Pipe Flow Research Articles

Convective Heat Transfer in Uniformly Accelerated and Decelerated Turbulent Pipe Flows

This study presents a detailed investigation of the temporal evolution of the Nusselt number (Nu) in uniformly accelerated and decelerated turbulent pipe flows under a constant heat flux using direct numerical simulations. The influence of different acceleration and deceleration rates on heat transfer is systematically studied, addressing a gap in the previous research. The simulations confirm several key experimental findings, including the presence of three distinct phases in the Nusselt number temporal response—delay, recovery, and quasi-steady phases—as well as the characteristics of thermal structures in unsteady pipe flow. In accelerated flows, the delay in the turbulence response to changes in velocity results in reduced heat transfer, with average Nu values up to 48% lower than those for steady-flow conditions at the same mean Reynolds number. Conversely, decelerated flows exhibit enhanced heat transfer, with average Nu exceeding steady values by up to 42% due to the onset of secondary instabilities that amplify turbulence. To characterize the Nu response across the full range of acceleration and deceleration rates, a new model based on a hyperbolic tangent function is proposed, which provides a more accurate description of the heat transfer response than previous models. The results suggest the potential to design unsteady periodic cycles, combining slow acceleration and rapid deceleration, to enhance heat transfer compared to steady flows.

Experimental investigation on the restart characterization of shale oil-water flow in a horizontal pipe

ABSTRACT With the dwindling conventional oil resources and increasing energy demand, shale oil development has gradually become a hot spot in the global energy industry. Moreover, the shale oil pipeline also inevitably experiences abnormal operations, such as shutdown and restart during regular maintenance or emergency accident repairs. However, previous restart research primarily focused on conventional crude oil pipelines, and there is still a research gap on shale oil-water flow. Therefore, this work conducted the shale oil-water restart flow experiment in the multi-test section pipe flow loop, considering the temperature (20–50℃), starting frequency (15–25 hz), and water content (0–80%). Based on the restart pressure and volume flow rate change, the response characteristics of start pressure are studied. Moreover, the changing rules of restart pressure are explored with starting frequency, temperature, and water content. Eventually, the variation trend of the restart pressure absolute errors between the calculated value and the experimental data with the starting frequency is analyzed. The results show that the restart pressure reaches the maximum around 10 s after the pump starts, and the maximum restart pressure is approximately 1.5 times the stabilized restart pressure. Moreover, the restart pressure increases linearly with the starting frequency and decays exponentially with the temperature and water content (after the inversion point). With the starting frequency reduced from 45 hz to 15 hz, the restart pressure reduces from 24.6 kPa to 10.0 kPa at 20°C. Furthermore, the empirical formulas can predict the starting pressure at low frequencies. This research lays a theoretical foundation for the safe restart of shale oil-water flow.

Experimental Investigation of Heat Pipe Flow Dynamics and Performance

Due to their safety, efficiency, and passive operation, heat pipes have found diverse applications that include nuclear microreactors. Heat pipes enable increased reliability in microreactors, as they eliminate the need for reactor coolant pumps and their associated auxiliary systems while resulting in a greatly reduced spatial footprint. Experimental work is needed to support and expedite the design and licensing of heat pipe microreactors, especially the validation of heat pipe performance, as key heat transfer components. The present work develops a comprehensive heat pipe experimental database covering a wide range of heat pipe operating conditions. In addition, two-phase thermosyphon experiments are conducted to serve as a benchmark for performance. The operating conditions are determined based on previously developed scaling laws for heat pipes and two-phase thermosyphons using low-temperature working fluids. The tested heat pipe is about 2 m long and equipped with in-house-developed annulus screen wicks. To allow for the investigation of heat pipe flow dynamics, various instruments are incorporated to acquire heat pipe pressures, pressure drops, and temperatures. In particular, a fiberoptic sensor is implemented to measure temperatures along the centerline of the entire heat pipe. The results can be directly applied to the advancement of numerical tools currently under development for heat pipe microreactor analysis.

IMPROVING METHODS FOR PREDICTING THE STRUCTURE OF GAS-LIQUID FLOW IN HORIZONTAL PIPES

Analysis of existing research on the hydrodynamics of two-phase mixtures allows us to trace the main trends in the development of engineering calculation methods, as well as identify the most promising approaches for developing algorithms for predicting the patterns of gas-liquid flows in horizontal pipes. Predicting the patterns of two-phase flows is necessary to solve a number of applied problems related to the design of field pipeline systems, monitoring of operational parameters during the transportation of well products, calculation of hydraulic pressure drop in pipes, etc. Conventionally, in creating methods for predicting flow regimes in horizontal pipes, there are stages based on empirical approaches, mechanistic modeling and unification of hydrodynamic criteria for assessing the processes of patterns transformations of two-phase flows. Approaches based on the unification of hydrodynamic models of gas-liquid flows are noted as promising directions in the development of hydrodynamic forecasting criteria. The principles of unification consist in bringing to uniformity a mathematical apparatus capable of predicting all possible patterns of gas-liquid flow in vertical, inclined and horizontal pipes based on known volumetric flow rates of liquid and gas. The article proposes the improvement of known unification approaches in the development of criteria for predicting the annular and dispersed-bubble patterns of gas-liquid flow in field pipes. The verification of the obtained algorithms for pattern prediction of annular and dispersed-bubble modes of horizontal gas-liquid flow was carried out.

Unsteady flow rate in transient, incompressible pipe flow

AbstractKnowledge regarding current flow rates through pipes and other components is crucial for most hydraulic systems. The hydraulic power can be computed in combination with the pressure, which may be used in many applications, such as predictive maintenance. Most flow rate sensors used in the field of fluid power operate invasively. Therefore, the measurement process itself alters the flow rate. Furthermore, most sensors operate accurately for stationary flow but produce inaccurate measurements for transient flow. A well‐known method of determining the flow rate is to measure the pressure difference between two points along a pipeline and calculate the flow rate based on the law of Hagen and Poiseuille. However, since the relation mentioned above only applies to laminar, steady, and incompressible flow, its usefulness for transient flows is limited. This paper derives a system equation based on the fundamental laws of fluid mechanics, which describe transient, incompressible pipe flow. As a result, the fundamental equations are solved in the Laplace domain and subsequently transformed back into the time domain. The four‐pole theorem relates the pressure difference and the volumetric flow rate. The analytical solution consists of a convolution integral containing a weighting function and the pressure difference. Compared to a simulation, the novel equation displays high accuracy for transient and stationary incompressible pipe flow. This equation paves the way for a soft sensor, which allows the noninvasive measurement of arbitrary volumetric flow rates within pipes.

Mechanical study and equations for gravity flow pipe liners stretching across ring fractures or joints under shear action

Cured-in-place-pipe (CIPP) liners have been widely used in rehabilitation of gravity flow pipelines. However, the host pipe rehabilitated by the CIPP liner may be subject to shear force and shear displacement at the joint. In this study, a finite element model of a rigid host pipe with liner under shear action is established and used to study the resulting behaviour. Controlling factors such as the gap spanned by the liner between host pipes across the joint, diameter, the liner thickness, the elastic modulus of the liner, and the coefficient of friction between host pipe and liner are studied. The liner stress, displacement, and shear force are reported. Shear stiffness and stress equations are then fitted based on 286 data points. The results show that the maximum stress on the inner surface of the liner occurs at the shoulder and haunch, and the maximum stress on the outer surface occurs at the springline. The inner surface stresses at the crown and invert decrease with increases in liner-host pipe friction, but increase at the shoulder and haunch. Coefficient of Friction has almost no effect on the stresses that develop on the outside surface of the liner.

Capabilities and limitations of smoothed particle hydrodynamics for the simulation of two‐phase flow instabilities

AbstractSmoothed particle hydrodynamics (SPH) is a mesh‐free, Lagrangian particle‐based method that is able to simulate multiphase flows in an economical manner. However, its ability to capture the flow regimes and regime transitions in two phase (liquid‐gas) internal flows, such as pipe or channel flows is not yet generally established. To address this lack in understanding, we first examine a laminar rising bubble case in order to evaluate the fluid‐fluid interface representation and transient interface evolution by the solver. With a focus towards the transition mechanism from a stratified flow regime to a slug flow regime, we investigate the Kelvin–Helmholtz instability (KHI) both qualitatively and quantitatively, initially focusing on a low density ratio () and then extending it to a high density ratio (). For the low density ratio, we conduct an analysis of the temporal evolution and demonstrate that the SPH solver captures the initial exponential growth in qualitative agreement with inviscid linear stability theory (LST) and reference numerical data for shear‐dominated flow with Richardson number . By conducting eight additional simulations for various for the high density ratio, we demonstrate that the numerically obtained parameter value for instability is around , which is in reasonable agreement with the theoretically expected value of . Based on the SPH results obtained for the range , we suggest a simple parameterization of the reduction of the effective growth rate proportional to .

Using computational fluid dynamics and deep learning for leak detection and localization in a smart water management system

Water leakages in distribution systems offer significant challenges, resulting in water loss, infrastructure damage, and environmental hazards. As urban populations grow and water resources become scarcer, water management systems’ efficiency becomes increasingly important. Traditional leak detection methods are inadequate and labour-intensive, making them unsuitable for large-scale infrastructure. In addition, limitations in the data representing pipes of varying diameters and materials under various leak scenarios leads to complexity in automatic water leak detection and localization. In response to this challenge, this research effort combines Computational Fluid Dynamics (CFD) and Deep Learning (DL) to enhance leak detection and localization. The study simulates water flow in pipes of varying diameters and materials under various leak scenarios using CFD. Consequentially deep learning models like the Bi-Layered ReLU Encoder + Softmax and Tri-Layered ReLU Encoder + Softmax are trained and tested. The results indicate improvements in detection accuracy by 2.4% and localization by 5.6%, highlighting the potential of this hybrid approach to enhance the reliability and efficiency of water management systems, ultimately promoting water conservation and reducing infrastructure damage.

Location and scales of drag reduction in turbulent pipe flow with wall oscillations at low Reynolds number

Location and scales of drag reduction in turbulent pipe flow with wall oscillations at low Reynolds number

Stabilizing Pipe Flow by Flattening the Velocity Profile

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.

A novel relaxed modified pipe hydrodynamic model for mixed flow simulation

In this study, we propose a novel modified pipe hydrodynamic model with a partial relaxation approach and develop a corresponding numerical algorithm within the framework of the finite volume method for its computation to enable robust, accurate, and comprehensive pipe modeling. The proposed numerical model provides some key improvements compared to existing numerical schemes for simulating mixed pipe flows: (1) it is capable of preserving both moving- and stationary-water steady states, and (2) it effectively reduces post-bore oscillations while maintaining second-order accuracy in the non-pressurized regime for unsteady pipe flows. Such improvements have been verified against theoretical and experimental data through tests involving both smooth and sharp-gradient steady and unsteady flows across various regimes in straight and locally bent circular pipes, which are fundamental elements of stormwater drainage, sewage networks, and industrial process pipelines. The proposed pipe flow model can be further improved regarding post-pore stability by utilizing specific post-bore oscillation suppression techniques, and it can be integrated into a practical hydraulic modeling tool for pipeline networks in future work.

Predicting straw drinking ability of liquid foods by pipe-flow rheometry

Designing the straw drinking experience is increasingly important in consumer-oriented liquid food innovation. The perceived ’straw drinking ease’ of liquid foods could be assessed by sensory analysis. However, challenges arise in linking instrumental measurements to the subjective quantification of sensory attributes due to the complexity of perceptual behaviors in drinking. Here, we developed a pipe-flow rheometry approach to predict straw drinking ability with minimized reliance on panel tests. We measured the instantaneous flow of liquid samples within straws and compared their flow profiles based on different yielding behaviors. The dynamic flow processes were simplified into steady-state pipe flow, and perceived straw drinking ability was modeled as the shear viscosity of liquid foods at specific flow rates. A power-law relationship was found between viscosity at sample-specific shear rates and straw drinking ability, regardless of whether the liquid foods exhibit yield stress. This approach provides opportunities for directly addressing the straw drinking experience through simple laboratory measurements when developing texture modulation systems for liquid foods.

Local two-group bubble size model for adiabatic air–water flow in a large diameter pipe using CFD code

Accurate prediction of bubble behavior in large diameter pipes is crucial for evaluating the performance of safety systems, steam generators, and heat exchangers in nuclear systems. Bubble behavior in large diameter pipes under two-phase flow significantly differs from that in small pipes. With the increasing use of computational fluid dynamics (CFD) codes, predicting interfacial area concentration (IAC) is critical for understanding multi-dimensional bubble behavior. This study developed a two-group local bubble size model for bubbly, slug, and churn flows under adiabatic conditions. The model includes correlations for void fraction and bubble sizes of two groups, which were implemented into CFD codes and validated against experimental data from large diameter pipes with low-pressure air–water flow. Results show the model's prediction accuracy surpasses existing correlations. The developed correlations are applicable across a range of flow conditions covering pipe diameters in the range 0.05–0.152 m, pressures from atmospheric to 300 kPa, superficial liquid velocities from 0.25 m/s to 2.85 m/s, and superficial gas velocities from 0.04 m/s to 5.48 m/s. The model is expected to enhance the prediction capabilities of CFD codes for the adiabatic two-group two-phase flows in the large diameter pipes.

Biofilm growth Dynamics in a Micro-Irrigation with Reclaimed Wastewater in the Field scale.

The dripper clogging due to the development of biofilm can reduce the benefits of micro-irrigation technology implementation using reclaimed wastewater. The narrow cross-section and labyrinth geometry of the dripper channel enhance the fouling mechanisms. The aim of this study was to evaluate the water distribution and biofouling of drip irrigation systems at the field scale during irrigation with treated wastewater. Six 100 m lines of commercial pipes with two pressure-compensating dripper types (flow rate, Q, of 0.65 L.h-1 and 1.5 L.h-1, respectively) were monitored for four months. Different zones along the pipes were selected to evaluate the influence of hydrodynamical conditions (Reynolds number = 5400 to 0) on biofouling. Destructive methods involving the biofilm extraction by mechanical means, showed little biofilm development without significant differences in dry and organic matter content in function of the sampling location along the pipe or dripper flow rate (Q0.65 and Q1.5). These results were confirmed by non-destructive methods, such as optical coherence tomography, that nevertheless showed that biofouling concerned 15-20% of the total dripper labyrinth volume. Total organic carbon monitoring and its composition (by three-dimensional excitation and emission matrix fluorescence microscopy) showed that the biofilm did not significantly influence the organic matter nature. Our results indicated that the biological activity and biofilm development in irrigation systems were more affected by the environmental conditions, particularly water temperature, rather than flow conditions. This confirmed that treated wastewater with low organic content can be used in micro-irrigation systems without significant loss of efficiency, even in conditions requiring intensive irrigation, such as the Mediterranean climate.

A Computational Fluid Dynamics Study on the Effect of Drilling Parameters on Wellbore Cleaning in Oil Wells

Poor wellbore cleaning is a significant challenge in oil drilling, primarily due to the accumulation of cuttings at the bottom of the well, particularly in deviated and horizontal wells. This study addresses this issue by employing Computational Fluid Dynamics (CFD) with the commercial software ANSYS FLUENT (2023-R1) to simulate a solid–liquid multiphase flow in an annulus. The primary objective is to analyze the cuttings concentration, pressure loss, and solid velocity profiles across various drilling parameters, including drill pipe rotation, the flow rate, rate of penetration, inclination angle, and fluid rheology. Our results underscore the critical role of these parameters in enhancing cuttings transport efficiency. Specifically, the drill pipe rotation, flow rate, and rate of penetration emerge as the most influential factors affecting the wellbore cleaning performance. With a validated model exhibiting an average error of 4.24%, this study provides insights into optimizing drilling operations to improve wellbore cleaning and increase hydrocarbon recovery.

Mass distribution impacts on particle translation and orientation dynamics in dilute flows

We present a novel model for tracking particles (based on Lagrangian particle tracking) with inhomogeneous mass distribution. Without loss of generality, the presented approach captures inhomogeneity by assuming an offset spherical inclusion in an elongated ellipsoidal particle matrix. The model is first validated on simplified flow configurations such as particles settling in vacuum or air as well as suspended in simple shear and laminar pipe flow, where we achieved an excellent agreement with the available reference results. Furthermore, we investigate the impact of the inclusion parameters on the particle motion. Finally, the deposition of inhomogeneous particles in a simplified bifurcation is analyzed. We conclude that the consideration of inhomogeneity significantly alters the translational and orientational dynamics of the particles. Consequently, we advocate for the consideration of more realistic mass distributions to increase the accuracy of modeling and predicting the motion of inhomogeneous particles in flows for real-world applications.

Comparative study of turbulent round jet flows through direct numerical simulation at medium–high Reynolds numbers

This study examines a spatially evolving turbulent round jet at a Reynolds number of Re = 7000 based on the bulk velocity Ub and the orifice diameter D and a Prandtl number of Pr = 0.71 using direct numerical simulation (DNS). Statistical data are collected over 30 000D/Ub time units, including mean quantities, Reynolds stresses, heat fluxes, mixed moments, Reynolds stress and turbulent kinetic energy budgets, and probability density functions. Comparative analysis with a previous DNS at Re = 3500 (Nguyen and Oberlack, 2024a; 2024c) shows that the higher Reynolds number leads to a shift of the self-similarity to a greater distance from the orifice. A larger Reynolds number leads to higher magnitudes of different statistical moments, dissipation and production. In addition, a maximum visible in the near-field of the turbulence intensity components is smoothed at the larger Reynolds number. The probability density functions of the axial velocity and the passive scalar show Gaussian behavior on the centerline, but with larger standard deviations compared to the lower Reynolds number. The study highlights the significant impact of using a fully developed turbulent pipe flow profile as the inlet condition, which significantly reduces the size of the potential core by introducing initial turbulence intensities at the orifice.

Radial Mixing in Steady and Accelerating Pipe Flows

Radial Mixing in Steady and Accelerating Pipe Flows

Comparative Analysis of Sponge City Drainage System Schemes Based on SWMM

In this paper, the drainage system schemes of sponge city are compared and analyzed based on Storm Water Management Model (SWMM). First, this paper builds a model in SWMM to explore the effect of green roof, rain garden and reservoir on solving the excessive pressure of urban drainage system during rainstorm, and analyzes the results of the model. Through comparative analysis, the best scheme is obtained. The results show that the green roof has the best effect among the three schemes, which can reduce the flow of the pipeline, increase the drainage cycle and thus reduce the pressure of the drainage system. Second, limited by the size of the area, it can only reduce the flow of the drainage system. The reservoir has the worst effect, mainly because the intensity is not large enough, and if it encounters greater rainfall, the reservoir can play a key role in regulating and storing. Through the analysis of the model results, an effective scheme can be obtained to relieve the pressure of urban drainage system in rainstorm, so as to reduce the drainage pipe flow and reduce the risk of urban waterlogging. The purpose of this paper is to provide effective reference for the construction of sponge city, relieve the pressure of drainage system and reduce the hidden danger of urban waterlogging.

Nonlinear evolution of vortical disturbances entrained in the entrance region of a circular pipe

The nonlinear evolution of free-stream vortical disturbances entrained in the entrance region of a circular pipe is investigated using asymptotic and numerical methods. Attention is focused on the low-frequency disturbances that induce streamwise elongated structures. A pair of vortical modes with opposite azimuthal wavenumbers is used to model the free-stream disturbances. Their amplitude is assumed to be intense enough for nonlinear interactions to occur inside the pipe. The formation and evolution of the perturbation flow are described by the nonlinear unsteady boundary-region equations in the cylindrical coordinate system, derived and solved herein for the first time. Matched asymptotic expansions are employed to construct appropriate initial conditions and the initial–boundary value problem is solved numerically by a marching procedure in the streamwise direction. Numerical results show the stabilising effect of nonlinearity on the intense algebraic growth of the disturbances and an increase of the wall-shear stress due to the nonlinear interactions. A parametric study is carried out to evince the effect of the Reynolds number, the streamwise and azimuthal wavelengths, and the radial length scale of the inlet disturbance on the nonlinear flow evolution. Elongated pipe-entrance nonlinear structures (EPENS) occupying the whole pipe cross-section are discovered. EPENS with $h$ -fold rotational symmetry comprise $h$ high-speed streaks positioned near the wall, and $h$ low-speed streaks centred around the pipe core. These distinct structures display a striking resemblance to nonlinear travelling waves found numerically and observed experimentally in fully developed pipe flow. Good agreement of our mean-flow and root mean square data with experimental measurements is obtained.