Complex Flow Patterns Research Articles

Supercritical flow in circular pipe bends

In this paper a complex flow pattern occurring in a closed conduit bend with supercritical flow is analyzed. The research was done by a scale (physical hydraulic) model, and a numerical model developed in Ansys (Fluent) program surrounding. This article compares the results obtained by numerical and physical (scale) models, providing comments and recommendations for their application. Based on these results, simple empirical relationships were developed, describing the effects of the bend deflection angle and approach flow conditions (non dimensional depth and the Froude number upstream from the bend) on the considered flow.

A New Method Using Inverse Theory for Estimation of Dynamic Response in Frequency Domain for Operating Piping

Abstract Vibration failure of piping is a serious problem and a matter of concern for safety and reliability of plant operations. Presently there is no general analytical method available for a proper engineering design of the piping for operational vibration and mostly severity charts are being used as a cook-book approach. The major difficulty lies in the realistic estimation of the dynamic forces arising out of complex flow pattern. In mathematical terms, these are ill posed problems and no conventional or direct methods can be adopted for their solutions. In our study we have proposed a method on the basis of Inverse Theory[1-3]along with numerical simulations and followed bya case study as an application.

Genetic structure and gene flow in Beta vulgaris subspecies maritima along the Atlantic coast of France

Locating and quantifying genetic variation within crop wild relatives is an ongoing activity of gene banks tasked with ex situ conservation. Without detailed information about the population genetics of a species, geography often serves as a reasonable proxy for differentiation. With this in mind, this paper examines the genetic diversity and differentiation of Beta vulgaris subsp. maritima accessions collected along a well-studied latitudinal gradient along the French Atlantic coast of France as well as Corsica, for use as representative genotypes from the Mediterranean basin. The aim of this work is to identify the scale and magnitude of differentiation and diversity in this set of accessions, using both molecular and quantitative traits. We assessed clinal variation and admixture in genetic and morphometric data along this latitudinal gradient. Results from this study revealed a complex pattern of recent gene flow and immigration on a historical biogeographic structure. Our data suggest that a presumed latitudinal cline is in reality an admixed mosaic of genotypes.

PIV measurements in a compact return diffuser under multi-conditions

Due to the complex three-dimensional geometries of impellers and diffusers, their design is a delicate and difficult task. Slight change could lead to significant changes in hydraulic performance and internal flow structure. Conversely, the grasp of the pump's internal flow pattern could benefit from pump design improvement. The internal flow fields in a compact return diffuser have been investigated experimentally under multi-conditions. A special Particle Image Velocimetry (PIV) test rig is designed, and the two-dimensional PIV measurements are successfully conducted in the diffuser mid-plane to capture the complex flow patterns. The analysis of the obtained results has been focused on the flow structure in diffuser, especially under part-load conditions. The vortex and recirculation flow patterns in diffuser are captured and analysed accordingly. Strong flow separation and back flow appeared at the part-load flow rates. Under the design and over-load conditions, the flow fields in diffuser are uniform, and the flow separation and back flow appear at the part-load flow rates, strong back flow is captured at one diffuser passage under 0.2Qdes.

Distributional Patterns of Arsenic Concentrations in Contaminant Plumes Offer Clues to the Source of Arsenic in Groundwater at Landfills

The distributional pattern of dissolved arsenic concentrations from landfill plumes can provide clues to the source of arsenic contamination. Under simple idealized conditions, arsenic concentrations along flow paths in aquifers proximal to a landfill will decrease under anthropogenic sources but potentially increase under in situ sources. This paper presents several conceptual distributional patterns of arsenic in groundwater based on the arsenic source under idealized conditions. An example of advanced subsurface mapping of dissolved arsenic with geophysical surveys, chemical monitoring, and redox fingerprinting is presented for a landfill site in New Hampshire with a complex flow pattern. Tools to assist in the mapping of arsenic in groundwater ultimately provide information on the source of contamination. Once an understanding of the arsenic contamination is achieved, appropriate remedial strategies can then be formulated. © 2013 Wiley Periodicals, Inc.*

Development of a patient-specific simulation tool to analyse aortic dissections: Assessment of mixed patient-specific flow and pressure boundary conditions

Aortic dissection has high morbidity and mortality rates and guidelines regarding surgical intervention are not clearly defined. The treatment of aortic dissection varies with each patient and detailed knowledge of haemodynamic and mechanical forces would be advantageous in the process of choosing a course of treatment. In this study, a patient-specific dissected aorta geometry is constructed from computed tomography scans. Dynamic boundary conditions are implemented by coupling a three element Windkessel model to the 3D domain at each outlet, in order to capture the essential behaviour of the downstream vasculature. The Windkessel model parameters are defined based on clinical data. The predicted minimum and maximum pressures are close to those measured invasively. Malperfusion is indicated and complex flow patterns are observed. Pressure, flow and wall shear stress distributions are analysed. The methodology presented here provides insight into the haemodynamics in a patient-specific dissected aorta and represents a development towards the use of CFD simulations as a diagnostic tool for aortic dissection.

Experimental and Simulation Study of Fluidization Behavior of Palm Biomass in a Circulating Fluidized Bed Riser

Circulating fluidized bed combustion (CFBC) technology is being used for few decades to burn biomass wastes while meeting the stringent emission standards; however, much is needed to be understood about the complex flow patterns that are encountered. This work is aimed at understanding the major fluidization characteristics in a CFB loop for palm shell waste powders. Effects of inlet air on the fluidization behavior were experimentally investigated. The voidage of the bed material was found to be a function of axial distance above the distributor. The CFD modeling has also been done to quantify the riser exit effects. The flow was simulated using the “algebraic slip mixture (ASM)” model. In the simulation results the deviation of velocity contours owing to variation in riser exit geometries is discussed. It was found that the influence is found to be significant in the upper region of the riser column and the velocity contours are also swayed by the exit geometry.

Simulation of mixed electroosmotic/pressure-driven flows by utilizing dissipative particle dynamics

In this paper, we present an extension of dissipative particle dynamics method in order to study the mixed electroosmotic/pressure-driven micro- or nano-flows. This method is based on the Poisson–Boltzmann equation and has a great potential to resolve the electric double layer (EDL). Hence, apart from studying the bulk flow, it also provides a strong capability in order to resolve the complex phenomena occur inside the EDL. We utilize the proposed method to study the pure electroosmotic and also the mixed electroosmotic/pressure-driven flow through the straight micro-/nano-channels. The obtained results are in good agreement with the available analytical solutions. Furthermore, we study the electroosmotic flow and motion of DNA molecules through a T-shaped micro-channel. We show that neglecting the EDL and utilizing the slip wall boundary condition model can result in crucially misleading hydrodynamic characteristics if the EDL is comparable to the width of the channel. Finally, we utilize the presented method in order to study the complex flow patterns, which are created due to the heterogeneous distribution of the electric potential of the walls. These complex flow patterns usually are utilized in order to enhance the efficiency of mixing process in micro-/nano-length scales. In addition, we show that they can also be utilized effectively in order to separate the different macro-molecules such as polymers, DNA molecules and so on, according to their length of chain.

Surges around the Hawaiian Islands from the 2011 Tohoku Tsunami

[1] The 2011 Tohoku tsunami devastated the northeastern Japan coasts and caused localized damage to coastal infrastructure across the Pacific. The tsunami resulted in strong currents around the Hawaiian Islands that led to closure of harbors and marinas for up to 38 h after its arrival. We utilize a nonhydrostatic model to reconstruct the tsunami event from the seismic source for elucidation of the physical processes and inference of the coastal hazards. A number of tide gauges, bottom pressure sensors, and ADCPs provided point measurements for validation and assessment of the model results in Hawaii. Spectral analysis of the computed surface elevation and current reveals complex flow patterns due to multiscale resonance. Standing waves with 33–75 min period develop along the island chains, while oscillations of 27 min or shorter are primarily confined to an island or an island group with interconnected shelves. Standing edge waves with periods 16 min or shorter, which are able to form nodes on the reefs and inside harbors, are the main driving force of the observed coastal currents. Resonance and constructive interference of the oscillation modes provide an explanation of the impacts observed in Hawaii with implications for emergency management in Pacific island communities.

An analytical model for solute transport through a water-saturated single fracture and permeable rock matrix

An analytical model for solute transport through a water-saturated single fracture and permeable rock matrix J. E. Houseworth, 1 D. Asahina, 1 and J. T. Birkholzer 1 The problem of solute transport through a water-saturated single fracture in a permeable rock matrix is examined using an analytical modeling approach. A closed-form analytical solution is obtained that accounts for transverse and longitudinal advective transport in the fracture and matrix and transverse diffusion in the matrix. The solution also accounts for both diffusive and advective solute exchange between the fracture and matrix and a general solute source position in either the fracture or matrix. The novel features are the incorporation of advective transport in the matrix and a general source position into a closed-form solution for the solute-transport problem. Examples of the solution behavior are presented, which demonstrate the effects of matrix advection in combination with advection along the fracture, transverse diffusion in the matrix for solute release in the fracture and matrix. A semianalytical solution in the form of a superposition integral is also derived that includes these transport features, plus independent levels of longitudinal diffusion and dispersion in the matrix and fracture, respectively. Examples are presented that include advective transport in the fracture and matrix, longitudinal and transverse diffusion in the matrix, longitudinal dispersion in the fracture, as well as solute release from the fracture and matrix. An approximate criterion is proposed to evaluate the significance of longitudinal diffusion and dispersion relative to longitudinal spreading caused by fracture- matrix interaction. Flow through fractures displays highly heterogeneous and complex flow patterns controlled by small-scale fracture features. Furthermore, transport processes at small scales that govern fracture-matrix exchange can dramatically influence larger-scale transport behavior [Grisak and Pick- ens, 1980]. Transport through saturated fractured rock was first investigated in an analytical model by Neretnieks [1980]. Tang et al. [1981] extended this work to include the effects of longitudinal dispersion in the fracture, and Sudicky and Frind [1982] and Maloszewski and Zuber [1985] further generalized the transport problem from a single fracture to a system of parallel fractures with interceding rock matrix. Sharifi Haddad et al. [2012] developed a semianalytical model of solute transport in a system of parallel fractures for a radially symmetric flow field associated with well injection. Maloszewski and Zuber [1990] considered the effects of linear kinetic interactions between solute and the rock for a single fracture and rock matrix. All of these mod- els were restricted to advective transport in the fracture, transverse diffusion in the matrix, and diffusive fracture- matrix solute exchange. A review of these modeling approaches among others is provided by Bodin et al. [2003a, 2003b]. Cihan and Tyner [2011] developed exact analytical solutions for advective transport through cylin- drical macropores and diffusive exchange with a soil ma- trix, for an instantaneous release of solute into a macropore, a constant concentration of solute at the top of a macropore, and a pulse release of solute into a macropore. 1 Introduction Solute transport in groundwater flow through frac- tured rock is a subject that has been investigated for nuclear waste disposal and other environmental groundwater con- tamination problems [National Research Council, 1996]. Fractures are a common feature of consolidated rock sys- tems and typically present much higher permeability than unfractured rock matrix, such that flow through fractures often dominates overall flow behavior. Matrix, on the other hand, typically dominates the overall pore volume of a fractured rock. These attributes often lead to much higher solute-transport velocities through fractures than in unfrac- tured rock or unconsolidated soils [Berkowitz, 2002]. This behavior often makes fracture flow and transport critical characteristics to examine for any geologic site where sol- ute transport is a concern. However, despite their impor- tance, fractures remain a difficult feature to represent accurately in mathematical models for groundwater flow and transport [Matth€ai et al., 2009 ; Wu and Pruess, 2000]. Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA. Corresponding author : J. E. Houseworth, Earth Sciences Division, Law- rence Berkeley National Laboratory, Berkeley, CA 94720, USA. (jehouseworth@lbl.gov)

Propagation and dissipation of the internal tide in upper Monterey Canyon

[1] Submarine canyons are sites of intense turbulence and mixing. Monterey Canyon cuts into the continental shelf off California, and is defined by its sinuous nature. Temperature, salinity, and current velocity measurements were made over 21 days in April 2009 with a depth-cycling towed body to understand internal tide propagation and dissipation through the canyon bends. Cross-canyon transects reveal complex flow patterns that follow large-scale bathymetry on scales greater than 5 km. Changes in thalweg direction deflect baroclinic energy flux, but the bends in the measurement region are too sharp for the flux to follow the thalweg. Ridges that form the bends in the canyon act as obstacles to the flow, and turbulent dissipation rates greater than 1 × 10−5 m2 s−3 were observed on their flanks, especially at the largest meander (the Gooseneck). The canyon-integrated baroclinic energy flux increased from 2.7 MW at the most western section to 3.7 MW at the Gooseneck Ridge, which has a nearly critical bottom slope with respect to the semidiurnal baroclinic tide on the western side; baroclinic energy flux was 50% less on the eastern side of the ridge. While measured dissipation near the Gooseneck Meander was sufficient to explain the flux divergence, turbulence near the Gooseneck may have been undersampled. Between the Gooseneck Ridge and the most eastern cross-canyon transect, dissipation may account for the decrease in the energy flux; though a local energy balance does not hold, the energy budget is balanced over the larger scale of the measurement region east of the Gooseneck Ridge.

Mixing layer in open-channel junction flows

When two open-channel flows merge in a three-branch subcritical junction, a mixing layer appears at the interface between the two inflows. If the width of the downstream channel is equal to the width of each inlet channel, this mixing layer is accelerated and is curved due to the junction geometry. The present work is dedicated to simplified geometries, considering a flat bed and a \(90^{\circ }\) angle where two configurations with different momentum ratios are tested. Due to the complex flow pattern in the junction, the so-called Serret–Frenet frame-axis based on the local direction of the velocity must be employed to characterize the flow pattern and the mixing layer as Cartesian and cylindrical frame-axes are not adapted. The analysis reveals that the centerline of the mixing layer, defined as the location of maximum Reynolds stress and velocity gradient, fairly fits the streamline separating at the upstream corner, even though a slight shift of the mixing layer towards the center of curvature is observed. The shape of the mixing layer appears to be strongly affected by the streamwise acceleration and the complex lateral confinement due to the side walls and the corners of the junction, leading to a streamwise increase of the mean velocity along the centerline and a decrease of the velocity difference. This results in a specific streamwise evolution of the mixing layer width, which reaches a plateau in the downstream region of the junction. Finally, the evaluation of the terms in the Reynolds-Averaged-Navier–Stokes equations reveals that the streamwise and normal acceleration and the pressure gradient remain dominant, which is typical of accelerated and rotational flows.

A CFD Model of a Swirl Diffuser for Heating and Cooling Modes

The aim of this study was to develop a simplified CFD model for the inlet jet of a swirl diffuser for the simulation of room airflow patterns. The swirl diffuser creates a complex flow pattern with high induction of room air, thus possessing a challenge for simulation. The studied diffuser was a model intended to be used in large enclosures. The flow pattern was adjustable between two basic modes: radial swirl jet for cooling conditions and compact downward swirl jet for heating conditions. For developing the CFD model, a series of laboratory measurements of the flow field was carried out. The boundary conditions for the diffuser were determined from the near field velocity measurements close to the diffuser surface. For validating the model, velocity distributions were measured at different distances from the diffuser. The aim was to develop a single model that can be used for both heating and cooling adjustments. The dimensions of the model were designed to follow approximately the geometry of the diffuser. The boundary conditions were calculated from the measured momentum and mass flow rates from the diffuser openings. The estimated momentum loss between the diffuser and the nearest measurement plane was added to the inlet momentum. The developed model was validated in isothermal conditions for both adjustments and for non-isothermal conditions for the heating mode. The model was found to predict well the flow patterns and velocity levels in both modes. Two turbulence models were used in the simulations, k-ε and SST. The differences between the results of the two models were small.

Numerical study of surface water waves generated by mass movement

In this paper waves generated by two-dimensional mass movement are simulated using a numerical model based on the full hydrodynamic coupling between rigid-body motion and ambient fluid flow. This approach has the capability to represent the dynamics of the moving rigid body, which avoids the need to prescribe the body velocity based on the data measurements. This model is implemented in the CFX code and uses the Reynolds average Navier–Stokes equations solver coupled to the recently developed immersed solid technique. The latter technique allows us to follow implicitly the motion of the solid block based on the rigid body solver. The volume-of-fluid method is used to track the free surface locations. The accuracy of the present model is firstly examined against the simple physical case of a freely falling rigid body into water reproducing Scott Russell's solitary waves. More complex and realistic simulations of aerial and submarine mass-movement, simulated by a rigid wedge sliding into water along a 45° slope, are then performed. Simulated results of the aerial mass movement show the complex flow patterns in terms of the velocity fields and free surface profiles. Results are in good agreement with the available experimental data. In addition, the physical processes associated with the generation of water wave by two-dimensional submarine mass-movement are explored. The effects of the initial submergence and specific gravity on the slide mass kinematics and maximum wave amplitude are investigated. The terminal velocity and initial acceleration of the slide mass are well predicted when compared to experimental results. It is found that the initial submergence did not have a significant effect on the initial acceleration of the slide block centre of mass. However, it depends nonlinearly\\vadjust{\ ewpage} on the specific gravity. The maximum wave amplitude and the time at which it occurred are also presented as a function of the initial submergence and specific gravity.

Experiment and Numerical Simulation of Rotating Speed of Blade in Sandstone Wastewater of Rotational Flow Grit Chamber

The high-turbidity solid-liquid two-phase problem of the complex flow pattern is of greatest importance for the grit chamber with rotational flow. An Eulerian-Eulerian two-phase model for describing the collision force between particles in sandstone wastewater properly was developed. A bench scale experiment combining with a hydroelectric project was conducted. By analyzing the removal efficiency at different speeds of blade, the optimized rotating speed was obtained. Based on the optimized rotating speed, three-dimensional numerical simulation of the two-phase flow field was studied. The simulation results showed that when the number of blade is four, the optimum removal efficiency can be reached, which was found to be in reasonable agreement with the experimental data.

Optimization Simulation on Blade Number of Grit Chambers with Rotational Flow

The grit chambers with rotational flow find wide range of application for the treatment of sandstone wastewater in hydropower stations. Aiming at the high-turbidity solid-liquid two-phase problem of a complex flow pattern, an Eulerian-Eulerian two-phase model was built, which can describe the collision term between particles in sandstone wastewater. By using CFD technology, the velocity distribution of flow at the blade position was analyzed and the different effects caused by blade numbers to the particle removal efficiency were discussed. The results show that the removal efficiency of grit chamber with rotational flow increased gradually at first and then decreased slightly. Then the number of blade is four, the optimum removal efficiency can be reached, which provided theoretical and referential basis for engineering design and operation.

Quantification of aortic flow by phase-contrast magnetic resonance in patients with bicuspid aortic valve

Bicuspid aortic valve (BAV) causes complex flow patterns in the ascending aorta (AAo), which may compromise the accuracy of flow measurement by phase-contrast magnetic resonance (PC-MR). Therefore, we aimed to assess and compare the accuracy of forward flow measurement in the AAo, where complex flow is more dominant in BAV patients, with flow quantification in the left ventricular outflow tract (LVOT) and the aortic valve orifice (AV), where complex flow is less important, in BAV patients and controls. Flow was measured by PC-MR in 22 BAV patients and 20 controls at the following positions: (i) LVOT, (ii) AV, and (iii) AAo, and compared with the left ventricular stroke volume (LVSV). The correlation between the LVSV and the forward flow in the LVOT, the AV, and the AAo was good in BAV patients (r = 0.97/0.96/0.93; P < 0.01) and controls (r = 0.96/0.93/0.93; P < 0.01). However, in relation with the LVSV, the forward flow in the AAo was mildly underestimated in controls and much more in BAV patients [median (inter-quartile range): 9% (4%/15%) vs. 22% (8%/30%); P < 0.01]. This was not the case in the LVOT and the AV. The severity of flow underestimation in the AAo was associated with flow eccentricity. Flow measurement in the AAo leads to an underestimation of the forward flow in BAV patients. Measurement in the LVOT or the AV, where complex flow is less prominent, is an alternative means for quantifying the systolic forward flow in BAV patients.

Field-scale prediction of enhanced DNAPL dissolution based on partitioning tracers

The equilibrium streamtube model (EST) has demonstrated the ability to accurately predict dense nonaqueous phase liquid (DNAPL) dissolution in laboratory experiments and numerical simulations. Here the model is applied to predict DNAPL dissolution at a tetrachloroethylene (PCE)-contaminated dry cleaner site, located in Jacksonville, Florida. The EST model is an analytical solution with field-measurable input parameters. Measured data from a field-scale partitioning tracer test were used to parameterize the EST model and the predicted PCE dissolution was compared to measured data from an in-situ ethanol flood. In addition, a simulated partitioning tracer test from a calibrated, three-dimensional, spatially explicit multiphase flow model (UTCHEM) was also used to parameterize the EST analytical solution. The EST ethanol prediction based on both the field partitioning tracer test and the simulation closely matched the total recovery well field ethanol data with Nash-Sutcliffe efficiency E=0.96 and 0.90, respectively. The EST PCE predictions showed a peak shift to earlier arrival times for models based on either field-measured or simulated partitioning tracer tests, resulting in poorer matches to the field PCE data in both cases. The peak shifts were concluded to be caused by well screen interval differences between the field tracer test and ethanol flood. Both the EST model and UTCHEM were also used to predict PCE aqueous dissolution under natural gradient conditions, which has a much less complex flow pattern than the forced-gradient double five spot used for the ethanol flood. The natural gradient EST predictions based on parameters determined from tracer tests conducted with a complex flow pattern underestimated the UTCHEM-simulated natural gradient total mass removal by 12% after 170 pore volumes of water flushing indicating that some mass was not detected by the tracers likely due to stagnation zones in the flow field. These findings highlight the important influence of well configuration and the associated flow patterns on dissolution.

Endothelial Cell Sensing of Flow Direction

Atherosclerosis-prone regions of arteries are characterized by complex flow patterns where the magnitude of shear stress is low and direction rapidly changes, termed disturbed flow. How endothelial cells sense flow direction and how it impacts inflammatory effects of disturbed flow are unknown. We therefore aimed to understand how endothelial cells respond to changes in flow direction. Using a recently developed flow system capable of changing flow direction to any angle, we show that responses of aligned endothelial cells are determined by flow direction relative to their morphological and cytoskeletal axis. Activation of the atheroprotective endothelial nitric oxide synthase pathway is maximal at 180° and undetectable at 90°, whereas activation of proinflammatory nuclear factor-κB is maximal at 90° and undetectable at 180°. Similar effects were observed in randomly oriented cells in naive monolayers subjected to onset of shear. Cells aligned on micropatterned substrates subjected to oscillatory flow were also examined. In this system, parallel flow preferentially activated endothelial nitric oxide synthase and production of nitric oxide, whereas perpendicular flow preferentially activated reactive oxygen production and nuclear factor-κB. These data show that the angle between flow and the cell axis defined by their shape and cytoskeleton determines endothelial cell responses. The data also strongly suggest that the inability of cells to align in low and oscillatory flow is a key determinant of the resultant inflammatory activation.

Bubbles in Non-Newtonian Fluids: A Multiscale Modeling

In this paper, the concept of a multiscale modeling approach is highlighted with which physical phenomena at different scales can be studied. The work reports a multiscale approach to describe the dynamics of a chain of bubbles rising in non-Newtonian fluids. By means of the Particle Image Velocimetry (PIV) and the Lattice Boltzmann (LB) simulation, a deep understanding of the complex flow pattern around a single bubble is gained at microscale. The interactions and coalescences between bubbles rising in non-Newtonian fluids are experimentally investigated by the PIV measurements, birefringence and rheological characterization for both an isolated bubble and a chain of bubbles formed from a submerged orifice. Two aspects are identified as central to interactions and coalescence: the stress creation by the passage of bubbles and their relaxation due to the fluid’s memory. This competition between the creation and relaxation of stresses displays non-linear complex dynamics. Along with the detailed knowledge around a single bubble, these fundamental mechanisms governing bubbles’ collective behavior in a train of bubbles at mesoscale lead to a cognitive modeling based on behavioral rules. By simulating bubbles as adaptive agents with the surround fluid via residual stresses, model predictions for consecutive coalescence between a great number of bubbles compare very satisfactorily with the experimental investigation at macroscale. Obviously this new approach captures important quantitative and qualitative features of the collective behaviors of bubbles at macroscale level which are predicted by the mesoscopic cognitive modeling approach of the interactions rules which are deduced from the understanding of the microscopic mechanism of the flow around a single bubble.