bluuebunny/crossref_metadata_2025 huggingface dataset:
DEM Simulations of Particle Clustering at High Solids Concentrations (Keynote)
Authors: Lasinski M. , Pekny J. , Sinclair Curtis J.
Published: October 2008

One limitation of two-fluid computational fluid dynamics models for gas-particle flow is the inability of these models to properly describe the effects of particle-particle interactions in the case of large St at high solids concentrations. Discrete element methods (DEM) present an opportunity to study such interactions. In gas-particle flows with higher solids loadings, particle-particle interactions give rise to particle clustering and/or microstructure formation. In this paper we show how DEM can be used to determine not only the particle-phase stress (required for gas-particle two-fluid CFD models) in the case of particle clustering, but also how DEM can be used to determine the nature, size and composition of the observed microstructure. Specifically, we investigate, using a computationally efficient DEM simulation, the dependence of particle-phase stress in systems with high solids concentration on the solids coefficient of restitution (0.6 to 0.9) and solids volume fraction (0.05 to 0.3). We investigate both monodisperse and bidisperse particle systems. We show how a widening of the particle size distribution reduces the particle-phase stress and inhibits the formation of particle clusters. We also show in our bidisperse simulations how smaller particles (yet still inertia-dominated) are more evenly distributed throughout the system. Finally, we highlight the dependence of the particle-phase stress on the domain size of the simulation and emphasize that a sufficiently large domain size is necessary to accurately describe the clusters which form at higher particle concentrations.
Oscillation Behavior of Water Droplets on Solid Surfaces
Authors: Lin Z. Y. , Peng X. F. , Wang X. D.
Published: October 2008

An experimental investigation was conducted to describe the oscillation behavior of water droplets on solid surfaces as air flew through over the droplets, and the dynamical process was recorded using a high-speed CCD. Two liquid drop oscillation modes, forward-backward and upward-downward, and their mutual conversion were visually observed. Accounting for the internal flow and pressure distribution inside a liquid drop, a phenomenological explanation was proposed to understand the oscillation characteristics of two modes and the mutual conversion mechanisms.
Case Study of Multi-Stage Impeller with Guidevane
Authors: Tsugawa Takuji
Published: October 2008

In the previous paper, the optimum meridian profile of impeller was obtained for various specific speed by means of eight shape factors, that is, inlet relative flow angle β1, turning angle Δβ, axial velocity ratio kc = Cm2/Cm1, impeller diameter ratio kd = D1c/D2c, outlet hub-tip ratio ν2, tip solidity σtimp, mid span solidity σcimp and hub solidity σhimp. In this paper, the optimum meridian profile of multi-stage impeller with guidevane was obtained by means of twelve shape factors. The additional four shape factors are guidevane tip solidity σtgv, mid span solidity σcgv, hub solidity σhgv and coefficient of peripheral velocity at impeller inlet or guidevane outlet kCu1c. In the optimum method, the hydraulic efficiency and suction specific speed are calculated by diffusion factor. In the optimum condition, the best hydraulic efficiency or the best suction specific speed is obtained. In the cyclic flow condition of multi-stage impeller with guidevane, the absolute flow velocity of guidevane outlet is equal to that of impeller inlet, and the diameter of guidevane outlet is equal to that of impeller inlet. In this calculation, the diameter of impeller outlet is equal to that of guidevane inlet. The total calculation number of case study is very large, so the number of each parameter is about between four and seven. The best 1000 optimum meridian profiles and the best design parameter are selected for few kinds of specific speed using twelve dimensional optimum method. As the result of this calculation, the optimum meridian profile of multi-stage impeller and guidevane. The more detailed optimum multi-stage mixed flow impeller and guidevane profile is drawn. For, example, the 1000 specific speed is selected for case study of multi-stage mixed flow impeller. At first, the approximate optimum shape factors are present shape factors. And the optimum shape factors which have better efficiency are tried to find near the present shape factors. Then the study of shape factor changes is the objective of this paper.
Mass Conservation in the Immersed Boundary Method
Authors: Muldoon Frank , Acharya Sumanta
Published: October 2008

The immersed boundary approach for the modeling of complex geometries in incompressible flows is examined critically from the perspective of satisfying boundary conditions and mass conservation. The system of discretized equations for mass and momentum can be inconsistent if the real velocities are used in defining the forcing terms used to satisfy the boundary conditions. As a result, the velocity is generally not divergence free and the pressure at locations in the vicinity of the immersed boundary is not physical. However, the use of the pseudo velocities in defining the forcing (as frequently done when the governing equations are solved using a fractional step or projection method) combined with the use of the specified velocity on the immersed boundary is shown to result in a consistent set of equations which allows a divergence free velocity but, depending on the time step used to obtain a steady state solution, is shown to have an undesirable effect of allowing significant permeability of the immersed boundary. An improvement is shown if the pressure gradient is integrated in time using the Crank-Nicholson scheme instead of the backward Euler scheme. However, even with this improvement a significant reduction in the time step and hence increase in computational expense is still required for sufficient satisfaction of the boundary conditions.
Rheological Property Measurements on Viscoelastic Tribological Nanosystems
Authors: Bakhtiyarov Sayavur I.
Published: October 2008

This paper presents some results of rheological measurements on viscoelastic tribological nanosystems. Conventional standard and in-house made custom equipments and techniques were used to measure the rheological properties of the test liquid lubricants at different shear rates and temperatures.
3D Measurements of the Mean Velocity and Turbulence Structure Within the Near Wake of a Rotor Blade
Authors: Soranna Francesco , Chow Yi-Chih , Uzol Oguz , Katz Joseph
Published: October 2008

Stereoscopic PIV measurements examine the flow structure and turbulence within a rotor near wake located in a non-uniform field generated by a row of Inlet Guide Vanes (IGVs). The experiments are performed in a refractive index matched facility that provides unobstructed view of the entire flow field. The data are acquired at 10 closely spaced radial planes located near mid-span, which enable measurements of all the components of the mean strain rate and Reynolds stress tensors. Chopping and variations of advection speed of the upstream IGV wakes, as they pass along the rotor blade, create a non-uniform flow that shears the rotor wake. However, the phase averaged flow at mid span remains almost two-dimensional. Due to the overwhelming effects of the non-uniform strain field, the presently observed trends of the Reynolds stresses within the sheared wake differ from those measured in previous studies of curved wakes. The axial velocity fluctuations increase along the suction/outer side of the wake, while the other components decay. On the pressure/inner part of the wake the circumferential velocity fluctuations are higher. The shear stress has a complex distribution, but is also higher on the suction side. To explain these trends the stresses and production rates are examined in coordinate systems aligned with the principal strain directions. As expected, the production is high along the compressive directions and low, even negative, in the extensive directions. Accordingly, the compressed normal stress component increases along the wake, while the extended component decays. The in-plane shear stress component and its associated production remain very high in the principal coordinate system of the strain. Projecting the stresses back to the laboratory coordinate system explains the observed inhomogeneous anisotropic distribution of Reynolds stresses within the kinked wake.
A Comparison of Unsteady RANS Simulations With PIV Data in an Axial Turbomachine
Authors: Brzozowski Daniel , Uzol Oguz , Chow Yi-Chih , Katz Joseph , Meneveau Charles
Published: October 2008

This paper presents a comparison of 2D unsteady Reynolds Averaged Navier-Stokes (RANS) simulations using two standard turbulence models, i.e. RNG k-ε and a Reynolds Stress Transport Model, with experimental data, obtained using two-dimensional Particle Image Velocimetry (PIV) measurements within an entire stage of an axial turbomachine. The computations are performed using the commercial flow solver FLUENT™. A sliding mesh interface between the rotor and stator domains is used. The PIV measurements are performed in a refractive-index-matched facility that provides unobstructed view, and cover the entire 2nd stage of a two-stage axial pump. The inlet velocity and turbulence boundary conditions are provided from the experimental data. Detailed side-by-side comparisons of computed and measured phase-averaged velocity as well as turbulence fields within the entire stage are presented. Quantitative comparisons between the experiments and the computations are also included in terms of line distributions within the rotor-stator gap and the stator wake regions. The results show that, although there is reasonable agreement in general between the experimental results and the computational simulations, some critical flow features are not correctly predicted. The turbulent kinetic energy levels are generally too high in the simulations, with substantial amount of unphysical turbulence generation near the blade leading edges, especially in the case of RNG k-ε model.
Distal Placement of an End-to-Side Bypass Graft Anastomosis: A 3-D Computational Study
Authors: DiCicco John R. , Demuren Ayodeji O.
Published: October 2008

A three-dimensional (3-D) computational fluid dynamics study of shear rates around distal end-to-side anastomoses has been conducted. Three 51% and three 75% cross-sectional area reduced 6 mm cylinders were modeled each with a bypass cylinder attached at a 30 degree angle at different placements distal to the constriction. Steady, incompressible, Newtonian blood flow was assumed, and the full Reynolds-averaged Navier-Stokes equations and turbulent kinetic energy and specific dissipation rate equations were solved on a locally structured multi-block mesh with hexahedral elements. Consequently, distal placement of an end-to-side bypass graft anastomosis was found to have an influence on the shear rate magnitudes. For the 75% constriction, closer placements produced lower shear rates near the anastomosis. Hence, there is potential for new plaque formation and graft failure.
A Laboratory Study of Sediment Transport in Free Surface Flow
Authors: Parr Alfred D.
Published: October 2008

This paper discusses an undergraduate fluid mechanics laboratory session. The lab allows the students to observe various sediment transport phenomena in a hands-on manner. The experiments are performed in a glass-walled, tilting sediment flume. The following sediment transport phenomena are created and observed by the students — bed load, suspended load, bed forms (ripples, dunes, antidunes...), surface waves over various bed forms and local scour at flow obstructions including bridge piers and abutments. Students are able to observe local scour using PVC pipes for bridge piers and dimension lumber for abutment scour. Since the flume is 12.2-m long, a large group of students can spread out along both sides of the flume to observe bed forms and to perform local scour tests.
Accurate Data Reconstruction Methods for Unstructured Grid
Authors: Zhang Sijun
Published: October 2008

This paper presents accurate data reconstruction methods for unstructured grid to enhance the accuracy and robustness of CFD simulations for practical problems. The schemes consist of five novel approaches to more accurately reconstruct 1) the cell-centered data to cell faces, 2) gradient estimations, 3) skew terms for diffusion, 4) skew terms for conjugate wall, and 5) skewness correction for pressure-velocity-density coupling equation. These schemes have demonstrated effectiveness on some critical cases and many problems, and strong potential to improve the accuracy and robustness of CFD computations.
The Swirling Orifice Plate: A Flowmeter for All Reasons
Authors: Ahmadi A. , Beck S. B. M. , Stanway R.
Published: October 2008

The orifice plate flow meter is the most common form of differential pressure flow meter used in industry. The standard discharge coefficient, which is defined by both British Standard and ISO 5167, is only valid if the flow approaching the meter is perfectly settled and fully developed. However, in practical applications the flow approaching the orifice meter is often disturbed by pipe-fittings and consequently the measurements become inaccurate. Basically, the design of the orifice plate meters that are independent of the upstream disturbances is a main goal for orifice plate metering. This task can be achieved either by using a long straight settling length upstream and downstream of the orifice plate or using a flow conditioner upstream of an orifice plate. In addition, the standard orifice plate is vulnerable when metering dirty flow due to the accumulation of dirt in front of the orifice plate which can alter the accuracy of metering as well. In this paper the effect of the swirler flow conditioner for both standard and non-standard flow conditions has been investigated in an experimental rig and validation of the results has been justified with the appropriate CFD domains. In these investigations the effect of different designs of swirler flow conditioners have been examined in asymmetric and swirling flow profiles. The results so far show the cone swirler flow conditioner has a desirable effect for both asymmetric and swirling flow disturbances. They also show the error of metering for non-standard velocity profiles with the swirler flow conditioner is typically 1.5% compared to around 4% for a standard orifice plate. Moreover using a swirler conditioner tends to keep particles in suspension and thus prevents the accumulation of dirt particles in front of orifice plate. All experimental and numerical results here are presented for different velocity profiles both swirling and asymmetric profiles, mass flow rates and for β = 0.5.
Experimental Evaluation of the Flow Inside an Open Faced Impeller
Authors: Berchane Nader , Morrison Gerald L.
Published: October 2008

The pressure distributions and forces presented in a thesis by Hossain [1] for a centrifugal pump illustrated a somewhat complex inter-relationship between various geometric and operating parameters of the pump studied. The pump had an open faced impeller of 33.65 cm diameter with 5 blades of backswept design. It was felt that the best way to resolve some of the questions related to Hossain’s results was to determine the fluid velocity field inside the pump. The flow field through the impeller passages was measured using a 1-D Laser Doppler Velocimetry (LDV) system. The LDV was used to measure the radial and tangential velocity components over the region accessible through the two optical windows in the front of the pump housing. Five axial planes were investigated by recording measurements along two radial lines at azimuthal angles of 45° and 315° (with respect to the horizontal axis of the pump) for design operating conditions. A once per revolution signal was used to supply the LDV system with a reference for the rotor position. It was found out that a leakage flow existed near the front wall of the impeller at z/h = 0.11, which was generated by the pressure difference between the impeller exit and inlet. It was also concluded that the velocity field was not fully two-dimensional in nature. This was believed to be a result of the 90° turn that the fluid endures as it enters the impeller inlet from the suction pipe.
Using X-Rays for Multiphase Flow Visualization
Authors: Heindel Theodore J. , Hubers Jeremy L. , Jensen Terrence C. , Gray Joseph N. , Striegel Alexander C.
Published: October 2008

Gas-liquid, gas-solid, liquid-solid, and gas-liquid-solid multiphase flows are difficult to visualize, characterize, and quantify because the systems are typically opaque. Invasive or noninvasive measurement methods are typically used for determining internal flow and transport characteristics of these complex flows. The difficulty with invasive methods is that they can alter the internal flow of a multiphase system causing interference with realistic process measurements. X-ray imaging provides one family of noninvasive measurement techniques used extensively for product testing and evaluation of static objects with complex structures. These techniques have been extended to visualize dynamic systems, such as those which characterize multiphase flows. This paper will describe a new X-ray flow visualization facility for large-scale multiphase flows. X-ray radiography and X-ray computed tomography of static and dynamic systems will be used to demonstrate system capabilities. Radiographic images will show bread dough rising, objects falling in a liquid, large bubbles rising in a 32 cm ID column of water, and operation of a 32 cm ID bubble column. X-ray computed tomography of a large static object will demonstrate visualization capabilities. X-ray computed tomography of a multiphase flow in a 32 cm bubble column will show local time-averaged gas holdup values for various operating conditions. Finally, challenges associated with X-ray stereographic imaging to capture time-resolved dynamic events will be outlined.
Numerical Simulation of 3D Flow in Turbomolecular Pump by Direct Simulation Monte Carlo Method
Authors: Wang S. , Ninokata H.
Published: October 2008

A Turbomolecular pump (TMP) is one of the key apparatus to produce high and ultrahigh vacuum. It works mainly in the conditions of free molecular and transitional regimes, where the Navier-Stokes equations of continuum gas dynamics can not be correctly applied. In this study, the flow field in single blade row of one stage TMP is investigated by direct simulation Monte Carlo (DSMC) method with a 3D analysis in a rotating reference frame. Considering the Coriolis and centrifugal accelerations, the equations about the molecular velocities and position are deduced on this frame. The VSS model and NTC collision schemes are used to calculate the intermolecular collisions. The diffuse reflection is employed on the molecular reflection from the surfaces of boundary. The transmission probabilities are calculated and applied to analyze the relationship between the outlet pressure and the maximum pressure ratio. The pumping performances between H2 and N2 on the same blade speed and same blade speed ratio are compared and analyzed carefully. The maximum pumping efficiencies on the different blade angles are also calculated. Numerical results show good quantitative agreement with existing experiment data.
Field-Scale Evaluation of Leak Detection for Gas-Liquid Two-Phase Flow in Deepwater Production Systems
Authors: Griffin John M. , Smith John Rogers
Published: October 2008

This paper focuses on validating a theoretical method for the detection of leaks in deep water, multi-phase pipelines. [1] Six field-scale, two-phase flow tests were conducted to compare small leaks with a no-leak condition. These tests qualitatively demonstrate the feasibility of Scott’s concept. Knowing the characteristic pressure loss versus throughput in a line without a leak provides a basis for determining the presence of a leak by measuring pressure loss and flowrate out of the line. If the pressure loss is higher than expected for that flowrate, a leak is a likely possible cause. In these full-scale tests, a leak was readily detectable once the leak rate exceeded 16 percent for the case where the average rate exiting the line was 547 MCFPD. These tests were performed on a 3.64 inch (9.25 cm) internal diameter 9,640 foot (2,938 m) long flow loop with the leak occurring at the midpoint.
CFD Simulation of Segregation in Particulate Multiphase Flows With Binary Solids
Authors: Hao Zuoxin
Published: October 2008

Segregation in particulate multiphase flow with binary solid mixture has extensive applications in industrial separation processes. Up to now there have been few attempts towards numerical simulation of segregation in particulate multiphase flow with binary mixture due to complexity of the problem. In view of this, the primary objective of present work is to simulate the problem by computational fluid dynamics (CFD) and to validate by comparison with experimental measurements. Eulerian-Eulerian approach, incorporating the granular temperature, an essential ingredient in the solids pressure and solids viscosity formulation, was used to model the flow field of multiphase flow and was solved by Fluent 6.0. The CFD simulation results have been validated by experiments of liquid fluidization of binary solid mixtures. Validation results show that CFD simulation predict segregation and solid volume fraction profile precisely, and in addition, it can supply a more realistic prediction of other hydrodynamic features of the multiphase flow, such as velocity vector of all phases and pressure drop. The success of such CFD simulations opens doors for many potential studies.
Traceability of Thermal Power Measurments: Modified Venturi Tubes
Authors: Estrada Herb , Augenstein Don , Hauser Ernie
Published: October 2008

This is the second of two papers describing the traceability of nuclear feedwater flow measurements. The first considered the challenges and methodology for establishing the traceability of chordal ultrasonic flow meters. This paper considers the challenges of establishing the traceability in a measurement using a flow element of the modified venturi tube type. It specifically considers the assumptions and uncertainties associated with the extrapolation, for use in the field, of tube calibration factors measured in the laboratory. To quantify these uncertainties, the in-situ performance of four modified venturi tubes is compared with the performance of four 8-path chordal ultrasonic flowmeters. The data analyzed were collected in the feeds of four steam generators in a large pressurized water reactor plant, each feed containing one meter of each type. The meters were initially calibrated in this series arrangement in a NIST traceable calibration lab and then operated in the same arrangement in the field.
A Study of Optimization of Blade Section Shape for a Steam Turbine
Authors: Chung Kyung-Nam , Kim Yang-Ik , Sung Ju-Heon , Chung In-Ho , Shin Sang-Hoon
Published: October 2008

In this study, an optimization design method is established for a rotor blade of a Curtis turbine. Bezier curve is generally used to define the profile of turbine blades. However, this curve is not proper to a supersonic impulse turbine. Section shape of a supersonic turbine blade is composed of straight lines and circular arcs. That is, it has several constraints to define the section shape. Thus, in this study, a blade design method is developed by using B-spline curve in which local control is possible. The turbine blade section has been changed by varying three design parameters of exit blade angle, stagger angle and maximum camber. Then flow analyses have been carried out for the sections. Lift-drag ratio of the blade section is used as the object function, and it is maximized in the optimization. Second-order response surface model is employed to express the object function as a function of design parameters. Central composite design method is used to reduce the number of design points. Then, an evolution strategy is employed to obtain the optimized section of the Curtis turbine blade.
Special Instrumentation and Hydraulic Turbine Flow Measurements Using a Pressure-Time Method
Authors: Kubiak Janusz , Urquiza Gustavo , Adamkowski Adam , Sierra Fernando , Janicki Waldemar , Rangel Reynaldo
Published: October 2008

The objective of the work was to evaluate the efficiency of a hydraulic turbine by means of the flow measurement, for a given water head. The hydraulic turbine of 180 MW output has been in service for 20 years. The real value of efficiency was needed in order to proceed with minor/mayor modifications to improve it. In a case of a runner deterioration the pressure-time (the Gibson) method was chosen to proceed with a test for flow determination. However, to measure the pressure in the penstock no access from the external space of the penstock was found, so the special instrumentation had to be developed, which could be installed inside different sections of the penstock for determination of the pressure as required by the Gibson method. After the successful installation of the pressure transducers and a special hermetic capsule, from which a cable was laid through the manhole to the control room, the test was carried out at different loads applying the Gibson method. Simultaneously, the instrumentation for the Winter-Kennedy method was installed and calibrated during the test. In the paper all the turbine measured characteristics are given and discussed. It was concluded that the efficiency of the hydraulic turbine was still high and no modifications were necessary. Having instruments calibrated for the Winter-Kennedy method other curves can be obtained at different heads.
A Volume Tracking Method Based on Advanced Subgrid Counting Algorithm
Authors: Hayashi Kosuke , Myint Win , Sou Akira , Tomiyama Akio
Published: October 2008

A volume tracking scheme, ASCA (Advanced Subgrid Counting Algorithm), which is easily extendable to three-dimensions and possesses a good volume conservation property, is proposed. To examine the potential of ASCA, several two-phase flow simulations are carried out. As a result, the following conclusions are obtained: (1) Predicted shapes and breakup characteristics of single fluid particles in simple shear flows agree well with available data even with a low spatial resolution, (2) A water drop impinging on water surface and an air bubble rising through a stagnant water are successfully simulated with little errors in volume conservation, (3) Predicted shapes and terminal velocities of single drops in stagnant liquids under wide ranges of the viscosity ratio and Morton number agree well with measured one, and (4) In spite of a low spatial resolution, vapor bubbles flowing in a strong shear flow are simulated with good volume conservation. The interface sharpness is well preserved even after a large deformation of bubbles.
Propagation of Pressure Waves, Caused by a Thermal Shock, in Liquid Metals Containing Gas Bubbles
Authors: Okita K. , Matsumoto Y. , Takagi S.
Published: October 2008

Propagation of pressure waves caused by a thermal shock in liquid metals containing gas bubbles is performed by a numerical simulation. The present study examined the influences of bubble radius and void fraction on the absorption of thermal expansion of liquid metals and attenuation of pressure waves. As the result of the calculation, since the large bubbles which have a lower natural frequency than the small bubbles cannot respond to the heat input, the peak pressure at the heated region increases with increasing bubble radius. Especially, when the bubble radii are around 500 μm, the pressure wave propagates through the mixture not with the sonic speed of the mixture but with that of liquid mercury. On the other hand, decreasing the void fraction makes behavior of bubbles nonlinear and a collapse of bubble produces a high pressure wave. However, the calculation shows that the method of introducing micro gas bubbles into liquid metals is effective to prevent cavitation erosion on the wall.
Gas-Core Turbulence Structure of Annular Flow Passing Through a Throat Section Affected by the Wavy Interface on Liquid Film Flow
Authors: Yoshida Kenji , Miyabe Masaya , Matsumoto Tadayoshi , Kataoka Isao
Published: October 2008

Experimental studies were made on the gas-core turbulence structure in vertical upward annular two-phase flow passing through a round tube with a throat section. The gas-core turbulence is affected and modified by the dynamic interaction between gas-core flow and liquid film flow through the wavy interface. The test channel has a throat section, which consist of nozzle, throat and diffuser part, where the cross sectional area of the channel is changed along the flow direction. In the throat section, the flow is in transient state because the flow is accelerated or decelerated along the flow direction as the cross sectional area of the channel is changes. The gas-phase turbulence structure such as the time-averaged velocity profiles and fluctuation velocity profiles were precisely measured by using the constant temperature hot-wire anemometer. For the liquid film flow, the time-averaged film thickness, base-film thickness and interfacial wave height were obtained by using the point electrode resistivity probe. Direct observations for the interfacial waves on liquid film flow such as disturbance waves and ripple were also carried out by using the high-performance camera system to make clear the interfacial wave structure.
Characteristics of Ambivalent Flows in Diamond-Shaped Cylinder Bundles With Slit Flow
Authors: Umeda S. , Manmoto S. , Horii K.
Published: October 2008

A new nozzle using a composite flow network has been developed for plain air film stabilization without film break. The design consists of a slit duct with layers of diamond-shaped cylinder bundles. Tests were conducted using air at average velocity of 8m/s. The new nozzle had a stabilized length in its flow direction stretching 2 times, compared to a conventional slit design. The development of new nozzle was based on fluid dynamic theory. A new type of intersecting flow networks, to be referred to as composite flow network, was constructed consisting of ambivalent flows superposed with con-current thin-film flows in diamond-shaped cylinder bundles. Our previous experiments have revealed the occurrence of flip-flop flow with self-sustained flow oscillations and the generation of longitudinal vortices in the diamond-shaped cylinder bundle. It is conceivable to extend longitudinal vortex flow in composite flow networks through interacting with flip-flop flow exiting from a pre-fixed multiple-intersecting flow network in order to strengthen and thus stretch its efflux.
Simulation of Cavitating Inducer in Rocket Engine Turbopump
Authors: Kimura Toshiya , Yoshida Yoshiki , Shimagaki Mitsuru
Published: October 2008

CFD simulations were applied to cavitating flows around an inducer of a liquid rocket engine turbopump. Unsteady simulations were performed for the full 3D model of an inducer using a cavitation model. The inducer has been tested with water in the cavitation tunnel at JAXA-KSPL to examine suction performance and unsteady cavitation phenomena such as rotating cavitation and cavitation surge. Experiments were conducted under various flow conditions to examine a break-down point of the suction performance and unsteady cavitation phenomena. They have suggested that the casing geometry affected the onset of unsteady cavitation phenomena. Simulations were, therefore, performed for various cavitation numbers. The steady state was firstly calculated without a cavitation model, and then the unsteady calculation was done with the bubble two-phase flow model as a cavitation model. The effect of different model parameters on cavity structure was also examined. In the calculated results, it was clearly observed that the cavity structure grew on the blade surface and accompanied with vortices. These cavities showed dynamic change of their shapes as the rotation of the inducer. The calculated head coefficient showed decrease for small cavitation numbers with similar gradient to that observed in the experiment.
Analysis of the Lubrication Condition of a Crosshead Pin Bearing of a Large Marine Diesel Engine
Authors: Abanteriba Sylvester
Published: October 2008

The main function of the crosshead bearing of a crosshead engine is to transmit the load from the connecting rod, which is directly attached to the piston of the engine, through a second rod to the guide shoe, which bears the entire crosshead. Apart from this function it enables the large normal forces, which are usually borne by the piston skirt in the case of a trunk piston engine, to be transmitted to the guide shoe from which it is subsequently transmitted to the rails along which the guide shoe glides. The dynamics of the crosshead bearing is such that the bearing pin is subjected to very low levels of incomplete rotation resembling that executed by a pendulum over a reduced arc. The bearing is also subjected to the load in only one direction. These operating conditions augur poorly for the formation of the hydrodynamic oil film necessary to support the imposed load. This type of bearing is therefore susceptible to considerable friction losses and significant wear as a result of lack of the capacity to generate lubrication film. This paper evaluates a model to determine the levels of achievable hydrodynamic film and the measures introduced to generate a hydrostatic squeeze lubricating film in the bearing as a result of the introduction of high pressure oil during part of the operating cycle of the engine.
Numerical Investigations of Transonic Cavity Flow Control Using Steady and Pulsed Fluidic Injection
Authors: Das K. , Hamed A. , Basu D.
Published: October 2008

A numerical study is conducted to investigate steady and pulsed fluidic actuation in transonic flow over an open cavity. Numerical results are obtained for the unsteady three-dimensional flow with three different steady mass injection rates and one pulsed injection upstream of the cavity. The simulations are carried out using the full 3-D Navier Stokes equations with the two-equation k-ε based Detached Eddy Simulation (DES) model to calculate the flow and acoustic fields. Computational results are presented for unsteady pressure fluctuations, vorticity contours and kinetic energy profiles at different injection ratios. The sound pressure level (SPL) and the kinetic energy spectra highlight the effectiveness of actuation in tone attenuation at peak frequencies. The computed sound pressure level (SPL) spectra with and without injection are compared with available experimental data and LES predictions.
Comparative Study of the Aeroacoustic Behavior of Two Axial Flow Fans With Different Sweep Angles
Authors: Kouidri S. , Djaafer F. , Belamri T. , Rey R.
Published: October 2008

The purpose of this study is to determine the effect of the sweep angle used in axial flow fans on their aerodynamic and acoustic behavior. To do so, two fans, having the same aerodynamic characteristics, were designed with forward and radial sweep angles. The 3D numerical simulation allowed obtaining steady and unsteady loading on the blades. Instantaneous velocity profiles, located downstream of the fans, will be presented and compared to the experimental data. The Ffowcs Williams & Hawkings formulation was used to model the acoustic spectra. The results from CFD simulation (acoustic rotating dipole) were used as input data for the acoustic modeling. Predicted and measured acoustic spectra will be presented. It was found that the forward fan has a uniform radial distribution of kinetic turbulence. Also, the three downstream velocity components have better radial distributions. This result was confirmed by the experimental and predicted aeroacoustic results.
Modelling of Three-Phase Flow in Electro-Chemical Machining
Authors: Tsuboi Ryo , Toda Kazuyuki , Yamamoto Makoto , Nohara Ryuki , Kato Dai
Published: October 2008

Electro-Chemical Machining (ECM) is an advanced machining technology. It has been applied to highly specialized fields such as aerospace, aeronautics and medical industries. However, it still has some problems to be overcome. The efficient tool-design, electrolyte processing, and disposal of metal hydroxide sludge are the typical issues. To solve such problems, CFD is considered to be a powerful tool in the near future. However, the numerical method that can satisfactorily predict the flow has not been established because of the complex flow natures. In the present study, we investigate the modelling of the three-phase flow (i.e. fluid, hydrogen bubble and metal sludge) in ECM process. First, the developed code is applied to the two-dimensional channel configuration. The interactions among three-phases and the dissolved wall are simulated, to verify the modelling and to determine the model parameters, Next, the sinusoidal channel is machined by our code. It is confirmed that hydrogen bubbles in the separation region suppress the dissolution of the wall, and make the final wall shape be wavy. Through this study, it is exhibited that our developed model and code are sound and useful for simulating ECM process.
Advances of the Correlation Mapping Method to Eliminate the Peak-Locking Effect in PIV Analysis
Authors: Chen Jun , Katz Joseph
Published: October 2008

The Peak-locking effect causes mean bias in most of the existing correlation based algorithms for PIV data analysis. This phenomenon is inherent to the Sub-pixel Curve Fitting (SPCF) through discrete correlation values, which is used to obtain the sub-pixel part of the displacement. A new technique for obtaining sub-pixel accuracy, the Correlation Mapping Method (CMM), was proposed by Chen & Katz [1, 2]. This new method works effectively and the peak-locking disappears in all the previous test cases, including applying to both synthetic and experimental images. The random errors are also significantly reduced. In this paper, an optimization of the algorithm is reported. Using sub-pixel interpolation, the cross-correlation function between image 1 and image 2 is expressed as a polynomial function with unknown displacement, in which the coefficients are determined by the autocorrelation function of the image 1. This virtual correlation function can be matched with the exact correlation value at every point in the vicinity of the discrete correlation peak (a 5×5 pixels area is chosen in the present study). A least square method is used to find the optimal displacement components that minimize the difference between the real and virtual correlation values. The performances of this method at the presence of background noise and out-of-plane motion are investigated by using synthetic images, as well as the influence of under-resolved particle images, and compared with the result of the SPCF method. The advantage of the CMM over SPCF is demonstrated in these studies.
Accommodating Last Minute Changes: Two Phase Separation Performance Validated by CFD
Authors: Swartzendruber Jason , Fadda Dani , Taylor David
Published: October 2008

At the last minute, a separation vessel is adapted in response to an unexpected alteration in its original design. While vessel internals are undergoing fabrication in the shop, a revised external piping layout necessitates changes to the overall vessel design. This vessel is compact and its design takes full advantage of its exact geometry. Specifically, the inlet and outlet orientations, to be modified, are critical to the original design. To keep the project on schedule, a new design, created and validated by an expedited computational fluid dynamics (CFD) study, is proposed for installation in 2005. The steps taken to validate the design are described in this paper.
Study the Structure of Three Dimensional Oblique Shock Waves Over Conical Rotor-Vane Surfaces
Authors: Alhussan Khaled
Published: October 2008

This paper will explain the numerical analysis and the mapping of the flow in a confined region. In this paper some characteristics of non-steady, compressible, flow are explored, including compression and expansion wave interactions and creation. The results will show a promising achievement, first, to understand the flow structure inside a supersonic confined region, second, to use this knowledge to interpolate the numerical results in order to achieve a design methodology that will benefit the industrial applications for example in turbomachinery. Results including contour plots of static pressure, total pressure, and Mach number will show the structure of oblique shock waves in a complex three-dimensional conical surface. A CFD analysis enables one to understand the complex flow structure inside this confined region. Through this computational analysis, a better interpretation of the physical phenomenon of the three dimensional rotting oblique shock waves can be achieved. It is essential to evaluate the ability of numerical technique that can solve problems in which compression and expansion waves occur. In particular it is necessary to understand the details of developing a mesh that will allow resolution of some discontinuities in similar flow.
Computational Analysis of High Speed Flow Over a Double-Wedge for Air as Working Fluid
Authors: Alhussan Khaled
Published: October 2008

The work to be presented herein is a Computational Fluid Dynamics analysis of flow over a 15-degree angle double wedge for a compressible air, with Mach number of 2.95. The problem to be solved involves formation of shock waves, expansion fans and slip surfaces, so that the general characteristics of supersonic flow are explored through this problem. Shock waves and slip surfaces are discontinuities in fluid mechanics problems. It is essential to evaluate the ability of numerical technique that can solve problems in which shocks and contact surfaces occur. In particular it is necessary to understand the details of developing a mesh that will allow resolution of these discontinuities. Results including contour plots of pressure, temperature, density and Mach number will show that CFD is capable of predicting accurate results and is also able to capture the discontinuities in the flow, e.g., the oblique shock waves and the slip surfaces. The global comparison of some parameters between the numerical and the analytical values show a good agreement.
Flow Modeling for a Simple Cycle Turbine Equipped With Selective Catalytic Reduction System for NOx Control
Authors: Nguyen Khoa , Fadda Dani , Buzanowski Mark
Published: October 2008

A selective catalytic reduction (SCR) system, when designed for a simple cycle turbine, presents a significant calculation and modeling challenge due to its compact design and stringent performance requirements. In particular, uniform flue gas velocity profiles, required by environmental catalysts installed in the ductwork of this system, must be met. Custom flow devices optimized for the turbine. SCR system and ductwork are required. Cold flow and computational fluid dynamics (CFD) modeling are employed to design flow devices that provide adequate velocity profiles. The purpose of this paper is to present (1) steps taken to optimize the ductwork internals and (2) measured and calculated velocity profiles.
Curvature Law of the Wall for Swirling Axial Flows
Authors: Xi Jinxiang
Published: October 2008

A new law of the wall accounting for curvature effects for swirling axial flows was derived. The curvature influence on turbulent mixing lengths in both axial and tangential directions was examined theoretically using Reynolds Stress Model. For equilibrium flows and weak curvature, identical mixing lengths were derived for both directions. In addition, the effect of shear stress ratio on the near-wall velocities was explored systematically. It was found that the curvature effect in swirling axial flows was suppressed by a factor of 1/(1+σw2) compared to that in curved channel flows. Considerably improved agreement with measurements was obtained for the new curvature law compared to the classical logarithmic law.
Steady Circulation Generated From Oscillating Flow Through a Hollow Cone at the Exit of a Pipe
Authors: Dean Adam , Smith Barton L. , Humes Zachary E.
Published: October 2008

A numerical approach to optimizing heat removal from a standing wave thermoacoustic engine by generating steady circulation at the outlet is described. The open-ended standing wave engine makes use of a hollow cone placed opening outwards and flush with the open end of the engine. Parallel paths within and without the cone create asymmetric minor losses. These are designed to induce circulation and heat removal. If successful, this will eliminate the need of a cold heat exchanger. The numerical models make use of the commercial RANS numerical solver FLUENT. Orders of magnitude increase in heat flux out of the engine’s open tube as compared to an engine without a cone are demonstrated. Three cones are evaluated at a range of flow parameters. Performance is found to be a strong function of the displacement amplitude compared to the engine diameter. In addition, these results are compared to an experiment that provides velocity data.
Effect of Tooth Bending Damage on the Leakage of Straight-Through Labyrinth Seals
Authors: Xu Jinming , Ambrosia Matthew S. , Rhode David L.
Published: October 2008

Unavoidable rotordynamic impacting on labyrinth seal teeth sometimes occurs when centrifugal compressors, for example, undergo transients. Consequently, the labyrinth seal teeth are damaged or disfigured in various ways when the surface opposite to the teeth is non-abradable. Thus far, no quantitative information concerning the effect on seal leakage is available. The present work focuses on the effect of seal leakage due to such permanently bent labyrinth seal teeth. The investigation was done numerically by solving the 2-D, axisymmetric RANS equations with a finite-volume algorithm. The high-Reynolds number k-ε turbulence model was used with standard wall functions. A broad variety of tooth seal bending was studied by varying the bending curvature and the length of bending, as well as the after-bend tooth radial clearance. The results show that the bending damage drastically affects the leakage as well as the flow pattern. This is due largely to the altered clearance caused by the bending. However, other bending factors, such as the bending curvature and the percentage of tooth length that is bent, also contribute to the change of leakage and flow pattern.
Oscillating Flow in Adverse Pressure Gradients
Authors: Smith Barton L. , Mortensen Kristen V. , Wendel Spencer
Published: October 2008

Separating oscillating flow in an internal adverse pressure gradient geometry is studied experimentally. Phase-locked PIV measurements and simultaneous pressure measurements reveal that during the accelerating portion of the cycle, the flow remains attached in spite of a very large adverse pressure gradient. During the decelerating portion of the cycle, the flow is more prone to separation. The duration and extent of the separation depend strongly on the oscillation displacement amplitude relative to the cross-stream dimension. In some cases, the flow separates but reattaches as the separated shear layer is accelerated temporally. The time-varying pressure measurements are used to determine the resultant minor losses for the flow in each direction. These are found to be an increasing function of displacement amplitude and independent of the Reynolds number.