Pipe Flow

Gas-solid fluidized beds are common in chemical processing and energy production industries. These types of reactors frequently have banks of tubes immersed within the bed to provide heating or cooling, and it is important that the fluid dynamics within these bundles is efficient and uniform. This paper presents a simple, low-cost method for quantitatively analyzing the behavior of gas bubbles within banks of tubes in a fluidized bed cold flow model. Two probes, one containing an infrared emitter and one containing an infrared (IR) detector, are placed into adjacent glass tubes such that the emitter and detector face each other. As bubbles pass through the IR beam, the detector signal increases due to less solid material blocking the path between the emitter and detector. By calibrating the signal response to known voidage of the material, one can measure the bubble voidage at various locations within the tube bundle. The rate and size of bubbles passing through the beam can also be...

One of the classical problems in fluid mechanics is the determination of the flow field around a bluff body represented by a circular cylinder. This is of great interest in many engineering applications, such as hydrodynamic loading on ocean marine piles and offshore platform risers and casing pipes etc. The hydrodynamic behavior of the complex flow field around variety of circular cylinders shall be investigated. Wave induced vibration of structure such as marine pipelines, oil terminals, tanks and ships by placing oscillatory pressure on the surface of the structure. Flow-induced vibrations of slender marine structures can result from external or internal flows. VIV phenomenon is widely seen in subsea applications for risers, conductors, seabed pipelines and other subsea structures. FLIP occurs for rough bore flexible pipes, i.e. pipes with a corrugated metallic inner liner carcass is used for dry gas transport. As dry gas passes through a flexible riser, an unstable shear layer is generated off each of the internal corrugations which make up the internal carcass. Above a certain flow velocity vortices are shed from the carcass, at a frequency resulting in the generation and propagation of acoustic vibrations that lead to fatigue damage to topside and subsea small bore piping. The experimental work is carried to determine the dependence of the exact geometry i.e. corrugation geometry, length of the corrugated tube and the boundary conditions on the generation of pulsations. The obtained analytical tools will be validated by detailed CFD simulations and laboratory experimental tests.

A fundamental understanding of the transition from fluid-like to gel-like behavior is critical for a range of applications including personal care, pharmaceuticals, food products, batteries, painting, biomaterials, and concrete. The pipe flow behavior of a Herschel-Bulkley fluid is examined by a combination of rheology, ultrasound imaging velocimetry and pressure measurements together with modeling. The system is a solution of 0.50 wt.% polyelectrolytes of sulfated polysaccharides in water that solidifies on cooling. Fluids with different ionic strengths were pumped at various rates from a reservoir at 80 o C into a pipe submerged in a bath maintained at 20 o C. The fluid velocity, pressure drop ∆𝑃, and temperature were monitored. The same quantities were extracted by solving continuity, energy, and momentum equations. Moreover, the modeling results demonstrate that the local pressure gradient along the pipe 𝑑𝑃 𝑑𝑥 | 𝑥 is related to the local yield stress near the pipe wall 𝜏 𝑦 𝑤𝑎𝑙𝑙 | 𝑥 , which explains the variations of 𝑑𝑃 𝑑𝑥 | 𝑥 along the pipe. Experimental results show much lower values for ∆𝑃 compared to those from modeling. This discrepancy is exacerbated at higher ionic strengths and smaller flow rates, where fluid shows a higher degree of solidification. The tabulated experimental ∆𝑃 data against the solidification onset length 𝐿 𝑜𝑛𝑠𝑒𝑡 (where the fluid is cool enough to solidify) along with the ultrasound imaging velocimetry associate these discrepancies between experiments and models to a depletion layer of ~1 𝜇𝑚, reflecting the lubrication effects caused by the water layer at the wall.

Multiphase flow occurs in almost all producing oil and gas/condensate wells .Wellhead chokes are special equipment that widely used in the petroleum industry to control flow rate, to maintain well allowable, to protect surface equipments, to prevent water and gas coning and to provide the necessary backpressure to reservoir to avoid formation damage from excessive drawdown. Accurate modeling of choke performance and selection of optimum choke size is vitally important for a petroleum engineer in production from reservoirs due to high sensitivity of oil and gas production to choke size. Two main approaches have been proposed for prediction of multiphase flow through chokes can be classified as either analytical or empirical and majority of correlations were developed for critical flow conditions. Although most of the correlations available to petroleum engineers are for critical flow but in lots of high rate gas/condensate wells subcritical flow occurs in large choke sizes.There is no empirical correlation for wellhead choke performance under subcritical condition for high rate gas condensate wells, especially in large choke sizes. The first aim of this paper is to develop a new simple empirical Gilbert type correlation for high rate gas condensate wells under subcritical flow in large choke sizes (40/64 in. to 192/64 in.) using non-linear regression analysis based on 61 field data points of 15 wells from ten different fields. The second is to extend the work of Al-Attar for high rate gas condensate wells flowing through large choke size under subcritical flow conditions and check the applicability and advantages.Finally, statistical comparison between these two approaches is done with different error parameters.

The fully developed laminar flow in a helical circular pipe under the influence of both curvature and torsion is studied analytically. The solutions are obtained by the double series expansion method which perturbs the exact solution derived in this work for a twisted circular pipe. The perturbed parameters selected are dimensionless curvature K and dimensionless torsion 7 . Since the expanded governing equations and series solutions have been arranged in a compact form, the complete solutions can be computed by a systematic procedure on computer. In addition, the accuracy of the solutions is only confined by the natural limitation of the series expansion method because no approximation was made in the governing equations. The 'torsion number' Tn which can be considered as the measure of the torsion effect that swirls the flow is defined Tn = 279, where W is the Reynolds number. The characteristics of the flow in the helical circular pipe are thus controlled by three parameters: W , Dean number K and Tn. The flow rate solution of the extended Dean equations of Germano (1989) is then found. The effects of finite curvature and torsion on the flow rate, axial velocity and secondary flow are also found. The inconsistency of torsion effect on the secondary flow between Wang (1981) and Germano (1982, 1989) is also quantitatively explained by the different coordinate systems used.

A large eddy simulation (LES) with an extended Smagorinsky model has been carried to investigate numerically the fully developed turbulent flow of a shear thinning fluid (n=0.75) in a stationary pipe at a simulation's Reynolds number equals to 4000 with a grid resolution of 65 3 gridpoints in axial, radial and circumferential directions and a domain length of 20R. The present study set out to critically evaluate the influence of the Non-Newtonian rheological and hydrodynamic behaviour on the turbulence main features, as well as to ascertain the accuracy and reliability of the laboratory code predicted results. The turbulent flow statistics obtained compared reasonably well with the experimental data and DNS results. A reasonably good agreement has been obtained between the predicted results and available results of literature. The main findings suggest that the mean axial velocity fluctuations were generated in the wall vicinity and transferred to the radial and spanwise compone...

In a recent paper by C. Bogey, O. Marsden, and C. Bailly [“Large-eddy simulation of the flow and acoustic fields of a Reynolds number 105 subsonic jet with tripped exit boundary layers,” Phys. Fluids 23(3), 035104 (2011)], simulation results were presented for round jets with tripped boundary layers, displaying nozzle-exit conditions typical of initially nominally turbulent, transitional jets, namely laminar mean velocity profiles and high fluctuation intensities. The velocity spectra evaluated just downstream of the nozzle exit are re-examined here with respect to literature data. They agree qualitatively very well with spectra obtained in a fully turbulent pipe flow using direct numerical simulation. The wave numbers dominating in the azimuthal direction are also consistent with measurements of spanwise energy distribution in fully turbulent boundary layers. The initial turbulent structures in the jets, therefore, appear to be organized similarly to those in fully developed wall-b...

Whether physicians should ask their patients to attend for a regular review of their health status not motivated by any particular problem has been a longstanding issue in primary care. A google search for "regular health check ups" yielded 4,810,000,000 hits in less than one second. Scanning the first couple of pages, most of the advice/comments suggest such health checks are a good idea; indeed, most are enthusiastic advocates.

Abstract-This paper presents the automatic calculation program for steady water flow, RIMIS and the physical model developed by authors for the study of water motion in a distribution network. The study was concentrated upon looped type networks, frequently used in water ...

The stability of polymer melt shear flows is explored using the recently proposed eXtended Pom-Pom (XPP) model of . We show that both the planar Couette and the planar Poiseuille flow are stable for 'small' disturbances. From our 1-dimensional eigenvalue analysis and 2-dimensional finite element calculations, excellent agreement is obtained with respect to the rate of slowest decay. For a single mode of the XPP model, the maximum growth of a perturbation is fully controlled by the rightmost part of the continuous eigenspectrum. We show that the local fourth order ordinary differential equation has three regular singular points that appear in the eigenspectrum of the Couette flow. Two of these spectra are branch cuts and discrete modes move in and out of these continuous spectra as the streamwise wavelength is varied. An important issue that is addressed is the error that is contained in the rightmost set of continuous modes. We observe that the XPP model behaves much better as compared to, for example, the Upper Convected Maxwell (UCM) model in terms of approximating the eigenvalues associated with the singular eigenfunctions. We demonstrate that this feature is extended to the 2D computations of a periodic channel which means that the requirements on the spatial grid are much less restrictive, resulting in the possibility to use multi mode simulations to perform realistic stability analysis of polymer melts. Also, it is shown that inclusion of a nonzero second normal stress difference has a strong stabilizing effect on the linear stability of both planar shear flows.

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We explore a new application of the quadrant method in the context of the double-averaged Navier-Stokes equations for studying open channel flow near rough beds. Quadrant analysis is applied to spatial disturbances of time-averaged velocity components, using the experimental data from flow over twodimensional regular transverse square-bar roughness. The spatial velocity disturbances change periodically performing a full cycle over a single roughness element, so that the quadrant diagrams are regular closed orbits. A colour code is used to produce a quadrant map of the flow cross-section, which reveals contributions from each quadrant to the time-averaged momentum transfer.

This work studies the momentum and energy transport mechanisms in the corner between a free surface and a solid wall. We perform large-eddy simulations of the incompressible fully developed turbulent flow in a square duct bounded above by a free-slip wall, for Reynolds numbers based on the mean friction velocity and the duct width equal to 360, 600 and 1000. The flow in the corner is strongly affected by the advection due to two counter-rotating secondary-flow regions present immediately below the free surface. Because of the convection of the inner eddy, as the free surface is approached, the friction velocity on the sidewall first decreases, then increases again. A similar behaviour is observed for the surface-parallel Reynolds-stress components, which first decrease and then increase again very close to the surface. The budgets of the Reynolds stresses show a strong reduction of all terms of the dissipation tensor in both the inner and outer near-corner regions. They exhibit a reduction in both production and dissipation towards the free surface. Very close to the solid boundary, within 15-20 viscous lengths of the sidewall, the turbulent kinetic energy production and the surface-parallel fluctuations rebound in the thin layer adjacent to the free surface. The Reynolds-stress anisotropy appears to be the main factor in the generation of the mean secondary flow. The multi-layer structure of the boundary layer near the free surface is also discussed.

Abstract-This paper presents the automatic calculation program for steady water flow, RIMIS and the physical model developed by authors for the study of water motion in a distribution network. The study was concentrated upon looped type networks, frequently used in water ...

A 2D analytical turbulent diffusion model for particle dispersion and deposition at different heights across the pipe flow and circumferential deposition has been developed. This liquid-solid turbulent diffusion model presented in this paper has emanated from an existing gas-liquid turbulent diffusion model. Simultaneously a comprehensive 3D numerical investigation has been carried out to study the above making of multiphase mixture model available in Fluent 6.1. In both studies different particles sizes and densities were used. The deposition was studied as a function of particle diameter, density and fluid velocity. The deposition of particles, along the periphery of the wall and at different depths, was also investigated. Both studies showed that the deposition of heavier particles at the bottom of the pipe wall was found to be higher at lower velocities and lower at higher velocities. The lighter particles were found mostly suspended with homogeneous distribution. Smaller partic...

A comprehensive 3D numerical investigation of hydrodynamics of particles flowing through a horizontal pipe loop consisting of four bends has been modeled. The multiphase mixture model available in Fluent 6. 1 [6] is used in this study. In this numerical simulation five different particles have been used as secondary phases to calculate real multiphase effect in which inter-particle interaction has been accounted. The deposition of particles, along the periphery of the wall around bends has been investigated. The effect of bend and fluid velocity on particle deposition has also been investigated. The maximum particle deposition is at the bottom wall in the pipe before entering the bends conversely, downstream of bends the maximum deposition is not at the bottom -as seen upstream of the bends -rather it occurs at an angle of 60 0 toward the inner side from the bottom. The larger particles clearly showed deposition near the bottom of the wall except downstream of the bends. As expected, the smaller particles showed less tendency of deposition and this is more pronounced at higher velocity. This numerical investigation showed good agreement with the experimental results conducted by CSIRO team [9].

Direct solutions of pipe flow problems are not possible because of the implicit form of Colebrook-White equation, which is most commonly used for determining the friction factor of commercial pipes. New empirical equations for head loss, h , due to friction undergone by water flowing in the PVC, commercial steel, asphalted cast iron, galvanized iron, cast iron and concrete pipes

Pressure surges in pipelines are caused due to different events either planned or accidental. It is essential to determine the magnitude and frequency of pressures and forces triggered due to these transients to estimate the stresses and vibration levels in the pipeline networks. In this paper an effort is made to study these transients in incompressible fluid flow systems and the development of a computer program HYTRAN is described. This program comprehensively incorporates the method of characteristics for the calculation of the time dependent head and velocity of the fluid at any point in a complex fluid/water pipeline network upon the onset of any event such as pump failure, load reduction on a turbine, etc. The time history of the machine parameters in the case of pumps and turbines during such events can also be obtained as output. Two case studies have been taken up and the results are discussed.

Gas flow through corrugated pipes is known to excite strong acoustic resonances within the pipe. In an attempt to better understand the flow acoustic phenomena involved, we have investigated experimentally a short pipe (0.6m long and 0.04m diameter) having a single small (5mm long, 2.5mm deep) circumferential cavity. It was found that if placed close to the pipe's inflow end, strong acoustic resonances were generated. The experimental results were compared to a model based on describing-function theory. The model involves two transfer functions, one associated with the pipe resonator, and the other the shear layer above the cavity. These are combined to a feedback system. This model gives the frequencies generated and the acoustic pressure levels (to within a constant) for different flow velocities. Reasonable agreement was obtained between the experimental results and the model predictions.

The effect of three-dimensional staggered circular cavities on a zero-pressure gradient incompressible turbulent boundary layer was studied. Two key parameters were varied, being the ratio of the diameter, d, to the depth, h, of the cavity, d/h, and the Reynolds number based on the diameter of the cavity, Rd. Velocity profile measurements showed that for the cases of d/h>1 an increase in skin friction drag was experienced with respect to a smooth surface, but for d/h ≤ 1 the drag increment was almost negligible and in some cases it was lower than that of a smooth surface by up to 10%. Measurements along the spanwise plane showed the presence of organised transverse velocity components which bear some resemblance with the flow over riblets. The skin friction drag appears to be a strong function of Rd, where for Rd > 5500 a drag increment is experienced which could potentially be due to shear layer breakdown and more production of turbulence.

Dimples are tiny indentations on the surfaces of the body that enhance heat transfer
and alter fluid flow characteristics on or within the body. Numerical investigations
were conducted to analyse the heat transfer and flow characteristics in a crosscombined dimple tube in the range of Reynolds numbers from 6000 to 14000. The
finite volume method recognised a novel enhancement model utilising methods for
composite-form surfaces. Compared to a smooth tube working similarly, the effects
significantly improve the heat transfer index, performance evaluation criteria, and
friction factor. A three-dimensional simulation was conducted to clarify the underlying
process by which dimples affect thermal performance. The simulation findings suggest
that the dimples effectively enhance heat transfer by altering the temperature
distribution and increasing the temperature gradient within the central area of the
dimple section. A concave surface profile disrupts the flow and prevents the formation
of a stable boundary layer, promoting the mixing of hot and cold fluids. Furthermore,
the study investigates how geometric characteristics impact thermal and hydraulic
efficiencies, emphasising that larger dimples improve overall thermo-hydraulic
performance. Specifically, the heat transfer enhancement achieved an average
increase of 17.3%, ranging from 18.03% to 38.6%, surpassing that of the traditional
smooth tube.

Theoretical and experimental works on microscale transport phenomena have been carried out in the past decade in the attempt to analyze possible new effects and to assess the influence of downscaling on the classical correlations which are used in macro-scale heat and fluid flow, following the need to supply engineers with reliable tools to be used in the design of micro-scale devices. These results were sometimes in mutual contrast, as is the case for the determination of the friction factor, which has been found to be lower, higher or comparable to that for macroscopic channels, depending on the researchers. In this work the compressible flow of nitrogen inside circular microchannels from 26 mm to 508 mm in diameter and with different surface roughness is investigated for the whole range of flow conditions: laminar, transitional and turbulent. Over 5000 experimental data have been collected and analysed. The data confirmed that in the laminar regime the agreement with the conventional theory is very good in terms of friction factors both for rough and smooth microtubes. For the smaller microchannels (<100 mm) when Re is greater than 1300 the friction factor tends to deviate from the Poiseuille law because the flow acceleration due to compressibility effects gains in importance. The transitional regime was found to start no earlier than at values of the Reynolds number around 1800. Both smooth and sudden changes in the flow regime have been found, as reported for conventional tubes. Fully developed turbulent flow was attained with both smooth and rough tubes, and the results for smooth tubes seem to confirm Blasius' relation, while for rough tubes the Colebrook-White correlation is found to be only partially in agreement with the experimental friction factors. In the turbulent regime the dependence of the friction factor on the Reynolds number is less pronounced for microtubes than the prediction of the Colebrook-White correlation and the friction factor depends only on the microtube ''relative roughness''.

Various technologies have been used, including a regular tube with the inclusion of dimples, which are widely used to enhance the thermo-hydraulic performance of engineering applications. A numerical analysis involving this work of the thermohydraulic performance of water flow in a scarred pipe. By numerical solution using the Ansys Fluent 2023 R2 program to model the flow through the pipe, the effect of different dimple shapes (square, circular, and triangle) has been studied. The finite volume method identified a new enhancement model that makes use of compositeform surface techniques. To assess the effect of scarring on the field of velocity and turbulent flow, the continuity, momentum, and heat energy equation represented by the three-dimensional governing differential equations was studied using the k-epsilon flow model for the Reynolds number range of (3500-7000). The numerical results indicated the dimple surface of the pipe significantly improves the heat transfer rate and also increases the friction factor compared to the smooth pipe without dimple. Percentage (12.808, 17.987,.978%) of the increase in heat transfer rate enhancement (Nusselt number) for the three dimple shapes of the pipe (square, circular, and Triangle) respectively, moreover dimpled pipe has a higher coefficient of friction compared to the normal pipe.

To date, the most successful turbulence control technique is the dissolution of certain rheology-modifying additives in liquid flows, which results in a universal maximum drag reduction (MDR) asymptote. The MDR asymptote is a well-known phenomenon in the turbulent flow of complex fluids; yet recent direct numerical simulations of Newtonian fluid flow have identified time intervals showing key features of MDR. These intervals have been termed "hibernating turbulence" and are a weak turbulence state which is characterised by low wall-shear stress and weak vortical flow structures. Here, in this experimental investigation, we monitor the instantaneous wall-shear stress in a fully-developed turbulent channel flow of a Newtonian fluid with a hot-film probe whilst simultaneously measuring the streamwise velocity at various distances above the wall with laser Doppler velocimetry. We show, by conditionally sampling the streamwise velocity during low wall-shear stress events, that the MDR velocity profile is approached in an additive-free, Newtonian fluid flow. This result corroborates recent numerical investigations, which suggest that the MDR asymptote in polymer solutions is closely connected to weak, transient Newtonian flow structures.

The work and life of Piotr Szymański is reviewed. He is the author of a classical paper on accelerating pipe flow, but is relatively unknown to the scientific community of today. The paper by Szymański is one of the first related to unsteady friction, clearly explaining the underlying physics and with rigorous mathematics. Exactly half a century after his death, the authors of this current paper would like to pay a modest tribute to the man and his achievements.

In this study, vortex breakdown in swirling flows and critical swirl rate for its occurrence was experimentally and numerically investigated. In order to understand and control this interesting phenomenon, a special pipe flow test facility with a rotating honeycomb type swirl generator was constructed. Measurements of all velocity components were carried out by using LDV combined with refractive index matching

The flow of liquids through dielectric tubes is shown to produce a frictional electromotive force, and an empirical relation is established between the voltage generated and the various experimental factors controlling it. The application of the effect to the measurement of the flow rate and the electrical resistivity of fluids is discussed.

Interactions between nearly bicritical modes in Taylor-Couette flow, which have been concerned with the framework of weakly nonlinear theory, are extended to fully nonlinear Navier-Stokes computation. For this purpose, a standard Newton solver for axially periodic flows is generalized to compute any mixed solutions having up to two phases, which typically arise from interactions of two spiral or Taylor vortex modes. Also, a simple theory is developed in order to classify the mixed solutions. With these methods, we elucidate pattern formation phenomena, which have been observed in a Taylor-Couette flow experiment. Focusing on the counter-rotating parameter range, all possible classes of interaction of various solutions with different azimuthal and axial wave numbers are considered within our computational restriction, and we observe numerous connection branches, e.g., footbridge solutions. Some of the mixed solutions result in a three-dimensional wavy spiral solution with axial relative periodicity or an axially doubly periodic toroidally closed vortex solution. The possible connection of the former solution family to spiral turbulence, which has been observed in highly counter-rotating Taylor-Couette flow, is discussed.

Submitted for the DFD17 Meeting of The American Physical Society Invariant solutions organizing pipe flow turbulence SEBASTIAN ALTMEYER, BJRN HOF, Institute of Science and Technology (IST) Austria-Invariant unstable solutions such as (relative) periodic orbits (RPOs) and travelling waves (TWs) have been suggested to act as building blocks of turbulence in basic shear flows. A large number of such invariant solutions have been determined in recent years, yet most observed states typically possess spatial symmetry (e.g. to rotation, reflection or translation) due to artificial symmetry restrictions. In contrast turbulence does not have any of such symmetry in general. Commonly used recurrence methods are unlikely to capture orbits in full space due to their complexity and the short visiting times of turbulent trajectories. Nevertheless, looking for periodic modulations instead of full recurrences we have been able to extract asymmetric invariant solutions, RPOs and TWs, dynamically embedded in turbulence. Compared to other invariant solutions in subspaces, neither TWs or orbits the isosurfaces looks less smooth indicating various different length scales within these structures. This is a typical observation in turbulent flows which also show strong fluctuations, e.g. in the internal arrangement of high and low velocity streaks. The complexity of the underlying manifold results in closed curves either in Re and k defining parameters with up to four solutions of a single RPO.

Students designed a rotating pipe flow apparatus for the fluids laboratory. The project was funded by the ASHRAE Senior Undergraduate Project Grant Program. This paper describes a project where a group of undergraduate engineering students in the manufacturing processes, finite element methods and fluid mechanics courses designed, built, and tested a swirling pipe flow apparatus for measurements of friction factors. The overall objective was to engage the students in a design project. The paper will also provide details of assessment and outcomes for the project. The students had to choose materials, minimize production cost, and determine fabrication techniques for the apparatus. Students designed the apparatus using SolidWorks, and SolidWorks Flow Simulation software was used to simulate the swirling pipe flow. Students designed a pipe flow apparatus with static mixers, diffuser, settling chamber, honeycomb, screens and a contraction in order to minimize the disturbance level of the flow entering the pipe section. The pipe had a section that could be rotated in order to study the effects of swirling motion on the stability of pipe flow. Students were involved in the building of the apparatus and they performed pressure drop measurements and determined friction factors.

A new configuration for the transmitting optics of a laser Doppler anemometer has been developed in order to measure the velocity at two different points at the same time. From the simultaneous measurements at two points along the mean flow direction it is possible to evaluate the spatial correlations and to compare them with the temporal correlation to verify the validity limits of Taylor's hypothesis also known as the frozen turbulence hypothesis. The transfer function between the velocity signals at two different points has been introduced to better explain the differences between Taylot's hypothesis and non frozen flow. The analysis is carried out in a flow with high turbulence levels.

Models for the dynamic behaviour of transmission lines are essential for the understanding of wave propagation phenomena in hydraulic pipelines and hoses. If the Reynolds numbers are low enough to justify the assumption of laminar flow and if convective terms are negligible, the governing equations are linear and a very compact description of the input-output behaviour of a transmission line exists in the frequency domain. For a coupled simulation of networks of transmission lines interacting with other, possibly nonlinear components such as valves, there are numerous approaches for the approximation of the transcendental transfer functions arising from the transmission line modelling by finite dimensional models in the time domain. Discrete-time approaches such as the method of characteristics with a fixed grid are known to be very accurate but computationally ineffective due to the high number of state variables involved. This paper shows a method for the derivation of reduced order models with a trade-off between the degree of accuracy and the system order and with the additional feature that important properties like the passivity of the transmission line model is guaranteed.

Submitted for the DFD15 Meeting of The American Physical Society Direct Numerical Simulation of two superposed viscous fluids in a rough channel: effect of the position of the interface 1 ISNARDO ARENAS, STEFANO LEONARDI, The University of Texas at Dallas-Direct Numerical Simulations of two superposed fluids in a turbulent channel with cavities on one wall have been performed. Three different cases have been considered with either square cavities, longitudinal riblets or staggered cubes on the lower wall, the upper wall being smooth. Two viscosity ratios between the two fluids have been used, m = 0.1 (a fluid of lower viscosity inside the cavities), and m = 10. The interface between the two fluids is flat mimicking the case of an infinite surface tension. The Reynolds number based on the bulk velocity is Re = 2, 800 and it corresponds to a turbulent Reynolds number Re τ = 180 when both walls are smooth. The height is approximately h + = 9. The position of the interface between the two fluids has been varied in the vertical direction. Two cases have been considered, one where interface is above the crests plane, and one where the interface is below the crests plane. When a thin film of low viscosity fluid is above the crests, the stagnation point on the leading edge of the roughness elements moves upward and the form drag decreases thus leading to a drag reduction of up to 30%. Drag reduction can be achieved even for m > 1 due to the damping of wall normal velocity fluctuations.

The entropy generation due to heat transfer and friction has been calculated for fully developed, forced convection flow in a large rectangular duct. packed with spherical particles, with constant heat fluxes applied to both the top (heated) and bottom (cooled) wall. An approximate analytical expression for the velocity profile developed for packed bed with t-l/cJ, > 5 has been used together \vith the energy equation of fully developed flow to calculate the non

A new subgrid scale model is proposed for Large Eddy Simulations in complex geometries. This model which is based on the square of the velocity gradient tensor accounts for the effects of both the strain and the rotation rate of the smallest resolved turbulent fluctuations. Moreover it recovers the proper y3 near-wall scaling for the eddy viscosity without requiring dynamic

A simplified consistency condition for the production-to-dissipation ratio is developed to obtain an explicit algebraic Reynolds stress model. The stress expression is based on the well-known tensor representation derived from quasi-linear pressure-strain correlation models for two-dimensional mean flows in the weak-equilibrium limit. Results obtained for homogeneous turbulent flows, a backward-facing step flow, and a channel bend flow indicate that the model combines improved accuracy with computational efficiency.

This work presents the design of an experimental setup for swirling decaying flow investigations, alongside validation experiments and preliminary experimental work. The combinations of possible investigations using such an apparatus are limitless. As a means of validation, a series of flow visualisation images for pipe flow are presented. In addition to that, the design of the axial swirl vanes used in the study was also disclosed, alongside flow visualisation images and steady and unsteady heat transfer results. Experimental validation was conducted using the dye seeding method. Results show that the fully laminar and turbulent regime is similar to published results. Streak-lines produced for swirling decaying flow are clear and easily captured using normal digital cameras.

Nozzles are used in industry for several different purposes ranging from cooling, painting, and mixing to dosing or flow seeding. When multiple nozzles should be used alongside with each other at equal rates, flowrate of feeding lines should be carefully controlled with precision. This task can be undertaken by means of expensive and sophisticated instruments. However, application constraints may necessitate simpler and cost effective solutions. One of the such solutions is adopting a common-rail type fluid distribution nozzle. The nozzle should ensure equal flowrate distribution to the target nozzles while several other parameters should be maintained. One such parameter is static pressure that is also responsible for equal flowrate distribution. In the present study, an illustration case of nozzles is aimed to be simulated via Computational Fluid Dynamics (CFD). Also, the CFD methodology by the recent tools is evaluated in terms of multiple outlets. A three dimensional investigation domain was created instead of axisymmetric two dimensional numerical domains. The tree dimensional domain was then divided to finite volumes by meshing feature of the adopted software. Three different mesh densities were tried to have a favorable mesh setting. Laminar flow governing equations were selected for the solver since the target nozzle applications generally remain in the laminar regime. A nondimensionalization approach by modifying thermo-physical properties to obtain desired Reynolds number in the laminar interval was utilized. Viscous dissipation was ignored, and energy equation was disabled. It is seen that up to five times the nozzle feeding line diameter of the manifold diameter can be deemed sufficient for one percent mass flow rate difference between the nozzle feeding line mass flow rates. However, nozzle feeding line inlet effects considering their connection to the manifold create a fluctuation in the static pressure at the proximity and downstream. The fluctuations spatially diminish in about two to three nozzle feeding line diameters. The mass flow rate change is not monolithic through the inline nozzles.

Direct numerical simulation (DNS) of incompressible turbulent pipe flow was carried out on unstructured grids for a Reynolds number based on the friction velocity and the pipe diameter of Rcr = 360 using the spectral/hp element method (SEM) by Karniadakis and Sherwin [3]. The main objective was to investigate the computational aspects of this DNS with respect to accuracy, CPU time and memory requirements. DNS results of evaluated statistical moments of up to fourth order agree well with data from the literature. A conducted performance study reveals the computational requirements for DNS of turbulent flows using this SEM.

In the present paper we study the propagation of pressure waves in a barotropic flow through a pipe, with a possibly varying cross-sectional area. The basic model is the Saint-Venant system. We derive two multiscale models for the cases of weak and strong damping, respectively, which describe the time evolution of the piezometric head and the velocity. If the damping is weak, then the corresponding first-order hyperbolic system is linear but contains an additional integro-differential equation that takes into account the damping. In the case of strong damping, the system is nonlinear. The full and multiscale models are compared numerically; we also discuss results obtained by a largely used commercial software. The numerical experiments clearly demonstrate the efficiency of the multiscale models and their ability to yield reliable numerical approximations even for coarse grids, that is not the case for the full model.

The thermocapillary migration of a fluid particle in a tube, owing to an imposed axial temperature gradient, is studied theoretically for the case of steady, axisymmetric, creeping, translation in the absence of thermal convection and fluid particle distortion from sphericity, and for an insulated tube. Formulated with these assumptions, the migration is a linear Stokes flow which is separable into two fixed-fluid particle flow idealizations. One is the fluid motion in a quiescent continuous phase, owing only to the thermocapillary surface stress. This stress causes fluid streaming which exerts a lift force on the fluid particle in the direction of the warmer fluid described by a lift coefficient. The second idealization is uniform flow in the absence of thermocapillary forces. The force on the fluid particle owing to this flow represents the hydrodynamic resistance to the forward motion of the fluid particle in the presence of the tube wall, and is described in terms of a drag coef...

This paper presents a study of the steady, axisymmetric, creeping translation of a fluid sphere in a tube for the case in which surfactant is adsorbed onto the fluid sphere interface. Marangoni stresses caused by the convective redistribution of surfactant are computed perturbatively in the limit of sorption-controlled uniform retardation, and fully converged numerical solutions of the creeping-flow equations including the Marangoni stress are obtained by a collocation technique. The results indicate that when the fluid sphere moves in a liquid which is at rest at infinity, the Marangoni stress retards the particle velocity. This retardation generally increases with the sphere to tube diameter ratio up to a value of approximately 0.6, whereupon the retardation begins to level off or even become reduced. When the sphere is suspended in a Poiseuille flow, stagnation rings develop on the sphere surface, and the Marangoni stresses that derive from this surface convection pattern can accelerate the fluid particle when the particle velocity is small with respect to the Poiseuille centreline velocity, but in the same direction as that velocity.

With the ubiquitous use of computers in controlling physical systems, it requires to have a new formalism that could model both continuous flows and discrete jumps. Hybrid systems are introduced to this purpose. A hybrid system, which is modeled by a hybrid automaton in the thesis, is equipped with finitely many discrete modes and continuous real-valued variables. A state of it is then represented by a mode along with a valuation of the variables. Given that the system is in a mode , the variable values are changed continuously according to the Ordinary Differential Equation (ODE) associated to , or discretely by a jump starting from . The thesis focuses on the techniques to compute all reachable states over a bounded time horizon and finitely many jumps for a hybrid system with non-linear dynamics. The results of that can then be used in safety verification of the system. Flow* and SpaceEx. Legends: Var: number of variables, T : time horizon, δ: time step-size, k: TM order, P: precision, box: box over-approximation, octagon: octagon over-approximation, T.O.:

State-space models, and the state-space representation of data, are an important tool for econometric modeling and computation. However, when applied to observed (rather than detrended) data, many such models have a mixture of stationary and non-stationary roots. While Koopman (1997) and Durbin and Koopman (2002) provide “exact” calculations for models with non-stationary roots, these have not yet been implemented in most software. Also, neither the Koopman article nor the Durbin and Koopman book address (directly) the handling of models where a unit root is shared among several series—a frequent occurrence in statespace models derived from DSGE’s. This paper provides a unified framework for computing the finite and “infinite” components of the initial state variance matrix which is both flexible enough to handle mixed roots and also faster (even for purely stationary models) than standard methods. In addition, it examines some

This paper describes how geotechnical and hydraulic engineering concepts were combined to develop a computer model that can be used to simulate the rate and extent of breaching of earth embankments characterized by transverse cracks and foundations experiencing the presence of earth fissures. The rate of breaching is an important parameter for developing emergency evacuation plans once breaching occurs or is anticipated. In addition, breach rate and its maximum extent determines the outflow characteristics from the reservoir, which is required to conduct inundation modeling and mapping. Other uses of the model include evaluation of potential solutions to prevent breaching of the dams and foundations. The model computes the erosive power of water by making use of basic principles of hydraulics and boundary layer theory, and represents the erosion characteristics of the soil by making use of results from geotechnical testing executed with the Erosion Function Apparatus (EFA) and the Vertical Jet Tester (VJT). The former is executed in the laboratory and the latter insitu. The elements of the computer model are discussed in the paper, as is its qualitative verification.