scholarly journals Two-dimensional hydraulic modelling of submerged river training structures

2020 ◽  
pp. 79-96
Author(s):  
Davor Kvočka
Keyword(s):  
River Flow ◽  
Flow Direction ◽  
Empirical Studies ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Hydraulic Modelling ◽  
Training Structures ◽  
Main River ◽  
Complex Models ◽  
River Training

River training structures, such as dikes and chevrons, are commonly used for improving riparian navigation conditions. These structures are usually submerged under most flows and are aligned at variable angles to the main river flow direction. In this study, two different approaches for two-dimensional hydraulic modelling of submerged dikes and chevrons in MIKE 21 Flow Model FM have been analysed: (i) by representing the geometry of the structures explicitly in the bathymetry of the river channel (i.e. bathymetry approach), and (ii) by utilising the “dike” sub-grid module, where the flow past a structure is calculated by employing an empirical discharge relationship (i.e. dike module approach). The model results have been compared to theoretical and empirical studies, as well as to field observations and measurements. The obtained results indicate that the bathymetry approach is the more appropriate method for simulating predominantly submerged river training structures. However, these types of models should be used only for general assessment of potential river engineering solutions. For more detailed analysis of solution options, more complex models are recommended, e.g. three-dimensional hydrodynamic models.

scholarly journals An experimental and theoretical investigation of particle–wall impacts in a T-junction

2013 ◽  
Vol 727 ◽  
pp. 236-255 ◽  
Author(s):  
D. Vigolo ◽  
I. M. Griffiths ◽  
S. Radl ◽  
H. A. Stone
Keyword(s):  
Flow Direction ◽  
Three Dimensional ◽  
Stokes Number ◽  
Two Dimensional ◽  
Dimensional Model ◽  
Viscous Boundary Layer ◽  
Particle Tracing ◽  
Two Dimensional Model ◽  
Viscous Boundary ◽  
The Impact

AbstractUnderstanding the behaviour of particles entrained in a fluid flow upon changes in flow direction is crucial in problems where particle inertia is important, such as the erosion process in pipe bends. We present results on the impact of particles in a T-shaped channel in the laminar–turbulent transitional regime. The impacting event for a given system is described in terms of the Reynolds number and the particle Stokes number. Experimental results for the impact are compared with the trajectories predicted by theoretical particle-tracing models for a range of configurations to determine the role of the viscous boundary layer in retarding the particles and reducing the rate of collision with the substrate. In particular, a two-dimensional model based on a stagnation-point flow is used together with three-dimensional numerical simulations. We show how the simple two-dimensional model provides a tractable way of understanding the general collision behaviour, while more advanced three-dimensional simulations can be helpful in understanding the details of the flow.

scholarly journals Computational Study of Zigzag Spacer Design with Elliptical Cross-Section Filaments

2020 ◽  
Vol 307 ◽  
pp. 01047
Author(s):  
Gohar Shoukat ◽  
Farhan Ellahi ◽  
Muhammad Sajid ◽  
Emad Uddin
Keyword(s):  
Mass Transfer ◽  
Cross Section ◽  
Cross Sections ◽  
Computational Study ◽  
Flow Direction ◽  
Three Dimensional ◽  
Circular Cross Section ◽  
Two Dimensional ◽  
Permeate Flux ◽  
Elliptical Cross

The large energy consumption of membrane desalination process has encouraged researchers to explore different spacer designs using Computational Fluid Dynamics (CFD) for maximizing permeate per unit of energy consumed. In previous studies of zigzag spacer designs, the filaments are modeled as circular cross sections in a two-dimensional geometry under the assumption that the flow is oriented normal to the filaments. In this work, we consider the 45° orientation of the flow towards the three-dimensional zigzag spacer unit, which projects the circular cross section of the filament as elliptical in a simplified two-dimensional domain. OpenFOAM was used to simulate the mass transfer enhancement in a reverse-osmosis desalination unit employing spiral wound membranes lined with zigzag spacer filaments. Properties that impact the concentration polarization and hence permeate flux were analyzed in the domain with elliptical filaments as well as a domain with circular filaments to draw suitable comparisons. The range of variation in characteristic parameters across the domain between the two different configurations is determined. It was concluded that ignoring the elliptical projection of circular filaments to the flow direction, can introduce significant margin of error in the estimation of mass transfer coefficient.

Three-Dimensional Simulation of Gas Flow in Microducts

2005 ◽  
Author(s):  
Abhishek Agrawal ◽  
Amit Agrawal
Keyword(s):  
Aspect Ratio ◽  
Knudsen Number ◽  
Gas Flow ◽  
Flow Direction ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Streamwise Velocity ◽  
Theoretical Development ◽  
Width Ratio ◽  
Two Dimensional

Three-dimensional lattice Boltzmann method based simulations of a microduct have been undertaken in this paper. The objective is to understand the different physical phenomena occurring at these small scales and to investigate when the flow can be treated as two-dimensional. Towards this end, the Knudsen number and aspect ratio (depth to width ratio) are varied for a fixed pressure ratio. The pressure in the microduct is non-linear with the non-linearity in pressure reducing with an increase in Knudsen number. The pressure and velocity behaves somewhat similar to two-dimensional microchannels even when the aspect ratio is unity. The slip velocity at the impenetrable wall has two components: along and perpendicular to the flow. Our results show that the streamwise velocity near the centerline is relatively invariant along the depth for aspect ratio more than three, suggesting that the microduct can be modeled as a two-dimensional microchannel. However, the velocity component along the depth is never identically zero, implying that the flow is not truly two-dimensional. A curious change in vector direction in a plane normal to the flow direction is observed around aspect ratio of four. These first set of three-dimensional results are significant because they will help in theoretical development and flow modeling at micro scales.

scholarly journals Monitoring of Indoor Airflows with a New Two-Dimensional Airflow Sensor

2019 ◽  
Vol 111 ◽  
pp. 05005
Author(s):  
Yuanchen Wang ◽  
Christian Lodroner ◽  
Michael Müller ◽  
Konstantinos Stergiaropoulos
Keyword(s):  
Control Strategies ◽  
Flow Direction ◽  
Three Dimensional ◽  
Hvac Systems ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Thermal Discomfort ◽  
Indoor Airflow ◽  
Dimensional Section ◽  
Airflow Sensor

Although airflow is invisible, it has a big influence on the indoor environment. An incorrectly planned HVAC systems can lead to draught and thermal discomfort in occupied zones. Since the commissioning tests required after the installation of HVAC systems are generally performed without occupancy, the tests results do not always accurately represent the airflow that occurs during ordinary usage. The airflow needs to be continuously monitored and controlled by an intelligent HVAC system. The aim of this study is to develop a new two-dimensional airflow sensor for the monitoring of indoor airflow, which can also indicate the flow direction. Several of these sensors can be placed in a planar sensor array, by which a two-dimensional section of the flow field is created. By recording data from several of these arrays simultaneously, an image of the three-dimensional flow could be acquired. The prototype of the sensor, which is made by Hahn-Schickard Society for Applied Research is currently being validated at the Institute for Building Energetics, Thermotechnology and Energy Storage. When the development is completed, it will greatly contribute to the control strategies of HVAC systems.

A Numerical Analysis of Phonation Using a Two-Dimensional Flexible Channel Model of the Vocal Folds

2001 ◽  
Vol 123 (6) ◽  
pp. 571-579 ◽  
Author(s):  
Tadashige Ikeda ◽  
Yuji Matsuzaki ◽  
Tatsuya Aomatsu
Keyword(s):  
Channel Model ◽  
Flow Direction ◽  
Speech Sound ◽  
Three Dimensional ◽  
Vocal Folds ◽  
Two Dimensional ◽  
Threshold Values ◽  
One Dimensional ◽  
Frequency Components ◽  
Main Flow Direction

A two-dimensional flexible channel model of the vocal folds coupled with an unsteady one-dimensional flow model is presented for an analysis of the mechanism of phonation. The vocal fold is approximated by springs and dampers distributed in the main flow direction that are enveloped with an elastic cover. In order to approximate three-dimensional collision of the vocal folds using the two-dimensional model, threshold values for the glottal width are introduced. The numerical results show that the collision plays an important role in speech sound, especially for higher resonant frequency components, because it causes the source sound to include high-frequency components.

scholarly journals The computation of the velocity field

1984 ◽  
Vol 221 (1223) ◽  
pp. 189-220 ◽  
Keyword(s):  
Velocity Field ◽  
Fundamental Problem ◽  
Empirical Studies ◽  
Three Dimensional ◽  
Human Motion ◽  
Dimensional Structure ◽  
Two Dimensional ◽  
Physical Assumption ◽  
Intensity Changes ◽  
Significant Intensity

The organization of movement in the changing retinal image provides a valuable source of information for analysing the environment in terms of objects, their motion in space, and their three-dimensional structure. A description of this movement is not provided to our visual system directly, however; it must be inferred from the pattern of changing intensity that reaches the eye. This paper examines the problem of motion measurement, which we formulate as the computation of an instantaneous two-dimensional velocity field from the changing image. Initial measurements of motion take place at the location of significant intensity changes. These measurements provide only one component of local velocity, and must be integrated to compute the two-dimensional velocity field. A fundamental problem for this integration stage is that the velocity field is not determined uniquely from information available in the changing image. We formulate an additional constraint of smoothness of the velocity field, based on the physical assumption that surfaces are generally smooth, which allows the computation of a unique velocity field. A theoretical analysis of the conditions under which this computation yields the correct velocity field suggests that the solution is physically plausible. Empirical studies show the predictions of this computation to be consistent with human motion perception.

The effect of topography on earthquake ground motion: A review and new results

1988 ◽  
Vol 78 (1) ◽  
pp. 42-63
Author(s):  
Louis Geli ◽  
Pierre-Yves Bard ◽  
Béatrice Jullien
Keyword(s):  
A Priori ◽  
Three Dimensional ◽  
Earthquake Ground Motion ◽  
Two Dimensional ◽  
Sh Waves ◽  
Amplification Ratio ◽  
Seismic Motion ◽  
Incident Plane ◽  
Complex Models ◽  
Plane Sh Waves

Abstract A brief review of experimental and theoretical results about the effect of topography on seismic motion shows that they are consistent only on a qualitative basis. Amplification at mountain tops for wavelengths comparable with mountain widths is predicted and observed, but the numerical simulations often underestimate the actual observed effects. We propose that this disagreement is because current models are not complex enough. We therefore computed the response to incident SH waves of a set of different complex configurations that include two-dimensional surface topography, with or without periodic ridges and subsurface layering. The results show that: (1) the topographic effect in itself is difficult to isolate from other effects, like surface layering, and therefore the amplification on top of geomorphologically complex sites cannot be predicted by a priori estimations based solely on topography; and (2) the high crest/base amplification ratio observed in the field cannot, usually, be matched even with complex two-dimensional structures with incident plane SH waves, which suggests that more complex models are needed to incorporate more complex wave fields (e.g., SV, surface) and three-dimensional geologic configurations.

Modelling faecal coliforms dynamics in the Seine estuary, France

2006 ◽  
Vol 54 (3) ◽  
pp. 177-184 ◽  
Author(s):  
T. Garcia-Armisen ◽  
B. Thouvenin ◽  
P. Servais
Keyword(s):  
River Flow ◽  
Three Dimensional ◽  
Longitudinal Distribution ◽  
Seine Estuary ◽  
Faecal Coliforms ◽  
Seine River ◽  
Model Calculations ◽  
Model Free ◽  
Main River ◽  
The Impact

A model describing the dynamics of faecal coliforms (FC) in the Seine estuary has been developed and coupled with a three-dimensional hydrodynamic model. As input to this model three types of FC sources were considered: (1) FC transported by the Seine river flow at the estuary entrance at Poses dam; (2) FC brought in through the tributaries of the Seine estuary; and (3) the outfalls of the treated effluents of the WWTPs located along the estuary. As previous studies in the Seine estuary showed that a large proportion of FC was attached to SM, two pools of FC were considered separately in the model: free FC and FC attached to SM. Two main processes controlling the fate of FC in the estuary were considered: mortality and settling. The model calculates for a given discharge of the Seine river at Poses the longitudinal distribution of FC along the estuary. The model was validated by comparison of model calculations with experimental data in various hydrological conditions. The model also correctly reproduced the impact of the main river flow rate on the level of estuarine water's contamination. Finally, the model was used to test different scenarios of sanitation, suggesting priorities for sanitation efforts.

Investigation of Turbulence Modeling in a High Speed Centrifugal Pump With an Inducer

2007 ◽  
Author(s):  
Behrooz Jafarzadeh ◽  
Reza Mokhtarpoor ◽  
Mohammad Mehdi Alishahi ◽  
Mohammad Hadi Akbari
Keyword(s):  
Centrifugal Pump ◽  
High Speed ◽  
Turbulence Modeling ◽  
Flow Direction ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Governing Equations ◽  
Flow Rates ◽  
Pressure Fields ◽  
Three Dimensional Simulations

In this paper, investigation of turbulence modeling for a centrifugal pump is presented in the form of characteristic curves. A commercial CFD code was used to solve the governing equations of the flow field. Turbulent flow is simulated by employing standard k-ε, RNG and RSM models. Existence of an inducer in the flow direction to prevent cavitation makes two-dimensional simulations of the present configuration impossible. Three-dimensional simulations were therefore performed to predict velocity and pressure fields at different flow rates. Considering the only one available experimental data, the optimum turbulence model for the problem was found. Additionally, effect of number of blades on the efficiency of pump was studied. The number of blades was changed from 6 to 5 and 7, then all calculations were performed afresh. Investigations of this kind may help reduce the required experimental work for the development and design of such devices.

Three-dimensional disturbances in flow between parallel planes

1960 ◽  
Vol 254 (1279) ◽  
pp. 562-569 ◽  
Keyword(s):  
Reynolds Number ◽  
Dimensional Stability ◽  
Flow Direction ◽  
Simple Procedure ◽  
Three Dimensional ◽  
Stability Diagram ◽  
Wave Number ◽  
Two Dimensional ◽  
General Answer ◽  
The Stability

The close connexion between the stability of three-dimensional and two-dimensional disturbances in flow between parallel walls has been examined and this has led to the formation of a three-dimensional stability diagram where ‘stability surfaces’ replace stability curves. The problem which has been investigated is whether the most highly amplifying disturbance at any given Reynolds number above the minimum critical Reynolds number is a two-dimensional or a three-dimensional disturbance. It has been shown that the most unstable disturbance is a two-dimensional one for a certain definite range of Reynolds number above the critical. For Reynolds numbers greater than this no definite general answer has been found; each basic undisturbed flow must be treated separately and a simple procedure has been given which, in principle, determines the type of disturbance which is most unstable. Difficulty arises in following this procedure because it requires knowledge of the two-dimensional stability curves in a certain region where this knowledge is very scanty at the moment. Althoughth is difficulty arises, in Poiseuille flow the calculations available indicate very strongly that the most unstable disturbance at any given Reynolds number above the critical is two-dimensional. Further, it is believed that this result holds for all other basic flows. A second result is that if the wave number (a) in the flow direction is specified, as well as the Reynolds number, then for a in a certain range, the most unstable disturbance is three-dimensional.

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