Characterization Of Flow Regimes Research Articles

Impacts of flow regime characterization on selected water quality parameters in Mthatha River catchment

Abstract The effects of altered streamflow types on selected water quality parameters provide useful knowledge and information for prompt water pollution management. This study assesses the impacts of inter- and intra-year seasonal variability in streamflow types on selected water quality parameters. The study uses percentiles, multivariance correlation, and agglomerative hierarchical clustering analysis (AHC) in XLSTAT statistics software to achieve the study aim. Historical dataset for streamflow, rainfall, and selected water quality parameters between 2012 and 2020 for the Mthatha River catchment (MRC), Eastern Cape, South Africa were used to characterize the different seasonal variability impacts with the selected water quality parameters at both the upper and lower reach of the river. The result of the inter and intra-year seasonal variability analyses show that the catchment's flow magnitude varies between 2.0 and 2.7 m3/s in summer while the results of the nonlinear polynomial relationship between the grouped streamflow regime show a coefficient of correlation (R2) values of 0.4264 and 0.5643, suggesting that a mild alteration occurs in the catchment. Decision-makers would find the study useful in controlling the pollutant effluent discharge into the river at different times and maintaining standard effluent requirements as mitigation strategies for sustaining the river ecosystem.

Flow regime identification using fuzzy and neuro-fuzzy inference applied on differential pressure sensor

Intelligent identification of two-phase flow regime is indispensable for the safe design of industrial systems. This work presents the development and examination of intelligent prediction methods based on fuzzy logic designed to operate on a differential pressure sensor signal for two-phase flow regime identification. The effectiveness of intelligent paradigms for flow regime identification is established using experiments carried out in a 0.9 mm circular glass tube kept horizontally. Air and water are the two-phase fluids. Three flow regimes, namely bubbly, slug and annular flows are observed for various combinations of superficial fluid velocities. The pressure drop in the flow system is measured and recorded online using a differential pressure sensor connected to a data acquisition system. Signal features such as peak current, the difference in current and signal frequency are extracted after extensive analysis. Fuzzy rules are outlined and flow regime output is analyzed. The bottleneck observed in these techniques is qualitatively designated in terms of accuracy and required high human effort. A solution to this bottleneck is found out using adaptive neuro-fuzzy inference system (ANFIS). ANFIS applied on pressure sensor signal is found to provide an accurate characterization of flow regime.

Characterisation of Flow Regimes in the Bow Wave of a Surface Piercing Cylinder

Characterisation of Flow Regimes in the Bow Wave of a Surface Piercing Cylinder

Experimental investigation of two-phase flow regimes in rectangular micro-channel with two mixer types

This study primarily aimed to explore the two-phase flow characteristics in a rectangular channel with a hydraulic diameter of 1.33 mm. High-speed video imaging techniques were used to capture two-phase flow behavior corresponding to different superficial gas and liquid velocities. To examine the effect of the gas–liquid mixer configuration on two-phase flow patterns, experiments were conducted using two types of mixers. The results show that the mixer configuration can affect the flow structure only in the slug flow regime. The present study provides a more detailed classification of flow regimes than previous studies. The flow regimes observed were classified into seven categories: slug, aerated-slug, transition, multiple, wavy-annular, smooth-annular, and dispersed-annular flows. Moreover, the quantitative characterization of flow regimes and transition boundaries in micro-channel flows using the standard deviation of differential pressure fluctuations was attempted. This study comprehensively reviews and assesses previous two-phase flow regime maps for both macro-channels and mini/micro-channels. It is shown that the two-phase flow pattern in mini/micro-channels is influenced by various factors, such as the channel hydraulic diameter, the channel cross-sectional shape, the gas–liquid mixer configuration, the difference in the hydraulic diameters between the mixer outlet and test channel, and the thermophysical properties of the working fluids. The comparison between the present experimental data and predictions of the previous flow regime maps demonstrates the necessity of developing a new flow regime map to accurately predict two-phase flow regimes in micro-channels.

Flow regime characterization of a silicon-based vaporizing liquid microthruster

The present work discusses an experimental investigation of the flow into a silicon-based vaporizing liquid microthruster equipped with sensing capabilities and low-power on-channel secondary heaters. The sensing capabilities (resistance temperature detectors and capacitive void fraction sensors) are used to investigate the flow instability and to evaluate its performances. The device has a sandwich structure composed of a silicon substrate and a glass substrate. This last one allows optical access into the device. The main heating of the propellant is provided using a platinum resistive heater placed on the bottom of the silicon layer. By varying the electrical power supplied to the main heater at fixed mass flow rate, three flow regimes have been observed and investigated: fully liquid flow, two-phase flow, and fully vaporized flow. Their dynamics have been captured through high-speed micro-flow visualizations under rough vacuum conditions (about 29 kPa). Furthermore, the expansion of the exhaust vapor plume exiting from the micronozzle has been analyzed via Schlieren visualizations. Results highlighted the occurrence of a cyclic flow behavior during the two-phase flow regime. In contrast, the flow exhibits the presence of both liquid and vapor phases at the micronozzle exit. Once the fully vaporized flow regime is established, the two-phase flow dynamics into the inlet chamber become more stable with complete filling and more uniform distribution of the flow at the microchannels entrance. Schlieren imaging captured the increase of the exhaust plume spreading half-angle when moving from ambient condition towards rough vacuum.

Holdup Measurements of Aqueous Foam Flows and Flow Regime Characterization through Image Processing

Summary One of the most critical issues in the oil and gas industry is the dewatering of the pipelines used for natural gas transportation, and foam injection seems to be a prominent solution. This work has two goals: The main one concerns the development of an optical tool to measure the liquid holdup in foamy flows and perform the flow regime characterization, whereas the secondary goal is to quantify the effectiveness of surfactant injection in reducing the liquid loading. In this paper, we present the results of an experimental campaign aimed at the characterization of gas-liquid-foam flows in a horizontal pipe. Initially, liquid loading measurements for gas and liquid superficial velocities, ranging from 0.41 to 2.30 m/s and from 0.03 to 0.06 m/s, respectively, were performed by means of a specifically developed optical method. For each liquid superficial velocity, the minimum liquid holdup was found to lie in the proximity of the boundary between plug and stratified flow regime, with a superficial gas velocity between 0.44 and 0.90 m/s. Hence, the plug flow region corresponds to the best operating condition to perform the pipeline dewatering procedure. Moreover, the drift-flux model usually adopted for ordinary two-phase gas-liquid flows seems to fit well with the measured values of void fraction.

Multiphase Flow Regime Characterization and Liquid Flow Measurement Using Low-Field Magnetic Resonance Imaging.

Multiphase flow metering with operationally robust, low-cost real-time systems that provide accuracy across a broad range of produced volumes and fluid properties, is a requirement across a range of process industries, particularly those concerning petroleum. Especially the wide variety of multiphase flow profiles that can be encountered in the field provides challenges in terms of metering accuracy. Recently, low-field magnetic resonance (MR) measurement technology has been introduced as a feasible solution for the petroleum industry. In this work, we study two phase air-water horizontal flows using MR technology. We show that low-field MR technology applied to multiphase flow has the capability to measure the instantaneous liquid holdup and liquid flow velocity using a constant gradient low flip angle CPMG (LFA-CPMG) pulse sequence. LFA-CPMG allows representative sampling of the correlations between liquid holdup and liquid flow velocity, which allows multiphase flow profiles to be characterized. Flow measurements based on this method allow liquid flow rate determination with an accuracy that is independent of the multiphase flow profile observed in horizontal pipe flow for a wide dynamic range in terms of the average gas and liquid flow rates.

Classification and Prediction of Natural Streamflow Regimes in Arid Regions of the USA

Understanding how natural variation in flow regimes influences stream ecosystem structure and function is critical to the development of effective stream management policies. Spatial variation in flow regimes among streams is reasonably well understood for streams in mesic regions, but a more robust characterization of flow regimes in arid regions is needed, especially to support biological monitoring and assessment programs. In this paper, we used long-term (41 years) records of mean daily streamflow from 287 stream reaches in the arid and semi-arid western USA to develop and compare several alternative flow-regime classifications. We also evaluated how accurately we could predict the flow-regime classes of ungauged reaches. Over the 41-year record examined (water years 1972–2013), the gauged reaches varied continuously from always having flow > zero to seldom having flow. We predicted ephemeral and perennial reaches with less error than reaches with an intermediate number of zero-flow days or years. We illustrate application of our approach by predicting the flow-regime classes at ungauged reaches in Arizona, USA. Maps based on these predictions were generally consistent with qualitative expectations of how flow regimes vary spatially across Arizona. These results represent a promising step toward more effective assessment and management of streams in arid regions.

Characterization of R134a two-phase flow regimes in horizontal and vertical smooth tubes with capacitive sensors

This paper presents the identification of slug/stratified-wavy, stratified-wavy and annular regimes for horizontal flow (in the range of mass fluxes 40 – 150 kg m−2 s−1), and slug, churn, and annular flow regimes for vertical upward flow (in the range 65 – 115 kg m−2 s−1) for R134a flow through 7 mm ID tube. Flow regimes are characterized based on time plot of normalized capacitive signals, kernel density estimation (KDE), power spectral density (PSD), and visualization results from a high-speed camera. Sensors with different axial lengths (D, 2D/3, and D/2) are also tested to study the adequacy of shorter sensors for the characterization of flow regimes. Results show that all three sensors have a similar capability of characterizing flow regimes, justifying the use of the shorter sensors in many applications with limited space.

Multi-index summer flow regime characterization to inform environmental flow contexts: A New England case study

Abstract Summer flow regime is an important determinant of the health and integrity of riverine ecosystems. In particular, summertime low flows and the range of variability impact the extent and connectivity of habitat, production in and composition of ecosystems, as well as water quality. Four streamflow-based metrics are used in the analysis and assessment of summertime hydrologic variability and trends: Lane Index, UK Institute of Hydrology Index, Base Flow Index, and 7-day Minimum Flow Index. In this study, historical streamflow records at 33 locations in New England (USA) were analyzed to understand the nature of trends as well as the extent of changes, individually and collectively, for the four indices. The main contribution of this paper is to develop a comprehensive characterization of the regional flow regime and trends therein. Two complementary statistical analyses applied in this study are: (a) quantile regression-based estimates of the spatial and temporal patterns of changes in flow indices variability over the past six decades and (b) interrelationship between flow indices based on non-parametric probability density estimation approach. The multi-index regional analysis revealed that flow variability (based on the Lane Index) within the summer season has increased significantly, with 25 out of the 33 streamgages showing increases, of which 12 are highly significant. Similar trends are mirrored in the UK Institute of Hydrology Index based analysis. Base Flow Index trends show decreases across 30 of the 33 streamgages at the median level, and 19 are highly significant. Trends are most pronounced at the upper quartile level, with 21 highly significant. Regional analysis of 7-day Minimum Flow Index reveal broad patterns towards increases at the three selected quantile levels ( τ = 0.25 , 0.5 , 0.75 ) with 29, 22, and 19 streamgages showing increases, of which 13, 10, and 6 are highly significant respectively. There is also diversity in trends across quantiles, wherein 17 locations show increases at all quantile levels, while 22 stations showed increases at the median level. The analysis of interrelationships between the four indices revealed inverse variations between Lane Index and 7-day Minimum Flow, and also a diversity of relationships ranging from weakly to strongly nonlinear. As such, our analysis underscores the importance of the use of multiple indices to fully assess variability and change of relevance to management and policy concerns, such as Maine’s water allocation rulemaking.

Experimental Study of the Two-Phase Flow Patterns of Air-Water Mixture at Vertical Bend Inlet and Outlet

Air-water two-phase flow in pipes introduces a noticeable challenge due to the complexity of the fluids. Thus, to estimate the best design and reasonable financing cost of the transportation pipelines where the bends are presenting a part of their accessories, the investigators should have been able to estimate the flow regime occurring at different directions. An experiment was carried out by using a 90o bend fixed with two pipes where the flow was upstream from a vertical to a horizontal pipe which were representing the bend inlet and outlet respectively. Two wire-mesh sensors were used for obtaining the data of the void fractions (α) at water superficial velocities (Usl) which changed from 0.052 to 0.419m/s, and air superficial velocities (Usg) from 0.05 to 4.7m/s. Furthermore, the characterization of flow regimes of the air-water flow at both bend inlet and outlet were competed accurately by using void fraction analysis of the time series, Power Spectral Density (PSD), tomographic images observed by the sensor program, and the Probability Density Function (PDF) method. The flow regimes of vertical flow lines at the bend inlet were observed as bubbly, cap-bubble, slug, and churn flow, whereas the flow regimes of the horizontal flow line at the bend outlet were characterized as having stratified, stratified wavy, bubbly, plug, slug, wavy annular, and semi-annular flow due to the gravity and bend effects.

Uncertainty of modelled flow regime for flow-ecological assessment in Southern Europe

Sustainable water basin management requires characterization of flow regime in river networks impacted by anthropogenic pressures. Flow regime in ungauged catchments under current, future, or natural conditions can be assessed with hydrological models. Developing hydrological models is, however, resource demanding such that decision makers might revert to models that have been developed for other purposes and are made available to them (‘off-the-shelf’ models). In this study, the impact of epistemic uncertainty of flow regime indicators on flow-ecological assessment was assessed at selected stations with drainage areas ranging from about 400 to almost 90,000km2 in four South European basins (Adige, Ebro, Evrotas and Sava). For each basin, at least two models were employed. Models differed in structure, data input, spatio-temporal resolution, and calibration strategy, reflecting the variety of conditions and purposes for which they were initially developed. The uncertainty of modelled flow regime was assessed by comparing the modelled hydrologic indicators of magnitude, timing, duration, frequency and rate of change to those obtained from observed flow. The results showed that modelled flow magnitude indicators at medium and high flows were generally reliable, whereas indicators for flow timing, duration, and rate of change were affected by large uncertainties, with correlation coefficients mostly below 0.50. These findings mirror uncertainty in flow regime indicators assessed with other methods, including from measured streamflow. The large indicator uncertainty may significantly affect assessment of ecological status in freshwater systems, particularly in ungauged catchments. Finally, flow-ecological assessments proved very sensitive to reference flow regime (i.e., without anthropogenic pressures). Model simulations could not adequately capture flow regime in the reference sites comprised in this study. The lack of reliable reference conditions may seriously hamper flow-ecological assessments. This study shows the pressing need for improving assessment of natural flow regime at pan-European scale.

Characterization of flow regimes in fluidized beds by information entropy analysis of pressure fluctuations

Flow regimes in a gas‐solid cylindrical fluidized bed of 150 mm (i.d.) × 1.2 m (high) with three different sand masses (1.5, 3, and 4.5 kg) were studied via information entropy analysis of pressure fluctuations. Three classes of methods of information entropy were adopted to characterize the flow regimes. It is shown that the first‐class dimensional methods are suitable for illustrating the distinct characteristic of the flow regimes under different operating conditions, while the other two dimensionless methods are appropriate for finding the similarities or common rules. Tsallis entropy and Renyi entropy do not provide more valuable information than Shannon entropy. Most importantly, the Shannon entropy method is a good choice for characterizing the flow regimes but is weak at revealing the transition velocity (Uc) clearly. This deficiency can be made up by the method of component Shannon entropy. Shannon entropy is partitioned into 4 component Shannon entropies (named CH1CH4), which may be related with a 4‐stage fluidization process assumption. A rule is found that the transition of flow regimes transition from bubbling bed to turbulent bed takes place when the contribution proportion of CH3 is exceeded by that of CH1, and it brings new enlightenment on interpretation of the transition mechanism.

Nonintrusive Optical Validation of Two-Phase Flow Regimes in a Small-Diameter Tube

While the majority of studies examining the relationship between flow regime and thermofluid performance rely on subjective flow regime determination, objective techniques are needed to more firmly establish the nature and repeatability of these phenomena. This study describes a nonintrusive optical flow regime characterization methodology used to study horizontal, adiabatic, two-phase flow of water–water vapor and water–nitrogen gas in small (8.84 mm) diameter tubes. The method relies on shining a fiber-optic light source through the top of a borosilicate glass tube at the outlet of a smooth copper tube, using a CMOS camera to capture light rings resulting from total internal reflection at the liquid–vapor interface, and extracting a film thickness profile from successive images. Using these unique temporally varying film profiles, quantitative identification measures were developed for the primary flow regimes, including the ability to explain and quantify the more subtle transitions that exist between dominant regimes as the two-phase flows progress from saturated liquid to qualities of 0.32. Application of this methodology has shown the Taitel–Dukler, Ullmann–Brauner, and Wojtan et al. phenomenological flow regime maps to capture the salient features and transition boundaries, with varying accuracy, for small-diameter two-phase flow in a mass flux range of 15 to 230 kg/m2-s.

Numerical analysis of granular flows in a silo bed on flow regime characterization.

The flow characteristics of a gravity-driven dense granular flow in a granular bed with a contracted drainage orifice are studied by using discrete element method and quantitative analysis. Three values of discharging rates, ranging from fast to slow dense flows, are investigated. Time variations and derivatives of mean forces and velocities, as well as their respective correlations, are analyzed to quantitatively depict the characteristics of granular flow as well as flow regime categorization. The auto-correlation functions, as well as their Fourier spectrums, are utilized to characterize the differences between the mechanisms of slow and fast granular flows. Finally, it is suggested that the flow regimes of slow and fast flows can be characterized by the kinetic and kinematic flow properties of particles.

CFD characterization of flow regimes inside open cell foam substrates

In this work a combination of micro-CT, image-based modeling and CFD has been applied to investigate the pressure drop in open-cell foams. The analysis covers a range of flow regimes and is aimed at determining the effects of important morphological parameters on the pressure drop. The adoption of micro-CT technology along with detailed CFD modeling allows the investigation of phenomena occurring in real foam micro-structures. Moreover, by means of image processing tools, the geometry can be artificially modified in order to investigate the effects of mathematical transformation of the geometrical parameters of a real foam, one parameter at a time, e.g. varying pore size without affecting the porosity. Non-dimensional coefficients have been defined for the analysis of the results, with the purpose of describing the pressure drop as a function of the Reynolds number. The proposed formulation allows us to relate the permeability properties of an open-cell foam to its morphology alone, without any dependence on the properties of the fluid adopted or on the effective characteristic dimension of the foam micro-structure (pore or cell size). Comparison with experimental results available in the literature is also provided for one of the cases studied.

A statistical, parsimonious, empirical framework for regional flow duration curve shape prediction in high permeability Mediterranean region

Summary The flow duration curve (FDC) can provide information about the integral catchment response to rainfall events that span from low volume events to events of flood magnitude, and the FDC is particularly useful for low flow regime characterization. The focus of this study was to introduce a statistical, parsimonious approach with a conceptually based parameterization that can lead to simple and practical tools for FDC predictions that can be applied to contexts, such as the Mediterranean climate, that involve scarce data and regional geological and hydro-geological features that strongly affect low-flow hydrological regimes. At-site, dimensionless, empirical FDCs were represented with three-parameter log normal distributions, the variations in the corresponding parameters versus the base flow index (BFI) were explored, and the conceptual relationship of these parameters is further discussed. In cases of ungauged catchments for which the BFI is not known, a priori estimates of such indices can be derived from permeability indices, as BFIs are strongly related to permeability indices in the studied region ( Longobardi and Villani, 2008 ). For moderate to large permeability catchments, which represent the largest fraction of the investigated catchments, prediction errors associated with the proposed regional method of FDC assessment, which is particularly suited for regions for which only scarce or poor data are available, averaged approximately 18%.

Flow Regime Characterization of the Gas-assisted Gravity Drainage Process

Flow regime characterization is helpful in designing efficient gas injection programs in commercial floods. Lenormand et al.'s (1988) phase-diagram is commonly used for flow regime identification of gravity drainage. Lenormand's phase-diagram was developed using horizontal micro-model displacement experiments, whereas the gas-assisted gravity drainage process is vertical displacement, so Lenormand et al.'s plot is not applicable for gas-assisted gravity drainage floods. Inspection of the recovery plots against dimensionless numbers and physical interpretation of dimensionless groups guide flow regime identification. Oil recovery of the gas-assisted gravity drainage process was calculated by using a black oil simulator at different injection rates and aspect ratios. Flow regime of the gas-assisted gravity drainage process was developed based on gravity number and capillary number at different aspect ratios.

Identifying natural flow regimes using fish communities

Summary Modern water resources management has adopted natural flow regimes as reasonable targets for river restoration and conservation. The characterization of a natural flow regime begins with the development of hydrologic statistics from flow records. However, little guidance exists for defining the period of record needed for regime determination. In Taiwan, the Taiwan Eco-hydrological Indicator System (TEIS), a group of hydrologic statistics selected for fisheries relevance, is being used to evaluate ecological flows. The TEIS consists of a group of hydrologic statistics selected to characterize the relationships between flow and the life history of indigenous species. Using the TEIS and biosurvey data for Taiwan, this paper identifies the length of hydrologic record sufficient for natural flow regime characterization. To define the ecological hydrology of fish communities, this study connected hydrologic statistics to fish communities by using methods to define antecedent conditions that influence existing community composition. A moving average method was applied to TEIS statistics to reflect the effects of antecedent flow condition and a point-biserial correlation method was used to relate fisheries collections with TEIS statistics. The resulting fish species–TEIS (FISH–TEIS) hydrologic statistics matrix takes full advantage of historical flows and fisheries data. The analysis indicates that, in the watersheds analyzed, averaging TEIS statistics for the present year and 3 years prior to the sampling date, termed MA(4), is sufficient to develop a natural flow regime. This result suggests that flow regimes based on hydrologic statistics for the period of record can be replaced by regimes developed for sampled fish communities.

Flow Regime Characterization in a Diseased Artery Model

Cardiovascular disease mostly in the form of atherosclerosis is responsible for 30% of all world deaths amounting to 17 million people per year. Atherosclerosis is due to the formation of plaque. The fatty plaque may be at risk of rupture, leading typically to stroke and heart attack. The plaque is usually associated with a high degree of lumen reduction, called a stenosis. The initiation and progression of the disease is strongly linked to the hemodynamic environment near the vessel wall. The aim of this study is to validate the flow of blood mimic through an arterial stenosis model with computational fluid dynamics (CFD) package. In experiment, an axisymmetric model constructed consists of contraction and expansion region that follow a mathematical form of cosine function. A 30% diameter reduction was used in this study. Particle image velocimetry (PIV) was used to characterize the flow. The fluid consists of rigid spherical particles suspended in water- glycerol-NaCl mixture. The particles with 20 μm diameter were selected to follow the flow of fluid. The flow at Re=155, 270 and 390 were investigated. The experimental result is compared with FLUENT simulated flow that account for viscous laminar flow model. The results suggest that laminar flow model was sufficient to predict flow velocity at the inlet but the velocity at stenosis throat at Re =390 was overestimated. Hence, a transition to turbulent regime might have been developed at throat region as the flow rate increases. Keywords—Atherosclerosis; Particle-laden flow; Particle image velocimetry; Stenosis artery