Flow Regime Research Articles

Investigation of the Influence of Flow Pattern on the Internal Corrosion in Horizontal–Vertical Downward Pipe With Oil–Water Flow

Abstract In the petroleum and petrochemical industries, oil–water flow is widespread inside the pipes. The existence of water often results in internal corrosion in the horizontal–vertical downward pipe when water contacts the pipe wall. Surface wetting behavior and wall shear stress (WSS) are two important factors affecting corrosion procedure, which are governed by the flow patterns. With the propose to mitigate corrosion, focus shall be concentrated on the impact of flow pattern toward corrosion. In this work, the flow regime with oil–water flow in the horizontal–vertical pipe is investigated by computational fluid dynamics simulations. The cases with different mixture velocity (0.1 m/s–2.2 m/s) and different water cut (3%–40%) are investigated. The key discovery in this paper is that five types of flow patterns can be identified based on the multiphase flow in the horizontal–vertical pipe, which is rarely reported in recent work. According to the results of the surface wetting status and wall shear stress distribution, the severe corrosion area is predicted and classified into five types. The inside wall of elbows and the outside wall of vertical pipes are the area's most susceptible to corrosion, and the results are well in line with the on-site data.

Investigation on the rheological properties of dense granular inertial flow based on the contact features of four dual-partitioned subnetworks

The rheological properties of shear granular system under inertial flow regimes are investigated by fully considering both strong/weak and sliding/non-sliding contact features of four dual-partitioned subnetworks. Discrete element simulation results reveal that strong non-sliding subnetwork plays a dominant role in bearing external load. For strong sliding and weak non-sliding subnetworks, their anisotropy principal directions of normal contact forces undergo dynamic deflections during evolution, resulting in the lateral support of microstructures being primarily borne by unstable sliding contacts. Although the subnetworks display substantial variations in stability, their strong spatial correlation makes these variations complement each other, forming an intrinsic coupling relationship.

Assessment of land use/ land cover change derived catchment hydrologic response: An integrated parsimonious hydrological modeling and alteration analysis based approach

Land use/land cover (LULC) change, often a consequence of natural or anthropogenic drivers, plays a decisive role in governing global catchment dynamics, and subsequent impact on regional hydrology. Insight into the complex relationship between the drivers of LULC change and catchment hydrology is of utmost importance to decision makers. Contemplating the dynamic rainfall-runoff response of the Indian catchments, this study proposes an integrated modeling-based approach to identify the drivers and relative contribution to catchment hydrology. The proposed approach was evaluated in the tropical climate Nagavali River Basin (NRB) (9512 km2) of India. The Soil and Water Assessment Tool (SWAT) hydrological model, which uses daily-scale rainfall, temperature, wind speed, relative humidity, solar radiation, and streamflow information was integrated with the Indicators of Hydrologic Alteration (IHA) technique to characterize the plausible changes in the flow regime of the NRB. Subsequently, the Partial Least Squares Regression (PLSR) based modeling analysis was performed to quantify the relative contribution of individual LULC components on the catchment water balance. The outcomes of the study revealed that forest land has been significantly converted to agricultural land (45–59%) across the NRB resulting in mean annual streamflow increase of 3.57 m3/s during the monsoon season. The affinity between land use class and streamflow revealed that barren land (CN = 83–87) exhibits the maximum positive response to streamflow followed by the built-up land (CN = 89–91) and fallow land (CN = 88–93). The period 1985–1995 experienced an increased ET scenario (911–1050 mm), while the recent period (2005–2020) experienced reduced ET scenario owing to conversion of forest to agricultural land. Certainly, the study endorses adopting the developed methodology for understanding the complex land use and catchment-scale hydrologic interactions across global-scales for early watershed management planning.

Inflow Conditions and the Flow Behavior of Submerged Annular Viscoplastic Non-Newtonian Jets

Abstract Submerged annular viscoplastic jet flows were studied numerically within the steady laminar flow regime. The impacts of inner-to-outer annular nozzle diameter ratio, and yield number, for uniform and fully-developed inflow conditions, were investigated. The extent of the outer recirculation region and recirculation intensities of both the central and outer regions were found to substantially diminish with the yield number, resulting in the elimination of recirculation throughout the whole flow field at high yield numbers. The axial penetration of the jet decreases with both the yield number and the annular diameter ratio. The impact of inflow conditions on the flow structure and decay characteristics of the jet are more pronounced at low yield numbers.

High Spatiotemporal Resolution River Networks Mapping on Catchment Scale Using Satellite Remote Sensing Imagery and DEM Data

AbstractCharacterizing and understanding the changes in the flow regimes of rivers have been challenging. Existing global river network data sets are not updated and can only identify rivers wider than 30 m. We propose a novel automated method to map river networks on a monthly basin scale for the first time at 10‐m resolution using Sentinel‐1 Synthetic Aperture Radar, Sentinel‐2 multispectral images, and the AW3D30 Digital Surface Model. This method achieved an overall accuracy of 95.8%. The total length of the Yellow River network produced is 40,280 km, approximately 3.2 times that of the Global River Widths from Landsat (GRWL) database, more effectively covering small and medium rivers. The monthly river geometry revealed a positive correlation between river network area and precipitation. This study is expected to provide a cost‐effective alternative to accurately mapping global river networks and advance our understanding of the changes and drivers of river systems.

Nonlinear ice sheet/liquid interaction in a channel with an obstruction

The interaction between the flow in a channel with an obstruction on the bottom and an elastic sheet representing the ice covering the liquid is considered for the case of steady flow. The mathematical model based on the velocity potential theory and the theory of thin elastic shells fully accounts for the nonlinear boundary conditions at the elastic sheet/liquid interface and on the bottom of the channel. The integral hodograph method is employed to derive the complex velocity potential of the flow, which contains the velocity magnitude at the interface in explicit form. This allows one to formulate the coupled ice/liquid interaction problem and reduce it to a system of nonlinear equations in the unknown magnitude of the velocity at the interface. Case studies are carried out for a semi-circular obstruction on the bottom of the channel. Three flow regimes are studied: a subcritical regime, for which the interface deflection decays upstream and downstream; an ice supercritical and channel subcritical regime, for which two waves of different lengths may exist; and a channel supercritical regime, for which the elastic wave is found to extend downstream to infinity. All these regimes are in full agreement with the dispersion equation. The obtained results demonstrate a strongly nonlinear interaction between the elastic and the gravity wave near the first critical Froude number where their lengths approach each other. The interface shape, the bending moment and the pressure along the interface are presented for wide ranges of the Froude number and the obstruction height.

Numerical study of functional parameters of compact heat exchanger with the corrugated wall in steady state

Compact heat exchangers have several benefits over other types of heat exchangers, including compactness, a high surface area to volume ratio, and a low-temperature differential. They are frequently employed in the heat integrating process. Herein, a compact heat exchanger is simulated in a steady state using the AnsysFluent 17.2 software pack. The flow regime is laminar and water enters the exchanger at a temperature of 298.15 K, assuming a constant wall temperature condition. This study examines the effects of wall wave formation on fluid flow and heat transfer characteristics. The two parameters, wave altitude, and wave angle, are verified and the resultant corrugation is fitted as a sinusoidal function. As the wave height factor increases, the results show that the temperature and velocity values in the solution field climb. More than 4.5% more has been added to the highest temperature value. It is also shown that the velocity values rise with the wave angle coefficient. The greatest rise is 50%. The Performance Ratio is also examined in this study. The findings show that the angle coefficient of 0.5π and π and the altitude coefficient of 0.2 provide values for the Performance Ratio that are higher than the unit.

Water Reserves for the Environment: A Strategic and Temporal Analysis (2012–2022) for the Implementation of Environmental Flows in Mexico

In Mexico, the evaluations of environmental flows are regulated by the Mexican Norm NMX-AA-159-SCFI-2012, and they warrant the establishment of water reserves for the environment. However, the pressure or demand for water use limits the establishment of said reserves because their implementation is generally conditioned to water availability. This research aimed to evaluate the changes through time of the variables that serve as a basis for the implementation strategy by the Mexican government. A geographical information system was built with updated information on water availability, conservation values, and pressures for all basins nationwide. Their desired conservation status was analyzed, and the potential reserves were estimated based on the reference values. The results were examined according to the ranking changes in environmental water reserves enactment feasibility and desired conservation status of Mexican basins, the progress achieved to date, and the potential contribution to the conservation of protected areas and their connectivity if the gaps of reserves were implemented. The outcomes point towards an administrative implementation strategy with positive results despite the growing demand for water use, with a change rate higher than the one for the creation of new protected areas. Currently, basins with low demand and high conservation value have the potential to meet people’s and the environment’s water needs, and contribute to 86% of the goal set by the present administration without affecting water availability. Finally, reserving water in the priority basins would guarantee the legal protection of the flow regime in 48–50% of the hydrographic network (63,760–66,900 km) in a desired conservation status, 43–49% of wetlands of international importance (48,650–49,600 km2) and other protected areas (128,700–136,500 km2) in 85–89% of the global ecoregions represented in Mexico (780,500–852,200 km2).

Brine-water experimental study on the natural ventilation flow rate induced by a localized buoyancy source in an inclined narrow space

Natural ventilation is an energy-saving strategy for diluting indoor contaminants. A series of brine-water experiments are conducted to investigate the mechanisms influencing the ventilation flow rate induced by stratified buoyancy-driven flows in inclined narrow spaces, such as tunnels, corridors and pathways. The results indicate that the flow stratification is determined by source location, tunnel inclination and source buoyancy flux. While Bernoulli’s theorem still can be used to estimate the ventilation flow rate, flow stratification and the buoyant layer thickness should be taken into consideration in such an inclined configuration. The flow is divided into three flow regimes in terms of the mechanisms controlling the flow rate q. A dimensionless parameter η is proposed to categorize the flow regimes. When η < 0.5, the air inflow is mainly induced by plume entrainment and q is approximately equal to that in a horizontal tunnel. When 0.5 < η < 2, q is influenced by the stratification and increases with η. When η > 2, the flow is approximately well-mixed and a constant dimensionless ventilation flow rate is obtained. Models are proposed to estimate q in different flow regimes. The study can be a reference for natural ventilation design in such configurations.

Double-diffusive thermosolutal Hadley–Prats flow: stability analysis

ABSTRACT A mathematical model is formulated to study the onset of double-diffusion fluid flow through an infinite permeable channel with internal heat source and viscous dissipation effects under the influence of convection conditions. Numerically, the dimensionless emerging eigenvalue problem is tackled using the fourth-order Runge–Kutta scheme, specifically applied to longitudinal roll disturbances. Critical values of wave number and vertical thermal Rayleigh number are determined. A higher value of Gebhart number is observed to correlate significantly with the destabilizing phenomena in Hadley–Prats flow. Concentration-based internal heat generation also strongly modifies the critical thermal Rayleigh number. Also, it is found that the horizontal mass flow and viscous dissipation exert a substantial influence on the onset of instability in the flow regime. Linear instability analysis indicates that greater values of Lewis number in the porous medium stabilize the convection process for both values of mass diffusion parameter ( C z ) . Enhancing C z from negative to positive values diminishes the critical thermal Rayleigh ( R z ) value and consequently induces instability in the porous medium. Increased concentration-based internal heat generation generates the destabilization process in the flow region.

Prediction of Bedform Dimensions on Alluvial Bed in Unidirectional Flow

In this study, the bedform dimensions of an alluvial bed in a unidirectional flow were experimentally investigated. A series of flume experiments was conducted; 700 sets of flume and field data were used in developing formulae for predicting the bedform dimensions on alluvial beds in unidirectional flow. Bedform dimensions include the length and height of bedforms generated by the lower and upper flow regimes; the resistance coefficient for the flow in different flow regimes is introduced into the proposed formulae. The momentum boundary-layer thickness was introduced as an independent variable instead of the flow depth. Based on a large amount of flume and field data, the coefficients of each parameter were determined; four typical formulae were used to compare the accuracy of the proposed formulae. The experimental results show that the momentum boundary-layer thickness, hydraulic radius, and resistance coefficient for the flow in different regimes correlate well with the bedform dimensions. The calculation results show that the dimensionless particle size should not be ignored in the calculation of bedform dimensions. The bedform dimensions have an obvious trend of rapid increase with an increase in the ratio of flow depth to sand size (H/d). The bedform dimensions obtained using the van Rijn method and the Engelund and Hansen method did not represent the variation trend of the bedform length in the upper flow regime with an increase in H/d when H/d was greater than 103. The calculations using the proposed formulae are more accurate and reasonable than those in previous studies predicting the bedform height and length on an alluvial bed in a unidirectional flow.

Risk assessment on the impact of Non-Darcy flow on unconventional well performance.

Nano-pores in unconventional reservoirs can cause deviations from Darcy's law where permeability becomes a strong function of pore size and pore pressure. As pores become smaller, the interaction of gas molecules with the pore walls becomes increasingly dominant compared to interactions between gas molecules. This increases gas mobility leading permeabilities measured in the lab not to be accurate at reservoir conditions. Thus, corrections to Darcy flow may be needed when analyzing well production behavior. This paper demonstrates a novel workflow for modeling the impact of non-Darcy flow regimes (i.e., gas slippage, transition flow and Knudsen diffusion) from pore scale characterization to reservoir scale flow simulation. A stochastic approach is used for uncertainty assessment on non-Darcy corrections needed for methane mobility as pore pressure depletes based on reservoir properties, pore sizes, rock compressibility and compaction. Flow simulations are conducted for a range of scenarios to test the impact on the recovery of an unconventional well. Study is conducted using a commercial simulator since workflow modifies the input to the simulator and does not need a new code development. The workflow is demonstrated using field data and shows that non-Darcy flow regimes can have significant impact by increasing gas mobility at low pore pressures near hydraulic fractures. For the field under study, ignoring non-Darcy flow risks up to 20% lower estimations in cumulative gas production under certain scenarios.

New Approaches for Prediction of Flow Regime Boundaries and Overall Gas Holdups in a Bubble Column Operated with Aqueous Solutions of 2-Pentanol

New Approaches for Prediction of Flow Regime Boundaries and Overall Gas Holdups in a Bubble Column Operated with Aqueous Solutions of 2-Pentanol

Pore-scale simulation of low-salinity waterflooding in mixed-wet systems: effect of corner flow, surface heterogeneity and kinetics of wettability alteration

The initial wettability state of the candidate oil reservoirs for low-salinity waterflooding (LSWF) is commonly characterized as mixed-wet. In mixed-wet systems, both the two-phase flow dynamics and the salt transport are significantly influenced by the corner flow of the wetting phase. Thus this study aims at comprehensive evaluation of LSWF efficiency by capturing the effect of corner flow and non-uniform wettability distribution. In this regard, direct numerical simulations under capillary-dominated flow regime were performed using the OpenFOAM Computational Fluid Dynamics toolbox. The results indicate that corner flow results in the transport of low-salinity water ahead of the primary fluid front and triggers a transition in the flow regime from a piston-like to multi-directional displacement. This then makes a substantial difference of 22% in the ultimate oil recovery factors between the 2D and quasi-3D models. Furthermore, the interplay of solute transport through corners and wettability alteration kinetics can lead to a new oil trapping mechanism, not reported in the literature, that diminishes LSWF efficiency. While the findings of this study elucidate that LSWF does exhibit improved oil recovery compared to high-salinity waterflooding, the complicating phenomena in mixed-wet systems can significantly affect the efficiency of this method and make it less successful.

Multiobjective optimization of Vortex Generators for heat transfer enhancement in turbulent flows

Convective heat transfer can be enhanced by streamwise vortices and coherent flow structures produced downstream Vortex Generators (VGs). The thermal performance depends on the VG shape which controls the intensity and topology of the vortices. Thus, VG shape optimization is a major challenge in designing sustainable and efficient heat exchangers. In the present study, a multi-objective optimization is performed through large space exploration design to find optimal VG shapes that adapt to different flow regimes. Simulations are carried out in parallel plate turbulent flow for three different Reynolds numbers; Re1=4600,Re2=9920, and Re3=30050. The present numerical results are first validated against numerical and experimental data from the open literature. Then, and for the first time, seven design parameters are investigated, based on VG shape dimensions. The new optimized VG show a thermal enhancement factor between 11 and 35%, relative to a smooth channel case, and between 3 and 14%, relative to different VG shapes from the recent open literature. The present results are analyzed in details by focusing on the physics of the flow structure and its correlation to the convective heat transfer enhancement using local criteria for flow visualization and vortex intensity quantification.

Numerical Study of Rarefied Gas Flow in Diverging Channels of Finite Length at Various Pressure Ratios

In the present work, the gas flows through diverging channels driven by small, moderate, and large pressure drops are studied, considering a wide range of the gas rarefaction from free molecular limit through transition flow regime up to early slip regime. The analysis is performed using the Shakhov kinetic model, and applying the deterministic DVM method. The complete 4D flow problem is considered by including the upstream and downstream reservoirs. A strong effect of the channel geometry on the flow pattern is shown, with the distributions of the macroscopic quantities differing qualitatively and quantitatively from the straight channel flows. The mass flow rate data set from the complete solution is compared with the corresponding set obtained from the approximate kinetic methodology, which is based on the fully developed mass flow rate data available in the literature. In addition, the use of the end-effect approach significantly improves the applicability range of the approximate kinetic methodology. The influence of the wall temperature on the flow characteristics is also studied and is found to be strong in less-rarefied cases, with the mass flow rate in these cases being a decreasing function of the temperature wall. Overall, the present analysis is expected to be useful in the development and optimization of technological devices in vacuum and aerospace technologies.

Experimental study on the heat flux of transitional shock wave–boundary layer interaction at Mach 6

The shock wave–boundary layer interaction (SWBLI) phenomenon was investigated experimentally to explore the heat flux distribution characteristics of SWBLIs under different boundary layer flow regimes and the influence/mechanism of different transition positions on peak heat flux of SWBLI. Experiments were conducted in a flow of Mach number 6. The shock generator deflected the flow by 20 °, 22 °, 25 ° and 30 ° resulting in an oblique shock impinging on a flat plate. The rough elements with different heights were arranged to achieve different transition positions. The influence of the relative position of transition and interference zone on the peak heat flux and its physical mechanism are revealed. The results demonstrated that the transitional SWBLI has a higher peak heat flux than the turbulent SWBLI, however the overshoot phenomenon is not reflected in the peak pressure. The increment of heat flux peak in transitional SWBLI is related to the relative positions of transition and interference zones. The increment of heat flux peak of transitional SWBLI compared to turbulent SWBLI can reach 25.5–38.9% and 51.9–65.1% when transition approaches the separation zone and reattachment zone, respectively. This overshoot phenomenon is caused by the streamwise vortex in transitional and so-called laminar SWBLIs, which enhances the energy exchange in the boundary layer and leads to an increase in heat flux. However, in the turbulent SWBLI, the energy mixing in the boundary layer is not significantly enhanced due to the breakup of the large scale streamwise vortex into turbulent small-scale structure.

Swing and reverse swing of a cricket ball: laminar separation bubble, secondary vortex and wing-tip-like vortices

Large eddy simulation of flow past a cricket ball with its seam at $30^\circ$ to the free stream is carried out for $5 \times 10^4 \le Re \le 4.5 \times 10^5$ . Three regimes of flow are identified on the basis of the time-averaged swing force coefficient ( $\bar {C}_Z$ ) – no swing (NS), conventional swing (CS, $\bar {C}_Z&gt;0$ ) and reverse swing (RS, $\bar {C}_Z&lt;0$ ). The effect of seam on the boundary layer is investigated. Contrary to the popular belief, the boundary layer does not transition to a turbulent state in the initial stages of CS. The seam energizes the laminar boundary layer and delays its separation. The delay is significantly larger in a region near the poles, whose extent increases with an increase in $Re$ causing $\bar {C}_Z$ to increase. Here $\bar {C}_Z$ assumes a near constant value in the later stage of CS. The boundary layer transitions to a turbulent state via formation of a laminar separation bubble (LSB) in the equatorial region and directly, without a LSB, in the polar region. The extent of the LSB shrinks while the region of direct transition near the poles increases with an increase in $Re$ . A LSB forms on the non-seam side of the ball in the RS regime. A secondary vortex is observed in the wake bubble. While it exists on the non-seam side for the entire range of $Re$ considered, the mixing in the flow introduced by the seam causes it to disappear beyond a certain $Re$ on the seam side. The pressure difference between the seam and non-seam sides sets up wing-tip-like vortices. Their polarity reverses with the switch from the CS to RS regime.

Rheological behavior of particle-filled polymer suspensions and its influence on surface structure of the coated electrodes

Abstract Capacitive deionization electrode prepared by coating was commonly investigated, with polymer solution as binder and active particles as adsorbent. In the coating process, microstructure constituted by the two components was damaged by shear, then rebuilt when shear was removed. The microstructure strongly influenced the surface structure of the coated electrodes, further to performance and cycle life. The discussion of the interaction between the components in the coating process facilitates the identification of structural mechanisms. Rheology bridged the flow regimes in macroscale and interaction in microscale, through which the interaction between the polymer and particles can be investigated in a macroscopic phenomenon. In this study, hydrophilic polymer, poly(vinyl alcohol) (PVA), and poly(ethylene oxide) (PEO) were used as binders to prepare the suspension for coating. The influence of polymer molecular structure to interaction and microstructure was investigated by rheology. Results showed that the flexibility of polymer determined the adsorption morphology, leading to different flocculation structures. For rigid PVA, a 3d-crosslinked network was formed, giving a tough coating. While for flexible PEO, encapsulation structure was formed, leading to a brittle coating. A model based on bridging flocculation was evaluated to describe the formation and destruction of the flocculation structure. And a rheological method for binder selection and coating operation was proposed.

Climate change is poised to alter mountain stream ecosystem processes via organismal phenological shifts

Climate change is affecting the phenology of organisms and ecosystem processes across a wide range of environments. However, the links between organismal and ecosystem process change in complex communities remain uncertain. In snow-dominated watersheds, snowmelt in the spring and early summer, followed by a long low-flow period, characterizes the natural flow regime of streams and rivers. Here, we examined how earlier snowmelt will alter the phenology of mountain stream organisms and ecosystem processes via an outdoor mesocosm experiment in stream channels in the Eastern Sierra Nevada, California. The low-flow treatment, simulating a 3- to 6-wk earlier return to summer baseflow conditions projected under climate change scenarios in the region, increased water temperature and reduced biofilm production to respiration ratios by 32%. Additionally, most of the invertebrate species explaining community change (56% and 67% of the benthic and emergent taxa, respectively), changed in phenology as a consequence of the low-flow treatment. Further, emergent flux pulses of the dominant insect group (Chironomidae) almost doubled in magnitude, benefitting a generalist riparian predator. Changes in both invertebrate community structure (composition) and functioning (production) were mostly fine-scale, and response diversity at the community level stabilized seasonally aggregated responses. Our study illustrates how climate change in vulnerable mountain streams at the rain-to-snow transition is poised to alter the dynamics of stream food webs via fine-scale changes in phenology-leading to novel predator-prey "matches" or "mismatches" even when community structure and ecosystem processes appear stable at the annual scale.