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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.
2
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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Daish, N. C. "Shear dispersion problems in open-channel flows". Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372648.
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Bayat, David, i 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.
9
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.
10
McClymont, David W. "Exploring open channel block of the NMDA receptor". Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/12996/.
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The G1uN3 subunits of the NMDA receptor are thought to reduce the Ca 2+ permeability and Mg2+ sensitivity of NMDA receptors. cRNA for rat NMDA receptor subunits were injected into Xenopus oocytes and responses were recorded using two electrode voltage clamp at -100, -75 and -50 mV. G1uN1-1a/2A, GluN1-1a/2A/3A and G1uN1-1a/2A/3B containing receptors were characterised using Mgz+, memantine, philanthotoxin-343, methoctramine and MK-801. IC50 values were calculated and generally showed significant increases between those containing G1uN1-1a/2A/3 subunits and G1uN1-1a/2A, while those with G1uN3B were found to be significantly higher than G1uN3A. Activity was also typically shown to be partially restored with mutations at the N and N+1 site asparagines of G1uN3A. As the ICS0 was only partially restored the changes cannot be attributed to the loss of the N-site alone. Further differences may be due to a constricted threonine ring within the M3 vestibule region, or due to continued reduced flux through the channel. Another possibility is that to restore block it may require both the double N and N+1 mutation at the N-site. Multi-target-directed ligands combine two pharmacophores to produce drugs which retain the properties of the constituents. Memantine has been approved for use in Alzheimer's disease and there is a search for drugs that have similar actions. A range of multi-target compounds were tested to determine if NMDA receptor blockade activity was obtained. The pharmacophores explored were tacrine, donepezil, lipoic acid carvedilol and dimebon. The most promising compounds were carbacrine(3) (tacrine and carvedilol) and lipocrine (lipoic acid and tacrine), and it was found that the former was equipotent and the latter more potent than memantine. Potency was likely due to the tacrine moiety. These compounds should be further categorised to determine if they retain the kinetics that gives memantine its favourable side effect profile.
11
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.
14
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.
15
Aya, Shirou. "Longitudinal and Transverse Mixing in Open-Channel Flows". Kyoto University, 1991. http://hdl.handle.net/2433/74583.
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16
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.
17
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.
18
Belcher, Brian James. "VORTEX MODEL OF OPEN CHANNEL FLOWS WITH GRAVEL BEDS". UKnowledge, 2009. http://uknowledge.uky.edu/gradschool_diss/702.
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Turbulent structures are known to be important physical processes in gravel-bed rivers. A number of limitations exist that prohibit the advancement and prediction of turbulence structures for optimization of civil infrastructure, biological habitats and sediment transport in gravel-bed rivers. This includes measurement limitations that prohibit characterization of size and strength of turbulent structures in the riverine environment for different case studies as well as traditional numerical modeling limitations that prohibit modeling and prediction of turbulent structure for heterogeneous beds under high Reynolds number flows using the Navier-Stokes equations. While these limitations exist, researchers have developed various theories for the structure of turbulence in boundary layer flows including large eddies in gravel-bed rivers. While these theories have varied in details and applicable conditions, a common hypothesis has been a structural organization in the fluid which links eddies formed at the wall to coherent turbulent structures such as large eddies which may be observed vertically across the entire flow depth in an open channel. Recently physics has also seen the advancement of topological fluid mechanical ideas concerned with the study of vortex structures, braids, links and knots in velocity vector fields. In the present study the structural organization hypothesis is investigated with topological fluid mechanics and experimental results which are used to derive a vortex model for gravel-bed flows. Velocity field measurements in gravel-bed flow conditions in the laboratory were used to characterize temporal and spatial structures which may be attributed to vortex motions and reconnection phenomena. Turbulent velocity time series data were measured with ADV and decomposed using statistical decompositions to measure turbulent length scales. PIV was used to measure spatial velocity vector fields which were decomposed with filtering techniques for flow visualization. Under the specific conditions of a turbulent burst the fluid domain is organized as a braided flow of vortices connected by prime knot patterns of thin-cored flux tubes embedded on an abstract vortex surface itself having topology of a Klein bottle. This model explains observed streamline patterns in the vicinity of a strong turbulent burst in a gravel-bed river as a coherent structure in the turbulent velocity field.
19
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.
20
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.
21
Dvorak, Joseph Scot. "An optical water velocity sensor for open channel flows". Diss., Kansas State University, 2012. http://hdl.handle.net/2097/13979.
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Doctor of PhilosophyDepartment of Biological and Agricultural Engineering
Naiqian Zhang
An optical sensor for determining water velocity in natural open channels like creeks and rivers has been designed and tested. The sensor consists of a plastic body which is shaped so that water flows through a U-shaped channel into which are mounted LEDs and matching phototransistors at various angles. A small amount of dye is injected into the water just upstream of two sets of LEDs and phototransistors which are spaced 4 cm apart. The time delay between the dye’s effects on these signals depends on water velocity and is determined using a biased cross correlation calculation. In addition to providing velocity, the LEDs and phototransistors can also be used to estimate soil sediment concentration. A previous version of the sensor was tested in enclosed flow to confirm that the general design of the sensor, including LEDs, phototransistors, dye and electronics, would indeed work to detect the velocity of water flowing through the sensor. Although the conditions for the test were unlike those experienced in natural open channels, the ability to catch all the fluid flowing through the sensor provided a simple confirmation of the velocity estimate that was not available in field settings. Further testing in the field then confirmed that the sensor worked in the field but also identified several areas needing improvement. Computational fluid dynamics was used to improve the sensor body. The electronics and program running the sensor were also redesigned. After making these improvements, a new version of the sensor was produced. The testing of the new version of the sensor confirmed its ability to accurately detect velocity in natural open channels. The velocity measurements from this sensor were compared to the commercially available Flowtracker velocity sensor. A regression analysis on the measurements from the two sensors found that the velocity measurements from each sensor were nearly identical across a range of velocities. Other tests established that the electronics and programming running the sensor performed as designed. The development and testing of this sensor has resulted in a system which works in natural open channels like creeks and rivers.
22
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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WAI, THWE AUNG. "DEVELOPMENT OF FUNDAMENTAL THEORY ON UNSTEADY OPEN CHANNEL FLOWS". Kyoto University, 2019. http://hdl.handle.net/2433/244536.
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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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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.
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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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Osawe, Maxwell Osayande. "Open channel turbulence modelling using layer-averaged large eddy simulation". Thesis, Queen Mary, University of London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.392113.
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Beaman, Faye. "Large eddy simulation of open channel flows for conveyance estimation". Thesis, University of Nottingham, 2010. http://eprints.nottingham.ac.uk/11130/.
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Prediction of conveyance capacity in open channel flows is complex and requires adequate modelling of flow features such as secondary circulation cells and, specifically for over-bank channels, the momentum exchange that occurs at the main channel/floodplain interface. A variety of conveyance estimation methods have been developed with the objective of accurately capturing these flow characteristics through a simplified user-friendly approach. However, these methods usually require calibration of one or more empirical constants. Within this thesis in-bank and over-bank channels have been numerically simulated using Large Eddy Simulation (LES) in order to predict accurate open channel flow behaviour. The LES results are validated against experimental data and then utilised to advise on values of calibration constants f, λ and Γ within a conveyance estimation method, the Shiono and Knight Method (SKM), which has recently been adopted by the Environment Agency (EA) for England and Wales as part of its new Conveyance Estimation System (CES). The LES results are shown to accurately predict the flow features, specifically the distribution of secondary circulations in in-bank channels of aspect ratio as large as 40 and for over-bank channels at varying depth and width ratios. The LES derived f, λ and Γ values are then utilized in the analytical solution of the SKM in order to compute depth averaged velocity profiles for comparison to LES results, producing very good agreement with simulated and experimental profiles. As well as the derivation the calibration constants, the apparent shear stress at the main channel/floodplain interface is investigated and the contributions from both Reynolds stress and secondary circulation terms compared. Also, instantaneous velocity data available from monitor points at the main channel/floodplain interface within over-bank channel simulations is utilized to investigate wave periods of interfacial vortices through spectral analysis. Comparable result to available experimental and stability analysis data are obtained.
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Lagoa, Sérgio Miguel Chilra. "Open economy New Keynesian macroeconomic models and the cost channel". Thesis, University of Leicester, 2010. http://hdl.handle.net/2381/8596.
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Evidence in the literature points to a puzzling initial increase in inflation after an increase in nominal interest rates. This can be explained by the fact that firms have to borrow money to pay wages in advance, i.e., by the cost channel. In this paper, the study of the cost channel is extended to an open economy with sticky prices. It is shown that a broadened concept of the cost channel has significant implications for the economy's dynamics and monetary policy, and also contributes to explain some interesting empirical evidence. Supply side effects of interest rates and import prices on inflation have important implications for monetary policy. Usually such effects are estimated using the New Keynesian Phillips Curve (NKPC). However, the estimation of the cost channel maybe distorted when import prices are omitted from that curve. To address this issue, we estimate empirically the NKPC for domestic and CPI inflations. In relation with this, we also study if imports of consumption goods are paid in advance, whether there is an immediate pass-through of exchange rates, and if imports should be treated as final consumption goods and/or as inputs in production. Another concern of monetary policy in a monetary union is inflation differentials, since they can undermine the success of the union. Against this background, our goal is to explore the determinants of inflation differentials in twelve euro area countries, focusing on the role of the business cycle. On one hand, convergence of inflation rates and business cycles is analysed with both an unobserved component model estimated with the Kalman filter and a common factor approach. On the other hand, an econometric analysis of the determinants of inflation differentials is performed.
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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.
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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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Kawamoto, Hideko. "Summer rain part 1, Summer rain - dawn, for two channel tape ; part 2, After the summer rain, for piano and two channel tape /". connect to online resource. Access restricted to the University of North Texas campus, 2001. http://www.library.unt.edu/theses/open/20013/kawamoto%5Fhideko/index.htm.
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Welch, Chapman. "Tele using vernacular performance practices in an eight channel environment /". Thesis, connect to online resource, 2003. http://www.library.unt.edu/theses/open/20032/welch%5Fchapman/index.htm.
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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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Afzalimehr, Hossein. "Contribution to non-uniform open channel flows over gravel and cobble". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0013/NQ36222.pdf.
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Tachie, Mark Francis. "Open channel turbulent boundary layers and wall jets on rough surfaces". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ63927.pdf.
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Wang, Kun-Pao, i 王昆保. "Open-Channel Chute Flow Analysis". Thesis, 1997. http://ndltd.ncl.edu.tw/handle/22950202375055464346.
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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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Yang, Ching-Hsu, i 楊景旭. "90 degree Dividing Open-Channel Flow". Thesis, 1997. http://ndltd.ncl.edu.tw/handle/85394637105908981463.
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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, i 樊運成. "90 degree Dividing Open-channel Flow". Thesis, 1998. http://ndltd.ncl.edu.tw/handle/01088593417882090150.
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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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WU, YING-BIN, i 吳慶彬. "Wave deformation in open channel of abrupt transitions of channel width". Thesis, 1989. http://ndltd.ncl.edu.tw/handle/13400964832284106807.
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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.
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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, i 李政璞. "A Study of Open-Channel Chute Flow". Thesis, 2001. http://ndltd.ncl.edu.tw/handle/43530004196557697508.
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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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Li, Wei-Yi, i 李威毅. "Design of Non-contactive Open-channel Flowmeter". Thesis, 1999. http://ndltd.ncl.edu.tw/handle/00994582701707992505.
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碩士國立中央大學
電機工程研究所
87
In industry, flow velocities and volumes are both very important parameters, but it is not easy to be measured accurately. Traditional flowmeters have some limitations, such as high temperature, erosive, poison, inflammable environment. Hence, they are only used in certain types of fluid and may cause great inaccuracy or inconvenience. Moreover, highly accurate flowmeters are expensive in both price and maintenance. Consequently the motive of this dissertation is coming out. The aim of this project is to measure flow velocity in open channel. The measurement theory is based on the Cross-Correlation Technique ,which calculates the relationship between two groups of signal. Two optical sensors are placed in line above the open channel and along the direction of flow. Because of the continuity of the flow, the time delay between the two received signals can be calculated by the cross-correlation function. The flow velocity can then be calculated by dividing distance by the time laterly. The non-contative flowmeter using the cross-correlation technique can avoid the complexity caused by different fluid properties. A 8052 single chip is used in the circuit. This makes the other merits of the circuit. Programmable softwares in the chip are designed to replace complex hardware circuit, to minimize the size of the flowmeter, and to reduce the cost of the development and maintenance. Moreover, it can achieve real-time measurement and display of the velocity of the flow. The data can be transmited to the PC, the curves of cross-correlation function, flow velocity and volume are displayed on screen. It is very helpful in verifying the correction of calculation process and the results of measurement.
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Kuo, Po-Wen, i 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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Subrahmanya, Praveena Alangar, i 蘇邁亞. "Pool boiling on open trapezoidal channel surface". Thesis, 2015. http://ndltd.ncl.edu.tw/handle/82191724169102979509.
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碩士國立中央大學
能源工程研究所
103
In this thesis pool boiling experiment is carried out on open trapezoidal channel surface to study the effect of channel top width (0.4mm, 0.8mm, 1.4mm and 2.0mm) and fin pitch using saturated methanol as working fluid at one atmospheric pressure along with bubble dynamic visualisation. The channel were cut using wire electro-discharge machining technique and results are compared with corresponding plane surfaces. Plain boiling surface with comparatively high roughness value (manufactured by wire electro-discharge machining) consistently showed higher heat transfer performance than emery surface with lower roughness value. All channel surfaces performed better than plain surface prepared by emery paper. For all the tested trapezoidal channel surfaces, bubbles only generated from the channel surface because of high roughness on channel surface. There was no bubble generation from fin top surface. Therefore overall channel surface area played major role along with the effect of channel geometry on HTC & CHF and the results are meant to compare with plain surface made by EDM process. Two distinctive bubble dynamics are observed as the channel top width increased. For channel having top width 0.4mm, single bubble generated across the channel and it attached to channel side surface and grew on top of channel till the departure. Therefore the heat transfer performance increased as the fin pitch reduced. But in comparison with Plain EDM surface, its nucleate boiling HTC found to be lower because overall available boiling surface area (ie channel surface area) is lower. From channel having top width 0.8mm to 2.0mm, number of nucleation sites across channel surface increased accordingly with the channel cross section area. Therefore multiple bubble nucleation sites were observed. On these channel top width surfaces, a heat transfer enhancement mechanism observed. Therefore even though the channel surface area was lower than that of plain EDM surface, nucleate boiling HTC were either equal or more than plain EDM surface observed. Reduction in fin pitch had no major effect on HTC. For channel made by EDM process having different roughness value in comparison with fin top surface has different liquid and vapor flow path ways. Majority of the liquid supply to rewet the boiling surface (i.e channel surface) were from fin top surface. As the fin pitch decreases, CHF found to increase for all tested channel top widths because of increases in channel surface area as well as enhancement in heat transfer mechanism over channel surface.
50
Yu, Wen-Pu, i 游文圃. "Energy Loss for series Cylinders along channel bank in Open-Channel Flow". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/22786350800670770832.
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碩士淡江大學
水資源及環境工程學系碩士班
100
This study uses the model and simulation to analyze the Energy Loss for series cylinders along channel bank in Open-Channel Flow. The test model to placed on straight channel. The experiment was conducted in flume 10.50m long, 0.39m wide and 0.19m high with bed slope=0.003. Placed in the channel one to nine cylindrical,cylinder width of 3.4cm and 4.0cm,cylindrical center distance is 4.0cm The test set Different boundary conditions up to Energy loss of series cylinder under various Froude numbers. This study uses the FLUENT to establish the unsteady flow numerical model. Simulate with turbulence model based on three-dimensional model. The simulation conditions and model conditions are the same. Compare and analyze simulation and experimental results.