Showing papers on "Open-channel flow published in 1999"
TL;DR: In this paper, numerical simulations of fully developed turbulent channel flow at three Reynolds numbers up to Reτ=590 were reported, and it was noted that the higher Reynolds number simulations exhibit fewer low Reynolds number effects than previous simulations at Reτ = 180.
Abstract: Numerical simulations of fully developed turbulent channel flow at three Reynolds numbers up to Reτ=590 are reported. It is noted that the higher Reynolds number simulations exhibit fewer low Reynolds number effects than previous simulations at Reτ=180. A comprehensive set of statistics gathered from the simulations is available on the web at http://www.tam.uiuc.edu/Faculty/Moser/channel.
2,618 citations
TL;DR: In this paper, a systematic experimental investigation of two-phase flow patterns in microchannels was the objective of this study, using air and water, experiments were conducted in circular micro channels with 1.1 and 1.45mm inner diameters, and in semi-triangular (triangular with one corner smoothed) cross-sections with hydraulic diameters 1.09 and 149mm.
822 citations
TL;DR: In this paper, the inertial migration of a small rigid sphere translating parallel to the walls within a channel flow at large channel Reynolds numbers is investigated, and the method of matched asymptotic expansions is used to solve the equations governing the disturbance flow past a particle at small particle Reynolds number and to evaluate the lift.
Abstract: The inertial migration of a small rigid sphere translating parallel to the walls within a channel flow at large channel Reynolds numbers is investigated. The method of matched asymptotic expansions is used to solve the equations governing the disturbance flow past a particle at small particle Reynolds number and to evaluate the lift. Both neutrally and non-neutrally buoyant particles are considered. The wall-induced inertia is significant in the thin layers near the walls where the lift is close to that calculated for linear shear flow, bounded by a single wall. In the major portion of the flow, excluding near-wall layers, the wall effect can be neglected, and the outer flow past a sphere can be treated as unbounded parabolic shear flow. The effect of the curvature of the unperturbed velocity profile is significant, and the lift differs from the values corresponding to a linear shear flow even at large Reynolds numbers.
640 citations
479 citations
TL;DR: In this paper, a single-phase forced convection in deep rectangular microchannels has been studied for developing laminar flow and the results show that, in terms of flow and heat transfer characteristics, the microchannel system designed for developing Laminar Flow outperforms the comparable single channel system for turbulent Flow.
350 citations
TL;DR: In this article, the effects of the Reynolds and Prandtl numbers on the turbulent heat transport in a fully developed turbulent channel flow with uniform heating from both walls were investigated and the instantaneous flow and thermal fields were visualized in order to investigate the structures of streaks and vortices.
335 citations
TL;DR: In this paper, the steady solution of the Camassa-holm equation with the mean flow of the Reynolds equation is compared with empirical data for turbulent flows in channels and pipes.
Abstract: In this paper we discuss recent progress in using the Camassa–Holm equations to model turbulent flows. The Camassa–Holm equations, given their special geometric and physical properties, appear particularly well suited for studying turbulent flows. We identify the steady solution of the Camassa–Holm equation with the mean flow of the Reynolds equation and compare the results with empirical data for turbulent flows in channels and pipes. The data suggest that the constant α version of the Camassa–Holm equations, derived under the assumptions that the fluctuation statistics are isotropic and homogeneous, holds to order α distance from the boundaries. Near a boundary, these assumptions are no longer valid and the length scale α is seen to depend on the distance to the nearest wall. Thus, a turbulent flow is divided into two regions: the constant α region away from boundaries, and the near wall region. In the near wall region, Reynolds number scaling conditions imply that α decreases as Reynolds number increas...
267 citations
01 Jan 1999
TL;DR: A physical model is a scaled representation of a hydraulic flow situation as discussed by the authors, which can help the decision-makers to visualize and to picture the flow field, before selecting a ''suitable'' design.
Abstract: A physical model is a scaled representation of a hydraulic flow situation. Both the boundary conditions (e.g. channel bed, sidewalls), the upstream flow conditions and the
flow field must be scaled in an appropriate manner (Fig. 14.1). Physical hydraulic models are commonly used during design stages to optimize a structure and to ensure a safe operation of
the structure. They have an important further role to assist non-engineering people during the `decision-making' process. A hydraulic model may help the decision-makers to visualize and to
picture the flow field, before selecting a `suitable' design. In civil engineering applications, a physical hydraulic model is usually a smaller- size representation of the prototype (i.e.
the full-scale structure) (e.g. Fig. 14.2). Other applications of model studies (e.g. water treatment plant, flotation column) may require the use of models larger than the prototype. In
any case the model is investigated in a laboratory under controlled conditions.
254 citations
TL;DR: In this article, a broadband acoustic doppler current profiler (ADCP) was used to measure profiles of turbulence quantities using a broadband ADCP and the results of the analysis were compared to theory.
Abstract: In this paper we present a method for measuring profiles of turbulence quantities using a broadband acoustic doppler current profiler (ADCP). The method follows previous work on the continental shelf and extends the analysis to develop estimates of the errors associated with the estimation methods. ADCP data was collected in an unstratified channel and the results of the analysis are compared to theory. This comparison shows that the method provides an estimate of the Reynolds stresses, which is unbiased by Doppler noise, and an estimate of the turbulent kinetic energy (TKE) which is biased by an amount proportional to the Doppler noise. The noise in each of these quantities as well as the bias in the TKE match well with the theoretical values produced by the error analysis. The quantification of profiles of Reynolds stresses simultaneous with the measurement of mean velocity profiles allows for extensive analysis of the turbulence of the flow. In this paper, we examine the relation between the turbulence and the mean flow through the calculation of u * , the friction velocity, and C d , the coefficient of drag. Finally, we calculate quantities of particular interest in turbulence modeling and analysis, the characteristic lengthscales, including a lengthscale which represents the stream-wise scale of the eddies which dominate the Reynolds stresses.
249 citations
TL;DR: In the early stages of Kilauea Volcano, lava cooling and crystallization was observed to occur in the upper parts of the lava channel as mentioned in this paper, and the transition from pahoehoe to pyroxene microlites occurred at a distance of 1.9 km from the vent.
Abstract: Samples collected from a lava channel active at Kilauea Volcano during May 1997 are used to con- strain rates of lava cooling and crystallization during early stages of flow. Lava erupted at near-liquidus tem- peratures (F1150 7C) cooled and crystallized rapidly in upper parts of the channel. Glass geothermometry indi- cates cooling by 12-14 7C over the first 2 km of trans- port. At flow velocities of 1-2 m/s, this translates to cooling rates of 22-50 7C/h. Cooling rates this high can be explained by radiative cooling of a well-stirred flow, consistent with observations of non-steady flow in proximal regions of the channel. Crystallization of plag- ioclase and pyroxene microlites occurred in response to cooling, with crystallization rates of 20-50% per hour. Crystallization proceeded primarily by nucleation of new crystals, and nucleation rates of F10 4 /cm 3 s are similar to those measured in the 1984 open channel flow from Mauna Loa Volcano. There is no evidence for the large nucleation delays commonly assumed for plagioclase crystallization in basaltic melts, possibly a reflection of enhanced nucleation due to stirring of the flow. The transition of the flow surface morphology from pahoehoe to 'a'aoccurred at a distance of 1.9 km from the vent. At this point, the flow was thermally stratified, with an interior temperature of F1137 7C and crystallinity of F15%, and a flow surface tempera- ture of F1100 7C and crystallinity of F45%. 'A'afor- mation initiated along channel margins, where crust was continuously disrupted, and involved tearing and clotting of the flow surface. Both observations suggest that the transition involved crossing of a rheological threshold. We suggest this threshold to be the develop- ment of a lava yield strength sufficient to prevent vis- cous flow of lava at the channel margin. We use this concept to propose that 'a'aformation in open chan- nels requires both sufficiently high strain rates for con- tinued disruption of surface crusts and sufficient groundmass crystallinity to generate a yield strength equivalent to the imposed stress. In Hawai'i, where lava is typically microlite poor on eruption, these combined requirements help to explain two common observations on 'a'aformation: (a) 'a'aflow fields are generated when effusion rates are high (thus promoting crustal disruption); and (b) under most eruption conditions, lava issues from the vent as pahoehoe and changes to 'a'aonly after flowing some distance, thus permitting sufficient crystallization.
248 citations
TL;DR: In this article, the authors evaluate the extent to which 3D models improve predictive ability and prediction utility compared to two-dimensional (2D) applications and show that the 3D model has a higher predictive ability, particularly if the 2D model is not corrected for the effects on flow structure.
TL;DR: A debris flow event occurred in June 1997 in the Dolomites (Eastern Alps, Italy) and was directly observed in the field and recorded by a video camera near its initiation area as discussed by the authors.
TL;DR: In this paper, the effects of small-scale velocity fluctuations on the motion of tracer particles are investigated by releasing particles in a turbulent channel flow at Reτ=175, and following their motion in time.
Abstract: In this study, the effects of small-scale velocity fluctuations on the motion of tracer particles is investigated by releasing particles in a turbulent channel flow at Reτ=175, and following their motion in time. Two types of numerical experiments were carried out: first, the Eulerian velocity field was evaluated by the direct numerical simulation (DNS) and the particles were advanced in time using the resolved and several filtered velocity fields to study the effect of the subgrid-scale velocity fluctuations on particle motion without the influence of modeling errors. In the second stage, the particle-motion study was performed using independent DNS and large-eddy simulations (LES), thus including the effect of interpolation and subgrid-scale stress modeling errors on the dispersion statistics. At this Reynolds number the small scales were found to have a limited effect on the statistics examined (one-particle dispersion, one-particle velocity autocorrelation, Lagrangian integral time scale, turbulent di...
TL;DR: In this article, an adiabatic concurrent vertical two-phase flow of air and water in vertical rectangular channels (12×260mm) with narrow gaps of 0.3, 0.6 and 1.0mm was investigated experimentally.
TL;DR: In this paper, a depth-integrated 2D hydrodynamic and sediment transport model, CCHE2D, is presented to study steady and unsteady free surface flow, sediment transport, and morphological processes in natural rivers.
Abstract: In this paper a depth-integrated 2D hydrodynamic and sediment transport model, CCHE2D, is presented. It can be used to study steady and unsteady free surface flow, sediment transport, and morphological processes in natural rivers. The efficient element method is applied to discretize the governing equations, and the time marching technique is used for temporal variations. The moving boundaries were treated by locating the wet and dry nodes automatically in the cases of simulating unsteady flows with changing free surface elevation in channels with irregular bed and bank topography. Two eddy viscosity models, a depth-averaged parabolic model and a depth-averaged mixing length model, are used as turbulent closures. Channel morphological changes are computed with considerations of the effects of bed slope and the secondary flow in curved channels. Physical model data have been used to verify this model with satisfactory results. The feasibility studies of simulating morphological formation in meandering chan...
TL;DR: In this article, a backward-facing step flow with a fully developed channel flow inlet was investigated, and the authors measured gas-phase velocities in the presence of 3-40% mass loadings of three different particle classes (90 and 150 μm diameter glass and 70 μmiameter copper spheres) and found that the level of attenuation decreased with decreasing particle Stokes number, particle Reynolds number and mass loading.
Abstract: The current study investigates turbulence modification by particles in a backward-facing step flow with a fully developed channel flow inlet. This flow provides a range of flow regimes in which to compare turbulence modification under the same experimental conditions. Gas-phase velocities in the presence of 3–40% mass loadings of three different particle classes (90 and 150 μm diameter glass and 70 μm diameter copper spheres) were measured. Attenuation of the streamwise fluid turbulence of up to 35% was observed in the channel-flow extension region of the flow for a 40% mass loading of the largest particles. The level of attenuation decreased with decreasing particle Stokes number, particle Reynolds number and mass loading. No modification of the turbulence was found in the separated shear layer or in the redevelopment region behind the step, although there were significant particle loadings in these regions.
TL;DR: In this paper, Meneveau et al. applied the Lagrangian-ensemble approach to the simulation of two flows, a high Reynolds number plane channel flow and a three-dimensional, nonequilibrium flow.
Abstract: Scale-similar models employ multiple filtering operations to identify the smallest resolved scales, which have been shown to be the most active in the interaction with the unresolved subgrid scales. They do not assume that the principal axes of the strain-rate tensor are aligned with those of the subgrid-scale stress (SGS) tensor, and allow the explicit calculation of the SGS energy. They can provide backscatter in a numerically stable and physically realistic manner, and predict SGS stresses in regions that are well correlated with the locations where large Reynolds stress occurs. In this paper, eddy viscosity and mixed models, which include an eddy-viscosity part as well as a scale-similar contribution, are applied to the simulation of two flows, a high Reynolds number plane channel flow, and a three-dimensional, nonequilibrium flow. The results show that simulations without models or with the Smagorinsky model are unable to predict nonequilibrium effects. Dynamic models provide an improvement of the results: the adjustment of the coefficient results in more accurate prediction of the perturbation from equilibrium. The Lagrangian-ensemble approach [Meneveau et al., J. Fluid Mech. 319, 353 (1996)] is found to be very beneficial. Models that included a scale-similar term and a dissipative one, as well as the Lagrangian ensemble averaging, gave results in the best agreement with the direct simulation and experimental data.
TL;DR: In this paper, a new theoretical 1D model of compound channels flows, the exchange discharge model, is presented, where the interactions between main channel and floodplains are taken into account as a momentum transfer proportional to the product of the velocity gradient at the interface by the mass discharge exchanged through this interface due to turbulence.
Abstract: A new theoretical 1D model of compound channels flows-the exchange discharge model-is presented. The interactions between main channel and floodplains are taken into account as a momentum transfer proportional to the product of the velocity gradient at the interface by the mass discharge exchanged through this interface due to turbulence. Geometrical changes in cross sections are also modeled; they generate a similar momentum transfer, proportional to the actual mass transfer. Both effects are incorporated into the flow equations as an additional head loss. This make the formulation suitable for stage-discharge computation but also enables practical water-profile simulations. The model is tested successfully against available experimental data for (1) stage-discharge relations; and (2) water-profile computation applied to a field case.
TL;DR: In this article, the mass flow rate of rarefied gas through a long channel with a rectangular cross section has been calculated based on the model kinetic equation for the whole range of the Knudsen number and in the wide range of height-to-width ratio.
Abstract: The mass flow rate of a rarefied gas through a long channel with a rectangular cross section has been calculated based on the model kinetic equation for the whole range of the Knudsen number and in the wide range of the height-to-width ratio. First, the reduced flow rate through a cross section has been calculated as a function of the local rarefaction parameter assuming the pressure gradient to be small. A criterion of the lateral wall influence on the flow rate has been given. Then, the mass flow rate has been calculated as a function of the rarefaction parameters on the channel ends. The last result is obtained for any pressure ratio even if the flow varies along the channel from the hydrodynamic regime to the free molecular one.
TL;DR: In this paper, an experimental study of the structure of flow in a vertical slot fishway of an effective and simple design was carried out and it was found that for a slope of 5, the main flow travels from one slot to the next through the pool as a 2D curved jet with two recirculation regions.
Abstract: This pape presents the results of an experimental study of the structure of flow in a vertical slot fishway of an effective and simple design. The flow at the slot could be treated as a plane jet, but there are a number of differences from the plane jet. It was found that for a slope of 5%, the main flow travels from one slot to the next through the pool as a 2D curved jet with two recirculation regions—one on each side. For slopes of 10 and 20%, the main flow is 3D. Water flows toward the side wall between the long baffles near the bed and piles up along the side wall; part of the flow rises to the surface and then travels to the outlet. The decay of longitudinal velocity in the pool is much larger than that of the plane jet. The volume averaged velocity head of the water in the pool was found to be ∼12% of Δ\ih, the head drop per pool. The volume of the recirculation region between the short baffles was ∼28% of the volume of the pool for all three slopes and all discharges whereas the corresponding volume of the horizontal eddy just downstream of the long baffles for the two larger slopes was ∼10%. The relative volume of the two recirculation regions was ∼73% for the 5% slope and ∼38% for the 10 and 20% slopes.
TL;DR: In this paper, a 3D numerical model for predicting steady, in the mean, turbulent flows through lateral intakes with rough walls is developed, validated, and employed in a parametric study.
Abstract: A three-dimensional (3D) numerical model for predicting steady, in the mean, turbulent flows through lateral intakes with rough walls is developed, validated, and employed in a parametric study. The method solves the Reynolds-averaged Navier-Stokes equations closed with the isotropic k-ω turbulence model of Wilcox, which resolves the near-wall flow and accounts for roughness effects in a straightforward manner. Calculations are carried out for flows through rectangular closed-duct and open-channel T-junctions. Comparisons of the predicted mean velocity field with laboratory measurements indicate that the model captures most experimental trends with reasonable accuracy. For the parametric study, flows are predicted for a range of discharge ratios, aspect ratios, and main channel-bed-roughness distributions. The numerical solutions are examined to elucidate the complex 3D flow patterns of lateral-intake flows, including zones of flow division, separation and reversal, vortices, and singular points within th...
TL;DR: A generalized model of flow in meandering subaqueous and subaerial channels is developed in this paper, where conservation equations of mass and momentum are integrated, normalized, and represented as deviations from a straight base state.
Abstract: A generalized model of flow in meandering subaqueous and subaerial channels is developed The conservation equations of mass and momentum are depth/layer integrated, normalized, and represented as deviations from a straight base state This allows the determination of integrable forms which can be solved at both linear and nonlinear levels The effects of various flow and geometric parameters on the flow dynamics are studied Although the model is not limited to any specific planform, this study focuses on sine-generated curves In analysing the flow patterns, the turbidity current of the subaqueous case is simplified to a conservative density flow with water entrainment from above neglected The subaqueous model thus formally corresponds to a subcritical or only mildly supercritical mud-rich turbidity current By extension, however the analysis can be applied to a depositional or erosional current carrying sand that is changing only slowly in the streamwise direction By bringing the subaqueous and subaerial cases into a common form, flow behaviour in the two environments can be compared under similar geometric and boundary conditions A major difference between the two cases is the degree of superelevation of channel flow around bends, which is modest in the subaerial case but substantial in the subaqueous case Another difference concerns Coriolis effects: some of the largest subaqueous meandering systems are so large that Coriolis effects can become important The model is applied to meander bends on the youngest channel in the mid-fan region of the Amazon Fan and a mildly sinuous bend of the North-West Atlantic Mid-Ocean Channel In the absence of specific data on the turbid flows that created the channel, the model can be used to make inferences about the flow, and in particular the range of values of flow velocity and sediment concentration that would allow the growth and downfan migration of meander bends
Book•
14 Dec 1999
TL;DR: Fluid Statics and Fluid Motion I. Introduction to Fluid motion II. Equations of Motion in Integral Form. Dimensional Analysis as mentioned in this paper and differential equations of motion.
Abstract: Fluid Statics. Introduction to Fluid Motion I. Introduction to Fluid Motion II. Equations of Motion in Integral Form. Differential Equations of Motion. Incompressible, Irrotational Flows. Dimensional Analysis. Viscous Internal Flows. Viscous External Flows. Open Channel Flow. Compressible Flow. Turbomachines. Environmental Fluid Mechanics. Historical Notes. Appendices. Answers to Selected Problems. Index.
TL;DR: In this paper, the Rouse number is used to determine the suspended load component of sediment transport in open-channel flow, and the vertical distribution of the concentration of suspended particles is of importance.
Abstract: To determine the suspended load component of sediment transport in open-channel flow, the vertical distribution of the concentration of suspended particles is of importance. It is usual to determine this distribution by solving the diffusion-convection equation under appropriate boundary conditions. The exponent in the resulting equation is the Rouse number, defined as z′ = vss/βκ¯u*. The β¯-value has been the subject of much research. In natural alluvial channels the sediment-laden flow is usually in capacity (saturation) condition, implying that the flow will charge (saturate) itself with particles available in the bed load and/or on the bed itself. However, simulation of sediment-laden flow in a laboratory flume is achieved typically by externally adding particles to the flow. Consequently, it is not certain that the flow was in capacity condition. The resulting β¯-values are often values for noncapacity conditions. They should not be used for natural alluvial channels, because they are misleading. Rep...
TL;DR: In this article, a Large Eddy Simulation (LES) finite element code is developed for the Reynolds Averaged Navier-Stokes (RANS) equations and validated for grid turbulence and channel flow.
TL;DR: In this article, a direct numerical simulation of the three-dimensional Navier-Stokes equations is used to obtain the structure of the free-surface turbulence and the promotion of turbulent scalar transfer at the free surface by vortex/interface interactions.
Abstract: Dynamics of well-organized tube-like coherent structures under a free surface and turbulent scalar transfer across the free surface in fully developed turbulent flow in an open channel is investigated. A direct numerical simulation of the three-dimensional Navier–Stokes equations is used to obtain the structure of the free-surface turbulence. First, the effect of the free surface on fully developed turbulence statistics is described. Anisotropy of velocity and vorticity under the free surface are given. Next, the dynamics of the intermittent vortex tubes beneath the free surface are stated. The genesis and development of these coherent structures and their interactions with the free surface are demonstrated. The role of the vortex/surface interactions on the dynamics of turbulence under the free surface, particularly intercomponent energy transfer due to the pressure–strain effect, is discussed. In addition, passive scalar transfer across the free surface is studied. Finally, the promotion of turbulent scalar transfer at the free surface by the vortex/interface interactions is discussed.
TL;DR: In this paper, a distributed parameter linear model is derived from simplified physical equations of one dimensional open channel hydraulics, which is then identified analytically to a second order transfer function with delay, that can be used for controller synthesis.
TL;DR: In this article, the influence of the inertia forces on the free surface shapes, interfacial undulations, and flow patterns of a long bubble is analyzed, and numerical results reported complete previous descriptions of the creeping flow regime.
Abstract: In this work the interfacial shapes and the flow occurring at the trailing meniscus of a long bubble is numerically analyzed. The technique employed solves the complete set of governing equations simultaneously. The numerical results reported complete previous descriptions of the creeping flow regime; the influence of the inertia forces on the free surface shapes, interfacial undulations, and flow patterns is also analyzed.
TL;DR: In this paper, the characteristics of flow in separated, attached and cavitated flow regions are determined and it is shown that while the discharge coefficient scales with the Reynolds number and aspect ratio in the attached flow regions, the diameter influences the discharge coefficients in the separated flow region.
TL;DR: In this article, the Stokes equations for turbulent nonlinear free-surface flows are applied to simulations of a laminar standing wave and turbulent open-channel flow with a finite-amplitude surface wave.