bluuebunny/crossref_metadata_2025 huggingface dataset:
Contrasting microbial assemblages in adjacent water masses associated with the East Australian Current
Authors: Seymour Justin R. , Doblin Martina A. , Jeffries Thomas C. , Brown Mark V. , Newton Kelly , Ralph Peter J. , Baird Mark , Mitchell James G.
Published: June 2012

Different oceanographic provinces host discrete microbial assemblages that are adapted to local physicochemical conditions. We sequenced and compared the metagenomes of two microbial communities inhabiting adjacent water masses in the Tasman Sea, where the recent strengthening of the East Australian Current (EAC) has altered the ecology of coastal environments. Despite the comparable latitude of the samples, significant phylogenetic differences were apparent, including shifts in the relative frequency of matches to Cyanobacteria, Crenarchaeota and Euryarchaeota. Fine‐scale variability in the structure of SAR11, Prochlorococcus and Synechococcus populations, with more matches to ‘warm‐water’ ecotypes observed in the EAC, indicates the EAC may drive an intrusion of tropical microbes into temperate regions of the Tasman Sea. Furthermore, significant shifts in the relative importance of 17 metabolic categories indicate that the EAC prokaryotic community has different physiological properties than surrounding waters.
Ranking of healthcare programmes based on health outcome, health costs and safe delivery of care in hospital pharmacy practice
Authors: Brisseau Lionel , Bussières Jean-François , Bois Denis , Vallée Marc , Racine Marie-Claude , Bonnici André
Published: June 2012

Objectives

To establish a consensual and coherent ranking of healthcare programmes that involve the presence of ward-based and clinic-based clinical pharmacists, based on health outcome, health costs and safe delivery of care.

Methods

This descriptive study was derived from a structured dialogue (Delphi technique) among directors of pharmacy department. We established a quantitative profile of healthcare programmes at five sites that involved the provision of ward-based and clinic-based pharmaceutical care. A summary table of evidence established a unique quality rating per inpatient (clinic-based) or outpatient (ward-based) healthcare programme. Each director rated the perceived impact of pharmaceutical care per inpatient or outpatient healthcare programme on three fields: health outcome, health costs and safe delivery of care. They agreed by consensus on the final ranking of healthcare programmes.

Key findings

A ranking was assigned for each of the 18 healthcare programmes for outpatient care and the 17 healthcare programmes for inpatient care involving the presence of pharmacists, based on health outcome, health costs and safe delivery of care. There was a good correlation between ranking based on data from a 2007–2008 Canadian report on hospital pharmacy practice and the ranking proposed by directors of pharmacy department.

Conclusions

Given the often limited human and financial resources, managers should consider the best evidence available on a profession's impact to plan healthcare services within an organization. Data are few on ranking healthcare programmes in order to prioritize which healthcare programme would mostly benefit from the delivery of pharmaceutical care by ward-based and clinic-based pharmacists.
Personal beliefs about illness questionnaire‐revised (PBIQ‐R): Reliability and validation in a first episode sample
Authors: Birchwood Max , Jackson Chris , Brunet Kat , Holden Judith , Barton Karen
Published: June 2012

Objective. To further develop the Personal Beliefs about Illness Questionnaire (PBIQ), which reflects current constructs of social rank theory in relation to people experiencing psychosis.

Method. Drawing on extensive clinical and research experience and after consultation with other mental health professionals and service users, 17 new items were added to 12 from the original 16 PBIQ questions. These made up five theoretical constructs (entrapment, loss, social marginalization, shame, and control). A total of 150 people who had just experienced a first episode of psychosis completed the newly devised PBIQ‐R. To test the validity of its five subscales, a small sub‐sample (N= 66) for whom follow‐up data was available also completed measures of depression, insight, and other social rank appraisals.

Results. All five subscales of the PBIQ‐R were found to be reliable, valid, and sensitive to change.

Conclusions. Although the PBIQ‐R was not designed to produce an overall ‘personal beliefs about illness’ score, its five subscales provide a rapid and valid method to assess and measure common psychological reactions to a first episode of psychosis. It will have relevance for use in older, multiple episode samples although further validation may be needed.
Optimization of the Effective Shear Properties of a Bidirectionally Corrugated Sandwich Core Structure
Authors: Besse Camille C. , Mohr Dirk
Published: June 2012

The transverse shear stiffness of a newly-developed all-metal sandwich core structure is determined experimentally and numerically. The core structure is composed of a periodic array of domes which are introduced into an initially flat sheet through stamping. A finite element model of the stamping process is built and validated experimentally. A parametric study is performed to choose the stamping tool geometry such that the resulting core structure provides maximum shear stiffness for a given relative density. It is found that the optimal geometries for relative densities ranging from 0.2 to 0.35 all feature the same dome shape with the same height-to-width ratio. The simulation results also show that the estimated transverse shear strength of the proposed core structure is the same as that of hexagonal honeycombs of the same weight for high relative densities (greater than 0.35), but up to 30% smaller for low relative densities (lower than 0.2). In addition to numerical simulations of a representative unit cell, four-point bending experiments are performed on brazed prototype sandwich beams to validate the computational model.
Numerical Simulation of Supercritical Water in T-Shaped Channel Across Critical Point
Authors: Furusawa Takashi , Yamamoto Satoru
Published: June 2012

Mixing flows of supercritical fluid and liquid assuming the supercritical hydrothermal synthesis (SCHS) reactor are calculated using the numerical method developed by our group. First, the influence of thermophysical properties near the critical point to the flows is evaluated. The flows ignoring density change and specific heat change become a steady-state flow and are obviously different from flows considering all thermophysical properties. These results indicate that the large density difference in fluid at a narrow region caused by a peak of specific heat induces unsteady flows in the reactor. While higher bulk pressure results in a steady flow because of the moderate change of thermophysical properties. Next the flows in a sub channel changing the width are calculated. The channel with a smaller width makes a strong injection and the mixing occurs mainly at the downstream of the main channel. The tiled sub-channel may suppress the flow recirculation in the main channel.
Artificial Compressibility Method and Preconditioning Method for Solving Two Dimensional Incompressibile Flow
Authors: Lee Hyungro , Kwak Einkeun , Lee Seungsoo
Published: June 2012

In this study, two commonly used numerical methods for the analysis of incompressible flows (or low Mach number flows), Chorins’ artificial compressibility method and Wiess and Smith’s preconditioning method are compared. Also, the convergence characteristics of two methods are numerically investigated for two-dimensional laminar and turbulent flows. Although the two methods have similar governing equations, the eigensystems and other details are very different. The eigensystems of the artificial compressibility method and the preconditioning method are analytically examined. An artificial compressibility code that solves the incompressible RANS (Reynolds Averaged Navier-Stokes) equations is newly developed for the study. An artificial compressibility code and a well-verified existing low Mach number code uses Roe’s approximate Riemann solver in conjunction with a cell centered finite volume method. Using MUSCL extrapolation with nonlinear limiters, 2nd order spatial accuracy is achieved while maintaining TVD (total variation diminishing) property. AF-ADI (approximate factorization-alternate direction implicit) method is used to get the steady solution for both codes. Menter’s k–ω SST turbulence model is used for the analysis of turbulent flows. Navier-Stokes equations and the turbulence model equations are solved in a loosely coupled manner.
Development of a 2-D Flow Solver on Hybrid Unstructured and Adaptive Cartesian Meshes
Authors: Jung Min Kyu , Kwon Oh Joon
Published: June 2012

In the present study, a two-dimensional hybrid flow solver has been developed for the accurate and efficient simulation of steady and unsteady flow fields. The flow solver was cast to accommodate two different topologies of computational meshes. Triangular meshes are adopted in the near-body region such that complex geometric configurations can be easily modeled, while adaptive Cartesian meshes are utilized in the off-body region to resolve the flow more accurately with less numerical dissipation by adopting a spatially high-order accurate scheme and solution-adaptive mesh refinement technique. Adaptive Cartesian meshes can be generated automatically and allow to handle data efficiently via quad-tree data structures. A chimera mesh approach has been employed to link the two flow regimes adopting each mesh topology. A second-order accurate vertex-centered scheme and a 3rd- or 5th-order accurate cell-centered WENO scheme have been utilized in the near-body region and in the off-body region, respectively. Validations were made for the unsteady inviscid vortex convection and the steady and unsteady turbulent flows over an NACA0012 airfoil, and the results were compared with other computational and experimental results.
The Application of Adaptive Wavelet Method to Multi-Dimensional Limiting Process for Enhancement of Computational Efficiency
Authors: Kang Hyungmin , Park Kyunghyun , Lee Dongho , Kim Kyuhong , Park Seunghwan , Lee Dohyung
Published: June 2012

An adaptive wavelet method is applied in order to enhance the computational efficiency of enhanced Multi-dimensional Limiting Process (e-MLP) without deterioration of the numerical accuracy of original Computational Fluid Dynamics (CFD) scheme. For this purpose, higher order of adaptive wavelet method is constructed including higher order of wavelet decomposition and modified thresholding. Besides, the locations of crucial features such as shock, vortex core, etc. are automatically and accurately searched in the CFD dataset through wavelet transformation. Only on these locations, high order spatial interpolation scheme with e-MLP are performed; in the other locations, interpolation method is utilized to compute residual values, which reduces the computational time of flux evaluation. This high order adaptive wavelet method was applied to unsteady Euler flow computations such as shock-vortex interaction problem. Throughout these processes, it was verified that computational efficiency was enhanced with preservation of numerical accuracy of CFD solver.
Effect of Axial Flow on Taylor-Couette Stability
Authors: Ashrafi N. , Hazbavi A.
Published: June 2012

Stability of the shear thinning flow between rotating coaxial cylinders with axial flow is carried out. The fluid is assumed to follow the Carreau-Bird model and mixed boundary conditions are imposed. The four-dimensional low-order dynamical system, resulted from Galerkin projection of the conservation of mass and momentum equations, includes additional nonlinear terms in the velocity components originated from the shear-dependent viscosity. In absence of axial flow the base flow loses its radial flow stability to the vortex structure at a lower critical Taylor number, as the shear thinning effects increases. The emergence of the vortices corresponds to the onset of a supercritical bifurcation which is also seen in the flow of a linear fluid. Existence of an axial flow, manifested by a pressure gradient appears to further advance each critical point on the bifurcation diagram. Complete flow field together with viscosity maps and stress distributions are given for different scenarios in the bifurcation diagram.
A POD-Based Solver for the Advection-Diffusion Equation
Authors: Merzari Elia , Pointer W. David , Fischer Paul
Published: June 2012

We present a methodology based on proper orthogonal decomposition (POD). We have implemented the POD-based solver in the large eddy simulation code Nek5000 and used it to solve the advection-diffusion equation for temperature in cases where buoyancy is not present. POD allows for the identification of the most energetic modes of turbulence when applied to a sufficient set of snapshots generated through Nek5000. The Navier-Stokes equations are then reduced to a set of ordinary differential equations by Galerkin projection. The flow field is reconstructed and used to advect the temperature on longer time scales and potentially coarser grids. The methodology is validated and tested on two problems: two-dimensional flow past a cylinder and three-dimensional flow in T-junctions. For the latter case, the benchmark chosen corresponds to the experiments of Hirota et al., who performed particle image velocimetry on the flow in a counterflow T-junction. In both test problems the dynamics of the reduced-order model reproduce well the history of the projected modes when a sufficient number of equations are considered. The dynamics of flow evolution and the interaction of different modes are also studied in detail for the T-junction.
Direct Numerical Simulation for Streamwise Rotating Turbulent Flow Through a Square Duct
Authors: Okamoto Masayoshi
Published: June 2012

The direct numerical simulation for the turbulent square duct flow with the streamwise system-rotation is performed. The streamwise system-rotation effect is closely related with the secondary flow in the square-duct cross-section and the cyclonic secondary flow is strengthened as the system angular velocity increases. The distribution of the mean quantities is affected by the rotating secondary flow. Moreover, it is found that the two-point correlations in the cross-section and propagation velocity profiles, which are estimated from the two-time and two-point correlations, change drastically.
Simulation of Flow Through Conical Diffusers With and Without Inlet Swirl Using CFD
Authors: Dhiman Sushant , Foroutan Hosein , Yavuzkurt Savas
Published: June 2012

One of the major problems encountered in the operation of hydraulic turbines (such as Francis turbines) is a rotating vortex rope which forms in the draft tube under part load conditions. Overall goal of the present research is to study the formation of this oscillating vortex rope using CFD and understand the fundamental mechanisms governing this flow phenomenon. A systematic step by step CFD approach is chosen starting from the simplest to the most complicated flow. The current CFD study reported here therefore aims at studying flows in conical diffusers with and without swirl as a simplified draft tube flow. Two test cases are considered, one is flow with inlet swirl and the other without swirl in a conical diffuser. CFD simulations were carried out using five different turbulence models, namely standard, realizable and RNG k-ε (along with the enhanced wall treatment for near-wall region), SST k-ω and the Reynolds stress model (RSM). Wall pressure coefficient along the diffuser, streamwise and circumferential mean velocity, turbulent kinetic energy (TKE) and Reynolds stress profiles are compared with the experimental data as well as CFD results from literature. It is shown that the moderate levels of swirl cause improvement in the pressure recovery in the diffuser as much as 15%. Also, the standard k-ε and RSM models perform best in predicting turbulent swirling flow behavior. Profiles of the streamwise velocity obtained from these models are in relatively good agreement with the experimental data (with maximum deviation of 25%), while the predictions of the SST k-ω show as much as 60% difference. Also, there is only 8% difference between the level of Reynolds stress obtained from the standard k-ε model and those from the experimental data. Overall, however, all turbulence models need to be improved in order to fully capture the details of the swirling flow in a diffuser and certainly the flow in a draft tube of a hydroturbine where vortex rope breakdown and/or boundary layer separation occurs.
Assessment of Various Inviscid-Wall Boundary Conditions: Applications to NACA65 Compressor Blade
Authors: Khazaei Habib , Madadi Ali , Kermani Mohammad Jafar
Published: June 2012

Boundary condition is one of the major factors to influence the numerical stability and solution accuracy in numerical analysis. One of the most important physical boundary conditions in the flow field analysis is the wall boundary condition imposed on the body surfaces. To solve a three-dimensional compressible Euler equation (with five coupled PDE’s), totally five boundary conditions at the body surfaces should be prescribed. The momentum equation in the direction normal to the inviscid solid wall provides the pressure at the surface of the wall. For the cases with no-heat source or sink, the total temperature at the wall and the incoming flow should remain constant, when the steady condition is prevailed. The no-penetration condition through the solid wall and slip condition provides an equation relating the three velocity components. Assuming identical flow direction at the wall with the adjacent node, the last thing is the velocity magnitude that should be cast in such a way to give accurate, stable and robust solution. In this paper, four different methods for calculation of the wall velocity magnitude are proposed and applied to an identical test case of subsonic and supersonic flows such as: (1) Inviscid flow in a 3D converging-diverging nozzle, (2) Inviscid subsonic flow in a single 90° elbow, (3) Inviscid supersonic flow over a wedge, and (4) Inviscid flow through a compressor blade geometry of NACA 65410. A recently implemented 3D in-house CFD code (based on the flux difference splitting scheme of Roe (1981)) is used to compute compressible flows in generalized coordinates. It is found that the way to specify the additional numerical wall boundary condition strongly affects the overall stability and accuracy of the solution. It is concluded that there is no best boundary condition to cover all of the test cases, but the best wall boundary condition should be introduced very carefully for each type of flow.
A Robust and Simple Low-Mach Number Solver for Flapping-Wing Simulations
Authors: Hu Jeu-Jiun , Niu Yang-Yao
Published: June 2012

In the current study, a very simple preconditioned Navier-Stokes solver based on Roe type numerical fluxes is developed to investigate the unsteady aerodynamics around the flapping wings. A modified Osher-Chakravarthy (MOC) upwind finite-volume scheme is used for space discrete. To evaluate unsteady accuracy, a dual-time stepping strategy including the second-order Euler implicit method and diagonal dominant alternating direction implicit scheme (DDADI) are selected for the physical time and pseudo time stepping implements. In the test cases, two-dimensional airfoil in pure plunging and pitching motion are computed for validation of purpose scheme, respectively. The present numerical results are in good agreement with other’s numerical results. Then, the simulation is carried out on a NACA0012 wing oscillating in heave motion. As a result, the frequency of thrust coefficient is twice the plunging frequency since the maximum thrust is occurred as the airfoil passes the neutral position twice in one period and the frequency of the lift coefficient is the same. By testing the aerodynamic force varying with the reduce frequency of pure heave motion airfoil, the results indicate that the mean thrust output increasing and propulsion efficiency decreasing while reduce frequency is increasing.
Numerical Modeling and Experimental Study of the Mechanical Flocculation Process
Authors: Yan Bipeng , Shen Feng
Published: June 2012

Flow characteristics are one of the main factors affecting the flocculation process. The flow field in the flocculation tank was numerically modeled using the κ-ε turbulent flow model by considering different hydraulic conditions such as the flow rate, paddle rotating speed, dimension and its installation positions. The numerical modeling and experiment observation indicates that the turbulent momentum κ and effective energy consumption ε can be used as an indicator of flocculation efficiency. The rectangular shaped flocculation tank can dampen the flow effectively, but in the four corners there is a lack of mixing, which can be solved by installing baffles to promote the flocs growth. A proper paddle rotating speed can increase the collisions between particles in the main flocculation area; while still keep the formatted flocs from being damaged by shear force. Increasing the paddle service range appropriately can enlarge the main flocculation area. The paddle installation height should consider the turbulent conditions in both the upper and lower part of the flocculation tank. A set of parameters was recommended for the mechanical flocculation tank design.
Numerical Analysis of Flow Distribution for Combined Weapon System in Environmental Tester
Authors: Kim Sung-Dae , Lee Dong-Yob , Baek Sang-Hwa , Lee Jeong-Yong , Park So-Jin , Ko Han Seo , Kim Chul-Ju
Published: June 2012

Thermal behaviors of combined weapon systems have been analyzed in this study by developed computational programs. Also, temperature distributions of the materials of the system have been measured for the experimental conditions. Field tests in the large environmental tester have been prepared by the calculated thermal flow characteristics and the measured temperature distributions of the materials for the weapon systems. The boundary conditions of the analysis are composed of inlet and outlet conditions of the environmental tester and the limit of low temperature of −32°C. The soaking time of the system including a fuel tank and a battery in the environmental tester has been obtained by developed programs in this study to carry out the experiment in the predicted conditions.
A Numerical Analysis for the Flow and Heat Transfer in a Large Plate Heat Exchanger by Using a Porous Media Approach
Authors: Lee Myungsung , Jung Jae Hyuk , Hur Nahmkeon
Published: June 2012

A numerical analysis was conducted to investigate the flow and heat transfer in a large plate heat exchanger. For the purpose of investigation on the whole flow field inside a large plate heat exchanger, the microscopic method by using actual geometry is not practical since it requires huge computational resources. In the present study, a semi-microscopic method by using a porous media approach has been adopted in order to predict the overall flow and heat transfer performance for the large plate heat exchanger. The pressure drop and heat transfer characteristics of the flow passages inside the heat exchanger was obtained first from the microscopic simulation for the flow inside passages and heat transfer through the plates by using the detailed geometry of one representative repeating section of the heat transfer plate. These results were used as characteristics of the porous media replacing the complex flow passages to simulate the large plate heat exchanger as a whole. The overall performance predicted from the semi-microscopic method agrees well with available experimental data. The numerical method in the present study can be applicable to the different types of large heat exchangers that have complex geometry in order to predict the overall performance.
A Parametric Study of the Effect of Wall-Shape on Laminar Flow in Corrugated Pipes
Authors: Rosen Esquivel Patricio I. , ten Thije Boonkkamp Jan H. M. , Dam Jacques A. M. , Mattheij Robert M. M.
Published: June 2012

In this paper we study the effect of wall-shape on laminar flow in corrugated pipes. The main objectives of this paper are to characterize how the flow rate varies with wall-shape, and to identify which shapes enhance the flow rate. We conduct our study by numerically solving the Navier-Stokes equations for a periodic section of the pipe. The numerical model is validated with experimental data on the pressure drop and friction factor. The effect of wall-shape is studied by considering a family of periodic pipes, in which the wall-shape is characterized by the amplitude, and the ratio between the lengths of expansion and contraction of a periodic section. We study the effect that varying these parameters has on the flow. We show that for small Reynolds numbers, a symmetric shape yields a higher flow rate than an asymmetric shape. For large Reynolds numbers, a configuration with a large expansion region, followed by a short contraction region, performs better. We show that when the amplitude is fixed, there exists an optimal ratio of expansion/contraction which maximizes the flow rate. The flow rate can be increased by 8%, for a geometry with small period; in the case of a geometry with large period, the flow rate increases by 35%, for large Reynolds number, and even 120% for small Reynolds numbers.
Study on General Wall Damping Functions Definition: A Low Reynolds Number Bounded Flows Validation
Authors: Pellegrini Marco , Endo Hiroshi , Ninokata Hisashi
Published: June 2012

A modification of the damping functions in the turbulent dissipation rate transport equations is proposed based on the study given by [1]. The modification accounts for a generalization of the applicability to complex geometries and complex flows. The validation of the proposed model is carried out with Computational Fluid Dynamics (CFD) against a fully developed pipe flow and sharp-bent pipe, both at transitional Reynolds numbers where common turbulence models fail in an accurate predictions of the flow and turbulent characteristics. The results achieved for both geometries demonstrate that the present formulation is able to provide higher agreement and accuracy in the prediction of the flow, in relation to velocity and turbulence characteristics. It has been concluded therefore that the present formulation shows a higher generality in comparison with previously available models, accounting for a more reliable applicability and wider number of cases.
Application of an Arbitrary Lagrangian Eulerian Method to Describe High Velocity Gas-Particle Flow Behavior
Authors: Fox D. M. , Lee J. S.
Published: June 2012

Novel computational and small-scale experimental investigations were performed in order to better understand the high velocity flow behavior of gas-particle mixtures. The motion of solid objects impacted by the flow of the mixtures was measured by use of high-speed digital video photography. Computations were performed by use of an arbitrary Lagrangian Eulerian (ALE) treatment in a nonlinear finite element code. Constitutive models for description of the solid component of the gas-particle blend were developed based on quasi-statically determined test results. It was observed that there was very close agreement between experimental and computational results and that it was possible to accurately predict the high velocity flow behavior of the gas-particle mixture using quasi-statically determined constitutive models.
Effects of Wall Condition of a Plunging Body on Splash
Authors: Yokoyama Masao , Kubota Yoshihiro , Mochizuki Osamu
Published: June 2012

Splashes generated by hydrogel sphere were simulated numerically and experimentally for investigating the effects of slip like mucus of living things. Numerical simulation using MPS (Moving Particle Semi-implicit) method was carried out. We defined the slip ratio as the swelling degree of hydrogel and installed the slip ratio into the MPS method. The swelling degree is the ratio of the weight of water against that of hydrogel. We simulated the splashes generated by the hydrogel spheres which had the different swelling degree plunging into water. As the evaluation of swelling degree on the surface of actual hydrogel spheres we also tested by using the hydrogel spheres plunging into water experimentally. The height of splash as a result of reaction of the air cavity became higher according to the increase of the swelling degree. The speed of hydrogel sphere sinking in water tank was also quicker in the numerical simulation. The reason of these results was that the velocity of water around the hydrogel sphere became quicker due to the slip on the surface.
Numerical Simulation of the Flow in a Toroidal Thermosiphon
Authors: Merzari Elia , Fischer Paul , Ninokata Hisashi
Published: June 2012

Buoyancy-driven flows are widespread in diverse engineering applications. Such flows have been studied in great detail theoretically, experimentally, and numerically. The prototype of passive, residual heat removal systems is the toroidal thermosiphon. The stability properties of such systems were first examined in detail by Creveling et al. in the mid-1970s, who reported flow reversals and instability in this geometry. Traditionally, however, the stability analysis of natural convection loops has been confined to one-dimensional calculations, on the argument that the flow would be monodimensional when the ratio between the radius of the loop and the radius of the pipe is much larger than 1. Nevertheless, accurate velocity measurements of the flow in toroidal loops have shown that the flow presents three-dimensional effects. In the present work we analyze the stability problem in a toroidal loop and then use computational fluid dynamics to evaluate the relative importance of these three-dimensional effects with regard to stability. We performed a series of high-fidelity numerical simulations using the spectral element code Nek5000. We compared the results to the available data and calculations performed with the code STAR-CCM+ 5.06. The results show a much richer dynamics than expected from either previous calculations or stability theory. The results also point to some outstanding issues in the RANS modeling of such flows.
Liquid Mixing in a Bubble Column
Authors: Shimada Naoki , Saiki Rina , Dhar Abhinav , Tomiyama Akio
Published: June 2012

In most of the bubble column design, it is assumed that liquid phase is well mixed and spatial distributions of molar concentrations for all components are uniform. However, there is liquid mixing in actual bubble column reactors. The performance of a bubble column strongly depends on the liquid mixing induced by bubbles in the column. Those assumptions therefore cause some errors in column optimum design. Only a few quantitative investigations have been carried out on two-phase turbulence and liquid mixing. In this study, numerical simulations for liquid mixing in a bubble column have been carried out and compared with experiments. The transient behavior of tracer concentration was measured for test columns of 0.3 m in diameter. The height of the columns was 1 m. Bubbles were supplied by using two types of spargers: ring spargers and a perforated plate. A hybrid method, NP2-3D, which is based on the combination of multi-fluid and interface tracking methods, was used to simulate the flow. In a two-phase turbulence model, linear superposition of bubble-induced turbulence and shear-induced turbulence was assumed. Numerical prediction could qualitatively describe the effects of column diameter and gas inlet on the liquid mixing in a column.
An Adaptive Moving-Mesh Relaxation Scheme for Compressible Two-Phase Barotropic Flow With Cavitation
Authors: Shyue Keh-Ming
Published: June 2012

We describe a simple relaxation scheme for the efficient numerical resolution of compressible two-phase barotropic flow with and without cavitation on moving meshes. The algorithm uses a curvilinear-coordinate formulation of the relaxation model proposed by Saurel et al. (J. Comput. Phys. 228 (2009) 1678–1712) as the basis, and employs a wave-propagation based relaxed scheme to solve the model system on a mapped grid that is constructed by a conventional mesh-redistribution procedure for better solution adaptation. Sample numerical results in both one and two space dimensions are present that show the feasibility of the proposed method for practical problems.
A Numerical Study on the Entry Problem of an Elastic Body Using Level Set Method and Combined Formulation
Authors: Choi Hyoung Gwon
Published: June 2012

A finite element method based on level set and combined formulation was studied for the analysis of entry problem of an elastic body. Both free surface tracking and the interaction of an entry body with the fluid flow need to be considered in the entry problem. Free surface tracking was achieved using a level set method in which advection and reinitialization equations for level set variable were discretized using a least square finite element method. The coupling of the motion of the elastic body with fluid flow was conducted using combined mixed finite element formulation. ALE (arbitrary Lagrangian Eulerian) method was adopted for the movement of a grid since the downward motion of the body is dominant in entry problem. Since a mixed finite element is adopted, a linear basis function that belongs to H1 space is used for velocity and level set variables on each sub-element (Th) while a linearly interpolated pressure variable that belongs to L2 space is adopted on each element (T2h). The level set method based on a least square finite element method was verified by solving some free surface tracking problems and then, the finite element formulation for entry problem was validated by comparing with an existing experimental results. Further, the comparison of the entry of an elastic body with that of a rigid body was investigated.
Application of an Improved Ghost Fluid Method to the Collapse of Non-Spherical Bubbles in a Compressible Liquid
Authors: Takahira Hiroyuki , Jinbo Yoshinori
Published: June 2012

The ghost fluid method (GFM) is improved to investigate violent bubble collapse in a compressible liquid, in which the adaptive mesh refinement with multigrids, the surface tension, and the thermal diffusion through the bubble interface are taken into account. The improved multigrid GFM is applied to the interaction of an incident shock wave with a bubble. The multigrid GFM captures the fine interfacial and vortex structures of the toroidal bubble when the bubble collapses violently accompanied with the penetration of the liquid jet and the formation of the shock waves. The multigrid GFM is also applied to the bubble collapse near a tissue surface in which the tissue is modeled with gelatin in order to predict the tissue damage due to the bubble collapse; the motions of three phases for the gas inside the bubble, the liquid surrounding the bubble, and the gelatin boundary are solved directly by coupling the level set method with the improved GFM. Two kinds of level set functions are utilized for distinguishing the gas-liquid interface from the liquid-gelatin interface. It is shown that the impact of the shock waves generated from the collapsing bubble on the boundary leads to the formation of depression of the boundary; the toroidal bubble penetrates into the depression. Also, the surface tension effects are successfully included in the improved GFM. The thermal effects of internal gas on the bubble collapse are also discussed by considering the thermal diffusion across the interface in the GFM. The thermal boundary layers of the toroidal bubble are captured with the method. The result shows that the smaller the initial bubble radius becomes, the lower the maximum temperature inside the bubble becomes because of the thermal diffusion across the interface.
Numerical Simulation of Multiphase Flows With Material Interface on Unstructured Grid System
Authors: Myong Hyon Kook
Published: June 2012

Two-dimensional multiphase flows with material interface due to density difference are numerically simulated on unstructured grid system by an in-house solution code (PowerCFD). This code employs an unstructured cell-centered method based on a conservative pressure-based finite volume method and adopts a high resolution method (CICSAM) in a volume of fluid (VOF) scheme for the accurate phase interface capturing. The test cases are the Rayleigh-Taylor instability (density ratio of 2), the oil bubble rising in a partially filled container (density ratio of 2), the air bubble rising in a fully filled container with bubble shedding (density ratio of 100) and the droplet splash (density ratio of about 1000), which are typical benchmark problems among multiphase flows with material interface due to density difference. The present results are compared with other numerical solutions found in the literature. It is found that the present method simulates efficiently and accurately complex interface flow such as multiphase flows with material interface due to both density difference and instability.
Numerical Study of Cavitating Turbulent Flow Around Propellers: Relationship of Cavity Volume Evolution and Pressure Fluctuation
Authors: Ji Bin , Luo Xianwu , Peng Xiaoxing , Wu Yulin , Xu Hongyuan
Published: June 2012

The cavitating turbulent flows around two marine propellers, where one is a conventional propeller (CP) and the other is a highly skewed propeller (HSP), operating in non-uniform wake have been simulated by applying a mass transfer cavitation model based on Rayleigh-Plesset equation and k-omega SST turbulence model. From comparison of the numerical results with the experiment, it is noted that the unsteady cavitation patterns as well as the pressure oscillation amplitudes of the dominant components of marine propellers in non-uniform wake are reasonably predicted by present numerical methods. The results indicate that the effect of skew angle is very important on the cavitation characteristics as well as pressure fluctuations, and the amplitude of pressure fluctuation for HSP is reduced by 50–70% compared with that for CP. Therefore, the HSP propeller may help to avoid noise and vibration rather than the CP propeller. Further, the relation between hull pressures and changing cavitation patterns is verified based on CFD results, as the blades sweep through the high wake region. It is demonstrated that volumetric acceleration is the main reason for the pressure fluctuation, which agrees with the experiment by Duttweller and Brennen (2002).
Robust Shape Optimization of Uncertain Dense Gas Flows Through a Plane Turbine Cascade
Authors: Hercus Samuel J. , Cinnella Paola
Published: June 2012

A robust shape optimization procedure based on a multi-objective genetic algorithm coupled to a non-intrusive uncertainty quantification analysis was applied to a transonic inviscid flow of a dense gas over a plane turbine cascade. The goal was to simultaneously improve the mean turbine performance and the system stability under fluctuating thermodynamic inlet conditions. Despite an elevated computational cost, the optimization procedure was capable of generating a Pareto front of turbine geometries which improved the mean isentropic turbine efficiency μ(ηs) over the baseline profile, while limiting the solution variability in terms of the coefficient of variation of the power output CV(P2D). In addition to demonstrating an excellent parallel scalability over 1600 processors, the robust optimization revealed that variability of CV(P2D) depends more on the variation of inlet conditions than turbine geometry. A posteriori stochastic analyses on selected optimized turbine geometries allowed an investigation of flow behavior variability, as well as propositions for the improved selection of robust optimization cost criteria in future simulations.
OpenFOAM Turbo Tools: From General Purpose CFD to Turbomachinery Simulations
Authors: Jasak Hrvoje , Beaudoin Martin
Published: June 2012

OpenFOAM is an established object-oriented library for Computational Continuum Mechanics, with emphasis on CFD. It implements physical models of fluid flow, structural analysis, heat and mass transfer using equation mimicking, with unstructured polyhedral mesh support and massive parallelism in domain decomposition mode. In order to use OpenFOAM in turbomachinery CFD, its “general purpose” capabilities are enhanced with turbo-specific features, related to physics of rotating regions and rotor-stator interfaces. Handling for geometric simplifications of multi-blade and multi-stage rotating machines are implemented, including simple stage interfaces, non-equal pitch of blade passages, pitch-wise cyclicity and mixing plane averaging. In this paper we describe the implementation of turbomachinery-specific features in OpenFOAM, in the spirit of object orientation and C++. Emphasis is given to the basic functionality of turbo tools, software layout in OpenFOAM, numerical formulation of stage interfaces and their place in overall code design. The paper is concluded with examples of turbomachinery simulations, illustrating the capability of turbo tools on industrial cases of incompressible and compressible turbomachinery flows.
Development of High Efficiency Propeller Fan for Heat-Pump Unit Using CFD and Numerical Optimization
Authors: Yamakawa Hironobu , Iwase Taku , Funabashi Shigehisa , Sakamoto Kouichi , Enokizu Yutaka , Gonmori Masahiko
Published: June 2012

We developed a high-efficiency propeller fan to reduce electric power consumption of the fan motor for outdoor heatpump units, and we developed a designing tool combining computational fluid dynamics (CFD) with multi-objective optimization techniques based on the genetic algorithm (GA). In CFD, a numerical model is calculated using commercial software based on steady state, Reynolds-averaged Navier-Stokes (RANS) and k-ε turbulent flow model. The objective functions are fan efficiency and fan noise for optimization. Fan efficiency is calculated directly from the CFD results, and fan noise is calculated using an aerodynamic noise prediction model using the relative inlet and outlet velocities of the fan blades from the CFD results. We fabricated a high-efficiency propeller fan characterized with curled trailing edge tips from Pareto optimal solutions. The experimental results from the performance of the fan showed the developed fan was more efficient than conventional fan.
Guide Vanes Inference on Hydraulic Characteristics of Tubular Pump
Authors: Yan Jin , Chao Liu , Tanaka Takaharu
Published: June 2012

The blade number of pump guide vane is an important factor that affects hydraulic characteristics of the pumping system, since the diffusion angle after the impeller is larger than as usual. It is necessary to pay more attention for its calculation and analysis. By CFD method the numeric simulation was conducted to a bulb tubular pump with different guide vane blades and the three dimensional flow fields within whole passage of pumping system was obtained. There are five different number of guide vane blades (4 blades, 5 blades, 7 blades, 8 blades and improved 5 blades) selected for the simulation and performance prediction. The influences of the guide vanes numbers on the system performance are analyzed. The hydraulic losses increases with the increase of the number of guide vane blades while the efficiency of pumping system is not fully comply with this relationship. The system efficiency for which 5 guide vanes were adopted is higher than others with different number of guide vane blades; also the velocity and the pressure distribution of flow fields are more uniform. The system efficiency for which 5 improved guide vanes is the highest with lowest hydraulic losses. The recommended alternative of guide vane is presented for the pump impeller.
Fluid Dynamic Forces Acting on the Rotor of a Shaft-Less Miniature Pump
Authors: Zhuang Baotang , Luo Xianwu , Wang Xin , Ji Bin , Xu Hongyuan
Published: June 2012

For a miniature pump used in many social fields, it is expected to be able to operate without any shaft and mechanical bearing. Recently, a double-suction shaft-less miniature pump has been developed at the Lab of Multiphase Flow and Biomechanics, Tsinghua University. Because the rotor of the miniature pump is rotating inside the pump casing, a fluid dynamic bearing is necessary to support the pump rotor. In this paper, a fluid dynamic bearing was designed to support the rotating impeller and motor rotor, and was manufactured combined with the miniature pump. In order to evaluate the bearing capability, the numerical simulation based on Reynolds equation was conducted for the fluid dynamic bearing. Both the performance experiment of the pump and the numerical results for the bearing indicate that the fluid dynamic bearing designed for the miniature pump in this study is usable and reliable. It is also noted that the performance including the liquid film thickness distribution, static pressure distribution, bearing capability, etc. of the bearing has been reasonably predicted using the present numerical methods. Further, the bearing capability increased remarkably with eccentric ratio between the bush and journal, and rotational speed of the pump for the fluid dynamic bearing.
Performance Improvement of a Mixed-Flow Pump by Optimization Techniques
Authors: Kim Jin-Hyuk , Jin Chong-Hwi , Kim Kwang-Yong
Published: June 2012

This paper presents an optimization procedure for high-efficiency design of a vane diffuser in a mixed-flow pump. Optimization techniques based on a radial basis neural network model are used to improve the performance of a vane diffuser in a mixed-flow pump. In flow analyses, three-dimensional Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model are discretized by using finite volume approximations and solved on hexahedral grids to evaluate the efficiency as the objective function. The numerical results are validated through a comparison with experimental data for the head, power and efficiency. Latin-hypercube sampling method as design-of-experiments is used to generate the design points within the design space. In order to improve the efficiency of a mixed-flow pump, four variables defining the lean angle at diffuser vane tip span, the distance between trailing edge of impeller blade and leading edge of diffuser vane, the straight vane length ratio, and the diffusion area ratio are selected as design variables in the present optimization. As a result of the present study, the efficiency at the design point is remarkably enhanced through the design optimization.
Experimental Investigation of Relationship Between Pressure Fluctuations and Vibrations for a Double Suction Centrifugal Pump
Authors: Yao Zhifeng , Wang Fujun , Xiao Ruofu , He Chenglian , Liu Zhuqing
Published: June 2012

Double-suction centrifugal pumps are widely employed in large-scale pumping stations, which generally run in the conditions of large discharge with huge energy consumption. Pressure fluctuation caused by internal flow due to tongue-impeller interaction is the primary source of pump vibration. In this paper, pressure fluctuations and vibrations signals on volute casing wall were experimentally obtained at five flow rates ranging from 59% to 121% of nominal flow rate. Time and frequency domains of the signals were mainly analyzed by using statistical and fast Fourier transform methods. The results show that rotational frequency, blade passing frequency and their harmonic frequencies of pressure fluctuations as well as vibrations are clearly identified. The magnitude at blade passing frequency has close relationship with the measurement location related to the volute tongue, and becomes larger when the flow rate deviates from the nominal flow rate. The magnitudes at blade passing frequency can increase by 70% and 151% at high flow rate over that at the nominal flow rate for pressure fluctuations and vibrations, respectively. While the magnitude of vibration at rotational frequency keeps nearly constant at partial flow rate, and decreases at high flow rate.