bluuebunny/crossref_metadata_2025 huggingface dataset:
Wavelet Analysis of Reynolds Number Effect on 3-D Vorticity in a Turbulent Near Wake
Authors: Yiu M. W. , Li H. , Zhou Y.
Published: February 2009

When Reynolds number, Re (≡U∞d/v, where U∞ is the free stream velocity, d is the cylinder diameter and v is the kinematic viscosity of the fluid), is in the range of 103 to 104, there is a large variation in the near-wake formation region in terms of the base pressure coefficient, the fluctuating lift coefficient, the vortex formation length, which have previously been connected to the generation of small-scale Kelvin-Helmholtz vortices. This work aims to investigate how this Re variation affects the three components of vorticity in terms of time-averaged and small-scale structures and also to provide a relatively complete set of 3-D vorticity data. All three components of vorticity data were simultaneously measured in the intermediate region of the turbulent wake using a multi-wire vorticity probe. It is observed that the root-mean-square (rms) values of the three vorticity components increase with Re, especially the streamwise component, which shows a large jump from Re = 5×103 to 104. At the central frequencies of f0 and 2f0, the contributions from the large-scale and intermediate-scale structures of ωzi2/(ωz2)max decreases 13% and 16% respectively as the Re. increases. However, at the central frequency of 16f0, the contribution of the small-scale structure of ωzi2/(ωz2)max dramatic suddenly 7% increase at Re = 5×103 to 104. The result suggest the generation of small-scale Kelvin-Helmholtz vortices in the spanwise structure. The effect of Re on vorticity signals, spectra, contributions from the wavelet components to the vorticity variances are also examined.
Nondimensional Analysis of Electrorheological and Magnetorheological Dampers Using a Herschel-Bulkley Constitutive Model
Authors: Wereley Norman M.
Published: February 2009

Quasisteady modeling of linear stroke flow mode magnetorheological (MR) and electrorheological (ER) dampers has focused primarily on the utilization of the Bingham-plastic constitutive model to assess performance metrics such as damping capacity. In such Bingham-plastic MR (or ER) flows, the yield stress of the fluid, τy, is activated by applying magnetic (or electric) field. The Bingham-plastic model assumes that the material is in either (1) a preyield condition where the local shear stress is less than the yield stress, τ < τy, or (2) a postyield condition, where the local shear stress is greater than the yield stress, τ > τy, so that the material flows with a constant postyield viscosity. The objective of this paper is to analyze the damping capacity of such a controllable MR or ER damper in the situation when the field dependent fluid exhibits postyield shear thinning or thickening behavior, that is, the postyield viscosity is a function of shear rate. A Herschel-Bulkley model with a field dependent yield stress is proposed, and the impact of shear rate dependent viscosity on damping capacity is assessed. Key analysis results — velocity profile, shear stress profile, and damping coefficient — are presented in a nondimensional formulation that is consistent with prior results for the Bingham-plastic analysis. The nondimensional analysis formulated here clearly establishes the Bingham number as the independent variable for assessing flow mode damper performance.
Smart Blending: Functional Fine-Scale Structures Formed by Intelligent Agitations in Multi-Component Melts
Authors: Zumbrunnen D. A.
Published: February 2009

In viscous melts, turbulence often does not arise. Consequently, opportunities exist for controllably organizing melt components into functional structures that can have very small feature sizes. In this paper, concepts and results of smart blending are described. Smart blending entails the controllable development in situ of a variety of fine-scale structures in the melt by intelligent agitations. Once formed, structures may be useful in the melt or may be captured in applicable products by extrusion and solidification. Chaotic advection is an enabling recent sub-field of fluid mechanics for smart blending since it provides a means to stretch and fold melt domains and evolve a multi-layer structure leading to derivative arrangements, or indirectly manipulate solid additives. Applications include the production of plastics with enhanced mechanical properties, electrically conducting plastics and glasses, low permeation films, membranes, and nano- and molecular-scale composites.
High Speed Hydrogen Jets: Stability and Instability (Keynote Paper)
Authors: Hayashi A. Koichi
Published: February 2009

High speed hydrogen jets have been used in many technological fields such as chemical industries, automotive industries, etc. and gradually become important recently since fuel cell technology will become popular and its safety problem such as high pressure hydrogen tank leakage must be cleared and solved by the time of its use. In this paper the stability and instability of high speed hydrogen jet flames and their control are focused on. First of all nature of high speed hydrogen diffusion jet flames are shown experimentally to discuss their instability problems. Secondly numerical analysis of high speed jet flame is shown to explain the details of jet instability with heat releases. Then thirdly as an application a control of high speed hydrogen lifted jet flame is discussed experimentally and numerically.
The Noise Radiated by High-Speed Jets: Recent Insights From Numerical Simulations (Keynote Paper)
Authors: Lele Sanjiva K.
Published: February 2009

The noise emanating from high-speed jets consists of jet mixing noise and shock-associated noise with its tonal and broadband components. This paper summarizes well-known features of high-speed jet flows and their relationship to the noise radiated by the jet. Open issues on which different opinions exist are also noted. In this context key findings from numerical simulations of jet flows, and model problems related to jet flows are highlighted. The mechanism responsible for the generation of strong screech noise is discussed, and the role of large-scale structures in jet mixing noise and broadband shock-associated noise are stressed. Implications of a new analytical model of shock-cell noise generation are discussed, and in particular the scaling of shock-associated noise from heated jets.
Frequency-Response Characteristics of Interaction Tone Noise Radiated From a Centrifugal Compressor
Authors: Ohta Yutaka , Masui Shunsuke , Fuyumuro Toshiya , Outa Eisuke
Published: February 2009

Frequency-response characteristics of interaction tone noise radiated from a centrifugal compressor with vaned diffuser are discussed by experiments and also by noise transmission model. The interaction tone noise is supposed to be caused by the periodic pressure fluctuation in the vicinity of the leading edge of diffuser vanes, and to show the characteristics of dipole noise source, noise source characteristics in an ideal sense should increase in the 6th power against the flow velocity. Then the level discrepancy between the noise source and measured sound pressure level is considered to be affected simply by the frequency-response characteristics of the noise transmission passage which are predicted by introducing a one-dimensional linear wave model. In the model, leading edge of the diffuser vane is considered to be a noise source, and sound wave travels through the passages of main and splitter blades in the impeller, inducer and inlet duct as a plane wave. The modeled data is found satisfactorily to predict the response characteristics of the noise transmission passage. The noise source characteristics are also discussed by precise measurements of pressure fluctuation level within impeller passages.
Study on the Hydraulic Performance of a Turbopump Inducer
Authors: Choi Chang Ho , Hong Soon-Sam , Cha Bong Jun , Yang Sooseok
Published: February 2009

The present study focuses on the flow analysis of a turbopump inducer by performing both numerical and experimental methods to provide designers with valuable information. Global performance data (head and efficiency), and detail flow fields (outlet flow angles, pressures and velocity vectors) are measured and compared with the computational data. Generally a good agreement is obtained between both results. But some discrepancies are observed due to complex flows such as backflows at the inlet, etc. The visualization of the backflow at the inducer inlet is also conducted for the validation showing that the prediction overestimates the size of the backflow. And it is shown that the slight modification of the trailing edge shape of the inducer can affect the performance of the inducer.
Experimental and Numerical Analysis of the Flow Structure and Dust Separation Inside a Pre-Swirl Cooling Air System
Authors: Schneider O. , Dohmen H. J. , Benra F.-K. , Brillert D.
Published: February 2009

Improvements in efficiency and performance of gas turbines require a better understanding of the internal cooling air system which provides the turbine blades with cooling air. With the increase of cooling air passing through the internal air system, a greater amount of air borne particles is transported to the film cooling holes at the turbine blade surface. In spite of their small size, these holes are critical for blockage. Blockage of only a few holes could have harmful effects on the cooling film surrounding the blade. As a result, a reduced mean time between maintenance or even unexpected operation faults of the gas turbine during operation could occur. Experience showed a complex interaction of cooling air under different flow conditions and its particle load. To get more familiar with all these influences and the system itself, a test rig has been built. With this test rig, the behavior of particles in the internal cooling air system can be studied at realistic flow conditions compared to a modern, heavy duty gas turbine. It is possible to simulate different particle sizes and dust concentrations in the coolant air. The test rig has been designed to give information about the quantity of separated particles at various critical areas of the internal air system [1]. The operation of the test rig as well as analysis of particles in such a complex flow system bear many problems, addressed in previous papers [1,2,3]. New theoretical studies give new and more accurate results, compared to the measurements. Furthermore the inspection of the test rig showed dust deposits at unexpected positions of the flow path, which will be discussed by numerical analysis.
Fluid Particle’s Rotational Speed at the Trailing Edge of Impeller Outlet of Centrifugal Pump
Authors: Tanaka Takaharu
Published: February 2009

Mechanical force caused by mechanical energy acts real and imaginary forces on impeller blade. Therefore, impeller blade moves in the direction of real force, straightly forward in the direction of tangent perpendicular to rotational radius and the direction of imaginary force, circularly forward in the direction of tangent perpendicular to rotational radius. Former real movement causes on fluid particle radial outward movement, resulting to flow rate Q. Latter imaginary movement causes on fluid particle a rotational motion under the external centripetal and imaginary centrifugal force, resulting to pump head. Pump head is equivalent to external centripetal force and balanced with imaginary centrifugal force in the rotating flow passage.
Computational Flow Simulation for the Entire Nano-Filter
Authors: Nakamura S. , Park Jungwan
Published: February 2009

This paper describes the computational models to analyze fluid flow characteristics in a nano-filter made from silicon wafer, then illustrates analyses of the external and ion electric potential distribution, ion transport, and fluid flow velocity distribution. Although no optimization of the design parameters is attempted, the illustrative analyses using the computational model reveal that unless the nano-filter design is carefully optimized the flow distribution can become very nonuniform over the entire filter and thus inefficient.
Numerical Modeling of Micro-Channel Flows by a DPD Method
Authors: Czerwinska Justyna , Adams Nikolaus A.
Published: February 2009

This paper proposes new computational technique to model micro-flows. The presented below method is based on the meso-scale description of fluid. Dissipative Particle Dynamics (DPD) method is derived from Molecular Dynamics by means of coarse graining procedure. The dissipative particle is defined as a Voronoi cell with variable mass and size; evolves similarly to the Molecular Dynamics particles, except that inter-particle forces have additionally fluctuating, dissipative and stochastic component. This representation leads to the set of equations describing DPD approach. In this paper the outline of the DPD method for application to micro-fluidics flow is presented. DPD method in the form of Soft Fluid Particle model, was mainly applied in material science simulation. This paper presents new approach to model micro-flow by Voronoi Particle DPD method. As a particular example the gas flow in micro-channel flow is computed.
Trend Predictions in Effect of Spoilers for a Mini Car: A Low Cost Solution
Authors: MathiArasu N. , Srinivasan P. S. S. , Vijayakumar K. C. K.
Published: February 2009

Most of the CFD analysis on car aerodynamics published so far is being carried out with high-end workstations and many days of computation time, which only few laboratories in the world can afford to. In developing economies like India, many car users use large number of add-on devices, which can have significant impact on the fuel consumption, which they are not aware of. The focus of the present paper is to expose such aspects using a simple personal computer with few hours of computational time, which must be economical. A most popular mini-car on Indian roads is taken for analysis. A two dimensional CFD analysis using commercial finite element based CFD software is used. The analysis has revealed that position and size of front and rear spoilers have significant impact on Lift i.e. vehicle stability and moderate impact on Drag i.e. Fuel consumption. The effect of speed on different geometries is studied and the variations are found to be linear.
Development of Prediciton Methods for Film Thickness in Electro-Deposition Coating Process
Authors: Komoriya Toru , Shin Kenei , Mohri Masayasu
Published: February 2009

We have developed a simulation code which predicts the film thickness of the electro-deposition coating for automotive bodies. The time-dependent electro-potential distribution in the paint materials is predicted based on an electro-potential diffusion equation. As for descretization, we adopt the unstructured finite volume method. In order to verify the code accuracy, we have done a calculation for the electro-paint deposition experiment of a small box with 3 plates inside in it. The calculated results agreed with the test results very well not only qualitatively, but also quantitatively, especially in the range of 10 micron, which is included in the thickness criteria for automotive design. In addition, we applied the code to the real center pillar of an automobile. The analysis results mostly agreed with the results obtained from the experiment with the center pillar. This paper will describe the application case of this analysis code.
Dynamic Break-Up and Drop Formation From a Liquid Jet Spun From a Rotating Orifice: Part I — Experimental
Authors: Wong David , Simmons Mark , King Andrew , Decent Stephen , Parau Emilian
Published: February 2009

The dynamics of the break-up of curved jets produced by the prilling process were studied. The effects of liquid dynamic viscosity, rotation rate and orifice size upon the surface tension driven instabilities were investigated. Liquid dynamic viscosity was varied by using mixtures of glycerol and water which gave dynamic viscosities ranging from 0.001 to 0.081 Pa.s at 20°C. Over the range of experimental parameters studied, four different break-up modes were identified. For each mode, considerable differences in the break-up mechanism and in the drop size distributions produced were observed. Dimensional analysis has shown that the break-up modes can be predicted from a plot of Reynolds number against Weber number. The break-up mode observed is a strong function of viscosity and highly nonlinear effects were observed with the most viscous solutions used. The effect of rotation rate on the jet break-up length was inconclusive from the experiment.
VOF-Simulations of Mass Transfer From Single Bubbles and Bubble Chains Rising in Aqueous Solutions
Authors: Bothe Dieter , Koebe Mario , Wielage Kerstin , Warnecke Hans-Joachim
Published: February 2009

This paper presents numerical simulations of two-phase flow with high-density ratio, taking into account mass transport of a soluble component and its interfacial mass transfer. The mathematical model and the numerical method allow for different solubility of the species in the respective fluid phases, while volume changes due to mass transfer are neglected. The discontinuous changes in species concentrations at the interface are modeled by means of Henry’s law. Simulations are carried out with an extended version of the highly parallelized code FS3D, which employs an advanced Volume-Of-Fluid (VOF) method. Transfer and transport of oxygen is examined in case of single bubbles as well as bubble chains rising in aqueous solutions. Numerical simulations show good qualitative agreement with experimental data and render the observed mass transfer phenomena correctly.
Interaction of Free Surface Flows With Unrestrained Solid-Porous Bodies
Authors: Bidoae Razvan , Ciobotaru Remus M. , Raad Peter E.
Published: February 2009

This paper presents an extension of the Eulerian-Lagrangian Marker and Micro Cell (ELMMC) method, developed to numerically simulate the interaction between clear fluid flow and composite obstacles. The method can simulate both transient and pseudo-steady state problems that involve wave breaking, impact between fluid fronts, and impact between free surfaces and solid or porous boundaries. The newest capability added to the ELMMC method can simulate interaction between fluid fronts and unrestrained solid/porous obstacles. The extension of the ELMMC method is presented here in detail, including the estimation of the hydrodynamic forces induced by the flow on the solid/porous obstacles, the calculation of the final velocity fields, and the computation of the velocity of the solid/porous obstacles. The capabilities of the new method are demonstrated by simulating two representative problems, namely, a solid/porous sphere falling in a reservoir and a single large wave impacting an unrestrained solid/porous structure.
Evaluation of Volume Tracking Algorithms for Gas-Liquid Two-Phase Flows
Authors: Sou Akira , Hayashi Kosuke , Nakajima Tsuyoshi
Published: February 2009

Qualitative and quantitative evaluations of volume tracking algorithms such as DA, FLAIR, MARS, CIP and VTEMC were conducted. Wide variety of two-dimensional test problems including (1) a circle transported in simple translation and rotational field, (2) a bubble rising in 45° slanted gravity field, (3) zigzag motion of a bubble in a vertical channel, and (4) a bubble rising in a stagnant liquid in axissymmetric cylindrical coordinate were chosen in the present study. As a result of these tests, the superiority of the cell-centered piecewise linear algorithm with the divergence treatment in operator split and especially with embedded micro cells was confirmed. Applicability of these algorithms to three-dimensional problems has to be examined in the future works.
Transient CFD Visualization of Fossil Fuel Combustion Simulations
Authors: Dotson Brian , Eshenberg Kent , Guenther Chris , O’Brien Thomas
Published: February 2009

The design of high-efficiency lower-emission coal-fed power plants is facilitated by the extensive use of computational fluid dynamics (CFD) simulations. This paper describes work conducted at the National Energy Technology Laboratory (NETL) and Pittsburgh Supercomputing Center (PSC) to provide an environment for the immersive three-dimensional visualization of CFD simulation results. A low-cost high-resolution projection system has been developed in the visualization lab at NETL. This multi-wall system consists of four projection screens, three of which are tiled into four quadrants. The graphics for the multi-wall system are rendered using a cluster of eight personal computers. A high-level visualization interface named Mavis has also been developed to combine the powerful 3D modules of OpenDX with methods developed at NETL for studying multiphase CFD data. With Python, a completely new OpenDX user interface was built that extends and simplifies the features of a basic graphics library.
Visualization of Fluid Flows in Virtual Environments
Authors: Ziegeler Sean B. , Gopal Gopi Prasshanth , Blades Eric , Moorhead Robert J. , Marcum David L. , Guan Yanlin
Published: February 2009

As computational methods keep improving and computational resources are entering a new era, the solution to physical problems is available at very high resolutions. Unfortunately, the computational resources that are available for interactive visualization of the solution at this resolution are not as accessible, hence the need to resort to alternative display techniques which can portray a better understanding of the solution, even at a lesser resolution. In this paper, we discuss methods for visualizing fluid data in a virtual environment. For steady-state data sets, we employ a feature-based streamline seeding technique. For time-variant data sets, we utilize view-dependent seeded pathlines. These methods address the aforementioned problems with high resolution data sets. In addition, we present the advantages of using virtual environments for flow visualization, and how analysts benefit from these advantages.
Near-Wall Turbulence of Drag Reduction and Promotion in Unsteady Turbulent Pipe Flows
Authors: Takami Toshihiro , Kita Yoshinori
Published: February 2009

An unsteady behavior of the wall-drag, the velocity and the turbulence is experimentally investigated in the unsteady turbulent pipe flow, under several flow conditions with a rapid to slow time-variation and a large distortion of the flow-rate imposed stepwise. The instantaneous wall-shear stress and three-components of instantaneous velocities are simultaneously measured using the HWA technique of a surface hot-wire and a non-orthogonal triple-sensors probe. In the present study, to understand the unsteady behavior of the relation between the wall-drag and the velocity distribution, the unsteady response of the turbulence to the imposed unsteady flow is investigated by analyzing the relation between the unsteady Reynolds stress and the instantaneous velocity fluctuation during the accelerating and decelerating phase. It is found that, near the pipe-wall, the statistical parameter of the phase-average turbulence structure and the phase-average quadrant contribution rate of instantaneous velocity fluctuations to the Reynolds stress are almost similar to those in the steady turbulent flow, although the drag-reduction and the drag-promotion occurs during the accelerating and decelerating phase respectively.
Numerical Simulation of a Compound Round Jet by Three-Dimensional Vortex Method
Authors: Uchiyama Tomomi
Published: February 2009

A jet issuing with velocity U0 from a round nozzle of diameter D into the same fluid co-flowing with velocity Ua is simulated by the three-dimensional vortex method. The velocity ratio Ua/U0 is 0.27, while the Reynolds number based on U0 and D is 5.5×104. The number of vortex elements drastically increases in the region where the stretch and contraction of the vortex element occur due to the appearance of turbulence. When applying the core distribution function proposed by Winkelmans and Leonard, the time-averaged velocity successfully satisfies the self-preservation distribution, and the axial component of the turbulent intensity almost agrees with the experimental result. The Reynolds shear stress takes its maximum value at the periphery of the jet in accordance with the experimental result, though it is higher than the experiment.
Experimental Study on Compound Swirl Jet
Authors: Nozaki Tsutomu , Ochiai Takashi , Kai Tomonari
Published: February 2009

This paper concerns the fundamental study on the push-pull type ventilator, especially applied to the smoking table. In order to achieve more effective cleaning of the dirty air, a compound swirl jet, which consists of a round free jet having thick rim and a coaxial annular swirl jet was proposed by the authors. It was found that the compound flow is very useful for the push flow of the push-pull type ventilator selecting the suitable flow rate ratio of the annular swirl jet to the free jet. As a fundamental study on the compound swirl jet, the flow visualization was also carried out using the smoke method. At the same time, the mean velocity components were measured using the cobra Pitot tube. It was found from the results of these experiments that the unique flow structure by the interaction of two jets is created in the compound swirl jet choosing the adequate flow rate ratio, which is suitable for the push flow of the push-pull type ventilator.
Energy Dissipation Mechanisms in Water Distribution Systems
Authors: Karney Bryan W. , Filion Yves R.
Published: February 2009

An important issue in the context of design and analysis of a water distribution system is the rate of energy dissipation of a transient disturbance. In this paper, a preliminary numerical investigation is undertaken to establish the role and significance of primary energy dissipation mechanisms commonly found in water transmission and distribution systems. The role of steady friction, unwanted leaks, topological complexity and surge control devices in the decay of transient energy is preliminarily investigated. An energy approach previously derived is reviewed and used to track the progress of dissipation in a system. Transient simulations are run on a hypothetical series pipeline and distribution network with a waterhammer simulator to explore the dissipative effectiveness of some of the primary mechanisms.
Rational Polynomial Transfer Function Approximations for Fluid Transients in Lines
Authors: Wongputorn Patompong , Hullender David A. , Woods Robert L.
Published: February 2009

This paper introduces a simple approach utilizing MATLAB® computational tools for generating rational polynomial transfer functions for fluid transients in both liquid and gas fluid transmission lines. These transfer functions are obtained by curve fitting in the frequency domain the exact solution to the distributed parameter laminar flow “Dissipative Model” for fluid transients that includes nonlinear frequency dependent viscous friction terms as well as heat transfer effects in gas lines. These transfer functions are formulated so they are applicable to arbitrary line terminations and so they can be inserted directly into SIMULINK® models for time domain simulation and analysis of a total system of which the fluid lines are only internal components. The inputs to the algorithm are the internal radius and length of the line; the kinematic viscosity, density, Prandtl number, and speed of sound of the fluid; and the maximum frequency to which an accurate curve fit of the exact solution is desired. This maximum frequency normally is equal to or greater than the bandwidth of the other components in the total system to be analyzed or the maximum frequency associated with the input. The simplicity of use and accuracy in the results of the exact solution representations are demonstrated for examples of a blocked fluid line and of a line terminating into a tank. The computational algorithms are available for download from the Author’s web site. This is the first of two papers pertaining to transfer functions for fluid transients. The second paper pertains to formulating simulation diagrams for total systems containing fluid lines represented by rational polynomial transfer functions.
Surge Pressure Calculation and Its Simplification Method for Check Valve
Authors: Yong Qiwei , Li Xudong , Zhang Weiming , Huang Lei
Published: February 2009

Check valves are important valves in pipeline system. However, the closure of them may provoke serious turbulence. It is very important and essential for pipeline systems to correctly predict and calculate the surge pressure due to the closure of check valves. Firstly, the solution of differential equations governing movement of the clack of swing check valve is derived, and the surge pressure is computed by characteristics method. Secondly, for the purpose of simplification, a simple and applicable method for calculating the closure pressure is put forward by making use of the dynamic characteristic of check valve. All these could be of referenced value to engineering design and selection of check valves.
Critical Stable Sectional Area of Downstream Throttled Surge Tank
Authors: Lai Xu , Yang Jiandong , Chen Jianzhi
Published: February 2009

With the Thoma’s assumption, the critical sectional area for flow stability of the downstream throttled surge tank is derived theoretically. The effects of the velocity head and momentum exchange at the Tee junction between the surge tank riser and the tail water tunnel on the critical sectional area of the downstream tank have been analyzed using the Gardel’s head loss formula. The study shows that the velocity head has an unfavorable effect on the water level stability in the downstream surge tank while the effect of the momentum exchange is positive. Two effects counteract. Thus the critical sectional area of a downstream throttled surge tank is close to that of a corresponding simple surge tank. However, if the size and shape of a riser are optimized, the area of the downstream surge tank may be further reduced. It is also demonstrated that a downstream throttled surge tank can reduce electricity loss and meet the requirements of stability easily in large flow oscillations compared to a simple downstream tank.
Surge Associated With Air Expulsion in Near-Horizontal Pipelines
Authors: Vasconcelos Jose G. , Wright Steven J.
Published: February 2009

A number of situations of engineering interest are associated with the relatively rapid filling of a nearly horizontal pipeline. The displacement of the air may lead to a number of different transient conditions of concern in engineering design. Our specific application relates to the use of underground storage tunnels to mitigate combined sewage overflows. Historically, the operation of these system have created surges initiated when the tunnel passes to a surcharged condition that have resulted in “geysering” in which an air/water combination is expelled to the ground surface through manholes or other risers. Numerical models that have been created to describe the phenomena generally treat the air as a passive phase that exists at atmospheric pressure and disappears when the water fills the tunnel. In an attempt to understand the conditions leading to extreme surges, a physical model that reproduced the essential elements of the tunnel filling process was created. This model was filled at one end in a fill box in which the maximum water level was controlled with an overflow weir. A surge riser was mounted at the opposite end of the pipeline to observe the magnitudes of surges created under a number of different flows created by varying the inflow rate, the initial water level in the pipe, and the pipe slope. In general, initiation of the filling process generated a hydraulic bore that propagated through the system until the tunnel reached a surcharged state and the maximum surge generated depends on the dynamics of the bore. However, under certain flow conditions, the water level in the surge riser was observed to increase prior to the arrival of the bore, an occurrence that can only be explained by pressurization of the air in the pipe. Subsequent experiments confirmed this explanation and a modified experimental setup was created to elucidate the important effects of the air. Measurements were made of a number of key flow variables and are found to be consistent with the predictions of a numerical model that considers the elementary dynamics of the air.
A New Type of Water Hammer in Gas-Liquid Two-Phase Fluid Lines
Authors: Kim Din Cher
Published: February 2009

As far as the author is aware there has been no previous work on the problem addressed in the present paper, namely water hammer analysis in two-phase flow pipes in which a bubble-bubble interaction, deformation of the tube cross-section, shear stress, and compressibility of liquid phase play a significant role. In this paper, new mathematical model that couples the generalized inhomogeneous wave equation of Lighthill-type with the generalized Rayleigh-Plesset equation is derived to simulate unsteady, quasi-one-dimensional bubbly flows. We should stress that all of above mentioned effects have been included in the formulation deduced from proposed theory. A high effective and accurate finite difference technique for the exact solution of governing equations and new parallel program by using MPI are developed. Based on the developed algorithm and computer parallel program various numerical experiments have been carried out to investigate the major fluid dynamical features of the water hammer in horizontal pipes. It is found from these computations that the advantages of our model and numerical technique are evident especially in the area of hydraulic transients dominated by bubble dynamics. We have revealed the oscillatory water hammer with fine structure and the low-amplitude high-frequency wave called the precursor.
Research on Waterhammer Caused by a Rapid Gas Production in an LWR Severe Accident: 1 — Experiment Using a Model Containment Vessel
Authors: Shiozaki Koki , Adachi Masaki , Inasaka Fujio , Aya Izuo , Yoshie Shinji
Published: February 2009

In the severe accident of an LWR (Light Water Reactor), a steam explosion caused by an injection of molten core into a water pool is one of the factors whose possibility still cannot be neglected completely. According to a rapid bubble growth by a steam explosion, if the water mass is pushed up having a coherency in time and direction in its movement, it would give a severe waterhammer to the structure. In this research, we conducted an experiment using a cylindrical model containment vessel with 1 m diameter and 6 m height, and investigated the behavior of water mass pushed up by a growing bubble. In addition, we also conducted an experiment using a small-scale vessel with 0.428 m diameter to know the scale effects of this phenomenon. In these experiments, a rapid bubble growth of a steam explosion was simulated by injecting high-pressure air into a water pool. According to a rapid bubble growth at the bottom of the water pool, it was observed that the water mass was pushed up without an air penetration until the water level reached a certain elevation. The elevation became considerably high in the case where the initial water level was almost equivalent to the diameter of the vessel. Water surface velocities at the air penetration reached 10–35 m/s. After the air penetration, the water having these high velocities continued to move up and hit the orifice plate installed at the middle of the vessel. The maximum waterhammer pressure measured at the orifice exceeded 10 MPa. In that case, the total load to the vessel measured at the foot of the vessel reached about 540 kN, which corresponds to about 55 ton. The results of this study suggest that the possibility of waterhammer as well as the direct impact of pressure wave should be paid attention in the assessment of a steam explosion.
Study of Cavitation Light Emission Generated by a Waterhammer
Authors: Tabei Katsuine , Mashiko Shunji , Shirai Hiroyuki
Published: February 2009

Cavitation light emission generated by a waterhammer is investigated experimentally and theoretically for water containing a small amount of rare gas (xenon and argon). In the experiment, the water is forced to flow upwards in an evacuated vertical circular tube by the rapid opening of a ball valve that is connected to the liquid reservoir. The liquid vaporizes until the flow reaches the top end of the tube, and many minute cavitation bubbles are generated in the liquid. When the water column collides with the end of the closed pipe, a waterhammer with a pressure of over 1 MPa is generated in the multi-phase liquid, and it progresses toward the reverse direction. In such a process, the cavitation bubble collapses, and emits an instantaneous flash of light. Physical quantities such as the propagation velocity of the pressure waves and the cavitation emission intensity are measured. In addition, the momentary patterns of the bubbly flow and the light emission are also visualized by using an image intensifier and a stroboscope. The theory is constituted for the multi-phase flow of the waterhammer, in which the Keller and Miksis’ equation for the collapse of a bubble includes the effect of the ionization reaction of rare gas in the bubble. From the study, the following features are shown: Light emission occurs only at the front of the shock wave of the waterhammer. The position of light emission moves exactly at the same speed as the propagation speed of the pressure wave. Changes of pressure and emission intensity in the waterhammer are both strongly dependent on a void fraction. The ratio of emission intensity for water dissolved with argon and water dissolved with xenon is nearly 1:5.
Dynamic Properties of the Pressure Exerted on the Material Surface by Water Jet Impingements
Authors: Kiyono Fumio
Published: February 2009

It is interesting to know dynamic properties of the water jet pressure acting on the surface of a cutting object in order to clarify the cutting mechanism. This pressure includes wide range of frequency components that vary from the pulsation of a plunger pump to the water hammer pressure caused by impingements of droplets. In such case the transducers’ characteristics affect the detected wave seriously, and source wave of the pressure differs from detected wave. To eliminate the transducers characteristics and obtain the original wave form, special techniques, so called the deconvolution method or the source wave analysis method, are necessary. This paper presents the method to obtain the source wave of impingement pressure of water jets and demonstrates how it works correctly. Pressures acting on the material surface were measured directly by making water jets to impinge upon the pressure sensor. After experiments, detected wave data were processed by the deconvolution method. In addition, relationship between characteristics of the impingement pressure of water jet and flow structure of water jet is examined by flash photography using pulsed laser light. As a result, it becomes clear that dynamic property of the impingement pressure is closely related to the flow structure of water jet.
A High-Pressure Pulsed Water Jet Cutting System by Means of Water Hammer in a Convergent Pipeline
Authors: Yamane Koji , Sasaki Hiromitsu , Shimamoto Yuzuru
Published: February 2009

One of the authors has developed a high-pressure fuel injection system using an oil hammer for diesel engines in 1993. In the present study, we applied this novel principle of the fuel injection system to the water-jet cutting system, and a pulsed water jet cutting system by means of water hammer in convergent pipeline caused by strong spool acceleration was developed. The system consisted of a pump having a small size plunger and spool, a convergent pipeline, and automatic injector having a hole-type nozzle with a small orifice. This pump, generating strong compression waves at the convergent pipeline inlet by strong acceleration of spool and plunger, is controlled by the low source oil pressure and electromagnetic valve. The wave propagated in the convergent pipeline is dynamically intensified by water hammering in the pipeline. High pressure is then developed at the nozzle. The injection pressure and injection frequency are fully controllable by the source pressure, and by the valve-opening frequency of the electromagnetic valve (EMPV). A computer simulation demonstrated that an operation and the injection pressure are satisfactory as a water jet cutting system. It is shown that a pressure of 140 MPa is obtained in nozzle inlet by a source pressure of 11.8MPa in experiments. The dimension of the nozzle orifice was determined by visualizing the spray origin using a laser-sheet imaging technique. Stagnation force and its spectrum of water jet on work was measured to evaluate effects of injection period and standoff distance on punching time and area. Practical feasibility of water jet cutting system was demonstrated by cutting/punching tests for soft/no-heating materials or metal plates and by paint removing tests.
Noise Prediction of the Cavitation Tunnel
Authors: Kudo Toshifumi , Nishimura Masaharu , Sawada Shinichi , Mori Takayuki , Sato Ryuichi
Published: February 2009

The present paper is concerned with the prediction technique of back ground noise in the cavitation tunnel generated by flow-induced noise and the mechanical noise. To predict the back ground noise level, acoustic power balance method has been applied as computation technique. This method is based on the balance of acoustic power flow propagating left and right hand direction individually, in each element and among adjacent elements. In order to establish balance equations, many acoustic characteristics can be considered which are absorption, transmission, attenuation, reflection, radiation, noise sources and so on. Then the coefficient for these characteristics have been estimated by the measured data of a cavitation tunnel in MHI (Mitsubishi Heavy Industries, Ltd.) in Japan. Calculation results show good agreement with the measured values of another cavitation tunnel in IHI (Ishikawajima-Harima Heavy Industries, Ltd.) in Japan.
Comparison Tests for Checking Relations for Cavitation Scale Effects
Authors: Keller Andreas P. , Pan Sensen , Yang Zhiming
Published: February 2009

The problem with model tests for cavitation phenomena are the so-called “scale effects”. There are numerous examples where the model was observed to be cavitation free at design operation conditions, however, the prototype suffered extensive cavitation to severe damage under similar conditions. The real heart of a successful cavitation study is to scale the information from model test to prototype conditions correctly. Therefore many efforts are made world wide to find relations for the most crucial scale effects associated with size and velocity. After carrying out extensive test series on all kinds of test body families at the VAO, by taking care of the test water quality with respect to its cavitation susceptibility, strikingly simple and clear relations for scale effects appeared. In order to check these scaling relations comparison tests were carried out in three different institutes: The Brodarski Institute (BI) in Zagreb, the Wuhan University (WHU), and the China Ship Scientific Research Center (CSSRC) in Wuxi. The test results of the model body families tested in the new CLCC at CSSRC do not confirm the velocity scaling relation found at the VAO, however, this velocity scaling relation is confirmed very well by the results of WHU and BI. On the other side all results do show a distinct size scale effect and confirm the size scaling relation.
Inception and Dynamics of Traveling-Bubble-Type Cavitation in a Venturi
Authors: Sato Keiichi , Hachino Kouji , Saito Yasuhiro
Published: February 2009

The inception of cavitation is basically caused by a bubble nucleus which flows into the low pressure region in the liquid flow. Therefore the phenomenon is dependent on the tensile strength or the nuclei concentration of tested water. The cavitation susceptibility of water which controls the cavitation inception point has been made clear though various methods were proposed to measure the nuclei concentration. Cavitation susceptibility meter using a small venturi tube is also one of the methods to measure the nuclei concentration. It is pointed out that this method can be directly related to active nuclei for cavitation inception and gives a useful and simple device to estimate the tensile strength of water. In the present paper, to establish a measurement method of cavitation susceptibility using a venturi tube, the following points are investigated, such as; the relation between the occurrence, count rate of cavitation bubbles and cavitation number, the measurement of positions and local pressure of bubble occurrence and the high-speed video observation of bubble aspects from inception to collapse. As the result, the main points obtained are as follows. A traveling-bubble cavitation appears dominantly in a nozzle-type venturi tube with little possibility of flow separation. Cavitation aspects and the bubble occurrence count rate change with cavitation number and water quality (dissolved gas content). Unstable sheet cavitation can be also observed near the venturi diffuser and at relatively low cavitation number. The various behaviors of traveling bubble cavitation in a venturi are observed from inception to collapse using a high-speed video camera system.
Development and Validation of Continuous Models for Simulation of Turbulent Flows
Authors: Hussaini M. Yousuff , Thangam Siva , Woodruff Stephen L. , Zhou Ye
Published: February 2009

The development of a continuous turbulence model that is suitable for representing both the subgrid scale stresses in large eddy simulation and the Reynolds stresses in the Reynolds averaged Navier-Stokes formulation is described. A recursion approach is used to bridge the length scale disparity from the cutoff wavenumber to those in the energy-containing range. The proposed model is analyzed in conjunction with direct numerical simulations of Kolmogorov flows.
Dissipation in Implicit Turbulence Models: A Computational Study
Authors: Margolin L. G. , Smolarkiewicz P. K. , Wyszogrodzki A. A.
Published: February 2009

We describe a series of computational experiments that employ nonoscillatory finite volume methods to simulate the decay of high Reynolds number turbulence. These experiments cover a broad range of physical viscosities and numerical resolutions. We have extracted a data set from these experiments detailing the energy dissipation by physical viscosity and by the numerical algorithm. We offer a preliminary analysis of this data, including new insights into the (computational) transition between direct numerical simulation and large eddy simulation.