bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Physical Properties and Experimental Behaviour of High Turbulent Flow in Cross-Flow Microfiltration of Ac¸ai Juice
Authors: Haneda Renata Natsumi , Fontes Se´rgio Rodrigues
Published: July 2010

This paper presents an experimental investigation of the cross-flow microfiltration process applied to the clarifying of ac¸ai (Euterpe oleracea Mart.) juice. Ac¸ai juice is a complex fluid, similar to a suspension of particles (fibers and cellulose) mixed in water, which contains ions of iron, zinc, maganese and pigments, as anthocyanins. In this study, a commercial membrane of α-alumina (Al2O3) in the form of a tube with 1.2μm of average pore size was utilized to investigate the clarifying of juice. This pore size of the ceramic structure was utilized in an attempt to reduce the polarization phenomenon and improve the permeate flux without utilizing the usual enzymatic treatment made in the microfiltration processes. The rheological behaviour of the suspension was investigated in a cone/plate rheometer (model, DVIII-Ultra) and a cylindrical rheometer (model, DVIII+), both by Brookfield/USA, as the shear stress (τ) in function of shear rate (γ) was fitted and analyzed with the power-law and Herschel-Bulkley’s models. All the mixtures showed flow behaviour index values (n) near to one, characterizing Newtonian fluids (pseudo-plastic). The particle size distribution (PSD) of the samples of suspension and permeate were analyzed by APS100 (ultrasound spectroscopy) by Matec/USA. The analysis of the suspension showed the presence of particles of size equal 0.16micra, while the permeate did not present particles. The experiments were performed in a turbulent range higher than 2400 until 57500 and with variation to values of transmembrane pressure from 1 to 4bar; the usual and direct correlation between transmembrane flux and transmembrane pressure was not observed in the experiments and a new correlation to the dimensionless of TMP (trans-membrane pressure) and Reynolds (Re) was presented.
Development and Validation of an Augmentation to the Commercial CFD Software FLUENT™ Enabling the Tracking of Ellipsoidal Particles in Low Reynolds Number Flows
Authors: Shanley Kevin T. , Ahmadi Goodarz
Published: July 2010

A majority of the commercially available computational fluid dynamics packages are equipped with a module for Lagrangian tracking of spherical particles. No such module exists in an off-the-shelf product enabling the Lagrangian tracking of ellipsoidal shaped particles. This work took advantage of the user defined function facilities provided in FLUENT™ to gain this capability. Three user defined functions were implemented to transpose the spherical geometry to an ellipsoidal geometry. The orientation of the ellipsoid was determined by numerically solving the equations of rotational motion. Hydrodynamic drag was taken to be a function of Reynolds number and orientation. Two tests were performed to validate the rotational and translational motions of the ellipsoid in low Reynolds number flows. First, a simple shear configuration was examined with a single particle suspended at the center of the domain. The particle was allowed to rotate without translation. This was repeated for several particle sizes and flow rates and the simulated time for the particle to perform a single rotation was compared with the theoretical findings of Jeffery (1922). The results showed strong agreement for the range of particle sizes and flow rates examined. Second, a horizontal pipe with circular cross-section setup was simulated. Particles were injected from the pipe inlet and their motions were analyzed. Deposition efficiency was shown to be a function of aspect ratio and dimensionless relaxation time. Strong agreement was shared with a previously published empirical expression.
Near-Field Characteristics of a Turbulent Jet With Ring Injectors
Authors: Rahai Hamid R. , Moayedian Shahab
Published: July 2010

Mixing effectiveness of a heated turbulent jet with two-hole and three-hole ring injectors was experimentally investigated. The injectors were rings with square cross section with side dimensions of approximately 5 mm. The ratio of the ring thickness to the jet inner diameter was 4.7%. For the two-hole injector, the injecting holes were at 180 degrees from each other and for the three-hole injectors, the holes were spaced at 120 degrees. The maximum mean velocity of the jet was at approximately 4 m/s which corresponds to an approximate Reynolds number based on the jet inner diameter of 14,676. The total blowing ratio as compared to the axial momentum for each configuration was at 2%. Results indicate significant increases in RMS fluctuation and mean velocity decay with the ring injectors with these effects being more pronounced for the three-hole injection. Axial variation of momentum thicknesses indicates a possibility of axis switching in the near field for the three-hole ring injector.
Design of High Efficiency Blowers for Future Aerosol Applications
Authors: Chadha Raman , Morrison Gerald L. , McFarland Andrew R.
Published: July 2010

High efficiency air blowers to meet future portable aerosol sampling applications were designed, fabricated, and their performance evaluated. A preliminary blower design based on specific speed was selected, modeled in CFD, and the flow field simulated. This preliminary blower size was scaled in planar and axial directions, at different rpm values, to set the Best Efficiency Point (BEP) at a flow rate of 100 L/min (1.67×10−3 m3/s @ room conditions) and a pressure rise of 1000 Pa (4″ WC). Characteristic curves for static pressure rise versus air flow rate through the impeller were generated. Experimentally measured motor/blower combination efficiency (ηEXP) for the preliminary design was around 10%. The low value was attributed to the low efficiency of the D.C. motor used (Chadha, 2005). CFD simulations using the κ–ε turbulent model and standard wall function (non-equilibrium wall functions) approach overpredicted the head values. Enhanced wall treatment under-predicted the head rise but provided better agreement with experimental results. The static pressure rise across the final blower is 1021 Pa at the design flow rate of 100 L/min. Efficiency value based on measured static pressure rise value and the electrical energy input to the motor (ηEXP) is 26.5%, a 160% improvement over the preliminary design.
The Experimental Evaluation of the Performance of Multiphase Flow Meter: Effect of the Distance Between Two Meters
Authors: Park Sang Hyun , Morrison Gerald L.
Published: July 2010

In the previous studies of slotted flow meters, the repeatibility and reproducibility were studied under different flow conditions and different configurations. In accordance with these work, the present study examines the affects of the distance between the slotted plate. The preset 5D distance is expanded to the 10D. The flow coefficient, KY, the pressure drop, and the uncertainty analysis dependence upon this change is examined. There are definite changes in the results between the 5D distance and the 10D distance. As a base line, the flow coefficient, KY, showed 0.8% to 2% difference between the 5D and the 10D distance case. Depending upon the upstream flow conditions, the reproducibility of the slotted flow meter was affected. The pressure drop increased as the upstream Reynolds number increases. The result from the analysis of a water cut meter mounted downstream of a slotted flow meter showed that there are definitive relationships between the output of the water cut meter and the parameters of the flow.
Irradiation and Temperature Effects on Anti-Foam Agent Performance in a Non-Newtonian Waste Slurry Simulant
Authors: Guerrero Hector N. , Fowley Mark D. , Sherwood David J.
Published: July 2010

Foaming tests were performed in a bench-scale foam column and 1/9th-scale mechanically-agitated mixing system at the Savannah River National Laboratory (SRNL) for a simulant of waste slurry from the Hanford Tank 241-AZ-101. This featured additions of DOW Corning Q2-3183A antifoam agent (AFA) to prevent foaming, especially in the evaporators. These waste slurries (typically 15 wt% solids) are particularly prone to particle-stabilized foaming. Previous studies have shown that up to 20% of the polydimethyl siloxane (PDMS) portion of the AFA mixture is degraded by radiation. The high temperature (90°C) for 48 hrs of a caustic leaching process may have a similar effect on the polymer. The objective of this study was to determine how well degraded AFA works. Key results are that: • Without addition of this AFA, the 1/9th-scale system had about 100% foaming at 1 mm/s air velocity and the bench-scale system had over 400% foaming for an air flow of 10 mm/s. • The effect of irradiating 350 ppm AFA was to increase foaming from 6% to 30% in the foam column and 7.6% to 13.7% in the 1/9th-scale system at an air flow of 1 mm/s at room temperature. • The effect of heating the AFA to 90°C was to increase foaming by a factor of 1.6 in the foam column. But while the effectiveness of the irradiated AFA was reduced, it still provided a significant reduction in foaming. AFA additions required to mitigate the combined effects of high temperature and radiation were also determined.
A PZT Micropump With Planar Passive Valves and its Flow Measurements
Authors: Hsu Chia-Jui , Sheen Horn-Jiunn
Published: July 2010

In this paper, a simply-designed reciprocating-type micropump is presented. We also report the coupling effects between the valve motion and the flow behaviors, which were studied using a micro-PIV technique. The fluids were easily driven by a PZT plate and net flow was directed toward the outlet after rectification by two planar passive valves. The results revealed that good pumping performance was obtained even at a low excitation voltage of 10V. The optimum flow rate was measured at a frequency of 0.8kHz and the maximum flow rate was 275μl/min at 30V. The micropump was uniquely characterized by the existence of a linear relationship between the flow rate and the driving frequency, which enabled this micropump to be easily operated and controlled. The experimental results showed that the micropump was reliable in terms of the high linearity and repeatability, which is very favorable for portable microfluidic systems. The micro-PIV measurements of the transient motions of the valve and the flow behaviors clearly revealed that the valve efficiency depended on the mass inertia of the moving part, excitation frequency, and voltage. The present results are useful for the optimum design of this planar passive valve to improve the pumping efficiency.
Micro Particle Detachment in Turbulent Flows With Electrostatic and Capillary Effects and Surface Deformation
Authors: Zhang Xinyu , Ahmadi Goodarz
Published: July 2010

Rolling detachment of micro particles in the presence of electrostatic and capillary forces based on the maximum adhesion resistance was studied. The effective thermodynamic work of adhesion including the effects of electrostatic and capillary forces was used in the analysis. The JKR and DMT models for elastic interface deformations and the Maugis-Pollock model for the plastic deformation were extended to include the effect of electrostatic and capillary forces. Under turbulent flow conditions, the turbulence burst model was used to evaluate the airflow velocity near the substrate. The critical shear velocities for removal of particles of different sizes were evaluated and the results were compared with those without electrostatic and capillary forces. It shows that the capillary forces significantly increases the critical shear velocities for particles of all sizes, while the electrostatic forces only have major effects on large particles. The model predictions were compared with the available experimental data and good agreement was observed.
A Study on Back Flow Structure in a 2-Bladed Helical Inducer at a Partial Flow Rate
Authors: Watanabe Satoshi , Inoue Naoki , Ishizaka Koichi , Furukawa Akinori , Kim Jun-Ho
Published: July 2010

The attachment of inducer upstream of main impeller is an effective method to improve the suction performance of turbopump. However, various types of cavitation instabilities are known to occur even at the designed flow rate as well as in the partial flow rate region. The cavitation surge occurring at partial flow rates is known to be strongly associated with the inlet back flow. In the present study, in order to understand the detailed structure of internal flow of inducer, we firstly carried out the experimental and numerical studies of non-cavitating flow, focusing on the flow field near the inlet throat section and inside the blade passage of a two bladed inducer at a partial flow rate. The steady flow simulation with cavitation model was also made to investigate the difference of the flow field between in the cavitating and non-cavitating conditions.
An Experimental Investigation of the Effects of Vaneless Diffuser Geometry on the Stall Characteristics
Authors: Ahmed Saad A. , Gadalla Mohamed
Published: July 2010

An experimental investigation of the flow instability characteristics in a radial vaneless diffuser of a centrifugal blower was carried out. The mass flow rate of air through the diffuser could be gradually reduced to zero value. The flowfield in the diffuser was measured using dynamic and static pressure transducers and the results are reported for steady and stall conditions. The objectives of this experimental investigation are to investigate, understand, and document the effects of diffuser geometry on the inception and fundamental characteristics of rotating stall, and also to provide a benchmark set of experimental data to aid stall model development. The results of this investigation showed that the maximum number of stall cells was two. The rotating pressure pattern with one stall cell was dominant; especially, if the mass flow rate is lower than the critical value for stall inception. The speeds of stall cells increase linearly with the impeller speed and they decrease with the increase of the diameter ratio. On the other hand, the effect of diffuser width ratio on the pressure pattern frequency is insignificant; therefore, it is not presented.
Experimental Study of Three-Dimensional Laminar Wall Jets of Non-Newtonian Fluid
Authors: Adane Kofi K. , Tachie Mark F.
Published: July 2010

A particle image velocimetry technique was employed to study three-dimensional laminar wall jet flows of a non-Newtonian shear-thinning fluid. The wall jet was created using a circular pipe of diameter 7 mm and flows into an open channel. The Reynolds numbers based on the pipe diameter and jet exit velocity were varied from 250 to 800. The PIV measurements were performed in various streamwise-transverse and streamwise-spanwise planes. From these measurements, the velocity profiles, jet growth rate and spread rates were obtained to study the characteristics of three-dimensional wall jet flows of a non-Newtonian fluid.
Optimal Fire Pump Design: CFD-Aided Redesign of a Fire Pump
Authors: Tchavdarov Boyko , Hardersen Denairic , Sdano Arnie
Published: July 2010

The design criteria of rotodynamic pumps with optimal efficiency have been covered widely in the literature for many years, however little attention has been given to hydraulic design of centrifugal fire pumps. Fire pumps have different design objectives than commercial pumps. Cost effective design solutions for fire pumps require a more comprehensive analysis of pump performance characteristics in order to achieve the desired curve shape while minimizing the driver size. Computer-aided design (CAD) and Computational-Fluid Dynamics (CFD) analyses of pump hydraulic components have been performed for several decades, and today they are highly sophisticated tools that can not only aid in designing better products but also allow for the optimization of designs. A significant reduction of the input power of a rotodynamic fire pump, while retaining its primary point of operation, is demonstrated in multi-variant CFD-aided redesign.
Flow Around Finite Circular and Square Cylinders in an Open Channel
Authors: Paul S. S. , Agelinchaab M. , Tachie M. F.
Published: July 2010

An experimental investigation was performed to study the structure of the flow field around finite circular and square cylinders in a water channel. Detailed velocity measurements using a particle image velocimetry (PIV) system and proper orthogonal decomposition (POD) analysis were conducted to examine the structures in the near-wake region. Iso-contours and profiles of mean velocities and some turbulent quantities at various streamwise locations were reported. The proper orthogonal decomposition was applied to provide insight into the structure of the flow. The results show that the vortex in the square cylinder is bigger and extends to cover part of the free end of the cylinder. There is also an up-wash flow from the base of the cylinders to form saddle points. The saddle point in the square cylinder is closer to the free end than in the circular cylinder. The low order reconstructed turbulent intensities from POD show that the square cylinder has more large scale structures than the circular cylinder.
CFD Computation of Water Injection on Lift and Drag of a Hydrofoil With Cavitation
Authors: Izadi Mohammad J. , Fetratjou Pejman Hazegh
Published: July 2010

The occurrence of cavitation on hydrofoils can cause undesirable effects such as a decrease in lift, and an increase in drag. The goal of this research is to investigate the effect of water injection on the lift and drag coefficient of a hydrofoil. An unsteady uniform flow of water over a 3-D NACA hydrofoil is numerically simulated. For the numerical simulation of a cavitating flow, a bubble dynamics cavitation model is used to describe the generation and evaporation of the vapor phase. The RNG k-ε turbulence model is used as a turbulence model. A modification to the turbulent viscosity, which is necessary to simulate the cloud cavitation, is implemented. This simulation is implemented for various angles of attack and different injection velocities. Comparison between experimental data and the numerical simulation obtained here is done to validate the numerical results. The results presented show that, as the mass flow of the water injection increases, the lift coefficient decreases for all angles of attack but the rate of this decrease decreases for higher angles of attack. As the mass flow rate increases, the drag coefficient increases more for small angles of attack, and decreases for larger angles of attack, and the injection does not change the drag coefficient as much for large angles of attack. In general, water injection does not increase the lift and does not decrease the drag for all angles of attack.
Dynamics of Swirling Flow in a Dump Combustor at Elevated Pressures
Authors: Yadav N. P. , Kushari Abhijit
Published: July 2010

This paper reports an experimental investigation of the flow field inside a low aspect ratio dump combustor with inlet swirl and choked exit. The length of the combustor studied was less than the reattachment length for the separated flow. The tapered exit of the combustor was choked by a needle valve to investigate the effect of elevated chamber pressure on the flow field of the combustor. The variation in wall pressure and velocity at different locations and Reynolds number was studied. It was observed that the turbulent intensity increased with the swirling flow and decreased with an increase in the chamber pressure. The exit choking reinforced the recirculation. The velocity distributions were corroborated by comparing the frequency spectrum with the wall pressure distributions and the results were found to be in good qualitative agreement with each other. This study will be helpful to design the combustor for different operating conditions.
Numerical Investigations About the Effect of Non-Condensable Gas on Cavitating Flows
Authors: Sadeghi Hamed , Darbandi Masoud
Published: July 2010

A series of numerical investigations was carried out to study the behavior of cavitating turbulent flows in an orifice. In the present work, two different cavitation models were used for the simulation. In the first model, flow was modeled as two interpenetrating fluids (liquid and vapor), and in the second model, the working fluid was assumed to be a mixture of three fluids (liquid, vapor and non-condensable gas). In both cases, we used a finite volume method to discretize the equations and SIMPLEC algorithm to link the pressure and velocity fields. An upwind scheme was used to model convective fluxes and other transport equations. Turbulence effects were considered using the k-ε model. Computations were performed at various inlet pressures and a fixed outlet pressure. The values of discharge coefficient obtained from the simulations were compared with published experimental data. Better agreement was found with the second model. This revealed the importance of non-condensable gases on cavitation. Furthermore, the distributions of vapor volume fraction and velocity magnitude were investigated with using both models. The results showed considerable differences between two models in description of inception of cavitation, distributions of vapor volume fraction and velocity magnitude.
Computational Study of Taper Effect of a Hydrofoil at Different Reynolds Numbers on the Length of Cavity and Lift and Drag Coefficients
Authors: Izadi Mohammad J. , Mirtorabi Mahdi
Published: July 2010

In this paper a cavitating flow around a three dimensional tapered hydrofoil in an incompressible fluid is modeled and studied. The variables in this study are the taper ratio, angle of attack and the Reynolds number. The taper ratio changes from 0.2 to 1, the angles of attack varies from −2 to 12 degrees and all these are computed at two Reynolds numbers (Re = 5.791·107 and Re = 1.99·108). The flow is assumed to be unsteady and isothermal. Coefficients of drag and lift and also the cavity length are computed numerically. Comparing the numerical results of five investigated models (five tapered hydrofoils) and the work done by Kermeen experimentally, it can be seen that the tapered hydrofoil in some cases gave better results, reducing the cavity length and improving the lift coefficient. At the low Reynolds number, the length of the cavity is calculated to be small in comparison with the length gained at the high Reynolds number, and therefore the change of the taper and the angles of attack did change the amount of the lift coefficient as much. For high Reynolds number, as the angle of attack increased, the tapering effect became more important and the best lift coefficient and minimum cavity length is obtained at a taper ratio of 0.4 for an averaged angles of attack.
Numerical Study of Twist Effect of a Hydrofoil on the Length of Cavity and Lift and Drag Coefficients in Different Reynolds Numbers
Authors: Izadi Mohammad J. , Mirtorabi Mahdi
Published: July 2010

In this study a cavitating flow around a three dimensional twisted hydrofoil in an incompressible fluid is modeled. The variables in this study are; the twist angle, the angle of attack and the Reynolds number. The twist angle changes from 0.0 to 5.0 degrees with respect to the root, the angles of attack changes from −2 to 12 degrees and all these are computed at two Reynolds numbers of 5.791·107, and 1.99·108. The flow is assumed to be unsteady and isothermal. Coefficients of the drag and lift and also the cavity length are computed numerically. Numerical simulations are carried out and the cavitation number is set at σ = 1.2. The numerical results show that, as the twist angle increases, the cavity length (along the chord) did not change much, but the width of the cavity (along the span) increased very much, and this caused an increase of lift coefficient. However, a twisted hydrofoil has more variation of span-wise lift distribution, which is resulted by the downwash at the center part and an up-wash at the tips of the hydrofoil. Comparing the lift and the drag coefficient results of two twisted and no-twisted hydrofoil, the twisted hydrofoil show some notable increase of lift and a decrease of the drag coefficients. The best results are obtained around 5 degrees of twist angle.
Time-Resolved Particle Image Velocimetry (PIV) Measurements in a Radial Diffuser Pump
Authors: Feng Jianjun , Benra Friedrich-Karl , Dohmen Hans Josef
Published: July 2010

The truly time-variant unsteady flow in a low specific speed radial diffuser pump stage has been investigated by time-resolved Particle Image Velocimetry (PIV) measurements. The measurements are conducted at the midspan of the blades for the design condition and also for some severe part-load conditions. The instantaneous flow fields among different impeller channels are analyzed and compared in detail, and more attention has been paid to flow separations at part-load conditions. The analysis of the measured results shows that the flow separations at two adjacent impeller channels are quite different at some part-load conditions. The separations generally exhibit a two-channel characteristic.
Two-Fluid CFD Model of Adiabatic Air-Water Upward Bubbly Flow Through a Vertical Pipe With a One-Group Interfacial Area Transport Equation
Authors: Prabhudharwadkar Deoras , Bailey Chris , Lopez de Bertodano Martin , Buchanan John R.
Published: July 2010

This paper describes in detail the assessment of the CFD code CFX to predict adiabatic liquid-gas two-phase bubbly flow. This study has been divided into two parts. In the first exercise, the effect of Lift Force, Wall Force and the Turbulent Diffusion Force have been assessed using experimental data from the literature for air-water upward bubbly flows through a pipe. The data used here had a characteristic near wall void peaking which was largely influenced by the joint action of the three forces mentioned above. The simulations were performed with constant bubble diameter assuming no bubble interactions. This exercise resulted in selection of the most appropriate closure form and closure coefficients for the above mentioned forces for the range of flow conditions chosen. In the second exercise, the One-Group Interfacial Area Transport equation was introduced in the two-fluid model of CFX. The interfacial area density plays important role in the correct prediction of interfacial mass, momentum and energy transfer and is affected by bubble breakup and coalescence processes in adiabatic flows. The One-Group Interfacial Area Transport Equation (IATE) has been developed and implemented for one-dimensional models and validated using cross-sectional area averaged experimental data over the last decade by various researchers. The original one-dimensional model has been extended to multidimensional flow predictions in this study and the results are presented in this paper. The paper also discusses constraints posed by the commercial CFD code CFX and the solutions worked out to obtain the most accurate implementation of the model.
Lateral Migration of Neutrally-Buoyant Particles in a Square Microchannel at Low Reynolds Numbers
Authors: Cho Byung Rae , Kim Young Won , Yoo Jung Yul
Published: July 2010

Lateral migration of particles has drawn a lot of attention in suspension community for the last 50 years. Since there is no need for extra external forces, lateral migration of particles plays an important role in constructing microfluidic devices in diverse engineering applications. In this paper, an experimental study on lateral migration of neutrally-buoyant spherical particles transported through a square microchannel is carried out using a fluorescent microscope at low Reynolds numbers. Fluorescent microspheres with diameters of d = 6 μm, 10 μm, and 16 μm are adopted as the test particles, which yield channel-to-particle size ratios of 13.3, 8 and 5, respectively. Spatial distributions of the particles in dilute suspension are visualized at different Reynolds numbers. It is shown that particles are uniformly distributed over the channel cross-section at relatively low Reynolds numbers. As the Reynolds number increases, however, particles migrate inward from the wall and away from the central axis of the channel, so that consequently they accumulate at an equilibrium position, exhibiting the so-called “tubular pinch effect”, first observed by Segre´ and Silberberg as early as in 1962. Experimental results obtained in this work offer design rules for microfluidic channels that play important roles of particle separation or particle focusing.
An Ex-Situ Study of Water Droplet Formation and Detachment in Gas Diffusion Layers of Proton Exchange Membrane Fuel Cells
Authors: Ma Yue , Jia Li , Zhang Zhuqian , Wang Xia
Published: July 2010

This paper proposed an ex-situ experimental test to investigate the transport of liquid water through a gas diffusion layer (GDL) in a proton exchange membrane fuel cell. A transparent test cell was made which allowed the visualization of water droplet formation and detachment on the surface of a GDL through a CCD camera. The breakthrough pressure, at which the liquid water penetrates the GDL and starts to form a droplet, was measured. The breakthrough pressure was found to be different for the GDLs with different porosities. The equilibrium pressure, at which the speed of the liquid droplet formation equals to the speed of liquid droplet detachment, was also recorded. For the same GDL, the equilibrium pressure was found to be much lower than the breakthrough pressure. The difference between these two pressures might be due to the surface tension between the liquid water and the GDL. The results of this paper will be useful in re-examining the mathematical models describing the liquid water transport in the porous GDL.
Similarities in the Development of Numerical Schemes and Sub-Grid Modeling in Large-Eddy Simulations
Authors: Sampaio L. E. B. , Nieckele A. O.
Published: July 2010

Schemes for the discretization of spatial derivatives commonly employed in the numerical solution of Partial Differential Equations present intrinsic errors that become more important as the wave number content of solution field approaches the Nyquist criteria based on the mesh spacing. In many situations, this can be overcome by simply refining the mesh, so that the wavelength of the structures becomes much larger than the mesh spacing, and the discretization errors become again negligible. However, in some other cases, like in Large-Eddy Simulations of highly turbulent flows, the cost per discretization element is so high that further mesh refinement is prohibitive. In this case, it is more appropriate to work towards understanding and improving the numerical schemes, so that the wider possible range of the spectrum is accurately resolved, and the fewest possible number of degrees of freedom is needed to provide a satisfactory solution. By analyzing the similarities between the problems faced by numerical schemes and the challenges of sub-grid modeling in Large-Eddy Simulations (LES), an alternative for the numerical simulation of turbulence in the context of Large-Eddy Simulation is developed, that accumulates two main functionalities: represent the interaction between unresolved and resolved scales, while keeping the discretization errors at acceptable levels. The proposed scheme is of advective nature and has been applied in several test cases, ranging from simple one-dimensional convection of a passive scalar, to more complex turbulent flows. As a result, a better understanding of the role of discretization errors in Large-Eddy Simulation was obtained.
An Investigation of Muscle Stresses in Swimming Hydromedusae
Authors: Lipinski Doug , Mohseni Kamran
Published: July 2010

We investigate several preliminary models for the muscle stress produced during the swimming of a hydromedusa, Sarsia tubulosa, which relate the pressure on the hydromedusa to the stress in the musculature. Our calculations are based on the solution of the Navier-Stokes equations for the flow around a swimming hydromedusa. This numerical model allows us to obtain detailed pressure information in any area of interest on or near the hydromedusa. Initially, we investigate the pressure distribution on the surface of the hydromedusa and find that it is quite uniform in space. We present an original model based on a force balance created using the actual hydromedusa’s geometry and compare the results we obtain to the stress in a pressurized thin walled cylinder or sphere of equal radius. Our model allows us to calculate and estimated muscle stress at any point along the hydromedusa. By doing so, we are able to validate the assumptions made by modeling the subumbrellar cavity as a pressurized cylinder or sphere.
The Use of Real Gas Properties for Design and Flow Field Simulations of a Small Centripetal Steam Turbine
Authors: Feng Jianjun , Benra Friedrich-Karl , Dohmen Hans Josef
Published: July 2010

In this paper, the applied design procedure for generation of a small-capacity ORC centripetal steam turbine working with the fluid 1, 1, 1, 3, 3-Pentafluoropropane (R245fa) is described with consideration of real gas effects. After specification of the turbine geometry in an iterative process using different commercial design tools which have been enhanced in order to work with real gas conditions, CFD simulations based on the real gas properties of the fluid have been conducted for the originated geometry. The simulations are performed by using the CFD code ANSYS-CFX11 with a pre-prepared real gas property (RGP) table, which comprises the required gas properties at different discrete pressure and temperature values. In addition, the flow fields inside the turbine obtained from the real gas model is compared to those flow fields which are obtained by the ideal gas model and also by the Redlich-Kwong model.
CFD Prediction and LDV Validation of Liquid and Particle Velocities in a Submerged Jet Impinging a Flat Surface for Different Viscosities and Particle Sizes
Authors: Zhang Yongli , Okita Risa , Miska Stephen , McLaurt Brenton S. , Shirazi Siamack A. , Rybicki Edmund F.
Published: July 2010

Solid particle erosion commonly occurs in the oil and gas industry and can cause severe damage to flow lines and equipment. One successful approach to predicting erosion, and mitigating sand erosion damage, is through the application of computational fluid dynamics (CFD) modeling of the fluid flow, sand particle movement within the flow, and erosion resulting from the sand particles hitting the metal surface [1, 2, 3]. A key ingredient to predicting erosion damage is having an equation to represent erosion damage due to sand particles hitting the metal surface. This equation, called the erosion equation, usually includes the properties of the sand, the particle impact speed, and the angle of impact. The particle impact speed is known to be a major factor affecting the severity of erosion and can be found in most erosion equations in the literature. The erosion equation is usually material specific and its validation is very important before being applied in engineering calculations to predict erosion of flow lines, tubing, and equipment. Carrier fluid properties have a substantial effect on particle trajectories. The present studies were performed to examine the effect of fluid viscosity on the particle impacting velocity. Direct impingement tests, which consist of a submerged fluid jet containing aluminum particles impinging on a flat surface, were conducted. Carrier fluids with viscosities ranging from 1 cP to 100 cP and three types of aluminum particles with average diameters of 3 μm, 120 μm, and 550 μm were tested in the experiments. The distance between the nozzle exit and the target surface is 12.7 mm and the nozzle diameter is 8 mm. The flow rate through the nozzle is 8 GPM, which corresponds to an average flow velocity of about 10 m/s. Particle velocities at different locations between the nozzle exit and the target surface were measured using a laser Doppler velocimeter (LDV). CFD simulations for all test conditions were also run using FLUENT 6. The predicted solid particle velocities were compared with the LDV data and good agreement was achieved. Both experiments and simulations indicate that flow in the nozzle and near the target undergoes a transition from turbulent to laminar flow when the fluid viscosity is increased and this greatly affects particle velocities near the target.
Study of Internal Flow and Emulsification Process in a Homogenizer
Authors: Sumitomo Takashi , Fukutomi Junichiro , Shigemitsu Toru , Ishida Naoki , Yoshimura Yoshio
Published: July 2010

The pressure homogenizer is extensively used to emulsify, disperse the products in various industrial fields including: food, chemical, pharmaceutical and biotechnology. The homogenizer basically consists of a high-pressure plunger pump usually with triple plungers to minimize pressure fluctuations and a homogenizing valve with a narrow gap. The homogenizing valve consists of a valve, valve seat and impact ring. The homogenizer exerts effects, such as a shear, an impingement, and a cavitation to fluid momentarily. The relatively large polydisperse oil globules of a coarse oil-in-water emulsion are subdivided into a large number of smaller globules in a narrow size range by a homogenizer. However, the flow within the homogenizing valve is not clarified theoretically. Therefore the action of a high-pressure, radial-flow homogenizer in breaking up the internal phase of oil drops in a coarse emulsion was investigated theoretically and experimentally. If the flow pattern within the homogenizing valve could be solved, a more efficient and stabilized emulsification could be carried out. In this paper, the influence of shape modification of the homogenizing valve was investigated in the emulsification action. The experiments using a small homogenizer are conducted and the experimental results were compared with the numerical simulation results. In short, we compared the calculated flow pattern (velocity distributions, pressure distributions, shear stress) with the drop size distribution result obtained in the experiment, and investigated the relation between the flow and the emulsification action in the homogenizing valve. In this experiment, two valve types (Sharp type and Flat type) were applied. In the experiment, the pressure drop in the valve, the distance from a valve outlet to an impact ring and the parallel gap part length were changed. The flow patterns were investigated using a Computational Fluid Dynamic model of the flow in the homogenizing valve. Here, a k-ε turbulent model was used for the modeling of the flow in the homogenizing valve. The flow in the homogenizing valve was calculated as a two-dimensional axisymmetric flow. The purpose of this paper is to clarify the effects of differences in the shapes of valves on the results of emulsification through the above experiments and numerical simulations.
Verification of a Lattice-Boltzmann Method by Using Analytical Flow Solutions of Standard Flow Problems
Authors: Bo¨hle Martin , Becker Richard
Published: July 2010

Within the last ten years Lattice Boltzmann solvers have become very popular. They are used for flows inside complex geometries and around bodies like cars, for example. Lattice Boltzmann codes are easy to program because no complex linear equation systems must be solved. Furthermore it is easy to implement different kind of flow models, for example models for multiphase flows. The present paper points out the advantages of Lattice Boltmann methods by comparing results of the Lattice Boltzmann method with analytical and standard CFD results. Under standard CFD the application of a commercial CFD-code is meant. Two standard flows are considered. The first flow under consideration is the laminar boundary layer flow. For example, skin friction values calculated by both a standard CFD-code (FLUENT is applied) and a Lattice Boltzmann code are compared. For the laminar boundary layer flow an analytical solution is available. In the present paper all three results (analytical solution, FLUENT solution, Lattice Boltzmann solution) are compared and discussed. It is demonstrated that the results are in good agreement. Additionally, the 2D-flow around a cylinder for Reynold number 35 is considered. It is also demonstrated that the Lattice Boltzmann results are in good agreement with the results calculated by the application of FLUENT.
A Numerical Study of Natural Convection Inside an Automobile Compartment Due to Solar Radiation
Authors: Kader Md. Faisal , Jun Yong-du , Lee Kum-bae
Published: July 2010

In summer, the temperature of a parked automobile compartment increases extremely high under a sunny condition. Investigation of this fluid flow and heat transfer characteristics is very important for controlling the effect of major design parameters. This paper address the behavior of fluid flow through convection and air temperature inside a car parked in the sun. The numerical solution was done by a new and operation friendly CFD code – SC/Tetra with a full scale model of a SM3 car and turbulence was modeled by the standard k-ε equation. It can be seen that solar radiation is an important parameter to raise the compartment temperature above the ambient temperature during summer. Numerical analysis of the three-dimensional model predicts a detailed description of fluid flow and temperature distribution driven by the incoming solar radiation (insoaltion) in the passenger compartment.
Cylindrical Couette Flow of a Rarefied Gas From Macro- to Micro-Scales
Authors: Wang Sheng , Lei Kangbin , Luo Xilian , Kase Kiwamu , Merzari Elia , Ninokata Hisashi
Published: July 2010

The cylindrical Couette flow of a rarefied gas from macro- to micro-scales, in the case where the inner cylinder is rotating whereas the outer cylinder is at rest, is extensively investigated by direct simulation Monte Carlo (DSMC) code incorporated with a Volume-CAD software. The generalized soft sphere (GSS) model is applied to an intermolecular collision calculation. The diffuse reflection model and Cercignani-Lampis-Lord (CLL) model are used to model the molecule-surface interaction by considering the accommodation coefficients on inner cylinder (ACI hereafter) and outer cylinder (ACO hereafter) separately. The contents in this paper include following three aspects: I the flow field characteristics and force and torque on inner cylinder for eccentric Couette flow between different scales with same non-dimensional parameters (accommodation coefficients, eccentricity-clearance ratio, Knudsen number and Reynolds number) are compared; the flow field characteristics for different scales are same; with the increase of the scale, the total force on the inner cylinder increases slightly, while the torque is proportional to the scale; II the velocity profiles in concentric Couette flow under different non-dimensional parameters are studied; the result shows that the phenomenon of inverted velocity profile in the concentric Couette flow is only induced by a smooth outer cylinder; the non-dimensional tangential velocity, as well as its gradient is high at low Reynolds number; the Knudsen number has great impact on the tangential velocity profile, and the velocity profile may not be inverted in the case of low Knudsen number; III the flow field characteristics in eccentric Couette flow under different non-dimensional parameters are obtained; the recirculation zone may not appear when Knudsen number is high; the position of its center may be different depending on Reynolds number; with the increase of Reynolds number, the compressibility effect becomes important; stratified distribution of the density becomes obvious at low Knudsen number.
Direct Numerical Simulation of the First Stages of a Plunging Breaker Using a Level Set Method
Authors: Go´mez Pablo , Zanzi Claudio , Palacios Julia´n , Lo´pez Joaqui´n , Herna´ndez Julio
Published: July 2010

A numerical study of wave breaking in shallow water is presented. The jet formed at the wave crest and the subsequent splash-up phenomenon resulting from the impact of the jet on the liquid surface are analyzed. The wave is assumed to be generated by an accelerated piston in an open channel containing liquid. The two-dimensional, incompressible, unsteady Navier-Stokes equations are solved using a local level set method to treat the interface evolution [Go´mez et al., Int. J. Numer. Meth. Engng, 63, pp. 1478–1512, 2005], which permits to analyze the combined air-liquid flow. Viscous and capillary effects are retained. The level set transport and reinitialization equations are solved in a narrow band around the interface using an adaptive refined grid. Two different approaches are considered to take into account the relative movement between the piston and the end wall of the channel. The first one uses a fixed grid and introduces a mass force per unit mass equal to the piston acceleration, and the second one is based on using a moving grid, which is compressed as the piston moves forward, and an arbitrary Lagrangian-Eulerian method. The numerical results obtained for the evolution of the wave shape during the breaking process, particularly the evolution of the plunging jet, the air cavity and the complex flow resulting from the impact of the plunging jet, are compared with experimental visualization results obtained for a small-scale breaking wave, for which the breaking process is strongly influenced by surface tension. A good degree of agreement was observed between both types of results during the first stages of the breaking process.
Simulation of Dendritic Growth Using a VOF Method
Authors: Lo´pez Joaqui´n , Herna´ndez Julio , Zanzi Claudio , Faura Fe´lix , Go´mez Pablo
Published: July 2010

The volume of fluid (VOF) method is one of the most widely used methods to simulate interfacial flows using fixed grids. However, its application to phase change processes in solidification problems is relatively infrequent. In this work, preliminary results of the application of a new methodology to the simulation of dendritic growth of pure metals is presented. The proposed approach is based on a recent VOF method with PLIC (piecewise linear interface calculation) reconstruction of the interface. A diffused-interface method is used to solve the energy equation, which avoids the need of applying the thermal boundary conditions directly at the solid front. The thermal gradients at both sides of the interface, which are needed to accurately obtain the front velocity, are calculated with the aid of a distance function. The advection equation of a discretized solid fraction function is solved using the unsplit VOF advection method proposed by Lo´pez et al. [J. Comput. Phys. 195 (2004) 718–742] (extended to three dimensions by Herna´ndez et al. [Int. J. Numer. Methods Fluids 58 (2008) 897-921]). The interface curvature is computed using an improved height function (HF) technique, which provides second-order accuracy. The assessment of the proposed methodology is carried out by comparing the numerical results with analytical solutions and with results obtained by different authors for the formation of complex dendritic structures in two and three dimensions.