Showing papers on "Pipe flow published in 2022"

An AI-based Domain-Decomposition Non-Intrusive Reduced-Order Model for Extended Domains applied to Multiphase Flow in Pipes

Abstract: The modeling of multiphase flow in a pipe presents a significant challenge for high-resolution computational fluid dynamics (CFD) models due to the high aspect ratio (length over diameter) of the domain. In subsea applications, the pipe length can be several hundreds of meters vs a pipe diameter of just a few inches. Approximating CFD models in a low-dimensional space, reduced-order models have been shown to produce accurate results with a speed-up of orders of magnitude. In this paper, we present a new AI-based non-intrusive reduced-order model within a domain decomposition framework (AI-DDNIROM), which is capable of making predictions for domains significantly larger than the domain used in training. This is achieved by (i) using a domain decomposition approach; (ii) using dimensionality reduction to obtain a low-dimensional space in which to approximate the CFD model; (iii) training a neural network to make predictions for a single subdomain; and (iv) using an iteration-by-subdomain technique to converge the solution over the whole domain. To find the low-dimensional space, we compare Proper Orthogonal Decomposition with several types of autoencoder networks, known for their ability to compress information accurately and compactly. The comparison is assessed with two advection-dominated problems: flow past a cylinder and slug flow in a pipe. To make predictions in time, we exploit an adversarial network, which aims to learn the distribution of the training data, in addition to learning the mapping between particular inputs and outputs. This type of network has shown the potential to produce visually realistic outputs. The whole framework is applied to multiphase slug flow in a horizontal pipe for which an AI-DDNIROM is trained on high-fidelity CFD simulations of a pipe of length 10 m with an aspect ratio of 13:1 and tested by simulating the flow for a pipe of length 98 m with an aspect ratio of almost 130:1. Inspection of the predicted liquid volume fractions shows a good match with the high fidelity model as shown in the results. Statistics of the flows obtained from the CFD simulations are compared to those of the AI-DDNIROM predictions to demonstrate the accuracy of our approach.

Experimental study of laminar-to-turbulent transition in pipe flow

Abstract: This paper describes an experimental study of the unforced laminar-to-turbulent transition in pipe flow. Two pipes with different length-to-diameter ratios are investigated, and the transition phenomenon is studied using pressure measurements and visual observations. The entropy change and force balance are examined, and the peak powers are measured through fast Fourier transform analysis at various Reynolds numbers. Visual observations show that the flow structure changes at the Reynolds numbers corresponding to the peak powers. There is no clear dependency of the transition on the ratio of pipe length to diameter. The flow conditions are classified as laminar flow, transitions I, II, and III, and turbulent flow, separated by Reynolds numbers of approximately 1200, 2300, 7000, and 12 000, respectively. The transition at a Reynolds number of 1200 is caused by the force balance between the laminar and turbulent flows. The other transitions are related to the flow condition in the development region upstream of the pipe flow region. That is, the laminar-to-turbulent transition in the development region affects the transition condition in the downstream pipe flow. The laminar and turbulent development length ratios derived from the entropy changes are in reasonable agreement with the formulas for both laminar and turbulent flows. At large Reynolds numbers, the laminar flow condition will be established through the creation of a laminar-flow velocity profile at the entrance to the pipe.

Numerical Studies On Turbulent Flow Field in a 90° Pipe Bend

Abstract: The present paper deals with modelling of turbulent flow through a 90° pipe bend using an unsteady Reynolds averaged Navier-Stokes (U-RANS) approach where k- e model is used for turbulence closure. While limitations in solving complex flows of the k- e model have been reported in literature, this study demonstrates that for pipe flows with curvature, the k - e model performs reasonably well. Investigation have been carried out to find out the influence of Reynolds number (Re) and bend curvature ratio (Rc/D) on turbulent flow parameters, namely; instantaneous axial velocity, turbulent kinetic energy, turbulent intensity, and wall shear stress. Bend curvature is found to strongly influence the turbulent flow characteristics, while no such high Reynolds number dependency is observed in the present study range. In general, this paper presents a computationally cost-effective numerical study on the time-averaged turbulent flow field in a 90° pipe bend, which may be used for design and development of 90° pipe bends at a high Reynolds number regime.

Stability of a laminar pipe flow subjected to a step-like increase in the flow rate

Abstract: We perform the linear modal stability analysis of a pipe flow subjected to a step-like increment in the flow rate from a steady initial flow with flow rate, $Q_i$, to a final flow with flow rate, $Q_f$, at the time, $t_c$. A step-like increment in the flow rate induces a non-periodic unsteady flow for a definite time interval. The ratio, $\Gamma_a={Q}_i/{Q}_f$, parameterizes the increase in the flow rate, and it ranges between $0$ to $1$. The stability analysis for a pipe flow subjected to a step-like increment in the flow rate from the steady laminar flow ($\Gamma_a>0$) is not reported in the literature. The present work investigates the effect of varying $\Gamma_a$ on the stability characteristics of an unsteady pipe flow. The step-like increment in the flow rate for $0\leq\Gamma_a\leq0.72$ induces a viscous type instability for a definite duration and the flow is modally unstable. The non-axisymmetric disturbance with azimuthal wavenumber, $m=1$ is the most unstable mode. The flow is highly-unstable for $\Gamma_a=0$ and the flow becomes less unstable with an increase in $\Gamma_a$. The flow becomes stable before it attains the steady-state condition for all $\Gamma_a$.

A new proposed method for observing fluid in rock fractures using enhanced x-ray images from digital radiography

Abstract: Fluid in rock fractures continually induces geocatastrophes in water–rock system engineering. Intuitively observing fluid in fractures is the key method for revealing the interaction mechanism of water and rock under different engineering backgrounds and providing some insights for solving engineering issues. This study proposes a visualization method for fluid in rock fractures using enhanced X-ray image digital radiography (EXIDR) and carries out coupled hydromechanical tests on the basis of the material scale of carbonate rocks, red bed mudstone (RBM) and coal. The experimental results show the transition mechanism of pipe flow (PF) to fissure flow (FF) during carbonate rock failures. The flow regime undergoes an evolution process from laminar flow to turbulent flow, which also changes with the fractal characteristics of PF-FF in carbonate rocks under multilevel stress loading. Additionally, the damage coefficient of RBM under coupled hydrodynamics and multilevel stress loading nonlinearly increases. Therefore, the initial permeability of RBM under hydrodynamics is significant for geohazard prevention in engineering and is induced by seepage and diffusion effects. In addition, the mean square flow describes how the flow rate varies with fracture growth and extension, i.e., the fractional exponential evolution relationship transitions from superdiffusion flow to subdiffusion flow. This indicates that fluid in fractures shows the dual behaviors of anomalous diffusion and nonlinear flow during coal and rock failures.

Extension of the 1D Unsteady Friction Model for Rapidly Accelerating and Decelerating Turbulent Pipe Flows

Abstract: This work aims to examine the flow dynamics that contribute to the transient wall shear stress τw(t) of accelerating and decelerating turbulent pipe flows, using a series of direct numerical simulations (DNSs) of accelerating and decelerating flows between two fully turbulent states. Results show that accelerating and decelerating pipe flows exhibit different time dependence, especially in their turbulence response. It is observed that decelerating flows respond earlier than accelerating flows; however, they also require more extensive periods in which to relax towards their final turbulent state than accelerating flows. An identity that decomposes τw(t) into its dynamic contributions was used to determine the dominant flow dynamics involved within the different stages experienced by these flows. It is revealed that one of the existing 1D unsteady friction models accurately predicts one of the components of the dynamic decomposition of τw. Nonetheless, it is noted that the 1D model does not capture the transient response of the laminar and turbulent contributions. Consequently, the identity mentioned above was utilized as a framework to develop a hybrid model that improves the current 1D unsteady friction approaches.

Experimental Techniques against RANS Method in a Fully Developed Turbulent Pipe Flow: Evolution of Experimental and Computational Methods for the Study of Turbulence

Abstract: Fully developed turbulent flow in a pipe was studied by considering experimental and computational methods. The aim of this work was to build on the legacy of the University of Manchester, which is widely regarded as the birthplace of turbulence due to the pioneering work of the prominent academic Professor Osborne Reynolds (1842–1912), by capturing the evolution of fluid turbulence analysis tools over the last 100 years. A classical experimental apparatus was used to measure the mean velocity field and wall shear stress through four historical techniques: static pressure drop; mean square signals measured from a hot-wire; Preston tube; and Clauser plot. Computational Fluid Dynamics (CFD) was used to simulate the pipe flow, utilizing the Reynolds-averaged Navier–Stokes (RANS) method with different two-equation turbulence models. The performance of each approach was assessed to compare the experimental and computational methods. This comparison revealed that the numerical results produced a close agreement with the experiments. The finding shows that, in some cases, CFD simulations could be used as alternative or complementary methods to experimental techniques for analyzing fully developed turbulent pipe flow.

Polymer-turbulence interactions in a complex flow and implications for the drag reduction phenomenon

Abstract: We present direct numerical simulation data for turbulent duct flow of a finite-extensibility non-linear elastic dumbbell model with the Peterlin approximation (FENE-P) fluid in the high drag reduction regime. While the secondary flow pattern is qualitatively similar to that in a Newtonian fluid, its magnitude is significantly reduced, resulting in a less uniformly distributed velocity profile and hence smaller gradients at the wall. The Reynolds stress tensor in the polymer-laden flow was found to be increasingly anisotropic with most of the turbulent kinetic energy retained in the streamwise component, [Formula: see text]. We introduce a novel approach for investigating polymer stretching using the anisotropy invariant map of the polymer stress tensor and observe the persistence of both uniaxial and biaxial extension. Analysis of the transport equation for the mean kinetic energy indicates that polymer stretching and relaxation is a highly dissipative process; hence, the introduction of an additional channel for dissipation in a flow is key to drag reduction.

Direct numerical simulations of turbulent pipe flow up to $Re_\tau \approx 5200$

Abstract: Abstract Well-resolved direct numerical simulations (DNS) have been performed of the flow in a smooth circular pipe of radius $R$ and axial length $10{\rm \pi} R$ at friction Reynolds numbers up to $Re_\tau =5200$ using the pseudo-spectral code OPENPIPEFLOW. Various turbulence statistics are documented and compared with other DNS and experimental data in pipes as well as channels. Small but distinct differences between various datasets are identified. The friction factor $\lambda$ overshoots by $2\,\%$ and undershoots by $0.6\,\%$ the Prandtl friction law at low and high $Re$ ranges, respectively. In addition, $\lambda$ in our results is slightly higher than in Pirozzoli et al. (J. Fluid Mech., vol. 926, 2021, A28), but matches well the experiments in Furuichi et al. (Phys. Fluids, vol. 27, issue 9, 2015, 095108). The log-law indicator function, which is nearly indistinguishable between pipe and channel up to $y^+=250$, has not yet developed a plateau farther away from the wall in the pipes even for the $Re_\tau =5200$ cases. The wall shear stress fluctuations and the inner peak of the axial turbulence intensity – which grow monotonically with $Re_\tau$ – are lower in the pipe than in the channel, but the difference decreases with increasing $Re_\tau$. While the wall value is slightly lower in the channel than in the pipe at the same $Re_\tau$, the inner peak of the pressure fluctuation shows negligible differences between them. The Reynolds number scaling of all these quantities agrees with both the logarithmic and defect-power laws if the coefficients are properly chosen. The one-dimensional spectrum of the axial velocity fluctuation exhibits a $k^{-1}$ dependence at an intermediate distance from the wall – also seen in the channel. In summary, these high-fidelity data enable us to provide better insights into the flow physics in the pipes as well as the similarity/difference among different types of wall turbulence.

A Study of the Interface Fluctuation and Energy Saving of Oil–Water Annular Flow

Abstract: Oil–water annular flow is an efficient method of heavy oil transportation for energy-saving. To deeply study the influencing factors of the energy savings of oil–water annular flow, this paper compares the interface fluctuation and energy-saving situation of oil–water annular flow under different pipe structures (such as straight pipe, sudden-contraction pipe, and elbow pipe), flow parameters, and fluid properties. In the straight pipe, the flow parameters can impact the oil–water annular flow pattern and the energy savings, and the interface fluctuation is consistent with the energy savings. The stable oil–water core annular flow has slight interface fluctuation and significant energy savings. At the same time, the influences of pipe structure and fluid properties on energy saving are also analyzed. In the sudden-contraction pipe, the oil–water interface fluctuates, largely due to the sharp changes in flow cross-section, which leads to reduced energy savings. In the elbow, the oil–water interface fluctuates greatly due to the influence of centrifugal force caused by flow direction variation, and also leads to a decline in energy savings. The effects of oil property or annulus liquid property on the interface fluctuates, and the energy savings are analyzed; reducing surface tension is an effective measure to provide an energy-saving effect. These results can provide a reference for the design of heavy-oil-transportation pipelines, the analysis of interface fluctuation, and the energy-saving evaluation of oil–water annular flow.

Non-Intrusive Pipeline Flow Detection Based on Distributed Fiber Turbulent Vibration Sensing

Abstract: We demonstrate a non-intrusive dynamic monitoring method of oil well flow based on distributed optical fiber acoustic sensing (DAS) technology and the turbulent vibration. The quantitative measurement of the flow rate is theoretically acquired though the amplitude of the demodulated phase changes from DAS based on the flow impact in the tube on the pipe wall. The experimental results show that the relationships between the flow rate and the demodulated phase changes, in both a whole frequency region and in a sensitive-response frequency region, fit the quadratic equation well, with a max R2 of 0.997, which is consistent with the theoretical simulation results. The detectable flow rate is from 0.73 m3/h to 2.48 m3/h. The experiments verify the feasibility of DAS system flow monitoring and provide technical support for the practical application of the downhole flow measurement.

Experimental study on pressure characteristics of direct water hammer in the viscoelastic pipeline

Abstract: With the increasing popularity of long-distance water supply projects and the development of materials technology, the variation of water hammer characteristics in the viscoelastic pipeline has become the focus of researchers. To find out the mechanism of water hammer in the viscoelastic pipe of both elastic and viscous properties, an experiment was set up to study the direct water hammer generated by rapid closure of the downstream valve in the polymethyl methacrylate (PMMA) pipe, with six flow velocities in nearly 70 tests. The experimental results showed that the maximum water hammer pressure generated in the viscoelastic pipe in all flow velocities was (20% at most) greater than the traditional value of Joukowsky's formula. A faster closing time of the valve caused a higher water hammer pressure. The difference in water hammer pressure generated between the fastest and the slowest closing time of the valve was 14–17% at each flow velocity. Based on the relationship between the stress and strain of the pipe wall in the viscoelastic pipe, the reason that the water hammer characteristic in the viscoelastic pipeline was different from the traditional value was explained. The study provides a reference for the mechanism of transient flow in viscoelastic pipelines.

Measurement of Pipe and Liquid Parameters Using the Beam Steering Capabilities of Array-Based Clamp-On Ultrasonic Flow Meters

Abstract: Clamp-on ultrasonic flow meters (UFMs) are installed on the outside of the pipe wall. Typically, they consist of two single-element transducers mounted on angled wedges, which are acoustically coupled to the pipe wall. Before flow metering, the transducers are placed at the correct axial position by manually moving one transducer along the pipe wall until the maximum amplitude of the relevant acoustic pulse is obtained. This process is time-consuming and operator-dependent. Next to this, at least five parameters of the pipe and the liquid need to be provided manually to compute the flow speed. In this work, a method is proposed to obtain the five parameters of the pipe and the liquid required to compute the flow speed. The method consists of obtaining the optimal angles for different wave travel paths by varying the steering angle of the emitted acoustic beam systematically. Based on these optimal angles, a system of equations is built and solved to extract the desired parameters. The proposed method was tested experimentally with a custom-made clamp-on UFM consisting of two linear arrays placed on a water-filled stainless steel pipe. The obtained parameters of the pipe and the liquid correspond very well with the expected (nominal) values. Furthermore, the performed experiment also demonstrates that a clamp-on UFM based on transducer arrays can achieve self-alignment without the need to manually move the transducers.

Explicit Solution for Pipe Diameter Problem Using Lambert W -Function

Abstract: Determining the pipe diameter is one of the principal problems encountered in designing and analyzing pipe flow lines. However, the direct determination of a pipe’s diameter is not possible because of the implicit form of the Colebrook resistance flow formula through commercial pipes. Traditionally, the pipe diameter is determined using a trial procedure. In this paper, the pipe diameter problem was solved using explicit equations in terms of the Lambert W-function. The maximum relative errors of the developed solutions are less than 0.013% for the rough and smooth flow regimes and less than 0.8% and 0.6% for the transition flow region between them. In addition, a method for determining pipe diameter under uncertainty, including design graphs, is presented. It is hoped that the developed solution for predicting pipe diameter will be helpful in the analysis of pipe flow and the design of pipelines and water distribution networks.

Analysis on annular flow of liquid transported through a partially filled axially rotating pipe

Abstract: In rotary tube reactors, rotary evaporators, or rotary atomizers, liquid is transported through a partially filled axially rotating pipe. The flow is annular when the pipe rotation is fast enough, as in most engineering applications; in this research, we investigated the steady and transient behavior of annular flows in a partially filled axially rotating pipe. First, the governing equations of a laminar annular flow were derived, solved, and verified. Then, the theory was used to study the transient flow behavior. The responses of the outlet flowrate to inlet flowrate variations and pressure fluctuations were investigated. To clarify the system parameters in which the theory holds, we also conducted experiments to find flow mode boundaries between the non-annular flow and the annular flow. Steady state solutions of the theory were then used to find system parameters in which the flow is laminar. The effects that a screw inserted inside the pipe has, on both the flow mode boundaries and the transient flow characteristics, are also demonstrated. To the best of our knowledge, this is the first inspection of the transient characteristics of an annular flow and the effects of an inserted screw on this type of flow.

Investigation of the effects of pipe diameter of internal multiphase flow on pipe elbow vibration and resonance

Abstract: Computational fluid dynamics modelling of internal two-phase flow induced transient forces at 90° elbows have been carried out to evaluate the effect of pipe diameter on the characteristics of multiphase flow induced vibration. Simulations of two-phase flows of slug, cap bubbly and churn induced vibration at a pipe elbow were carried out using the volume of fluid model for the two-phase flows and the k – ε model for turbulence. Modal analysis has been carried out to evaluate the risk of resonance. Results were compared across three geometrically similar pipes of different diameters. Simulation results showed that the behaviours of the flow induced forces at the pipe elbow as a function of gas velocity for internal diameters of 0.0525 and 0.2032 m are similar. However, the multiphase flow induced force characteristics are different in the 0.1016 m diameter (intermediate) pipe. It can be attributed to the transition behaviour of gas–liquid two-phase flows caused by Taylor instability in an intermediate sized pipe. The predicted root-mean-square flow induced forces as a function of Weber number were correlated with an existing empirical correlation for a wider range of pipe sizes and gas volume fractions between 40% and 80%. Furthermore, the pipe natural frequencies increase with the increase of gas volume fraction in smaller pipes and the resonance risk increases with the increase of pipe diameter.