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Article type: Cover
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Published: September 20, 2002
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Article type: Appendix
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App1-
Published: September 20, 2002
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Article type: Index
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Toc1-
Published: September 20, 2002
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Masatoshi KURETA, Hajime AKIMOTO
Article type: Article
Pages
1-2
Published: September 20, 2002
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New 3D void fraction measurement system has been developed using neutron radiography technique. The purpose of this development is to measure the void fraction in tight lattice bundles which simulates the Reduced-Moderation Water Reactor (RMWR) core. In this paper, data flow in the image processing and the air-water two-phase flow experiments are mainly described. Especially, we focused on an algorism of a γ-ray noise reduction in the chapter of an image processing. It was confirmed that the γ-ray noise on original images can clearly be reduced by the new noise reduction algorism. Next, measured 3D void fraction was displayed. It was found from the observation of the data that water tends to remain between the rods.
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Teiichiro IKEDA, Shin YOSHIZAWA, Rieko SAITO, Shu TAKAGI, Yoichiro Mat ...
Article type: Article
Pages
3-4
Published: September 20, 2002
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Microbubbles are used as contrast agents for ultrasound imaging. For the clear image it is essential to take a real understanding of the dynamics of them in ultrasound field. When the microbubbles are subjected to the ultrasonic oscillation field, it takes on strong nonlinearity as the increase of ambient pressure amplitude. Since these dynamics of bubbles are strongly influenced by the thermal phenomena inside them, it is necessary to take these phenomena into account to analyze the behavior of the micro bubbles precisely. The volumetric change and the acoustic emission from a single microbubbles and bubble cluster are numerically simulated.
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Daiju MINATO, Tomohiko TANAKA, Akiko FUJIWARA, Koichi HISHIDA, Yoichir ...
Article type: Article
Pages
5-6
Published: September 20, 2002
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The objective of present study is to elucidate the mechanism of modification of turbulence structure in gas-liquid bubbly flow. The experiment consisted of a fully developed vertical upward pipe flow with 9700 of Reynolds number and less than 1.0% of void fraction. In order to obtain fundamental knowledge of the effects of void fraction and bubble diameter on modification of turbulence structure experimentally, we explored the two-dimensional flow structure in the vicinity of bubbles by applying PIV with fluorescent tracer particles, and also bubble shapes and positions were obtained by projecting shadow-image technique. It is suggested that the high concentrated bubbles in the vicinity of the wall disturb the transport of turbulence energy produced by the wall shear layer toward the middle of pipe. Thus the fluctuation velocity is remarkably reduced at the wide region of the pipe center.
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Yuichi Murai, Masaaki Ishikawa, Yoshiaki Ryono, Shinichi Toda, Akira E ...
Article type: Article
Pages
7-8
Published: September 20, 2002
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Heat exchange tubes of helical coil type are utilized in the steam generator of the fast breeder prototype reactor "Monju". The gas-liquid two-phase flow in the tube is affected by the centrifugal acceleration owing to the constant curvature of the tube. This paper presents the flow pattern map obtained by visualization, and the interfacial structure analyzed by stereoscopic image processing for isothermal air-water system. The measurement results have shown that the flow pattern map was widely occupied by slug and plug flows, and the internal liquid slug had asymmetric behavior due to the curvature of the flow.
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Hiroshi NAKAYAMA, Masafumi HIROTA, Takuya OKUDA, Yasuhiro ONO, Hideomi ...
Article type: Article
Pages
9-10
Published: September 20, 2002
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The experimental study for the flow characteristics in the square channels with a sharp 180-deg turn which frequently used as heat exchangers was conducted. PIV measurements were performed both in symmetry plane and in four cross-section planes after the turn at a Reynolds number of 2.0×(10)^4. Proper orthogonal decomposition (POD) which decomposing a field of a time-dependent variable into an orthogonal set of deterministic functions was demonstrated on the PIV snapshots to identify coherent structures in the flow. Based on the data, the unsteady flow characteristics in the channel with a sharp 180-deg turn are discussed.
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Hiroshi HIGO, Kazuhiro TANAKA, Yoh IMAI, Kiyofumi HATAKENAKA
Article type: Article
Pages
11-12
Published: September 20, 2002
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We have proposed and demonstrated the new flow measurement method using low coherent light source. This method consists of a pair of Michelson-type interferometers. Flow velocity is calculated by correlating two interference signal between the Michelson-type interferometers. And the direction of velocity is known from the locations of probe lights and interference points. Advantages of this method are that to move measuring point is easily realized and 3-dimensioal velocity measurement can be applied even in turbid flow. We developed this measurement system and measured velocity in a flow passage by this system. The measured velocity and true velocity agree well and the error of flow direction was about 2 degree.
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Kouju SHIOZAKI, Hiroyuki HIRAHARA, Masaaki KAWAHASHI
Article type: Article
Pages
13-14
Published: September 20, 2002
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Two fluids mixing flow under alternating acceleration was investigated with a visualization and numerical analysis. The visualization was carried out with ink-dyed method, LIF method and LIF-PIV technique. The mixing process depending on the acceleration and amplitude of oscillation starts in a cubic test container with 50mm sides. As a test fluid, water and brine which density is 1.2g/(cm)^3,was used. The interface between water and brine is perturbed due to Rayleigh-Taylor instability. From the flow visualization, density waves were observed in the interface through the mixing process. Small perturbation was generated beside the wall of test section, and long wave-length of perturbation was developing. Finally the flow in the test section became chaotic. The equilibrium state of the mixing depends on the acceleration and frequency. PIV data shows the vortex structure in the mixing process. In the mixing process, it might be taken long time until the kinetic energy distributed to the high frequency of vortex structure. Numerical simulation shows the more quick mixing process than the experimental result.
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Jun SAKAKIBARA, Ronald J. ADRIAN
Article type: Article
Pages
15-16
Published: September 20, 2002
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Time-dependent instantaneous planar distribution of water temperature in a Rayleigh-Bernard convection was measured by using two-color laser induced fluorescence technique. Two fluorescent dyes, Rhodamine B and Rhodamine 110,were used as temperature indicators. A laser light sheet excited the fluorescent dyes, and an optical system involving a color beam splitter gave the intensity distribution of the individual fluorescent dyes on the two separate high-resolution monochrome CCD cameras. The ratio of these fluorescence intensities at each point of the image was calibrated against the temperature to eliminate the effect of the fluctuation of illuminating light intensity. It was visualized that the mushroom-like thermal plumes were generated from bottom and top surfaces.
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Ikuo NAKAMURA, Takashi WATANABE, Yorinobu TOYA, Hiroyuki FURUKAWA
Article type: Article
Pages
17-18
Published: September 20, 2002
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In this report a problem of application of a branch-of artificial intelligence that is qualitative physics to the fluids engineering is discussed. A brief review is given for this problem specifically our recent studies are summarized. In order to construct a program which drives a computer as recognize a flow that has a vortex or not, we must clarify the various aspects of human recognition of the flow field. With this respect, we cannot avoid the problem of language that is the most important difference between human ability and animal's one. We recognize a vortex in a flow field when we see it in a situation which means us some merit or some demerit, and we articulate it as some signal. Computer should designate it as human and make an output that correspond a vortex.
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Haruo TERASAKA, Sensuke SHIMIZU, Yuriko TAKESHIMA
Article type: Article
Pages
19-20
Published: September 20, 2002
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Large-scale computational fluid dynamics (CFD) are frequently attempted to obtain high resolution solutions or to solve large scale problems and then, bulky numerical data are generated. Data compression and reconstruction are indespensable to handle such kind of large data. The authors studied to apply flow analysis procedure to data compression and reconstruntion. In our method, the original data are compressed approximately by 1/100 by thinning out the data properly and by shortening the data bit length and reconstructed by applying an interpolation and simplefied fluid analysis technique. In this paper, we attenpt a multi-level data reconstruction to avoid the out-of-core memory problems and to reduce the processing time. By applying a local mesh refinement technique, only a part of the compressed data are reconstructed according to sub-regions to be displayed on monitor screen in this method. Furthermore, the reconstruction level is chosen appropriately depending on resolution displayed.
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Masato FURUKAWA, ChoonMan JANG, Masahiro INOUE
Article type: Article
Pages
21-22
Published: September 20, 2002
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Data mining for extraction of fluid dynamic knowledge from large-scale numerical simulation results is crucial to analyzing complex unsteady three-dimensional flow phenomena in engineering application. It is indicated that identification of vortex cores and wavelet analysis of unsteady flow field are very useful to the data mining. Applications of the present data mining methods to unsteady three-dimensional vortical flow simulations in turbomachinery are presented.
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Shigeru Obayashi
Article type: Article
Pages
23-24
Published: September 20, 2002
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Self-Organizing Map (SOM) has been applied to analyze exhaust manifold design solutions obtained during multiobjective optimization using Evolutionary Algorithms. All the numerical data (design variables and the corresponding objective function values) are mapped onto the two-dimensional SOM where global tradeoffs are successfully visualized. SOM is confirmed to be a versatile datamining tool for fluid engineering.
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Yuriko TAKESHIMA, Shigeo TAKAHASHI, Issei FUJISHIRO, Haruo TERASAKA
Article type: Article
Pages
25-26
Published: September 20, 2002
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In order to grasp the inner structure of three dimensional data efficiently, various volume visualization techniques have been widely used. However, appropriate parameter values for such visualization techniques are difficult to be chosen without taking into account the features of volume data. We have developed a method for setting parameter values by analyzing the topological transitions of the isosurfaces within the volumetric domain. In this paper, we newly apply the topological framework to a fluid dataset, and adaptively choose target values for extracting iso-pressure surfaces embeded in the dataset.
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Takashi NAGUMO, Kazuyuki TODA, Makoto YAMAMOTO
Article type: Article
Pages
27-28
Published: September 20, 2002
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We have been investigating a new cycle concept for advanced propulsion system, in which hydrogen gas is directly injected from turbine blade surfaces and combusted within turbine blade passages. However, in the previous studies, we found that the aerodynamic performance of the blade is largely decreased due to the previous studies, we found that the aerodynamic performance of the blade is largely decreased due to the hydrogen injection. For the purpose of realizing our concept, turbine blade is required to have the adequate performance even with fuel injection. In the present study, we develop the shape optimization procedure for hydrogen injection. Our procedure is based on the gradient method, and composed of some elements, including CFD, geometry modification and design point arrangement, in which design points are automatically clustered around the complicated surface. Through the application of our procedure to 2 types of turbine blade with different injection, we confirm how blade geometry is suitable for carrying out hydrogen-fueled combustion.
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Keisuke NISUGI, Atsushi SHIRAI, Toshiyuki HAYASE
Article type: Article
Pages
29-30
Published: September 20, 2002
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The new flow field analysis system of "Hybrid Wind Tunnel" is proposed. The basic idea of this facility is an integration of experimental measurement and computer simulation for general flow related problems. The problem treated in this work is well-known flow field as Karman Vortex Street in a wake of a column. The fundamental system components and first-step results are investigated in previous report. In the report, favorable results have been earned even if it used a course grid system. It is generally known that very-fine grid spacing and time increment are necessary for high-accurate numerical analysis. So it needs a huge calculation load. In this paper, the hybrid wind tunnel is compared to the ordinary numerical analysis with fine grid spacing and time increments in its analysis performance including accuracy and calculation time. As a result, calculation load is drastically decreased with valid accuracy.
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Takashi WATANABE, Hiroyuki FURUKAWA, Ikuo NAKAMURA
Article type: Article
Pages
31-32
Published: September 20, 2002
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Taylor-Couette flows developing between two rotating cylinders have various flow modes which show different flow patterns even though the length of cylinders and the Reynolds number are kept constant. In this paper, we show that the non-unique phenomena are found not only in the steady flows but also during the formation processes of final flows. Subjective observations of flow vectors or contours of flow functions are usually used to determine flow modes. We introduce a new quantitative mode-detection method that is based on the human knowledge about the vortices appearing in the flow fields. This method is utilized to estimate the information given by the nonlinear dynamics found in Taylor-Couette flows.
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Jinhao Qiu, Junji Tani, Toshiyuki Hayase, Takashi Okutani, Kazumasa Sa ...
Article type: Article
Pages
33-34
Published: September 20, 2002
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In this study, three types of surface motion of smart skins were proposed and used to control the Tollmien-Schlichting(T-S) wave in the laminar boundary layer of a plate. These three types of motion are standing transverse wave (with out-of-plane displacement), progressive transverse wave and standing longitudinal wave (with in-plane displacement). The length of smart skin was set to 1,2 or 3 cycles of waveform. Numerical simulation was performed on the dependence of control effect on the amplitude and the phase of the surface motion, and the number of waveform was investigated.
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Junichi MIWA, Takahide ENDO, Nobuhide KASAGI
Article type: Article
Pages
35-36
Published: September 20, 2002
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In order to investigate the fluid-dynamic effect of a deformable actuator to be used in practical turbulence control, direct numerical simulation of associated laminar flow is carried out. It is shown that the actuator induces much larger wall-normal and spanwise velocities compared to an equivalent local blowing actuator. The streamwise vorticity induced at the wall is proportional to both surface velocity and displacement, whilst the spanwise and wall-normal vorticities are independent of the surface velocity. Induced vorticities are more than 10 times larger than the rms values in turbulent flow, in spite the surface velocity is on the order of 1/100 of the centerline velocity. These results suggest a possibility of effective turbulence control through the manipulation of vortex sheets in the viscous sublayer.
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Takashi YOSHINO, Yuji SUZUKI, Nobuhide KASAGI
Article type: Article
Pages
37-38
Published: September 20, 2002
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A prototype system for feedback control of wall turbulence is developed, and its performance is evaluated in a physical experiment. Arrayed micro hot-film sensors with 1mm spanwise spacing are employed for the measurement of streamwise shear stress fluctuations, while arrayed magnetic actuators of 3mm in diameter are used to introduce control input through wall deformation. The frequency response of the sensors and actuators is found to be sufficiently high for the flow conditions presently considered. The wall-normal velocity fluctuations above the actuator is significantly increased, and this indicates that the present actuators can introduce sufficiently large disturbances into the flow field. A preliminary feedback control experiment is also made using a genetic algorithms-based optimal control scheme. Although the number of generations is much smaller than that for convergence, the Reynolds shear stress is decreased for several sets of control parameters among 50 trials.
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Takehiko Segawa, Hiroyuki Abe, Yoshihiro Kikushima, Hiro Yoshida
Article type: Article
Pages
39-40
Published: September 20, 2002
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A fiber Bragg grating (FBG) system for evaluating real time variations of skin-friction drags introduced by several turbulence control actuators is tested in the wind tunnel with 1000×500×5000(mm)^3 test section. Two FBG sensors are for measuring the frictional drags and they are stringed between the fixed plate and floating plate. The other FBG sensor is for monitoring temperature and is mounted on a 500mm long floating flat plate. The plate is hanged by four stainless steel wires of 0.3mm diameter and set in the 3000mm in the downstream from the entrance. By using those sensors, skin-friction drage of the floating plate can be measured at the accuracy of less than 1mN. Several actuator arrays for turbulence control are placed in the upstream of the floating plate and variations of skin-friction drags are monitored by the FBG system.
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Hirosi NAGAMINE, Thoru MURATA, Astushi TAKI, Yoshimichi HAGIWARA, Ryoi ...
Article type: Article
Pages
41-42
Published: September 20, 2002
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Direct numerical simulation has been conducted for turbulent water flow around a waving surface with the separation of skin in order to examine the turbulence modification due to the surface deformation and skin separation. The cluster models of beads, springs and dashpots are used for simulating the tiny piece of skin. An unsteady generalized curvilinear coordinate is used for transforming from waving boundary to flat boundary. The computational results show that the surface waving due to sheer stress is effective for drag reduction. On the other hand, the cluster models separated by high shear are accumulated in the low-speed streak region. These models are found to enhance ejection and sweep nearby.
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Souichi SAEKI, Kakuji OGAWARA
Article type: Article
Pages
43-44
Published: September 20, 2002
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This paper presents an active flow control using Synthetic Jets with fluidic nozzle. The control system is composed of Particle Tracking Velocimetry, Neural Network computing and Pyragas' Delayed Feedback control theory. Synthetic Jets are set on both side of main flow, and connected to fluidic nozzle. The actuators can easily vector a main flow upward or downward by synthesizing suction and blowing actions. This system is applied to water flow with free surface in a rectangular tank having an inlet on the right side wall and outlet at the bottom. Two flow patterns are found to be stable in this tank. Under one condition, inlet flow goes directly to outlet and clockwise circulating flow is observed. Under the other one, while, inlet flow is attached to free surface, resulting in counterclockwise circulating flow. Any other flow pattern is unstable and stabilized to either two stable ones. A target flow pattern is stabilized by the present system although it is naturally unstable.
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Shinya YASUI, Tomoya HOURA, Hirofumi HATTORI, Yasutaka NAGANO
Article type: Article
Pages
45-46
Published: September 20, 2002
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A detailed knowledge of both velocity and thermal fields in wall turbulence disturbed by a row of ribs on the wall is important for clarifying the chief factors of fluid and thermal dynamics related to the control of heat transfer. In this study, in order to elucidate the effects of roughness on the statistical quantities in the velocity and thermal fields, direct numerical simulations (DNS) of heat transfer in turbulent channel flows with transverse-ribs roughness have been performed by varying their interval, width and height. It is found that since turbulent mixing is promoted by arranging ribs, the distributions of mean velocity and temperature become asymmetric markedly. And the systematic variations of secondary flow patterns between ribs are clearly identified. With the k-type roughness, the best heat transfer performance is found to be obtained.
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Tsuneo AZUMA, Koichi ARAGA
Article type: Article
Pages
47-48
Published: September 20, 2002
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Generation and growth of isolated turbulent puff and slug in the initial stage of a transitional pipe flow of dilute surfactant (C_<14>TABr) water solution were investigated by LDV and wall pressure measurement. The experiment was carried out using straight grass tubes of inside diameter D=2.61mm and total length L=1527mm and D=5.02mm and L=2712mm. Large perturbation was introduced by a ring-shaped roughness element installed at a downstream location of 77D from the pipe entrance. The puff generated at larger concentration than 260ppm and the critical Reynolds number, at which the puff began to generate, increased with the concentration.
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Hiroshi SUZUKI, Gerald G. FULLER, Hong Phuc NGUYEN, Hirmoto USUI
Article type: Article
Pages
49-50
Published: September 20, 2002
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The birefringences of dilute cationic surfactant solution were measured to investigate for the time characteristics of the solution casing drag reduction in a pipe flow. The concentration of surfactants was kept constant at 500ppm and shear rate ranged from 10 to 500s^<-1>. From the present results, the build-up time reaching shear induced structure (SIS) of micelles is found to be very long and it can be estimated from the results that the entry length required for flow fully developing in a pipe is longer than 1,250 times of pipe diameter. The SIS retardation and relaxation times also indicate that longer pipe is required for discussions on fully developed flow of drag-reducing surfactant solution.
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Satoshi OGATA, Keizo WATANABE, Yoshihisa OSANO
Article type: Article
Pages
51-52
Published: September 20, 2002
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The flow around a circular cylinder in surfactant solution was investigated experimentally by measurement of the drag in the Reynolds number range 500 < Re < 6,000. The experiments were performed in a vertical re-circulating water tunnel. The drag coefficient was measured by the apparatus, which could measure the drag acting on the circular cylinder directly. Three cylinders of diameter d=10,19 and 25mm were tested, the ratio of length to diameter was (l/d)=11.2. Test surfactant solution was aqueous solution of Ethoquad O/12 (Lion Co.) at concentrations of 200ppm, and sodium salicylate was added as a counterion. It was cleared that the drag coefficient of a circular cylinder in surfactant solution larger than that in tap water at the Reynolds number range 500 < Re < 4,000. The value of the drag coefficient in surfactant solution was dependent on not only (l/d) but also cylinder diameter. According to the increase of the Reynolds number, the drag coefficient decreased by (Re)^<-3/2>. On the other hand, the value of the drag coefficient in surfactant solution became smaller than that in tap water at Re≅5,000.
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Atsuhide KITAGAWA, Shigeki NAGAYA, Koichi HISHIDA, Yoshiaki KODAMA
Article type: Article
Pages
53-54
Published: September 20, 2002
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The skin friction reduction improves the transport efficiency of ships because the skin friction acting on large ships occupies the majority of the total drag. Recently, a technique to reduce the skin friction by injecting microbubbles into the turbulent boundary layer have been investigated for application to ships. However, the mechanism on its reduction is still not fully understood yet. In this study, the turbulence structure in the turbulent boundary layer with microbubbles was investigated experimentally by using the PIV/LIF measurement for the horizontal channel flow. In addition, a new system based on the combination of PIV, LIF and IST is proposed in order to obtain the distribution of microbubbles.
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T. Kawamura, Y. Moriguchi, H. Kato, A. Kakugawa, Y. Kodama
Article type: Article
Pages
55-56
Published: September 20, 2002
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Three different methods have been investigated for generating microbubbles to control the bubble diameter separately from the main flow velocity. The first two methods achieve this by adjusting the local shear stress where bubbles are generated, while the third method uses foaming of dissolved air to generate very small bubbles. The average diameter of bubbles was successfully controlled by the first two method within the range of 0.5-2mm for the fixed main flow velocity of U=3m/s, while the very small bubbles of 20-40μm were generated by the third method. The influence of the bubble diameter on the frictional drag reduction was investigated for a diameter range of 0.5-2mm, and was found to be insignificant.
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Takao FUJITA, Keizo WATANABE
Article type: Article
Pages
57-58
Published: September 20, 2002
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Recently, it has noticed the flow characteristics of a liquid on a highly water -repellent wall that the gas-liquid interface occurs near the solid surface. We reported the drag reduction of flow around a circular cylinder with a highly water-repellent wall, that fluid slip occurred at the wall and the separation point moved to the downstream direction comparing with the smooth solid surface circular cylinder. The purpose of this study is experimentally to clarify the motion of a highly water-repellent sphere in Newtonian Fluids. Experiments were carried out the measurement of the fall velocity by the falling sphere experiment. The drag coefficient of a highly water-repellent sphere increases comparing with that of the smooth sphere. It can be considered the buoyancy increases in the effect of the gas phase of the sphere surface. The experimental results obtained in this study can be applied to prevent the precipitation of solid particle by suspensions.
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Hiroyuki ABE, Takehiko SEGAWA, Takayuki MATSUNUMA, Hiro YOSHIDA
Article type: Article
Pages
59-60
Published: September 20, 2002
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Solid (fin)type vortex generators are known to be effective on suppressing flow separations and widely used at various fluid mechanical elements such as intakes or airfoils of airplanes. But the solid type generators themselves are the cause of extra flow drag. In this study we designed a blowing jet type vortex generator to realize smart control of flow separation. The present vortex generators are consisted of small jets properly distributed on wall surface. Therefore, the present vortex generators are considered to minimize the extra drag compared to the solid type. The VG was found to be able to generate a single longitudinal vortex near wall. Next step is to try active flow control of airfoil MEL001 at low Reynolds number.
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Akira NISHIZAWA, Shohei TAKAGI, Hiroyuki ABE, Yoshihiro KIKUSHIMA, Ryu ...
Article type: Article
Pages
61-62
Published: September 20, 2002
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So far quite a few papers have been published on controlling separated flow around wings. However, attempts to establish a self-contained, feedback control system for the separation seem to be just started recently. Fundamental elements of the control system are sensor, actuator, and controller. In order to establish a basis of a smart control system for wing separation, an attempt was made to detect separation flow in use of a new receptor sensor on a slope simulating suction surface of wing. It was found that the output of the sensor worked well as flow-direction discriminator. In the present experiment, flows with and without separation were controlled by using a static, roughness element. Results of the separation experiment gave us important hints regarding specifications of actuators to be developed.
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Michihiro NISHI, Xiaomin LIU, Kouichi YOSHIDA, Toshihiko KISHI
Article type: Article
Pages
63-64
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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The time-averaged flows in a 14 deg conical diffuser with and without vortex generator jets (VGJs) have been studied numerically by solving the RANS equations with the κ-ε turbulence model. The diffuser performance was investigated associated with the velocity ratio (ratio of the jet speed to the mainstream velocity). The results indicated that the Cp-VR curve is reasonably simulated. However, the separation point in the diffuser without VGJs was not predicted satisfactorily. Further, attempts have been made to correlate the pressure recovery and longitudinal vortices in the diffuser.
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Hidesada KANDA
Article type: Article
Pages
65-66
Published: September 20, 2002
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A conceptual model has been constructed for the problem of determining a critical Reynolds number Rc from laminar to turbulent flows in a circular pipe and between parallel plates (Kanda [2-3]). For circular pipe flow, the minimum critical Reynolds number Rc(min) of approximately 2040 was obtained. In order to prove the validity of the model, another verification is required. Thus, for flow between parallel plates, results of previous investigations were studied, focusing on experimental data on Rc, the entrance length, and the transition length. Consequently, the model was confirmed and an experimental value of Rc(min) was found to exist in the neighborhood of 1300,based on the channel height and average velocity. For flow between parallel plates, the author obtained Rc(min) of approximately 1230 when using J0=101 grid points in the y-direction, and 910 when J0=51.
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Takayuki YANAGIYA, Hidesada KANDA
Article type: Article
Pages
67-68
Published: September 20, 2002
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In experimental studies of circular pipe flow the entrance of pipes is rounded for avoiding entrance eddies. Until now it is not considered well how such bellmouth entrances influence the flow in circular pipes. In this study, numerical calculation of flow in a circular pipe with a bellmouth entrance is done. The vorticity transport equation is solved by the finite difference method. The velocity, vorticity, and pressure drop are investigated in steady flow. Then, bellmouth effect is considered. It is found that the velocity distribution is not uniform at the end of the bellmouth entrance. We also calculated the equivalent length of the pipe with bellmouth in comparison with that of straight pipe, which equals approximately the results based on the boundary layer theory.
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Toshihiro TAKAMI, Keisuke HIRAGA
Article type: Article
Pages
69-70
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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The effect of the injection of swirling motion into turbulent flows through a curved pipe is studied experimentally by meauring distributions of wall shear stress and three-component velocities. The high and low region of wall shear stress corresponds to the fast and slow region of primary flow near the wall, which is governed by the vortical structure of secondary flow. The flow friction of the average wall shear reduces when the injected swirl is weak.
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Kakuji OGAWARA, Souichi SAEKI, Naoki NAKATANI, Hidenobu TAKAO
Article type: Article
Pages
71-72
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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This paper presents a novel actuator for flow control, namely Plasma Actuator. This is a glow-discharge actuator, which is composed of the electrodes with AC signal. In the present study, it was applied to the separation control of airfoil. Actuator. The NACA0012 airfoil, in which this actuator was embedded, was set in the wind tunnel. The wake velocity behind airfoil was measured with or without operating the actuator. Consequently, the expected effect of proposed actuator could not be observed. One of the reason was thought to be a large separation bubble causing under low Reynolds number condition. The actuator would be completely involved in this, and thus was no seen to be effective to the separation control.
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Yuji IKEDA, Laurent ZIMMER
Article type: Article
Pages
73-74
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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The main purpose of this study is to investigate the flame holding mechanism in premixed CH_4 turbulent flame. Chemiluminescent images have been acquired at equivalence ratios of 0.61,0.58 and 0.51,which is near the leanest limit to clarify the anchor point area experimentally. The main focus of this study is the anchor points and shapes of (OH)^*, (CH)^* variations with equivalence ratio. Moreover, the instabilities and fluctuations of combustion were investigated by time series measurement of local of chemiluminescent radical intensities at the anchor points using both FFT and wavelet decomposition.
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Shunsuke TSUKINARI, Toshihiko SAITO, Gyung Min CHOI, Mamoru TANAHASHI, ...
Article type: Article
Pages
75-76
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Simultaneous measurement of OH and CH radicals by planar laser induced fluorescence (PLIF) is conducted for laminar premixed flames and lean premixed cellular flames. Effectiveness of CH PLIF as an indicator of the heat release rate is shown by comparing the results of CH PLIF experiments with numerical simulations. In laminar flames, the change of CH mole fraction with the equivalence ratio can be represented by CH PLIF. In addition, even in lean cellular flames, in which CH mole fraction is significantly low, CH fluorescence can be measured. These results imply that CH PLIF can be applicable to estimate spatial variation of the heat release rate in the turbulent premixed flames.
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Masato TAGAWA, Takaya KATSURAGAWA, Yasuhiko OHTA
Article type: Article
Pages
77-78
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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This paper deals with the possibility of controlling various aspect of a non-premixed turbulent flame using an externally-imposed pressure gradient. From Turbulence measurement of the flame formed in a curved channel, it was shown that the mean pressure gradient caused the onset of counter-gradient heat transfer on the high-pressure side of the flame and promoted gradient diffusion on the low-pressure side. The flame behavior was strongly affected by these two contrasting phenomena. The present results indicate that we may find a novel approach to controlling turbulent combustion effectively using pressure gradients.
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Hiroyuki SATO, Yasuo YAMAZAKI, Takashi ENDO, Koichi HAYASHI, Satoru OG ...
Article type: Article
Pages
79-80
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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In this experiment, swirler is set at each angle; α(α=15,30 and 45 deg.), and the swirl number is 0.162,0.334 and 0.519,respectively. As the result, in the case of α=15 deg., two different modes of oscillatory flame were observed in the same condition of air flow rate. In the cases of α=30 deg. and the oscillatory frequencies were varied ranging from 125 Hz to 160 Hz. Furthermore, it was found that these frequencies corresponded to the noise level. So the system of the active control is established with the sound level meter (sensor) and mass flow meter (actuator). Figure 1 shows a result of the active control. In this system, air flow rate was controlled when the noise level was to be about 86 dB. Then, the oscillatory flame was changed into a stable flame with low-level noise. The present system is fundamental for the active combustion control. However, we could get a good result for a future closed-loop system.
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Masaaki TAKIGUCHI, SHINJI Oshida, Masataka IKEDA
Article type: Article
Pages
81-82
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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If it is intended to apply cooled EGR to heavy-duty diesel engine for a more reduction of NO_x emission, it will also be necessary at the same time, to reduce corrosive wear induced by condensed water including the acids on piston rings and cylinder liner due to cooled EGR. This study aims at making clear the effects of condensed water supplied to the combustion chamber on the cylinder oil film formation when the temperature of EGR gas becomes lower. The piston friction has been measured under various temperatures of EGR gas for the verification of lubricating condition of piston and piston ring. As a result, it is found that the piston friction spiky increase just after TDC where the EGR gas temperature becomes lower and that the condensed water easily reaches the cylinder wall surface through the oil film.
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Mitsuhiro SOEJIMA, Yoshito EJIMA, Hiroshi TAKASAKI
Article type: Article
Pages
83-84
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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The soot contamination of engine oil seriously influences the tribo-characteristics for engine components. In the present study, the changes of the friction and wear characteristics for the cam and follower of the valve train are examined by using test oils blended with the dispersant and ZnDTP and/or MoDTC additives and mixed with carbon black substituted for engine soot. The object cam-followers are a slipper follower and a roller tappet. Key results of study are summarized as follows.(1) When lubricated with the oil mixed with carbon black, the friction and wear characteristics of cam and slipper follower are approximately similar to those lubricated with the oil mixed with exhaust gas soot. Also, even if the oil film becomes as thick as the size of co-aggregated carbon black, the friction is kept lower with less fluctuation and the wear rate is kept a little lower than those of thinner oil film.(2) In case of the roller tappet, the friction slightly changes with the carbon black contamination.
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Hidetsugu YAMAMOTO, Miki SASAKI, Noboru FURUKI, Mineo KAGAYA, Naochika ...
Article type: Article
Pages
85-86
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Increase of soot contaminated in engine oil caused by EGR system accelerates diesel engine wear, especially valve train wear. In order to evaluate the wear of valve train parts mainly caused by abrasive wear, a rig test (Shell-4-ball-tester) has been conducted by using oil that contained the carbon black. In this study, the standard oil that contained a similar carbon black to the wear characteristic of the engine soot was developed.
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Kenichi KUBO, Hideyuki TSUNEMOTO, Hiromi ISHITANI
Article type: Article
Pages
87-88
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Recently, European car companies change passenger car engines from gasoline ones to diesel ones due to low CO_2 emission. However high power engines need in Europe, so small-sized high speed turbo-charged DI diesel engines were developed. In this engine since the combustion pressure increases over 15MPa, the reliability and durability are most important factor in mass-production. In this study, we investigated the stress characteristics on cylinder head and on the exhaust manifold. Moreover we examined the relations between the strain and engine acceleration. As a result, it was found that there is the influence of engine vibration for the strain change at high speed and high load.
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Tatsumi KITAHARA, Kotaro FUJISAKI, Masaru OTSUBO
Article type: Article
Pages
89-90
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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Calculations were carried out to clarify the oil film characteristics of the corsshead-pin bearing with a very low clearance ratio and wedge geometry incorporated oil-grooves for large size two-stroke diesel engines. Reducing the clearance ratio is advantageous for enhancing squeeze action on the entirety of the bearing pads to decrease the maximum oil film pressure. However, this also has a negative aspect reducing wedge action, thereby causing the oil film thickness to decrease. When the clearance ratio becomes very low, incorporating a proper wedge geometry on both sides of the oil-grooves is an effective means to improve wedge action, and thereby to increase the oil film thickness without a significant raise in the oil film pressure.
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Yasuo HARIGAYA, Akiko SHIMADA, Michiyoshi SUZUKI, Fujio TODA
Article type: Article
Pages
91-92
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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The effect of lubricant viscosity on the temperature and thickness in oil film on a piston ring in a diesel engine was analyzed by using unsteady state thermohydrodynamic lubrication model. The oil film viscosity was then estimated by using the temperature and the shear rate for multi grade oil. Under low temperature condition, the viscosity becomes lower due to viscous heating and shear rate, and under higher temperature condition, the viscosity affected by the shear rate becomes lower. The oil film thickness between the ring and liner decreases with decrease of the oil viscosity, and it is the thinnest that the oil film thickness is calculated by using the viscosity estimated from both the shear rate and the oil film temperature.
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Hiroaki WATANABE, Kenkichi WATANABE
Article type: Article
Pages
93-94
Published: September 20, 2002
Released on J-STAGE: August 01, 2017
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This paper describes load sharing of piston skirt in mixed lubrication. It can be estimated that piston friction coefficient is approximately same level as piston ring o measured friction at firing condition. Experimental results by means of both change of oil supply and applied load, using test piece with streak shape indicate that piston skirt is under mixed lubrication at least in expansion stroke because of starved oil supply. Also, it is found that load supported by fluid film is closely related with average depth of worn streak and oil starvation level, but without nearly applied load.
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