bluuebunny/crossref_metadata_2025 huggingface dataset:
Injury and Mortality to Fish Passing Through Pumping Stations
Authors: van Esch Bart
Published: June 2012

An unwanted side effect of pumping stations is that fish suffer from injury and mortality when passing through the pumps and that fish migration is hampered. In recent years, the development of so-called “fish-friendly pumping stations” is becoming a hot topic among European governmental institutions and pump manufacturers. In the Netherlands, many field studies have been conducted over the last decade, to assess the chances of survival for fish passing through pumps. However, a clear correlation between observed injury or mortality and (for example) flow rate, shaft speed or pump type could not be established. This paper presents a new analysis of the above mentioned field studies. It makes use of American studies on the biological criteria for fish injury, the most important of which are pressure changes, shear forces, and mechanical injury. A blade strike model was adapted to fish passing through centrifugal pumps of radial, mixed-flow, and axial type. It reveals the relation between fish injury and the type of pump, its size, shaft speed, and pressure head. The results correlate well with experiments. The flow through a typical mixed-flow pump is calculated using CFD. The results show that pressure fluctuations and shear forces are not likely to add to fish mortality. The paper concludes with guidelines for the design and selection of “fish-friendly pumps” in pumping stations.
An Acoustics Method of Judging Inception Cavitation of Runner of Model Pump Turbine on Pump Condition
Authors: Zhao Yue , Liu Zhiliang , Zhao Yingnan , Guo Quanbao
Published: June 2012

To determine the inception cavitation of model pump-turbine runner blade still depends on the artifical way, hence the results differ by the observers. An acoustics method is performed to determine the inception cavitation of model pump-turbine runner blade by abstracting and analyzing the characteristic parameters of the cavitation noise acquired with the hydrophone. The rationality and accuracy of this method have been verified by the tests, and it is significant to determine the inception cavitation instead of the experimental way.
Computational Investigation of the Flow Field Inside an Submersible Tubular Pump
Authors: Jin Yan , Liu Chao , Zhou Jiren , Tang Fangping
Published: June 2012

Submersible tubular pump is particularly suitable for ultra-low head (net head less than 2 m) pumping station which can reduce the excavation depth, lower engine room height, simplify hydraulic structure, and save civil engineering costs. Submersible tubular pump with smaller motor unit can reduce the flow resistance. The flow field inside the submersible tubular pump is simulated in a commercial computation fluid dynamics (CFD) code FLUENT. The RNG k-ε turbulent model and SIMPLE algorithm are applied to analyze the full passage of a submersible tubular pump, the performance of pump such as head, shaft power and efficiency are predicted based on the calculation of different operating conditions. The simulations are carried out over a wide range of operating points, from 0.8 of the reference mass flow rate at the best efficiency point (BEP) to the 1.28 of the BEP flow rate at the same rotating speed. For verifying the accuracy and reliability of the calculation results, a model test is conducted. The comparison of simulation results and the experiment data show that the calculation performances are agree with the experiment results in the high efficiency area and large discharge condition, but in the condition of low discharge, it exists deviations between the two results. Compare with the numerical simulation and experiment, which can provide more evidences for the hydraulic performance prediction and optimization design of submersible tubular pump pumping system.
Three-Dimensional Blade Design of Helico-Axial Multiphase Pump Impeller Based on Numerical Solution of Meridian Flow Net and Blade Mean Camber Lines
Authors: Zhang Jinya , Zhu Hongwu , Wei Huan
Published: June 2012

The three-dimensional blade design method is adopted to design the blades of the impeller of a helico-axial multiphase pump. In this design method, the flow field of the impeller is computed with the hypothesis of multiphase homogeneous flow on the basis that it is the practical flow regime in the multiphase pump. The shape of the blade is obtained from a numerical solution of the meridian flow net the on meridional plane and blade mean camber lines on stream-surfaces of revolution. First, the contour shape and size of the meridian flow channel of the impeller blade is determined by parameterization design. Second, according to the discrete data of the contour shape, the meridian streamlines are determined by iterative computation based on solving the gas-liquid two phase meridional velocity gradient equation and the two phase coupled equations with quasi-orthogonals, and the flow parameters of the meridian flow net are computed simultaneously in order that the characteristics of the meridian fluid flow can be determined. And then the distribution of velocity moments can be obtained further. Third, the blade mean camber line equation is integrated with the point-by-point integral method, and then the blade mean camber line on the stream-surface of revolution which corresponds to every meridian streamline is obtained in order to form the shape of the impeller blade surface. At last, the meridional blade elements, which are the intersecting curves of blade shape surface with several meridional planes at different angles, and the variation of blade thickness, are determined. After that, the solid modeling of the three-dimensional blade of the impeller is formed. In addition, the characteristics of the flow field of the impeller and the performance of the multiphase pump are computed by CFD numerical simulation. The position where air blocking is tends to occur was analyzed on the basis of the result of numerical simulation.
Experimental and Numerical Investigation of Blades Effect on Aerodynamic Performance of Small Axial Flow Fan
Authors: Zhang Li , Jin Yingzi , Zhao Yi , Liu Pin
Published: June 2012

To explore the effect of blade numbers on aerodynamic performance and noise of small axial flow fan, the steady flow field and the unsteady flow field of fan models with 6 different blade numbers (such as 5, 7, 9, 11, 13, 15) are numerically calculated. Then the internal flow distribution, static characteristic and aerodynamic noise are analyzed among six different fan models. The analysis results show: (1)Total pressure and efficiency generally maintain the trend of first increasing and then decreasing with increasing blade numbers, and it is the maximum when fan blade number is 11. The flow rate coupled with the maximum efficiency has never changed with increasing the blade numbers. (2)With increasing blade numbers, overall sound pressure level of the aerodynamic noise is gradually decreasing near the outlet of fan tip, while it is first decreasing and then increasing before decreasing again at 1 meter away from the central axis of the impeller along the outlet. When fan blade number is 11, overall sound pressure level of the aerodynamic noise is the greatest. Furthermore, the aerodynamic performance tests of fan models with 6 different blade numbers are carried out, the results of between the tests and the numerical calculations are roughly consistent. The research results will provide the proof of the parameter optimization and the structure design for high performance and low noise small axial fans.
Experimental Characterization of Thermal Cavitation Effects on Space Rocket Axial Inducers
Authors: Pasini Angelo , Torre Lucio , Cervone Angelo , d’Agostino Luca
Published: June 2012

The paper shows the results of an experimental campaign conducted in the CPRTF (Cavitating Pump Rotordynamic Test Facility) at ALTA S.p.A., aimed at characterizing the cavitation thermal effects on two tapered-hub, variable-pitch inducers, designated as DAPAMITO. The semi-empirical method proposed by Ruggeri and Moore for scaling the thermal cavitation effects has been successfully applied and, consequently, a further validation of this method has been provided. The influence of the temperature on the intensity of the performance degradation associated with the attached cavitation instability has been identified as a new typology of cavitation thermal effects. In this case, the inhibition of the bubble growth due to thermal effects can be detected by the reduction of the performance degradation usually associated with this type of instability.
A Numerical Study of Pump Characteristics of a Concrete Volute Pump With Various Types of Volutes
Authors: Kim Jin Young , Chung Kyung Nam , Kim Yong Kyun
Published: June 2012

The concrete volute pump with a specific speed of 460 has been designed. The performance characteristics and radial thrust has been investigated for three types of volute casings by using CFD. The first one is a conventional volute casing, the second one is the volute with diffuser and the third one is a double volute, respectively. Here the volutes have been designed by the constant velocity method. The effects of the diffuser and the double volute on the radial thrust have been compared by using the transient calculation. The analysis results show that radial force of the volute with a diffuser decreases at off-design conditions compared to the other volutes.
Effect of Leading Edge Sweep on Cavitation Performance of Two-Bladed Flat Plate Inducer
Authors: Igoshi Takaki , Uchinono Yuki , Koroitamana Emosi , Ishizaka Koichi , Watanabe Satoshi , Furukawa Akinori
Published: June 2012

The installation of inducer upstream of main impeller is an effective method to improve the suction performance of turbopump. However, various types of cavitation instabilities are known to occur even at the designed flow rate as well as in the partial flow rate range. In the present study, we focus on the leading edge sweep of inducer and investigate its effect on the suction performance as well as on the onset of cavitation surge phenomenon. Flow measurements including casing wall pressure measurements, high-speed video observations, and limiting streamline observations are carried out, and discussions will be made based on those results about the influence of backward leading edge sweep on the internal flow of the inducer as well as its relation to the cavitation performance.
Numerical Simulation of the Internal Flow of a New-Type Shaft Tubular Pumping System
Authors: Zhu Honggeng , Dai Longyang , Zhang Rentian , Zhu Guoxian , Yao Linbi , Luo Jianqin
Published: June 2012

The structural features of a pumping system will directly affect the investment of the pumping station and its pumping efficiency. In the design and construction of low head or extra-low head pumping stations, bulb tubular pumping system and shaft tubular pumping system are widely adopted. So far all the 5 large tubular pumping stations finished or under construction took the form of rear type bulb tubular pumping system (bulb is arranged inside the discharge passage) in China’s Eastern Route Project of South-to-North Water Diversion. However, front type shaft tubular pumping systems (shaft is arranged inside the suction box) are more widely used in city flood-control pumping stations, which are characteristic of large amounts and medium or small scale. To improve the reliability of city flood-control pumping stations, the authors have invented a new-type shaft tubular pumping system featuring shaft suction box, siphon-type discharge passage with vacuum breaker valve as the cutoff device, which is possessed of such advantages as simpler structure, reliable cutoff and better energy performance. Taking an real pumping station in Yancheng city of China as an example, the computational fluid dynamics method was adopted in this paper to simulate the three dimensional turbulent flow of a model new-type tubular pumping system (impeller diameter D = 0.3m, rotational speed n = 1100r/min and specific speed ns is about 1500) and predict its performance, to improve the pumping system efficiency through hydraulic design optimization. Computation results show that the efficiency of the new-type shaft tubular pumping system reached 56.0% when the design head and discharge are 1.15m and 0.326m3/s respectively, and up to 68.8% when the maximum head and relevant discharge are 1.95m and 0.296m3/s respectively, having more extensive foreground for low-head, especially extra-low-head city flood-control pumping stations.
Research on Cavitation Induced Noise in a Centrifugal Pump
Authors: Gao Bo , Yang Minguan , Li Zhong , Kang Can
Published: June 2012

To study the cavitation flow field and cavitation induced noise features in a centrifugal pump, a model pump is chosen as the research object. Cavitation flow field at design and off-design operating conditions is visualized by high speed camera. The cavitation bubbles spatial distribution changing with pump net positive suction head (NPSH) value have been captured. Meanwhile, cavitation noise signals from the pump at the corresponding operating conditions have been acquired in the frequency band from 10 up to 8kHz. Noise levels at broadband frequency and discrete frequency, such as rotating frequency (RF) and blade pass frequency (BPF), are discussed. It is of help to recognize the relationship between cavitation bubbles and emitted noise spectrum characteristics. Experimental results indicate that the total noise level is unlikely to raise before and in the cavitation inception period. But sound pressure level (SPL) over high frequency broadband increases obviously, as well as SPL at BPF and half of that. It is hard to change at RF. When the NPSH goes down until to the onset of cavitation damage, cavitation cloud appears. The volume fraction of bubbles in every impeller passage is different. The total and high frequency noise level reach peak values near the NPSH critical point. The discrete tone at half of BPF also raises steeply. Cavitation bubbles are filled both on suction and pressure side of the blades in fully developed cavitation stage. Emitted noise energy fluctuates due to the unsteady features of internal flow in the pump.
Numerical Analysis of Influence of Pipe Length on Cavitation Surge
Authors: Iga Yuka , Nishitanaka Hayato , Yoshiki Yoshida
Published: June 2012

Generally, in boundary condition of numerical simulation of internal flow, flow velocity is fixed in the inlet boundary and static pressure is fixed in the outlet boundary or the inverse condition, which is supposed that upstream and downstream pipes and the uniform flows inside the pipes extend infinitely from the boundaries. Therefore, a numerical simulation of influence of pipe length of fluid machinery cannot be realized by changing a boundary position of the computational region. In the present study, a boundary condition which is taking into account a pipe length is used to numerical simulation of unsteady cavitation in three-blade cyclic cascade, where generalized unsteady Bernoulli equation is adapted to one dimensional region from a upstream tank to the inlet boundary. In the study, cavitation surge frequencies reproduced in the present study are compared with empirical and theoretical characteristics of cavitation surge frequencies. Then, it shows good agreement with empirical frequency of cavitation surge although it does not take into account of the system such as pipe length. On the other hand, the theoretical frequency, which takes into account of the system, predicts a value which is less than half of the present numerical result.
Flow Field in the Vaned Diffuser of a Centrifugal Pump at Different Vane Setting Angles
Authors: Boccazzi A. , Sala R. , Gaetani P.
Published: June 2012

Particle image velocimetry (2D-PIV) has been used for the investigation of the time averaged flow field inside the vaned diffuser of a centrifugal pump operating at best efficiency point. Pump performances and the diffuser flow field were analysed for three different vane setting angles. It was evidenced that flow coefficient at the best efficiency point decreases with the diffuser setting angle reduction. From 2D-PIV measurements in five different blade to blade planes, span-wise averaged flow angles and velocity distribution were computed. It was evidenced an influence of the diffuser setting angle on the span-wise distribution of the flow rate and of the absolute mass averaged flow angle at impeller discharge. An overturning, at the diffuser discharge was also evidenced for the two highest setting angles. 2D-PIV flow fields are presented in three different pseudo-secondary planes in order to enlighten the cross flows affecting the diffuser flow field.
Effects of the Pump-Circuit Acoustic Coupling on the Blade-Passing Frequency Perturbations
Authors: Keller Jens , Barrio Rau´l , Parrondo Jorge , Ferna´ndez Joaqui´n , Pe´rez Javier
Published: June 2012

Centrifugal pumps are a source of pressure and flow rate perturbations in hydraulic pumping systems. In particular, a significant excitation is usually induced at the blade-passing frequency and harmonics as a consequence of the fluid-dynamic interaction between the rotor and the stator. The magnitude of this excitation is very dependent on the internal geometry of the pump and on its point of operation, but it depends also on the acoustic response to the perturbations of the hydraulic network. The induced and transmitted perturbations can be either amplified or reduced depending on the pump-circuit acoustic coupling, and thus they can lead to excessive levels of noise and vibration under certain conditions. The purpose of the present investigation is the theoretical and experimental characterization of the perturbations induced in a laboratory pumping system, as a function of the acoustic impedance of the pipelines. For different operation points of the pump, the blade-passing frequency impedance is changed by varying the speed of rotation and, additionally, by modifying a dead-end region of the hydraulic system (that is, in the absence of net flow through it). For the theoretical calculations an acoustic model, based on matrix formulation, is applied to obtain the influence of different acoustic impedances of the suction side on the pressure fluctuations at the pump. Test measurements with a fast-response piezoelectric pressure transducer which is situated at the tongue region of the pump under the same system configurations confirm the significant effect of the pump-circuit acoustic coupling on the pressure perturbations.
A Test System for Pressure Pulsation and Hydrodynamic Noise in Centrifugal Pump Based on Virtual Instrument Technology
Authors: Luo Yin , Yuan Shouqi , Tang Yue , Yuan Jianping , Zhang Jinfeng
Published: June 2012

A system based on virtual instrument was set up to test and analyze the pressure pulsation and hydrodynamic noise in centrifugal pump. It has adjustable sampling time length and frequency which can avoid the disadvantages of data loss and redundancy caused by fixed sampling parameters. A signal preprocessing toolkit compiled by LabVIEW was set up, which can anti the aliasing of the signal by use of the low pass filter, decrease the noise in the concerned frequency by the wavelet de-noising and efficiently reduce the error caused by test system. Meanwhile, the data analysis toolkits in this system not only include signal power spectrum and octave for obtaining the frequency characteristic, but also include correlation analysis between the measured waveforms and wavelet analysis for detecting the signature of the signal. All of the toolkits could be used as an automatic real-time system. The feasibility of this system has already been evaluated in a centrifugal pump system, and it is testified that this system can realize and analyze the pressure pulsation and inner hydrodynamic noise automatically.
An Experimental Study on Opening Delay of a Reed Valve for Reciprocating Compressors
Authors: Yoshizumi Fumitaka , Kondoh Yasuhiro , Yoshida Kazunori , Moroi Takahiro , Obayashi Masakazu , Kimura Naofumi , Tamano Shinji , Morinishi Yohei
Published: June 2012

Automatic reed valves are widely used to control refrigerant gas flow in reciprocating compressors for automotive air conditioners. The oil film in the clearance between the reed and the valve seat causes a delay in opening of the valve. This opening delay of the discharge valve leads to over compression, which increases losses such as friction in sliding components and gas overheating. Therefore it is important to understand the behavior both of the oil film and the elastic reed deformation in order to reduce losses due to the delay. This study aims to develop an experimental setup that enables simultaneous visualization of the oil film rupture and measurement of the reed deformation, and to observe this behavior during the valve opening process. The gas-compression stroke is simulated by controlling compressed air with an electromagnetic valve. The oil film rupture is visually observed using a high speed camera through a special valve seat made of glass. The total deformation of the cantilever reed is identified by multipoint strain measurement with 12 strain gauges. The experiment finds that the opening process is divided into four stages. In the first stage, the reed remains stuck to the seat and deforms while the bore pressure increases. In the second stage, cavitation occurs in the oil film and the film starts to rupture. In the third stage, the oil film ruptures and the bore pressure starts to decrease. Finally, in the fourth stage, the reed is separated from the seat and the gas flows through the valve. Reducing the reed/seat contact area changes the reed deformation in the first stage, thereby increasing the reed/seat distance and realizing an earlier oil film rupture and a shorter delay.
Floating Type Ocean Wave Power Station (Unique Work of Oscillating Platform)
Authors: Otsubo Takahiro , Orita Masayuki , Kinoshita Tatsuya , Kanemoto Toshiaki , Kokubu Kiyoshi
Published: June 2012

This paper presents the unique ocean wave power station, which is composed of the floating type platform with a pair of the floats lined up at the interval of one wave length and the counter-rotating type power unit submerged in the seawater at the middle position of the platform. Such profiles make the flow velocity through the turbines two times faster than that of the traditional OWC types, and make the turbine diameter large as possible because the rotational moment hardly acts on the platform. The previous paper verified that the station is effective to get the power from the ocean wave at the normally oscillating motion. Continuously, this paper discusses the effect of the wave length on the motion of the platform and present the flow conditions around Wells type hydraulic turbine in CFD. The platform in which the floats are at the symmetrical position to the anti-node oscillates normally irrespective of the stationary wave length. On the contrary, the platform with the floats the asymmetrically arranged or being at the progressive wave plays in the dutch-roll condition and does not get the fruitful power.
Flow Characteristics of Freely Rotating Rectangular Cylinders With Different Width to Height Ratios
Authors: Park Y. G. , Yoon H. S. , Ha M. Y.
Published: June 2012

The present study numerically investigates flow past freely rotating rectangular cylinders with different width to height ratios. The immersed boundary method (IBM) to model the rectangular cylinder based on the finite volume method is used to study a two-dimensional (2-D) laminar fluid flow for different Reynolds numbers of 50, 100, and 150 in the range of 0.2 ≤ W/H ≤ 1.0, where W/H is the width to height ratio. There are three different regimes of motion. The first one is the periodic oscillation regime. The second one is rotation with reversal of direction regime. The last one is the rotation with one direction regime. All the cases are periodic oscillation regime except the cases of Re = 100 and 150 with W/H = 1.0. For Re = 100 and 150 with W/H = 1.0, the regimes are the rotation with reversal of direction regime and the rotation with one direction regime, respectively. The Strouhal number decreases with increasing the width to height ratio for Re = 50, 100 and 150. However, for Re = 100 and 150, the Strouhal number disappears at a width to height ratio of 1.0. The present study reports the detailed information of flow structure on the cylinder surface at different width to height ratio.
Implicit LES Simulations for an Aspect Ratio Two Flexible Membrane Wing
Authors: Gordnier Raymond E. , Attar Peter J.
Published: June 2012

Development of an aeroelastic solver with application to flexible membrane wings for micro air vehicle applications is presented. A high-order (up to 6th order) Navier-Stokes solver is coupled with a geometrically nonlinear p-version Reissner-Mindlin finite element plate model to simulate the highly flexible elastic membrane. An implicit LES approach is employed to compute the mixed laminar/transitional/turbulent flowfields present for the low Reynolds number flows associated with micro air vehicles. Intitial computations for a baseline rigid membrane wing are presented to understand the complex vortex dynamics associated with these flows before proceeding with the more challenging flexible cases.
Experimental Visualization of Sound Pressure Level and Vibration Around a Soundproof Barrier
Authors: Shimizu Fumio , Tanaka Kazuhiro , Yamamoto Koji , Shigefuji Hiroshi
Published: June 2012

The noise and vibration control are the one of important issues. A soundproof barrier, which covers a sound source with sound absorbing materials, is very useful for the noise reduction. When large noise and high temperature heat emit from the sound source, we must also consider the heat radiation as well as the noise reduction. The purpose of the present study is to investigate the relationship between sound pressure level and vibration on a soundproof barrier around a sound source. The effect of heat radiation hole on the sound insulation performance of the soundproof barrier is also investigated. The sound pressure level and the vibration displacement were similarly distributed on the surface of the barrier. Therefore, the vibration of the barrier was strongly influenced to the sound pressure level of the transmitted sound.
Cooling and Dehumidification Characteristics of Desiccant Cooling System in a Residential Environment
Authors: Yun Changho , Ahn Joon , Kang Byung Ha
Published: June 2012

Desiccant and water evaporation based cooling system is recently suggested as an alternative to refrigeration systems using typical vapor compression cycle for the purpose of energy saving and greenhouse gas reduction. The system receives the heat for the regeneration of the rotor from district heating, which is waste heat from a CHP plant or an incineration plant. KDHC (Korea District Heating Corporation) installed 4 systems at 4 individual houses in Su-Won, Korea and conducted field tests from Aug. 2010 to Sep. 2010. In this study, indoor conditions have been measured when the system is off as well as in operation. Also indoor conditions have been characterized according to outdoor conditions and users’ operation. Referring the ASHRAE standard, the cooling system in operation has been checked whether it could make indoor conditions comfortable or not. By analyzing the monitored variables, performance characteristics of the system were figured out. Major characteristics such as cooling capacity, heat & electricity consumption, and the COP of the system have been compared with those from the previous laboratory experiment.
Wake Structure Around Moving Elastic Airfoils With Projections and Their Characteristics of Dynamic Forces by Fluid Structure Interaction Simulation
Authors: Aphaiwong Junchangpood , Nagata Tetsushi , Fuchiwaki Masaki , Tanaka Kazuhiro
Published: June 2012

The flow around an elastic body is treated as a fluid-structure interaction (FSI), numerous fluid-structure coupled problems have been performed. Recently, two-way coupled analysis, which considers the fluid-structure interaction, has been performed extensively. In the present paper, we simulate a flow field around an elastic heaving flat plate with a variable surface shape and various Young’s moduli and perform bi-directional coupling analysis using ANSYS 12.1/ANSYS-CFX 12.1. In the case of the results without projection, the vorticity that grows along the plate surface, rolled up from the trailing edge, and developed in the wake are dependent on Strouhal number, independent of the Young’s modulus. However, in the case of the results with the projections, the vortex behaviors are different with the Young’s modulus. At E = 3.53 [MPa], the projections effect on the vortex behavior and the dynamic thrust exhibit approximately the same tendency with or without a projection. On the other hand, at E = 10.0 [MPa], the projection effect has an impact on the vortex behavior and the dynamic thrust. The vorticity and the dynamic thrust of E = 10.0 [MPa] become smaller than that of E = 3.53 [MPa] because of strong effects from the projections of the heaving elastic plate.
Direct Numerical Simulation of Global Instability in a Hole-Tone Feedback System
Authors: Matsuura Kazuo , Nakano Masami
Published: June 2012

Direct computations and experiments of a hole-tone feedback system are conducted. The mean velocities of an air-jet are 8 and 10 m/s in the computations, 6–13 m/s in the experiments. The diameters of a nozzle and an end plate hole are both 50 mm, and an impingement length between the nozzle and the end plate is 50 mm. The computational results agree well with the experimental data in terms of qualitative vortical structures and a relationship between the most dominant hole-tone frequency and a jet speed. Based on the computational results of the air-jet speed of 8 m/s, a Proper Orthogonal Decomposition (POD) analysis of the whole pressure fluctuation field is conducted. The 1st and 2nd POD modes are nearly in anti-phase, and alternatively appearing helical structures are observed upstream of the end plate hole in an isosurface plot of the eigenfunctions of the modes. Dominant behaviors of vortex shedding from the end plate hole are represented by the 3rd and 4th modes. As the result, dominant variation of the pressure fluctuation field is successfully extracted by the present POD analysis.
Interfacial Instability of Particulate Suspension in Narrow Channel
Authors: Watanabe Kensuke , Shiotani Taiga , Kondo Megumi , Sato Kodai , Harada Shusaku
Published: June 2012

The gravitational settling of particulate suspension in a narrow channel has been studied experimentally and theoretically. In our previous study, it has been found that the gravity-induced instability of suspension-fluid interface governs the particle settling motion and the suspension behaves as a continuous fluid for high concentration and small particle size. The purpose of this study is to investigate how such a suspension-fluid interface behaves in a narrow channel. The experimental and theoretical results indicate that the aspect ratio of the channel cross-section is an important parameter for describing the settling behavior of particulate suspension.
Simulation of Solid-Liquid Interaction in Presence of a Free Surface
Authors: Mirzaii Iman , Passandideh-Fard Mohammad
Published: June 2012

In this study, a numerical algorithm is developed for simulating the interactions between a liquid and solid object in presence of a free-surface flow. The presented model is that of the fast-fictitious-domain method integrated into the volume-of-fluid (VOF) technique used for tracking the free surface motion. The developed model considers the solid object as a fluid with a high viscosity resulting in a rigid motion of the object and solves the governing equations everywhere in the computational domain including the solid object. In this methodology, the application of the no-slip condition on the solid-liquid interface and the evaluation of the acting forces on the solid object are performed implicitly. The developed model is validated by a comparison of the simulation results with those of the available experiments in the literature for the free fall of one and two circular disks in a liquid domain and a sphere during its entry into a more dense liquid through a free surface. For all cases considered, the results are in good agreement with those of the experiments and other numerical studies. The model is then used to simulate the complex liquid-solid interaction during the entry of a spinning disk into a liquid free surface.
Effects of Viscosity, Particle Size, and Particle Shape on Erosion in Gas and Liquid Flows
Authors: Okita Risa , Zhang Yongli , McLaury Brenton S. , Shirazi Siamack A. , Rybicki Edmund F.
Published: June 2012

Although solid particle erosion has been examined extensively in the literature for dry gas and vacuum conditions, several parameters affecting solid particle erosion in liquids are not fully understood and need additional investigation. In this investigation, erosion ratios of two materials have been measured in gas and also in liquids with various liquid viscosities and abrasive particle sizes and shapes. Solid particle erosion ratios for aluminum 6061-T6 and 316 stainless steel have been measured for a direct impingement flow condition using a submerged jet geometry, with liquid viscosities of 1, 10, 25, and 50 cP. Sharp and rounded sand particles with average sizes of 20, 150, and 300 μm, as well as spherical glass beads with average sizes of 50, 150 and 350 μm, were used as abrasives. To make comparisons of erosion in gas and liquids, erosion ratios of the same materials in air were measured for sands and glass beads with the particle sizes of 150 and 300 μm. Based on these erosion measurements in gas and liquids, several important observations were made: (1) Particle size did not affect the erosion magnitude for gas while it did for viscous liquids. (2) Although aluminum and stainless steel have significant differences in hardness and material characteristics, the mass losses of these materials were nearly the same for the same mass of impacting particles in both liquid and gas. (3) The most important observation from these erosion tests is that the shape of the particles did not significantly affect the trend of erosion results as liquid viscosity varied. This has an important implication on particle trajectory modeling where it is generally assumed that particles are spherical in shape. Additionally, the particle velocities measured with the Laser Doppler Velocimetry (LDV) near the wall were incorporated into the erosion equations to predict the erosion ratio in liquid for each test condition. The calculated erosion ratios are compared to the measured erosion ratios for the liquid case. The calculated results agree with the trend of the experimental data.
Studies on the Hydrodynamic Phenomena in Frosting and Defrosting
Authors: Kataoka Isao , Yoshida Kenji , Mizutani Keiichi , Nishiguchi Hiroshi
Published: June 2012

The phenomena of frosting and defrosting are quite important in evaluation of efficiency of various heat equipments such as heat pump etc. In this paper, hydrodynamic phenomena in frosting and defrosting were studied experimentally. Cooling surfaces were flat or artificially grooved with the size of several tens of microns in pitch and depth. In frosting process, super cooled small water droplets were formed on the cooling surface. In the flat surface, droplets are formed around the cavities which are small holes or scars on the surface. In the artificially grooved surface, droplets are formed in the groove or flat part between grooves. Maximum size of droplets on the artificially grooved surface was controlled by pitch and depth of the grooves. In the defrosting, larger water droplets or water films were formed on the cooling surface. On the flat surface, water droplets or films remained on the surface for long time. On the other hand, on the grooved surface, water droplets or films were drained rapidly through microgroove due to the capillary driven flow.
A Newly Developed Technique for Detection of a Contact Position in Bubble Measurements by a Single-Tip Optical Fiber Probe
Authors: Mizushima Yuki , Saito Takayuki
Published: June 2012

An optical fiber probe has been frequently employed to measure bubble diameters, velocities, and local void fractions simultaneously in gas-liquid two-phase systems. For the application of the probe to tiny-bubble measurement, one of the authors already developed a Single-Tip Optical fiber Probe (STOP). The purpose of this study is to rapidly improve the measurement accuracy of the S-TOP. A bubble chord length pierced by the S-TOP is obtained. Consequently, the chord length depends on the pierced position. The chord lengths measured by the S-TOP include an error owing to the random positions pierced by the S-TOP; i.e. the measured chord length becomes shorter than the bubble minor axis, with a shift of the contact position towards the outer edge of the bubble. The S-TOP axis crosses the direction of the bubble motion at a random angle. This also causes a miscalculation of the chord lengths. In order to correct these errors in the S-TOP measurement, we need to detect the contact position and the intersection angles. To realize this, using a pre-signal is quite effective. The pre-signal is generated clearly and intensively, only when the S-TOP sensing tip is ground in a wedge shape and the tip touches vertically the center region of the bubble frontal surface. The pre-signal becomes weak and indistinct under the other contact conditions. Making the smart use of these phenomena, we are able to solve the above defects of the S-TOP. First, the relationship between the intensity of the pre-signal and the pierced positions/angles is systematically quantified. Second, a signal processing to detect the pierced positions/angles, based on the relationship, is established. Third, we discuss a mechanism of the pre-signal. We determine the most suitable S-TOP size, tip diameter and wedge-angle, for the most accurate measurement. Finally, we demonstrate the effectiveness of our newly proposed method.
Modelling Two-Phase Heat Exchanger Performance in the Annular-Mist Flow Regime Considering Entrainment and Deposition Phenomena
Authors: Pacio Julio C. , Dorao Carlos A.
Published: June 2012

Two-phase flow heat exchangers are main components of large cryogenics, power generation, refrigeration and liquefaction of natural gas plants, both in terms of capital cost and technical challenges. A major challenge in their design is the prediction of local heat transfer coefficients and pressure gradients for the evaporating or condensing fluids. Traditional heat exchanger models are based on one single correlation for predicting the heat transfer in the entire saturated boiling regime, disregarding the flow structure. However, the structure of the flow dictates how the different physical processes (nucleate boiling, convective heat transfer to the liquid and vapour phase, thin film evaporation) interact and contribute to the total heat transfer. In particular, a relevant flow-regime transition for the sizing of heat exchangers is the occurrence of dryout during the evaporation process in the annular-mist flow regime. The objective of this work is to present a three-field model for describing the annular-mist flow considering a liquid film, liquid droplets and a vapor phase, and predicting the occurrence of dryout. The flow structure is affected by the entrainment, deposition and evaporation. These processes are studied on the base of semi-empirical models. The final mathematical model is implemented into an in-house solver. The model is validated with uniform heat flux data available in the open literature. While the model performs well in the case of water flows (within 10% error), the uncertainties are larger for other fluids, probably due to the applicability range of the empirical models. Finally, two numerical examples considering the sensitivity of the input parameters and axial power distribution are studied.
Fluctuation of Void Fraction in the Microbubble Generator With a Venturi Tube
Authors: Uesawa Shin-ichiro , Kaneko Akiko , Nomura Yasumichi , Abe Yutaka
Published: June 2012

Microbubbles are tiny bubbles with less than 1 mm diameter. These bubbles are utilized in various engineering fields, and it is very important to understand physics of flow with microbubbles. Especially, void fraction is one of the significant parameter for two-phase flow. Thus, developments of real-time measurement systems of void fraction are required. In the nuclear power engineering, electrical void fraction measurement methods have been proposed as one of the real-time measurement techniques. In the present study, we apply this method to a microbubble generator with a venturi tube and examine the performance of the generator. Constant electrical current method is adopted as electrical measurement method of void fraction. Microbubbles are generated with a bubble collapse phenomenon through a venturi tube. We can generate microbubbles in high void fraction. However, mechanism of bubble collapse in a ventrui tube is not made clear and void fraction distribution toward flow direction is less understood. The applicability of constant electrical current method in bubbly flow and the process of the bubble breakup in a venturi tube are discussed. In this experiment, a voltage between two electrodes in the generator is measured with various gas-liquid volume flows as inlet conditions. From results we succeeded to measure the void fraction profile in the venturi tube with constant electrical current method. The void fractions achieve a peak before the bubble collapse and it decreased drastically for 10 mm after collapse.
Effect of Channel Wetting Properties on Flow Characteristics of Gas-Liquid Two-Phase Flow in a Microchannel
Authors: Ide Hideo , Kimura Ryuji , Kawaji Masahiro
Published: June 2012

An optical measurement system and video camera were used to investigate gas-liquid two-phase flow characteristics in wetting and poorly wetting circular microchannels of 100 μm diameter. By examining the optical sensor signals from which void fraction and the lengths and velocities of gas slugs and liquid slugs were measured, the effects of wetting on the adiabatic two-phase flow characteristics of nitrogen gas and water were investigated. The data were obtained using a T-junction with the same internal diameter as the microchannel, but the T-junction itself was well wetting in both experiments. Besides the flat nose and tail of gas slugs at low gas and liquid flow rates, poorly wetting microchannel showed higher void fraction and friction pressure drop compared to the well wetting microchannel. The poorly wetting microchannel also showed the presence of short and low moving liquid slugs which were absent in well-wetting microchannel.
High-Speed Gas-Liquid Two-Phase Nozzle Flow for CO2 (Effect of Inlet Temperature)
Authors: Kinoue Yoichi , Shiomi Norimasa , Setoguchi Toshiaki
Published: June 2012

Experimental and analytical investigations were made into the high-speed gas-liquid two-phase nozzle flow for CO2. In order to examine the effect of inlet temperature of the nozzle, two cases are examined for 17 °C and 27 °C of ambient temperatures. The experimental pressure of CO2 in the nozzle decreases remarkably, which shows suitable acceleration of CO2 in the nozzle. As for the experimental temperature decrease in the nozzle, the temperature decrease for 27 °C of ambient temperature is much lower than the one for 17 °C of ambient temperature. One-dimensional analytical model is proposed, which assumes steady, adiabatic, frictionless and equilibrium. The flow in the nozzle of convergent part is treated as single-phase flow in the model, whereas the flow in the nozzle of divergent part is treated as separated two-phase flow with saturation in the model. Analytical values of temperature or pressure profile along the nozzle agree well with the experimental values for 27 °C of ambient temperature, whereas analytical values are lower than the experimental values for 17 °C of ambient temperature.
Study on Bubble Breakup Mechanism in a Venturi Tube
Authors: Nomura Yasumichi , Uesawa Shin-ichiro , Kaneko Akiko , Abe Yutaka
Published: June 2012

Microbubbles are expected to be applied in various subjects such as engineering and medical fields. Thus, on-demand microbubble generation techniques with high efficiently are required. In the present study, the microbubble generator using a venturi tube (converging-diverging nozzle) is focused. Although this technique realizes generation of many tiny bubbles with less than several-hundred-micrometer diameter, there are several unsolved parts of flow structure in a venturi tube on bubble breakup behavior. The purpose of this study is to clarify the bubble breakup mechanism in a venturi tube for practical use. In the present study, using a high speed camera for detailed observation of bubble behavior, the following features were obtained. In low velocity conditions, bubbles are divided in several pieces with a jet penetrating from the top (downstream) to the bottom (upstream) part of the bubble. In high velocity conditions, bubbles collapse in countless microbubbles with a drastic bubble expansion and shrinkage. Also, in order to clarify the flow structure in a venturi tube, pressure profile is measured in detail. Under chocking condition, the pressure profile shows the tendency of supersonic flow in a Laval nozzle and sudden pressure gradient appears in the diverging section. There are strong correlations between bubble fission points and pressure recovery points. It is suggested that bubble collapse is strongly influenced with pressure recovery in the diverging section.
The Motion of a Bubble Swarm in Decaying Oscillating-Grid Turbulence and the Modulation of the Liquid-Phase Motion
Authors: Nagami Yasuyuki , Saito Takayuki
Published: June 2012

The modulation induced by interaction between bubble motion and liquid-phase motion is important to deeply understand the multi-scale structure of a bubbly flow. In order to quantitatively and systematically clarify the interaction between the bubble swarm and the ambient liquid-phase motion, ideally controlled turbulence and bubble swarm are required. In the present study, we employed the decaying turbulence formed by oscillating grid and a well-controlled bubble swarm launched by hypodermic needles and audio speakers. We formed homogenous isotropic turbulence by using an oscillating grid (oscillating frequency: 4 Hz, stroke: 40 mm) in a cylindrical acrylic pipe (diameter: 149 mm, height: 600 mm) filled with ion-exchanged and degassed water. The decaying turbulence was formed after stopping the oscillating grid. A bubble swarm (: the member bubble rose zigzagging in stagnant water) was launched into the decaying turbulence after two seconds from stop of the oscillating grid. We measured the bubble swarm motion by visualization and did the liquid-phase motion by PIV/LIF system with high-speed video cameras. The measurements were performed under three experimental conditions; the first one is only the decaying turbulence (Condition-O), the second one is the bubble swarm launched into the stagnant water (Condition-B), the third one is the bubble swarm launched into the decaying turbulence (Condition-OB). From the visualization results, it was found out that the positions of the bubbles were expanded in the horizontal direction compared with that under Condition-B. This indicates the transition of the bubble motion from two-dimensional motion to three-dimensional motion was enhanced by the ambient turbulence. We calculated standard deviations of the liquid-phase velocities from the PIV results. When the bubble swarm was launched into the decaying turbulence, the decay rates of the liquid-phase velocities were enhanced; i.e. the decay rates under Condition-OB were larger than those under Condition-O.