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Showing papers on "Pipe flow published in 2018"


Journal ArticleDOI
TL;DR: In this paper, the authors used the nano-scale thermal anemometry probe (NSTAP), developed at Princeton University to conduct velocity measurements in the high Reynolds number boundary layer facility at the University of Melbourne.
Abstract: Fully resolved measurements of turbulent boundary layers are reported for the Reynolds number range . Despite several decades of research in wall-bounded turbulence there is still controversy over the behaviour of streamwise turbulence intensities near the wall, especially at high Reynolds numbers. Much of it stems from the uncertainty in measurement due to finite spatial resolution. Conventional hot-wire anemometry is limited for high Reynolds number measurements due to limited spatial resolution issues that cause attenuation in the streamwise turbulence intensity profile near the wall. To address this issue we use the nano-scale thermal anemometry probe (NSTAP), developed at Princeton University to conduct velocity measurements in the high Reynolds number boundary layer facility at the University of Melbourne. The NSTAP has a sensing length almost one order of magnitude smaller than conventional hot-wires. This enables us to acquire fully resolved velocity measurements of turbulent boundary layers up to . Results show that in the near-wall region, the viscous-scaled streamwise turbulence intensity grows with in the Reynolds number range of the experiments. A second outer peak in the streamwise turbulence intensity is also shown to emerge at the highest Reynolds numbers. Moreover, the energy spectra in the near-wall region show excellent inner scaling over the small to moderate wavelength range, followed by a large-scale influence that increases with Reynolds number. Outer scaling in the outer region is found to collapse the energy spectra over high wavelengths across various Reynolds numbers.

96 citations


Journal ArticleDOI
TL;DR: In this paper, the authors demonstrate that appropriate distortions to the velocity profile lead to a complete collapse of turbulence and subsequently friction losses are reduced by as much as 90%. But the return to laminar motion is accomplished by initially increasing turbulence intensities or by transiently amplifying wall shear.
Abstract: Turbulence is the major cause of friction losses in transport processes and it is responsible for a drastic drag increase in flows over bounding surfaces. While much effort is invested into developing ways to control and reduce turbulence intensities 1–3 , so far no methods exist to altogether eliminate turbulence if velocities are sufficiently large. We demonstrate for pipe flow that appropriate distortions to the velocity profile lead to a complete collapse of turbulence and subsequently friction losses are reduced by as much as 90%. Counterintuitively, the return to laminar motion is accomplished by initially increasing turbulence intensities or by transiently amplifying wall shear. Since neither the Reynolds number nor the shear stresses decrease (the latter often increase), these measures are not indicative of turbulence collapse. Instead, an amplification mechanism 4,5 measuring the interaction between eddies and the mean shear is found to set a threshold below which turbulence is suppressed beyond recovery.

80 citations


Journal ArticleDOI
TL;DR: In this paper, a pipe flow model comprised of energy and momentum conservation equations is developed for the mixture flow in both inner tubing and annuli, coupled with the S-R-K real gas model, variable mass flow model and transient heat transfer model in oil layer, a comprehensive mathematical model is established.

77 citations


Journal ArticleDOI
TL;DR: In this paper, a linear instability of pressure-driven pipe flow of a viscoelastic fluid, obeying the Oldroyd-B constitutive equation commonly used to model dilute polymer solutions, was shown to exist at Reynolds numbers significantly lower than those at which transition to turbulence is typically observed for Newtonian pipe flow.
Abstract: Newtonian pipe flow is known to be linearly stable at all Reynolds numbers. We report, for the first time, a linear instability of pressure-driven pipe flow of a viscoelastic fluid, obeying the Oldroyd-B constitutive equation commonly used to model dilute polymer solutions. The instability is shown to exist at Reynolds numbers significantly lower than those at which transition to turbulence is typically observed for Newtonian pipe flow. Our results qualitatively explain experimental observations of transition to turbulence in pipe flow of dilute polymer solutions at flow rates where Newtonian turbulence is absent. The instability discussed here should form the first stage in a hitherto unexplored dynamical pathway to turbulence in polymer solutions. An analogous instability exists for plane Poiseuille flow.

76 citations


Journal ArticleDOI
TL;DR: In this paper, a framework for investigating and modeling the pressure drop of CPB during pipe transportation with complex circuit shapes has been presented, based on the experimental data, gradient boosting regression tree (GBRT) was utilized to develop a prediction model for the CPB pressure drop in the pipe loop.

75 citations


BookDOI
19 Dec 2018
TL;DR: In this article, the authors present a model of a cloud of Particle Clouds in a Turbulent Fluid Brownian Motion, Coagulation, and Agglomeration.
Abstract: INTRODUCTION Scope and Applications Elementary Particle-Fluid Interactions Heat and Mass Transfer from a Sphere Deformable Particles Momentum Transfer in a Nonuniform Fluid Motion of a Particle Suspended in a Fluid Particle Diffusivity Electrostatic Charging Multiphase Flow Systems Exercise Problems BASIC EQUATIONS Intraphase Equations and Balances at the Interfaces Significance of Phase Configurations Averages and Averaging Theorems Volume Averaged Equations of Conservation and Interface Balance Equations Closure Relations Simplified Formulations Exercise Problems TRANSPORT PROPERTIES AND PROCESSES Drag, Heat, and Mass Transfer of a Particle Cloud Interaction of Particles with Surfaces and Momentum Transfer Transport Processes among Particle Clouds-Single Scattering Viscosity and Thermal Conductivity of Particle Clouds Flow Regimens of a Cloud of Particles in a Turbulent Fluid Brownian Motion, Coagulation, and Agglomeration Exercise Problems EFFECTS OF WAVES AND ELECTRICITY AND SURFACE BOUNDARY CONDITIONS Interaction with Radiation Interaction with Sound Waves Interaction with an Ionized Gas Mobility and Electrical Conductivity Charge Distribution Boundary Conditions of Suspensions Exercise Problems ONE-DIMENSION MOTIONS Adiabatic Flow One-Dimentional Steady Motion Adiabatic Flow through a Nozzle Gas-Liquid Systems Unsteady Flow Shock Waves in Dusty Gas Settling in an External Field Settling of Charged Dusts Exercise Problems PIPE FLOW OF A SUSPENSION Experimental Studies on Dilute Suspensions Basic Relations of Pipe Flow Fully Developed Pipe Flow Sedimentary Flow Flow of Suspension of Fibers Heat Transfer in Pipe Flow Cyclone Separation Exercise Problems GENERAL MOTION OF DILUTE SUSPENSIONS Vortex Motion Eletrohydrodynamic Flow Laminar Boundary Layer Motion over a Flat Plate Particulate Suspension in a Turbulent Fluid Jets and Sprays Diffusion and Fall-Out from Point Sources Flow Over a Cylinder Exercise Problems DENSE SYSTEMS Some Fundamental Nature of Dense Suspensions Pipe Flow Porous Media and Moving Beds Observations on Fluidized Beds Bubbles in Fluid Beds Circulatory Motion in Fluidized Beds Transport Prodesses in Fluidized Beds Exercise Problems

69 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the heat transfer characteristics of developing and fully developed flow in smooth horizontal tubes in the transitional flow regime at a constant heat flux, and found that the Reynolds number at which transition started was independent of axial position, and transition occurred at the same moment in time along the whole tube length.

62 citations


Journal ArticleDOI
TL;DR: In this article, a well-defined texture with streamwise grooves at the walls in which the gas is expected to be entrapped is considered, and a substantial drag reduction is observed which strongly depends on the grooves' dimension and on the solid fraction, i.e., the ratio between the solid wall surface and the total surface of the pipe.
Abstract: The drag reduction induced by superhydrophobic surfaces is investigated in a turbulent pipe flow. Wetted superhydrophobic surfaces are shown to trap gas bubbles in their asperities. This stops the liquid from coming in direct contact with the wall in that location, allowing the flow to slip over the air bubbles. We consider a well-defined texture with streamwise grooves at the walls in which the gas is expected to be entrapped. This configuration is modeled with alternating no-slip and shear-free boundary conditions at the wall. With respect to the classical turbulent pipe flow, a substantial drag reduction is observed which strongly depends on the grooves’ dimension and on the solid fraction, i.e., the ratio between the solid wall surface and the total surface of the pipe’s circumference. The drag reduction is due to the mean slip velocity at the wall which increases the flow rate at a fixed pressure drop. The enforced boundary conditions also produce peculiar turbulent structures which on the contrary d...

56 citations


Journal ArticleDOI
TL;DR: In this article, the relationship between heat transfer and pressure drop in smooth horizontal circular tubes in the laminar, transitional, quasi-turbulent and turbulent flow regimes was investigated.

56 citations


Journal ArticleDOI
TL;DR: In this paper, visualization experiments were performed to reveal the mechanism of two-phase flow inside a centrifugal pump, and the flow patterns in the impeller and volute can be classified into plug flow and stratified flow distinguished by the critical inlet gas volume fraction (IGVF).

48 citations


Journal ArticleDOI
TL;DR: A left-side, Caputo type, space fractional-order constitutive equation (FCE) is reported using a nonlocal, fractional velocity gradient and then interprets physical properties of non-Newtonian fluids for steady pipe flow and leads to analytical tools and criterion that can extend standard models in quantifying the complex dynamics ofnon- newtonian fluid flow.

Journal ArticleDOI
TL;DR: Overall, it is concluded that both D3Q19 and D3 Q27 simulations yield accurate turbulent flow statistics, which are compared systematically with both published experimental and other DNS results based on solving the Navier–Stokes equations.

Journal ArticleDOI
TL;DR: In this paper, a mathematical model is proposed for estimating the key water properties in offshore concentric dual-tubing wells (OCDTW) at supercritical state, where the effect of heat loss to seawater as well as formation is taken into consideration.

Journal ArticleDOI
TL;DR: In this paper, the authors performed direct numerical simulations to study the heat transfer within a suspension of neutrally buoyant, finite-size spherical particles in laminar and turbulent pipe flows, using the immersed boundary method to account for the solid fluid interactions and a volume of fluid (VoF) method to resolve the temperature equation both inside and outside the particles.

Journal ArticleDOI
TL;DR: The system frequency response (SFR) based method has been widely developed and applied for the modelling of transient pipe flow and the assessment of pipeline system conditions as discussed by the authors, where the linearity of the SFR model has been evaluated.
Abstract: The system frequency response (SFR) based method has been widely developed and applied for the modelling of transient pipe flow and the assessment of pipeline system conditions. The lineari...

Journal ArticleDOI
TL;DR: In this article, a unified set of closures have been applied to simulating different configurations and fluids, i.e. pipe flow and bubble column, air/water and air/liquid metal.

Journal ArticleDOI
Ali Triki1
TL;DR: In this paper, a dual-technique-based inline strategy was investigated as a sustainment to conventional techniques in terms of limitation of wave oscillation period spread-out, and the efficiency of the dual technique was considered for two operating conditions associated with up-and down-surge frames.
Abstract: A dual-technique-based inline strategy was investigated in this study as a sustainment to conventional-technique skills in terms of limitation of wave oscillation period spread-out. Instead of the single polymeric short section employed by the latter technique, the former is based on replacing an up- and downstream short section of the primitive piping system using another couple made of polymeric pipe-wall material. Numerical computations used the method of characteristics for the discretization of unconventional water-hammer model based on the Vitkovsky and the Kelvin–Voigt formulations. The efficiency of the dual technique was considered for two operating conditions associated with up- and downsurge frames. Moreover, two pipe-wall material types were utilized for short-section pipe wall, namely the HDPE or LDPE materials. Additionally, the conventional technique was also addressed in this study, for comparison purposes. First, analyses of pressure-head, circumferential-stress and radial-strain wave patterns, along with wave oscillation periods examination, confirmed that the dual technique could improve the efficiency of the conventional one, providing acceptable trade-off between the attenuation of pressure-head and circumferential-stress peaks (or crests), and limitation of period spreading and radial-strain amplification. Second, a parametric study of the sensitivity of the wave damping to the employed short-section dimensions was performed in terms of short-section length and diameter. This parametric study helped estimate the near-optimal values of the short-section dimensions.

Journal ArticleDOI
TL;DR: In this article, a planar particle image velocimetry (PIV) technique was used to measure the slip velocity at the interface between the porous media and free flow.
Abstract: The aim of this work is to experimentally examine flow over and near random porous media. Different porous materials were chosen to achieve porosity ranging from 0.95 to 0.99. In this study, we report the detailed velocity measurements of the flow over and near random porous material inside a rectangular duct using a planar particle image velocimetry (PIV) technique. By controlling the flow rate, two different Reynolds numbers were achieved. We determined the slip velocity at the interface between the porous media and free flow. Values of the slip velocity normalized either by the maximum flow velocity or by the shear rate at the interface and the screening distance K1/2 were found to depend on porosity. It was also shown that the depth of penetration inside the porous material was larger than the screening length using Brinkman’s prediction. Moreover, we examined a model for the laminar coupled flow over and inside porous media and analyzed the permeability of a random porous medium. This study provided ...

Journal ArticleDOI
TL;DR: In this article, the authors show that with increasing Weissenberg number (Wi), turbulence exhibits long periods of hibernation if the domain size is small and, upon an increase in Wi, the flow fully relaminarises, in agreement with recent experiments.
Abstract: Polymer additives can substantially reduce the drag of turbulent flows and the upper limit, the so called "maximum drag reduction" (MDR) asymptote is universal, i.e. independent of the type of polymer and solvent used. Until recently, the consensus was that, in this limit, flows are in a marginal state where only a minimal level of turbulence activity persists. Observations in direct numerical simulations using minimal sized channels appeared to support this view and reported long "hibernation" periods where turbulence is marginalized. In simulations of pipe flow we find that, indeed, with increasing Weissenberg number (Wi), turbulence expresses long periods of hibernation if the domain size is small. However, with increasing pipe length, the temporal hibernation continuously alters to spatio-temporal intermittency and here the flow consists of turbulent puffs surrounded by laminar flow. Moreover, upon an increase in Wi, the flow fully relaminarises, in agreement with recent experiments. At even larger Wi, a different instability is encountered causing a drag increase towards MDR. Our findings hence link earlier minimal flow unit simulations with recent experiments and confirm that the addition of polymers initially suppresses Newtonian turbulence and leads to a reverse transition. The MDR state on the other hand results from a separate instability and the underlying dynamics corresponds to the recently proposed state of elasto-inertial-turbulence (EIT).

Journal ArticleDOI
TL;DR: In this article, the authors study the evolution of pipe flow patterns for arbitrary long times, and find that after times in excess of advective time units, indeed a statistical steady state is reached.
Abstract: In pipes, turbulence sets in despite the linear stability of the laminar Hagen–Poiseuille flow. The Reynolds number ( ) for which turbulence first appears in a given experiment – the ‘natural transition point’ – depends on imperfections of the set-up, or, more precisely, on the magnitude of finite amplitude perturbations. At onset, turbulence typically only occupies a certain fraction of the flow, and this fraction equally is found to differ from experiment to experiment. Despite these findings, Reynolds proposed that after sufficiently long times, flows may settle to steady conditions: below a critical velocity, flows should (regardless of initial conditions) always return to laminar, while above this velocity, eddying motion should persist. As will be shown, even in pipes several thousand diameters long, the spatio-temporal intermittent flow patterns observed at the end of the pipe strongly depend on the initial conditions, and there is no indication that different flow patterns would eventually settle to a (statistical) steady state. Exploiting the fact that turbulent puffs do not age (i.e. they are memoryless), we continuously recreate the puff sequence exiting the pipe at the pipe entrance, and in doing so introduce periodic boundary conditions for the puff pattern. This procedure allows us to study the evolution of the flow patterns for arbitrary long times, and we find that after times in excess of advective time units, indeed a statistical steady state is reached. Although the resulting flows remain spatio-temporally intermittent, puff splitting and decay rates eventually reach a balance, so that the turbulent fraction fluctuates around a well-defined level which only depends on . In accordance with Reynolds’ proposition, we find that at lower (here 2020), flows eventually always resume to laminar, while for higher ( ), turbulence persists. The critical point for pipe flow hence falls in the interval of $2020 , which is in very good agreement with the recently proposed value of . The latter estimate was based on single-puff statistics and entirely neglected puff interactions. Unlike in typical contact processes where such interactions strongly affect the percolation threshold, in pipe flow, the critical point is only marginally influenced. Interactions, on the other hand, are responsible for the approach to the statistical steady state. As shown, they strongly affect the resulting flow patterns, where they cause ‘puff clustering’, and these regions of large puff densities are observed to travel across the puff pattern in a wave-like fashion.

Journal ArticleDOI
TL;DR: In this paper, the role of buoyancy in modulating the turbulence in a flow where properties are spatially varying was investigated by means of direct numerical simulations with a uniform heat flux imposed at the wall at an inlet bulk Reynolds number of 5400.
Abstract: A numerical investigation of cooling of a fluid at supercritical pressure has been performed by means of direct numerical simulations. The simulations were conducted with a uniform heat flux imposed at the wall at an inlet bulk Reynolds number of 5400. The aim of this work is to understand the role of buoyancy in modulating the turbulence in a flow where properties are spatially varying. Heat transfer deterioration followed by recovery is observed in the downward flow while enhancement occurs in the upward flow as compared to forced convection. The decomposition of the skin friction factor and the Nusselt number was performed. The major effects on the skin friction factor were brought by the non-uniform body force due to the gravity. The turbulent parts equally influence the Nusselt number as well as the skin friction factor in supercritical flows. Quadrant analysis and its weighted joint probability density function were analyzed to understand the role of sweep (Q4) and ejection (Q2) events. During the heat transfer deterioration, sweep and ejection events are decreased greatly, triggering the reduction in turbulence. The recovery in turbulence is brought by the Q1 and Q3 (also known as outward and inward interaction) events, contrary to the conventional belief about turbulence generation. The turbulence anisotropy of the Reynolds stress tensor is investigated showing that the turbulence structure becomes rod-like during the deteriorated heat transfer regime in the downward flow and disc-like for the upward flow.

Journal ArticleDOI
TL;DR: In this paper, the authors report the results of a combined experimental and numerical study of specific finite-amplitude disturbances for transition to turbulence in the flow through a circular pipe with a sudden expansion.
Abstract: We report the results of a combined experimental and numerical study of specific finite-amplitude disturbances for transition to turbulence in the flow through a circular pipe with a sudden expansion. The critical amplitude thresholds for localized turbulent patch downstream of the expansion scale with the Reynolds number with a power law exponent of −2.3 for experiments and −2.8 for simulations. A new mechanism for the periodic bursting of the recirculation region is uncovered where the asymmetric recirculation flow develops a periodic dynamics: a secondary recirculation breaks the symmetry along the pipe wall and bursts into localized turbulence, which travels downstream and relaminarises. Flow visualizations show a simple flow pattern of three waves forming, growing, and bursting.

Journal ArticleDOI
01 Jul 2018-Water
TL;DR: In this article, an additional friction function was proposed to evaluate the influence of the air content on the attenuation of the water hammer in a gravitational pipe with continuous air entrainment, and a corresponding experiment was conducted to optimize the numerical model.
Abstract: Water hammer is an undesired hydraulic shock phenomenon in water supply pipe systems. It is very important to simulate water hammer for preventing the hazard of over pressure. In order to predict the transient pressure caused by a valve closing in a gravitational pipe with continuous air entrainment, a numerical model based on the Lax-Wendroff format is established, and the matched boundary model is provided. Compared with the traditional methods, this study provides another access by considering the influence of the pipe flow velocity on the wave propagation to simulate transient processes. A corresponding experiment is conducted to optimize the numerical model. Based on the experimental result, an additional friction function is proposed to evaluate the influence of the air content on the attenuation. The result shows that the energy dissipation of the shock waves may be underestimated in air-water mixture flow using the common steady friction. By introducing the additional friction function, the improved model can more accurately simulate the attenuation of the water hammer in the gravitational pipe with continuous air entrainment. As there are plenty of practical water supply systems running with air content, the improved Lax-Wendroff Method (LWM) is valued in accurately predicting water hammer processes especially in those conditions.

Journal ArticleDOI
TL;DR: In this paper, the heat transfer behavior of carbon nanotubes nanofluids under laminar forced flow in horizontal pipe is investigated and the results are presented and discussed for various Re numbers, in a wide range of 500-2000 and it was noticed that the convective heat transfer coefficient of nanophotonics is better for low Re number and higher particle loading, while the nanophase works in non-Newtonian flow.


Journal ArticleDOI
TL;DR: In this paper, a novel numerical model is presented to analyze the heat and mass transfer characteristics of superheated steam (SHS) flow in horizontal wellbores with toe-point injection technique.
Abstract: Little efforts were done on the heat and mass transfer characteristics of superheated steam (SHS) flow in the horizontal wellbores. In this paper, a novel numerical model is presented to analyze the heat and mass transfer characteristics of SHS in horizontal wellbores with toe-point injection technique. Firstly, with consideration of heat exchange between inner tubing (IT) and annuli, a pipe flow model of SHS flow in IT and annuli is developed with energy and momentum balance equations. Secondly, coupled with the transient heat transfer model in oil layer, a comprehensive mathematical model for predicting distributions of pressure and temperature of SHS in IT and annuli is established. Then, type curves are obtained with numerical methods and iteration technique, and sensitivity analysis is conducted. The results show that (1). The decrease in SHS temperature in annuli caused by heat and mass transfer to oil layer is offset by heat absorbtion from SHS in IT. (2). SHS temperature in both IT and annuli increases with the increase in injection pressure. (3). IT heat loss rate decreases with the increases in injection pressure. (4). Increasing pressure can improve development effect.

Journal ArticleDOI
TL;DR: A novel technique using double-sided thin film heat flux gauges for measuring the heat transfer coefficient from a direct oil-cooled electrical machine with segmented stator is presented and new nondimensional correlations of the Nusselt number with Reynolds number are developed.
Abstract: The heat transfer coefficient (HTC) is a critical parameter that is required for accurate thermal modeling of electrical machines. This is often achieved from empirical correlations of ideal geometries or computational fluid dynamics (CFD) simulations. This paper presents a novel technique using double-sided thin film heat flux gauges for measuring the HTC from a direct oil-cooled electrical machine with segmented stator. While thin film gauges are often used in transient measurements of the HTC on gas turbine components, their application to electrical machines has been largely unexplored. This is the topic of this paper. Due to the large viscosity of the coolant, the transient technique was found to be inadequate and a steady-state adaptation for oil-cooled machines was developed. This paper explores the challenges linked with this measurement technique when applied to oil-cooled machines, and develops new nondimensional correlations of the Nusselt number with Reynolds number. These correlations are applicable to machines with different geometries, flow, and coolant properties. The experimental results were compared to CFD simulations and existing pipe flow correlations. It is shown that these underpredict the HTC by approximately 60% at Re = 20. The discrepancy gradually decreases to around 10% at Re = 200.

Journal ArticleDOI
TL;DR: In this article, the effects of periodically structured surface roughness upon flow field and pressure drop in a circular pipe at low Reynolds numbers were investigated. But the authors focused on the effect of roughness on fully developed Stokes flow in the pipe.
Abstract: Fluid flow and pressure drop across a channel are significantly influenced by surface roughness on a channel wall. The present study investigates the effects of periodically structured surface roughness upon flow field and pressure drop in a circular pipe at low Reynolds numbers. The periodic roughness considered exhibits sinusoidal, triangular, and rectangular morphologies, with the relative roughness (i.e., ratio of the amplitude of surface roughness to hydraulic diameter of the pipe) no more than 0.2. Based upon a revised perturbation theory, a theoretical model is developed to quantify the effect of roughness on fully developed Stokes flow in the pipe. The ratio of static flow resistivity and the ratio of the Darcy friction factor between rough and smooth pipes are expressed in four-order approximate formulations, which are validated against numerical simulation results. The relative roughness and the wave number are identified as the two key parameters affecting the static flow resistivity and the Da...


Journal ArticleDOI
TL;DR: In this article, a direct numerical simulation (DNS) was performed for a spatially developing 90° bend pipe flow to investigate the unsteady flow motions downstream of the bend.