bluuebunny/crossref_metadata_2025 huggingface dataset:
Suppression Effect of Vortex Generator Jets With Non-Circular Orifices on Separating Flow
Authors: Hasegawa Hiroaki , Matsuuchi Kazuo , Komatsuzaki Yasuhiro
Published: February 2009

Jets issuing through small holes in a wall into a freestream have proven effective in the control of boundary layer separation. Longitudinal (streamwise) vortices are produced by the interaction between the jets and the freestream. This technique is known as the vortex generator jet method of separation or stall control because it controls separation in the same general way as the well-known method using solid vortex generators. The vortex generator jet method is active control of flow separation that has the ability to provide a time-varying control action to optimize performance under wide range of flow conditions. In this study, the suppression effect of the jet orifice shape of vortex generator jets on flow separation in the diffuser is investigated for three types of jet orifice (circular, triangle and square orifices). The triangle orifice makes strong the vorticity of longitudinal vortices and effective the pressure recovery in the diffuser in comparison with the other orifice shapes. Furthermore, it is found that the orifice shape of vortex generator jets causes the different tendency of the pressure recovery in the downstream direction.
Near-Wall Turbulent Structure for the Boundary Layer Developing Over a K-Type Rough Wall in Low-Reynolds-Number
Authors: Kameda Takatsugu , Osaka Hideo , Mochizuki Shinsuke
Published: February 2009

Measurements of the mean and the turbulent velocities have performed in the vicinity of a roughness element for the turbulent boundary layer developed over a k-type rough wall, which consists of two-dimensional square ribs (10mm × 10mm × 400mm) arrayed with pitch ratio of 4. The Reynolds-number Rθ and k+ based on momentum thickness θ and roughness height k are about 500 and 50 respectively, and relative roughness height k / δ = 0.156. LDV (Laser Doppler Velocitimetry) that it is possible to measure reverse flow was applied to investigate the momentum-exchange process in the open-face (yT = 0(mm)) over cavities. The variation of the mean and turbulent quantities profiles at yT = 0(mm) depend on the evolution of a free-shear layer formed behind roughness elements and the behavior of eddies in the cavity. Pressure drag coefficient acting on the roughness element in the local skin friction coefficient is 88% in the present k-type rough wall. The momentum exchange for the mean flow and turbulence contribute 6% and 56% respectively to the local skin friction coefficient.
Unsteady Separation and Vortex Around Moving Airfoils
Authors: Fuchiwaki Masaki , Yang Chang Jo , Tanaka Kazuhiro
Published: February 2009

The dynamic behavior of vortices shed from the leading edge of two kinds of pitching airfoils, such as NACA65-0910 and BTE, was visualized by dye flow visualization and schlieren visualization for Re = 4.0 × 103. Moreover, the dynamic lift acting on them was measured by a six-axes sensor in a water tunnel for Re = 4.0 × 104. In case of both airfoils, the reattachment appeared at the higher angle of attack with higher non-dimensional pitching rate. The dynamic behavior of the reattachment depended on the airfoil configuration and the recirculation region was formed by a few discrete vortices. The scale of discrete vortex shed from the leading edge was about one fourth of the chord length and it did not depend on the airfoil configuration. The length of the recirculation region to the chord length determined the number of discrete vortex consisting there. The discrete vortex shedding frequency did not depend on the airfoil configuration, however the dynamic behavior of discrete vortex depended on the airfoil configuration. Moreover, the dynamic lift increased because of the reattachment of the discrete vortices, and the dynamic behavior of discrete vortices influenced much on the dynamic lift.
Suppression of Aero-Acoustic Noise Over a Cavity
Authors: Kuroda Masafumi , Izawa Seiichiro , Xiong Ao-Kui , Fukunishi Yu
Published: February 2009

The aim of this research is to develop a method to suppress the aerodynamic noise generated by a turbulent flow over a cavity. The results of an active control experiment and a passive control experiment are reported. In the active control experiment, the phases of velocity fluctuations along the spanwise direction are changed using piezo-electric actuators, so that the sound waves generated by these velocity fluctuations will eventually cancel each other in the far field. As a result of the active control, an aerodynamic noise suppression of 30 dB is achieved. In the passive control experiment, even a greater noise suppression effect, up to 65 dB is achieved. It is shown that the location and the size of the plate have a strong influence on the noise suppression for passive control.
Visualizing Computational Simulation Results Using Virtual Reality Technology
Authors: Sezer-Uzol Nilay , Modi Anirudh , Long Lyle N. , Plassmann Paul E.
Published: February 2009

The visualization of computational simulations of complex physical problems using virtual reality technology is demonstrated in this study. A general-purpose computational steering system (POSSE) which can be coupled to any C/C++ simulation code, has been developed and tested with a 3-D parallel Navier-Stokes flow solver (PUMA2) [1]. In addition, the visualizations can be displayed using virtual reality facilities (such as CAVEs and RAVEs) to better understand the 3-D nature of the flowfields. The simulations can be run on parallel computers such as Beowulf clusters, while the visualization is performed on other computers, through a client-server approach. A key advantage of our system is its scalability. Visualization primitives are generated on the parallel computer. This is essential for large-scale simulations, since it is often not possible to post-process the entire flowfield on a single computer due to memory and speed constraints. Example applications of time-dependent and three-dimensional computational flow simulations performed at Penn-State are presented to show the usefulness of POSSE and virtual reality systems. The examples include CFD predictions for unsteady simulations of a helicopter rotor, unsteady ship airwake simulations, helicopter tail fan-in-fin flow simulations and simulations of time-accurate flow and noise due to a landing gear.
Looking Just Like It Doesn’t: Perception and Illusion in Scientific Visualization
Authors: Horowitz Jay G.
Published: February 2009

Scientific visualization, particularly of fluid flow, maps abstract characteristics of the data onto geometric structures that can be represented visually. The characteristics of those structures, in turn, are inferred by their perceived shape, color, surface properties, motion, etc. Virtual reality (VR) technology has the potential for enhancing the ability to discern subtle properties of those structures by recruiting a richer set of sensory tools such as stereopsis, positional interaction, and expanded peripheral vision. However, the perceived VR environment derives from several illusions created by the interaction between the display hardware and our sensory and cognitive systems. Understanding how one assigns properties to objects in that virtual world is critical for generating valid inferences about the underlying data. It also provides fascinating insight into our own role as a measuring device.
Multiphase Flows Rendered in Virtual Reality
Authors: Sherman William , Loth Eric
Published: February 2009

A virtual reality (VR) technique has been developed to allow user immersion (stereo-graphic rendering, user tracking, and object interactivity) in generic unsteady three-dimensional multi-phase flow data sets. This article describes the structure and logic used to design and construct a VR technique that employs a multi-phase flow-field computed a priori as an input (i.e. simulations are conducted beforehand with a researcher’s multi-phase CFD code). The input field for this flow visualization is divided into two parts: the Eulerian three-dimensional grid nodes and velocities for the continuous fluid properties (specified using conventional TECLOT data format) and the Lagrangian time-history trajectory files for the dispersed fluid. While tracking the dispersed phase trajectories as animated spheres of adjustable size and number, the continuous-phase flow can be simultaneously rendered with velocity vectors, iso-contour surfaces and planar flood-contour maps of different variables. The geometric and notional view of the combined visualization of both phases is interactively controlled throughout a user session. The resulting technique is demonstrated with a 3-D unsteady data set of Lagrangian particles dispersing in an Eulerian description of a turbulent boundary layer, stemming from a Direct Numerical Simulation of the Navier-Stokes equations.
An Immersive and Interactive Visualization System for Large-Scale CFD
Authors: Matsuo Yuichi
Published: February 2009

We have been long involved in large-scale computational fluid dynamics (CFD) simulations in aerospace research. These days, as the computer power grows, output data from the simulations becomes larger and larger, and we feel that the current visualization methodology has its limitation in understanding. Thus, with the target concepts of reality, collaboration, and communication, we has built an immersive and interactive visualization system with a large-sized wall-type display. The system, which has been in operation since April 2001, is driven by a SGI Onyx 3400 server with 32 CPUs, 64Gbytes memory, and 6 IR3 graphics pipelines, and comprises a 4.6×1.5-meter (15×5-foot) rear projection screen with 3 high-resolution CRT projectors, supporting stereoscopic viewing, easy color/luminosity matching, and accurate edge-blending. The system is mainly used for visualization of large-scale CFD simulations. This paper will describe the new visualization system introduced at the National Aerospace Laboratory of Japan, and the features of the system are discussed while illustrating some typical visualized examples.
Investigation of Near-Wall Coherent Structures by Stereo Particle Image Velocimetry
Authors: Nguyen C. V. , Wells J. C.
Published: February 2009

We consider issues of camera calibration and measurement validation for a stereo P.I.V. system designed for high-resolution measurements at 15 Hz in a cross-stream plane of an open channel flow, in which Willert’s “front-and-rear” stereo camera arrangement is applied with a new three-dimensional calibration target. The most commonly used mathematical expression of the pinhole camera model contains eleven constants, even though an ideal camera, i.e. one free from lens aberrations and with a uniform and rectilinear distribution of pixels on the sensor face, is characterized by only seven constants with respect to a given physical coordinate system. Thus this mapping function is in fact more general than the pinhole model, and four of its constants are in principle determined by the other seven. However, it has the advantage that the constants may be found from calibration photographs by linear least squares, and in a previous communication (10th International Symposium on Flow Visualization, 2002), we verified experimentally that this form of the pinhole model may by applied without modification to a Scheimpflug camera as used in our setup. In the present paper, we show that when looking through an air-water interface at an angle close to 90 degrees, for which the pinhole model is not valid, this redundant camera model is still applicable, thus explaining why our experimental check gave very good results. We also provide refined data from a previously reported cross-check on the two horizontal components of instantaneous velocity vectors, using a third camera viewing from below with beam illumination (rather than sheet illumination).
Single-Camera 3-D Particle Tracking Velocimetry Using Liquid Crystal Image Projector
Authors: Ido Takehiro , Shimizu Hiromasa , Nakajima Yoichi , Ishikawa Masa-aki , Murai Yuichi , Yamamoto Fujio
Published: February 2009

Three-dimensional Particle Tracking Velocimetry (3-D PTV) is one of a useful measurement tools to understand complicated structure of flow. This paper concerns with a system of 3-D PTV based on color image processing using a liquid crystal image projector. The merit of the present system is inexpensive setup and needless of complicated procedure for stereo-pair matching of particles since all the process are carried out by single-camera. The accuracy of color-based PTV depends on the image quality and the optical characteristics of color-light scattering on tracer particles. After detailed discussion on these technical problems is mentioned, two kinds of experimental demonstration are shown by a chamber-inside steady flow and a vortex-shedding flow behind rectangular cylinder.
Stereoscopic PIV Measurement on Multi-Blade Fan
Authors: Cho G. R. , Kawahashi M. , Hirahara H. , Kitadume M.
Published: February 2009

There are many sources of noise in multi-blade fan near the trailing edge of blades or cut-off region of the casing. The flows passing through the impeller of a multi-blade fan that is now being used as a blower for automobile air conditioner system have been successfully quantified by a stereoscopic PIV technique. Eight test sections are chosen at the inlet flow of the impeller changing the measurement angles, 0, 45, 90, 135, 180, 225, 270 and 315 degrees from cut-off point of its casing. The calibration for cameras is conducted at 9 planes within the blade width of the impeller. It is revealed that the velocity distributions are strongly influenced by the casing and cone shape, and there exists a symmetrical spiral flows in the inner part of the impeller because cut-off part of its casing disturb the fluid flow.
Three-Dimensional Velocity and Droplet Size Measurements of Spray Flow (Keynote Paper)
Authors: Zama Yoshio , Kawahashi Masaaki , Hirahara Hiroyuki
Published: February 2009

The present investigation describes an application of a novel technique of simultaneous measurement of droplet size and three-dimensional components of velocity in a high density spray with swirl. The spray has a complicated and three-dimensional structure caused by mixing with surrounding airflow entrained by high speed fuel jet issuing from a nozzle. The breakup process of fuel film to fine-droplet-cloud, the droplet size dispersion and the velocity distribution of droplets are important factors in practical application of fuel spray for combustors. The conventional technique can be applied to local measurement of droplet speed and size. Recent methods, based on optical and image processing techniques, provide measurement of the velocity and droplet size distribution in observation area or volume. Maeda et al. proposed an excellent measurement technique of the size and the velocity distribution of droplet in spray based on interferometric laser imaging in which the fringe pattern is generated at the out of focus plane by interference between 0th order and 1st order refractions of droplet illuminated by high power laser light sheet. And also, in this technique, the separation of overlapping droplets image has been successfully done by optical method. As a practical application, the size and velocity distributions of droplets in a high density spray without swirl have been measured by this technique. In general, the droplet motion in a spray field is highly three-dimensional. Especially, a spray generated by a swirl nozzle shows complicated droplet motion in the three-dimensional field. In order to analyze the configuration of a complicated spray field, three-dimensional velocity measurement of droplets must be required. In the present paper, a combined measurement technique of the size and three velocity components of droplets in three-dimensional spray field based on doublet imaging technique of droplets and stereoscopic PIV method has been developed. And its feasibility and applicability was confirmed by practical application to measurements of spray fields induced by a swirl jet nozzle using in gas turbine.
Particle Tracking Velocimetry Measurement of Bubble-Bubble Interaction
Authors: Ashihara Masa-aki , Kitagawa Atsuhide , Ishikawa Masa-aki , Nakashinchi Akihiro , Murai Yuichi , Yamamoto Fujio
Published: February 2009

Bubble-bubble interaction is a quite fundamental issue to understand multiphase flow dynamics and to improve mathematical models of dispersed multiphase flow for higher volume fraction of dispersion. In this study, the bubble-bubble interaction is measured using Particle Tracking Velocimetry (PTV) in various environments. First, bubbles sliding on a vertical wall are measured using 2-D PTV. Second, the free rising bubbles in an unbounded space are measured applying 3-D PTV. Third, the simultaneous measurement for gas and liquid phases in the layer of wall-sliding bubbles is carried out. The measurement data have shown that the average bubble-bubble interaction patterns in the wall-sliding bubbles and in the free rising bubbles were attractive in the vertical direction and repulsive in the horizontal direction. The relation between the carrier phase flow structure and the bubbles’ motion is detected to explain the mechanism of the bubble-bubble interaction.
Spray Formation and Fuel Flow Rate at the Multi-Stage Injections Injected From the Swirl Nozzle
Authors: Sawada Kokichi , Nakao Shinji , Ishima Tsuneaki , Obokata Tomio , Kawachi Katsuyoshi , Kobayashi Kazumitsu
Published: February 2009

The structure, droplet characteristics and instantaneous fuel injection rate of two stage injection spray designed for direct injection gasoline engine were analyzed experimentally. A particle image velocimetry (PIV) to evaluate the instantaneous two-dimensional velocity field, a phase Doppler anemometer (PDA) and an instantaneous fuel flow rate meter based on a laser Doppler anemometer (LDA flow rate meter) were applied for the measurements. A swirl nozzle injector was used and injection conditions were 25 Hz of spray frequency, 2 ms and 1ms of the first and the second injection durations and 2.4, 3.3 and 9.1 ms of valve opening intervals. The initial jet of the second stage injection can overtook the main spray body of the first stage injection under the valve opening interval of 2.4 and 3.3 ms. The LDA flow rate meter made the injection rate measurement with sufficient accuracy in the two stage injection and showed the unstable second injection due to remaining pressure oscillation in the injection pipe. Both time averaged and time resolved PDA results were compared in the intermittent spray. The interaction between the first and the second sprays was also demonstrated in vector map obtained by the PIV measurement.
PTV Processing Technique Considering Relative Position of Velocity Data to Deforming Boundaries (Keynote Paper)
Authors: Yamamoto Yasufumi , Uemura Tomomasa , Yonehara Noriyoshi , Akamatsu Yuya
Published: February 2009

In this paper, a post-processing technique for PTV measurement of flow around a deforming object is proposed. In general PTV, a position of velocity vector is defined as the midpoint of a tracer particle’s displacement obtained by two sequential images. This is because this velocity vector is close to the tangent vector of the path line. In this case, however, position of the object boundary at the middle time between two sequential PIV images must be interpolated. In this paper, a technique using three-frame images and Eulerian averaging in order to obtain velocity distribution on the regular grid points is proposed and evaluated. As the result, it is found that smooth and correct velocity distribution on the boundary of a bubble is obtained by the present approach.
Improvement of the Noise Filtering and Image Registration Methods for PSP Experiments
Authors: Fujimatsu Nobuyoshi , Fujii Kozo , Tamura Yoshiaki
Published: February 2009

Image processing procedure for noise reduction and image registration in the PSP experiments is investigated. A few kinds of filter are examined for the shot noise reduction caused by the CCD camera. The algorithm to detect a marker cell located on the model surface is proposed and an appropriate number size is shown. The algorithm using the wavelet transform is investigated to sharpen the edge around the model. The results indicate that the method developed in this paper effectively removes the shot noise and corrects the displacement of the model during wind-on.
Turbulence Modulation in an Initially Quiescent Two-Phase Flow at High Volume Fractions Using Stereoscopic PIV
Authors: Stoddard N. R. , Richards C. D. , Crowe C. T. , Troutt T. R.
Published: February 2009

Turbulence data for 5 mm solid, spherical particles falling at terminal velocity through an initially quiescent vertical water channel are obtained using a Scheimpflu¨g stereo-PIV system. The system was successfully implemented into the flow facility and optimized to provide 3-D velocity field information for volume fractions at 2.71% and 5.24%. Vector validation played a significant role in reducing the data to obtain turbulence intensities as a function of particle fall time. The system was shown to be capable of measuring in-plane and out-of-plane displacements (velocities) with an error of less than 0.6%, despite blockage effects by the particles and inherent experimental errors. Since similar data in current literature is sparse, a popular length-scale model is provided in support of the data.
Visualization of Micro- and Macromixing in Liquid Mixtures of Reacting Components (Keynote Paper)
Authors: Kling Kerstin , Mewes Dieter
Published: February 2009

Micromixing is visualized inside a stirred vessel by using two different optical measurement techniques, the optical tomography and the Planar Laser Induced Fluorescence technique (PLIF). In order to distinguish between macro- and micromixing, a mixture of two dyes is injected into the mixing vessel. One of the dyes is an inert dye whereas the second dye is undergoing a fast chemical reaction with the vessel content. The distribution of the inert dye serves as a tracer for the macromixing but does not predicate the mixing quality on the nano scale. The chemical reaction requires mixing on the molecular scale. Therefore the reacting dye, which is changing its emission characteristics during the reaction, indirectly visualizes the micromixing. The tomographical dual wavelength photometry is used to measure the three-dimensional, transient concentration fields in the whole vessel at the same time. Measurements with the Planar Laser Induced Fluorescence technique are performed in an arbitrary plane of the vessel. This restriction on a two-dimensional concentration field is recompensed with a much higher spatial resolution which allows to visualize small scale structures in the order of mm. For both techniques low Reynolds number measurements are performed in a mixing vessel equipped with a Rushton turbine. Results are presented as two- or three-dimensional concentration fields. Areas of micromixing are detected by calculating the local degree of deviation from the concentration fields. They are depending on the injection position of the dye and are mainly found in the boundary layer of the lamellas.
Flow Characteristics of Round Jet Issuing Into Counter-Flowing Uniform Stream
Authors: Miyata Masafumi , Yagi Tatsushi
Published: February 2009

Two-color four beam LDV measurements were conducted for the round jet issuing into a counter-flowing uniform stream under well controlled boundary conditions. A comprehensive set of the velocity data was documented for velocity ratios from 0.8 to 7. The linear dependence of jet penetration length on velocity ratio was confirmed for all conditions investigated, including those with velocity ratios less than 1. The proportional coefficient estimated is substantially larger than those reported for similar jets in a water channel. The streamwise variations of mean velocity and turbulence intensity on the jet axis also depend only on velocity ratio. It is very interesting to know that the streamwise turbulence intensity on the jet axis, non-dimensionalized by uniform velocity, is at a maximum near at the stagnation point and that the maximum has a constant value near 1 for velocity-ratios greater than 2. The static pressure was found to become near to zero at the stagnation point and is negative in the core of the recirculation region.
Propulsive Vortical Patterns and Unsteady Fluid Forces of a Flapping Airfoil
Authors: Yang Chang-Jo , Fuchiwaki Masaki , Tanaka Kazuhiro
Published: February 2009

It is known that a flapping airfoil can produce a thrust force through the generation of a reversed Ka´rma´n vortex street and this can be expected to be a new highly effective propulsion system. A flapping airfoil model was made and it was operated within a water channel. The wake formation behind the flapping airfoil was visualized and a dynamic thrust force was measured using a 6-axis force sensor based on force and moment detectors. We have examined various conditions such as reduced frequency and amplitude in a NACA 0010 airfoil. The results of the analysis showed that the unsteady fluid forces of the flapping airfoil increased with Strouhal number.
Reynolds Stress Field of a Stronger Wall Jet Managed by a Streamwise Vortex: Effect of Periodic Perturbation
Authors: Mochizuki Shinsuke , Yamada Seiji , Osaka Hideo
Published: February 2009

Six Reynolds stress components were studied experimentally to understand evolution of streamwise vortex and a plane wall jet. It is seen that periodic perturbation are able to modify non-isotropic Reynolds stress field involved in the transport equation for streamwise vorticity. Modified Reynolds stress field accelerates development of vortex radius in spanwise direction. Interaction between streamwise vortex and spanwise eddies in the outer layer of the plane wall jet strengthen both velocity and length scales of large-scale eddies and increase streamwise momentum flux in enhancement of entrainment process.
Flow Visualization of Excited Coaxial Water Jet With Phase Difference
Authors: Kiwata Takahiro , Okajima Atsushi , Kimura Shigeo , Ishii Kazumasa
Published: February 2009

Flow visualization and measurements of mean and fluctuating velocities were performed on a coaxial jet at a Reynolds number of 3000 in an open water tank using hot-film anemometry, particle image velocimetry (PIV) and laser-induced fluorescence (LIF). The coaxial jet, with a velocity ratio of 0.6, was excited at the forcing frequencies fe = fn, fn/2, where fn is the initial vortex frequency of the unexcited jet. The annular and circular jets were subjected to differently phased excitation of the vortical structure in the inner and outer shear-layers, and the effects were studied. For a coaxial jet excited at half of the initial vortex frequency, the vortex pattern and interaction dynamics in the near-field of the jet depend on the phase of the excitations. Vortex-pairing is promoted by forced excitation with specific phase differences, which produces rapid diffusion of the jet width. For the forcing frequency fe = fn, forced excitation with various phase differences has little effect on the vortex pattern in the shear-layers, but the center-line velocity increases more than that of a coaxial jet subjected to a forced excitation of fe = fn/2.
Generation Mechanism of Streaky Structure in Natural Transition
Authors: Inasawa Ayumu , Lundell Fredrik , Matsubara Masaharu , Alfredsson P. H. , Kohama Yasuaki
Published: February 2009

In a transitional boundary layer subjected to free-stream turbulence, streaky structures develop and eventually break down to turbulence after wavy motions. The purpose of the present study is to reveal the dominant scales of the streaky structures using a novel stereo PTV system measuring the streamwise and wall-normal velocities. The correlation of the streamwise velocity exhibit a negative peak at a certain spanwise separation. If normalized with the local boundary layer thickness, the spanwise separation minimizing the correlation decreases downstream and reaches the boundary layer thickness at the most downstream position. The streamwise correlation coefficient is asymptotically decreasing to zero and the streamwise integral scales are increasing downstream, indicating the large streamwise elongation of the streaky structure. The normalized spanwise scale of the wall-normal disturbance velocity also decreases downstream and it is always narrower than the width of the disturbances of the streamwise velocity. In contrast to the elongating streamwise velocity disturbance, the integral scale in the streamwise direction of the wall-normal disturbance is constant with downstream position. The length scales of the wall-normal disturbance are more less constant with the streamwise position and this result concludes that the wall-normal disturbance is simply convected by the mean flow after the receptivity process.
Active Control of Flow Field Structure in a Transitional Flat Plate Boundary Layer
Authors: Sakai Takeshi , Shibamoto Koichi , Izawa Seiichiro , Xiong Ao-Kui , Fukunishi Yu
Published: February 2009

The aim of this study is to develop a method to control two-dimensional Tollmien-Schlichting wave (T-S wave) and oblique wave at the early stage of transition of a flat-plate boundary layer. Small and thin piezo-ceramic (PZT) actuators are used as the control device. In this study, twelve actuators are attached in line in the spanwise direction on the flat-plate surface and wired independently from each other. These actuators are used to generate a wave with the same amplitude and opposite sign of the incoming wave in order to cancel it. From the experimental results, it is found that the cancellation of the velocity fluctuation is successful while the sweep angle of target wave is small. However, as the sweep angle becomes larger, the canceling effect becomes insufficient in some spanwise locations even when the phases and the amplitudes of the controlling signals are fine-tuned. It is also shown that the difficulty in the fine-tuning is due to the deformation of the velocity fluctuation pattern introduced by each actuator.
Control of Jets by Very Small Signals
Authors: Ogawa N.
Published: February 2009

It is very important that a very small signal can control flow fields for selection of various control methods. Author developed a method to control the jets by very small signal in process of investigating flow fields of turbulent opposed jets. That is to say, a very thin cylinder in the jet center can control an impact position and also turbulence in the jet center play an important role. Many methods are acceptable to produce the turbulence in the jet center. And we can select various physical phenomena for input to control the jet flow fields. Here I propose a method using an arc discharge to control the axisymmetric jets.
The Velocity Field of an Annular Jet With “Cross-Member”
Authors: Foss John F. , Prevost Richard J. , Bade Kyle M. , Levasseur Aure´lien
Published: February 2009

An annular jet has been created by supporting a streamlined plug (dia = D1) in a delivery tube (dia = D2) with a narrow cross-member. PIV measurements have been carried out at x/D2 = 8 for four D1/D2 ratios. These observations, and the motivating criteria for this study, were used to select D1/D2 = 0.746 for detailed, near exit, velocity field measurements. Significant three-dimensional effects of the cross-member have been observed. Velocity field data, from a “sting supported, flat disk” (axisymmetric geometry) central plug provide comparative measurements. These comparisons are considered in detail.
Experimental and Computational Investigation on Submerged Entry Nozzle Jet Control
Authors: Arruda M. P. , Lawson N.
Published: February 2009

Two-dimensional Laser Doppler anemometry (LDA) and computational fluid dynamics (CFD) are used to investigate the influence of cross-flow and momentum addition on flow features of a submerged entry nozzle (SEN) jet in a rectangular cavity (Rejet ≈ 95000). Round sidewall control jets are used to attempt to deflect and attenuate the main jet oscillation (St,W = 0.012). Feedback loop flow manipulation by injecting in the cross-flow region has shown to be an effective control configuration and a steady deflected jet has been computationally achieved. Higher control sensitivity has been observed for a variation on lateral jet momentum rather than for a variation of mass rate injected.
A Simplified Method for Formulating the Simulation Diagram for Systems Containing Lines With Fluid Transients
Authors: Wongputorn Patompong , Hullender David A. , Woods Robert L.
Published: February 2009

The overall objective of this paper is to present a simplified approach to formulating a time domain simulation diagram for a dynamic system containing liquid or gas lines with significant fluid transients without having to use questionable simplifying assumptions for the fluid transients model. To achieve this objective, formulation of a two-port model for the fluid transients in a line that is compatible with any line termination conditions and represented by rational polynomial transfer functions is presented. This linear two-port model is first achieved by obtaining an input/output causality matrix for a line with linear flow resistances representing transition losses or flow restrictions at each end. The laminar flow “Dissipative Model” for fluid transients that accounts for nonlinear frequency dependent friction effects and thermal effects in gas lines is used in the formulation in order to achieve the most comprehensive model for axial flow in a constant diameter tube. The next step in achieving the overall objective is to obtain rational polynomial transfer function approximations for the three transfer functions in the reformulated “Dissipative Model”. These rational polynomial transfer function approximations are obtained from least-squares curve fits in the frequency domain of the exact transfer functions from the “Dissipative Model”. Then, two step-by-step procedures, using these transfer functions, for drawing a simulation diagram for a dynamic system containing fluid lines are presented.
Numerical Analysis of Pipeline Equipment Effect on Water Hammer Using Characteristic Method
Authors: Ansari Mohammad R. , Davari Abdolreza
Published: February 2009

In this attempt effect of pipeline equipment behavior was considered on water hammer numerically. The effect includes opening / closing of the shut off valves, loss of coefficient of the outlet bypass pipe for the air chamber, elasticity of the pipeline and loss coefficient due to friction. In order to study the behavior, mass and momentum conservation equations were solved numerically using characteristic method during transient conditions. As a water hammer phenomena accompanies with large pressure gradient, so the pipeline equipment behavior and their effect were analyzed with respect to the maximum pressure occurrence. For a pipeline of 5000 m length, 1 m diameter, 1 m3/s discharge and 100 m height between upstream and downstream, the following result were concluded: 1-If the moment of inertia of the pump impeller increases by 400 percent, the maximum pressure occurred by the water hammer will decrease by 9 percent. 2-During on and off of the shut off valve, 80 percent of pressure increase due to water hammer was created during the last 15 percent of valve closure. 3-If pressure wave velocity increases by 75 percent, then the maximum pressure generated due to the water hammer will increase by 27 percent. 4-If the loss coefficient of the by pass line of the air chamber decreases by 90 percent, then the maximum pressure due to the water hammer will decrease by 20 percent. 5-If the pipeline Moody friction coefficient increases by 92 percent, the maximum pressure due to the water hammer will increase by 66 percent.
Transient Pressure Measurements by Recess-Mounted Transducers
Authors: Liou Jim C. P. , Li Guohua
Published: February 2009

Recess-mounted diaphragm-type pressure transducers are often used in measuring transient pressures. When the rise time of the source pressure is very fast, ringing of the transducer may occur. This study investigates the ringing of such a transducer numerically and experimentally for the purpose of developing a general method to recover transient source pressures. The approach is based on modeling the transient hydraulics of the measurement system. Favorable comparisons between the recovered pressure traces with those measured by a flush-mounted transducer were obtained. The proposed method makes recess-mounted transducers viable for measuring rapidly changing pressures in both liquid and gaseous media.
Swing Check Valve Characterization and Modeling During Transients
Authors: Li Guohua , Liou Jim C. P.
Published: February 2009

The torque exerted by the flow around a swing check valve disk during transients strongly influences the dynamic valve-fluid interaction. This torque is difficult to quantify due to a lack of characterization data. Hydraulic torque can be separated into two components: the torque due to the flow around a stationary disk, and the torque due to the rotation of the disk. These components are expressed in terms of stationary and rotational torque coefficients. Laboratory tests on a 50 mm swing check valve show that the stationary coefficient is a function of the angular position of the valve disk only. The rotational coefficient is a function of disk angle, disk angular velocity, and the magnitude and direction of the through flow. Using these coefficients, numerical simulations of check valve slam transients can be made and the results compared with measured disk angle and pressure traces during such transients. The validity of the check valve characterization is demonstrated by the close agreement between the simulation results and the measurements.
Pipe Systems With Micro-Turbines: Water Hammer Considerations
Authors: Zhang Qinfen , Karney Bryan
Published: February 2009

Micro and small turbines, as a means of producing clean and renewable energy by transforming hydropower to electricity, can be used extensively in pipe systems. With respect to hydraulic transient modeling, governed turbines have two additional features compared to the more familiar pump boundary condition: namely, wicket gate adjustments and more complicated device characteristics. Based on head balance (or nodal flow balance) considerations, torque (or speed change) relations, and the governor equation, a numerical model of the turbine boundary condition in a pipe system is established. The combinations of the three basic equations under specific situations are then discussed. To verify in a general way this numerical model, a penstock failure at Lapino Power Plant (Poland) is simulated. The current work sets the stage for a more comprehensive analysis of turbines and related unsteady flow issues in topologically complex pipe networks.
Optimum Selection of Hydraulic Devices for Water Hammer Control in the Pipeline Systems Using Genetic Algorithm
Authors: Jung Bong Seong , Karney Bryan W.
Published: February 2009

Genetic algorithms have been used to solve many water distribution system optimization problems, but have generally been limited to steady state or quasi-steady state optimization. However, transient events within pipe system are inevitable and the effect of water hammer should not be overlooked. The purpose of this paper is to optimize the selection, sizing and placement of hydraulic devices in a pipeline system considering its transient response. A global optimal solution using genetic algorithm suggests optimal size, location and number of hydraulic devices to cope with water hammer. This study shows that the integration of a genetic algorithm code with a transient simulator can improve both the design and the response of a pipe network. This study also shows that the selection of optimum protection strategy is an integrated problem, involving consideration of loading condition, device and system characteristics, and protection strategy. Simpler transient control systems are often found to outperform more complex ones.
Transient Analysis of Mixed Free-Surface-Pressurized Flows With Modified Slot Model: Part 2 — Similarity Law and Eigenvalue Problem
Authors: Arai Kazutoshi , Yamamoto Katsuhiro , Saitou Mitsuhiro , Fukumoto Shigeru
Published: February 2009

To analyze transient free-surface-pressurized flows with entrapped air in a drainage system, a virtual slot model with ceiling has been introduced. Using this model, calculations for the reduced model and the actual size model are carried out to examine a scale effect on the transient flow. The results show that up-scaling the system causes the increase in compressibility of entrapped air so that the rate of pressure rise decreases. Next, it is confirmed that the partial differential equations for the modified slot model have real eigenvalues and then the initial value problem is well-posed when the velocity difference between air and water is not so large. The increase in the velocity difference yields a system having complex eigenvalue, however the well behaved numerical solutions can be obtained since the friction terms in the differential equations suppress the numerical instability.
Transient Flow Modeling of Networks With Both Implicit and Explicit Components
Authors: Schohl Gerald S.
Published: February 2009

The computer code TFSIM simulates transient and steady flow in networks defined by any combination of explicit pipes, implicit pipes, implicit open channels, and various other implicit components. Flow in explicit pipes is modeled using the fixed-grid method of characteristics. Flow in implicit pipes and open channels is modeled using Preissmann’s weighted four-point scheme. For solution at each time step, a network is organized into explicit components and implicit clusters, where an implicit cluster is defined as a grouping of implicit components bounded by explicit components and external boundary conditions. Each implicit cluster is solved using the Newton-Raphson technique with the double-sweep method, modified for loops, used to solve the matrix of linearized equations at each iteration. While the explicit method of characteristics is the preferred numerical method for transient analysis of pipe flow, the implicit Preissmann’s scheme can provide nearly identical solutions for slower transients while allowing larger time steps. By using a mix of implicit and explicit pipes, large, complex networks with many pipes of many different lengths can be analyzed using a time step based on resolving the time-varying boundary conditions rather than solely on satisfying the Courant condition in every pipe segment.
Hydrodynamic Loads Calculation of Pressurizer Safety Valve Discharge Piping Using RELAP5/MOD3.1 Computer Code
Authors: Lee Kyu Bok , Lee Heedo , Jeung Jae Sik , Ko Hee Jin , Kim Chang Hyo
Published: February 2009

An assessment was performed with RELAP5/MOD3.1 computer code for EPRI/CE Test No. 917 which was a simulation of a hot water loop seal discharge followed by steam discharge through a pressurizer safety valve. In the RELAP5/MOD3.1 calculation, the input data such as valve opening characteristics, initial fluid conditions, system nodalizations, and system component modeling, were modeled to be identical to those in the RELAP5/MOD1 calculation performed by EPRI. In addition, the input data such as options applied to volumes and junctions, heat transfer to the pipe walls, and pipe orientations, were modeled in accordance with the modeling guidelines suggested in NUREG/IA-0093 which was a RELAP5/MOD3/5m5 code assessment for EPRI/CE Test No. 917. The calculation results were compared with the experimental data as well as the RELAP5/MOD1 calculation to assess the applicability of the RELAP5/MOD3.1 for the hydrodynamic loads calculation. It was demonstrated from the comparisons that the RELAP5/MOD3.1 computer code yielded very similar hydrodynamic loads to the experimental data as well as the RELAP5/MOD1 calculation results, even though minor discrepancies were also identified. Therefore, it is concluded from the assessment that the RELAP5/MOD3.1 computer code can be used as a suitable design tool to calculate the hydrodynamic loads for the hot water loop seal discharge followed by steam discharge transient.
Numerical Modeling of Fluid Transients by a Finite Volume Procedure for Rocket Propulsion Systems
Authors: Majumdar Alok K. , Flachbart Robin H.
Published: February 2009

This paper describes the application of a finite volume procedure for a fluid network to predict fluid transients following a rapid valve closure in a long cryogenic pipeline. The conservation equations of mass, momentum, energy, and the equation of state for real fluids are solved in the fluid network consisting of nodes and branches. In the present formulation, the speed of sound does not appear explicitly in the governing equations. Instead, the equation of state for a real fluid is solved in conjunction with the conservation equations to calculate the compressibility factor for modeling the wave propagation phenomenon. The numerical procedure is also capable of modeling the wave propagation due to phase change and gas-liquid mixture. The predicted history of pressure and velocity variation in a single pipe has been compared to the solution by the method of characteristics (MOC) for liquid oxygen (LO2), liquid hydrogen (LH2), and water (H2O). The paper also presents the numerical solution of pressure surges for a gas-liquid mixture, condensation of vapor, and flow circuit with parallel branches and tailpipe.
Onset of Water Hammer Phenomenon Following Flow Surge Characteristics in Tube-Type Condensing Flows
Authors: Bhatt B. L.
Published: February 2009

Two-Phase region, in condensing flow undergoing complete condensation inside a tube, acts as an amplifier of any small internal or external disturbances. A small, externally imposed change in the inlet vapor flow rate, or heat flux, leads to substantial surges in the outlet liquid flow rate, including the possibility of flow reversals. Also, if the conditions are right, slight internal disturbances as a result of vapor/liquid interaction, can lead to sustained oscillations of large amplitude, such as in the outlet liquid flow rate. Such surging characteristics coupled with rapid bubble collapse may lead to water hammer phenomenon. This paper will summarize both experimental observations and theoretical models as a result of externally imposed, or internally induced, flow changes in condensing flows. The physics of the processes, including liquid/vapor density ratio, vapor compressibility, bubble collapse, and liquid inertia will be highlighted. The condensing flow stability criterion will be used to provide a possible physical and an analytical basis for the catastrophic piping failure due to a condensation induced water hammer.