bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Approach to the Aeroelastic Behaviour of an Oscillating Plate Impinged by Interacting High Velocity Gas Jets
Authors: Regardin C. , Szechenyi E. , Marmonier F. , Nyirumulinga Y. , Ohayon R.
Published: July 2010

Strip vibration is an important issue in the industrial steel cooling process using arrays of gas jets. Indeed, the recent growing demand for “rapid cooling” has led to a significant increase in jet velocities and some complex sheet flutter phenomena have appeared where, under certain conditions, the strip motion couples with the aerodynamic action of the jets. This aeroelastic behaviour can cause large strip oscillations and even divergence implying a strong risk of contact with the blowing boxes, which can seriously damage the strip. From observations it was assumed relevant to consider the strip as a rigid plate oscillating on its fundamental torsion mode. Hence the system is modelled as a damped oscillator with one degree of freedom in torsion and the aeroelastic forces on the plate are assumed to be a linear combination of the plate’s angular position and its time derivative. These forces can be expressed in terms of an aeroelastic stiffness coefficient and an aeroelastic damping coefficient. If one of these two coefficients becomes critical, one of two instabilities can occur: namely either divergence or flutter. A simplified half-scale model of an industrial cooling unit was built, in line with the above assumptions consisting of a rigid plate oscillating in torsion between arrays of round jets impinging on it on both sides. The measured angular position of the plate yielded the aeroelastic stiffness and damping coefficients. A parametric study led to the definition of a relevant governing reduced velocity based on the jet-to-plate distance and showed different blowing configurations where existing divergence was shifted to higher reduced velocities or even totally cancelled. Although the divergence instability of the system was well demonstrated, the role of the aeroelastic damping coefficient on the plate’s oscillations was not well identified and the industrial problem thus remains unsolved. Therefore further work is focusing on the aeroelastic behaviour of different configurations of interacting jets impinging on a rigid plate. Here the plate is forced to oscillate in torsion and is instrumented with pressure sensors (96 for an 18 cm2 jet impingement surface) to measure the unsteady jet force and provide local aeroelastic coefficients. As the plate can be translated in the three coordinate directions, surface mappings of the unsteady jet forces are obtained and analysed to give some insight into the characteristics of the aeroelastic behaviour. The integrated forces are also correlated with the earlier results.
Multiphase Modelling of the Steel Grade Transition in a Continuous Casting Tundish
Authors: Ferna´ndez Oro Jesu´s Manuel , Santolaria Morros Carlos , Rodri´guez Somoano Javier , Alvarez Ordieres Mo´nica
Published: July 2010

Nowadays, continuous casting is extremely conditioned by sequences of different steel grades that produce a large amount of intermixed steel. Due to customer requirements, steel producers are forced to deliver a few slabs of high-specialized steels, so the number of castings handling steels of dissimilar grades has been significantly increased in recent years. As a consequence, manufacturers are particularly concerned with the development of practical methods to know exactly where the mixed regions begin and end, in order to make a precise classification of the steel grade that has been produced and avoid further downgrading. Pioneering works by Huang and Thomas introduced a 1-D model to estimate the intermixed region during a grade transition. This model reached a notable popularity because of its ability to provide on-line predictions, though it is assumed that mixing inside the tundish is globally determined with a number of fixed parameters. Recently, Cho and Kim have introduced a modification reducing the number of parameters required, but with the full unsteady description of the tundish flow still unresolved. Moreover, all these models require experimental calibration, using the results from full-scale water models. Additionally, other researchers have been focused on the development of numerical simulations to analyze the flow structures and mixing features of the tundish, mainly during stable operation, but using limiting simplifications and/or steady schemes. In the present investigation, to the author’s knowledge, a 3D, unsteady numerical simulation using a volume-of-fluid formulation is carried out for the first time. With this technique, the transient behavior of the tundish during the ladle change can be fully modelled, tracking the free surface and extending the computations towards the steady state. A transport equation is resolved for a non-reactive scalar, representing a dimensionless concentration, so it is possible to predict the mixing degree of the steel at the tundish exit for different operating conditions. The final objective is the development of an off-line methodology to estimate precise intermixing periods during grade transition in continuous casting.
Unsteady Flow Over a Dragonfly Wing-Section Model
Authors: Salajegheh Sadid , Tadjfar Mehran
Published: July 2010

Here we study the flapping of a dragonfly’s wing section where the frequency of the wing flapping is about 25–30 HZ. We have translational and rotational velocities in a single stroke. In this article we investigate dragonfly’s 2D sections and we want to study the effect of the corrugations during unsteady flight at low Reynolds number. We find that in contrast to the published results for steady flow over the wings, where the corrugation seems to have improved the performance over a profiled wing-section, here a simple flat plate seems to perform better than the corrugated one. However, the corrugated wing-sections have a better aerodynamic performance than the traditional profiled wing-sections. The flow Reynolds number in this study is 8000.
Comparison Between Grad’s and Quadrature-Based Methods of Moments for the Numerical Simulation of Unsteady Particle-Laden Flows
Authors: Le Lostec Nechtan , Villedieu Philippe , Simonin Olivier
Published: July 2010

We present here a new method of moments for the numerical simulation of particle-laden flows. The closure needed in Eulerian methods relies on writing the kinetic descriptor, the velocity destribution function, as a sum of delta-functions instead of the one-delta-function or close-to-Maxwellian assumption in existing methods. The closure velocity distribution function parameters are computed from the transported moments using a quadrature method. Simulation results are compared to those of a close-to-Maxwellian-based Eulerian method and those of a reference Lagrangian simulation, considering only transport and drag of particles in a Taylor-Green fluid flow. For a particular Stokes number of 1 the velocity distribution function is far from equilibrium and particle trajectory crossing is an important feature. We find that the quadrature-based method performs better than the close-to-equilibrium-based method, giving moment profiles closer to those of the Lagrangian reference simulation. However significant differences still remain between quadrature-based and Lagrangian methods results.
Fluid-Structure Interaction Simulation of Blood Flow Inside a Diseased Left Ventricle With Obstructive Hypertrophic Cardiomyopathy in Early Systole
Authors: Moghaddaszade-Kermani Ahmad , Oshkai Peter , Suleman Afzal
Published: July 2010

Mitral-Septal contact has been proven to be the cause of obstruction in the left ventricle with hypertrophic cardiomyopathy (HC). This paper presents a study on the fluid mechanics of obstruction using two-way loosely coupled fluid-structure interaction (FSI) methodology. A parametric model for the geometry of the diseased left ventricular cavity, myocardium and mitral valve has been developed, using the dimensions extracted from magnetic resonance images. The three-element Windkessel model [1] was modified for HC and solved to introduce pressure boundary condition to the aortic aperture in the systolic phase. The FSI algorithm starts at the beginning of systolic phase by applying the left ventricular pressure to the internal surface of the myocardium to contract the muscle. The displacements of the myocardium and mitral leaflets were calculated using the nonlinear finite element hyperelastic model [2] and subsequently transferred to the fluid domain. The fluid mesh was moved accordingly and the Navier-Stokes equations were solved in the laminar regime with the new mesh using the finite volume method. In the next time step, the left ventricular pressure was increased to contract the muscle further and the same procedure was repeated for the fluid solution. The results show that blood flow jet applies a drag force to the mitral leaflets which in turn causes the leaflet to deform toward the septum thus creating a narrow passage and possible obstruction.
Pump Mixing Process Calculations
Authors: Strongin Mikhail P.
Published: July 2010

The mixing of two or more liquids is very common in many industrial applications. In some cases the liquids set on the pump inlet. The mixing process of two fluids in a pump is investigated in the presented work. Different pump geometries have been studied with comparison of steady state and transient results. Turbulence closure model k-w has been used for simulations. The pump model consists of suction, impeller and discharge parts which were meshed and calculated together. This, for instance, naturally permits the effects of non-uniformity of velocity and liquids concentrations distribution on the impeller eye and on the inlet of the discharge segment to be taken into account. Commercial code Fluent 6.3.26 was used for CFD computations. A sliding mesh for transient calculations and the Multiple Reference Frame (MRF) model for steady state calculations were used with the total number of cells from four to eight million. The results show a significant change in the mixing uniformity coefficient γ, depending on where on the inlet the injected fluid is located. In the annular injection on the pump inlet, γ is close to 1 (an ideal mixture) on the outlet; whereas, γ is less than 0.9 for strong angular asymmetry injection on the pump inlet. The latter is not sufficient for some applications. Furthermore, the following transient effect is observed. Large oscillations of concentration and γ with the blade passing frequency takes place on the impeller section. However, the value of γ oscillations on the impeller – discharge interface is relatively small and fades very quickly when the distance from the impeller outlet exceeds two outlet diameters.
On Modeling of Condensation-Induced Water Hammer in Horizontal Pipe
Authors: Tiselj Iztok , Sˇtrubelj Luka
Published: July 2010

Condensation-induced water hammer, which appears when horizontal pipe filled with hot vapor is being slowly flooded with cold liquid, is known to be very stochastic phenomena. Time and position of the slug that is followed by the rapid condensation of the bubble behind the slug, is very sensitive to the minor changes in the experimental setup and consequently: results of the simulations are also very sensitive to the minor changes of the physical and numerical parameters in the model. Selected condensation-induced water hammer experiments performed on PMK-2 (AEKI, Hungary) device were numerically modeled with three-dimensional two-fluid model of computer codes NEPTUNE CFD. In most of the experimental cases, slow flooding of the pipe was abruptly interrupted by a strong slugging and water hammer, while in the experimental runs selected in the present work, the transition from the stratified into the slug flow was not accompanied by the water hammer pressure peak. That makes these cases more suitable tests for evaluation of the various condensation models in the horizontally stratified flows and puts them in the range of the available CFD (Computational Fluid Dynamics) codes. The key models for successful simulation appear to be the condensation model of the hot vapor on the cold liquid and the interfacial momentum transfer model. The surface renewal types of condensation correlations, developed for condensation in the stratified flows, were used in the simulations and were applied also in the regions of the slug flow. The CFD simulations quantitatively capture the main phenomena of the experiments, while the stochastic nature of the particular condensation-induced water hammer experiments does not allow detailed prediction of the time and position of the slug formation in the pipe. It is shown that even the selected experiments without water hammer present a tough test for the applied CFD codes.
Development and Experimental Validation of 3D Acoustic-Vortex Numerical Procedure for Centrifugal Pump Noise Prediction
Authors: Timushev Sergey
Published: July 2010

Numerical procedure of 3D flow induced noise modeling in centrifugal pumps is developed by linking the acoustic-vortex computational method of pseudo-sound and noise prediction that earlier was implemented in two dimensional prediction of pressure pulsations and noise and CFD code FlowVision. The 3D CFD–CAA acoustic-vortex method is validated by experiments on axial and centrifugal ventilators. Measurements of pressure pulsations and noise are completed for a wide range of rotation speeds. Further computational tests are made for a centrifugal boiler feed pump stage with and without vane diffuser.
The Effects of Various Surface Forces on Low-Density Particle Motion
Authors: Dorgan Andrew J. , Loth Eric
Published: July 2010

A new equation of motion is applied to bubbles and sand particles injected near the wall in a direct numerical simulation of a turbulent boundary layer of water. The surface-forces are considered systematically to assess their effect on particle motion, concentration, diffusion rates, and Lagrangian statistics. The results show that strong lift forces can be obtained when the particle’s terminal velocity is aligned with the freestream direction but only small effects are obtained if the terminal velocity is directed away from the wall. While finite Reynolds number effects are found to be small for the quasi-steady drag force, the choice of history force model is quite sensitive—an effect attributed to the long “memory” of the creeping flow expression. In general, the Lagrangian statistics were found to be the most sensitive output, sometimes varying largely between choice of surface-forces.
Analysis of Cavitation Instabilities in a Four Blade Inducer
Authors: Coutier-Delgosha O. , Dazin A. , Caignaert G. , Bois G.
Published: July 2010

The cavitating behavior of a four blade inducer tested in the LML laboratory large test facility is considered in the present paper. Experimental investigations based on unsteady pressure measurements and records from a six components balance mounted on the inducer shaft are performed. Spectral analysis of the signals enables to detect several characteristic frequencies related to unbalanced two-phase flow patterns. The objective of the present paper is the understanding of the physical phenomena associated to these frequencies. Therefore, wavelet decomposition, flow visualizations, and direct analysis of the high-frequency force, moment, and pressure signals are applied. Results at nominal flow rate only are considered. Not only classical unbalanced cavitation patterns, but also unexpected flow organizations are discussed.
Topology Optimization for Thermal Transport
Authors: Pingen Georg , Meyer David
Published: July 2010

The design of flow channels and surfaces to promote maximum heat transfer is of great importance, for example, in electronic cooling applications. In order to design surfaces optimized for maximum heat transfer under known flow conditions, a coupled thermal-fluid topology optimization approach based on the thermal lattice Boltzmann method (LBM) is introduced. Based on prior hydrodynamic topology optimization work, a Brinkman type porosity model is used. Every computational element/LBM node is varied continuously from fluid to solid, as traditionally done in fluidic topology optimization. This allows the formation of new boundaries and the generation of new designs. In addition, the present approach varies the thermal diffusivity from that of a fluid to that of a solid, permitting topology optimization for heat transfer applications while considering the thermal properties of both fluid and structure. The formulation of the optimization problem and sensitivity analysis is discussed and illustrated for a 2D example applicable to electronic cooling.
A Study of Propagating Speed of Rotating Cavitation Based on Numerical Analysis
Authors: Iga Yuka , Yoshida Yoshiki
Published: July 2010

In this study, by reproducing flowfields of several kinds of cavitation instabilities by numerical simulation of unsteady cavitation in three blades cyclic cascade, occurrence mechanism of rotating cavitations in cascade are attempted to clarify. “The order of appearance of rotating cavitations” and “the discontinuity of the propagation speed at the transition” are still not clarified. From the present study, it is found that they can be explained by existence of latent rotating-stall and decrease of frequency of cavity break-off with development of the cavity. And our numerical results agree with the predicted rotating speed of rotating cavitation and break-off frequency of cavitation. Additionally, difference of sub-synchronous rotating cavitation and rotating-stall cavitation, they are both sub-synchronous phenomenon but have different propagation speed, is explained according to their occurrence mechanism.
Fluid Flow Phenomena and Droplet Size Distribution Along the Feed Spreader of Large Oil/Water Tank Separators
Authors: Severino Jose G. , Gomez Luis E. , Leibrandt Steve J. , Mohan Ram S. , Shoham Ovadia
Published: July 2010

Large gravity separation tanks play an essential role in crude oil production in many fields worldwide. These tanks are used to separate water from an oil-rich stream before safely returning it to the environment. The oil/water dispersion enters the tanks through a feed spreader consisting of an array of pipes with small effluent nozzles. A major challenge is being able to predict oil/water dispersion distribution along the spreader as well as, the maximum water droplet size exiting through the effluent nozzles, under a given set of conditions. The capacity of the studied tank is 80,000 barrels (12,719 m3). Current feed stream is about 60,000 bpd (9,540 m3/day) of wet crude containing about 20% water by volume. A significant increase in flow rates and water volume fraction is anticipated [7], as more wells are added and existing ones mature. This work is aimed at investigating the separation performance of these tanks under current and future flow conditions; focusing primarily on the flow phenomena and droplet size distribution inside the spreader. The main objective is then to identify the impact of the spreader’s geometry and piping configuration on flow behavior and tank’s separation efficiency. The final product provides key information needed for mechanistic modeling the tank separation performance and optimizing tank components’ design. The feed spreader is simulated using Computational Fluid Dynamics (CFD) to assess oil/water flow distribution inside the network. Droplet size distribution along branch-pipes effluent nozzles in, including droplet breakup and coalescence has been studied using the Gomez mechanistic model [2] with input from CFD results. An experimental investigation of the spreader using a scaled prototype was also conducted to better understand flow phenomena and verify the CFD models. Results confirm the occurrence of significant maldistribution of the water and oil phases along the spreader that could impair separation efficiency.
Investigation of Hydraulic Design for High Performance Multi-Stage Pump Using CFD
Authors: Nagahara Takahide , Inoue Yasuhiro
Published: July 2010

We investigated the hydraulic design and flow field in a multi-stage pump to achieve high efficiency and low cavitation performance using computational fluid dynamics (CFD) and experimental approaches. The subject of the investigation is a four-stage centrifugal pump, which consists of a suction bend, impellers, stators, and a discharge volute. In designing a high performance multi-stage pump, it is important to investigate the interaction of flows between the stator and impeller, which were also investigated individually for minimizing hydraulic loss. The flow field in the suction bend, therefore, was simulated first using conventional CFD based on the Reynolds-Averaged Navier-Stokes (RANS) equations, and the calculated result of the flow field at the outlet of the suction bend was used to design the impeller inlet shape at the design-flow rate. To obtain a high-performance impeller shape, the effect of the meridional configuration of the impeller on hydraulic loss was examined using a parameter design based on conventional CFD results. The meridional shape was composed of several design parameters such as inlet, outlet diameter and so on, and a few parameters, which contribute to reducing hydraulic loss significantly, were extracted using the parameter design. Therefore, we obtained a highly efficient impeller shape by adjusting those important parameters. Finally, to evaluate and confirm the interaction of the flows between the stators and impeller, a numerical calculation of the four-stage pump was carried out using advanced large eddy simulation (LES). As a result, we obtained the predicted flow field in the four-stage pump. There was no significant flow separation at the inlet of each impeller and it was confirmed that the blade design was appropriate. The hydraulic performance of the four-stage pump was also confirmed using a model pump test. The inception of cavitation was observed and the cavitation coefficient estimated using experimental results was in good agreement with the CFD prediction. As a result of this development including the investigation described above, the hydraulic shape of a highly efficient and high-cavitation performing four-stage pump was obtained.
Study of Foam Flow in a Gas-Liquid Cylindrical Cyclone (GLCC) Compact Separator
Authors: Guzma´n No´lides M. , Shoham Ovadia , Mohan Ram
Published: July 2010

Aqueous foam flow behavior in a Gas-Liquid Cylindrical Cyclone (GLCC) is studied experimentally and theoretically with the objective of determine the operational envelop for foam break up. An existing experimental two-phase facility was modified to enable foam flow characterization. Several experimental data were acquired for aqueous foam using a compact inlet cyclone. These include: foam characterization in static trap sections, and foam flow behavior in the cyclone. Saint-Jalmes et al. (2000) model has been modified for characterization of foam evolution in static trap sections including the prediction of the drainage interface height with time. In addition, a new model for the prediction of the operational envelop for foam break up in the cyclone based on foam characteristics was developed. Good agreement is observed between the experimental data and the predictions of the models. It can be concluded that depending on the operational conditions the GLCC can act either as a foam breaker or as a foam generator. The developed model for the prediction of the operational envelop for foam break up separates these two modes of operations of the GLCC.
Experimental Investigation of Liquid Entrainment in Gas in Horizontal Pipes
Authors: Mantilla I. , Gomez L. , Mohan R. , Shoham O. , Kouba G. , Roberts R.
Published: July 2010

The objective of this project is to investigate experimentally the phenomena of liquid entrainment in gas in horizontal pipes. This report contains the results of an experimental study on wave characterization. Entrainment in annular flow in horizontal pipes has been studied experimentally. It has been found out that wave characteristics and entrainment fraction are strongly interrelated and must be utilized together in any related analysis. Two experimental facilities, 2-inch and 6-inch diameter, have been designed, constructed and utilized for entrainment measurements in stratified and annular horizontal flow. For the 2-inch flow loop, the range of superficial liquids velocities are 0.35 cm/s to 10 cm/s, and from 2 m/s to 80 m/s for the superficial gas velocities. For the 6-inch flow loop, the ranges of the superficial liquid velocities and superficial gas velocities are from 0.35 cm/s to 10 cm/s and from 2 m/s to 20 m/s, respectively. Appropriate instrumentation for entrainment (adjustable liquid film extractor) and liquid film characteristics (conductance probes and multi-channel conductivity meter) measurements have been developed and implemented. The effects of fluid properties on entrainment and wave characteristics have been studied by utilizing air-water-Butanol solution (surface tension effects) and air-water-Glycerin solution (viscosity effects). Simultaneous measurements have been carried out for both wave characteristics and entrainment for a wide range of flow conditions. Closure relationships have been developed based on the data for wave celerity, frequency, amplitude and spacing. The entrainment fraction has been normalized with the maximum entrainment fraction and correlated with the ratio of the superficial gas velocity to the superficial gas velocity at the onset. The wave amplitude (Δhw) normalized by the film thickness (hL) tends to values of Δhw / hL = 0.2 to 0.3 for high gas rates. The wave spacing (Lw) for air-water normalized by the mean film thickness (hL) exhibits a clear linear behavior with gas velocity, almost independent of the liquid velocity.
Intelligent Control of Compact Multiphase Separation System (CMSS©)—Part II: Experimental Investigation
Authors: Sampath V. , Mohan R. , Wang S. , Gomez L. , Shoham O. , Marrelli J.
Published: July 2010

In this investigation, an intelligent control system has been developed for Compact Multiphase Separation System (CMSS©) which consists of integrated configurations of three compact separators, namely, Gas-Liquid Cylindrical Cyclone (GLCC©), Liquid-Liquid Cylindrical Cyclone (LLCC©) and Liquid-Liquid Hydrocyclone (LLHC). This is a two-part paper, the first part deals with the Modeling and Simulation of the CMSS© and the second part (current paper) deals with Experimental Investigation. A new dual differential pressure sensor system has been implemented and tested for GLCC©, to eliminate the error in liquid level measurement due to change in watercut. A new watercut based control system using downstream pump speed control has been designed and tested for the LLCC© system. A new cascaded control strategy for change in set-point of differential pressure ratio using underflow quality from hydrocyclone has been designed and developed. Comparison of CMSS© performance simulator and experimental results shows that the control system simulator is capable of representing the real physical system and can be used to validate the controller design. Fuzzy logic controller has been successfully implemented and tested. Experimental results show a similar trend as the dynamic simulator results for the various input conditions and scenarios. The results from theoretical and experimental studies have shown that Free Water Knock Out (FWKO) CMSS© system can be readily deployed in the field using the control system strategies designed, implemented and tested in this study. Reliability analysis for FWKO CMSS© system has been conducted. System reliability has been calculated from reliability of components and performance reliability of the system. A new protocol has been introduced to calculate performance reliability based on performance failure of the system from simulation data. This protocol has been proven to predict performance reliability of a new system which does not have prior information on failure of components or devices.
Optimum Design Configuration of Helical Savonius Rotor via Numerical Study
Authors: Zhao Zhenzhou , Zheng Yuan , Xu Xiaoyun , Liu Wenming , Zhou Daqing
Published: July 2010

A helical Savonius rotor with two blades and 180 degree helical angle is researched to optimize the rotor power coefficient CP via numerical study from different parameters like overlap ratio, diameter of endplates, and number of inner plates within buckets and aspects ratio. The results from the study show that the rotor gets better performances when overlap ratio equals to 0.19, or the diameter of end plates is around 10% more than that of the rotor rotation, or the number of inner plates is 6, or aspects ratio is 6.0. The maximum power coefficient CPmax of rotor reaches 0.21 when overlap ratio equals to 0.19, and the diameter of end plates is around 10% more than that of the rotor rotation, and the number of inner plates is 6, and aspects ratio is 6.0. The numerical study results coincide well with experimental results, that means the model results is credible.
A Fast 3D Inverse Design Based Multi-Objective Optimization Strategy for Design of Pumps
Authors: Zangeneh M. , Daneshkhah K.
Published: July 2010

A methodology for designing pumps to meet multi-objective design criteria is presented. The method combines a 3D inviscid inverse design method with a multi-objective genetic algorithm to design pumps which meet various aerodynamic and geometrical requirements. The parameterization of the blade shape through the blade loading enables 3D optimization with very few design parameters. A generic pump stage is used to demonstrate the proposed methodology. The main design objectives are improving cavitation performance and reducing leading edge sweep. The optimization is performed subject to certain constraints on Euler head, throat area, thickness and meridional shape so that the resulting pump can meet both design and off-design conditions. A Pareto Front is generated for the two objective functions and 3 different configurations on the Pareto front are selected for detailed study by 3D RANS code. The CFD results confirm the main outcomes of the optimization process.
A Study on Flow Through an Orifice With Prediction of Cavitation and Hydraulic Flip
Authors: Darbandi Masoud , Sadeghi Hamed
Published: July 2010

The phenomena of cavitation are very important in a variety of industrial processes and engineering applications. Therefore, the simulation of cavitating flows in high-pressure devices has become a very challenging topic in the fields of computational fluid dynamics. This paper reports recent developments and application studies on computational fluid dynamic (CFD) for cavitating flows inside a circular orifice. A new cavitation model named as full cavitation model is employed for simulations. In this model, the working fluid is assumed to be a mixture of three phases (liquid, vapor and non-condensable gas). In all simulations, finite volume scheme is used, and SIMPLEC algorithm is utilized for the pressure and velocity linkage. Upwind scheme is used to model convective fluxes and other transport equations. Turbulence effects are considered using the k-ε model. Measurements are performed at various inlet pressures and a fixed outlet pressure. The results are compared with the published experimental data and have an acceptable accuracy. It is observed that increasing inlet pressure has considerable influence on the inception of cavitation and development of cavitation. The inception of cavitation is observed at inlet pressure of 225000 Pa and cavitation zone grows near the wall with increasing of inlet pressure. The simulation shows that if the pressure is high enough, the cavitation cloud grows and reaches the nozzle outlet, resulting in a so-called hydraulic flip.
Optimization of a Centrifugal Pump Impeller: Coupling a Hybrid Stochastic Method to a Potential Flow Solver
Authors: Antonakis Nikolas
Published: July 2010

An optimization process is employed to improve the performance of an industrial radial flow pump impeller. A hybrid optimization scheme is coupled to a cost effective potential flow solver that computes the flow through the blade channel. The impeller geometry is parameterized to reproduce variations over a wide design space and the objective function is evaluated at each iteration to account for the performance of each candidate blade. The concept of the hybrid approach is to employ a global stochastic optimization method for the diversification of the design space and a deterministic local method for efficiently intensifying the search towards the optimum. The trend of computer industry to multi-core processors is a promising platform for population based optimization methods and even on a quad core the timescales needed to solve the problem with the proposed methodology are reasonable. Results present an optimised impeller with improved performance but also a clear trade-off among contradictory design objectives.
Free-Surface Measurements in a Tow Tank Using LiDAR
Authors: Fu Thomas C. , Fullerton Anne M. , Drazen David A.
Published: July 2010

Light Detection and Ranging, or LiDAR, is a remote sensing technique that can be utilized to collect topographic data. These systems have been used extensively to measure open ocean and ship generated waves. Recently LiDAR systems have been used to measure the transom wave of the R/V Athena I and ambient ocean waves. This work has primarily focused on providing the time averaged, and spectral content of the wave field, by scanning the laser to measure wave profiles evolving in time. This paper describes recent efforts to utilize LIDAR systems to measure free-surface elevations in laboratory tow tanks. LiDAR measurements are limited to the white-water breaking regions of the flow, due to the limited strength of the signal return from non-breaking regions. In extending LiDAR measurements to a laboratory tow tank environment the lack of surface roughness and hence the lack of surface light scatterers needed to be addressed. A number of laboratory measurement applications will be described including a tow tank measurement similar to the R/V Athena I effort, and also measurement of regular and irregular breaking waves.
Priori Test of the Flow in an Annular Channel With Differential Heating at the Walls
Authors: Merzari Elia , Ninokata Hisashi
Published: July 2010

A priori testing is an important tool in LES modeling. It allows to test, at the core, the validity of the assumption of a given SGS model. In the present work we intend to examine the alignment between SGS stresses and strain in the case of an annular duct subject to differential heating, as a step into the development of a LES methodology in boundary fitted coordinates apt to simulate buoyancy-related phenomena. Thus the simulation flow in a concentric annular channel with differential heating at the walls has been conducted. The buoyancy contribution to the momentum equation has been modeled through the Boussinesq approximation. The code employed is based on the boundary fitted coordinates framework and the fractional step algorithm. The pressure equation is solved using a pseudo-spectral method in the stream-wise direction. The convective term has been discretized through fourth-order schemes and advances temporally through a second order scheme. The agreement with available experimental data was found overall good. A database of instantaneous snapshots of the flow field has then been collected. The flow filed has been filtered spatially and the assumptions of the LES models under examination have been tested.
Large Eddy Simulation of the Flow in Tight-Lattice Rod Bundles at Low Reynolds Number
Authors: Merzari Elia , Khakim Azizul , Ninokata Hisashi
Published: July 2010

Tightly packed rod-bundles are looked upon as possible configurations for the core of a nuclear reactor. Unfortunately the flow in such rod bundles is accompanied by oscillations and strong turbulent mixing. In particular it exhibits large scale coherent structures in the gap regions between the rods. In the present work we propose an LES, with Dynamic Smagorinsky modeling, in boundary fitted coordinates aimed at reproducing such flow features. The algorithm is based on the fractional-step framework. Time advancement is carried out through a second order scheme, while the convective term is discretized through a second (or fourth) order scheme. The geometries under consideration are an infinite triangular lattice of cylindrical pins and an infinite triangular lattice of an innovative pin design we will refer to as “exotic” pins. The Volume Fraction in both cases is equal to 0.67. The Reynolds number under investigation (6,400) is not comparable to current reactor designs but it is relevant to the investigation of innovative designs and incidental conditions.
Simulated Helical Gear Pump Analysis Using a New CFD Approach
Authors: Heisler Aaron S. , Moskwa John J. , Fronczak Frank J.
Published: July 2010

The purpose of this paper is to focus on cavitation prediction at high-speeds in helical gear pumps for the purpose of hydrostatic dynamometer system development. Details of the fluid motion will be described through various stages of fluid transfer from the pump inlet to the outlet using various mesh densities. Using the results of these simulations, a discussion of design improvements for high-speed hydrostatic dynamometer operation is included. Conducting CFD simulations on external gear pumps is a difficult problem depending upon the complexity of the individual components. Simulating helical gears is especially taxing due to the complexity of the gear tooth profile. The additional detail in a helical gear pump model leads to an increase of the required mesh density and therefore increased computation time. A less computationally complex approach to simulating helical gears is to consider a helical gear as a series of thin spur gears rotated according to a predetermined helix angle. Details of this approach and results are discussed in this paper.
Numerical Model for the Unsteady Flow Features of a Squirrel Cage Fan
Authors: Ballesteros-Tajadura Rafael , Guerras Colo´n Francisco Israel , Velarde-Sua´rez Sandra , Ferna´ndez Oro Jesu´s Manuel , Argu¨elles Di´az Katia Mari´a , Gonza´lez Jose´
Published: July 2010

This paper shows a numerical research on the unsteady flow field inside a squirrel cage fan. The studied features are both the instantaneous flow fields and the average fluid flow associated to the blade passage frequency. The squirrel cage fan studied is a small centrifugal fan with a twin impeller configuration, each with 23 forward curved blades. The blades chord is 0.013 m and each impeller has a diameter of 0.08 m and a width of 0.094 m. The impellers operate inside an external spiral casing with a rectangular exit, followed by the outlet duct. A first series of experimental tests were performed in order to characterize the unit. The performance curves (head, power and efficiency versus flow rate) were measured. These tests show a nominal flow rate at around 0.098 m3/s and a specific speed ωs = 1.9. From there on, three different flow rates were considered to study different flow behaviours in the impeller. In parallel with the mentioned experimental study, the unsteady 3D flow field inside the fan equipped with the same impeller was modelled for the referred flow rates, by means of the commercial CFD code FLUENT. To facilitate the modification of any geometrical feature, the mesh of the modelled fan was divided in several regions: inlet duct, impeller, volute and diffuser with outlet duct. The main goal of the paper is to show the numerical results obtained on the absolute and relative frames. Three main flow features will be analysed: the inlet flow distribution, the blade to blade field and the impeller exit flow. At the fan inlet, special care will be taken to detect possible recirculation or separation zones. On the other hand, and for each studied flow rate, the distribution of outlet flow field is also analysed. Conclusions on flow uniformity are drawn.
The Convective Instability of Boundary-Layer Flows Over Rotating Spheroids
Authors: Samad A. , Garrett S. J.
Published: July 2010

The continuous development of spinning projectiles and other industrial applications has led to the need to understand the laminar boundary-layer flow and subsequent onset of transition over the general family of rotating spheroids. We begin by finding the laminar boundary-layer flow over a general spheroid. In particular, we distinguish between prolate and oblate spheroids and use an appropriate spheroidal coordinate system in each case. The laminar-flow equations are established for each family of spheroid rotating in otherwise still fluid. An eccentricity parameter e is used to distinguish particular bodies within the oblate or prolate families. In each case, setting e = 0 reduces the equations to those already established by Howarth [2] and Banks [4] for the rotating sphere. In this preliminary study the laminar-flow equations at each latitude are solved by extending the original series solutions due to Howarth and Banks for the rotating sphere. The laminar flows obtained are consistent with established results for the rotating sphere as e tends to zero, and tend to the von Ka´rma´n [5] solution for the rotating disk as the latitude is reduced close to the nose. Analyses of the convective instability are performed on the rotating prolate family. These extend the linear analyses previously published by Malik, Lingwood and Garrett & Peake [6–10] on related geometries. An investigation into the relative importance of type I (crossflow) and type II (streamline curvature) modes is also presented. At low latitudes increasing eccentricity has negligible effects on the stability characteristics of the flow. However as the latitude increases, eccentricity is seen to lower the upper (type I) branch of the neutral curve, reducing the region of instability.
Dynamics of Biological Cells in Shear Flows Using an Implicit Fluid-Structure Interaction Method Based on the ALE Approach
Authors: Choi Choengryul , Kim Chang Nyung
Published: July 2010

We develop a fluid-structure interaction (FSI) method based on the ALE method and a dynamic mesh method with an ultimate aim which is to simulate the complicated dynamics of rigid particles in shear flow and to investigate the rheological behavior of the suspension. Because the motion of the fluid and particles in fluid-particle suspension problems is strongly linked, the governing equations are sequentially solved in each solver and the computation is iterated until the solutions converge in a two-way coupling fashion. The mesh system initially designed is deformed or re-meshed in accordance with the moving particles by a dynamic mesh method. Numerical simulation is entirely implemented by our FSI code in the framework of FLUENT. The present simulations have demonstrated the capability of the developed FSI method in simulating the dynamics of single and multiple particles with different arbitrary shapes in shear flows.
Application of the Immersed Boundary Method and Direct Numerical Simulation for the Heat Transfer From Particles
Authors: Feng Zhi-Gang , Michaelides Efstathios E.
Published: July 2010

A combination of the Direct Numerical Simulation (DNS) with the Immersed Boundary (IB) method has been developed to solve the momentum and heat transfer equations for the computation of thermal convection in particulate flows. This numerical method makes use of a finite difference method in and uses a regular Eulerian grid to solve the modified momentum and energy equations for the entire flow region simultaneously. In the region that is occupied by the solid particles, a second particle-based Lagrangian grid is used, which tracks all the particles, and a force density function or an energy density function is introduced to represent the momentum interaction or thermal interaction between the particulate phase and fluid phase. The numerical methods presented have been validated by comparing the results of the simulation with similar numerical results obtained by others. Among the advantages of this computational method is that it may be used for the determination, stipulation and validation of boundary conditions in particulate flows that may be used with larger Eulerian codes.
A Study of Performance Improvement of Vertical Diffuser Pumps
Authors: Chung Kyung-Nam , Kim Jin-Young , Park Jong-Hwoo , Kim Yong-Kyun , Kim Hae-Chun
Published: July 2010

In this study we introduce pump design work in which two vertical diffuser pumps are designed by using computational fluid dynamics and vane shape optimization. The first pump is a submergible pump having the specific speed of 300(m3/min-m-rpm). The effects of vane shape change on pump performance have been studied for this pump. Some effects of impeller inlet profile and diffuser blade angle are shown. Since this pump has very high head, the impeller exit angle of the first design model has been increased to get the specified head. This modification induces flow separation on the impeller blade. Blade angle distribution has been modified to eliminate the flow separation so that pump efficiency is maintained as high as in the base model. The second pump is a CWP for power plants having specific speed of 330. Blade shape is designed by using fractional factorial design method. The main effects and the interactions of design parameters are investigated. Impeller inlet diameter is increased to get better NPSH required performance. Flow analysis shows that the design model has higher efficiency and better cavitation performance than the existing model.
Experimental Study of Unsteady Cavitating Flow Around Flat Plate Hydrofoil With/Without Tip Clearance
Authors: Watanabe Satoshi , Suefuji Takanari , Ikeda Atsumu , Furukawa Akinori , Nishii Kazufumi
Published: July 2010

Unsteady cavitating flow around a flat plate hydrofoil was studied in order to investigate the effect of tip leakage vortex cavitation on the unsteady character of the cavitating flow. A two-dimensional flat plate hydrofoil having rounded leading and trailing edges with/without a tip clearance was tested for several angles of attack. The cavitating flow was filmed from the top and the side simultaneously using two high speed video cameras, and the unsteady static pressures just upstream and downstream of the hydrofoil were also simultaneously measured with the high speed video camera recording. It was found that, with the tip clearance, the partial cavity at the same cavitation number became more or less shorter and thinner than that without the tip clearance. Even under the existence of the tip leakage vortex cavity, the Strouhal number rule of the unsteady cavitating flow based on the attached cavity length still stood in our experiments.