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1
Hopton, Stephen. "Modelling open channel flow." Thesis, University of Nottingham, 2010. http://eprints.nottingham.ac.uk/11594/.
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The study of open channel flow and dam breaking is not a new topic in computational fluid dynamics. However it has only recently started to gain significant attention from researchers using meshless methods, i.e. numerical modelling techniques which do not rely on the use of a mesh to discretise the domain. The research presented here is an attempt to use the meshless method known as smoothed particle hydrodynamics (SPH) to simulate the flow of water down a channel. Hydra, a pre-existing SPH code designed originally for astrophysical simulations, was converted to simulate water flow and then applied to the problem of dam bursting and flow over a weir. The conversion of the code to its new purpose was verified by simple code tests and then extensive validation was performed via the modelling of multiple dambreaks. The validation process can be split into three broad categories: 1) Comparison against the published data gained from other numerical methods both meshless and traditional. 2) Comparison against physical experiments performed by the author. 3) Comparison against independent experimental data found in the literature. Hydra in its newly converted form was satisfactorily applied to the majority of the tests presented to it and the same level of accuracy was achieved as with any of the other codes tested. A limit to the SPH method for performing this type of simulation was proposed based on particle number, smoothing length and initial conditions. A formula for the calculation of the number of ghost particles required to prevent spurious boundary pressures was also proposed. An analysis of various kernels used by different SPH researchers was presented and it was discovered that a relatively simple cubic spline kernel proved sufficient and that increasing complexity did not provide an increase in solution accuracy. The flow of water over a weir was presented next and results compared to published data which utilised a leading mesh based fluid simulation package. Results gained from Hydra simulations showed good downstream water level prediction but overestimation of upstream levels. A steady state solution was achieved within a similar timeframe compared to the grid based method. It was concluded that use of the SPH method and the Hydra code in particular can provide solutions to problems involving water flow down a channel and accuracy on the dambreak tests was equal to any rival codes/methods tested. However when the complexity of the boundaries involved in the model increased there was some evidence that the CFX simulation package could be used to achieve a more accurate solution than Hydra. Suggestions for continuation of research into Hydra as a water flow modelling code are presented in addition to recommendations for improving the experimental methods used.
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Delis, Anargiros. "Computational modelling of open channel flow." Thesis, University of the West of England, Bristol, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244309.
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Moores, Andrew. "Solute mixing in open channel flow." Thesis, Heriot-Watt University, 1996. http://hdl.handle.net/10399/686.
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Shrestha, Purushottam. "Steady flow in steep open channel systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0026/MQ31403.pdf.
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Dickman, Brian Daniel. "Large scale roughness in open channel flow." Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/22953.
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Legono, D. "Behaviour of flow in open channel bends." Thesis, City University London, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375820.
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Bayat, David, and Fabian Grönvik. "Demonstration station for open water channel flow." Thesis, KTH, Skolan för teknikvetenskap (SCI), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-276582.
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Once a year an event is being held at the fluid physics lab at KTH. One of the main purposes of this event is to awaken an interest in the visiting students from other universities, by demonstrating fluid physics phenomena. Showing the transition from laminar to turbulent flow in an open water channel is one of the demonstrations. This will give the students a feel for the theoretical Reynolds number. The existing water table used for this purpose was lacking in some areas. The purpose of this project is to construct, design and test a rig for openwater channel flow which can be used for the event in the coming years.The character of the flow in an open channel depends on the velocity of the fluid. When the velocity get to a critical level, the flow shifts from a laminar to a turbulent one. It is however difficult to see water flows with the naked eye which makes it difficult to demonstrate this phenomena. There are ways to solve this, that is whatis called flow visualisation. In this project a visualisation method using small hydrogen bubbles in the flow as tracer particles is investigated. The channel design and the visualisation method are investigated experimentally and documented and also compared to existing theory within these areas. The results are deemed satisfactory and the method is documented for further work.
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Arshad, Arslan. "Flow characteristics of narrow vegetated open channels." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2023. https://ro.ecu.edu.au/theses/2649.
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Vegetation offers higher resistance to the flow as compared to the bed of the channel causing the rise in water level. This idea has been proposed by numerous studies to be used in the channels with low flows to raise the water level enabling these channels useful for navigation and transportation. Raising the water levels artificially comes with challenges like the change in the aspect ratio (width to depth ratio, b/H). Generally, open channels experience a dip near the surface when the water level is increased, and the b/H becomes lower than a typical value of 5. The effect of dip near the surface in the partially vegetated channels remains unknown. Similarly, the literature focuses on the vegetation on one side of the wide channels, but the vegetation on both sides of narrow channels needs further exploration.
A series of experiments have been conducted to understand the above-mentioned research gaps by installing wood dowels in the flume. It has been found that unlike the channels without vegetation, the dip near the surface begins even for b/H>5 which restricts the expansion of the shear layer and the KH vortices in the canopy free region. The vortex structures captured using PIV further revealed that because of limited expansion in the canopy free region, the KH vortices are stretched. The stretching of the vortices in the shear region causes significantly higher shear stress at the canopy interface. The values of the shear stress increase as the aspect ratio are decreased. Moreover, most of the mass flux is diverted away from the canopy region towards the other side wall which offers relatively lesser drag.
The study of the canopies of similar densities but different stem sizes reveals that the velocities inside the canopy region are independent of the stem size and mostly depend on the relative spacing (average spacing between the stems to stem diameter). The distribution of the velocity in the canopy free region beyond the influence of the shear layer remains unaffected. However, the channels with canopies of bigger stem sizes tend to have lower velocities in the shear region as compared to the channels with smaller stems. The smaller velocities in the shear region for bigger stems result in relatively lower vortex stretching and smaller friction velocities.
The results of the experiments conducted in the channels with vegetation on both sides show that the shear layers are created at the interfaces of both canopies. The vortices generated inside these shear layers mutually interact and adjust to form pairs of vortices. The strength of these vortices is increased due to mutual interaction which is reflected in the form of higher friction velocities at both interfaces. When these friction velocities are compared with the friction velocities in the channels with canopies of similar characteristics and same flow depths, the friction velocities are significantly higher when canopies are on both sides.
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Roberts, Matthew Vincent Taylor. "Flow dynamics at open channel confluent-meander bends." Thesis, University of Leeds, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414170.
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MacDonald, Ian. "Analysis and computation of steady open channel flow." Thesis, University of Reading, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336664.
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Stewart, Mark Thomas. "Turbulence structure of rough-bed open-channel flow." Thesis, University of Aberdeen, 2014. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=210848.
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Open-channel flows are ubiquitous in nature and play a central role in many hydraulic engineering problems. This flow type occurs almost exclusively under fully-rough turbulent conditions and it is not uncommon for the relative submergence of these flows to be low. Despite this, most theory has so far been developed for smooth wall flows or rough-bed flows at high submergence while its applicability at low relative submergence remains questionable. This thesis therefore aims to contribute towards an improved understanding of turbulence structure in rough-bed open-channel flow at low to intermediate relative submergence. Experiments were conducted to collect turbulent velocity field data for nine different flow scenarios, covering roughness Reynolds numbers between 175 and 900, and relative submergence between 2.5 and 7.5. Each flow scenario was measured independently using particle image velocimetry (PIV) in five distinct configurations. The PIV system was first configured to make two-component velocity measurements with a very wide field of view (up to twenty flow depths) along the channel centreline in a streamwise-wall-normal plane. These measurements were supplemented with three-component stereoscopic PIV recordings along the same plane albeit with a shorter field of view. The third, fourth and fifth set ups involved stereoscopic PIV in three separate transverse-wall-normal planes and thus ensured the complete lateral coverage of the flow field from the sidewall to the centreline. The four-camera arrangement of each of the present stereoscopic PIV configurations was exploited to obtain velocity field statistics with significantly reduced contributions from measurement noise. The thesis reports distributions of bulk velocity statistics and spectra of all three velocity components. In addition, characteristic large scale features of the instantaneous flow are examined using velocity field visualisation, two-point velocity correlations and premultiplied velocity spectra. Further analysis is carried out on the time-averaged flow field to visualise secondary current patterns and to study their lateral extent.
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Burger, Johannes Hendrik. "Non-Newtonian open channel flow: the effect of shape." Thesis, Cape Peninsula University of Technology, 2014. http://hdl.handle.net/20.500.11838/1296.
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Thesis submitted in fulfilment of the requirements for the degree
Doctor of Technology: Mechanical Engineering
in the
Faculty of Engineering
at the
Cape Peninsula University of Technology
2014Open channels, flumes or launders are used in the mining industry to transport slurries during processing and to disposal sites. Water plays a major part in the makeup of these slurries, its usage and availability is critical in countries where there are strict water usage management programs. The optimisation of flume design involves the maximisation of solids transport efficiency whilst, at the same time reduces water usage. The design of open channels is complex as it is dependent on both the slurry rheology and the channel shape. Very little has been reported in the literature for predicting non-Newtonian laminar flow in open channels of arbitrary cross-section. The only method available was that proposed by Kozicki and Tiu (1967, 1986). The shape factors they used were those evaluated from analytical solutions for flow of Newtonian fluids in open channels of the same cross-section. However, they carried out no experimental work to validate their model. Few experimental studies have been made on the effect of shape on non-Newtonian flow in open channels. Naik (1983) tested kaolin in water suspensions in a rectangular channel. Coussot (1994) provided some data for the flow of a Herschel-Bulkley fluid in rectangular and trapezoidal channels. Fitton (2007; 2008) obtained data for flow of three different non-Newtonian fluids (carboxymethylcellulose, carbopol and thickened tailings) in a semi-circular channel. A large experimental database for non-Newtonian flow in rectangular open channels was published by Haldenwang (2003) at the Flow Process Research Centre, Cape Peninsula University of Technology. Guang et al. (2011) performed Direct Numerical Simulations of turbulent flow of a yield- pseudoplastic fluid in a semi-circular channel. They compared their simulations with actual field measurements and found them to over-predict the flow velocity by approximately 40%. The source for this discrepancy was difficult to ascertain. A comprehensive database was compiled during this research of the flow of three non–Newtonian fluids in rectangular, trapezoidal, semi-circular and triangular channels. The flow of carboxymethylcellulose solutions and aqueous kaolin and bentonite suspensions was investigated in a 10 meter long flume at angles ranging from 1° to 5° from the horizontal plane. The effect of channel shape on the friction factor-Reynolds number relationship for laminar and turbulent open channel flow of these three fluids was investigated. New models for the prediction of laminar and turbulent flow of non-Newtonian fluids in open channels of different cross-sectional shapes are proposed. The new laminar and turbulent velocity models are compared with three previously-published velocity models for laminar flow and five previously-published velocity models for turbulent flow using average velocity as comparison criteria. For each channel shape, the laminar flow data can be described by a general relationship, f = K/Re where f is the Fanning friction factor and Re is the appropriate Haldenwang et al. (2002) Reynolds number. The K values were found to be 14.6 for triangular channels with a vertex angle of 90°, 16.2 for semi-circular channels, 16.4 for rectangular channels and 17.6 for trapezoidal channels with 60 degree sides. These K values were found to be in line with those reported by Straub et al. (1958) and Chow (1969) for open channel laminar flow of Newtonian fluids as opposed to the assumption made by Haldenwang et al. (2002; 2004) of using a constant value of 16 based on the pipe flow paradigm for all channel shapes. This new laminar model gave a closer fit to the laminar flow data than those from the three previously-published models. However, the presence of the yield stress still presents a problem, which makes the flow prediction in laminar flow for such fluids not very accurate. The investigation on non-Newtonian turbulent flow of the three fluids in the four different shaped open channels revealed that the data was described by the modified Blasius equation f = a Re b where a and b are constant values determined for each channel shape and Re is the Haldenwang et al. (2002) Reynolds number. Values of a and b for a rectangular channel were found to be 0.12 and -0.330, for a semi- circular channel 0.048 and -0.205, for a trapezoidal channel with 60° sides, 0.085 and -0.266 and for a triangular channel with vertex angle of 90°, 0.042 and -0.202. New laminar and turbulent velocity models were derived from using the new laminar f = K/Re and turbulent f = a Re b, friction factor-Reynolds number relationship. The laminar velocity model did not always give the best result, but the majority of the time it did, compared to the three previously published models. The new turbulent velocity model yielded the best results when compared to the five previously published models using average velocity as comparison criteria. The composite power law modelling procedure of Garcia et al. (2003) used for pipe flow predictions was extended to the present work on non-Newtonian flow in open channels of various cross-sections. The results show that the modelling technique used by Garcia et al. (2003) for pipe flow can be used to adequately predict flow in an open channel of a given cross-sectional shape provided that an appropriate Reynolds number is used to take into account the non-Newtonian behaviour of the test fluid. It was found that the results using the Haldenwang et al. (2002) Reynolds number yielded better results than those based on the adapted Metzner-Reed Reynolds number. The correlations and models developed and experimentally validated during this research can be used to further improve the design of rectangular, semi-circular, trapezoidal and triangular open channels to transport non-Newtonian fluids.
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Keogh, Darren Paul. "An experimental investigation on the flow characteristics of open-channel slot flow." Thesis, Edinburgh Napier University, 2000. http://researchrepository.napier.ac.uk/Output/4273.
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Hunt, Alan Ernest. "The behaviour of turbulence in unsteady open channel flow." Thesis, University of Canterbury. Civil Engineering, 1997. http://hdl.handle.net/10092/7722.
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An investigation into the behaviour of the turbulence during laboratory simulations of floods in rivers with mild bed slopes was undertaken. Computer control of the flow rate into the flume enabled reproducible flood waves to be generated. To rigorously model the energy gradients in a long channel, an interactive sluice gate control was developed for the downstream end of the flume. Mean flow unsteadiness effects on the turbulence were evaluated by considering different duration hydrographs with similar shapes and magnitudes. The investigation was limited to the longitudinal component of turbulence, as a one-component laser Doppler anemometer was employed for the determination of point velocities. Flow visualisation using a dye plume supplemented velocity data. It was observed that for events having a shorter duration the peak turbulent intensity had a greater magnitude, and occurred relatively earlier on the rising limb of the flood.
The turbulent energy peak coincided with the maximum flow rate divergence. For increasing flow divergence magnitude, which only occurs on the rising limb, the production of turbulence was larger than dissipation, with the transport of turbulence providing an additional sink for turbulent energy. After the depth had peaked the flow experienced pseudo-equilibrium conditions, where the transport mechanism was insignificant and the rate of production approximated dissipation. A feature of the falling limb was a period of inactivity, in which the magnitudes of production and dissipation were at minimum.
A second -5/3 slope region was observed in the energy spectra. The length scale associated with an energy source for this double structure was two orders of magnitude larger than the Kolmogorov dissipation length scale. Decay times for flow structures of this size are similar to the duration of these hydrographs.
It is possible that the unsteady flow created vortex structures that persisted for some time after the flow which generated them had moved downstream. These vortex structures, which provide a turbulence memory mechanism, and the state of pseudo-equilibrium on the falling limb are responsible for residual turbulent energy in the flow throughout the falling limb and immediately following the passing of the flood wave.
In addition, it is suggested that mean flow controls both the production and dissipation of turbulence, with the dissipation of turbulent kinetic energy being controlled by the diffusion of momentum during low speed streaks. The Kolmogorov scale may be interpreted as defining the critical damping condition along these streaks where Reynolds stresses balance viscous forces.
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Sharifi, Soroosh. "Application of evolutionary computation to open channel flow modelling." Thesis, University of Birmingham, 2009. http://etheses.bham.ac.uk//id/eprint/478/.
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This thesis examines the application of two evolutionary computation techniques to two different aspects of open channel flow. The first part of the work is concerned with evaluating the ability of an evolutionary algorithm to provide insight and guidance into the correct magnitude and trend of the three parameters required in order to successfully apply a quasi 2D depth averaged Reynolds Averaged Navier Stokes (RANS) model to the flow in prismatic open channels. The RANS modeled adopted is the Shiono Knight Method (SKM) which requires three input parameters in order to provide closure, i.e. the friction factor (\(f\)), dimensionless eddy viscosity (λ) and a sink term representing the effects of secondary flow (Γ). A non-dominated sorting genetic algorithm II (NSGA-II) is used to construct a multiobjective evolutionary based calibration framework for the SKM from which conclusions relating to the appropriate values of \(f\), λ and Γ are made. The framework is applied to flows in homogenous and heterogeneous trapezoidal channels, homogenous rectangular channels and a number of natural rivers. The variation of \(f\), λ and Γ with the wetted parameter ratio (\(P_b\)/\(P_w\)) and panel structure for a variety of situations is investigated in detail. The situation is complex: \(f\) is relatively independent of the panel structure but is shown to vary with P\(_b\)/P\(_w\), the values of λ and Γ are highly affected by the panel structure but λ is shown to be relatively insensitive to changes in \(P_b\)/\(P_w\). Appropriate guidance in the form of empirical equations are provided. Comparing the results to previous calibration attempts highlights the effectiveness of the proposed semi-automated framework developed in this thesis. The latter part of the thesis examines the possibility of using genetic programming as an effective data mining tool in order to build a model induction methodology. To this end the flow over a free overfall is exampled for a variety of cross section shapes. In total, 18 datasets representing 1373 experiments were interrogated. It was found that an expression of form \(h_c\)=A\(h_e\)\(^{B\sqrt S_o}\), where \(h_c\) is the critical depth, \(h_e\) is the depth at the brink, \(S_o\) is the bed slope and A and B are two cross section dependant constants, was valid regardless of cross sectional shape and Froude number. In all of the cases examined this expression fitted the data to within a coefficient of determination (CoD) larger than 0.975. The discovery of this single expression for all datasets represents a significant step forward and highlights the power and potential of genetic programming.
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Valyrakis, Manousos. "Initiation of Particle Movement in Turbulent Open Channel Flow." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/27289.
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The objective of this thesis is to investigate the flow conditions that lead to coarse grain entrainment at near incipient motion conditions. Herein, a new conceptual approach is proposed, which in addition to the magnitude of hydrodynamic force or flow power, takes into account the duration of the flow event. Two criteria for inception of grain entrainment, namely the critical impulse and critical energy concepts, are proposed and compared. These frameworks adopt a force or energy perspective, considering the momentum or energy transfer from each flow event to the particle respectively, to describe the phenomenon.
A series of conducted mobile particle experiments, are analyzed to examine the validity of the proposed approaches. First a set of bench-top experiments incorporates an electromagnet which applies pulses of known magnitude and duration to a steel spherical particle in a controlled fashion, so as to identify the critical level for entrainment. The utility of the above criteria is also demonstrated for the case of entrainment by the action of turbulent flow, via analysis of a series of flume experiments, where both the history of hydrodynamic forces exerted on the particle as well as its response are recorded simultaneously.
Statistical modeling of the distribution of impulses, as well as conditional excess impulses, is performed using distributions from Extreme Value Theory to effectively model the episodic nature of the occurrence of these events. For the examined uniform and low mobility flow conditions, a power law relationship is proposed for describing the magnitude and frequency of occurrence of the impulse events. The Weibull and exponential distributions provide a good fit for the time between particle entrainments. In addition to these statistical tools, a number of Adaptive Neuro-Fuzzy Inference Systems employing different input representations are used to learn the nonlinear dynamics of the system and perform statistical prediction. The performance of these models is assessed in terms of their broad validity, efficiency and forecast accuracy.
Even though the impulse and energy criteria are deeply interrelated, the latter is shown to be advantageous with regard to its performance, applicability and extension ability. The effect of single or multiple highly energetic events carried by certain coherent flow structures (mainly strong sweep events) with regard to the particle response is also investigated.Ph. D.
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Campbell, Lorna J. "Double-averaged open-channel flow over regular rough beds." Thesis, University of Aberdeen, 2005. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU214372.
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The majority of analysis of hydraulically rough open-channel flows has been founded on the temporally-averaged momentum equations (RANS). However, the structure of shallow open-channel flows over hydraulically rough beds, together with the near-bed region of deeper open-channel flows with rough beds awaits clarification. The purpose of this project was to conduct an extensive programme of laboratory-based experiments to gauge the applicability of the double-averaged momentum equations for shallow open-channel flows over simple rough beds (transverse square bars with varying centre-to-centre pitch). Proper assessment of the double-averaged equations requires comprehensive measurement of fluid velocities. Therefore, detailed Particle Image Velocimetry (PIV) measurements have been obtained of the streamwise and bed-normal velocity components, including their variation in both temporal and spatial domains. The results show that double-averaging is a powerful tool for the analysis of hydraulically rough flows. For a range of isolated flow types, the vertical distribution of the double-averaged streamwise velocity follows a linear trend between bars. Quadrant analysis has been applied to the spatial, rather than temporal, fluctuations of velocity components for the first time, and double-averaging analysis has revealed areas of intense local momentum transfer despite negligible global momentum exchange over the averaging window. This thesis also reports the discovery of an instability at the transition between wake interference and isolated roughness flows at which the overall properties of the flow are dramatically altered.
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Shumate, Eric Dean. "Experimental Description of Flow at an Open-Channel Junction." Thesis, University of Iowa, 1998. https://ir.uiowa.edu/etd/5368.
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Boxall, Joseph B. "Dispersion of solutes in sinuous open channel flows." Thesis, University of Sheffield, 2000. http://etheses.whiterose.ac.uk/14803/.
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The research undertaken for this Ph.D. thesis concerns the dispersion of solutes in sinuous open channel flows. The aim of the work is to address the void in knowledge and understanding of mixing and transport processes in natural watercourses. The influences of plan form curvature and non-uniform cross sectional shape on transverse and longitudinal mixing are specifically addressed. Experimental work was undertaken on the Flood Channel Facility at HR Wallingford Ltd. This involved creating a pseudo natural sand channel within the concrete meander plan form of the facility, and then stabilising the form. Tracer studies using instantaneous injection to investigate longitudinal mixing and continuous point source release to study transverse mixing were performed. Fluorescent tracer was used. Measurement was by six Turner Design Field Fluorometers in pump through mode and these were digitally logged. Detailed hydrodynamic measurements were made using a two-dimensional Laser Doppler Anemometer (LDA) fitted with a 14mm fibre-flow probe. The resulting data has undergone robust analysis and detailed interpretation. The conclusions are that the dominant processes in mixing, in the natural channel form studied, are shear effects. Simple equations for the prediction of flow fields have been investigated and validated against LDA measurements. It has been possible to make accurate predictions of the transverse and longitudinal mixing coefficients from the predicted flow fields. These predictions have been shown valid for the variations in mixing coefficients over the meander cycle and with discharge.
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Savio, Mario. "Turbulent structure and transport processes in open-channel flows with patchy-vegetated beds." Thesis, University of Aberdeen, 2017. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=237016.
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Flow-vegetation interactions are critically important for most hydraulic and sediment processes in streams and rivers and thus need to be accounted for in their management. The central goal of this project therefore was to improve the understanding of flow-vegetation interactions in patchy-vegetated river beds, which are typical in rivers. Based on laboratory experiments covering a range of selected hydraulic and patch mosaic scenarios, the hydraulic resistance mechanisms, turbulence structure, and transport mechanisms were studied. The effects of regular patch mosaic patterns (aligned and staggered) on the bulk hydraulic resistance were investigated first. For the cases in which the relative vegetation coverage BSA in respect to the total flume bed is low (BSA = 0.1), the patches mutual positions do not affect values of the friction factor. When the parameter BSA increases to intermediate values (BSA = 0.3), the spatial distribution of the vegetation patches and their interactions become crucial and lead to a significant increase in the bulk hydraulic resistance. When further increase of the vegetation cover occurs (BSA = 0.6), the effects on hydraulic resistance of patch patterns vanish. To clarify the mechanisms of the revealed patch effects on the overall hydraulic resistance, flow structure was assessed at both scales: individual patch and patch mosaic. The presence of a submerged isolated vegetation patch on the bed introduces a flow diversion which strongly alters the velocity field and turbulence parameters around the patch. Coherent structures, generated at the canopy top due to velocity shear, control the mass and momentum transfer between the layers below and above the vegetation patch. At the patch mosaic scale, a complex three-dimensional flow structure is formed around the patches which depends on the patch spacing and spatial arrangements. For the low surface area blockage factor (BSA = 0.1), the patches are sparsely distributed and the wakes are (nearly) fully developed before they are interrupted by the effects of the downstream patches. At the intermediate surface area blockage factor (BSA = 0.3), significant differences in flow structure between the aligned and staggered patches were observed. For the highest surface area blockage factor investigated (BSA = 0.6) both aligned and staggered patch mosaic configurations showed a similar behaviour. The results on the flow structure are used to provide mechanistic explanation of the observed patch mosaic effects on the bulk hydraulic resistance.
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Ma, Jianmin. "Numerical analysis of flow structures and bed entrainment in turbulent open-channel flow." Thesis, Queen Mary, University of London, 2009. http://qmro.qmul.ac.uk/xmlui/handle/123456789/524.
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The results from a Direct Numerical Simulation (DNS) and a Large Eddy Simulation (LES) are employed to study the large-scale coherent structures and bed entrainment in the turbulent open-channel flow. The gravel bed is represented by a hexagonal arrangement of uniform spheres. The large-scale coherent structures are composed of a group of quasistreamwise vortices and asymmetric hairpin vortices. The meandering structures are shown to be longer than the length of the computational box, more than 20 times the effective flow depth in this study, and the width tends to be one order of magnitude smaller than the length. The signature of the large-scale motion is elongated local maximum of streamwise velocity. It is also found that these structures contribute substantially to both of the Reynolds Stress (RS) and the Turbulent Kinetic Energy (TKE). The entrainment of bed gravels is investigated by the three-dimensional analysis of the relationship between near-wall coherent structures and the force moments exerted on the particles. It is found that the spanwise drag moment (MD2) is of the same order of magnitude compared with the streamwise drag moment (MD1). The majority of MD2 originates from pressure whilst the viscous force plays as an important role as pressure for MD1. The contributions of the forces at different heights of the particle to MD1 and MD2 are explored. The quasi-streamwise vortices are strongly associated with MD2 and the ejections are shown to be more favorable for bed entrainment than the sweeps in this bed condition.
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Vanyaza, Sydwell Luvo. "Non-newtonian open-channel flow : effect of shape on laminar and transitional flow." Thesis, Cape Technikon, 2004. http://hdl.handle.net/20.500.11838/874.
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Thesis (MTech (Chemical Engineering))--Cape Technikon, 2004When designing the open channels to transport the homogenous non-Newtonian slurries, the effect of channel shape is one of the parameters that should be checked and very little research has been conducted to address this matter. Open channels are commonly applied in the mining industry where mine tailings have to be transported to the disposal dams at high concentrations to save water consumption. This thesis addresses the effect of the cross-sectional shape of the channel with emphasis on laminar and transitional flow of non-Newtonian fluids. The literature review on the flow of Newtonian and non-Newtonian fluids has been presented. The most relevant one to this topic is the work done by Straub et al (1958) for Newtonian fluids and the analytical work presented by Kozicki and Tiu (1967) for non-Newtonian fluids. Authors like Coussot (1994) and Haldenwang (2003) referred to their work but did not comprehensively verified it experimentally. Three flume shapes were designed to investigate this problem namely, rectangular, semi circular, and trapezoidal flume shape. The test rig consisted of a 10 m long by 300mm wide tilting flume that can be partitioned into two sections to form a 150 mm wide channel. All three flume shapes were tested in both the 150 mm and 300 mm wide flumes. This flume is linked to the in-line tube viscometer with three tube diameters namely, 13 mm; 28 mm; and 80 mm. The experimental investigation covered a wide range of flow rates (0.1-45l/s), and flume slopes (1-5 degrees). The fluids tested were kaolin suspension (5.4 - 9% v/v), CMC solution (1 - 4% m/m), and bentonite suspension (4.6 and 6.2% mlm). The models found in the literature were evaluated with the large database compiled from the test results to predict the laminar and transitional flow of these fluids with the aim of checking the effect of the cross-sectional shape of these channels selected in these flow regimes. For all the flume shapes and non-Newtonian fluids selected in this thesis it was found that in predicting the laminar flow, the effect of shape is adequately accounted for by the use of hydraulic radius. In predicting the transitional flow, it was found that the effect of shape does not have to be included.
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Witz, Matthew J. "Mechanics of particle entrainment in turbulent open-channel flows." Thesis, University of Aberdeen, 2015. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=225690.
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An advanced understanding of particle entrainment is required to optimise the design and maintenance of numerous open channel hydraulic systems and structures placed in these systems; including river channels and canals. This study is on particle entrainment (defined as the movement of a particle from a stationary position to being mobile in the flow). Three aspects of particle entrainment were identified as the focus of this work: First, the waiting time for an exposed particle to entrain under constant flow conditions. Second, the flow features responsible for the entrainment of an individual exposed particle. Third, the motion of an entrained particle immediately after entrainment. Waiting time was found to be highly sensitive to protrusion, with a small increase in protrusion resulting in a significant decrease in waiting time. Contrary to previous suggestions the waiting time to entrainment was found to be poorly described by an exponential distribution; instead Weibull or gamma distributions provide an improved fit in both qualitative and quantitative terms. Ensemble averaged flow fields at the point of entrainment were computed to determine the features responsible for entrainment. The data from the transverse vertical PIV plane indicated the presence of two counter-rotating vortices, with the boundary between the vortices located directly over the entrainment particle. The streamwise vertical PIV measurements showed the presence of a structure extending for a considerable distance in the streamwise direction, the length of which appeared to be independent of submergence. Further, the inclination of the downstream end of the structure appeared to increase with submergence. From the point of entrainment particle dffusion in all three coordinate directions displays an exponent significantly greater than that of ballistic diffusion. From the point of entrainment particle diffusion in all three coordinate directions displays an exponent significantly greater than that of ballistic diffusion. The results highlight the clear difference in the local scale between the diffusion of an already mobile particle with one starting from a position of rest.
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Kim, Su Jin. "3D numerical simulation of turbulent open-channel flow through vegetation." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42892.
Full textAbstract:
A comprehensive understanding of the hydrodynamics in vegetated open-channels and flow-vegetation interaction is of high interest to researchers and practitioners alike for instance in the content of river and coastal restoration schemes. The focus of this study was to investigate the effect of the presence of vegetation on flow resistance, turbulence statistics, and the instantaneous flow in open channels by performing three-dimensional computational-fluid-dynamics (CFD) simulations.
Firstly, fully developed turbulent flow in fully-vegetated channel was analyzed by employing the method of high-resolution Large-Eddy Simulation (LES). Flow through a staggered array of rigid, emergent cylinders was simulated and the LES was validated through experiments. After validation, numerical simulations were performed at an extended parameter range of two different cylinder Reynolds numbers (ReD = 500 and 1340) and three different vegetation densities (φ = 0.016, 0.063, and 0.251). Flow structures and statistics were analyzed on the instantaneous flow and the effect of the vegetation density and cylinder Reynolds number was assessed. Moreover, drag forces exerted on the cylinders were calculated explicitly, and the effect of both ReD and φ on the drag coefficient was quantified. Secondly, two new alternative simulation strategies, a RANS based strategy with a vegetative closure model and a low-resolution Large-Eddy Simulation, were devised. They were evaluated by simulating several experimental cases with diverse conditions of the cylinder arrangement (i.e., staggered vs. random distribution), vegetation densities (φ = 0.016, 0.022, 0.063, 0.087, 0.091, 0.150, and 0.251), and cylinder Reynolds number (ReD = 170 - 1700). For the RANS based strategy, the importance of a-priori knowledge was assessed, and for the low-resolution LES, the efficiency and accuracy was demonstrated. Finally, a numerical strategy based on a porosity approach was developed and applied to open-channel flow through a natural plant. The simulated velocities were compared with experimentally acquired ones and results showed reasonable agreement.
The results obtained in this research contribute to the understanding of fundamental mechanism of flow-vegetation interaction in vegetated open-channels, resolving turbulent flow-vegetation interaction explicitly. In addition, the new numerical strategies developed as part of this research are expected to allow describing the behavior of turbulent flow through artificial and natural vegetation with high efficiency and accuracy.
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Lu, Zhihua. "Stochastic modelling of unsteady open channel flow and reliability analysis /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202008%20LU.
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Oelerich, Jerry J. "Open-channel capillary flow in micro-scale helical support structures." Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Thesis/Spring2009/J_Oelerich_042709.pdf.
Full textAbstract:
Thesis (M.S. in chemical engineering)--Washington State University, May 2009.Title from PDF title page (viewed on June 8, 2009). "Department of Chemical Engineering." Includes bibliographical references (p. 70-71).
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Siqueira, Renato do Nascimento. "Transport and mixing processes in stratified flow." Thesis, Loughborough University, 2002. https://dspace.lboro.ac.uk/2134/34335.
Full textAbstract:
The processes of transport and mixing in stratified open channel flows are investigated in this thesis. Detailed measurements of velocity and salinity were conducted, through the use of Laser-Induced Fluorescence (LIP) technique together with Laser Doppler anemometry, so that the effects of secondary current and stratification on the flow behaviour could be analysed. Two configurations were investigated: a rectangular open channel, and a compound open channel. For each configuration, four different stratification levels were analysed. The main flow characteristics, such as corner flow and velocity dip in a rectangular channel, and the twin vortices formed in compound channels, were found to be affected by stratification. In order to understand the mechanisms involved in secondary flow generation, the vorticity balance was carried out. Through the vorticity balance, the contribution of each term in the longitudinal vorticity equation could be evaluated. The mechanisms involved in the turbulence generation were also verified through the turbulent kinetic energy (TKE) budget. One of the contributions of this work refers to the understanding of the effects of stratification on turbulence and secondary flow generation. The exchange coefficients of momentum and solute were also investigated. These coefficients were found to depend not only on stratification level but also on other flow parameters, like for instance the aspect ratio. A new formulation is proposed for narrow channels, but more research is necessary in order to evaluate the effect of other parameters on the exchange coefficients.
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Khatibi, Rahman Haghi. "Mathematical open channel flow models and identification of their friction parameters." Thesis, University of London, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263145.
Full textAbstract:
This thesis l concerned with the mathematical modelling of open channel flows governed by the Saint-Venant equations, which are used as a prediction or identification tools. A survey of the literature in these fields identified the problems in need of Immediate research. Numerical test runs were then devised which led to projecting a clear picture as follows. The performance of twn widely used Implicit finite difference schemes, the 4-point box and 6-point staggered schemes were compared In a wide range of circumstances. it is concluded that both schemes produce 'very close results, but the staggered scheme is prone to convergence problems In some extreme cases. It was also noted that a sharp change in geometric configuration of compound channels produced discontinuous features on the aim ulated depth and discharge hydrographs. The inability of the staggered scheme In handling a head-discharge relationship as a downstream boundary condition was tackled by proposing and implementing a scheme of second order accuracy. As model data are generally corrupted withh errors and noise, their effects together with that of other factors on the Identified friction parameters we Investigated. The results demonstte the paramount Importance of the effect of a choice of objective function on the Identified parameters. While the individual values of the identified M2nning n may vary from one flood event to another, their mean is shown both numerically and rigorously to be dependent upon the choice of objective function. It is shown that an objective function formulated by using absolute errors performs ideally and produces reliable results even in the presence of autocorrelated Gaucian noise samples. The mean of the Identified parameters is also found to be adversely affected if the observation station is affected by localized disturbances. Sensitivity of objective functions to the variation In the value of the friction parameter Is also found to be an Important factor, as Insensitivity leads to ill-conditioning.
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Papadopoulou, Symela. "Velocity distribution in shallow open channel flow over square bar roughness." Available from the University of Aberdeen Library and Historic Collections Digital Resources, 2009. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=58994.
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Hurther, David. "3-D acoustic Doppler velocimetry and turbulence in open-channel flow /." Lausanne, 2001. http://library.epfl.ch/theses/?nr=2395.
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Kironoto, Bambang Agus. "Turbulence characteristics of uniform and non-uniform, rough open-channel flow /." [S.l.] : [s.n.], 1993. http://library.epfl.ch/theses/?nr=1094.
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Yulistiyanto, Bambang. "Flow around a cylinder installed in a fixed-bed open channel /." [S.l.] : [s.n.], 1997. http://library.epfl.ch/theses/?nr=1631.
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Stewart, Robert L. III. "DECELERATING OPEN CHANNEL FLOW OVER GRAVEL: TURBULENCE STRUCTURE & SENSOR DEVELOPMENT." UKnowledge, 2014. http://uknowledge.uky.edu/ce_etds/25.
Full textAbstract:
This dissertation describes investigations of fully turbulent decelerating hydraulically roughbed flow over gravel and the development of technology to measure turbulence and associated sediment transport in streams. Theory is developed for predicting velocity distributions in simple uniform flow using the asymptotic invariance principle and tested using laboratory and field collected data. A mixed scale is developed that accounts for bed derived turbulent structures throughout the flows depth and is used to parameterize the external boundary’s effect on the flow for the logarithmic and outer layers. The asymptotic invariance principle and similarity analysis is conducted for the equations of motion in the outer region of decelerating flow over gravel to define equilibrium conditions for this class of flows with the velocity scale is the freestream velocity. The combination of time series and time averaged statistical analysis of turbulent flow is used to elucidate the structure of flow under decelerating conditions. Time averaged statistical measures of turbulence confirm results of others for higher Froude number approaching transcritical and time series analysis shows the effects of decelerating flow on turbulence to be frequency dependent. Wireless velocity sensors were developed and found capable of measuring time averaged velocity and able to resolve macroturbulence from time series data. A semi-theoretical model of elastic deformation of cantilever beams under hydraulic forcing was coupled with circuit theory to develop a calibration procedure for the VBS that requires only three measurement points, one of which is at zero velocity. Light based sensors are developed to estimate light attenuation in water for ecological research or estimating sediment concentration in water. A semi-theoretical scaling of light attenuation and sediment properties was developed which predicts light attenuation from sediment properties. The combination of new theory on open channel velocity, turbulent structure and field sensors for measuring turbulence and sediment offers the possibility to extend our laboratory knowledge to realistic flow situations.
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Brevis, Vergara Wernher Ariel. "Experimental Investigation of the Flow Hydrodynamics in Open-Channel Dead Zones." Tesis, Universidad de Chile, 2009. http://repositorio.uchile.cl/handle/2250/102106.
Full textAbstract:
Uno de los principales factores que modifica el transporte de sustancias en aguas someras
es la presencia de fuertes cambios laterales de la sección transversal, los cuales generan
zonas de recirculación de gran escala que intensifican los procesos asociados a la
dispersión de masa. Además de los efectos físicos inducidos por estas zonas, ellas han
mostrado una importante contribución a la generación de condiciones hidrodinámicas
mejoradas para estimular el crecimiento de la flora y fauna acuática. Estas estructuras del
flujo reciben el nombre genérico de zonas muertas y se pueden formar por modificaciones
naturales o artificiales de la morfología.
En este trabajo se presenta una descripción experimental de la estructura del flujo
en zonas muertas formadas por una secuencia de bloques, para la llamada condición de
flujo emergida. En esta condición de flujo, la cota superior del bloque es mayor a la del
nivel de la superficie de agua y debido a esto el intercambio de masa y momentum ocurre
solamente a través de la capa de corte generada en la interfaz entre la zona muerta y el flujo
principal. Estudios anteriores han mostrado las características horizontales, normalmente
en la superficie, y, debido a esto, la principal contribución de este trabajo es la descripción
de la estructura vertical del flujo. Esta descripción es importante porque provee información
relevante para la comprensión de la condiciones de flujo cercanas al lecho, donde ocurren
gran parte de los procesos ecológicos. Este trabajo también contribuye con la descripción
de las características cuasi-bidimensionales y tri-dimensionales de las zonas muertas, la
identificación de estructuras coherentes, y la influencia de la distancia entre bloques en los
procesos físicos que gobiernan el intercambio de masa y momentum.
Para realizar los experimentos, uno de los objetivos de este trabajo fue el desarrollo
de una técnica sinóptica de velocimetría basada en el procesamiento de imágenes. Esta
contribución experimental está basada en nuevas modificaciones de algoritmos para
Velocimetría por Rastreo de Partículas (PTV), y en su integración en un algoritmo de
dos etapas. La nueva contribución es llamada “Integrated Cross-Correlation / Relaxation
Method”, ICCRM, y fue especialmente diseñada con el objetivo de ser una herramienta
flexible para investigar flujos con gradientes de velocidad intensos y condiciones de
sembrado de partículas no homogéneas.
Los resultados experimentales obtenidos de la aplicación del ICCRM al flujo en estudio
muestran que las estructuras formadas en la capa de corte que se produce en la interfaz
entre el flujo principal y la zona muerta impactan periódicamente el bloque de aguas abajo
con una distribución vertical de velocidad caracterizada por una magnitud máxima a media
profundidad. El impacto con el bloque da lugar a un sistema de vórtices de eje horizontal,
paralelo a los bloques, el cual es transportado hacia el interior de la cavidad. El flujo que
penetra a la zona muerta energiza un sistema de circulación horizontal de una o más celdas,
dependiendo de la razón de aspecto analizada (relación entre la longitud de los bloques
y su separación longitudinal), con una estructura vertical bastante uniforme en términos
de la velocidad media. Esto valida la suposición de flujo bidimensional en gran parte de
la región de flujo al interior de la cavidad. Sin embargo, los parámetros representativos de
la turbulencia (esfuerzos de Reynolds, pseudo-energía cinética turbulenta, espectros de energía, etc.) y las estructuras responsables del intercambio de masa entre la zona muerta
y el flujo principal son claramente tri-dimensionales.
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Peruzzo, Paolo. "Diffusion of floating particles in open channel flow through emergent vegetation." Doctoral thesis, Università degli studi di Padova, 2012. http://hdl.handle.net/11577/3422187.
Full textAbstract:
In this thesis we study the problem of the dispersion of floating particles within emergent vegetation through experimental, numerical and theoretical analysis of the mechanisms that rule their temporary retention and the
capture by plants.
In Chapter 1 we present early results of laboratory experiments performed to investigate the transport and the diffusion of floating particles e.g., buoyant seeds) in open channel flow with emergent vegetation. The experiments are aimed at providing a better understanding of the relevant
particle-vegetation interaction mechanisms responsible for the observed diffusion processes.
Qualitative observational data are then used to set up a stochastic model for floating particle transport and diffusion. Quantitative observations, such as the distribution of distances travelled by a particle before it is permanently captured by a plant (resembled spartina maritima) and the arrival
time distributions at prescribed cross sections along the vegetated test section, are instead used to calibrate and validate the model. The comparison between theoretical predictions and experimental results is quite satisfactory
and suggests that the observed relevant aspects of the particle-vegetation interaction processes are properly described in the model.
In Chapter 2 we present the results of a new laboratory investigation aimed at providing a better understanding of the transport and diffusion processes. The experiments are designed primarily to study the influence of vegetation density and flow velocity on the relevant interaction mechanisms between particles and vegetation. The aim is also to ascertain the validity of the stochastic model proposed in Chapter 1.
We find that i) the proper definition of plant spacing is given as 1/npdp, dp being the plant diameter and np the number of plants per unit area; ii) the particle retention time distribution can be approximated by a weighted combination of two exponential distributions; iii) flow velocity has a significant
influence on the retention time and on the efficiency of the different trapping mechanisms, iv) vegetation pattern and density have a minor or negligible influence on the capture probability and on the retention time.
In the first part of Chapter 3 we study, in details, through a numerical model, the dynamics of capture due to surface tension (i.e. the Cheerios effect) of a cylindrical collector. The analysis shows that when capillary force is comparable to inertial forces the capture efficiency of the collector
increases significantly with respect to the non-floating particle.
In the second part of Chapter 3, instead, we propose, and verify through laboratory experiments, some improvements to the model described in Chapter 1. In this case the emergent vegetation is simulated with an array of cylinders,
randomly arranged, with the mean gap between cylinders far greater than the particle size, so to prevent the trapping of particles between pairs of cylinders, referred to as net trapping in Chapter 1. A good agreement
is found also when comparing the model prediction with experimental data available in the literature for real seeds and more complex plant morphology.In questa tesi è stato studiato il problema della dispersione di particelle galleggianti in presenza di vegetazione emergente per mezzo di analisi sperimentali, numeriche e teoriche dei meccanismi che ne governano la ritenzione temporanea e la cattura da parte delle piante. Nel Capitolo 1 sono presentati i risultati delle prove di laboratorio effettuate per indagare il trasporto e la diffusione di particelle galleggiati (ad esempio alcune varietà di semi) in un canale con vegetazione emergente. Questi esperimenti sono stati svolti per fornire una comprensione più ampia dei principali processi di interazione particella-pianta responsabili del processo diffussivo osservato. Queste osservazioni qualitative sono state successivamente utilizzate per mettere a punto un modello stocastico per il trasporto e la diffusione di particelle galleggianti. Ulteriori dati raccolti sperimentalmente, quali la distribuzione delle distanze percorse dalle particelle prima di essere catturate permanentemente dalle piante e la distribuzione dei tempi di arrivo in alcune specifiche sezioni del tratto vegetato utilizzato nelle prove sperimentali, sono invece stati utilizzati per la calibrazione e la validazione del modello. Il confronto tra i risultati forniti dal modello e quelli sperimentali è soddisfacente e suggerisce che gli aspetti più rilevanti osservati nei processi di interazione particella-vegetazione sono opportunamente descritti dal modello. Nel Capitolo 2 sono presentati i risultati di nuove prove sperimentali effettuate per approfondire la conoscenza dei processi di trasporto e di diffusione. In questo caso le prove sono state realizzate per valutare l’influenza della densità della vegetazione e della velocità della corrente sui meccanismi di interazione precedentemente individuati. I risultati, infine, sono stati utilizzati per confermare la validità del modello proposto nel Capitolo 1. E' stato trovato che i) la definizione più corretta di interasse tra le piante è 1/npdp, dp, essendo dp il diametro della pianta e np il numero di piante per unità d’area, ii) la distribuzione dei tempi di ritenzione delle particelle può essere approssimato da una combinazione di due distribuzioni esponenziali opportunamente pesate, iii) la velocità della corrente ha un forte impatto sui tempi di ritenzione e sull'efficacia dei differenti meccanismi di cattura, mentre iv) la distribuzione e la densità della vegetazione gioca un ruolo di minor rilievo, se non addirittura trascurabile, sulla probabilità di cattura e sui tempi di ritenzione. Nella prima parte del Capitolo 3 è studiata nel dettaglio la dinamica di cattura di un collettore cilindrico dovuta alla tensione superficiale (cioè l’effetto Cheerios). Lo studio mostra che, quando la forza capillare è comparabile alle forze inerziali, l’efficienza di cattura del collettore aumenta significativamente rispetto al caso in cui le particelle siano non galleggianti. Nella seconda parte del Capitolo 3, invece, sono proposte e verificate attraverso prove di laboratorio, alcune migliorie al modello introdotto nel Capitolo 1. In questo caso la vegetazione emergente è simulata da una schiera di cilindri, disposti casualmente, e distanziati tra loro in modo tale che le particelle non possano essere soggette alla cattura dovuta ad una coppia di cilindri e definita net trapping nel corso del Capitolo 1. Una buona corrispondenza è stata trovata anche quando i risultati forniti dal modello sono stati confrontati con alcuni dati sperimentali reperiti in letteratura relativi a semi reali ed a piante aventi una morfologia più complessa.
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DALLALI, MARYAM. "Large Eddy Simulation of Suspended Sediment In Turbulent Open-Channel Flow." Doctoral thesis, Università degli Studi di Trieste, 2016. http://hdl.handle.net/11368/2908065.
Full textAbstract:
This study aims to shed light on the dark sides of sediment transport and meandering channel flow patterns. For this purpose, the Large Eddy Simulation methodology was used to investigate sediment transport in open-channel flow and also to predict the meandering channel flow pattern in two sine-generated channels.
In the turbulent flows the transported suspended sediments is usually assumed in a passive form. In other word, the feedback effect of sediment suspension on near-wall momentum transport is neglectable. The first phase of this research was devoted to quantify the just mentioned effect in the open channel flow. A single phase approach was used to gain better description of sediment-turbulence interaction. The contribution of the small scales was parametrized by a dynamic Smagorinsky model. Results revealed that - in presence of large suspension- the buoyancy effect modifies the dynamics of flows.
The second phase of the research was dedicated to the turbulent flow in meandering channels. These channels had initial deflection angles of 45 and 95 degrees. In both cases the width-to-depth ratio was equal to 15. The super-elevation of water in channel, which is impressed by secondary motion in the meandering channels, was considered in the numerical model. Analysis of numerical results was carried out on the basis of both instantaneous and time-averaged velocity fields. In addition, to provide an accurate description of the mean flow, this work explored the characterization of the cross-circulatory motion and the internal turbulence structure of flows. In particular, the sediment transport was investigated in the meandering channel to clarify the effect of bed shear stress variation induced by the channel curvature.
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Wang, Kun-Pao, and 王昆保. "Open-Channel Chute Flow Analysis." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/22950202375055464346.
Full textAbstract:
碩士淡江大學
水資源及環境工程學系
85
This study presents experimental analysis for open-channel chute flow at channel bed with 30, 35, 38, and 41 degrees. The channel bed was coated by plastic blankets with rough surface to simulate the Manning''s roughness coefficients. The Manning''s roughness coefficients were equal 0.020, 0.022, and 0.025. The location of white water inception point was found to be proportional to bed slope and inversely proportional to Reynolds number and Manning''s roughness coefficient. The Manning''s roughness coefficients were further modified by the experimental data. Relationships between the effective depth or the depth with air concentration being 95% and the depth calculated by the standard step without air concentration were found which enable the depth-averaged air concentration to be calculated.
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Chen, Jui-Yen, and 陳睿彥. "Flow-Depth Velocity Distribution Equationsfor Open Channel Flows." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/49242144806671080582.
Full textAbstract:
碩士國立成功大學
水利及海洋工程學系碩博士班
91
The log-low flow-depth velocity distribution equations for open channel flow and the Coles’ wake-flow function were reviewed wake-strength coefficient in the wake function at various flow conditions were compared. The result reveals that the values of are presented by previous investigators between -0.27 and 0.65. It is also found that Cloes’s revised wake-flow function can not well describe the velocity distributions for some open channel flows which are influenced by the pressure gradient and the side-wall-effects. We propose a method to overcome the problem. The velocity distribution is divided into upper region and lower region at the basis on the depth where the maximum velocity. When the two coefficients are the same which to be equal to the Cloes revised wake-flow function. Comparison of the proposed double-layer velocity distribution with measured data by Cloemen(1981) and Kirkgoz and Ardiclikglu(1997). The results show that the present proposed method can well describe the velocity distributions, with between 0.9 and 1.6 and between -0.02 and 0.69. Besides, the modified functions for the power-low equation are also investigated in the present study. A modified function F(y/ )= is proposed for the power-low velocity distribution, and compared with the measured data. It shows that the revised power-low equation can well describe the velocity distribution. Based on Coleman’s data , and the velocity correction is between 0.15 and 0.28, and proportional with the vertically averaged volumetric sediment concentration.
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Yang, Ching-Hsu, and 楊景旭. "90 degree Dividing Open-Channel Flow." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/85394637105908981463.
Full textAbstract:
碩士淡江大學
水資源及環境工程學系
85
Dividing flow are of considerable importance in study of open-channel. An experimental investigation of the flow structure at a right angles dividing open-channel flow is presented. The most comprehensive studies were concerned with backwater characteristic and energy losses. Most of the investigators have studied the problem depending on the control condition in the main channel and the branch channel. At present, the study of dividing flow problem restricted the width ration of the branch channel to the main channel 1.0 and 0.5. At the downstream of the branch channel, using a pump of 5 hp to pump. Result of this study indicates that the section U4 and the section LO and the section L4 has about equal depth. In the branch channel, the width of circulation zone is larger at the surface than at the surface than at the bottom. The energy loss is large in the branch channel.
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FAN, YUNN-CHERNG, and 樊運成. "90 degree Dividing Open-channel Flow." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/01088593417882090150.
Full textAbstract:
碩士淡江大學
水資源及環境工程學系
86
Dividing flow are of considerable importance in study of open- channel. An experimental investigation of the flow structure at a right angles dividing open-channel flow is presented. The most comprehensive studies were concerned with backwater characteristic and energy losses. Most of the investigators have studied the problem depending on the control condition in the main channel and thebranch channel. At present , the study of dividing flow problem restricted thewidth ration of the branch channel to the main channel 1.0 and 0.5. At thedownstream of the branch channel, using a pump of 5 hp to pump. Result of this study indicates that the section L0 and the section L4 has about equal depth. In the branch channel, the width of circulation zone is larger at the surface than at the bottom. The energy loss is large in the branch channel due to circulation.
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BHARDWAJ, DHARMENDRA. "FLOW ANALYSIS IN COMPOUND OPEN CHANNEL FLOW USING ANSYS." Thesis, 2017. http://dspace.dtu.ac.in:8080/jspui/handle/repository/15838.
Full textAbstract:
Flooding in Indian rivers is a very serious problem which affects the
livelihood and financial condition of that place. This problem has been
identified by many Researchers like Tominaga and Nezu , Ackers and V.T
Chow. A lot of research work has been devoted to find out desirable solution of
flooding problem. While flooding, river flows with high discharge which
overflows on its banks and excess water reaches to its flood plains, this excess
water leads to formation of compound channel. The nature of flow during
flooding is generally turbulent in nature. It has been found that the velocity of
flow in flood plain is less than the velocity of flow in main regular channel. It is
a well known fact that this change in velocity leads to formation of a shear
layer. These shear layers produce resistance to flow, which leads to uncertainty
in forecasting of flow and also increases resistance on channel. Geometric
similar model can be utilized to find out necessary information. Generally one
dimensional empirical model can be used to forecasting of flow taking
assumption that flow is uniform in compound channel. However, Compound
open channel has partially uniform flow due to momentum transfer in sub
sections and unexpected change in depth of flow. Hence the analysis of
turbulent flow is necessary in this situation. In Past, researchers have used
various models to analyze turbulent flow in compound open channels, basically
for low development length. Hence, in this study an effort is made to analyze
the turbulent flow by Large Eddy Simulation method (LES) to forecast the flow
and its resistance on channel. The LES is carried out by taking sufficient
development length so that uniform turbulent flow can be developed. The
development length is incorporated in the computational domain. It is fact that
experimentally flow analysis of compound open channels with various
hydraulic conditions is very expensive and difficult. Hence, this analysis of
flow is done by using software approaches such as used in Ansys Software.
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Haque, AKM Enamul. "Some characteristics of open channel transition flow." Thesis, 2009. http://spectrum.library.concordia.ca/976403/1/MR63268.pdf.
Full textAbstract:
Flow separation is a common phenomenon in decelerated subcritical flows as in open channel expansions. A highly distorted velocity and shear stress distribution due to flow separation can lead to a continuous reduction of energy and trigger an adverse pressure gradient resulting in flow separation. This causes loss of energy and hydraulic efficiency of the systems. An experimental investigation was conducted with the use of a gradual rising hump on the bed of an expansion in a rectangular open channel. Besides the hump, split vanes in the flow field were also used to reduce the expansion angle and in turn reduce the adverse effect of flow separation. These modifications resulted in a relatively more uniform velocity and shear stress distribution in the transition and in the channel downstream of the expansion. A laboratory model of rectangular open channel transition expanding was constructed with Plexiglas plates. It facilitated the measurement of the flow velocity and turbulence characteristics with the aid of Laser Doppler Anemometer (LDA). The total divergent angle of the transition was 19.78 degrees. Velocities were measured along the x, y and z directions, positioning the LDA from both the bottom and the side of the channel. Two humps with gradual linear rises of 12.5 mm and 25 mm were used. A second device included the use of a single vane and a three vane splitter plates system formed with thin Plexiglas plates. Mainly velocity distributions, with and without humps and the splitter vanes were the results sought. The variations of energy and momentum coefficients were analyzed to find the effectiveness of the devices used in the transition to control flow separation. As a small addition to the study, the use of computational fluid dynamics (CFD) to predict the flow characteristics of open channel was also undertaken. Due to their lower time demand and lower cost, these numerical methods are preferred to experimental methods after they are properly validated. In the present study, the CFD solution is validated by experimental results. A limited number of CFD simulations were completed using the commercial Software ANSYS-CFX. In particular, mean velocity distributions for the rectangular open channel transitions were used for model validation. To this end, the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations and the two equations k-[varepsilon] models were used. The validation of the model using test data was reasonable.
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Li, Cheng-Pu, and 李政璞. "A Study of Open-Channel Chute Flow." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/43530004196557697508.
Full textAbstract:
碩士淡江大學
水資源及環境工程學系
89
This study talks about the chute flow of open-channel at channel bed with 41 degrees .The channel bed was covered with plastic blankets to simulate the Manning’s roughness coefficients .The study lets the Manning’s roughness coefficients equal to 0.020. In the study , use hot-film anemometer and conical hot-film probe and water probe calibration to get a calibration value about voltage and velocity of water .After computing , produce a critical voltage value and get an air concentration value . Use the both values to abtain the air concentration distribution normal to the bed . And get a perturbation range value .The depth calculated and the depth with air concentration being 95% and the effective depth were found in the study.
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Kuo, Po-Wen, and 郭博文. "A Study for Unsteady Open Channel Flow." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/43664883488092232446.
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碩士淡江大學
水資源及環境工程學系
90
The objective of this study is to develop a linearized analytical solution for unsteady open channel flow. The method is applied to rectangular trapezoidal cross sections and natural stream flow. In the process, I neglected the inertia terms in the Saint-Venant moment equation. And obtained the linearized Saint-Venant equation by small perturbation method. Compare the analytical solutions with the numerical solutions, the linearized analytical solution can obtain a good approximation efficiently if we choose an appropriate reference discharge.
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Su, Kuo-Tseng, and 蘇國琮. "Non-Equal Width 30 Dividing Open Channel Flow." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/71408473259320875455.
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碩士淡江大學
水資源及環境工程學系碩士班
93
This study presents the experimental results for 30° divided sub- critical open-channel flow. The branch- to main-channel width ratios were 1, 1/2, and 1/3. For each run, 7 discharges were conducted in the ex- periments. The experimental results showed that the flow is fully de- veloped and uniformly distributed at 4 channel-widths upstream of dividing point. It also showed that the flow angle at the interface increases with increasing discharge ratio while the re-circulation width and the reattachment length decrease. The downstream- to upstream-depth ratio in the main channel depends on the discharge ratio and downstream Froude number. The depth ratio increases with increasing discharge ratio and decreases with increasing downstream Froude number. In addition, the energy loss coefficient increases with increasing width ratio.
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Wu, Han-Ping, and 吳翰泙. "A Study on Subcritical Open-Channel Junction Flow." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/22183803017085326686.
Full textAbstract:
碩士淡江大學
水資源及環境工程學系
89
This study is using the experimental data of previous studies to analysis the circumstances of subcritical open-channel junction flow. And describes a one-dimensional approach to solving both the upstream-to-downstream depth ratio and the energy loss coefficient through non-equal width junction flow over horizontial beds. The results are found to be in good agreement with the experimental data. The depth ratio and energy loss coefficient is increase with increase junction angle and with increase downstream Froude number. Besides, the cross-section mean flow angle at the branch channel entrance was determined through detailed measurement of velocity vectors and was found to decrease as the discharge ratio increases and the junction angle decreases.
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Ho, Tai-Yi, and 何泰亦. "Non-Equal Width 45° Dividing Open Channel Flow." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/74189245268291549733.
Full textAbstract:
碩士淡江大學
水資源及環境工程學系
91
The study on non-equal width open-channel flow is using three channel width ratio(branch to main 1 ,1/2 ,1/3)and seven discharge ratio under 45 degree angles dividing flow by hydraulic experiments. The channel bed of present study is horizontal and the cross section is rectangular.Besides, the main channel flow is subcritical. At the downstream of main and branch channel use gates to control the discharge ratio and depth.The measurement including the depth and velocity of upstream and downstream in main and branch channel. The reasons influence status of dividing flow are channel width ratio, slop of channel bed and angle between main and branch channel. According to the results of the experiment show that the flow angle will become smaller while the discharge ratio become larger and the width of channel become larger. The width of circulation zone near water surface is larger than at the bottom. The energy loss is large in the branch channel.
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Chen, Yan-Yuan, and 陳衍源. "Linear analysis of gradually flow in open channel." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/61360903754898636037.
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Wu, Feng Shuai, and 吳豐帥. "A Study on Subcritical Open-Channel Junction Flow." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/92804089359142611998.
Full textAbstract:
博士淡江大學
水資源及環境工程所
82
In river and drainage engineering the study of upstream water rises and downstream circulation with energy losses at junction region is still in its infancy. Most of the one dimensional numerical simulation at the junction region the energy equation are assumed either constant water level at the upstream, lateral and downstream sections or no energy losses at the junction. This study performed the variable angle junction flow experiments and developed an one dimensional analytical model to predict the constraction coefficient and the up- stream depth-rise by using mass, momentum, and energy conservation principles. The results show that constraction coefficients and depths are functions of discharge ratio, energy coefficient, momentum coefficient and the dowmstram froude number. A numerical model of two dimensional depth-averaged junction flow has been also developed. The simulated results for 90, 70 and 60 junction-angles flows at discharge ratio of 0.1, 0.5 and 0.9 are in good agreed to the experimental data and the results appear reasonably acceptable.
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Yang, Sen-Hao, and 楊森豪. "Numerical Study for 1D Open Channel Flow Equations." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/62968517411533574833.
Full textAbstract:
碩士輔仁大學
數學系
83
The purpose of study is to investigate about One-dimensional open channel flow equation of conservation laws. Furthermore, discuss both of the relations of St. Venant equations to Euler equations and St. Venant equations to shallow water equations, respectively. Moreover, because St. Venant Equations is resemble in many respects the equations of compressible flow, thus we can solve the Riemann problem by Roe and Roe-Sweby scheme, which used in gas dynamic's analysis. In numerical computation, we adopt Roe and Roe-Sweby scheme with Roe- averaged and new Roe's matrices, respectively, to solve the dam breaking and bore propagation problems. Final, compare and observe how is the numerical solutions, which obtained from these experiments.