with a 90° bend. The gathered results are discussed and compared to an existing fully coupled approach based on HLLC fluxes. Although both models equally perform regarding water levels, the weakly coupled model looks to better predict the bed evolution for the four test cases. In particular, its results are not affected by an excessive numerical diffusion encountered by the coupled model. Moreover, it usually better estimates the amplitudes of the maximum deposits and scours. It is also more stable when subject to high bed–flow interaction.

scholarly journals Uncertainty Quantification Methodologies Applied to the Rotor Tip Clearance Effect in a Twin Scroll Radial Turbine

Fluids ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 114
Author(s):  
Carlo Cravero ◽  
Andrea Ottonello
Keyword(s):  
Uncertainty Quantification ◽  
Leading Edge ◽  
Expansion Method ◽  
Quantitative Information ◽  
Tip Clearance ◽  
Simulation Tools ◽  
Numerical Predictions ◽  
Physical Experiments ◽  
Comparison Of The Results ◽  
Radial Turbines

In the last three decades computer simulation tools have achieved wide spread use in the design and analysis of engineering devices. This has shortened the overall product design cycle (physical experiments may be impossible during early design stages) and it has also provided better understanding of the operating behavior of the systems under investigation. As a consequence numerical simulation have led to a reduction of physical prototyping and to lower costs for manufacturing production chains. Despite this success, it remains difficult to provide objective confidence levels in quantitative information derived from numerical predictions. The complexity arises from the amount of uncertainties related to the inputs of any computation attempting to represent a physical system. This paper focuses on geometrical sources of uncertainty in the field of CFD applied to twin scroll radial turbines. In particular it has been investigated the effect of uncertainties on tip clearance values at rotor blade leading edge and trailing edge on selected turbine performance parameters. The analysis shows the use of the Surrogate-based uncertainty quantification technique that has been setup by the authors in the Dakota® environment. The polynomial chaos expansion method has been applied to the same case. The comparison of the results coming from the different approaches and the discussion of the pros and cons related to each technique lead to interesting conclusions, which are proposed as guidelines for future UQ applications on the theme of CFD applied to radial turbines.

scholarly journals Numerical study of cascading dam-break characteristics using SWEs and RANS

2019 ◽  
Vol 20 (1) ◽  
pp. 348-360 ◽  
Author(s):  
Shubing Dai ◽  
Yong He ◽  
Jijian Yang ◽  
Yulei Ma ◽  
Sheng Jin ◽  
...  
Keyword(s):  
Stokes Equations ◽  
Initial Conditions ◽  
Numerical Study ◽  
Air Entrainment ◽  
Dam Break ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Depth Ratio ◽  
Surface Profiles ◽  
Run Up

Abstract This paper investigates the cascading dam-break flood propagation on the downstream sloping channel and reservoir using the shallow water equations (SWEs) and the Reynolds-average Navier-Stokes equations (RANS). The calculated surface profiles, stage hydrographs and maximum run-up heights for 24 sets of initial conditions are elaborately compared with the experimental measurements, which show the SWEs reproduce the wave oscillation evolution and the maximum run-up height inaccurately. The maximum run-up heights calculated by the SWEs are all smaller than those by the RANS and the measured results, the maximum errors are within −10% to −25%, which may predict delay of the downstream dam-break. However, the maximum errors calculated by the RANS are within ±10%. So the RANS predict more accurate results than the SWEs. Additionally, the generation of short waves must be below a certain upstream-to-downstream ‘depth ratio’, roughly the ‘depth ratio’ <2/3 in this study. If the ratio is too high, it is difficult to form a wavy push due to air entrainment and turbulence. The SWEs predict more accurate results for shallow initial depths than deep initial depths. Therefore, the advantage of the RANS can be more obvious for deep initial depths.

Influence of Hydrodynamic Interaction on Jet Breakup and Fragmentation Behavior

2014 ◽  
Author(s):  
Shimpei Saito ◽  
Yutaka Abe ◽  
Akiko Kaneko ◽  
Yuzuru Iwasawa ◽  
Eiji Matsuo ◽  
...  
Keyword(s):  
High Speed ◽  
Hydrodynamic Interaction ◽  
Heat Removal ◽  
Leading Edge ◽  
Air Entrainment ◽  
Video Camera ◽  
Liquid System ◽  
Core Material ◽  
Edge Region ◽  
Jet Breakup

Mitigative measures against a Core Disruptive Accident (CDA) are important from the viewpoints of safety of a Fast Breeder Reactor (FBR). If a CDA occurs, Post Accident Heat Removal (PAHR) must be surely achieved. In the PAHR, molten materials are likely to be injected into the coolant like a jet and they must satisfy two requests simultaneously: fast ejection and stable cooling after quenched. In order to estimate the quench behavior of the molten jet, it is important to understand how the jet breaks up. The objective of this study is to clarify that the influence of hydrodynamic interaction between a jet and the surrounding fluid on jet breakup. Previous works have clarified that one cause of the jet breakup is provoked by fragmentation at the side of a jet. However, there are few detailed results describing the correlation between jet breakup and hydrodynamic interaction at the leading-edge region of a jet. Additionally, air entrainment with a jet is always observed in our past experiments using simulants, but its influence has not been discussed yet. In this study, jet injection experiments in liquid-liquid system were conducted for investigating the interaction a jet and an ambient fluid, and the effect of air entrainment on jet breakup behavior. Both simulant core materials and coolants were transparent liquids for visualization. The stored simulant core material was injected into a tank filled with the simulant coolant. In order to realize the condition without air entrainment, the air remaining within the nozzle was removed using a syringe. The jet breakup behavior was observed with a high speed video camera. A normal backlight system and a Laser Induced Fluorescence (LIF) system were employed for visualization. The inner velocity distribution of a jet was measured by Particle Image Velocimetry (PIV). As a result, in the experiments without air entrainment the jet breakup lengths were described by Epstein’s equation. In addition, a pair of vortices was observed at the leading-edge region. The vortices were generated at the leading edge and the leading edge rolled up by the vortices returned toward a jet core. Thus, it was very likely that the vortices at the leading edge region promoted jet breakup.

Numerical Investigation of Flow Through an Ultra-Micro Scale Gas Turbine

2017 ◽  
Author(s):  
Rohann D’souza ◽  
Rajnish Sharma
Keyword(s):  
Gas Turbine ◽  
Leading Edge ◽  
Integrated System ◽  
Tip Clearance ◽  
Cfd Modelling ◽  
3 Dimensional ◽  
Micro Scale ◽  
Viscous Heat ◽  
Flow Through ◽  
Nozzle Guide

The ultra-micro scale gas turbine (UMGT) is an ongoing area of research, as an alternate power source for portable electronic devices. To advance our understanding that will help in its development, this paper focuses on a numerical analysis via computational fluid dynamics (CFD) of flow through a 3 dimensional (3D) blade profiled UMGT turbine. CFD modelling was based off an integrated turbine that consists of a volute, nozzle guide vanes (NGV) and rotor. Firstly, the flow through the integrated system as well as each component was analyzed. Secondly, the turbine was simulated under three different isothermal conditions and compared to the adiabatic situation, in order to understand the loss mechanisms. Lastly, the effect of tip clearance was studied, where it was varied between 0–10% of the blade height. CFD results showed, the flow through the turbine was quite well behaved, however separation of flow at the NGV leading edge, and residual swirl at the rotor trailing edge, were observed. The effects of the isothermal wall boundary condition was very pronounced at the volute and NGV, resulting in a large amount of good heat to be conducted away, at the rotor however conduction was only a percentage of the viscous heat generated. Lastly tip clearance proved to have a linearly detrimental effect on power.

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