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Effective length of swirl flow is important for its application in the industry, however, the length of the swirl flow in a horizontal pipe is largely unexplored. In this article, effects of swirl on a horizontal bubbly flow and its development in a 25 mm horizontal pipe with a length of 4 m were studied by an experimental and theoretical method. In the experiments, the superficial gas velocities ranged from 0.068 to 0.566 m/s and the liquid velocities ranged from 0.283 to 1.132 m/s. The results show that: instead of dispersed bubbles in the non-swirl bubbly flow, a gas column flow is transformed downstream of the swirler; then, it breaks up into separated gas slugs, and finally, transforms to a non-swirl bubble flow. The pressure drop in the swirl flow gradually decreases and approximates to that in the non-swirl flow along the streamwise direction. The transition mechanism for the gas column flow was proposed here, and the transition criteria of the gas column flow were developed based on Kelvin–Helmholtz instability, then, the effective length of swirl on the gas column flow can be predicted. [ABSTRACT FROM AUTHOR]

Understanding solute transport in pipe flows is essential for ensuring consistent water quality throughout the entire drinking water supply network. This study used four planar laser-induced fluorescence (PLIF) units for the first time to quantify the cross-sectional concentration distribution resulting from a single pulse of tracer injected at an upstream location under both steady and accelerating flow conditions. Compared with conventional fluorometers, PLIF provides a better measure of the cross-sectional mean concentrations because it allows the cross-sectional distribution of the tracer to be quantified. Under steady turbulent flow conditions, the tracer was cross-sectionally well-mixed, and the concentration uniformity increased with increasing Reynolds number. In laminar flows, as a result of minimal radial mixing, the tracer exhibited a spatial distribution created by the longitudinal differential advection, transforming from a central core to an annulus, which expanded toward the pipe boundary. Under accelerating flows, the temporal concentration profiles displayed two peaks and the tracer close to the source was not cross-sectionally well-mixed. With increasing discharge, the tracer became cross-sectionally well-mixed while retaining the two peak profiles. These results have implications for water quality modeling in unsteady conditions, especially in domestic plumbing, when boundary and biofilm interactions control important processes. [ABSTRACT FROM AUTHOR]

Vehicle loads and differential ground movements can induce tensile strains in close-fitting polymer liners installed within gravity flow pipes, where the liner stretches across ring fractures or joints experiencing rotation (i.e., opening of the joint at the invert if the joint is moving down relative to the other ends of the pipe segments, or at the crown if the joint is moving upward compared with the other ends). A finite-element model is established and suitable pipe length and mesh size are determined. The stress and strain distributions along hoop and axial directions are then evaluated, considering factors such as inside diameter of the host pipe, liner thickness, rotation angle, liner elastic modulus, friction coefficient between the liner and host pipe, and Poisson's ratio of the liner. After that, curve fitting is used to develop design equations for estimating stress and strain, and their performance is evaluated against the finite-element data. Finally, the potential effects of gravity and buoyancy are investigated. For small rotations, the stress is proportional to strain, and the maximum stress of the liner occurs directly at the joint, at the point where joint opening is greatest. The friction coefficient and liner thickness have a small effect on the maximum stress, so this simplifies consideration of this limit state in design. The design equation for stress provides estimates within 8.6% of those obtained from the three-dimensional finite-element analysis (with R2 between 0.992 and 0.993). Subsequent evaluation of the proposed equation using strain measurements obtained from full-scale experiments is recommended. [ABSTRACT FROM AUTHOR]

It is important to control turbulence in industrial processes. Past experimental and numerical researches have shown that a turbulent puff in pipe flow can be removed or delayed by flattening the profile of the upstream velocity because a flattened velocity profile causes the point of inflection on it to collapse. The energy gradient theory has been developed to study turbulent transition, and the relevant studies have shown that turbulence arises due to the generation of singularities in the flow field. In pressure-driven flows like the pipe flow, the point of inflection on the velocity profile leads to the appearance of a singular point in the unsteady Navier–Stokes equation. In this study, the energy gradient theory is used to demonstrate why the point of inflection on the profile of velocity of pipe flow is the critical point for generating turbulence. Then, it is shown how flattening the velocity profile leads to the elimination of the point of inflection on the velocity profile of pipe flows to delay turbulent transition. It is also clarified why this technique is not effective at higher Reynolds number because the flattened velocity profile violates the criterion for flow stability relating to transition to turbulence. [ABSTRACT FROM AUTHOR]

A gas pressure distribution calculation method for viscous laminar and intermediate flows is developed. By introducing the pseudo-conductance for viscous laminar flow, linearized equations describing pressure distribution are obtained. In intermediate flow, the pressure distribution is iteratively obtained. The validity of the method is confirmed by demonstrating a pressure in a long-tube flow path with various flow rates. The result smoothly connects theoretical curves of molecular flow and viscous laminar flow between two regions. Then, the calculation method is applied to an actual device and is compared to the measurement. The comparison between the calculation and measurement shows the qualitative agreement and reveals the requirement for a more detailed implementation of the actual conditions. [ABSTRACT FROM AUTHOR]

In order to study the changes in two‐phase flow parameters after pipeline damage and the impact of gas injection on water leakage from damaged pipelines, experimental and simulation studies were conducted on the damaged pipelines. The main objective is to compare the void fraction in intact and damaged states and to investigate the factors influencing and variations in gas–liquid leakage flow rates. The results show that increasing the liquid superficial velocity can reduce the difference in void fraction distribution caused by different damage directions. The leakage flow rate is affected by the direction of damage and the superficial velocity of the respective phase. It has been discovered that gas injection in the pipeline can make it easier to find small‐area pipeline damage. The change rate of the volume void fraction shows different changes with the increase in gas proportion in different directions; the shape of the bubble has no bearing on this change. [ABSTRACT FROM AUTHOR]

Terrestrial shale oil resources in China are abundant. However, its development in China is still in the early stages. And its scale of transformation and production systems is still being explored. Currently, reservoir numerical simulation on shale oil reservoirs faces two main challenges: (1) multiscale flow of matrix–microfracture–hydraulic fractures in shale oil reservoirs and (2) bidirectional coupling of reservoir–wellbore–nozzle systems. This paper proposes a self‐flow model for horizontal shale wells that describes multiscale fractures and production controlled by the nozzle. The model integrates the embedded discrete fracture model (EDFM), pipe flow model, and nozzle flow model. The accuracy of the model has been validated through comparisons with other reference models and field data. Then, this study analyzes the effects of different natural fracture densities, horizontal section lengths, number of fracturing stages, and nozzle diameters on the production capacity during the self‐flow period. The results indicate that reservoirs with developed natural fractures can enhance the development efficiency during the self‐flow period, and appropriate horizontal section lengths and fracturing stages contribute to achieving maximum economic benefits in development. Additionally, smaller nozzle diameters lead to longer self‐flow periods and higher cumulative production. The research findings of this paper can be applied to simulate the production of hydraulic fractured horizontal shale wells. [ABSTRACT FROM AUTHOR]

A turbulent pipe flow experiment was conducted where the surface of the pipe was oscillated azimuthally over a wide range of frequencies, amplitudes, and Reynolds numbers. The drag was reduced by as much as 35%. Past work has suggested that the drag reduction scales with the velocity amplitude of the motion, its period, and/or the Reynolds number. Here, we find that the key parameter is the acceleration, which greatly simplifies the complexity of the phenomenon. This result is shown to apply to channel flows with spanwise surface oscillation as well. This insight opens potential avenues for reducing fuel consumption by large vehicles and for reducing energy costs in large piping systems. [ABSTRACT FROM AUTHOR]

This paper considers the double diffusive Brinkman flow in a semi-infinite pipe. By establishing a priori estimates of the solutions and setting an appropriate "energy" function, we not only obtain the continuous dependence and convergence of the solution on the Soret coefficient but also prove that the solutions decay exponentially with the distance from the finite end of the cylinder. [ABSTRACT FROM AUTHOR]

The article delves into the analysis of large-scale coherent structures in turbulent pipe flows at different Reynolds numbers. By utilizing the Karhunen-Loève decomposition and a unique Voronoi diagram method, the research identifies two categories of structures - wall-attached and detached eddies - based on their characteristics and energy contributions. The study demonstrates that as the Reynolds number increases, the energy distribution of these structures changes, with attached eddies scaling linearly with the wall-normal distance while detached eddies maintain a consistent size. This research sheds light on the spatial distribution of these structures, potentially aiding in understanding the variations in mean velocity between pipe and channel flows and enhancing the modeling of large-scale motions. [Extracted from the article]

The flow within different cross sections of T-shaped pipes is analyzed using experimental measurements using particle image velocimetry technology and simulation modeling at different fluid velocities and outlet diameters. The study shows that the flow within the pipes predominantly exhibits multiple vortex patterns, with the evolution of the vortex patterns at different cross sections showing similar patterns and some degree of periodicity. It is also found that as the pipe diameter increases, the flow pattern in the main pipeline is relatively stable, although vortices form on the underside of the outlet pipe walls. Conversely, if the pipe diameter is smaller, vortices will not form within the outlet pipe, and the vortex patterns within the blind pipe will be unstable. In particular, as the velocity increases and the diameter of the outlet pipe decreases, the period of the vortex oscillation shortens. The research establishes a numerical equation relating the dominant frequency of vortex oscillations to the velocity and outlet pipe diameter, further demonstrating the mathematical relationship between the three in the outlet pipe. [ABSTRACT FROM AUTHOR]

Flow-induced vibrations (FIVs) pose challenges and limit intended functionalities in many industrial sectors, especially in high-tech industries such as semiconductor manufacturing. Because of extreme precision requirements, any mechanical perturbation to the manufacturing process detrimentally affects production quality and process yield. The impact of FIV must, thus, be minimized. This study investigates the FIV reducing properties of triply periodic minimal surface (TPMS) inserts in industrial cooling systems by expanding the Darcy–Forchheimer model for flow through porous media to a turbulent regime. Using the expanded model, we performed full-scale finite-element simulations for high-speed flows in a pipe with an abrupt expansion of diameter and analyzed the effects of TPMS inserts on the reduction of induced turbulence and FIV. Our data revealed that the TPMS inserts exhibit promising characteristics for FIV mitigation revealing up to 97.6% reduction in turbulent kinetic energy and 32.7% reduction in vorticity. These results complement available data on using TPMS inserts to eliminate geometry-induced instabilities in internal pipe flows. [ABSTRACT FROM AUTHOR]

The classical Jeffery–Hamel flow at small wall convergence has received less attention than it should and is the subject here. While laminar flow through a plane channel displays only a parabolic velocity profile, for even small convergence angles, the Jeffery–Hamel equations display a variety of non-unique laminar flow solutions at a given Reynolds number. Three such solutions are shown to be stable at low Reynolds number and could possibly be attained in the experiment. Multiple critical layers can occur, and dissipation need not attain a maximum at the wall. In the one-lobed velocity profile, the critical Reynolds number for the first instability is known [K. Fujimura, J. Phys. Soc. Jpn. 51, 2000–2009 (1982); M. R. Jotkar and R. Govindarajan, Phys. Fluids 29, 064107 (2017)] to be an extremely sensitive function of the wall tilt angle, and we show that this is because the dominant balance in the critical layer is different from the traditional one in a plane channel. Finally, a direct analogy to divergent pipe flow is drawn. [ABSTRACT FROM AUTHOR]

Accurately identifying the onset of transitional and turbulent flow within any pipe flow environment is of great interest. Most often, the critical Reynolds number (Re) is used to pinpoint the onset of turbulence. However, the critical Re is known to be highly variable, depending on the specifics of the flow system. Thus, for flows (e.g., blood flows), where only one realization (i.e., one mean Re) exists, the presence of transitional and turbulent flow behaviors cannot be accurately determined. In this work, we aim to address this by evaluating the extent to which instantaneous time-frequency (TF)-based analysis of the fluctuating velocity field can be used to evaluate the onset of transitional and turbulent flow regimes. Because current TF analysis methods are not suitable for this, we propose a novel "wavelet-Hilbert time-frequency" (WHTF) method, which we validate herein. Using the WHTF method, we analyzed the instantaneous dominant frequency of three planar particle image velocimetry-captured pipe flows, which included one steady and two pulsatile with Womersley numbers of 4 and 12. For each case, data were captured at Re's spanning 800–4500. The instantaneous dominant frequency analysis of these flows revealed that the magnitude, size, and coherence of two-dimensional spatial frequency structures were uniquely different across flow regimes. Specifically, the transitional regime maintained the most coherent, but lowest magnitude frequency structures, while the laminar regime had the highest magnitude, lowest coherence, and smallest frequency structures. Overall, this study demonstrates the efficacy of TF-based metrics for characterizing the progression of transition and turbulent flow development. [ABSTRACT FROM AUTHOR]

We have recently demonstrated a magnetic resonance method using variable τ spin echoes to simultaneously determine both the average velocity and flow behavior index in a variety of pipe flows. In this work, we present a new, modular, low-field design built specifically for use with our methodology. The design is based on low-cost ceramic magnets. It consists of a sensor built using a pitched magnet arrangement in combination with several modular pre-polarizing units to facilitate a controlled pre-polarization length for measurements on flows that require a significant amount of time in a magnetic field to become polarized (e.g., aqueous solutions). Here, measurements made with this design are shown for a range of flow rates that span the laminar regime and into the turbulent regime. [ABSTRACT FROM AUTHOR]

Swirling flows are extensively used to enhance mixing in chemical and physical processes. Although many fundamental studies involve decaying laminar swirls in circular ducts with constant area—for which several theoretical descriptions exist—converging and diverging pipe sections are often employed, demanding the extension of the analysis to swirling laminar flows in pipes with varying areas. This work analytically investigates axial swirl decay in laminar axisymmetric flows in converging and diverging pipes at moderate Reynolds numbers. The theoretical model extends the classical theory for laminar low swirling flows in straight pipes with impermeable walls to pipes with slowly varying areas. Inlet Reynolds number and converging/diverging angle effects are analyzed for incompressible axisymmetric laminar flows in slender pipes (lengths much greater than the radius). Results show that diverging pipes enhance the swirl decay rate, whereas converging systems have a weakening effect for flows with the same inlet Reynolds number. Conversely, increasing the inlet angle in converging flows decreases the decay rate, whereas larger diverging pipe inlet angles promote swirl decay. A simplified eigenvalue analysis shows that the relationship between the swirl decay lengths in diverging ( ℓ d , div ), straight ( ℓ d , st ), and converging ( ℓ d , conv ) pipes is given by ℓ d , div < ℓ d , st < ℓ d , conv for flows with similar inlet Reynolds numbers. Comparisons with numerical simulations show that the model predictions are almost exact for nondimensional pipe lengths up to 5 × 10 − 2 times the inlet Reynolds number. Approximating the axial velocity profile through a fully developed function representative of laminar flows with heat transfer through the walls shows that the narrower axial velocity profile in diverging flows increases viscous effects, enhancing the swirl decay rate. On the contrary, the flatter axial velocity profile in converging pipes further extends the decay length. [ABSTRACT FROM AUTHOR]

The gas–liquid two-phase flow inside large aspect ratio lifting pipes is often characterized by a complex flow pattern, potentially causing coupling vibration of the lifting pipe. And produce a surge effect, aggravating the vibration of the lifting pipe and thus affecting its fatigue life and the lifting performance of the pipe. In this paper, a combination of numerical simulation and experiment is used to investigate the effects of inlet flow rate (Q) and tube diameter (D) on the vibration and lifting performance of the lifting tube. The obtained conclusions are as follows: with an increase in the inlet gas flow rate, the amplitude of the lifting pipe increases, and the lifting flow increases; with an increase in pipe diameter, the amplitude of the lifting pipe decreases and the overall lifting performance increases. According to the numerical simulation and experimental results, when D = 40 mm lifting pipe at the intake flow between Q = 50-60 L/min, the impact of surge effect is the least, and the liquid lifting quality also reaches the best state at this time, The research presented in this paper provides a reference for the selection of parameters for lifting pipes in engineering applications. [ABSTRACT FROM AUTHOR]

Changes in flow rates in pressurized pipeline systems, due to power loss in a pump, opening or closing of a valve, load rejection by a turbine, etc., may lead to unsteady conditions called fluid transients or water hammer in the pipeline, which, in turn, can lead to dangerous consequences. This potential phenomenon must be checked during the design phase of pipeline systems in order to prevent such dangerous situations. For this purpose, many software programs have been developed worldwide to analyze fluid transients. In this study, a computer software was developed that analyzes this type of flow in pipeline systems using C# programming language. In addition to simulating and solving problems in transient flows in pipeline systems, this will help the purpose of having a free domestic transient flow software for education and research purposes, avoiding expensive alternatives. The method of characteristics is used to solve the nonlinear, hyperbolic partial differential equations of unsteady pipe flow. The developed software was tested using various well-known benchmark cases for validation purposes. It was shown that the computed results of the new software are very similar to those obtained in the literature, proving the accuracy and reliability of the new program. In future studies, it is hoped that the program will be more comprehensive with more boundary conditions added to the program. In this paper, the developed program and some of its important features will be introduced, and validation of the program with certain benchmark studies will be provided. [ABSTRACT FROM AUTHOR]

Irrigation is crucial for sustainable agriculture and improving farm yields, but a significant gap exists between the irrigation potential created and its actual utilization. This gap is due to losses in canal conveyance and the inefficiency of conventional irrigation methods within canal command areas. Most modernization efforts in India focus on implementing micro-irrigation for tube well systems, addressing the problem of water table decline experienced in many districts. With this context, the present study examines the command area of Gadarjudda minor of the Upper Ganga Canal in Haridwar district, Uttarakhand, India, to assess the present state of the canal by conducting on-site surveys and feasibility of micro-irrigation by evaluating the viability of replacing minor canals with a gravity flow piped irrigation network. The evaluation involves assessing the current canal status, designing the gravity flow piped irrigation network, and conducting a social survey to determine farmers' willingness, awareness, and purchasing capacity toward adoptin of micro-irrigation systems on their farms. The study identifies high conveyance loss and poor maintenance in conventional irrigation methods, highlighting the importance of micro-irrigation in the study area. The profile of the minor canal is adequate to support gravity flow in the pipe network, with velocity and pressure head within permissible limits. A social survey revealed that 85% of farmers are willing to adopt micro-irrigation, but low purchasing capacity (36%) hampers its adoption. The study concludes that micro-irrigation is viable in the Gadarjudda minor canal command area as long as a piped irrigation network is implemented and farmers receive government subsidies and proper training. [ABSTRACT FROM AUTHOR]

A high-resolution numerical simulation of an air–water turbulent upward bubbly flow in a pipe is performed to investigate the turbulence characteristics and bubble interaction with the wall. We consider three bubble equivalent diameters and three total bubble volume fractions. The bulk and bubble Reynolds numbers are $Re_{bulk}= u_{bulk} D/\nu _w = 5300$ and $Re_{bub}= (\langle u_{bub}\rangle - u_{bulk}) d_{eq}/\nu _w = 533\unicode{x2013}1000$ , respectively, where $u_{bulk}$ is the water bulk velocity, $\langle u_{bub}\rangle$ is the overall bubble mean velocity, $D$ is the pipe diameter and $\nu _w$ is the water kinematic viscosity. The mean water velocity near the wall significantly increases due to bubble interaction with the wall, and the root-mean-square water velocity fluctuations are proportional to $\bar {\psi }(r)^{0.4}$ , where $\bar {\psi } (r)$ is the mean bubble volume fraction. For the cases considered, the bubble-induced turbulence suppresses the shear-induced turbulence and becomes the dominant flow characteristic at all radial locations including near the wall. Rising bubbles near the wall mostly bounce against the wall rather than slide along the wall or hang around the wall without collision. Low-speed streaks observed in the near-wall region in the absence of bubbles nearly disappear due to the bouncing bubbles. These bouncing bubbles generate counter-rotating vortices in their wake, and increase the skin friction by sweeping high-speed water towards the wall. We also suggest an algebraic Reynolds-averaged Navier–Stokes model considering the interaction between shear-induced and bubble-induced turbulence. This model provides accurate predictions for a wide range of liquid bulk Reynolds numbers. [ABSTRACT FROM AUTHOR]

Adding polymers to turbulent Newtonian fluid flows can have dramatic effects. A well-known example is a significant drag reduction by flexible polymers in turbulent wall-bounded flows. In numerical studies of polymer drag reduction, polymers are often modelled as dumbbells of two beads connected by a finitely extensible nonlinear elastic (FENE) spring. There are natural queries whether this highly simplified coarse-grained model is adequate for describing a polymer macromolecule in turbulent flows. By carrying out Eulerian–Lagrangian simulations of polymers, described by different models, in a turbulent pipe flow, Serafini et al. (J. Fluid Mech. , vol. 987, 2024, R1) have demonstrated that the FENE dumbbell model can accurately capture polymer extension statistics as compared with the realistic Kuhn chain model. Their work further reveals the surprising result that increasing the number of beads in a FENE chain worsens its accuracy in characterizing polymer spatial conformations at large Weissenberg numbers. [ABSTRACT FROM AUTHOR]

While exploring and developing oil and gas, well kick and overflow accidents are inevitable. In such an accident, if the drilling bit is not at the bottom of the well, the drilling tool is blocked, or the reservoir contains toxic gases such as hydrogen sulfide, the traditional technique for well control is no longer suitable, and the bullheading method must be adopted to kill the well. However, during bullheading, the flow patterns of gas and liquid are intricate, making gas velocity hard to predict. To solve these problems, a set of visual simulation experimental device for directional well bullheading was built to find out the effects of wellbore inclination, liquid viscosity, gas and liquid velocities, and bubble size on bubble migration characteristics in gas–liquid countercurrent (gas flowing in opposite direction to the liquid). Prediction models of bubble distribution coefficient and rising velocity considering liquid viscosity, bubble size, and wellbore inclination angle were worked out. The experimental results show that small bubbles are mainly located in the center of the wellbore and large bubbles tend to approach the wellbore wall in gas–liquid countercurrent. Increasing wellbore inclination, viscosity, and the velocity of the liquid flowing against the bubbles results in a gradual decrease in Taylor bubble migration speed, which promotes the bubbles' pressing-back, as inhibiting the upward movement of large bubbles is essential for effective bullheading operations. The prediction models of distribution coefficient and bubble migration velocity have an error of less than 10% and 9. 78%, respectively. [ABSTRACT FROM AUTHOR]

Deep-sea minerals are regarded as the most economically viable and promising mineral resource. Vertical hydraulic lifting represents one of the most promising methods for deep-sea mining lifting systems. To mitigate the potential for clogging due to the aggregation of particles in vertical pipe transport during deep-sea mining operations, this paper employs numerical simulations utilizing the computational fluid dynamics and discrete element method (CFD-DEM) model to investigate the swirling flow transportation of mineral particles. The characteristics of the swirling flow field and the motion law of double-size particles at different swirling ratios are investigated. The findings demonstrate that, in comparison to axial transport within the pipeline, the particle movement observed in swirling flow transport exhibits an upward spiral trajectory. This phenomenon facilitates the orderly movement of particles, thereby enhancing the fluidization of particles within the pipeline. An increase in the swirling ratio (SR) has a considerable impact on the velocity within the pipe. The tangential velocity distribution undergoes a gradual transition from centrosymmetric to non-centrosymmetric as the distance from the inlet increases. An increase in the SR results in an enhanced aggregation of particles at the wall, accompanied by a notable rise in the local particle concentration. The value of SR = 0.3 represents a critical threshold. When SR exceeds this value, the distribution of particles in the cross-section reaches a relatively stable state, rendering it challenging to further alter the distribution and concentration of particles, even if the SR is augmented. Furthermore, the maximum local particle concentration in the vicinity of the wall tends to be stable. These results provide valuable insights into vertical pipe swirling flow transport for deep-sea mining. [ABSTRACT FROM AUTHOR]

This article deals with the application of the temperature oscillation method (TOIRT method) to the laminar flow of water in a pipe. This dynamic and contactless method was derived for the assumption of homogeneous temperature on the fluid side, but this assumption is violated in the case of laminar flow. Numerical simulations were used to discover the fundamental influence of the amount of incident heat flux, which is modulated by the sine function, on the resulting local values of the heat transfer coefficient. The frequency of the transmitted signal, on the other hand, has no effect. The experimental measurement confirmed the numerical results even with a deviation of 25%, which is still a good result due to the sensitivity of the experimental method in this area. [ABSTRACT FROM AUTHOR]

Amputees often experience high temperatures between the amputated limb and the prosthetic socket, necessitating the use of cooling devices to mitigate this issue. However, challenges arise with the location and size of conventional heat sinks. This research proposes a novel heat sink utilising a phase change material (PCM) to dissipate heat. The leg was chosen as the site for the heat sink, designed in a cylindrical shape. Coolant flow pipes were arranged in a branched configuration inspired by constructal theory, constrained by the dimensions of the artificial leg. The degrees of freedom for the constructal design are branches akin to arterial and venous branching, aiming to minimise pressure drop. Four heat sinks with varying degrees of branching were compared based on temperature reduction, heat dissipation, pressure drop, phase change material melting capacity, and operational efficiency. The cylindrical heat sink measures 50 mm in diameter and 300 mm in length. Ice was employed as the PCM, with water served as the working fluid. The working fluid's temperature and flow rate were maintained at 40 °C and 0.2 L/min, respectively. The experimental work was prepared to validate the theoretical model. The study revealed that the proposed heat sink design, with increased branching, led to a significant temperature reduction, achieving up to 39.62%. Moreover, heat dissipation increased by 236% compared to a single-tube heat sink. The use of branched pipes resulted in a manageable increase in pressure drop, peaking at 39.9 Pa, well within pump specifications, while markedly enhancing heat dissipation. The melting time of the PCM and the melting area increased as the number of branches of the heat sink increased. Ultimately, applying constructal theory in heat sink design for PCM demonstrated its superior performance within spatial constraints, providing a promising solution for prosthetic cooling. [ABSTRACT FROM AUTHOR]

Understanding the flow dynamics of non-Newtonian fluids is crucial in various engineering, industrial, and biomedical applications. However, the existing generalized Reynolds number formulations for non-Newtonian fluids have limited applicability due to their dependencies on their specific viscosity models. In this study, we propose a new viscosity-model-independent generalized Reynolds number formulation for laminar pipe flow. The proposed method is based on the direct adaptation of the measurement principles of rotational viscometers for wall shear rate estimation. We assess the accuracy of this proposed formulation for power-law and Carreau-Yasuda viscosity models through robust friction factor experiments. The experimental results demonstrate the applicability and effectiveness of the proposed viscosity-model-independent Reynolds number, as the measured friction factor data align closely with our Reynolds number predictions. Furthermore, we compare the accuracy of our Reynolds number formulation against established generalized Reynolds formulations for pure shear-thinning (Carreau-Yasuda) and viscoplastic (Herschel-Bulkley-extended) models. The results of the comparative analysis confirm the reliability and robustness of this generalized Reynolds number in characterizing and interpreting flow behavior in systems with visco-inelastic non-Newtonian fluids. This unified generalized Reynolds number formulation presents new and significant opportunities for precise pipe flow characterization and interpretation as it is applicable to any visco-inelastic (time-independent) viscosity model without requiring additional derivations. [ABSTRACT FROM AUTHOR]

This paper designs and builds a stormwater pipe-river/channel experimental system at the first attempt to observe hydraulic dynamics between pipe flow and downstream water levels under different steady state conditions. In addition, a three-dimensional (3D) model is developed to facilitate the understanding of this complex hydraulic interaction, and the reliability of a widely used one-dimensional (1D) model is first investigated. Experiment and simulation results show that (1) a high downstream water level can increase pipe flow capacity at the early stage, and the pipe flow is followed by a slightly downward trend and finally rapidly decreased, (2) pipe flows exhibit complex behaviors during the transition from nonfull to full pipe flow by altering flow area and velocity, and (3) the observed flows are significantly lower than those from the 1D model for the nonfull pipe flow scenario. This study offers insights to the underlying complex hydraulic properties between pipe flows and downstream water levels, and also shows that the 1D model is insufficient to reveal such an interaction process, which may underestimate the urban flooding risk. [ABSTRACT FROM AUTHOR]

High-order accurate Large-eddy simulations (LES) have been carried out for compressible, turbulent flow through two bell-shaped convergent-divergent nozzles- one with a short divergent portion and the other with a longer one. An explicit filtering approach based on approximate deconvolution method is used for the LES. The nozzles have isothermal walls and circular cross-sections. The incoming flow is a turbulent, subsonic fully developed pipe flow at centreline Mach number of around 0.4 and friction Reynolds number 216. An adaptive filter is used to capture the shocks appearing in the divergent portion of the nozzles. The complicated behaviour of the mean flow, Reynolds stresses, production and pressure-strain terms of the axial Reynolds stress budget in the shock train region is shown. The broadband nature of the shock train oscillations having multiple dominant frequencies in these nozzles is observed in the present LES. [ABSTRACT FROM AUTHOR]

The characteristics of uniform momentum zones (UMZs) and UMZ interfaces in turbulent channel flow (TCF) at friction Reynolds number ranging from 600 to 2000 are investigated. The focus is on the Reynolds number effect and the difference among the turbulent channel flow, turbulent pipe flow (TPF), and turbulent boundary layer (TBL). The UMZ is identified using the approach of probability density histograms, a discrete approximation of the probability density function. We find that the average number of UMZs increases with the Reynolds number, similar to the findings in the TBL. The first group of UMZ in the TCF, namely the quiescent core, has a thicker thickness at a higher Reynolds number. Therefore, the UMZ closer to the channel centre significantly influences high Reynolds number wall turbulence by occupying a large portion of the channel. With increasing Reynolds number, the intensity of spanwise vorticity at the UMZ interface increases, while the thickness of the local maximum decreases. The dominance of prograde vorticity at the interface also increases with the Reynolds number. Moreover, the contortion of the UMZ interface is significantly enhanced at high Reynolds numbers than at low Reynolds numbers in both the streamwise and spanwise directions. Furthermore, the number of UMZ for a given snapshot is related to the overall velocity fluctuations in the subregion, increasing with large-scale Q2 events and decreasing with large-scale Q4 events. Comparing the three flow configurations, UMZs show similarities in their trends, along with two notable differences. First, the TPF has more UMZs compared to the TCF and TBL. Second, the innermost group in the TPF is considerably thicker than that of the higher ranks, a pattern absent in the TCF and TBL. The present findings advance the understanding of UMZs in TCF and demonstrate the similarities and differences between the cases of TCF and TBL. [ABSTRACT FROM AUTHOR]

The most common and destructive event of unsteady flow in pipes is water hammer. This phenomenon is caused by a sudden change in boundary conditions in pressurized pipes. Unsteady flow in pipelines can lead to a significant increase or decrease in pressure. This pressure generation may cause cavitation, bursting of pipes, and failure of the whole system. One type of equipment that can control both positive and negative pressure phases is a pressurized tank. Implementing such a pressure tank can impose increased costs. In order to reduce the design costs, the combination of a flywheel with the pressure tank can be used. In this study, a transmission pipeline from Zarineh River to Tabriz city is numerically simulated, and the effect of increasing the inertia of the flywheel on the reduction of the pressurized tank volume is investigated. The results show that increasing the flywheel inertia from 125 to 165 Nm2 can reduce the pressurized tank volume from 90 to 75 m3. [ABSTRACT FROM AUTHOR]

Suitable friction groups are provided for solving three typical hydraulic problems. While the friction group based on viscous forces is used for calculating the pressure drop or head loss in pipes and open channels, commonly referred to as the Type 1 problem in hydraulic engineering, additional friction groups with similar behaviors are introduced for calculating steady flow discharge as the Type 2 problem and, for estimating hydraulic diameter as the Type 3 problem. Contrary to the viscous friction group, the traditional Darcy–Weisbach friction factor demonstrates a negative correlation with the Reynolds number. This results in curves that slope downward from small to large Reynolds numbers on the well-known Moody chart. In contrast, the friction group used here, based on viscous forces, establishes a more appropriate relationship. In this case, the friction and Reynolds number are positively correlated, meaning that both increase or decrease simultaneously. Here, rearranged diagrams for all three mentioned problems show similar behaviors. This paper compares the Moody diagram with the diagram for the viscous force friction group. The turbulent parts of both diagrams are based on the Colebrook equation, with the newly reformulated version using the viscous force friction group. As the Colebrook equation is implicit with respect to friction, requiring an iterative solution, an explicit solution using the Lambert W-function for the reformulated version is offered. Examples are provided for both pipes and open channel flow. [ABSTRACT FROM AUTHOR]

We recorded aerodynamic roughness and shear velocity along transects on and around mature crescent‐shaped barchan dunes of 4.5m $4.5\ \mathrm{m}$ and 27m $27\ \mathrm{m}$ height above the horizontal rock‐covered Qatar desert by fitting to the log‐law time‐averaged vertical velocity profiles acquired from triads of ultrasonic anemometers penetrating the inner turbulent boundary layer. Shear velocity first decreased, then recovered as air climbed on the dune, with a local maximum ahead of the crest as predicted by the Jackson and Hunt (1975, https://doi.org/10.1002/qj.49710143015) theory. Unlike flows over gentler bedforms without a slope discontinuity, an anomalous peak of shear velocity also arose on the dune centerline at the brink, which the theory attributed to skewness in the dune transect profile. The onset of aeolian transport produced a log‐law passing through the Bagnold (1941, https://doi.org/10.1007/978‐94‐009‐5682‐7) focal point. It was bracketed by noticeable hysteretic peaks in the correlation between wind speed and entrained sand flux. The dunes' rocky surroundings and topography produced an aerodynamic roughness at odds with the Nikuradse (1933, https://ntrs.nasa.gov/citations/19930093938) data for fully developed turbulent boundary layers. Large‐eddy numerical simulations illustrated the sensitivity of shear velocity to wide changes in aerodynamic roughness from desert floor to dune surface. Plain Language Summary: Wind friction is the engine that erodes sand dunes, relentlessly pushing them over roads, houses, and infrastructure. Our records of wind speed on crescent‐shaped mobile dunes challenge the conventional understanding of this process. Comparing field measurements and models, we show that the highest friction occurs where the gentle upward dune surface abruptly gives way to a steeper avalanching downward slope. Our data also reveals that the "aerodynamic roughness," a measure of wind friction on sand, is at odds with historical data meant for turbulent pipe flow. Because numerical simulations are used to predict flow over landforms that are inaccessible to detailed measurements, we validate them against data on a large dune. Our observations imply that, to achieve greater fidelity, simulations should subdivide the fluid neighborhood of the dune more finely, and revisit how they treat aerodynamic friction on its surface. Although our work involved large desert dunes, we expect these suggestions to apply more broadly to atmospheric, fluvial or submarine landforms that are surrounded by rougher terrain or that feature sudden changes in slope. Key Points: At the brink of a mature barchan, theory, simulations and field data reveal a peak of shear stress rising with dune skewnessAerodynamic roughness on dunes with rocky surroundings disagree with Nikuradse's (1933, https://ntrs.nasa.gov/citations/19930093938) data for fully developed turbulent boundary layersWe discuss challenges that large‐eddy simulations face to reproduce turbulent flow on field‐size dunes [ABSTRACT FROM AUTHOR]

It is important to control turbulence in industrial processes. Past experimental and numerical researches have shown that a turbulent puff in pipe flow can be removed or delayed by flattening the profile of the upstream velocity because a flattened velocity profile causes the point of inflection on it to collapse. The energy gradient theory has been developed to study turbulent transition, and the relevant studies have shown that turbulence arises due to the generation of singularities in the flow field. In pressure-driven flows like the pipe flow, the point of inflection on the velocity profile leads to the appearance of a singular point in the unsteady Navier–Stokes equation. In this study, the energy gradient theory is used to demonstrate why the point of inflection on the profile of velocity of pipe flow is the critical point for generating turbulence. Then, it is shown how flattening the velocity profile leads to the elimination of the point of inflection on the velocity profile of pipe flows to delay turbulent transition. It is also clarified why this technique is not effective at higher Reynolds number because the flattened velocity profile violates the criterion for flow stability relating to transition to turbulence.

An experimental campaign is conducted to investigate the pressure drop during the restart of a heavy oil-water core-annular flow (CAF) from a stratified configuration in a polyvinyl chloride (PVC) horizontal pipe. The evolution characteristic of restart pressure drop along time is explored, and the effects of various factors including oil holdup (0.26-0.76), oil viscosity (1.0553-3.02 Pa·s), standstill period (0.5 & 1.0 h) and water cleaning superficial velocity (0.25-1.01 m/s) on maximum restart pressure drop are emphatically investigated. The results demonstrate that the restart process can be divided into decay and steady two stages. The maximum restart pressure drop generally increases along with the increase of oil holdup, oil viscosity, standstill period and water cleaning superficial velocity. Moreover, of all the measured variables, oil holdup and water cleaning superficial velocity have a significant influence on maximum restart pressure drop. The results obtained can provide a theoretical reference and practical guidance for the development of appropriate restart schemes for on-site shutdown pipelines. [ABSTRACT FROM AUTHOR]

Oil flow in a circular piping usually requires excessive modeling with detailed correlations to describe the oil flow behavior. The ineffective pour point depressants and the inefficient heat tracing makes oil flow simulation an essential task. Due to the varying of oil characteristics, a robust modeling approach is necessary to guarantee the integrity of the oil flow in the piping system and to avoid additional costs. In this work, a proposed approach coordinates the modeling tools (e.g. Aspen HYSYS®, COMSOL Multiphysics®) to simulate the oil flow in a circular pipe satisfactorily. The oil properties have been extracted from Aspen HYSYS® and used in COMSOL Multiphysics® to describe the varying in oil flow characteristics. Numerous computational trials have been conducted to estimate the oil temperature profiles in the axial and radial directions to ensure the oil flow above the pour point. Moreover, the numerical results were computed to estimate the oil temperature profiles for constant and temperature-dependent oil properties. Finally, an analytical approach was established using dimensional analysis to compare with COMSOL numerical results at constant oil properties. Both results showed a consistent trend match. [ABSTRACT FROM AUTHOR]

Controlling pressure impact of water hammer is an important guarantee for safe and stable running of pipeline systems. Previously, we proposed a spring self-adaptive auxiliary control (SAC) system to improve the pressure control ability of a surge tank. However, the working efficiency of the SAC system is affected by various parameters. A reasonable designing strategy becomes an urgent need to properly determine the parameters of the SAC controller. In this study, based on our calibrated numerical model, various transient responses of a SAC system with different parameters were further investigated. The latency response threshold and the spring orifice coefficient were identified to be the two most sensitive parameters that determine the controller working efficiency. Based on the objectives of reducing the in-pipe extreme pressure and in-tank water level fluctuation, an analytical dual-objective optimizing Method was proposed for application. The results demonstrated that the pressure control capability of SAC controller can be optimized by the proposed method. [ABSTRACT FROM AUTHOR]

The mass transfer from a stagnant CO2 gas pocket to the flowing water in a horizontal pipe was investigated experimentally, considering the application of pH adjustment by injecting gaseous CO2 for raw water in water treatment industries. In the experiments, the variation of the CO2 gas pocket volume and the corresponding pH values of the pipe flow with time under different conditions were recorded. The mass transfer coefficient of the CO2 gas pocket in the pipe flow was then calculated. The results showed that the injection of gaseous CO2 into the pipe flow could effectively adjust the pH. The volume of the CO2 gas pocket decreased exponentially. Different from most studies on bubble mass transfer, it was found that the ambient CO2 concentration could not be neglected in this study due to the large volume of the gas pocket and the restricted space in the pipe. The mass transfer coefficient increased with the increasing ratio of the CO2 injection rate to the water flow rate and exhibited a sharp reduction as the volume of the CO2 gas pocket decreased by about 80%. The outcomes of this paper can contribute to a better understanding of gas bubble mass transfer in pipe flows. HIGHLIGHTS The mass transfer of a large CO2 gas pocket in the horizontal pipe flow was investigated, which has been hardly reported before.; During mass transfer processes, the pH variation of the pipe flow could be divided into three regimes, and the volume of the gas pocket was reduced exponentially.; The CO2 concentration in the pipe flow is important to mass transfer due to the large volume of the gas pocket and the restricted space in the pipe.;

In data assimilation, observations are fused with simulations to obtain an accurate estimate of the state and parameters for a given physical system. Combining data with a model, however, while accurately estimating uncertainty, is computationally expensive and infeasible to run in real-time for complex systems. Here, we present a novel particle filter methodology, the Deep Latent Space Particle filter or D-LSPF, that uses neural network-based surrogate models to overcome this computational challenge. The D-LSPF enables filtering in the low-dimensional latent space obtained using Wasserstein AEs with modified vision transformer layers for dimensionality reduction and transformers for parameterized latent space time stepping. As we demonstrate on three test cases, including leak localization in multi-phase pipe flow and seabed identification for fully nonlinear water waves, the D-LSPF runs orders of magnitude faster than a high-fidelity particle filter and 3-5 times faster than alternative methods while being up to an order of magnitude more accurate. The D-LSPF thus enables real-time data assimilation with uncertainty quantification for the test cases demonstrated in this paper. [ABSTRACT FROM AUTHOR]

The formation of oxygen bubbles in the anodic circuit of a polymer electrolyte membrane (PEM) electrolyser is a major technological problem as it greatly affects heat transfer, process performance and safety. Overall, bubbles evolve in the pipe flow upstream of the gas separator due to oxygen super-saturation created by the chemical reaction at the anode. The accurate prediction of bubble formation in the pipes is important for the correct positioning and design of the gas separator. This paper therefore presents a cell-based one-dimensional numerical model that estimates bubble evolution in a horizontal pipe-flow. For this purpose, the model considers bubble growth at nucleation sites and in the flow, enabling the prediction of the corresponding gas fraction at different locations within the cooling circuit. Furthermore, a sensitivity analysis was conducted based on the derived model to evaluate the impact of various parameters on the degassing rate. It was found that the smaller the pipe diameter, the greater the initial gas content and the greater the number of nucleation sites, the shorter the pipe length required to achieve solubility. • Bubbles evolve in the cooling circuit of PEM-electrolysis due to super-saturation. • A cell-based 1D numerical model predicts the gas fraction at various locations. • A sensitivity analysis shows the impact of various parameters on the degassing. • Degassing is improved by smaller pipe diameters and a higher initial gas fraction. • The higher the number of nucleation sites, the better the degassing. [ABSTRACT FROM AUTHOR]

A numerical scheme of new class is presented for computing unsteady swirling flows in nozzles and pipes based on equations for a compressible inviscid gas. The main advantage of such schemes is that they are efficient as applied to unsteady multiscale problems. A scheme of this type is constructed using Godunov's well-known approach, according to which fluxes on faces of mesh cells (volumes) are computed by solving auxiliary one-dimensional problems near each face and by approximating conservation laws. An analysis of the current solution near the face is used to switch between explicit and implicit flux computation algorithms. The scheme is unconditionally stable, and it does not generate spurious oscillations. The performance of the scheme is demonstrated by computing unsteady swirling flows in nozzles and pipes. The features of the formulation of problems of this type are investigated, and variants of correct problem formulation are proposed. The properties of solutions of the swirling flow problem with a central body covering part of the axis of symmetry in the computational domain are studied. [ABSTRACT FROM AUTHOR]

Wax/paraffin deposition in production wells and oil pipelines is a major challenge for oil production. Extensive research has been conducted to improve understanding of this process. This paper presents a review of experimental work carried out with flow loops. Previous research investigated paraffin deposition process under the influences of temperature, flow rate/velocity, shear stress, water fraction, gas phase, pipe material, asphaltene concentration, and chemical inhibitors. Test results reveal that temperature and shear stress have significant impacts on wax deposition. Limited research has been conducted on wax deposition under multiphase flow. Even though more than 20 years of efforts have been spent on wax deposition studies, unfortunately we have not fully understood this phenomenon. [ABSTRACT FROM AUTHOR]

A three-lobed helical pipe was installed downstream of the bend of a vertical-horizontal pneumatic pipeline. The swirl characteristics under different helical pipe structures were investigated. Results show that: (a) the maximum velocity region rotates quasiperiodically, and the smaller the pitch, the faster the rotation; (b) the 3D morphological changes of the axial velocity distribution in downstream sections are similar: from an arch to a pit and finally to a uniform flat top. The tangential velocity appears as a Rankine vortex near the wall; (c) the swirl decays rapidly along the downstream. The initial swirl intensity, proportional to the helical pipe length, increases first and then decreases with decreasing pitch, whereas the structural parameters have minimal effect on the swirl decay rate; (d) the helical tube remarkably increases the system energy consumption, and the total pressure drop is inversely proportional to the pitch and proportional to the length. [ABSTRACT FROM AUTHOR]

Based on existence results for the Stokes operator and its solution properties in manifolds with cylindrical ends by Große et al. and Kohr et al., the Stokes flow in a three‐dimensional compact domain Ω+$$ {\Omega}&#x0005E;{&#x0002B;} $$ with circular openings Σj(j=1,2)$$ {\Sigma}_j\kern0.1em \left(j&#x0003D;1,2\right) $$ through which the fluid enters and leaves Ω+$$ {\Omega}&#x0005E;{&#x0002B;} $$ through unbounded cylindrical pipes the Stokes flow is modeled as a mixed boundary value problem Ω+$$ {\Omega}&#x0005E;{&#x0002B;} $$ whereas in the cylindrical ends, the velocities and pressures are constant on every straight line in the cylindrical directions with initial values from the openings Σj$$ {\Sigma}_j $$ of Ω+$$ {\Omega}&#x0005E;{&#x0002B;} $$. These values equal the velocities and pressures which are obtained from the mixed boundary values' solution in Ω+$$ {\Omega}&#x0005E;{&#x0002B;} $$ at the openings Σj$$ {\Sigma}_j $$. [ABSTRACT FROM AUTHOR]

Bentonite slurry is readily available, and extensively used in underground construction, where the in-situ infiltration behavior of the slurry is of great interest. As a solid–liquid biphasic fluid, slurry exhibits distinct fluid properties that set it apart from pure water. These unique properties play a significant role in determining its infiltration behavior during construction, making it a critical factor that cannot be overlooked. In this study, slurry shear tests were carried out using a rotational viscometer to characterize its fluid properties, and constant water head infiltration tests were conducted by a self-designed infiltration device to investigate the infiltration behavior of slurry in sand stratum. In addition, theoretical derivation based on the pipe flow was implemented to simulate the slurry flow in the stratum. The results show that, as the slurry infiltration continues, the relationship between the yield stress and initial hydraulic gradient experienced a "nonlinear to linear" process. The nonlinearity at the early stage of slurry infiltration is related to the evolution of the core phase of the slurry, which is the root cause of the nonlinear evolution of the fluid property and infiltration curves. A predicted relation between the fluid parameters of the slurry and its multiphase infiltration behavior was established, which are able to give a better understanding of the slurry behavior in engineering design. [ABSTRACT FROM AUTHOR]

The intermittency characteristics in transitional and turbulent flows can provide critical information on the underlying mechanisms and dynamics. While time–frequency (TF) analysis serves as a valuable tool for assessing intermittency, existing methods suffer from resolution issues and interference artifacts in the TF representation. As a result, no suitable or accepted methods currently exist for assessing intermittency. In this work, we address this gap by presenting a novel TF method—a Fourier-decomposed wavelet-based transform—which yields improved spatial and temporal resolution by leveraging the advantages of both integral transforms and data-driven mode decomposition-based TF methods. Specifically, our method combines a Fourier-windowing component with wavelet-based transforms such as the continuous wavelet transform (CWT) and superlet transform, a super-resolution version of the CWT. Using a peak-detection algorithm, we extract the first, second, and third most dominant instantaneous frequency (IF) components of a signal. We compared the accuracy of our method to traditional TF methods using analytical signals as well as an experimental particle image velocimetry (PIV) dataset capturing transition to turbulence in pulsatile pipe flows. Error analysis with the analytical signals demonstrated that our method maintained superior resolution, accuracy, and, as a result, specificity of the instantaneous frequencies. Additionally, with the pulsatile flow dataset, we demonstrate that IF components of the fluctuating velocities extracted by our method decompose energy cascade components in the flow. Additional investigations into corresponding spatial frequency structures resulted in detailed observations of the inherent scaling mechanisms of transition in pulsatile flows. [ABSTRACT FROM AUTHOR]

A combined positron emission particle tracking (PEPT) and X-ray computed tomography (CT) technique is presented, and its utility is demonstrated through investigation of flow in a pipe with twisted tape swirl insert with varying flow conditions (diameter-based Reynolds numbers 16,300–63,300). A description of this technique is given, as well as data handling practices used to relate geometric information captured by CT to fluid flow data gathered via PEPT. It is found that the CT component is readily capable of capturing the stainless steel insert geometry in this present system, but the use of combined plastic and metal materials leads to artifacts in imaging of the plastic surface. Nonetheless, CT data are related to PEPT flow measurements, and average velocity fields are calculated via a pseudo-framing and interpolation scheme and used to visualize and interrogate key flow phenomena within the system. Radial velocity profiles of the mean flow characteristics are seen to collapse to a nearly common form across all flow conditions considered. Helical vortices are seen propagating through the flow field, generated by bypass flow around the gap between the insert and pipe wall, with additional coherent secondary flow structures seen in the higher Reynolds number cases. These findings enhance the understanding of the mixing mechanisms in these swirl flows and encourage the continued development of PEPT-CT methodologies for 3D flow measurements in optically inaccessible systems. [ABSTRACT FROM AUTHOR]