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1
Dobson, M. K., and J. C. Chato. "Condensation in Smooth Horizontal Tubes." Journal of Heat Transfer 120, no. 1 (February 1, 1998): 193–213. http://dx.doi.org/10.1115/1.2830043.
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An experimental study of heat transfer and flow regimes during condensation of refrigerants in horizontal tubes was conducted. Measurements were made in smooth, round tubes with diameters ranging from 3.14 mm to 7.04 mm. The refrigerants tested were R-12, R-22, R-134a, and near-azeotropic blends of R-32/R-125 in 50 percent/50 percent and 60 percent/40 percent compositions. The study focused primarily on measurement and prediction of condensing heat transfer coefficients and the relationship between heat transfer coefficients and two-phase flow regimes. Flow regimes were observed visually at the inlet and outlet of the test condenser as the heat transfer data were collected. Stratified, wavy, wavy annular, annular, annular mist, and slug flows were observed. True mist flow without a stable wall film was not observed during condensation tests. The experimental results were compared with existing flow regime maps and some corrections are suggested. The heat transfer behavior was controlled by the prevailing flow regime. For the purpose of analyzing condensing heat transfer behavior, the various flow regimes were divided into two broad categories of gravity-dominated and shear-dominated flows. In the gravity dominated flow regime, the dominant heat transfer mode was laminar film condensation in the top of the tube. This regime was characterized by heat transfer coefficients that depended on the wall-to-refrigerant temperature difference but were nearly independent of mass flux. In the shear-dominated flow regime, forced-convective condensation was the dominant heat transfer mechanism. This regime was characterized by heat transfer coefficients that were independent of temperature difference but very dependent on mass flux and quality. Heat transfer correlations that were developed for each of these flow regimes successfully predicted data from the present study and from several other sources.
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Singh, Sanjeev, and Rajeev Kukreja. "An Experimental Investigation of Flow Patterns During Condensation of HFC Refrigerants in Horizontal Micro-Fin Tubes." International Journal of Air-Conditioning and Refrigeration 27, no. 01 (March 2019): 1950010. http://dx.doi.org/10.1142/s201013251950010x.
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Condensation heat transfer coefficients and flow regimes in two different horizontal micro-fin tubes are examined during the condensation of refrigerants R-134a and R-410A. The present investigation has focused on determination and prediction of condensation heat transfer coefficients and finding the interrelation between heat transfer coefficients and the prevailing flow regimes. During flow visualization, flow regimes have been captured using borosilicate glass tube at inlet and outlet of the test condenser using high speed digital camera. Stratified, stratified wavy, wavy annular, annular, slug and plug flows have been observed at different mass fluxes and vapor qualities of the refrigerants. The observed flow regimes are compared with the existing flow regime maps proposed by Breber et al. [Prediction of horizontal tube side condensation of pure components using flow regime criteria, J. Heat Transfer 102 (1980) 471–476], Tandon et al. [A new flow regime map for condensation inside horizontal tubes, J. Heat Transfer 104 (1982) 763–768.] and Thome et al. [Condensation in horizontal tubes, part 2: New heat transfer model based on flow regimes, Int. J. Heat Mass Transfer 46 (2003) 3365–3387.] Thome et al. [Condensation in horizontal tubes, part 2: New heat transfer model based on flow regimes, Int. J. Heat Mass Transfer 46 (2003) 3365–3387.] flow regime map shows good agreement with experimental data.
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Phung, Viet-Anh, and Pavel Kudinov. "Prediction of Flow Regimes and Thermal Hydraulic Parameters in Two-Phase Natural Circulation by RELAP5 and TRACE Codes." Science and Technology of Nuclear Installations 2015 (2015): 1–12. http://dx.doi.org/10.1155/2015/296317.
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In earlier study we have demonstrated that RELAP5 can predict flow instability parameters (flow rate, oscillation period, temperature, and pressure) in single channel tests in CIRCUS-IV facility. The main goals of this work are to (i) validate RELAP5 and TRACE capabilities in prediction of two-phase flow instability and flow regimes and (ii) assess the effect of improvement in flow regime identification on code predictions. Most of the results of RELAP5 and TRACE calculation are in reasonable agreement with experimental data from CIRCUS-IV. However, both codes misidentified instantaneous flow regimes which were observed in the test with high speed camera. One of the reasons for the incorrect identification of the flow regimes is the small tube flow regime transition model in RELAP5 and the combined bubbly-slug flow regime in TRACE. We found that calculation results are sensitive to flow regime boundaries of RELAP5 which were modified in order to match the experimental data on flow regimes. Although the flow regime became closer to the experimental one, other predicted thermal hydraulic parameters showed larger discrepancy with the experimental data than with the base case calculations where flow regimes were misidentified.
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Growns, Ivor, and Ivars Reinfelds. "Environmental flow management using transparency and translucency rules." Marine and Freshwater Research 65, no. 8 (2014): 667. http://dx.doi.org/10.1071/mf13192.
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River flow regimes and their variability are considered by many authors to be the most important factor structuring their physical and ecological environment. In regulated rivers, environmental or instream flows are the main management technique used to ameliorate the ecological effects of flow alteration. We highlight two concepts that are not commonly used in a managed flow regime but help return natural flow variability to a managed river, namely, transparent and translucent flow rules. Transparency flows target lower flows up to a defined threshold so that all inflows are released from a dam or are protected from abstraction. Translucency flows form a percentage of inflows greater than the transparency threshold that are released to maintain a proportion of flow pulses in the river system. The main ecological concept underlying transparency and translucency flows is that riverine biota are adapted to the historical flow regime. Although the loss of small to moderate flood events may arise from implementation of translucency and/or transparency flow regimes, we advocate that these rule types would, nonetheless, be beneficial in many managed flow regimes and present two case studies where they have been defined and implemented.
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Kunii, Kohei, Takahiro Ishida, Yohann Duguet, and Takahiro Tsukahara. "Laminar–turbulent coexistence in annular Couette flow." Journal of Fluid Mechanics 879 (October 1, 2019): 579–603. http://dx.doi.org/10.1017/jfm.2019.666.
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Annular Couette flow is the flow between two coaxial cylinders driven by the axial translation of the inner cylinder. It is investigated using direct numerical simulation in long domains, with an emphasis on the laminar–turbulent coexistence regime found for marginally low values of the Reynolds number. Three distinct flow regimes are demonstrated as the radius ratio $\unicode[STIX]{x1D702}$ is decreased from 0.8 to 0.5 and finally to 0.1. The high-$\unicode[STIX]{x1D702}$ regime features helically shaped turbulent patches coexisting with laminar flow, as in planar shear flows. The moderate-$\unicode[STIX]{x1D702}$ regime does not feature any marked laminar–turbulent coexistence. In an effort to discard confinement effects, proper patterning is, however, recovered by artificially extending the azimuthal span beyond $2\unicode[STIX]{x03C0}$. Eventually, the low-$\unicode[STIX]{x1D702}$ regime features localised turbulent structures different from the puffs commonly encountered in transitional pipe flow. In this new coexistence regime, turbulent fluctuations are surprisingly short-ranged. Implications are discussed in terms of phase transition and critical scaling.
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Wilson, Donna, David M. Hannah, and Glenn R. McGregor. "A large-scale hydroclimatological perspective on western European river flow regimes." Hydrology Research 44, no. 5 (November 9, 2012): 809–33. http://dx.doi.org/10.2166/nh.2012.201.
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A novel flow regime classification scheme was applied to 141 river basins across western Europe, providing more robust analysis of space–time variability in regimes and their driving hydroclimatological processes. Regime shape (timing) and magnitude (size) were classified to regionalise long-term average flow regimes and to quantify year-to-year variation in regimes for each basin. Six long-term regime shape regions identified differences in seasonality related to latitude and altitude. Five long-term magnitude regions were linked to location plus average annual rainfall. Spatial distribution of long-term regimes reflected dominant climate and runoff generation processes. Regions were used to structure analysis of (relative) inter-annual regime dynamics. Six shape and five magnitude inter-annual regimes were identified; and regime stability (switching) assessed at pan-European, regional and basin scales. In some years, certain regime types were more prevalent, but never totally dominant. Regime shape was more stable at higher altitude due to buffering by frozen water storage-release (cf. more variable rainfall-runoff at lower altitudes). The lower inter-annual magnitude regimes persisted across larger domains (cf. higher magnitude) due to the more widespread climatic conditions generating low flow. Notably, there was limited spatio-temporal correspondence between regime shape and magnitude, suggesting variations in one attribute cannot be used to infer the other.
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Liebenberg, Leon, John R. Thome, and Josua P. Meyer. "Flow Visualization and Flow Pattern Identification With Power Spectral Density Distributions of Pressure Traces During Refrigerant Condensation in Smooth and Microfin Tubes." Journal of Heat Transfer 127, no. 3 (March 1, 2005): 209–20. http://dx.doi.org/10.1115/1.1857942.
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This paper presents a flow pattern identifier of the prevailing flow regime during refrigerant condensation inside smooth- and microfin tubes. The power spectral density distribution of the fluctuating condensing pressure signal was used to identify the prevailing flow regime, as opposed to the traditional (and subjective) use of visual-only methods, and/or smooth-tube flow regime maps. The prevailing flow regime was observed by using digital cameras and was validated with the use of the conventional smooth-tube flow regime transition criteria, as well as a new flow regime map for microfin-tube condensation. Experimental work was conducted for condensing refrigerants R-22, R-407C, and R-134a at an average saturation temperature of 40°C with mass fluxes ranging from 300–800 kg/m2 s, and with vapor qualities ranging from 0.05–0.15 at condenser outlet to 0.85–0.95 at condenser inlet. Tests were conducted with one smooth-tube condenser and three microfin-tube condensers (with helix angles of 10°, 18°, and 37° respectively). The power spectral density distributions of the condensing pressure signals distinguish the annular and intermittent (slug and plug) flows. A very low resonant frequency (<40 Hz) and low power spectral density amplitude of the pressure oscillation denoted stratified and wavy flows. As the annular flow regime was approached, the oscillations became larger and their frequencies increased (typically 40–120 Hz). Intermittent flow showed the most distinct character of all flow regimes. Its trace consisted of large amplitude pressure pulses occurring at fairly constant frequencies (approximately 50, 60, 80, 100, and 120 Hz). As the transition from intermittent to annular flow began, the pressure fluctuations became less regular and the amplitude dropped sharply.
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Abbasian Arani, Ali Akbar, and Majid Dehghani. "Numerical Comparison of Two and Three Dimensional Flow Regimes in Porous Media." Defect and Diffusion Forum 312-315 (April 2011): 427–32. http://dx.doi.org/10.4028/www.scientific.net/ddf.312-315.427.
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The purpose of this work is to study the fluid flow regimes in a porous media with high enough velocities (in the range of laminar flow). In our study, the results obtained from expanding Darcy’s equation to Forchheimer’s equation with volume averaging method have been used for studdying the fluid flow behavior in 2D and 3D models. Results of numerical simulations show that in all cases, there are weak inertial regime, strong inertial regime and transition zone. In all the cases, the domain of weak inertial regime is relatively narrow, and this problem is intensified in the 3D numerical simulations. This could be the reason of missing the weak inertial regime in experimental studies on inertial fluid flow in porous media. The domain of strong inertial regime in 3D models is so wide that after Darcy’s regime, the governed regime is the strong inertial regime. To obtain more accurate and analytical results, more studies should be done on the 2D and the 3D flow regimes.
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van der Spek, Alex, and Alix Thomas. "Neural-Net Identification of Flow Regime With Band Spectra of Flow-Generated Sound." SPE Reservoir Evaluation & Engineering 2, no. 06 (December 1, 1999): 489–98. http://dx.doi.org/10.2118/59067-pa.
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Summary Multiphase production log interpretation requires that the flow regime along hole in the wellbore is known. Flow regime is the cased-hole analog of lithology. Knowledge of the flow regime will help to interpret tool signals, will help to evaluate the flow rate on a per phase basis, and will reduce post-processing load. The flow regime can be classified correctly by a neural net in up to 87% of all cases using 1/3 octave band spectra of flow-generated sound plus the pipe inclination angle. Without the inclination an 88% correct classification can be achieved. A neural net trained on commercially available tool data (noise cuts) appears to be too sensitive to the wellbore inclination. Hence, application of automated neural net interpretation of noise logs requires a new generation of noise logging tools. Introduction Flow regime is for the fluid dynamicist what lithology is for the petrophysicist. Without a lithology classification, it is difficult if not impossible to quantify hydrocarbon volumes in a reservoir. Likewise, without a flow regime classification, it is hard to quantify fluid flow rates in two-phase flow in a conduit. The conventional way to classify the flow regime is by visual observation of flow in a conduit by a human observer. Although downhole video surveys are commercially available, visual observation of downhole flow is not standard practice in (horizontal well) production logging, since it requires a special wireline (optical fiber cable). Moreover, downhole video surveys can only be successful in transparent fluids, either gas wells or wells killed with clear kill fluid. In oil wells, an alternative to visual observation for classifying the flow regime is needed. All flow regimes produce their own characteristic sounds. A trained human observer can classify the flow regime in a pipe by auditory rather than visual observations. Contrary to video surveys, sound logging services are readily available at low cost from various cased-hole wireline service providers. The traditional use of such sound logs is to pinpoint leaks in either casing or tubing strings. In addition to the sound logs recorded, the surface control panel is equipped with amplifiers and speakers that allow audible monitoring of downhole produced sounds. The sound log typically is a plot versus along hole depth of the (uncalibrated) sound pressure level in five different frequency bands with high pass cut-off frequencies equal to 200, 600, 1000, 2000 and 4000 Hz (noise cuts). In principle, the logging engineer, based on auditory observation of the downhole sounds, could carry out flow regime classification. This procedure, however, is impractical; it is prone to errors, it cannot be reproduced from recorded logs (the sound is not normally recorded on audio tape) and it relies on the experience of the specific engineer. The objective of this investigation was to establish the feasibility of classifying the flow regime by a neural net. A second objective was to identify the minimum required resolution of sound band spectra in order to allow a neural net to classify flow regime correctly in excess of, say, 85% of all cases. The figure 85% was chosen because, from the authors' experience human beings, using visual observations cannot classify the flow regime correctly in 10 to 20% of all cases. To meet these two objectives, an extensive experimental program was carried out whereby two-phase flow-generated sound was recorded as 1/3 octave spectra. Subsequently, a neural net was trained on various kinds of band spectra that could be derived from the recorded 1/3 octave spectra. Both objectives were met and it appears that a neural net can classify the flow regime correctly in up to 88% of all cases using 1/3 octave spectra of two-phase flow-generated sound. Successful application of neural net classification of the flow regime from sound logs in the field brings several benefits to the business. First of all it will allow the application of the correct, flow regime specific, hydraulic model to the task of evaluating horizontal well, two-phase flow production logs. Second, it will allow a more constrained consistency check on recorded production logging data. Last but not least, it alleviates the need to predict the flow regime using hydraulic stability criteria from first principles thereby reducing computational loads (from the authors' experience at least a factor of 10) and resulting in faster turn around times. Theory: Flow Regimes Two-phase flow is the interacting flow of two phases, liquid, solid or gas, where the interface between the phases is influenced by their motion.1 Many different flow patterns can result from the changing form of the interface between the two phases. These patterns depend on a variety of factors, for instance, the phase flow rates, the pressure and the diameter and inclination of the pipe containing the flow in question, etc. Flow regimes in vertical upward flow are illustrated in Fig. 1 and are described below.1Bubble flow: A dispersion of bubbles in a continuum of liquid.Intermittent or slug flow: The bubble diameter approaches that of the tube. The bubbles are bullet shaped. Small bubbles are suspended in the intermediate liquid cylinders.Churn or froth flow: A highly unstable flow of an oscillatory nature, whereby the liquid near the pipe wall continuously pulses up and down.Annular flow: A film of liquid flows on the wall of the pipe and the gas phase flows in the center.
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Lachmy, Orli, and Nili Harnik. "Wave and Jet Maintenance in Different Flow Regimes." Journal of the Atmospheric Sciences 73, no. 6 (June 1, 2016): 2465–84. http://dx.doi.org/10.1175/jas-d-15-0321.1.
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Abstract The wave spectrum and zonal-mean-flow maintenance in different flow regimes of the jet stream are studied using a two-layer modified quasigeostrophic (QG) model. As the wave energy is increased by varying the model parameters, the flow transitions from a subtropical jet regime to a merged jet regime and then to an eddy-driven jet regime. The subtropical jet is maintained at the Hadley cell edge by zonal-mean advection of momentum, while eddy heat flux and eddy momentum flux convergence (EMFC) are weak and concentrated far poleward. The merged jet is narrow and persistent and is maintained by EMFC from a narrow wave spectrum, dominated by zonal wavenumber 5. The eddy-driven jet is wide and fluctuating and is maintained by EMFC from a wide wave spectrum. The wave–mean flow feedback mechanisms that maintain each regime are explained qualitatively. The regime transitions are related to transitions in the wave spectrum. An analysis of the wave energy spectrum budget and a comparison with a quasi-linear version of the model show that the balance maintaining the spectrum in the merged and subtropical jet regimes is mainly a quasi-linear balance, whereas in the eddy-driven jet regime nonlinear inverse energy cascade takes place. The amplitude and wavenumber of the dominant wave mode in the merged and subtropical jet regimes are determined by the constraint that this mode would produce the wave fluxes necessary for maintaining a mean flow that is close to neutrality. In contrast, the equilibrated mean flow in the eddy-driven jet regime is weakly unstable.
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Pawloski, J. L., C. Y. Ching, and M. Shoukri. "Measurement of Void Fraction and Pressure Drop of Air-Oil Two-Phase Flow in Horizontal Pipes." Journal of Engineering for Gas Turbines and Power 126, no. 1 (January 1, 2004): 107–18. http://dx.doi.org/10.1115/1.1619429.
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The void fractions, flow regimes, and pressure drop of air-oil two-phase flow in a half-inch diameter pipe over a wide range of test conditions have been investigated. The flow regimes were identified with the aid of a 1000 frames per second high-speed camera. A capacitance sensor for instantaneous void fraction measurements was developed. The mean and probability density function of the instantaneous void fraction signal can be used to effectively identify the different flow regimes. The current flow regime data show significant differences in the transitional boundaries of the existing flow regime maps. Property correction factors for the flow regime maps are recommended. The pressure drop measurements were compared to the predictions from four existing two-phase flow pressure drop models. Though some of the models performed better for certain flow regimes, none of the models were found to give accurate results over the entire range of flow regimes.
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Umair Khan, William Pao, Nabihah Sallih, and Farruk Hassan. "Flow Regime Identification in Gas-Liquid Two-Phase Flow in Horizontal Pipe by Deep Learning." Journal of Advanced Research in Applied Sciences and Engineering Technology 27, no. 1 (July 16, 2022): 86–91. http://dx.doi.org/10.37934/araset.27.1.8691.
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Two phase flow commonly occurs in industrial pipelines, heat exchangers and nuclear power plants. A characteristic feature of two-phase flow is that it can acquire various spatial distribution of phases to form different flow patterns/regimes. The first step to successfully design, analyze, and operate gas-liquid system is flow regime identification. Flow regime identification is of huge importance to the effective operation of facilities for the handling and transportation of multiphase fluids, and it represents one of the most significant challenges in petrochemical and thermonuclear industries today. The objective of this study is to develop a methodology for identification of flow regime using dynamic pressure signals and deep learning techniques. Three different flow regimes were simulated using a Level-Set (LS) method coupled with Volume of Fluid (VOF) method in a 6 m horizontal pipe with 0.050 m inner diameter. Dynamic pressure readings were collected at a strategic location and were converted to scalograms to be used as inputs in deep learning architectures like ResNet-50 and ShuffleNet. Both architectures performed effectively in classifying different flow regime and recorded testing accuracies of 85.7% and 82.9% respectively. According to our knowledge no similar research has been reported in literature, where various Convolutional Neural Networks are used along with dynamic pressure signals to identify flow regime in horizontal pipe.
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Brunner, Manuela I., Daniel Farinotti, Harry Zekollari, Matthias Huss, and Massimiliano Zappa. "Future shifts in extreme flow regimes in Alpine regions." Hydrology and Earth System Sciences 23, no. 11 (October 30, 2019): 4471–89. http://dx.doi.org/10.5194/hess-23-4471-2019.
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Abstract. Extreme low and high flows can have negative economic, social, and ecological effects and are expected to become more severe in many regions due to climate change. Besides low and high flows, the whole flow regime, i.e., annual hydrograph comprised of monthly mean flows, is subject to changes. Knowledge on future changes in flow regimes is important since regimes contain information on both extremes and conditions prior to the dry and wet seasons. Changes in individual low- and high-flow characteristics as well as flow regimes under mean conditions have been thoroughly studied. In contrast, little is known about changes in extreme flow regimes. We here propose two methods for the estimation of extreme flow regimes and apply them to simulated discharge time series for future climate conditions in Switzerland. The first method relies on frequency analysis performed on annual flow duration curves. The second approach performs frequency analysis of the discharge sums of a large set of stochastically generated annual hydrographs. Both approaches were found to produce similar 100-year regime estimates when applied to a data set of 19 hydrological regions in Switzerland. Our results show that changes in both extreme low- and high-flow regimes for rainfall-dominated regions are distinct from those in melt-dominated regions. In rainfall-dominated regions, the minimum discharge of low-flow regimes decreases by up to 50 %, whilst the reduction is 25 % for high-flow regimes. In contrast, the maximum discharge of low- and high-flow regimes increases by up to 50 %. In melt-dominated regions, the changes point in the other direction than those in rainfall-dominated regions. The minimum and maximum discharges of extreme regimes increase by up to 100 % and decrease by less than 50 %, respectively. Our findings provide guidance in water resource planning and management and the extreme regime estimates are a valuable basis for climate impact studies. Highlights Estimation of 100-year low- and high-flow regimes using annual flow duration curves and stochastically simulated discharge time series Both mean and extreme regimes will change under future climate conditions. The minimum discharge of extreme regimes will decrease in rainfall-dominated regions but increase in melt-dominated regions. The maximum discharge of extreme regimes will increase and decrease in rainfall-dominated and melt-dominated regions, respectively.
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Poff, N. LeRoy, J. David Allan, Mark B. Bain, James R. Karr, Karen L. Prestegaard, Brian D. Richter, Richard E. Sparks, and Julie C. Stromberg. "The Natural Flow Regime." BioScience 47, no. 11 (December 1997): 769–84. http://dx.doi.org/10.2307/1313099.
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Vongvisessomjai, Suphat. "Regime of Oscillatory Flow." Journal of Waterway, Port, Coastal, and Ocean Engineering 111, no. 1 (January 1985): 96–110. http://dx.doi.org/10.1061/(asce)0733-950x(1985)111:1(96).
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Mier, Frank, Raj Bhakta, Nicolas Castano, John Garcia, and Michael Hargather. "Experimental Measurement of Steady and Transient Liquid Coiling with High-Speed Video and Digital Image Processing." Fluids 3, no. 4 (December 15, 2018): 107. http://dx.doi.org/10.3390/fluids3040107.
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Liquid coiling occurs as a viscous fluid flows into a stagnant reservoir causing a localized accumulation of settling material, which coils into a stack as it accumulates. These coiling flows are broadly characterized into three primary coiling regimes of viscous, gravitational, or inertial coiling, based on the velocity of the falling fluid, the height of the fall, the radius of the fluid rope, the stack height, and the fluid properties including viscosity. A computer-controlled flow delivery apparatus was developed here to produce precisely controlled flow conditions to study steady and transitional coiling regimes with independently varied parameters. Data were recorded using high-speed digital video cameras and a purpose-built digital image processing routine to extract rope and stack dimensions as well as time-resolved coiling frequency. The precision of the setup and data analysis methods allowed a detailed study of the transition between gravitational and inertial flow regimes. The results show a smooth transition between the regimes, with no evidence of the inertial-gravitational regime. Unsteady coiling was able to be momentarily produced by applying a perturbation to the system, but the unstable regime quickly decayed to either the base inertial or gravitational regime.
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Zhang, Weifeng (Gordon), and Steven J. Lentz. "Wind-Driven Circulation in a Shelf Valley. Part II: Dynamics of the Along-Valley Velocity and Transport." Journal of Physical Oceanography 48, no. 4 (April 2018): 883–904. http://dx.doi.org/10.1175/jpo-d-17-0084.1.
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AbstractThe dynamics controlling the along-valley (cross shelf) flow in idealized shallow shelf valleys with small to moderate Burger number are investigated, and analytical scales of the along-valley flows are derived. This paper follows Part I, which shows that along-shelf winds in the opposite direction to coastal-trapped wave propagation (upwelling regime) force a strong up-valley flow caused by the formation of a lee wave. In contrast, along-shelf winds in the other direction (downwelling regime) do not generate a lee wave and consequently force a relatively weak net down-valley flow. The valley flows in both regimes are cyclostrophic with O(1) Rossby number. A major difference between the two regimes is the along-shelf length scales of the along-valley flows Lx. In the upwelling regime Lx depends on the valley width Wc and the wavelength λlw of the coastal-trapped lee wave arrested by the along-shelf flow Us. In the downwelling regime Lx depends on the inertial length scale |Us|/f and Wc. The along-valley velocity scale in the upwelling regime, given byis based on potential vorticity (PV) conservation and lee-wave dynamics (Hs and Hc are the shelf and valley depth scales, respectively, and f is the Coriolis parameter). The velocity scale in the downwelling regime, given by is based on PV conservation. The velocity scales are validated by the numerical sensitivity simulations and can be useful for observational studies of along-valley transports. The work provides a framework for investigating cross-shelf transport induced by irregular shelf bathymetry and calls for future studies of this type under realistic environmental conditions and over a broader parameter space.
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Kawaji, M., Y. S. Ng, S. Banerjee, and G. Yadigaroglu. "Reflooding With Steady and Oscillatory Injection: Part I—Flow Regimes, Void Fraction, and Heat Transfer." Journal of Heat Transfer 107, no. 3 (August 1, 1985): 670–78. http://dx.doi.org/10.1115/1.3247476.
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Simultaneous void fraction and wall temperature measurements were made during bottom-reflooding of a vertical Inconel tube under both constant and oscillatory injection rates. To support interpretation of these data, flow regime visualization experiments were also conducted by reflooding a heated quartz tube. With constant, high reflooding rates, inverted annular, transition, and dispersed flow regimes exist above the quench front, with typical chordal-average void fractions in the ranges of 10–30 percent, 30–70 percent, and 70–90 percent, respectively. Each regime exhibits different heat transfer rates. With lower injection rates or higher heating rates, annular droplet and dispersed flow regimes appear with void fractions above 80 percent. For reflooding with oscillatory inlet flow and high injection rates, large oscillations are seen in void fraction and wall temperature, indicating periodic changes in the flow regime near the quench front: The regime alternated between inverted annular (during an upstroke) and annular droplet flow (during a downstroke). These flow regimes were observed in the flow visualization experiments to be qualitatively similar to those for the constant injection cases. Heat transfer rates are substantially affected by the flow regime and increase (or decrease) as the void fraction falls (or rises). Compared to the constant-injection tests, increased rates of entrainment were observed during the forced-oscillation tests.
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Jiang, Fengjian, Bjørnar Pettersen, and Helge I. Andersson. "Turbulent wake behind a concave curved cylinder." Journal of Fluid Mechanics 878 (September 18, 2019): 663–99. http://dx.doi.org/10.1017/jfm.2019.648.
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We present a detailed study of the turbulent wake behind a quarter-ring curved cylinder at Reynolds number $Re=3900$ (based on cylinder diameter and incoming flow velocity), by means of direct numerical simulation. The configuration is referred to as a concave curved cylinder with incoming flow aligned with the plane of curvature and towards the inner face of the cylinder. Wake flows behind this configuration are known to be complex, but have so far only been studied at low $Re$. This is the first direct numerical simulation investigation of the turbulent wake behind the concave configuration, from which we reveal new and interesting wake dynamics, and present in-depth physical interpretations. Similar to the low-$Re$ cases, the turbulent wake behind a concave curved cylinder is a multi-regime and multi-frequency flow. However, in addition to the coexisting flow regimes reported at lower $Re$, we observe a new transitional flow regime at $Re=3900$. The flow field in this transitional regime is dominated not by von Kármán-type vortex shedding, but by periodic asymmetric helical vortices. Such vortex pairs exist also in some other wake flows, but are then non-periodic. Inspections reveal that the periodic motion of the asymmetric helical vortices is induced by vortex shedding in its neighbouring oblique shedding regime. The oblique shedding regime is in turn influenced by the transitional regime, resulting in a unified and remarkably low dominating frequency in both flow regimes. Owing to this synchronized frequency, the new wake dynamics in the transitional regime might easily be overlooked. In the near wake, two distinct peaks are observed in the time-averaged axial velocity distribution along the curved cylinder span, while only one peak was observed at lower $Re$. The presence of the additional peak is ascribed to a strong favourable base pressure gradient along the cylinder span. It is noteworthy that the axially directed base flow exceeded the incoming velocity behind a substantial part of the quarter-ring and even persisted upwards along the straight vertical extension. As a by-product of our study, we find that a straight vertical extension of 16 cylinder diameters is required in order to avoid any adverse effects from the upper boundary of the flow domain.
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Ronshin, Fedor, Karapet Eloyan, and Viacheslav Cheverda. "Two–phase flow of air–water mixture in a minichannel." EPJ Web of Conferences 196 (2019): 00037. http://dx.doi.org/10.1051/epjconf/201919600037.
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Two-phase systems have a huge potential for solving problems of removing large heat fluxes. To date, mini-channel and microchannel systems are widespread. Of particular interest are the stratified flow regime and the annular flow regime in mini- and micro- channel. It is necessary to know in detail the map of flow regimes for the realization of these flow regimes. In this paper, we present an investigation of flow regimes for a rectangular mini- channel 10 mm wide and 1.1 mm high.
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Pena, Blanca, Ema Muk-Pavic, Giles Thomas, and Patrick Fitzsimmons. "Numerical analysis of a leading edge tubercle hydrofoil in turbulent regime." Journal of Fluid Mechanics 878 (September 6, 2019): 292–305. http://dx.doi.org/10.1017/jfm.2019.611.
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This paper presents a numerical performance evaluation of the leading edge tubercles hydrofoil with particular focus on a fully turbulent flow regime. Efforts were focused on the setting up of an appropriate numerical approach required for an in-depth analysis of this phenomenon, being able to predict the main flow features and the hydrodynamic performance of the foil when operating at high Reynolds numbers. The numerical analysis was conducted using an improved delayed detached eddy simulation for Reynolds numbers corresponding to the transitional and fully turbulent flow regimes at different angles of attack for the pre-stall and post-stall regimes. The results show that tubercles operating in turbulent flow improve the hydrodynamic performance of the foil when compared to a transitional flow regime. Flow separation was identified behind the tubercle troughs, but was significantly reduced when operating in a turbulent regime and for which we have identified the main flow mechanisms. This finding confirms that the tubercle effect identified in a transitional regime is not lost in a turbulent flow. Furthermore, when the hydrofoil operates in the turbulent flow regime, the transition to a turbulent regime takes place further upstream. This phenomenon suppresses a formation of a laminar separation bubble and therefore the hydrofoil exhibits a superior hydrodynamic performance when compared to the same foil in the transitional regime.
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An, Baizheng, Daniel Solorzano, and Qingwang Yuan. "Viscous Fingering Dynamics and Flow Regimes of Miscible Displacements in a Sealed Hele-Shaw Cell." Energies 15, no. 16 (August 10, 2022): 5798. http://dx.doi.org/10.3390/en15165798.
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Miscible viscous fingering occurs when a less viscous fluid displaces a more viscous one in porous media or a Hele–Shaw cell. Such flow instabilities are of particular interest in a variety of applications in flows and displacements in subsurface energy and environment systems. In this study, we investigate the miscible viscous fingering dynamics experimentally using water to displace glycerol in a sealed Hele–Shaw cell with two wells located in it instead of at the boundary or corners. We comprehensively examine the spatial and temporal variations of fingering dynamics, different flow regimes, and how they are affected by the water injection rate and control of pressure or rate at the outlet. Alongside the widely recognized diffusion-dominated and convection-dominated flow regimes, we identify three new regimes: a slow expansion regime prior to breakthrough, a rapid shrinkage regime immediately after breakthrough, and a uniform, slow expansion regime without fingering instability. Each regime is characterized by interesting flow dynamics, which has not been reported previously. The duration of each regime depends on the water injection rate and whether constant pressure or a constant production rate is applied at the outlet. The variations of swept area, interfacial length, and count of fingers are also quantitatively examined. This study provides new insights into the fundamental mechanisms for miscible fluid displacements in a variety of applications such as CO2 sequestration, hydrogen storage, enhanced oil recovery, and groundwater contaminate remediation.
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Colombo, Marco, Andrea De Santis, Bruce C. Hanson, and Michael Fairweather. "Prediction of Horizontal Gas–Liquid Segregated Flow Regimes with an All Flow Regime Multifluid Model." Processes 10, no. 5 (May 6, 2022): 920. http://dx.doi.org/10.3390/pr10050920.
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The generalized multifluid modelling approach (GEMMA) has been developed to handle the multiplicity of flow regimes and the coexistence of interfaces of largely different scales in multiphase flows. The solver, based on the OpenFOAM reactingEulerFoam family of solvers, adds interface resolving-like capabilities to the multifluid solver in the cells occupied by large interfaces. In this paper, GEMMA is further developed to predict stratified and slug flow regimes in horizontal ducts. The suppression of the turbulence and the wall-like behaviour of large interfaces is modelled with an additional dissipation source. This enables an accurate prediction of the velocity and of the turbulence kinetic energy in a stratified channel flow and the capturing of the formation and the travel of liquid slugs in an annulus. Large interfaces are identified and tracked, not only in the smooth and wavy stratified regimes but also in the much more perturbed interfaces of liquid slugs. The present work confirms GEMMA to be a reliable approach to provide all flow regime modelling capabilities. Further development will be focused on large interface momentum-transfer modelling, responsible for the overestimation of the interfacial shear and the limited liquid excursion during slugs, and the extension to interface break-up and the entrainment of bubbles and droplets, to handle the entire range of regimes encountered in horizontal flows.
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Brkić, Dejan, and Pavel Praks. "Unified Friction Formulation from Laminar to Fully Rough Turbulent Flow." Applied Sciences 8, no. 11 (October 24, 2018): 2036. http://dx.doi.org/10.3390/app8112036.
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This paper provides a new unified formula for Newtonian fluids valid for all pipe flow regimes from laminar to fully rough turbulent flow. This includes laminar flow; the unstable sharp jump from laminar to turbulent flow; and all types of turbulent regimes, including the smooth turbulent regime, the partial non-fully developed turbulent regime, and the fully developed rough turbulent regime. The new unified formula follows the inflectional form of curves suggested in Nikuradse’s experiment rather than the monotonic shape proposed by Colebrook and White. The composition of the proposed unified formula uses switching functions and interchangeable formulas for the laminar, smooth turbulent, and fully rough turbulent flow regimes. Thus, the formulation presented below represents a coherent hydraulic model suitable for engineering use. This new flow friction model is more flexible than existing literature models and provides smooth and computationally cheap transitions between hydraulic regimes.
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Habibzadeh, Alireza, Mark R. Loewen, and Nallamuthu Rajaratnam. "Turbulence measurements in submerged hydraulic jumps with baffle blocks." Canadian Journal of Civil Engineering 43, no. 6 (June 2016): 553–61. http://dx.doi.org/10.1139/cjce-2015-0480.
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Laboratory measurements of turbulence in submerged hydraulic jumps with blocks downstream of a sluice gate are presented. As observed previously two flow regimes were distinguished; the deflected surface jet (DSJ) and the reattaching wall jet (RWJ) regimes. In the DSJ regime considerable turbulent kinetic energy (TKE) was generated just downstream of the blocks and the rate of dissipation of TKE was found to be very high resulting in a rapid decay of TKE. In the RWJ flow regime the magnitude of both the TKE and the dissipation rate were considerably lower but because the TKE decayed more slowly higher levels of TKE persisted farther downstream. This study provides insights into the production and dissipation of turbulence in submerged flows and helps to explain why a submerged jump with blocks with a low submergence factor; i.e., the DSJ flow regime, is as effective as a free jump in dissipating energy.
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Krasovskaia, I., and L. Gottschalk. "Stability of River Flow Regimes." Hydrology Research 23, no. 3 (June 1, 1992): 137–54. http://dx.doi.org/10.2166/nh.1992.0010.
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One of the most important consequences of future climate change may be an alteration of the surface hydrological balance, including changes in flow regimes, i.e. seasonal distribution of flow and especially the time of occurrence of high/low flow, which is of vital importance for environmental and economic policies. Classification of flow regimes still has an important role for the analyses of hydrological response to climate change as well as for validating climate models on present climatic and hydrologic data, however, with some modifications in the methodology. In this paper an approach for flow regime classification is developed in this context. Different ways of flow regime classification are discussed. The stability of flow regimes is studied in relation to changes in mean annual temperature and precipitation. The analyses have shown that even rather small changes in these variables can cause changes in river flow regimes. Different patterns of response have been traced for different regions of the Nordic countries.
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Taghavi, S. M., K. Alba, T. Seon, K. Wielage-Burchard, D. M. Martinez, and I. A. Frigaard. "Miscible displacement flows in near-horizontal ducts at low Atwood number." Journal of Fluid Mechanics 696 (February 27, 2012): 175–214. http://dx.doi.org/10.1017/jfm.2012.26.
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AbstractWe study buoyant displacement flows with two miscible fluids of equal viscosity in the regime of low Atwood number and in ducts that are inclined close to horizontal. Using a combination of experimental, computational and analytical methods, we characterize the transitions in the flow regimes between inertial- and viscous-dominated regimes, and as the displacement flow rate is gradually increased. Three dimensionless groups largely describe these flows: densimetric Froude number $\mathit{Fr}$, Reynolds number $\mathit{Re}$ and duct inclination $\ensuremath{\beta} $. Our results show that the flow regimes collapse into regions in a two-dimensional $(\mathit{Fr}, \mathit{Re}\cos \ensuremath{\beta} / \mathit{Fr})$ plane. These regions are qualitatively similar between pipes and plane channels, although viscous effects are more extensive in pipes. In each regime, we are able to give a leading-order estimate for the velocity of the leading displacement front, which is effectively a measure of displacement efficiency.
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Chen, Shu-Hua, and Yuh-Lang Lin. "Effects of Moist Froude Number and CAPE on a Conditionally Unstable Flow over a Mesoscale Mountain Ridge." Journal of the Atmospheric Sciences 62, no. 2 (February 1, 2005): 331–50. http://dx.doi.org/10.1175/jas-3380.1.
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Abstract In this study, idealized simulations are performed for a conditionally unstable flow over a two-dimensional mountain ridge in order to investigate the propagation and types of cloud precipitation systems controlled by the unsaturated moist Froude number (Fw) and the convective available potential energy (CAPE). A two-dimensional moist flow regime diagram, based on Fw and CAPE, is proposed for a conditionally unstable flow passing over a two-dimensional mesoscale mountain ridge. The characteristics of these flow regimes are 1) regime I: flow with an upstream-propagating convective system and an early, slowly moving convective system over the mountain; 2) regime II: flow with a long-lasting orographic convective system over the mountain peak, upslope, or lee slope; 3) regime III: flow with an orographic convective or mixed convective and stratiform precipitation system over the mountain and a downstream-propagating convective system; and 4) regime IV: flow with an orographic stratiform precipitation system over the mountain and possibly a downstream-propagating cloud system. Note that the fourth regime was not included in the flow regimes proposed by Chu and Lin and Chen and Lin. The propagation of the convective systems is explained by the orographic blocking and density current forcing associated with the cold-air outflow produced by evaporative cooling acting against the basic flow, which then determines the propagation and cloud types of the simulated precipitation systems.
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Kyto¨maa, H. K., and C. E. Brennen. "Some Observations of Flow Patterns and Statistical Properties of Three Component Flows." Journal of Fluids Engineering 110, no. 1 (March 1, 1988): 76–84. http://dx.doi.org/10.1115/1.3243514.
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Vertical air-water flows, solids-water flows and three component air-solids-water flows were investigated in a Three Component Flow Facility. Visual observations of the flow patterns show that three component flows undergo transition and can exhibit strong unsteady vortical motions. Measurements of the fluctuations in cross-sectionally averaged volume fraction measurements were made. The statistical properties of the fluctuations are presented in terms of their amplitude and coherent time scale in the form of the Signal To Noise Ratio (STNR) and the Time Constant (ξ), respectively. Remarkably, the solids-water flows and the dispersed bubbly air-water flows exhibit almost identical values of STNR for the same volume fraction. Equally remarkable in the linear relationship between the Time Constant and the mean bubble or particle velocity; this relationship is found to have the same constant of proportionality for both species in the well behaved disperse regime. In the two-component churn-turbulent and the three-component agitated vortical regimes, the variables ξ and STNR significantly deviate from their dispersed regime values. The onset of large coherent structures characteristic of these regimes is reflected by a rise in the amplitude of the fluctuations and a marked increase in their coherent time scale. The results of this study demonstrate the large information content in the fluctuations of the measured quantity, both as a flow regime indicator and as a measure of flow quantities in two- and three-component flows.
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Taheri, Erfan, Ming Zhao, and Helen Wu. "Numerical Investigation of the Vibration of a Circular Cylinder in Oscillatory Flow in Oblique Directions." Journal of Marine Science and Engineering 10, no. 6 (June 1, 2022): 767. http://dx.doi.org/10.3390/jmse10060767.
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The response of an elastically mounted circular cylinder vibrating in an oscillatory flow oblique to the flow direction is investigated. Simulations are conducted for vibration angles ranging from 0° to 90°, with 0° and 90° corresponding to the cases where the vibration is inline and perpendicular to the flow direction, respectively. One mass ratio of 2, one Reynolds number of 150, and two Keulegan–Carpenter (KC) numbers of 5 and 10 and a wide range of frequency ratios that cover the lock-in regime are considered. The frequency ratio is the ratio of the oscillatory flow frequency to the natural frequency. The maximum vibration amplitude is highest when the cylinder vibrates in the flow direction (vibration angel = 0°) and gradually decreases with the increase of the vibration direction. All the identified flow regimes are mapped on the frequency ratio versus vibration angle space. In addition to the flow regimes that exist for a stationary cylinder, two variants of Regime F (F1 and F2), a new flow regime R and an unstable regime D/F are found. The vortex street directions of Regime F1 and F2 are the opposite to and the same as the direction of the vibration, respectively, Regime R is a regime where a dominant vortex circles around the cylinder and Regime D/F is an unstable regime where the flow changes between Regime D and F frequently. The contribution of the higher harmonics in the vibration increases with the increase of the vibration direction angle. As a result of the strong contribution of higher harmonics at large vibration angles and small frequency ratios, local peak values of the vibration amplitude are found at frequency ratios of 0.4 and 0.25 for KC = 5 and 10, respectively.
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CHEN, LI-WEI, CHANG-YUE XU, and XI-YUN LU. "LARGE-EDDY SIMULATION OF OPPOSING-JET-PERTURBED SUPERSONIC FLOWS PAST A HEMISPHERICAL NOSE." Modern Physics Letters B 24, no. 13 (May 30, 2010): 1287–90. http://dx.doi.org/10.1142/s021798491002344x.
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A supersonic flow past a hemispherical nose with an opposing jet placed on its axis has been investigated using large eddy simulation. We find that the flow behaviors depend mainly on the jet total pressure ratio and can be classified into three typical flow regimes of unstable, stable and transition. The unstable flow regime is characterized by an oscillatory bow shock with a multi-jet-cell structure and the stable flow regime by a steady bow shock with a single jet cell. The transition regime lies between the unstable and stable ones with a complex flow evolution. Turbulence statistics are further analyzed to reveal the relevant turbulent behaviors in the three flow regimes. The results obtained in this study provide a physical insight into the understanding of the mechanisms underlying this complex flow.
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Moghadam, Alireza A., and Rick Chalaturnyk. "Analytical and Experimental Investigations of Gas-Flow Regimes in Shales Considering the Influence of Mean Effective Stress." SPE Journal 21, no. 02 (April 14, 2016): 557–72. http://dx.doi.org/10.2118/178429-pa.
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Summary Flow conditions determine the flow regimes governing gas flow in porous media. Slip-flow regime commonly occurs in laboratory gas-permeability measurements, and one must consider the physics of that when finding the absolute permeability of a sample. Accurate permeability estimates are paramount for production forecasts, financial planning, and recovery estimation. Slip flow is present in low-permeability rocks, both in the laboratory environment and at reservoir conditions. Gas flow through the matrix lies under the slip-flow regime for the majority of low-permeability-reservoir production scenarios, and accurate prediction of pressure and production rate requires a good understanding of the flow regime. In this paper, an analytical study is conducted on the dominant flow regimes under typical shale-gas reservoir conditions. A flow-regime map is produced with respect to gas pressure and matrix permeability. Steady-state gas-permeability experiments are conducted on three shale samples. An analytical model is used to match the experimental results that could explain the order-of-magnitude difference between the permeabilities of gas and liquid in shales. Experimental results are combined with further tests available in the literature to inform a discussion of the model's parameters. The results improve the accuracy of gas-flow modeling and of absolute-permeability estimates from laboratory tests. Similar tests performed at various mean effective stresses investigate the influence of mean effective stress on flow regime and apparent permeability. The results indicate that flow regime is a function of mean effective stress, and that the apparent permeability of shale rocks is a function of both flow regime and mean effective stress.
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Peterson, A. W., and A. E. Peterson. "Mobile boundary flow: an assessment of velocity and sediment discharge relationships." Canadian Journal of Civil Engineering 15, no. 4 (August 1, 1988): 539–46. http://dx.doi.org/10.1139/l88-074.
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Using the data from Brownlie's update of the Compendium of Solids Transport Data, velocity and sediment discharge equations have been derived using regression analysis. Two velocity equations have been determined, one for the lower flow regime and the other for the upper flow regime. A single equation for sediment discharge covers both flow regimes. The equations provide estimation/prediction of sediment discharge and velocity that are simple to use.Plots of over 3000 test results show the relationship of sediment discharge, velocity, flow depth, energy gradient, and sediment size for the lower and upper flow regimes. Included in the plots are estimation and prediction limits for the velocity and sediment discharge relationships. Key words: sediment discharge, velocity, flow regime, weighted least squares, regression, prediction.
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Woo, Nam-Sub, Young-Ju Kim, and Young-Kyu Hwang. "Experimental Study on the Helical Flow in a Concentric Annulus With Rotating Inner Cylinder." Journal of Fluids Engineering 128, no. 1 (September 22, 2005): 113–17. http://dx.doi.org/10.1115/1.2136923.
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This experimental study concerns the characteristics of vortex flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one is rotating. Pressure losses and skin friction coefficients have been measured for fully developed laminar flows of water and of 0.4% aqueous solution of sodium carboxymethyl cellulose, respectively, when the inner cylinder rotates at the speed of 0-600rpm. The results of the present study show the effect of the bulk flow Reynolds number Re and Rossby number Ro on the skin friction coefficients. They also point to the existence of a flow instability mechanism. The effect of rotation on the skin friction coefficient depends significantly on the flow regime. In all flow regimes, the skin friction coefficient is increased by the inner cylinder rotation. The change in skin friction coefficient, which corresponds to a variation of the rotational speed, is large for the laminar flow regime, whereas it becomes smaller as Re increases for transitional flow regime and, then, it gradually approaches to zero for turbulent flow regime. Consequently, the critical bulk flow Reynolds number Rec decreases as the rotational speed increases. The rotation of the inner cylinder promotes the onset of transition due to the excitation of Taylor vortices.
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Hartman, Miloslav, Zdeněk Beran, Karel Svoboda, and Václav Veselý. "Operation Regimes of Fluidized Beds." Collection of Czechoslovak Chemical Communications 60, no. 1 (1995): 1–33. http://dx.doi.org/10.1135/cccc19950001.
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The state of the art has been reviewed in the analysis and description of flow or contacting pattern in gas-solid contacting units where a gas flows upwards through a bed of solids. The flow regime or contacting mode varies widely, depending on the particle size, particle density, gas density, gas viscosity, gas velocity and column geometry. The influence of such variables is reflected in the particle classification schemes and regime diagrams to cover the operation regions of common gas-solid reactors and contactors. In general, fluidized beds can be operated in six different regimes: particulate (homogeneous) fluidization, bubbling fluidization, slugging fluidization, turbulent fluidization, fast fluidization and pneumatic conveying. The bubbling beds can be further classified into three different modes of contacting: fast bubble regime, slow bubble regime and rapidly growing bubble regime. Characteristic features of all the regimes as well as the transitions between them are discussed. Current research interests, supported by practical needs, are oriented toward the operation conditions and contactor geometry of high velocity units.
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LATINI, MARCO, and ANDREW J. BERNOFF. "Transient anomalous diffusion in Poiseuille flow." Journal of Fluid Mechanics 441 (August 15, 2001): 399–411. http://dx.doi.org/10.1017/s0022112001004906.
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We revisit the classical problem of dispersion of a point discharge of tracer in laminar pipe Poiseuille flow. For a discharge at the centre of the pipe we show that in the limit of small non-dimensional diffusion, D, tracer dispersion can be divided into three regimes. For small times (t [Lt ] D−1/3), diffusion dominates advection yielding a spherically symmetric Gaussian dispersion cloud. At large times (t [Gt ] D−1), the flow is in the classical Taylor regime, for which the tracer is homogenized transversely across the pipe and diffuses with a Gaussian distribution longitudinally. However, in an intermediate regime (D−1/3 [Gt ] t [Gt ] D−1), the longitudinal diffusion is anomalous with a width proportional to t [Lt ] Dt2 and a distinctly asymmetric longitudinal distribution. We present a new solution valid in this regime and verify our results numerically. Analogous results are presented for an off-centre release; here the distribution width scales as D1/2t3/2 in the anomalous regime. These results suggest that anomalous diffusion is a hallmark of the shear dispersion of point discharges at times earlier than the Taylor regime.
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Zhu, Jia Song. "An Ensemble Learning Short-Term Traffic Flow Forecasting with Transient Traffic Regimes." Applied Mechanics and Materials 97-98 (September 2011): 849–53. http://dx.doi.org/10.4028/www.scientific.net/amm.97-98.849.
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Short-term traffic flow forecasting has a rich and substantive research history. For layered hybrid forecasting approaches, traffic flow series are classified into distinct regimes based on characteristics of different traffic conditions so that regime-specific forecasting models can be trained to adequately and consistently approximate dynamic traffic dynamic behaviors. However, traffic regimes are inherently changing and transient, making it a challenging task to perform regime-specific forecasting. In this paper, an ensemble learning approach is proposed and regime-based forecasting models are developed to address the nonlinearity and non-stationarity of traffic flow data. Case study results demonstrate that the proposed approach can effectively account for transient regimes and produce accurate online short-term traffic forecasts.
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Ebner, Lothar, and Marie Fialová. "On Instabilities in Horizontal Two-Phase Flow." Collection of Czechoslovak Chemical Communications 59, no. 12 (1994): 2595–603. http://dx.doi.org/10.1135/cccc19942595.
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Two regions of instabilities in horizontal two-phase flow were detected. The first was found in the transition from slug to annular flow, the second between stratified and slug flow. The existence of oscillations between the slug and annular flows can explain the differences in the limitation of the slug flow in flow regime maps proposed by different authors. Coexistence of these two regimes is similar to bistable behaviour of some differential equation solutions.
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Wang, Qiang, and Li Jing Ren. "Intelligent Identification Based on Wavelet Packet Decomposition and Adaptive Particle Swarm Optimization SVM." Applied Mechanics and Materials 380-384 (August 2013): 4043–46. http://dx.doi.org/10.4028/www.scientific.net/amm.380-384.4043.
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In this paper, a new Intelligent Identification method based on wavelet packet decomposition and APSO-SVM was put forward. As is known the characteristic of pressure drop is nonlinear and non-stationary. The wavelet packet transform can decompose signals to different frequency bands according to any time frequency resolution ratio, the features are extracted from the differential pressure fluctuation signals of the air-water two-phase flow in the horizontal pipe and the wavelet packet energy features of various flow regimes are obtained. The adaptive particle swarm ptimization support vector machine was trained using these eigenvectors as flow regime samples, and the flow regime intelligent identification was realized. The test results show the wavelet packet energy features can excellently reflect the difference between four typical flow regimes, and successful training the support vector machine can quickly and accurately identify four typical flow regimes. So a new way to identify flow regime by soft sensing is proposed.
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Loizou, Katerina, Voon-Loong Wong, and Buddhika Hewakandamby. "Examining the Effect of Flow Rate Ratio on Droplet Generation and Regime Transition in a Microfluidic T-Junction at Constant Capillary Numbers." Inventions 3, no. 3 (August 10, 2018): 54. http://dx.doi.org/10.3390/inventions3030054.
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The focus of this work is to examine the effect of flow rate ratio (quotient of the dispersed phase flow rate over the continuous phase flow rate) on a regime transition from squeezing to dripping at constant capillary numbers. The effect of the flow rate ratio on the volume of droplets generated in a microfluidic T-junction is discussed, and a new scaling law to estimate their volume is proposed. Existing work on a regime transition reported by several researchers focuses on the effect of the capillary number on regime transition, and the results that are presented in this paper advance the current understanding by indicating that the flow rate ratio is another parameter that dictates regime transition. In this paper, the transition between squeezing and dripping regimes is reported at constant capillary numbers, with a transition region identified between squeezing and dripping regimes. Dripping is observed at lower flow rate ratios and squeezing at higher flow rate ratios, with a transition region between the two regimes at flow rate ratios between 1 and 2. This is presented in a flow regime map that is constructed based on the observed mechanism. A scaling model is proposed to characterise droplet volume in terms of flow rate ratio and capillary number. The effect of flow rate ratio on the non-dimensional droplet volume is presented, and lastly, the droplet volume is expressed in terms of a range of parameters, such as the viscosity ratio between the dispersed and the continuous phase, capillary number, and the geometrical characteristics of the channels.
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Ren, Chengjiao, Liang Cheng, Feifei Tong, Chengwang Xiong, and Tingguo Chen. "Oscillatory flow regimes around four cylinders in a diamond arrangement." Journal of Fluid Mechanics 877 (September 2, 2019): 955–1006. http://dx.doi.org/10.1017/jfm.2019.609.
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Oscillatory flow around a cluster of four circular cylinders in a diamond arrangement is investigated using two-dimensional direct numerical simulation over Keulegan–Carpenter numbers (KC) ranging from 4 to 12 and Reynolds numbers (Re) from 40 to 230 at four gap-to-diameter ratios (G) of 0.5, 1, 2 and 4. Three types of flows, namely synchronous, quasi-periodic and desynchronized flows (along with 14 flow regimes) are mapped out in the (G, KC, Re)-parameter space. The observed flow characteristics around four cylinders in a diamond arrangement show a few unique features that are absent in the flow around four cylinders in a square arrangement reported by Tong et al. (J. Fluid Mech., vol. 769, 2015, pp. 298–336). These include (i) the dominance of flow around the cluster-scale structure at $G=0.5$ and 1, (ii) a substantial reduction of regime D flows in the regime maps, (iii) new quasi-periodic (phase trapping) $\text{D}^{\prime }$ (at $G=0.5$ and 1) and period-doubling $\text{A}^{\prime }$ flows (at $G=1$) and most noteworthily (iv) abnormal behaviours at ($G\leqslant 2$) (referred to as holes hereafter) such as the appearance of spatio-temporal synchronized flows in an area surrounded by a single type of synchronized flow in the regime map ($G=0.5$). The mode competition between the cluster-scale and cylinder-scale flows is identified as the key flow mechanism responsible for those unique flow features, with the support of evidence derived from quantitative analysis. Phase dynamics is introduced for the first time in bluff-body flows, to the best knowledge of the authors, to quantitatively interpret the flow response (e.g. quasi-periodic flow features) around the cluster. It is instrumental in revealing the nature of regime $\text{D}^{\prime }$ flows where the cluster-scale flow features are largely synchronized with the forcing of incoming oscillatory flow (phase trapping) but are modulated by localized flow features.
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CHARRU, FRANÇOIS, and E. JOHN HINCH. "‘Phase diagram’ of interfacial instabilities in a two-layer Couette flow and mechanism of the long-wave instability." Journal of Fluid Mechanics 414 (July 10, 2000): 195–223. http://dx.doi.org/10.1017/s002211200000851x.
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A unified view is given of the instabilities that may develop in two-layer Couette flows, as a ‘phase diagram’ in the parameter space. This view is obtained from a preliminary study of the single-fluid Couette flow over a wavy bottom, which reveals three flow regimes for the disturbances created at the bottom, each regime being characterized by a typical penetration depth of the vorticity disturbances and an effective Reynolds number. It appears that the two-layer flow exhibits the same flow regimes for the disturbances induced by the perturbed interface, and that each type of instability can be associated with a flow regime. Typical curves giving the growth rate versus wavenumber are deduced from this analysis, and favourably compared with the existing literature. In the second part of this study, we propose a mechanism for the long wavelength instability, and provide simple estimates of the wave velocity and growth rate, for channel flows and for semi-bounded flows. In particular, an explanation is given for the ‘thin-layer effect’, which is typical of multi-layer flows such as pressure driven flows or gravity driven flows, and according to which the flow is stable if the thinner layer is the less viscous, and unstable otherwise.
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Wrzesiński, Dariusz. "Uncertainty of Flow Regime Characteristics of Rivers in Europe." Quaestiones Geographicae 32, no. 1 (March 1, 2013): 43–53. http://dx.doi.org/10.2478/quageo-2013-0006.
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Abstract The aim of the paper is to describe spatial differences in the uncertainty of features of the flow regimes of rivers in Europe on the basis of measures whose methodological assumptions derive from Shannon’s information entropy theory (1948). They included: the entropy of monthly flow volumes, the entropy of the flow distribution over time, and the entropy of maximum and minimum monthly flows. An analysis was made of monthly flow series for the years 1951-1990 from 510 gauging stations located on 369 rivers in Europe. It allowed a quantitative determination of the degree of uncertainty of the four regime characteristics, indirectly establishing the predictability, regularity and stability of their appearance and their spatial variability. In the procedure of identification of spatial differences among rivers concerning the uncertainty of their flow regime features, use was made of local indices of spatial dependence. On application of LISA (Local Indicators of Spatial Association) based on Moran’s local Ii statistic, a typology of rivers was obtained in terms of the kind and statistical significance of spatial associations involving the uncertainty of the flow regime variables in question.
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Wu, Zhongwei, Chuanzhi Cui, Japan Trivedi, Ning Ai, and Wenhao Tang. "Pressure Analysis for Volume Fracturing Vertical Well considering Low-Velocity Non-Darcy Flow and Stress Sensitivity." Geofluids 2019 (November 20, 2019): 1–10. http://dx.doi.org/10.1155/2019/2046061.
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In general, there is stress sensitivity damage in tight reservoirs and fractures. Furthermore, the flow in tight reservoirs is the low-velocity non-Darcy flow. Currently, few researches of pressure analysis for volume fracturing vertical well are conducted simultaneously considering the low-velocity non-Darcy flow and stress sensitivity. In the paper, a novel flow model of a volume fractured vertical well is proposed and solved numerically. Firstly, the threshold pressure gradient, permeability modulus, and experimental data are, respectively, utilized to characterize the low-velocity non-Darcy flow, matrix stress sensitivity, and fracture stress sensitivity. Then, a two-region composite reservoir is established to simulate the vertical well with volume fracturing. After that, the logarithm meshing method is used to discrete the composite reservoir, and the flow model is solved by the method of finite difference and IMPES. Finally, the model verification is conducted, and the effects of the low-velocity non-Darcy flow and stress sensitivity on the pressure and pressure derivative are analyzed. The six flow regimes are identified by the dimensionless pressure and pressure derivative curve. They are, respectively, the fracture linear flow regime, early transition flow regime, radial flow regime, crossflow regime, advanced transition flow regime, and boundary controlling flow regime. The stress sensitivity and threshold pressure gradient have a great effect on the dimensionless pressure and pressure derivative. With the increase of reservoir stress sensitivity, the pressure and pressure derivative are upward at the advanced transition flow and boundary controlling regimes. However, the pressure and pressure derivative are downward at the advanced transition flow and boundary controlling regimes when the fracture sensitivity increases. An increase in the threshold pressure gradient results in a high dimensionless pressure and pressure derivative. This work reveals the effects of low-velocity non-Darcy flow and stress sensitivity on pressure and provides a more accurate reference for reservoir engineers in pressure analysis when developing a tight reservoir by using the volume fracturing vertical well.
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Gsell, Simon, Rémi Bourguet, and Marianna Braza. "Vortex-induced vibrations of a cylinder in planar shear flow." Journal of Fluid Mechanics 825 (July 20, 2017): 353–84. http://dx.doi.org/10.1017/jfm.2017.386.
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The system composed of a circular cylinder, either fixed or elastically mounted, and immersed in a current linearly sheared in the cross-flow direction, is investigated via numerical simulations. The impact of the shear and associated symmetry breaking are explored over wide ranges of values of the shear parameter (non-dimensional inflow velocity gradient, $\unicode[STIX]{x1D6FD}\in [0,0.4]$) and reduced velocity (inverse of the non-dimensional natural frequency of the oscillator, $U^{\ast }\in [2,14]$), at Reynolds number $Re=100$; $\unicode[STIX]{x1D6FD}$, $U^{\ast }$ and $Re$ are based on the inflow velocity at the centre of the body and on its diameter. In the absence of large-amplitude vibrations and in the fixed body case, three successive regimes are identified. Two unsteady flow regimes develop for $\unicode[STIX]{x1D6FD}\in [0,0.2]$ (regime L) and $\unicode[STIX]{x1D6FD}\in [0.2,0.3]$ (regime H). They differ by the relative influence of the shear, which is found to be limited in regime L. In contrast, the shear leads to a major reconfiguration of the wake (e.g. asymmetric pattern, lower vortex shedding frequency, synchronized oscillation of the saddle point) and a substantial alteration of the fluid forcing in regime H. A steady flow regime (S), characterized by a triangular wake pattern, is uncovered for $\unicode[STIX]{x1D6FD}>0.3$. Free vibrations of large amplitudes arise in a region of the parameter space that encompasses the entire range of $\unicode[STIX]{x1D6FD}$ and a range of $U^{\ast }$ that widens as $\unicode[STIX]{x1D6FD}$ increases; therefore vibrations appear beyond the limit of steady flow in the fixed body case ($\unicode[STIX]{x1D6FD}=0.3$). Three distinct regimes of the flow–structure system are encountered in this region. In all regimes, body motion and flow unsteadiness are synchronized (lock-in condition). For $\unicode[STIX]{x1D6FD}\in [0,0.2]$, in regime VL, the system behaviour remains close to that observed in uniform current. The main impact of the shear concerns the amplification of the in-line response and the transition from figure-eight to ellipsoidal orbits. For $\unicode[STIX]{x1D6FD}\in [0.2,0.4]$, the system exhibits two well-defined regimes: VH1 and VH2 in the lower and higher ranges of $U^{\ast }$, respectively. Even if the wake patterns, close to the asymmetric pattern observed in regime H, are comparable in both regimes, the properties of the vibrations and fluid forces clearly depart. The responses differ by their spectral contents, i.e. sinusoidal versus multi-harmonic, and their amplitudes are much larger in regime VH1, where the in-line responses reach $2$ diameters ($0.03$ diameters in uniform flow) and the cross-flow responses $1.3$ diameters. Aperiodic, intermittent oscillations are found to occur in the transition region between regimes VH1 and VH2; it appears that wake–body synchronization persists in this case.
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Umair Khan, William Pao, Nabihah Sallih, and Farruk Hassan. "Identification of Horizontal Gas-Liquid Two-Phase Flow Regime using Deep Learning." CFD Letters 14, no. 10 (October 28, 2022): 68–78. http://dx.doi.org/10.37934/cfdl.14.10.6878.
Full textAbstract:
Two-phase flow is of great importance in various industrial processes. A characteristic feature of two-phase flow is that it can acquire various spatial distribution of phases to form different flow patterns/regimes. The knowledge of flow regime is very important for quantifying the pressure drop, the stability and safety of two-phase flow systems and it holds great significance in petrochemical and thermonuclear industries today. The objective of this study is to develop a methodology for identification of flow regime using dynamic pressure signals and deep learning techniques. Stratified, slug and annular flow regimes were simulated using a Level-Set (LS) method coupled with Volume of Fluid (VOF) method in a 6 m horizontal pipe with 0.050 m inner diameter. Dynamic pressure signals were collected at a strategic location. These signals were converted to scalograms and used as inputs in deep learning architectures like ResNet-50 and ShuffleNet. Both architectures were effective in classifying different flow regime and recorded testing accuracies of 85.7% and 82.9% respectively. According to our knowledge no similar research has been reported in literature, where various Convolutional Neural Networks are used along with dynamic pressure signals to identify flow regime in horizontal pipe. This research provides a benchmark for future research to use dynamic pressure for identification of two-phase flow regimes. This research provides a benchmark for future research to use dynamic pressure for identification of two-phase flow regimes. This study can be extended by collecting data over broader range of flow parameters and different geometries.
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Boonprasop, Sutthichai, Benjapon Chalermsinsuwan, and Pornpote Piumsomboon. "Circulating turbulent fluidized bed regime on flow regime diagram." Powder Technology 350 (May 2019): 146–53. http://dx.doi.org/10.1016/j.powtec.2019.03.047.
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Bağcı, Özer, Nihad Dukhan, and Mustafa Özdemir. "Various Flow Regimes and Permeabilities for Packed-Spheres Porous Media." Defect and Diffusion Forum 364 (June 2015): 1–8. http://dx.doi.org/10.4028/www.scientific.net/ddf.364.1.
Full textAbstract:
Flow in porous media occurs in many naturally-occurring and engineered systems. One of the key properties for understanding the fluid flow and pressure drop in porous media is permeability, which is varies widely among researchers. The current work presents systematic experimental data for packed spheres of uniform size (3 mm) having a porosity of 36.6% subjected to water flow. The experiments covered a sufficiently broad range of flow Reynolds number such that all flow regimes are encountered: pre-Darcy, Darcy, Forchheimer and Turbulent. The pre-Darcy regime is very scarce or non-present in the literature. As a necessary initial step, flow regimes were identified and different permeabilities exhibited by the porous medium in each flow regime were calculated. The length scales in defining the Reynolds number included the diameter of the sphere and the square root of the various permeabilities in order to study the transitional Reynolds numbers among the flow regimes. It is shown that the permeability in the Darcy regime is most appropriate and produces results consistent with accepted understanding in the literature of porous media.
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Dijker, Thomas, Piet H. L. Bovy, and Raymond G. M. M. Vermijs. "Car-Following Under Congested Conditions: Empirical Findings." Transportation Research Record: Journal of the Transportation Research Board 1644, no. 1 (January 1998): 20–28. http://dx.doi.org/10.3141/1644-03.
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In traffic flow analysis several regimes are distinguished, such as congested and noncongested flow conditions. Indications exist that driving behavior differs by regime and that it may change discontinuously between regimes. In contrast most traffic flow models used today basically assume the same car-following behavior irrespective of the traffic flow regime. It is hypothesized that, because of this deficiency, these models do not always perform satisfactorily. To clarify this issue, differences in car-following between congested and noncongested flow are analyzed with data from two sites on Dutch freeways. It is shown that, at the same speeds, passenger car drivers follow with smaller headways in noncongested than in congested flow. Car-following of truck drivers does not show differences between regimes. Microscopic distance gap-speed models are established for several road-user classes, valid for each of the two flow regimes. To show the improvements resulting from these new microscopic relationships, the latter are implemented in a microscopic simulation model with which macroscopic patterns in traffic flow are modeled. The macroscopic findings produced with the regime-specific car-following rules show a considerable improvement in modeling performance.
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ZAREMBA, LILLIAN J., G. A. LAWRENCE, and R. PIETERS. "Frictional two-layer exchange flow." Journal of Fluid Mechanics 474 (January 10, 2003): 339–54. http://dx.doi.org/10.1017/s0022112002002720.
Full textAbstract:
A numerical model is developed to study the effects of friction on the steady exchange flow that evolves when a barrier is removed from a constriction separating two reservoirs of slightly different densities. The model has excellent agreement with an analytical solution and laboratory measurements of exchange flows through channels of constant width and depth. The model reveals three viscous flow regimes for a convergent–divergent contraction of constant depth, and three additional viscous flow regimes when an offset sill is introduced. Each regime is characterized by a different set of internal hydraulic control locations. Examination of the predicted interface profiles reveals that it is not possible to distinguish between different flow regimes on the basis of these profiles alone.