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Subcritical pipe flow transition has received a great deal of attention over the past decades, as it constitutes a quintessential bifurcation process between two metastable fluid states: the laminar and turbulent solutions. Coherent lower-branch structures, forming flow states that facilitate between these two attracting equilibria, have been proposed that together form an edge manifold in phase space separating relaminarizing from transitioning perturbations. Typically, direct numerical simulations or low-dimensional model equations have been used to study this edge manifold with bisection methods. In the article by Kaszás & Haller (J. Fluid Mech., vol. 979, 2024, A48), an effective nonlinear invariant-manifold technique has been applied to extract a low-dimensional, global representation of the phase-space dynamics directly from simulation data. It allows the computation of the intersection of the edge manifold with a low-dimensional surface that is strikingly accurate in predicting the long-term dynamics of perturbations about the lower-branch solution and thus provides an accessible parameterization of the edge manifold for subcritical pipe flow transition. [ABSTRACT FROM AUTHOR]

Wall-based spanwise forcing has been experimentally used with success by Auteri et al. (Phys. Fluids, vol. 22, 2010, 115103) to obtain large reductions of turbulent skin-friction drag and considerable energy savings in a pipe flow. The spatial distribution of the azimuthal wall velocity used in the experiment was not continuous, but piecewise constant. The present study is a numerical replica of the experiment, based on a set of direct numerical simulations (DNS); its goal is the identification of the effects of spatially discrete forcing, as opposed to the idealized sinusoidal forcing considered in the majority of numerical studies. Regardless of the discretization, with DNS the maximum drag reduction is found to be larger: the flow easily reaches complete relaminarization, whereas the experiment was capped at 33% drag reduction. However, the key result stems from the observation that, for the piecewise-constant forcing, the apparent irregularities of the experimental data appear in the simulation data too. They derive from the rich harmonic content of the discontinuous travelling wave, which alters the drag reduction of the sinusoidal forcing. A detailed understanding of the contribution of each harmonic reveals that, whenever for example technological limitations constrain one to work far from the optimal forcing parameters, a discrete forcing may perform very differently from the corresponding ideal sinusoid, and in principle can outperform it. However, care should be exercised in comparison, as discrete and continuous forcing have different energy requirements. [ABSTRACT FROM AUTHOR]

AbstractThe present investigation demonstrates the effect of red mud concentration on the rheological, pipe flow, and pipe wear behavior during slurry pipeline transportation. Rheology data indicate that 40–70 wt.% red mud slurries exhibit shear thinning flow behavior in the shear rate range of 15–300 s−1. Both slurry viscosity and shear stress increase with the increase in red mud concentrations. The yield stress and startup pressure exponentially vary with red mud concentrations. The critical velocity is estimated as 1.5 m/s, above which sedimentation of red mud particles can be avoided in the pipeline. The pipe head loss and specific energy consumption increase with red mud concentration and slurry velocity; however, these parameters decrease with an increase in pipe diameter. Results suggest that the repetitive impingement of the red mud particles on the surface of mild steel specimens causes erosion wear, which intensifies at higher solid loading and velocity. The abrasivity of red mud slurries and the abrasive response of the pipe material are found as a function of red mud concentration. A favorable economic flow condition is achieved, when 60–65 wt.% of red mud slurry is transported at a velocity of 1.5 m/s in a pipe of diameter 0.3 m. [ABSTRACT FROM AUTHOR]

The impact of pipe inclination angle on oil-water flow regimes transition boundaries is vital in various engineering applications, including pipeline and separator inlet design. Understanding this influence is crucial for identifying alternative and optimal designs. The standard way of presenting oil and water superficial velocities on 2D flow pattern maps doesn't consider how the flow pattern varies with pipe tilt angle. This article aims to clarify how the angle of pipe inclination affects oil-water flow regime transitions. This method uses pipe inclination angle as a direct representation, with the angle shown on the x-axis of a 2D flow pattern map, which has not been done before in literature. The y-axis, or ordinate, is a dimensionless number that accounts for mixture velocity, fluid densities, and pipe diameter. Two dimensionless numbers were utilized. The Froude number based on mixture velocity, Fr M, and the Reynolds number (Re OM) based on mixture velocity and oil properties, are plotted against pipe inclination angle. The evaluation and validation of the proposed methods for the effect of the inclination angle were performed using a database of more than 10,000 points established from studies reported in the literature. The findings show that both the Dispersed (DF) and Semi-Dispersed flow regimes (SDF) exhibit higher Fr M values than smooth stratified regardless of the pipe's incline. Moreover, the spreading area is symmetric around the horizontal line which means that the DF and SDF can be observed at similar Fr M for both positive and negative inclinations. Focusing horizontally, Fr M is highest for ST-MI, lower for SW, and lowest for ST. This paper also presents and demonestrates a case study showcasing a new application for flow pattern maps, illustrating their potential in design purposes. [ABSTRACT FROM AUTHOR]

A fundamental difficulty of studying gas–liquid pipe flows is the prediction of the occurrence and characteristics of the slug flow regime, which plays a crucial role in the safety design of oil pipelines. Current empirical methods and one-dimensional computational models only achieve limited success. While 3-D numerical simulations are highly recommended, they have been very seldom used. We perform 3-D Lagrangian numerical simulations of gas–liquid pipe flows by adapting an existing multi-phase smoothed particle hydrodynamics (SPH) method based on a Riemann solver to achieve an efficient solver. To realize the high inlet velocities of gas and liquid an in- and outlet boundary condition is presented. The results are validated against existing experimental data, numerical simulations and analytical solutions. Multiple gas–liquid pipe flow patterns are predicted, namely, smooth stratified, stratified wavy, bubble flow, slug flow and bubble flow. Several principle characteristics of slug flows, e.g., pressure gradient, slug development and slug frequency are analyzed in a 3-D fully Lagrangian framework. [ABSTRACT FROM AUTHOR]

This study investigates wave-stratified flow in a horizontal pipe at high pressure, and flow characteristics are obtained, such as flow pattern map, liquid film thickness, and pressure drop. Compared with a flow pattern map of a gas-liquid two-phase flow carried out at atmosphere, stratified flow zone is depressed with increasing system pressure and the critical gas superficial velocity decreases for smooth-wave-stratified flow transition, while the critical liquid superficial velocity increases for stratified-intermittent transition. On one hand, the compressed air results in an increase in momentum transfer between gas and liquid phases, which accounts for the smaller gas superficial velocity that is encountered in both smooth-wave and stratified-annular flow transition at higher pressure. One the other hand, it slows down the liquid below the crest, and it makes the interface wave crest unstable and split for the vortex shedding behind the wave crest, which accounts for flow regime transition in gas-liquid two-phase flows in pipelines. As a result, stratified-intermittent flow transition is depressed and delayed. The pressure influence on the liquid film profile is analyzed, and relationships between film thickness and dimensionless numbers are studied, such as liquid Weber number and gas Weber number. Friction factors on different interfaces at high pressure are studied, and new empirical formulas are deduced. [ABSTRACT FROM AUTHOR]

Urban floods/inundation disasters are becoming a prominent problem affecting urban public security due to the impact of global climate change and rapid urbanization. Therefore, research on urban flooding via numerical modelling has important practical significance. According to hydrological and hydrodynamic theories and methods, based on the Storm Water Management Model and the self-developed Graphics Processing Unit (GPU) Accelerated Surface Water Flow and Associated Transport (GAST) model, we explore the best coupling mode, and take Xiaozhai block in Xi'an, China, as the research object to study, through the selected mode, the impact of the change of local land use type on surface inundation and pipe network. The results show that the hydrology–hydrodynamic coupling model (G-S) is more realistic, and its simulation results are more in line with the actual urban flood processes. The results are expected to provide help to other experts and scholars in future model coupling research. [ABSTRACT FROM AUTHOR]

Long-distance pipeline hydro-transport of lignocellulosic biomass for industrial-scale biofuel production at levels comparable to conventional oil refineries presents an economically and logistically viable alternative to fossil fuels. There is very limited understanding on the behavior of the transportation of agricultural biomass slurries in an inclined pipeline. This research is focused on a laboratory-scale investigation of 6.4 mm nominal particle length (d50 = 4.85 mm) knife-milled wheat straw-water suspensions' uphill and downhill flows for a range of pipe inclination and saturated mass concentrations. The range of pipe inclination and saturated mass concentration was -7° to +21° and 5%-30%, respectively. The inclined test section was 29 m long with a 50 mm inside diameter of a closed pipeline loop. The accuracy of the measurements was verified by calibrating the inclined pipe section with fine sand (d50 = 0.103 mm)-aqueous slurries and comparing the results with established correlations. Most wheat straw-aqueous suspensions in the inclined flows showed the characteristics of the plug flow and the transition flow regions together for saturated mass concentration, Cm = 5%-30% and the entire flow range (0.5-4.7 m s-1), with a clear dependence of both the onset velocity of drag reduction (vOD) and drag reduction (%DR) on the pipe inclination as well as the slurry concentration and the critical concentration of maximum drag reduction (Cm)cr on a specific range of suspension velocity. Because of the accelerating effect of gravity, downhill slurry flows had the lowest vOD and the highest %DR at every Cm and pipe inclination with a maximum drag reduction of 25.53% at vm = 4.5 m s-1 and Cm = 25%. Uphill flows demonstrated some nonmonotonic changes in vOD and %DR, which need more experimental data for us to reach a firm conclusion. The research outcomes could help design and operate a long-distance integrated pipeline network for biomass transportation to produce biofuels on a large scale. [ABSTRACT FROM AUTHOR]

This study conducted wind tunnel tests to verify a passive jet flow control method for suppressing the aerodynamic force on a chamfered square cylinder at a moderate Reynolds number, focusing on the influence of the opening parameters and the spanwise spacing ratio of hollow pipes on the jet flow control effect. The pressure coefficient distribution on the surface of the cylinder and the overall aerodynamic coefficient were considered in order to systematically analyze the influence of opening shape, opening number, opening height, pipe height, and pipe radial thickness, and to determine the optimal combination of opening parameters. Subsequently, we analyzed the influence of the spanwise spacing ratio on passive jet flow control. Furthermore, the optimal arrangement of the hollow pipe was derived by comparing the aerodynamic coefficients of uncontrolled and controlled cylinders. The results revealed that the passive jet hollow pipe significantly reduces the root mean-square value of the pressure coefficient and the fluctuation of the lift coefficient. Moreover, the platform area of the mean pressure coefficient at the leeward side of the cylinder increases and the mean drag coefficient decreases. The spectrum analysis results showed that the passive jet flow control pipe alters the frequency and intensity of vortex shedding in the wake region. All results indicated that the aerodynamic forces and wakes of a chamfered square cylinder are effectively controlled through jet flow control with perforated hollow pipes. [ABSTRACT FROM AUTHOR]

Based on the magnetohydrodynamics model, this study numerically investigated the influence of a transverse non-uniform magnetic field on the flow and heat transfer characteristics of molten salt in a conductive pipe. The magnetic field was constructed with three sections including gradient and uniform regions, which was fitting to real application of the magnetic field. The flow and heat transfer of molten salt were studied within the ranges of 0 ≤ Ha ≤ 200 and 3000 ≤ Re ≤ 12 000. The results indicated that variation of magnetic field had significant effects on the flow velocity, turbulent intensity, and Joule heat, thus influencing the temperature and the Nusselt number of molten salt. Although the flow in core region was suppressed by the magnetic field, the flow velocity was enhanced and turbulence was reduced near the pipe wall, which was shown obviously different within three regions of the magnetic field. An interesting phenomenon of local heat transfer enhancement with increasing magnetic intensity was observed in the first section of the magnetic field, which was from the complex effects of flow velocity and turbulence. In addition, the Joule heat was calculated and analyzed to determine its influence on heat transfer under the magnetic field. A detailed analyzation of magnetic fluid flow in this study was provided to hopefully promote the molten salt in real application of flow and heat transfer. [ABSTRACT FROM AUTHOR]

An experimental–theoretical methodology is developed to investigate the characteristics of turbulence in horizontal particle-liquid pipe flows. Using a discrete wavelet transform, the three-dimensional Lagrangian trajectories of the liquid phase experimentally determined by positron emission particle tracking are decomposed into their deterministic and stochastic sub-trajectories, which are then utilized to construct profiles of local fluctuating velocity components and turbulent kinetic energy. The results for a single-phase flow are independently validated using computational fluid dynamic simulation and the analysis parameters are fine-tuned using direct numerical simulation data from the literature. In a particle-liquid flow, the investigation explores the influence of various factors including particle size, density, and concentration on turbulence intensity. Remarkably, the results demonstrate significant effects of the particle size and density on liquid turbulence. The enhanced understanding gained regarding turbulence intensity helps to advance our fundamental interpretation of the dynamics of particle-liquid flows, thus potentially aiding the rational design of such complex flows and associated equipment. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental studies of the flow of a dilute polymer solution in a converging pipe. Three geometries with restriction rates are considered: 2.41, 3.92, and 5.65. A water–glycerin solution of 0.1% polyacrylamide was used as a working fluid. Point velocity measurements are made by using the smoke image velocimetry technique, which previously was proved by the construction of velocity profiles corresponding to the laminar viscoelastic flow in a straight pipe. The influence of the Weissenberg number and the restriction rate of the channel on the velocity profiles are established for both transverse and longitudinal directions. For small Weissenberg numbers, the experimental results are compared with the numerical results obtained using the Giesekus and exponential form of Phan-Thien–Tanner rheological models. Three flow regimes are identified: flow without vortex, vortex enhancement, and divergent flow, which is consistent with published results on the abrupt contraction and converging flows. Vortex length for a wide range of Weissenberg numbers is well predicted by a logarithm function. Modified expression of stretch rate with location of detachment plane can predict the flow regimes and the onset of unsteady flow in converging channels. [ABSTRACT FROM AUTHOR]

The steady pipe flow of thixotropic yield stress fluids has been investigated theoretically based on a modified isotropic kinematic hardening (mIKH) model. Analytical solution is derived for a specific case (m = n = 1) and a general semi-analytical solution is put forward as well. The effect of thixotropic yield stress on shear rate and velocity profiles is illustrated by comparing to other well-known solutions. Moreover, the influences of model parameters are examined. It is worth noting that shear banding may occur at the yielded surface in case of a sufficiently large Bingham number, thixotropic number, and flow index, but a sufficient small value of structure-related exponent. [ABSTRACT FROM AUTHOR]

Experimental data for frictional pressure drop using both air–water and air–oil mixtures are reported, compared and used to evaluate predictive methods. The data were gathered using the 2-inch (54.8 mm) flow loop of the multiphase flow facility at the National University of Singapore. Experiments were carried out over a wide range of flow conditions of superficial liquid and gas velocities that were varied from 0.05 to 1.5 m/s and 2 to 23 m/s, respectively. Pressure drops were measured using pressure transducers and a differential pressure (DP) cell. A hitherto unreported finding was achieved, as the pressure drop in air–oil flow can be lower than that in air–water flow for the higher range of flow conditions. Using flow visualization to explain this phenomenon, it was found that it is related to the higher liquid holdup that occurs in the case of air–oil around the annular flow transition and the resulting interfacial friction. This additional key finding can have applications in flow assurance to improve the efficiency of oil and gas transportation in pipelines. Models and correlations from the open literature were tested against the present data. [ABSTRACT FROM AUTHOR]

This article deals with the mixing of a Newtonian material with a strongly viscous (nonNewtonian) material in a pipe with a static mixer. This problematic has a practical application in the food industry. CFD software ANSYS Fluent was used for numerical modeling. The mathematical model is defined using the basic balance equations, including the equation for species. The viscosity for a non-Newtonian highly viscous material (the working material) is defined using the Herschel-Bulkley model. A 3D computational model of a pipe with a static helical mixer is created in the DesignModeler program, which is part of the ANSYS software. The computational mesh was created in the Fluent Meshing program. The CFD modeling analysis is implemented for two different pipe diameters and different flow rates at the pipe inlet. The evaluation of the results is processed by the ANSYS Fluent program using the distribution of basic quantities and graphs. [ABSTRACT FROM AUTHOR]

The waxy oil-water interface has become a topic issue in the field of a two-phase oil-water pipe flow. Although some progress has been achieved in the understanding of interfacial rheological properties of the water-in-oil emulsion (W/O), the effect of surfactants (the main constituents of petroleum crude oil) still remains unclear. To test whether the structure of hydrophobic chains of surfactants influences the waxy oil-water interface, we monitored interfacial rheological parameters under different nonionic surfactants (Span80/60/65) using a DWR interfacial shear rheometer. Among these surfactants, the oil-water interface of Span65 characterized by multi-hydrophobic chains had the largest interfacial viscosity and critical storage modulus. A weak strain overshoot interface of Span65 suggested that sorbitan tristearate molecules provided a dominant contribution to the interfacial rheological properties of the waxy oil-water interface with much fewer effects of the interaction between wax molecules and surfactants. However, Span60/80 with a single hydrophobic chain was coupled to wax molecules and reshaped the waxy oil-water interface structure, which replaced the original wax crystal position (the interfacial viscosity and critical storage modulus decrease) and yielded an interfacial structure (the critical strain increase). The wax-surfactant interactions of Span60/80 with different hydrophobic chain saturation were discussed. These interfacial properties are of practical importance for the technological operations in oil production. [ABSTRACT FROM AUTHOR]

The primary goal of this study is to achieve isothermal temperature control of the fluid at the outlet of a circular pipe through a gradient-based method. Typically, temperatures are set on the outer wall of the pipe to warm the fluid and achieve the desired uniformly consistent exit temperature. However, maintaining a constant temperature on the outer wall of the pipe is challenging due to the heat exchange between the fluid and the wall, as well as external environmental factors. Thus, in this current investigation, the temperature distribution is designated along the inner pipe wall to heat the fluid, employing an optimization algorithm to deduce the appropriate optimal heating function on the outer wall. This enables the attainment of the specified temperature on the inner wall. To guarantee consistent temperature control during optimal heating procedures across extensive distances or expansive areas, a gradient-based optimization technique is employed. In the context of a smaller pipe diameter scenario, applying the designated floor function temperature distribution produces the most accurate outcomes for exit temperatures at the pipe exit. The assessed heating function exhibits abrupt surges and disjointed behaviors, which can be alleviated by introducing a weight coefficient into the cost function. This adaptation preserves the precision of exit temperature and its uniformity. In the context of a larger pipe diameter scenario, while adhering to the floor function temperature specification, the estimated exit temperature remains precise, and the uniformity reaches a contentedly acceptable level. This implies that a larger pipe diameter could potentially require a lengthened tube to enhance the uniformity of exit temperatures.

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.

Carbon fiber reinforced composites (CFRP) are susceptible to hidden damage from low velocity external impacts during their service life. To ensure the proper monitoring of the state of the composites, it is crucial to predict the location of an impact event. In this paper, fiber Bragg grating (FBG) sensors are affixed to the surface of a carbon fiber composite tube, and an optical sensing interrogator is used to capture the central wavelength shift of the FBG sensors due to low-velocity impacts. A discrete wavelet transform is used for noise reduction in the response signals. Then, the differences in the captured response signals of the FBG sensors at different locations of the impact were analyzed. Moreover, two methods were implemented to predict the location of low-velocity impacts, according to the differences in the captured response signals. The BP neural network-based method utilized three data sets to train the neural network, resulting in an average localization error of 20.68 mm. In contrast, the method based on error outliers selected a specific data set as the reference dataset, achieving an average localization error of 13.98 mm. The comparison of the predicted results shows that the latter approach has a higher predictive accuracy and does not require a significant amount of data. [ABSTRACT FROM AUTHOR]

Introducing swirling velocity at the inlet is one of the best ways to enhance the transport properties of flow through the pipes. Flow of fluids in small tubes have important applications involving fluid mixing or heat transfer and the flow in these small devices appears to be laminar in nature. Non-Newtonian fluids have wide variety of applications in small pipes ranging from heat-pipes to micro heat exchangers. Hence, it becomes very important to enhance the transport properties of fluids flowing through small devices. To enhance the transport characteristics, the method of introducing swirling of fluid at the inlet of the pipe is chosen. Further, the effect of important dimensionless parameters such as the power-law index of the fluid (characterizes fluid rheology), Reynolds number, the inlet swirl velocity profile shape (transition radius) and the inlet swirl number on the heat transfer characteristics is investigated. The qualitative and quantitative aspects of the heat transfer problem are discussed with particular focus on temperature contours and determination of Nusselt number. Results from the present study show that the power-law index of the fluid and Reynolds number plays an important role in enhancing the heat transfer. Increase in the flow Reynolds number and decrease in the power-law index tend to increase heat transfer strongly. It is also revealed that the inlet swirl number and the profile shape (transition radius) have a weak effect on the augmentation of heat transfer. A correlation is proposed to determine the heat transfer in the form of Nusselt number based on the flow Reynolds number and power-law index. [ABSTRACT FROM AUTHOR]

In this study, we investigated the effects of the viscosity ratio (β) and the angle of inclination (θ) on the change in the flow regime of two fluids undergoing exchange flow in a pipe, using a combination of experimental and theoretical methods. In our experiments, we observed that changing either the viscosity ratio or the inclination angle of the pipe causes a change in the fluidity of the two fluids. For the upward-flowing light fluid, we observed four flow regimes: axisymmetric core-annular flow (CAF), eccentric core-annular flow (ECAF), transitional side-by-side flow (eccentric and side-by-side flow at the same time) (TSBS), and side-by-side flow (SBS). In addition, the larger the viscosity ratio, the larger the critical angle at which the flow pattern eventually changes to side-by-side flow. When the tilt angle is larger than 16 ∘ , the flow pattern is a side-by-side flow, regardless of the viscosity ratio, and we find that the viscosity ratio and the inclination angle determine the ratio of the width of the rising fluid to the diameter of the pipe ( δ a ) and the velocity of the increasing fluid (V). We used the velocity model of the fluid in the pipe to compare with our experimentally measured velocities and found some similarities and differences, which we explained. For the downward-flowing heavy fluid, we divided the viscosity ratios into three ranges for our study and found that the changes in flow regimes were different for different ranges of viscosity ratios. [ABSTRACT FROM AUTHOR]

We extend the canonical problems of simulation and optimization of steady-state gas flows in pipeline networks with compressors to the transport of mixtures of highly heterogeneous gases injected throughout a network. Our study is motivated by proposed projects to blend hydrogen generated using clean energy into existing natural gas pipeline systems as part of efforts to reduce the reliance of energy systems on fossil fuels. Flow in a pipe is related to endpoint pressures by a basic Weymouth equation model, with an ideal gas equation of state, where the wave speed depends on the hydrogen concentration. At vertices, in addition to mass balance, we also consider mixing of incoming flows of varying hydrogen concentrations. The problems of interest are the heterogeneous gas flow simulation (HGFS), which determines system pressures and flows given fixed boundary conditions and compressor settings, as well as the heterogeneous gas flow optimization (HGFO), which extremizes an objective by determining optimal boundary conditions and compressor settings. We examine conditions for uniqueness of solutions to the HGFS, as well as compare and contrast mixed-integer and continuous nonlinear programming formulations for the HGFO. We develop computational methods to solve both problems, and examine their performance using four test networks of increasing complexity. • Models for Hydrogen-Natural Gas blends in pipeline networks. • Simulation of steady-flow of Hydrogen-Natural Gas blends in pipeline networks. • Operational optimization of steady-flow of Hydrogen-Natural Gas blends in pipeline networks. [ABSTRACT FROM AUTHOR]

The article presents the results of numerical studies of heat transfer and pressure drops in a channel with transverse micro-fins. The main aim of the study was to prepare the thermal and flow characteristics of such a channel for a variable longitudinal spacing of micro-fins. For the tested pipe with an internal diameter of D = 12 mm, the absolute height of the micro-fins was e = 0.243 mm, which is 2% of its diameter. The tests were carried out for turbulent flow in the range of Reynolds numbers of 5000–250,000 with the variable spacing of micro-ribs in the range of L = 0.28–13.52 mm, which corresponds to their dimensionless longitudinal distance, L/D = 0.023–1.126. For the studied geometries, the characteristics of the friction factor, ft(Re), and the Nusselt number, Nu(Re), are shown in the graphs. The highest values of Nu were observed for a spacing of L/D = 0.092 in the range of Re = 5000–60,000, while the lowest were observed for a geometry of L/D = 0.035 for Re = 60,000–250,000. The friction factors, however, were the highest for the two geometries L/D = 0.161 and L/D = 0.229 over the entire range of the tested Re numbers. A large discrepancy was observed between the friction factors calculated from the Colebrook–White equation (for irregular relative roughness depicted in the Moody diagram) and those obtained from simulations (for pipes with the same roughness height but regular geometry created by micro-fins). An analysis of the heat transfer efficiency of the tested geometries was also presented, taking into account the criterion of equal pumping power, i.e., the PEC (performance evaluation criteria) coefficient. The highest values of the PEC coefficient, up to 1.25–1.28, were obtained for micro-fin spacings of L/D = 0.069 and L/D = 0.092 in the Re number range of 20.000–30.000. [ABSTRACT FROM AUTHOR]

With a large number of railroad and highway tunnels opening for operation, the diseases caused by hidden lining defects are increasing. The study of flow characteristics of freshly mixed concrete during tunnel lining casting is the key to revealing the formation mechanism of hidden defects. This paper revealed the location of blank lining formation by investigating the circumferential and longitudinal flow characteristics of concrete in the vault during tunnel pouring to provide suggestions for improving the quality of tunnel lining pouring for the various projects. This paper adopted the method of indoor testing, selected the suitable working conditions and flow parameters, validated the accuracy of the test with a numerical simulation, and simulated the secondary lining pouring process of the tunnel arch from the circumferential direction and longitudinal direction. This revealed the flow characteristics of the freshly mixed concrete in the process of pouring the arch lining. The flow of concrete in the arch lining was basically characterized by two major features which were similar to the flow in the pumping pipe and the layered flow. It also revealed the relationship between the concrete flow rate, flow distance, and the location of the formation of the blank lining risk zone with the slump of the concrete, the pumping pressure, and the radius of the tunnel. [ABSTRACT FROM AUTHOR]

The coefficient of vertical permeability is a common filter design criterion for woven slit-film geotextiles. According to the pipe flow theory, a permeability coefficient model has been proposed for predicting the permeability coefficient of woven geotextiles, in which the pore characteristics were described by the Sierpiński carpet fractal theory. The verification of models is performed in 12 woven geotextiles of two types using a digital image method and a vertical water permeability test of the geotextile. The influence of the pore characteristics on the permeability coefficient is further explored using univariate and multivariate analyses. The results show that the porosity model can accurately predict the total percent pore area (POA) and the POA distribution of the woven geotextiles, and the permeability model can accurately predict the permeability coefficient of the geotextiles. The permeability coefficient of geotextiles decreases with the pore area fractal dimension and the minimum pore size under the action of a single factor. The permeability coefficient increases as the maximum pore size increases. POA and maximum pore size are the most significant independent variables affecting the permeability coefficients of geotextile under the action of multifactor. [ABSTRACT FROM AUTHOR]

Intake pipe structure has a pivotal impact on the distribution of vortices within the combustion chamber in a cycloidal rotary engine (CRE). Therefore, studying the influence of the intake pipe deflection angle (IPDA) on the in-cylinder airflow motion has significant importance for enhancing CRE performance. This study utilized computational fluid dynamics and chemical reaction kinetics methods to establish a numerical simulation model for the in-cylinder flow and combustion in the CRE. Subsequently, the Omega vortex identification method was employed to investigate the influence of IPDA on the vortex structures within the cylinder and to explore the relationship between CRE performance and the vortices. The research findings indicate that although the IPDA did not significantly alter the fuel mass injected into the cylinder, it increased the airflow velocity by 14.6% during the main intake stage and increased the mass fraction of the burned fuel at the compression top dead center by 19.1%. Additionally, the increased airflow velocity within the cylinder led to improvements in both the mean tumble ratio by 186.5% and the turbulent kinetic energy by 25.5%. Furthermore, the IPDA significantly changed the distribution of vortices within the cylinder, which is a key factor contributing to the combustion variation of the CRE. The case of IPDA = 16° provided the largest volume of the strong vortices and the highest mean in-cylinder pressure. Compared to the original design, the volume of strong vortices was 1323.6% greater, and the mean in-cylinder pressure was higher by 5.3%. [ABSTRACT FROM AUTHOR]

Pipeline junction plays a pivotal role in fluid mixing for biomedical, chemical, and industrial processes. This study introduces an I–L junction for pipeline systems, fostering concurrent flow between branch-pipe injection and the main pipe bulk flow. In contrast to the conventional T-junction with perpendicular injection, the I–L design demonstrates high potential in mitigating vibration-induced fatigue risks, given an optimal branch-to-main pipe diameter ratio, rd. Using unsteady Reynolds-averaged Navier–Stokes equations, the study assesses fluid mixing across a broad range of rd (1 / 12 – 1 / 2.5). The streamline geometry undergoes a transition from well-defined symmetric vortices to unsteady oscillations when the pipe diameters diverge beyond 1/4, arising from vortex shedding in the wake of the branch pipe. Despite the conventional T-junction showing a more homogeneous velocity distribution in the streamwise direction, its turbulent kinetic energy (TKE, both modeled and calculated from the resolved-scale velocities) near the junction is an order of magnitude larger, implying high overall inhomogeneity in the flow. The TKE decays rapidly to an equivalent level compared to the proposed I–L junction approaching discharge, indicating that the peaking of TKE in the T-junction does not significantly contribute to enhanced fluid mixing. Conversely, it can likely result in harmful vibrations inside the pipeline. While the turbulence statistics remain qualitatively unchanged for r d < 1 / 4 , an enlarged discrepancy in pipe diameters beyond r d < 1 / 6 yields more favorable mean surface pressure coefficient, C P ¯ . The results provide insights into pipeline design, recommending an optimal pipe diameter ratio for enhanced mixing of successively collected fluids while retaining improved system reliability. [ABSTRACT FROM AUTHOR]

The backflow phenomenon in shear-thinning and shear-thickening fluids is investigated in pipe flows at friction Reynolds number R e τ = 180 via direct numerical simulations. Conditional average results show that the extreme fluctuation of wall shear stress around the backflow regions is more abrupt under the shear-thinning effect. The statistical characteristics of the backflow at different flow indices from 0.5 to 1.5 show remarkable differences. The probability of the backflow events at the wall increases in both the shear-thinning and the shear-thickening fluids under different mechanisms. The backflow occurs more frequently and exists further away from the wall in the shear-thinning fluids owing to the suppressed near-wall turbulent structures and the laminarization at low flow indices. The increase in the probability of the backflow events in the shear-thickening fluids is caused by increased Q2 and Q4 events in the near-wall region. The variation in the size and the lifespan of the backflow regions with the flow index is very prominent which both increase with the shear-thinning effect and decrease as the flow becomes dilatant. In the weakly turbulent flow of shear-thinning fluid, large backflow regions appear near the leading edge of the turbulent spots where the off-axial turbulent fluctuations are significantly lowered. Observations show the linked evolution between the hairpin vortices and the backflow regions induced underneath the strong spanwise rotations. The backflow follows the auto-regeneration process of the hairpin vortices in a packet which results in coherent streamwise-aligned backflow regions under the hairpin packets confined closer to the wall. [ABSTRACT FROM AUTHOR]

This study presents an innovative dynamic subgrid-scale model for large eddy simulation based on the partial-averaging method. In this method, the partial-averaged velocity fluctuations, known as drift velocities, were used to formulate subgrid-scale turbulent viscosity. This feature enables the preservation of more comprehensive first-order turbulence information so that the anisotropic turbulent flow can be better predicted. Dynamic coefficient adjustment was adopted to effectively address the sharp change of subgrid-scale viscosity in complex flows. The proposed model was programed and employed to simulate a plane jet, a circular jet, a fully developed pipe flow, and a swirling jet based on OpenFOAM. The results indicate that the model exhibits high predictive accuracy, adapting well to free shear flows and wall-bounded shear flows. The distribution of drift velocities provides direct statistical information of turbulent flows and reveals anisotropic characteristics of turbulent fluctuations. [ABSTRACT FROM AUTHOR]

Modeling fully developed turbulent flow for Herschel–Bulkley (HB) fluids in pipes is a long-standing challenge. Existing semi-empirical, theoretical, and numerical methods are either inconsistent with experimental data or are validated for low Reynolds numbers. This study focuses on validating a novel approach using rheology-based wall functions within Reynolds-averaged Navier–Stokes solvers. Simulations of wall shear stress and velocity profiles were conducted across a wide range of Reynolds numbers using a single-phase HB fluid, with measurements taken both upstream and downstream of a 90° pipe bend. Two turbulence closure models, the k–ε model and the Reynolds stress model, were employed with the wall function implemented as a specified shear boundary condition. Results demonstrate significant improvements over the Newtonian-based models, such as standard wall function by Launder–Spalding or with available semi-empirical models, achieving strong statistical correlations and minimal deviation (from the experimental findings) at high Reynolds numbers. The study also examines the utility of the wall viscosity Reynolds number and assesses the reliability of semi-empirical models for HB fluids. These findings offer valuable insights for enhancing modeling accuracy in complex fluid flow scenarios, with potential applications spanning industries like mining, chemical processing, petroleum transportation, and sanitation systems, providing practical alternatives to costly experimental procedures in pipe systems. [ABSTRACT FROM AUTHOR]

An air pocket is very likely to be trapped in a downward-sloping pipe (DSP) when water fills an undulating pipeline consisting of a series of inclined U-shaped pipes. To investigate the entrainment and evolution behavior of the entrapped air pocket, a series of experiments was carried out using a self-built inclined U-shaped device. The results show that at the junction between the DSP and the upward-sloping pipe (USP), the water phase forms a liquid accumulation. In addition to the agreed mechanism of liquid film jet shear and turbulent pulsation, the initiation of air entrainment is promoted further by the unique entraining effect of the reverse upward movement of the liquid accumulation in the DSP. Based on this, the flow patterns in the DSP are classified into four categories, namely single long slug flow (SLSF), unsteady transitional flow (UTF), quasi-slug flow (QSF), and plug flow (PF). Among them, UTF identified in this paper is a new and unique flow pattern for U-shaped pipe. Due to the development of UTF, the additional head loss of the air pocket and the critical Froude number required to completely remove the air pocket are increased. The effects of pipe inflow Froude number, liquid film Reynolds number, and upward-inclination angle on flow pattern transition, bubble movement, and air removal are explained and discussed. [ABSTRACT FROM AUTHOR]

In this study, the influence of U-bends on the flow and pressure propagation characteristics of a gas–liquid two-phase flow in upstream and downstream straight pipes was investigated experimentally. The superficial velocities of the gas and liquid are 0.18–25.11 m/s and 0.20–1.98 m/s, respectively, covering plug flow, slug flow, and annular flow. The experiments were conducted in U-tubes with inner diameters of 9 mm and 12 mm and with a curvature ratio of 8.33. The U-tube was C-shaped. The pressure fluctuations at the axial measurement points of the straight tubes were measured. Flow images of the distal straight tubes and U-bends were obtained. The disturbance from U-bends in the two-phase flow in the vicinity of the bend is very obvious. The perturbation from U-bends in the fluid in the adjacent straight tubes is highly related to the incoming flow pattern. The slug flow has the most significant influence, whereas the effects of the plug and annular flows are small. Fundamentally, it mainly depends on the weight relationship between the gravity, centrifugal force, and inertial force of the gas–liquid two-phase fluid. The pressure fluctuation propagates in the form of a wave with the same dominant frequency in the straight pipes of the U-tube. The pressure pulsation energy in the straight tubes strengthens with decreasing distance from the 180° return bend. In addition, the pressure fluctuation energy downstream of the U-bend is greater than that upstream of the return bend. [ABSTRACT FROM AUTHOR]

The formation and behavior of gas bubbles is experimentally investigated in a liquid metal downward pipe flow, a configuration that largely corresponds to the situation in a submerged entry nozzle (SEN) in the continuous casting process in steel making. The experimental mockup is operated at room temperature using the ternary alloy GaInSn as model fluid. Argon gas is injected through an orifice located in the SEN wall. The gas distribution in the pipe is visualized by means of the X-ray radiography. The set-up is completed by an electromagnetic stirrer, which is used to create a swirling flow in the tube. Depending on the volume flow rates of the gas and the liquid metal, as well as the intensity of the swirl flow generated by the stirrer, 4 flow regimes are observed: (1) the formation of an almost stationary gas pocket in the region below the injection point without any electromagnetic stirring, (2) a twisted void zone along the side wall, (3) a straight void zone in the center of the pipe, and (4) a bubble chain in the core of the pipe flow. The experiments reveal that the wetting conditions at the inner SEN wall have a decisive influence on the resulting flow regime. [ABSTRACT FROM AUTHOR]

One of the often employed flow structures in vertical pumping stations is the siphon outlet pipe. It has a complicated geometric structure and internal flow field, which directly affects how effectively, safely, and steadily pumping stations operate. The entire flow conduit of the vertical axial flow pump device was adopted as the study object in order to elucidate the mechanism of the internal biased flow of the siphon outlet pipe caused by the axial flow pump under different flow conditions, and the three-dimensional unsteady flow field of the vertical axial flow pump device was numerically solved using the numerical simulation technique. Physical model tests were used to confirm the results of the numerical simulation. The findings demonstrate that there is a horizontal bias in the flow of the inlet surface and outlet surface of the elbow pipe of the siphon outlet pipe, and that when the flow rate rises, the degree of the horizontal bias in the flow gradually diminishes, and the ratio of biased flow gradually decreases. The flow in hump segment presents up-and-down flow, and when the flow rate increases, the ratios of biased flow first rises before falling. The major causes of the production of biased flow in the outlet pipe are residual velocity circulation at the guide vane's outlet, wall constraint at the elbow pipe, and flow inertia; Under various flow conditions, the morphologies of the vortex structures in the outlet pipe vary; the characteristics of the energy conversion of each part of the pump device are disclosed, with the inlet pipe having the lowest proportion of energy conversion. Under the optimal flow condition, the elbow-inlet pipe's proportion of energy conversion is only around 1.04%, and the proportions of the guide vane, 60° elbow pipe, and siphon outlet pipe's energy conversion are significant and fluctuate with time. The proportion of energy conversion in the elbow-inlet pipe and siphon outlet pipe steadily increases as flow rate rises, but the proportion in the guide vane and 60° elbow pipe drops initially before increasing. [ABSTRACT FROM AUTHOR]

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Direct numerical simulations are performed to study temporal variations of the wall shear stresses and flow dynamics in the turbulent pulsatile pipe flow. The mechanisms, responsible for the paradoxical phenomenon for which the amplitude of the oscillating wall shear stress in the turbulent flow is smaller than that in the laminar flow for the same pulsation conditions, are investigated. It is shown that the delayed response of turbulence in the buffer layer generates a large magnitude of the radial gradient of the Reynolds shear stress near the wall, which counteracts the effect of the oscillating pressure gradient on the change of the streamwise velocity and hence reduces the amplitude of the wall shear stress. Such a delayed response consists of two processes: the delayed development of near-wall streaks and the subsequent energy redistribution from the streamwise velocity fluctuation to the other two co-existing components. This is a dynamical manifestation of the viscoelasticity of turbulent eddies. As the frequency is reduced, the variation of the friction Reynolds number results in a phase-wise variation of the time scale and intensity of the turbulence response, causing the hysteresis of the wall shear stress. Such a phase asymmetry is amplified by the increase of the pulsation amplitude. An examination of the energy spectra reveals that the near-wall streaks are stretched in the streamwise direction during the acceleration phase, and then break up into small-scale structures in the deceleration phase, accompanied by the enhanced dissipation that transforms the turbulent kinetic energy into heat. [ABSTRACT FROM AUTHOR]

This study introduces an analytical solution for the laminar entrance flow in circular pipes, aiming to confirm the occurrence of velocity overshoot. Velocity overshoot is characterised by the maximum axial velocity appearing near the pipe wall instead of the central axis. Similar to the previous studies, the analytical solution is derived from the parabolised Navier-Stokes equation; however, the specific approach used in linearising the momentum equation has not been attempted before. The accuracy of this analytical solution has been verified through a comprehensive comparison with various published experimental data. The existence of velocity overshoot at a short distance from the inlet, which is evident in numerous numerical calculations based on the full Navier-Stokes equations and corroborated by recent magnetic resonance (MR) velocimetry experiments, is identified analytically for the first time. The parabolised Navier-Stokes equation has inherent self-similarity with respect to the Reynolds number, implying that Re is incorporated into the dimensionless variables rather than serving as an independent flow parameter. According to both MR velocimetry measurements and the present analytical solution, the self-similarity is not valid immediately following the pipe inlet, and this becomes more evident as Re decreases; hence, the analytical solution derived from the parabolised Navier-Stokes equation cannot accurately predict the evolution of the velocity profile within this region near the pipe inlet. [ABSTRACT FROM AUTHOR]

An extended turbulent state can coexist with the stable laminar state in pipe flows. We focus here on short pipes with additional discrete symmetries imposed. In this case, the boundary between the coexisting basins of attraction, often called the edge of chaos, is the stable manifold of an edge state, which is a lower-branch travelling wave solution. We show that a low-dimensional submanifold of the edge of chaos can be constructed from velocity data using the recently developed theory of spectral submanifolds (SSMs). These manifolds are the unique smoothest nonlinear continuations of non-resonant spectral subspaces of the linearized system at stationary states. Using very low-dimensional SSM-based reduced-order models, we predict transitions to turbulence or laminarization for velocity fields near the edge of chaos. [ABSTRACT FROM AUTHOR]

In both turbulent and laminar pipe flows, we were able to accurately forecast the beginning range of the convective thermal transferring coefficients of Al2O3 magnetized nanofluids using machine learning approaches. The simulations utilized two machine learning techniques: radial basis function-backpropagation (RB) and multiple linear regression analysis. First, we used multiple linear regression analysis to fit the polynomial equation. Afterwards, grid search cross-validation was employed to determine the optimal RB model with six hidden layer neurons. To evaluate the RB model, we compared numerical patterns of the parameters used to measure accuracy. The regression coefficient and mean square error were the most commonly utilized parameters in Reynolds number mass percentage simulations, R². In the case of a laminar flow, these numbers were found to be 0.99994 and 0.34, respectively. Additionally, the results for laminar flow conditions using Reynolds number-magnetic field strength simplification were ideal, with an mean square error of 3.85 and an R² value of 0.99993. By comparing the predicted values with the experimental results visually using 3-D smoothed surface plots, we were able to further prove that the model was valid and accurate. These revolutionary findings could spark new developments and encourage substantial improvements in nanotechnology and machine intelligence. These findings are an important asset for driving future research and development, which in turn makes significant contributions to the ever-expanding frontiers of these innovative fields. [ABSTRACT FROM AUTHOR]

The Archimedean spiral coil made of a transversely corrugated pipe represents the radiant heat absorber of a parabolic dish solar concentrator. The main advantage of the considered design is the coupling of two passive methods for heat transfer enhancement: coiling the flow channel and changing the surface roughness. The aim of this numerical study is to assess the capability of RANS models of different complexity (realizable k-ε, SST k-ω, and RSM linear pressure-strain) to adequately represent the heat transfer phenomena in the considered complex flow geometry for wide ranges of Reynolds and Prandtl numbers. The obtained results indicate that the realizable k-e model with enhanced wall treatment is inadequate to simulate the heat transfer for all flow conditions, while both SST and RSM slightly overestimate experimental data in the turbulent region and are able to predict laminarisation at low Reynolds numbers. The SST model predictions are more accurate in the transitional and at the beginning of the turbulent region, irrespective of the curvature ratio. The RSM predictions are generally more accurate in the turbulent region. Numerically obtained circumferential distributions of local Nusselt number reveal that considered turbulence models are unable to completely anticipate the interactions between the complex flow in the basic section of the pipe and the vortex flow within the corrugations. [ABSTRACT FROM AUTHOR]

The increase in freezing depth requires thicker, stronger, and colder freezing walls, and various complex factors in deep strata greatly increase the risk of freezing pipe fracture. To address the phenomenon of freezing pipe fracture, this paper designs freezing pipe and joint mechanical performance experiments based on acoustic emission (AE) technology, mainly testing the deformation of freezing steel pipes and composite joints at normal and low temperatures, changes in load bearing capacity, and corresponding AE characteristics of the process. Additionally, the associated AE characteristics throughout the process will be analyzed. The ultimate goal is to establish a discriminative pattern for identifying the critical fracture of freezing pipes based on the analysis of AE signal characteristics in conjunction with mechanical properties. The sensitivity of the AE system under low-temperature conditions and the reliability of the test were tested through pencil lead break experiments, and saltwater noise detection experiments were conducted to prevent noise interference from low-temperature saltwater flow and pipe wall friction in the identification of crucial signals for freezing pipe fracture. This study provides a basis for identifying the deformation mechanics and fracture warning of freezing pipes through dynamic analysis of AE monitoring information. [ABSTRACT FROM AUTHOR]

In this era of scarce and expensive energy, it has become imperative to devise means of reducing energy consumption, particularly in petroleum industries where huge amounts of energy are usually consumed. It is within this context that attempts have been made to reduce the energy consumption during pump-driven fluid transportation by the addition of drag-reducing polymers (DRPs), which mitigate the adverse frictional drag caused by the pipe wall. Hence, this study focused on quantifying the energy savings by the DRPs in dispersed oil-water flow at different Reynolds numbers using twelve DRPs, which possess different combinations of properties such as molecular weight, charge density, and ionic type. The results revealed substantial savings in energy in all cases with the highest saving of about 60.4%. Molecular weight posed a positive and most dominant impact among the three polymer properties investigated. The charge density slightly increased the energy savings at low values while the reverse was the case at high values. Cationic polymers produced slightly better performances than their anionic counterparts of comparable molecular weights and charge densities. Specifically, the energy saving at oil fractions of 0.1 and 0.3 increased from 6.9 to 60.4% and 5 to 51.9%, respectively, indicating the negative impact of the oil fraction. Overall, the use of DRPs has proved to be an efficient and sustainable means of saving substantial amounts of energy required to overcome the frictional drag in pipe flow. [ABSTRACT FROM AUTHOR]

This paper presents an optimized design method for an ultrasonic flow meter (USFM) used in the semiconductor manufacturing field for liquid flow measurement. Based on fluid simulation, the impact of different inlet tube section angles on the velocity distribution within the measuring tube section of the USFM was analyzed, and a suitable inlet tube section angle of 45° was determined. Based on the average flow velocity on the acoustic channel line and the average flow velocity in the measuring tube section, a velocity correction factor was calculated to adjust the measured flow velocity to the actual flow velocity of the tested fluid. The USFM prototype was calibrated for flow rate and a compensation factor obtained to correct measured flow rate. The accuracy of the USFM was tested and found to reach 1.5 level, meeting the needs for liquid flow measurement in the semiconductor manufacturing field. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to explore the transient characteristics of mixed-flow pumps during startup process. Design/methodology/approach: This study uses a full-flow field transient calculation method of mixed-flow pump based on a closed-loop model. Findings: The findings show the hydraulic losses and internal flow characteristics of the piping system during the start-up process. Research limitations/implications: Large computational cost. Practical implications: Improve the accuracy of current numerical simulation results in transient process of mixed-flow pump. Originality/value: Simplify the setting of boundary conditions in the transient calculation. [ABSTRACT FROM AUTHOR]

This work evaluates use of a dimensionally adaptive (DA) meshing technique to speed CFD modeling of non-reacting pressurized flow in a cylindrical geometry with a center jet and non-axisymmetric secondary jets. The DA-capable approach incorporates an a priori dimensional boundary location and extension of 3-D RANS flow solvers. Recirculation zone length, not flow asymmetry, was the limiting factor in placement of the dimensional boundary between 3-D and axisymmetric meshes. Boundary placement was based on confined turbulent jet theory, which suggests jet attachment is a linear function of cylinder radius, L, expressed as 5.85L. CFD results for a turbulent axial pipe flow showed that as the dimensional boundary was moved upstream, computational time dropped quadratically with the reduction in mesh cells. Further simulations of a 0.2032-m diameter, 1.5-m long reactor with turbulent center primary jet and outer radius secondary jets placed the dimensional boundary at 0.7 m. Results for pressures of 20, 10, and 5 bar and mass flow rates of 75% and 50% of baseline demonstrated two key results. First, flow similarity was preserved across all cases and the predicted jet attachment location was approximately 0.61 m, compared with the theoretical value of 0.594 m. Second, runtime reductions of 79% (pressure) and 82% (flow rate) were seen for the DA meshes compared with fully 3-D meshes. Differences in average exit axial velocities between DA and fully 3-D meshes were 2-4% for the pressure cases and 0.7-1.5% for the flow rate cases. Lastly, comparison with 3-D quartergeometry calculations showed the DA approach to be -10% faster with exit axial velocities within 3-5% of 3-D velocities. [ABSTRACT FROM AUTHOR]

The use of multiple perspective views is a possible pathway towards the combined measurement of multiple time-resolved flow properties by filtered Rayleigh scattering (FRS). In this study, a six view observation concept is experimentally verified on a aspirated pipe flow. The concept was introduced in our previous work, and it has the ability to simultaneously measure high-accuracy time-averaged and time-resolved three-component velocity, pressure and temperature fields. To simulate time-resolution, multi-view FRS data at a single optimised excitation frequency are selected and processed for multiple flow properties. Time-averaged and quasi-time-resolved FRS results show very good agreement with differential pressure probe measurements and analytical temperature calculations and lie within ± 2 m/s of complementary laser Doppler anemometry (LDA) velocity measurements for all operating points. The introduction of a multistage fitting procedure for the time-resolved analysis leads to a significant improvement of the precision by factors of 4 and 3 for temperature and axial velocity and 18 for pressure. Moreover, both processing methods show their capacity to resolve flow structures in a swirling flow configuration. It is demonstrated that the developed multi-view concept can be used to determine multiple flow variables from a single-frequency measurement, opening the path towards time-resolved multi-parameter measurements by FRS. [ABSTRACT FROM AUTHOR]

Addressing the issue of leakage in practical scenarios involving hose pumps, this paper conducts an analysis on hose pumps with existing compression gaps. The model is simplified to represent the two-dimensional Newtonian fluid pulsating flow of a single-sided sine wave passing through the tube. The study derives the axial flow velocity distribution within the tube while establishing correlations between the leakage volume, tube clearance, pressure differential, deformed cross-sectional length of the tube, rotor speed (which exhibits a negative correlation), the deformation length of the tube in the x-direction, and the fluid's dynamic viscosity (demonstrating a positive correlation). Utilizing a bidirectional fluid-structure coupling method, this analysis investigates hose pumps with compression gaps. Specifically, it examines the flow field pressure, velocity, and vortex intensity of two Newtonian fluids with Reynolds numbers of 10–30 and 6000–15 000, respectively, within a 180° bend tube with a curvature-to-inner-diameter ratio of 4.6. This analysis is conducted under inlet velocities of 0.32 and 0.6 m/s, and outlet pressures of 0 and 0.1 MPa. The study identifies the positions of extreme leakage rates, elucidating the flow field characteristics and their impact on leakage. Furthermore, it investigates the causes of secondary flows within the tube, concluding that the fluid inside the tube exhibits symmetric helical motion. This research establishes the periodic variations in flow field vortex intensity and secondary flow intensity, along with the conclusion that leakage rates are positively correlated with axial vortex intensity and negatively correlated with secondary flow intensity. [ABSTRACT FROM AUTHOR]

The friction factor is widely recognized as a pivotal parameter in the analysis of fluid–boundary interactions; however, a comprehensive grasp of friction mechanics remains elusive. This investigation revisits measurements from the benchmark Nikuradse measurements, furnishing indirect evidence of two critical points in pipe turbulence. It underscores that friction factors within laminar and turbulent regimes are intimately interconnected, bearing significant relations to subcritical and critical phenomena. The two critical points directing the laminar–turbulent transition consist of a standard non-equilibrium phase transition and a fully matured turbulent regime, accompanied by an extensive crossover to its asymptotic scaling. Relying on a mathematical model, the scaled friction factor for rough pipes converges into a unified curve. New formula of friction factor of pipe flow is derived, and it was illustrated that it can be derived as a geometric weighted parameter, bridging the laminar and turbulent friction factors. Conclusively, the proffered model was juxtaposed with pipe experimental data from the antecedent study and more contemporaneous transitional pipe data to authenticate the aptness of the suggested model, and it united the friction factor in all three regimes. [ABSTRACT FROM AUTHOR]