bluuebunny/crossref_metadata_2025 huggingface dataset:
Hysteresis of Flow Around an Elliptic Cylinder in Critical Reynolds Number Regime
Authors: Ota Terukazu , Takahashi Seijiro , Yoshikawa Hiroyuki
Published: October 2008

Experimental investigations of the flow around an elliptic cylinder of axis ratio 1:3 were carried out for several angles of attack in a wide range of Reynolds number. The flow characteristics were studied by measuring the fluid forces and the surface pressure. In the critical Reynolds number regime, a discontinuous change of flow state was observed. This change was accompanied by the remarkable hysteresis phenomenon. Details of this hysteresis process are described in the paper.
Level Set Based Finite Element Method of Bubble-in-Liquid Simulation
Authors: Choi Hyoung G. , Kang S. W. , Yoo J. Y.
Published: October 2008

As far as the author knows, few papers have been reported for the level set simulation of a two-phase (bubble-in-liquid or liquid droplet-in-gas) flow based on unstructured background mesh. Almost all existing studies are based on structured mesh using finite difference or finite volume method as spatial discretization. Therefore, the application of existing various level set methods based on structured mesh to a bubble-in-liquid flow problem in a complex geometry is not straightforward. In the present study, a level set based two-phase flow code has been developed using finite element discretization, which can be utilized for the analysis of a bubble-in-liquid flow problem in a complex geometry. Since the finite element method has been employed for the spatial discretization of governing equations, unstructured mesh can be naturally adopted for the level set simulation of a bubble-in-liquid flow without an additional load for the code development except that solution methods of the hyperbolic type redistancing and advection equations of the level set function should be devised in order to give a bounded solution on unstructured mesh. In this study, some issues of the level set simulation based on finite element method for a bubble-in-liquid flow problem are discussed including the discretization of the hyperbolic type equations using SUPG type formulation and a three-dimensional benchmark problem of a bubble-in-liquid motion have been solved and compared with the existing results. It has been shown that the present bubble-in-liquid simulation method based on FEM gives a satisfactory solution with the level set method alone while the other researches based on finite difference/volume method use a combined level-set/volume-of-fluid method (CLSVOF) or solve another equation of the volume conservation constraint in order to circumvent a volume loss/gain problem in a level set simulation.
Stability Analysis of a Plane Poiseuille Flow of Multilayered Viscoelastic Fluids: An Energetic Approach
Authors: Rousset Franc¸ois , Bourgin Patrick , Palade Liviu-Iulian
Published: October 2008

Coextrusion flows of compatible polymers are known to be generally more stable than the same flows of incompatible systems. It is shown in this paper that the weak response to disturbance of such flows can be predicted by formulating an energetic approach of the problem. The energy dissipated by the interdiffusion process is evaluated which allows stability maps to be obtained for Newtonian and Oldroyd-B fluids. These maps show the increase of the stable domain in the case of compatible polymeric systems for both Newtonian and viscoelastic fluids.
Design and Application: Slurry Pump Technology
Authors: Addie Graeme R. , Kadambi J. R. , Visintainer Robert
Published: October 2008

Slurry Pumps are used throughout the world for the Transportation of Solids in Coal, Copper Iron-Ore, Phosphate and other Mines. They are also used in Dredges cleaning Waterways in Sand and Gravel, and in Phosphoric Acid and Alumina Plants. About $500 million worth of slurry pumps and replacement parts are estimated to be produced every year. Slurry pumps are similar to water pumps so a lot of the available water pump technology can still be used. When it comes to determining pipeline velocities and heads, and the effect of slurries on performance, however, different technologies are found to be necessary. In designing for, and predicting pump wear performance, for example, special numerical modeling tools are found to be necessary. Pump system evaluations require a completely different approach. Cost of ownership calculations for slurry pumps must for example, consider wear parts life as they can be 50% of the total. When the whole system is considered, it needs to be in terms of the cost of transporting a number of tons of dry solids a given distance. Not water transported or pump efficiency. The writers in this presentation provides an outline of the different technologies involved in the design and application of centrifugal slurry pumps, how these are applied, and the insight they provide.
An Historical and Applied Aerodynamic Study of the Wright Brothers’ Wind Tunnel Test Program and Application to Successful Manned Flight
Authors: Dodson Michael G. , Miklosovic David S.
Published: October 2008

A replica wind tunnel was built and used to test the flow quality through the Wright Brothers’ wind tunnel. The research determined the effect flow quality and experimental method had on the Brothers’ results, and whether those results were useful in a quantitative sense. Particle image velocimetry revealed boundary layers extending 2.5” (63.5 mm) from each wall, and velocity gradients as large as 20% along the wind tunnel model span resulting in an asymmetric lift distribution. Similarly, the balance generated asymmetric wingtip vortices contributing to asymmetric downwash along the span of the model. Direct force measurements of a replica of the Wrights #12 airfoil showed their lift measurements were at least 7% and as much as 15% too low, and numerical analysis revealed wind tunnel predictions for lift, drag, and efficiency were not applicable to full scale design due to Reynolds number scaling effects.
A Numerical Method for Capillarity-Driven Free Surface Flows
Authors: Tong Albert Y. , Wang Zhaoyuan
Published: October 2008

The continuum surface force (CSF) method has been extensively employed in the volume-of-fluid (VOF), level set (LS) and front tracking methods to model surface tension force. It is a robust method requiring relatively easy implementation. However, it is known to generate spurious currents near the interface that may lead to disastrous interface instabilities and failures of grid convergence. A different surface tension implementation algorithm, referred to as the pressure boundary method (PBM), is introduced in this study. The surface tension force is incorporated into the Navier-Stokes equation via a capillary pressure gradient while the free surface is tracked by a coupled level set and volume-of-fluid (CLSVOF) method. It has been shown that the spurious currents are greatly reduced by the present method with the sharp pressure boundary condition preserved. The numerical results of several cases have been compared with data reported in the literature and are found to be in a close agreement.
3D Structure of the Rotor Wake of a Three Different Sweep Axial Fan
Authors: Kergourlay Ge´rald , Kouidri Smai¨ne , Rankin Gary W. , Rey Robert
Published: October 2008

This experimental study, applied to a three different sweep axial fan (backward, radial and forward), aims at determining the 3D structure of the rotor wake from unsteady velocity measurements. The hot-film anemometry is used to measure the 3D unsteady velocity components in nearfield, downstream the fan. The data analysis leading to averaged and turbulent velocities, the components of the Reynolds’ stress tensor and the turbulent kinetic energy is presented, in order to illustrate the influence of the sweep. A spectral analysis is also performed.
Cross-Flow Filtration Performance During the Washing of a Simulated Radioactive Waste Stream
Authors: Duignan Mark R. , Zamecnik John R.
Published: October 2008

Bechtel National, Inc. has been contracted by the Department of Energy to design a Waste Treatment and Immobilization Plant (WTP) to stabilize liquid radioactive waste that is stored at the Hanford Site as part of the River Protection Project (RPP). Because of its experience with radioactive waste stabilization, the Savannah River National Laboratory (SRNL) of the Westinghouse Savannah River Company is working with Bechtel and Washington Group International, to help design and test certain parts of the waste treatment facility. One part of the process is the separation of radioactive solids from the liquid wastes by cross-flow ultrafiltration. To test this process a cross-flow filter was used that was prototypic in porosity, length, and diameter, along with a simulated radioactive waste slurry, made to prototypically represent the chemical and physical characteristics of a Hanford waste in tank 241-AY-102/C-106. To mimic the filtration process the waste slurry undergoes several steps, including dewatering and washing. During dewatering the concentration of undissolved solids (UDS) of the simulated AY102/C106 waste is increased from 12 wt% to at least 20 wt%. Once at the higher concentration the waste must be washed to prepare for its eventual receipt in a High Level Radioactive Waste Melter to be vitrified. This paper describes the process of washing and filtering a batch of concentrated simulated waste in two cycles, which each containing 22 washing steps that used approximately 7.7 liters of a solution of 0.01 M NaOH per step. This will be the method used by the full-scale WTP to prepare the waste for vitrification. The first washing cycle started with the simulated waste that had a solids concentration of 20 wt% UDS. This cycle began with a permeate filter flux of 0.015 gpm/ft2 (3.68 cm/hr) at 19.6 wt% UDS with a density of 1.33 kg/L, consistency of 19.1 mPa·s, and yield stress of 8.5 Pa. At the end of the 22 washing steps the permeate filter flux increased to 0.023 gpm/ft2 (5.64 cm/hr) at 20.1 wt% UDS with a density of 1.17 kg/L, consistency of 12.6 mPa·s, and yield stress of 10.4 Pa. The average permeate filter flux during the 7 hours of Cycle 1 washing was 0.018 gpm/ft2 (4.41 cm/hr). During Cycle 2 the simulated waste started at a permeate filter flux of 0.025 gpm/ft2 (6.13 cm/hr). Note that the starting flux for Cycle 2 was greater than the ending flux for Cycle 1. The period between the cycles was approximately 12 hours. While no filtering occurred during that period either solids dissolution continued and/or the filter cake was dislodged somewhat with the stopping and starting of filter operation. At the end of the second set of 22 washing steps, the permeate filter flux increased to 0.032 gpm/ft2 (7.84 cm/hr) at 20.6 wt% UDS with a density of 1.16 kg/L, consistency of 9.0 mPa·s, and yield stress of 8.2 Pa. The average permeate filter flux during the 4 hours of Cycle 2 washing was 029 gpm/ft2 (7.11 cm/hr).
Numerical Study of Cavitation Instabilities Arising in Cascade With Slit
Authors: Iga Yuka , Hiranuma Makoto , Shimura Takashi , Ikohagi Toshiaki
Published: October 2008

In this study, unsteady cavitation and cavitation instabilities are numericaly analyzed around flate-plate cascade with slit in water/ air working fluid. In order to investigate the influence of location of slit between front and rear blades on cavitation characteristics, three kinds of two-stage cascade are arranged to have different length of front blade. Through comparisons with the results of previous study about cascade without slit, it is confirmed that cavitation instabilities are suppressed by slit effect in some cases without decline of cavitation performance of the cascade.
Rheological Measurements on Viscoelastic Self-Healing Composites Used in Oil Industry
Authors: Bakhtiyarov Sayavur I. , Panahov Geilani M. , Abbasov Eldar M. , Heydarov Chingiz Y.
Published: October 2008

In this paper we present the results of the rheological property measurements on viscoelastic composite materials used in oil industry. Laboratory experiments were carried out to determine important thermophysical, rheological and mechanical properties of the test materials using both the standard commercial and in-house made equipment. The composites with the paramagnetic particles (γ-iron oxide) are exhibited a significant magnetic memory after magnetic treatment. The measured value of the yield stress after the magnetic treatment increased almost twice in comparison with the yield stress value of the magnetically untreated composite. The yield stress of the composite material exponentially decreases with time and reaches its magnetically untreated value after 15 hours. The yield stress also increases with the amount of the paramagnetic powder additive, and it reaches a maximum value at 8 wt% of this additive. The obtained results provide a valuable information for computer modeling of the viscoelastic fluid flow in pipes of complex geometry.
Simulations and Measurements of Dredge Pump
Authors: Peng Guangjie , Wang Zhengwei , Yang Wen
Published: October 2008

Flow field of centrifugal pump (Pump flow passage includes suction pipe, impeller and volute casing.) obtained by solving the Reynolds average Navier-Stokes equation. Computational performance curve is compared with measuring curve. The result demonstrates that the computational head versus discharge curve is coincident with the measuring curve; the computational efficiency curve is coincident with the measuring curve in large-capacity area, in lower-capacity area not so well. Though the simulation result is not accurate highly in part operating domains, the pressure and velocity distribution and other flow characteristics in whole flow path in all operating domain produced by the simulation are also useful to analyze flow problems in dredge centrifugal pump.
CFD Modeling of Solid Fluidization in a Column
Authors: Lee Si Y.
Published: October 2008

Primary objective of the work is to model resin particles within the column during the particle fluidization and sedimentation processes and to understand hydraulic behavior for particles within column during the resin fluidization and sedimentation processes. The modeling results will assist in interpreting experimental results, providing guidance on specific details of testing design, and establishing a basic understanding of resin particle’s hydraulic behavior within the column. The model was benchmarked against the literature data and the test data conducted by Savannah River National Laboratory at Savannah River Site (SRS). A scoping analysis effort has been undertaken to address the feasibility of simulating the basic fluidization and sedimentation aspects pertinent to the resin addition/removal process considered here. The existing computational fluid dynamics (CFD) code Fluent was chosen for this effort. Both fluidization and sedimentation of granular particles (i.e., of varying sizes) were based on an Eulerian model for granular flow. A two-dimensional axial symmetrical cylindrical geometry was chosen to perform the solid-fluid simulations. The column consisted of a fluid region of 48” in diameter by 94” in height where at both the top and bottom boundaries liquid fluid could pass through, but resin particle could not (i.e., assuming screens at both ends).
Hydraulic Design Validation of the Suction Intake of a Vertical Centrifugal Pump Station by Use of Computational Fluid Dynamic (CFD) Analysis
Authors: Minisci Edmondo , Telib Haysam , Cicatelli Giancarlo
Published: October 2008

The correct operation of vertical centrifugal pumps is strongly dependent on the design of the entire pump intake system, which includes the suction sump and the associated piping. From the hydraulic point of view, the sump or pump intake design is one of the most critical aspect the designer is facing with: an incorrect sump dimensioning can determine the onset of detrimental fluid dynamic phenomena like pulsation, cavitation and a vortical activity which can easily lead to the appearance of undesired vibration of the entire pump structure. Basic guidelines for the sump and the intake pipeline design have been well established over the years and are now widely published. They include recommendations for the definition of the main sump dimensions, together with the minimum submergence as well as recommended typical velocities approaching the pump suction bell. When shape and dimensions are not standard, it is very often required to perform an experimental investigation of the sump characteristics with a scaled model to evaluate the hydraulic behavior of the intake system and, if necessary, provide indications for changes in the system layout to meet the required criteria. In the recent years, CFD has become a well established tool for the design validation of all pumps components. Nevertheless, numerical simulation applied to intake systems has not yet received the deserved attention, most probably due to the massive computational resources required for the modelization of complex intake structures. With the more extensive availability of powerful computers and advanced computational codes, this is not anymore an obstacle. In this respect, the numerical simulation can be seen as a realistic and more economical alternative to model testing. The paper presents an application of the CFD analysis to the hydraulic evaluation of a pump station intake. In the absence of a model test and thanks to a not complex geometry of the sump under investigation, the numerical results can be easily compared to the expected results obtained with the more traditional methods (i.e. Hydraulic Institute) for a basic validation of the numerical simulation. Eventually, the exercise claims to be a contribution to the rising debate on the applicability of numerical simulation to this kind of applications.
Design Process for an Advanced Reactor Coolant Pump for a 1400 MW Nuclear Power Plant
Authors: Knierim Claus , Baumgarten Sven , Fritz Jochen , Coon Michael T.
Published: October 2008

As part of the planning activities for a new 1400 MW nuclear power station with a pressurized water reactor, a new hydraulic system had to be designed for the reactor coolant pumps (RCPs). Starting from the design principles and the main dimensions of an existing pump a new diffuser and impeller had to be designed for the specified requirements which provided a specific speed of almost ns = 100 rpm (≈ 5100 in US units). The authors describe how impeller and diffuser of the hydraulic system were gradually optimized with the aid of computational fluid dynamics (CFD). The system had to meet demanding requirements, thus it was decided to build a model pump (on a scale ≈ 1:2) to demonstrate that the new pump would satisfy the specified duty parameters. Based on the spectra of tests performed on the model pump the authors discuss the resulting pump characteristics (Q, H, η, NPSH).
Flow Structure of an Axial-Flow Pump From Stable Operation to Deep Stall
Authors: Kosyna G. , Goltz I. , Stark U.
Published: October 2008

Different experimental techniques were used to investigate the structure of the rotor tip flow in a highly-loaded single-stage axial-flow pump. Probably the most important result of this investigation is the first-time visualization of a spiral-type vortex breakdown in an axial-flow turbomachine. The occurrence of the breakdown leads to a rapid expansion of the clearance vortex in stream wise, span wise and pitch wise direction and this has a major impact on stall inception. In deep stall the rotor tip flow is dominated by the well-known part load recirculation vortex as well as by a lesser-known cross passage vortex. Furthermore, the paper presents a simple but very effective type of casing treatment, which stabilizes the pump head characteristic completely.
Numerical Simulation of 3D Cavitating Flows: Analysis of Cavitation Head Drop in Turbomachinery
Authors: Pouffary Benoiˆt , Fortes Patella Regiane , Reboud Jean-Luc
Published: October 2008

The numerical simulation of cavitating flows in turbomachinery is studied at the Turbomachinery and Cavitation team of LEGI (Grenoble - France) in collaboration with the French space agency (CNES) and the rocket engine division of SNECMA Moteurs. A barotropic state law is proposed to model the cavitation phenomenon and this model has been integrated in the commercial CFD code Fine/TurboTM, developed and commercialized by Numeca International. The numerical aspects of the work are mainly focused on numerical stability and reliability of the algorithm, when introducing large density variations through the strongly non linear barotropic state law. This research conducted first to changes in the way preconditioning parameters are calculated. Internal flows in turbomachinery have been deeply investigated. A methodology allowing the numerical simulation of the head drop induced by the development of cavitation has been proposed on the basis of computations in inducers and centrifugal pumps. These simulations have allowed the characterization of the mechanisms leading to the head drop and the visualization of the effects of the development of cavitation on internal flows.
Numerical Analysis of Cavitation Instabilities In Inducer Blade Cascade
Authors: Pouffary Benoiˆt , Fortes Patella Regiane , Reboud Jean-Luc
Published: October 2008

The cavitation behavior of a four-blade rocket engine turbopump inducer was simulated by the CFD code Fine/TurboTM. The code was modified to take into account a cavitation model based on a homogeneous approach of cavitation, coupled with a barotropic state law for the liquid/vapor mixture [1–4]. In the present study, the numerical model of unsteady cavitation was applied to a four-blade cascade drawn from the inducer geometry. Unsteady behavior of cavitation sheets attached to the inducer blade suction side depends on the flow rate and cavitation number σ. Numerical simulations of the transient evolution of cavitation on the blade cascade were performed for nominal flow rate and different cavitation numbers, taking into account simultaneously the four blade-to-blade channels. Depending on the flow parameters, steady or unsteady behaviors spontaneously take place. In unsteady cases, sub synchronous or super synchronous regimes were observed. Some mechanisms responsible for the development of these instabilities are proposed and discussed.
Fluid-Dynamic Pulsations and Radial Forces in a Centrifugal Pump With Different Impeller Diameters
Authors: Blanco Eduardo , Barrio Rau´l , Parrondo Jorge , Gonza´lez Jose´ , Ferna´ndez Joaqui´n
Published: October 2008

A study is presented on the numerical computation of the unsteady flow through a single suction and single volute centrifugal pump equipped with three impellers of different outlet diameter. Computations were performed by means of the Fluent code, solving the 3D URANS equations. The study was focused on the effect of varying the impeller-volute radial gap on the flow perturbations associated to the fluid-dynamic blade-tongue interaction. In order to contrast the numerical predictions, an experimental series of tests was conducted for the pump with the bigger impeller, to obtain pressure fluctuation data along the volute front wall. Finally, the results from the numerical simulations were used to compute the radial forces at the blade passing frequency, as a function of flow-rate and blade-tongue radial gap.
Computation of the Unstable Behavior of a Hydraulic Circuit With a Centrifugal Pump Coupled to an Air Pocket
Authors: Parrondo Jorge , Antun˜a Juan , Prieto Jose´ I.
Published: October 2008

A theoretical and experimental study is presented on the mass oscillation instability in hydraulic systems with entrapped gas pockets and pumps with positive slope in the head curve. In order to simulate these systems, the one-dimensional unsteady equations for compressible liquid flow were solved by means of a suitable calculation algorithm, based on the method of characteristics. Additionally, a series of laboratory tests was conducted on a conventional centrifugal pump that operated in a circuit with a dead end and different amounts of entrapped air. In accordance with the predictions of the theoretical model, instability was found to develop with limit cycle pressure oscillations of frequency dependent on the trapped air amount.
Comparison of Different Methods for the Evaluation of Cavitation Damaged Surfaces
Authors: Bachert B. , Ludwig G. , Stoffel B. , Baumgarten S.
Published: October 2008

The experimental data which will be presented in this paper are the results of the comparison between different methods for evaluating damaged surfaces by cavitation erosion. The different methods are partly working in the initial stage of cavitation erosion and partly at developed cavitation erosion, where mass loss occurs. The used test rig consists basically of a rotating disc with a diameter of 500 mm on which four holes are located. Each hole generates a cavitation zone while the disc is rotating. The test objects are material specimens made of copper. Copper was used as test material in respect to reasonable durations for the tests. The specimen can be implemented in the casing of the test rig directly across the rotating disc on the diameter where the holes are located. This rotating disc test rig generates a very aggressive type of cavitation, so that mass loss, of course depending on the tested material, will appear after relatively short durations. Also the initial stage of cavitation erosion can be observed. The used test rig is very interesting regarding the possibility to apply different measuring techniques to characterize the erosive aggressiveness of cavitation. These techniques are at first the so-called Pitcount-Method, which allows investigations of cavitation erosion in the initial stage. The second one is an acoustic method, which is based on a structure-borne noise sensor and a specially developed signal processing system. The third method is the measuring of mass loss of the material specimen after several time steps. With the help of a CCD-camera and special digital image processing software, images of different cavitation conditions were recorded. The information obtained from these images should serve as support for the evaluation of the other used methods. After the evaluation with the above mentioned methods, the specimens were evaluated with a special device which works with the help of a white light interferometer. With this evaluation method three-dimensional information can be obtained in respect to the actually eroded volume of the specimens. With this information the lost mass of the specimens could be calculated directly. Especially the comparison of the results obtained from the Pitcount-Method, which is a two-dimensional evaluation method, and the three-dimensional results of the white light interferometer is an important point of the work within this paper.
Steady Analysis of Thermodynamic Effect of Partial Cavitation Using Singularity Method
Authors: Watanabe Satoshi , Hidaka Tatsuya , Horiguchi Hironori , Furukawa Akinori , Tsujimoto Yoshinobu
Published: October 2008

It is well known that the suction performance of turbopumps in cryogenic fluids is much better than that in cold water because of thermodynamic effect of cavitation. In the present study, an analytical method to simulate partially cavitating flow with the thermodynamic effect in a cascade is proposed; heat transfer between the cavity and the ambient fluid is modeled by one-dimensional unsteady heat conduction model under the slender body approximation and is coupled with a flow analysis using singularity methods. In this report, the steady analysis is performed and the results are compared with those of experiments to validate the model of the present analysis. This analysis can be easily extended into unsteady stability analysis for cavitation instabilities such as rotating cavitation and cavitation surge.
Influences of Impeller Diameter and Diffuser Blades on Air-Water Two-Phase Flow Performance of Centrifugal Pump
Authors: Matsushita Naoki , Furukawa Akinori , Okuma Kusuo , Watanabe Satoshi
Published: October 2008

A tandem arrangement of double rotating cascades and single diffuser cascade, proposed as a centrifugal pump with high performance in air-water two-phase flow condition, yields lower head due to the smallness of the impeller outlet in comparison with a impeller with large outlet diameter and no diffuser. Influences of impeller diameter change and installation of diffuser blades on two-phase flow performance were experimentally investigated under the case of the same volute casing. As the result, the similarity law of the diameter of impeller having the similar blade geometry and the rotational speed is satisfied even in two-phase flow condition. Comparing pump performances between a large impeller without diffuser blades and a small one with diffuser blades, higher two-phase flow performance is obtained by controlling the rotational speed of a small impeller with diffuser blades in the range of small water flow rates, while a large impeller with no diffuser gives high performance in the range of high water flow rate and small air flow rate.
Development of Autonomous Design Technique for Axial Fans Using Numerical Optimization
Authors: Iwase Taku , Sugimura Kazuyuki , Tanno Taro
Published: October 2008

We designed an axial fan for servers using computational fluid dynamics (CFD) and numerical optimization. The performance of the fan, namely static pressure rise and efficiency, was calculated using commercial CFD software based on an incompressible Reynolds-averaged Navier-Stokes (RANS) solver. An automatic program developed in-house was used to generate the grids for CFD calculation. Numerical optimization—using a simulated annealing algorithm (SA)—was used for determining the optimized shape of the fan. After optimizing the fan, initial and optimized fan designs were made for experiments using rapid prototyping, and their performances, based on such things as efficiency and noise level, were measured. Results demonstrated that the optimized fan design achieved higher efficiency than the initial design. Multi optimization was also developed for maximizing the fan efficiency and minimizing the casing height. An additional finding was that there was a trade-off between the fan efficiency and casing height.
Simulations of Inducers at Low-Flow Off-Design Flow Conditions
Authors: Hosangadi A. , Ahuja V. , Ungewitter R. J.
Published: October 2008

The ability to accurately model details of inlet back flow for inducers operating at low-flow, off-design conditions is evaluated. A sub-scale version of a three-bladed liquid hydrogen inducer tested in water with detailed velocity and pressure measurements is used as a numerical test bed. Under low-flow, off-design conditions the length of the separation zone as well as the swirl velocity magnitude was under predicted with a standard k-ε model. When the turbulent viscosity coefficient was reduced good comparison was obtained at all the flow conditions examined with both the magnitude and shape of the profile matching well with the experimental data taken half a diameter upstream of the leading edge. The velocity profiles and incidence angles at the leading edge itself were less sensitive to the back flow length predictions indicating that single-phase performance predictions may be well predicted even if the details of flow separation modeled are incorrect. However, for cavitating flow situations the prediction of the correct swirl in the back flow and the pressure depression in the core becomes critical since it leads to vapor formation. The simulations have been performed using the CRUNCH CFD® code that has a generalized multi-element unstructured framework and an advanced multi-phase formulation for cryogenic fluids. The framework has been validated rigorously for predictions of temperature and pressure depression in cryogenic fluid cavities and has also been shown to predict the cavitation breakdown point for inducers at design conditions.
Expansion Factor Tests in a 75 mm Diameter Orifice Meter Tube
Authors: Morrow Thomas B.
Published: October 2008

This paper presents new experimental data for orifice meter expansion factor tests flowing natural gas through a 75 mm (3-inch) diameter orifice meter tube for values of the orifice diameter ratio (β) between 0.60 and 0.75. The tests were performed in the Low Pressure Loop (LPL) of the Metering Research Facility (MRF) at Southwest Research Institute (SwRI). The new data complement previously reported results for 100 mm (4-inch) and 150 mm (6-inch) meter tubes for β values between 0.20 and 0.60.
Effects of Turbulence on the Breakup of Round Liquid Jets in Gaseous Crossflow
Authors: Sankarakrishnan R. , Sallam K. A. , Chambers F. W.
Published: October 2008

An experimental investigation of the effects of turbulence on primary breakup of round liquid jets subjected to gaseous crossflow is described. The paper investigates the effects of partial degrees of turbulence development in the liquid. Measurements of the properties of primary breakup were obtained using double-pulsed shadowgraphy in a subsonic wind tunnel having a test section of 0.3 m × 0.3 m × 0.6 m. Measurements included primary breakup regimes, conditions required for the onset of breakup, ligament properties along the liquid surface, drop size and velocity distributions after breakup along the liquid surface, conditions required for breakup of the liquid jet as a whole, and liquid jet trajectories.
Study on Flow Field of Impeller Tip Clearance in the Double Suction Pump
Authors: Xia Penghui , Liu Shuhong , Wu Yulin , Zhang Liang
Published: October 2008

According to Reynolds Average N-S Equation enclosed by standard k-ε turbulence model on the basis of pressure-velocity correction equation established with pressure-velocity connection algorithm SIMPLEC, numerical simulation for the three-dimensional incompressible turbulence flow of the double suction pump was carried out in this paper and then the distribution of axial velocity and static pressure within the tip clearance was obtained. The results indicate that the leakage flow and the secondary backflow, which occurs at some special regions, are observed obviously.
Implementation and Development of a Stochastic Turbulence Model Based on RANS Formulation for the Prediction of Aeroacoustic Noise
Authors: Niumsawatt Phachara , Abanteriba Sylvester
Published: October 2008

In the computation of aeroacoustic noise, both the Lighthill analogy and the linearized Euler approaches require the definition of source terms involving instantaneous flow fluctuations, which are generally obtained from either Direct Numerical Simulation (DNS) or Large Eddy Simulation (LES). However, these approaches are not economically viable in terms of computational resources, as they require very fine grids to deliver accurate results. Therefore, the Stochastic Velocity Field generation model (SVFG) has has been applied in this paper. The SVFG model is based on the concept of the Stochastic Noise Generation and Radiation (SNGR) without sound propagation and linearized equations. The SVFG model uses time-averaged quantities from the Reynolds Averaged Navier-Stokes equations (RANS) to generate a synthetic time dependent turbulent flow field. The turbulent fluctuations are modeled using a stochastic description of the three-dimensional turbulent motion with a discrete set of Fourier modes. This synthetic turbulent field represents many of the characteristics of real turbulence. Nevertheless, it still has some imperfections; although it exhibits the expected correlation length and the required ratio of length scales, it does not predict the convective properties of shear flow turbulence, as the approach generates homogenous and isotropic turbulence. These properties are shown in this paper with the test case of an axial-symmetrical subsonic jet. The SVFG model is used to generate the turbulent flow field, which then is used to compare with actual experiment measurement and other prediction methods. The results of the comparison show strengths and weaknesses of the model. Since the SVFG approach is relatively low cost when compared to both LES and DNS, it offers an attractive alternative to derive the turbulent flow field.
Numerical Investigation of the Transient Flow in a Centrifugal Pump Stage
Authors: Benra F.-K. , Dohmen H. J.
Published: October 2008

The knowledge of the flow behavior in pump stages which consist of an impeller, a bladed diffuser and a bladed return channel is of great importance for the design of multistage centrifugal pumps. Especially the Interaction of the impeller flow with the stationary diffuser blades and the behavior of the return channel blades affect the efficiency of a pump stage in a considerable way. In this contribution the transient flow in an industrial centrifugal pump stage, which has an impeller with seven blades, a radial diffuser with ten blades and a return channel with also ten separate blades, has been simulated numerical by using the commercial software code CFX-5.7. Because of the unfavorable ratio of blade numbers a complete meshing of all flow channels was necessary. In consequence the cumulative amount of grid nodes reached a number of nearly 6 million nodes. As a result of the numerical investigation of the time dependent flow accomplished for this contribution, the influence of the rotating impeller on the flow in the stationary parts of the pump is presented in detail. All flow parameters are shown as a function of time and are discussed with respect to the position of the impeller relative to the stator blades.
Calculation of Vortex Shedding From a Circular Cylinder in Uniform and Shear Flows
Authors: Basara Branislav
Published: October 2008

The present paper deals with numerical investigations of vortex shedding from a circular cylinder in uniform and shear flows. The computational approach is based on solving the complete Transient Reynolds-Averaged Navier-Stokes (TRANS) equations. The ζ-f model proposed recently by Hanjalic et al. (2004) is used for comparison with the recent computations of Basara et al. (2003) who used the Reynolds-stress model (RSM) developed by Speziale et al. (1991) and the hybrid EVM/RSM turbulence model developed by Basara and Jakirlic (2003). The recent study of the same flows (Basara, Jakirlic and Alajbegovic (2003)) showed that the wall treatment has an important role in correct predictions of forces acting on a cylinder. In this work, a new compound wall treatment (CWT) of Popovac and Hanjalic (2005) was used. A simple modification to the treatment of the dissipation rate of the original CWT is proposed. Furthermore, a new νt - k - ζ - f model is modeled on the basis of an exact form derived from the ζ-f model and the first results are given here. Calculations with the ζ-f model employed as a low-Re number model are performed and the results are compared with those obtained with the same model in conjunction with CWT.
The Effect of Wire Shape on the Flow Through Narrow Apertures in a Pulp Screen Cylinder
Authors: Mokamati S. V. , Oslon J. A. , Gooding R. W.
Published: October 2008

Turbulent flow over a rough surface with suction or blowing is a common fluid mechanics problem that has many practical applications including pulp screening. The present study is motivated by the optimization of aperture geometry in pulp screens used in the pulp and paper industry to separate unwanted contaminants from pulp fibres. In these devices, a dilute suspension of fibres is forced through fine slots to remove the oversized contaminants. To better understand the complex hydrodynamics at the critical region near the screen surface, a Computational Fluid Dynamics study has been conducted to examine how the geometry of the aperture entry, characterized by contour height and wire width, affect the details of the flow field. The results indicate that the flow is dominated by a separation vortex that covers the aperture. For low contour heights the flow is accelerated upstream of the aperture due to the high vorticity at the aperture entry and as profile height increases the turbulence intensity at the screen cylinder surface increases. Although the wire width has less of a impact on the flow field than contour height, the results show that decreasing wire width increases turbulence intensity at the surface due to a increase in apparent roughness of the cylinder.
Numerical Modeling of Upstream Nozzle Effect in Supersonic/Hypersonic Impactors for Nano-Particles
Authors: Abouali Omid , Ahmadi Goodarz
Published: October 2008

In this study the performance of supersonic and hypersonic impactors under various operating conditions was analyzed using a computer simulation model. The study was focused on the effect of the nozzle upstream condition on the performance of the supersonic and hypersonic impactors. In our earlier work, the computational domain covered downstream of the nozzle with a sonic boundary condition at the inlet. In the present study, the computational domain included the upstream nozzle where the flow and particles enter with at low velocities. Axisymmetric forms of the compressible Navier-Stokes and energy equations were solved and the gas flow and thermal condition in the impactor were for evaluated. A Lagrangian particle trajectory analysis procedure was used and the deposition rates of different size particles under various operating conditions were studied. For dilute particle concentrations, one-way interaction was assumed and the effect of particles on gas flow field was ignored. The importance of drag and Brownian forces on particle motions in supersonic/hypersonic impactors was analyzed. Sensitivity of the simulation results to the use of different expressions for the drag force was also examined. It was shown that when the upstream nozzle is included in the computational model, the Stokes-Cunningham drag with variable correction coefficient and a constant Cunningham correction factor based on stagnation point properties lead to the same results. Thus these drag laws are most suitable for computer simulation studies of nano-particles in supersonic/hypersonic impactors. The computer simulation results were shown to compare favorably with the experimental data.
Numerical Simulation of the Fuel-Oil Cooling Process in Wrecked Ship
Authors: Ferna´ndez Oro J. M. , Santolaria Morros C. , Argu¨elles Di´az K. M. , Garci´a Ybarra P. L.
Published: October 2008

This work deals with a numerical simulation developed to predict the characteristic cooling times of a low-thermal diffusivity fuel-oil confined in the tanks of a wrecked ship. A typical scenario has been introduced, through the definition of tanks geometries, physical boundary conditions (deep sea temperatures) and reological properties of the fuel-oil. The fluidynamic behaviour of the oil (forced convection) inside the tanks, as well as the heat exchange with surrounding sea water has been simulated throughout a commercial code, FLUENT, that solves directly the Navier-Stokes set of equations, including energy one. The purpose is focused on the prediction of both spatial and temporal evolution of the fuel-oil characteristic temperature inside the tanks. The final objective is placed on the determination of the deadline in which asymptotic temperature curve of the fuel-oil converges to deep sea thermal conditions. Inspectional analysis is also outlined, as a powerful tool to predict an order of magnitude in the cooling process.
Blade Tonal Noise Reduction Using Stator Trailing-Edge Articulation
Authors: Beal David N. , Huyer Stephen , Macumber Daniel L. , Annaswamy Anuradha M.
Published: October 2008

The biologically-inspired method of trailing-edge articulation is investigated as a means of reducing tonal noise due to the stator wake / rotor blade interaction in underwater vehicles. This work is experimental in nature and conducted in the closed channel water tunnel at Naval Undersea Warfare Center in Newport, Rhode Island. Tail articulation is carried out with a life scale stator model with hinged flapping tail designed to (i) operate in freestream velocities corresponding to Reynolds number in the range 75,000 < Re < 300,000 and (ii) operate at frequencies up to 30 Hz in order to investigate the range of Strouhal number 0.0 < St < 0.35. Velocity measurements in the active stator wake are carried out by Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV) in order to investigate the effects of tail articulation on the stator wake. Time averaged measurements of the stator wake by LDV show that Strouhal number of the tail articulation has a dominant effect on the time mean stator drag. Instantaneous phase-averaged measurements of the stator wake by PIV show three regimes of the stator wake as Strouhal number is increased; quasi-steady wake spreading, vortex roll up, and strong vortex wake. Ongoing experiments with an instrumented propeller will demonstrate the efficacy of stator trailing-edge articulation on reducing unsteady blade forces.
Simulations of Unsteady Valve Systems
Authors: Ahuja V. , Hosangadi A. , Cavallo P. A. , Ungewitter R. J. , Shipman J. D.
Published: October 2008

The safe and reliable operation of industrial facilities and high pressure test stands for engine and component testing is largely dependent on the smooth performance of control valves. However, such valves frequently experience pressure oscillations from hydrodynamic instabilities, cavitation and unsteady valve operation. In this paper, we present a series of high fidelity computational simulations of control valves primarily to understand the physics associated with the dominant instability modes. A generalized multi-element framework with sub-models for grid adaption, grid movement and multi-phase flow dynamics was used to carry out the simulations. We discuss the methodology in detail with the example of transient analyses of a gaseous hydrogen control valve and capture the fluid dynamic instability that results from valve operation. Additionally, we provide detailed analyses of a modal instability that is observed in the operation of a pressure regulator valve. In both cases, the instabilities are not localized and manifest themselves as a system wide phenomena leading to oscillations in mass flow and/or undesirable chatter.
Hydrofoil Test Facility at ARL Penn State
Authors: Stinebring David R. , Straka William A. , Willits Steven M.
Published: October 2008

The two-dimensional test section of the ARL/Penn State 12-inch water tunnel has been modified to allow a wide range of dynamic tests using hydrofoils. Three examples of test configurations for the hydrofoil test facility are given. These include tests of a single conventional hydrofoil with non-sinusoidal deflections, tests with two hydrofoils for studying tip vortex interactions, and tests of base ventilated supercavitating hydrofoils. When testing a single hydrofoil, the angle of attack can be varied as a function of time using a cam drive system. Arc length Reynolds number of over 1 million based on a 1.5-inch chord are possible. Hydrofoil lift, drag and pitching moment can be measured during transient operation with and without cavitation. Tip vortex interaction studies have been performed by using a second hydrofoil mounted upstream of the primary test hydrofoil. This upstream hydrofoil is inclined to the tunnel wall so only the tip projects in front of the downstream hydrofoil. The upstream hydrofoil can be traversed across the test section to study the tip vortex interactions. Supercavitating hydrofoils have been tested by ventilating behind a wedge installed along the tunnel wall upstream of the hydrofoil. A full range of test instrumentation is used to support the studies, such as LDV, PIV, high speed video, and acoustic measurements.