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Article type: Cover
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Published: July 31, 2000
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Article type: Appendix
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App1-
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Article type: Index
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Published: July 31, 2000
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Yoshifumi NISHIZAWA, Izumi USHIYAMA
Article type: Article
Pages
1-2
Published: July 31, 2000
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Savonius type and Cross-flow type windmills are vertical-axis windmills using drag force. In addition to the characteristic of no necessity of the directional control to pointing the wind direction, these windmills start easily even in low wind velocity and have high torque owing to their large swept area. Optimum design configuration of Savonius type and Cross-flow type windmills are reported by wind tunnel experiments conducted by many researchers. In these experiments, however, the performance of windmills are obtained from output characteristics through the measurement of torque and rotational speed by changing the factor of design configuration. Therefore, until now, the behavior of air flow between the buckets of Savonius type windmill, and the behavior of an inflow air to inside of the rotor of Cross-flow type windmill are not clarified. Consequently, the relation between windmill performance and the behavior of the air flow have been indistinct. In this research, using P.I.V. system, the behavior of the air flow in the inside of the model rotors of Savonius type and Cross-flow type windmills are clarified through visualization. Thus, the performance of these windmills are evaluated through the behavior of the air flow.
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Kazuichi SEKI, Keita SAGARA, Naoki YAMAMOTO
Article type: Article
Pages
3-4
Published: July 31, 2000
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In this paper we will present some novel results of our research and development in the filed of wind energy utilization. Our effort in this filed is mainly concentrated to the conceptual design of optimum airfoil sections for the blade of straight wing non-articulated vertical axis wind turbine which undergo cross wind motion. This concept was embodied in the design of a family of airfoil sections designated as Tokai Wind Turbine (TWT) sections and a series of wind tunnel testing was conducted to confirm its desired aerodynamic characteristics. Then, we designed an experimental straight wing non-articulated vertical axis wind turbine system with straight blades to evaluate system performance and structural analysis results, and furthermore to collect operating experiences under real, fluctuating wind conditions. We are now working for evaluating operational feasibility of five sets different straight wing non-articulated vertical axis wind turbines system, which are partially in service as pilot of regional energy development.
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Yasushi ONO, Yuichi MURAI, Yoriyasu MASUDA, Takuma NISHIMURA, Fujio YA ...
Article type: Article
Pages
5-6
Published: July 31, 2000
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Monument-types of savonius windmills designed by combining art sence and windmill technology are produced by the PROD cooperative companies. The "art-oriented" Savonius windmills have been installed in many public sites such as musiums, schools, stations and sight-seeing spots because of its good harmony with natural environment and cities. This report shows a first trial of numerical analysis of flow field around the "art-oriented" windmill. The numerical method is based on incompressible Navier-Stokes equations using Lagrangian markers which express the complex boundary conditions of rotating windmill blades.
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Makoto IIDA, Kengo Araki, Chuichi ARAKAWA
Article type: Article
Pages
7-8
Published: July 31, 2000
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The flow around a rotor blades of a wind turbines is usually governed by unsteady phenomena such as stall, separation bubble, turbulent transition and hysterisis due to the unsteady flow field and low Reynolds number effect. In order to simulate these phenomena, accurate numerical schemes are required. The purpose of this study is to apply an advanced technology of computational fluid dynamics to the performance prediction of a wind turbine rotor with higher accuracy. This paper describes the initial approach of the three-dimensional flow analysis around a horizontal axis wind turbine using pseudo-compressibility method combined with overset grid method. The study presents a three-dimensional flow analysis around horizontal axis wind turbines which are a small one for investigation at the design condition and off-design conditions. These numerical results provide some confidence in the availability of this CFD algorithm to predict wind turbine flow fields.
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Yukimaru SHIMIZU, Takao MAEDA, Yasunari KAMADA, Kazuhisa KONDOU
Article type: Article
Pages
9-10
Published: July 31, 2000
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This paper describes a first step the development of airfoil sections for wind turbines. The development of airfoil is given as one of the elements that contributes to the development of wind turbines technology. The improvement of airfoil performance at low Reynolds number is required in the development of the next generation wind turbines. This paper describes evaluating method for airfoil performance at low Reynolds number by both wind tunnel experiment and numerical analysis.
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Yutaka HASEGAWA, Koji KIKUYAMA, Kai KARIKOMI
Article type: Article
Pages
11-12
Published: July 31, 2000
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A wind field experienced by a Horizontal Wind Axis Wind Turbine (HAWT) is non-uniform in space and unsteady in time, namely turbulent. Turbulence characteristics of the wind incoming to a rotor bring about complicated aerodynamic loads on the wind turbine, which must be taken into account in the structual design process of the rotor blades. Our study is aimed at developing the method to simulate the turbulent wind field numerically and to calculate its influence on the fatigue loads experienced by the rotor blades. This paper presents the results of numerical analysis of the aerodynamic loads on HAWT rotor under two kind of uniform and unsteady wind conditions, the one is a stepwise change in wind velocity and the other is sinusoidal.
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Tetsuya WAKUI, Tsuyoshi ARIMA, Yoshiaki TANZAWA, Takumi Hashizume, Eis ...
Article type: Article
Pages
13-14
Published: July 31, 2000
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When introducing the variable speed operation for adequately utilizing wind energy, the small-scale systems have an advantage on net power extraction under fields wind conditions. This is because of the superior dynamic characteristics of the small-scale systems. Thus, in order to extract demanding electricity, it is necessary to adopt the parallel operation using plural wind turbines which have the appropriate system scale matching the wind condition. The purpose of this study is to propose the operating method of the parallel systems for higher power extraction than under the synchronous operation. At the first step, this paper examines the output characteristics of parallel system using two Darrieus-Savonius hybrid wind turbines and discusses the operating methods and points to extract maximum power output under two levels of input wind speed.
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Yukimaru SHIMIZU, Takao MAEDA, Yasunari KAMADA, Hiroshi YAMAGUCHI, Wai ...
Article type: Article
Pages
15-16
Published: July 31, 2000
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The purpose of this study is to decide the best arrangement of Wind Turbine on Wind Park. Therefore, this study calculated as a test of annual inflow energy by experiment used Wind Turbine model and topography model on the scale of 1/2000 in wind tunnel for measurement the received wind speed of each Wind Turbine model. And this study considered the best condition of experiment from result of calculation that changed Wind Turbine arrangement, Wind speed recovery ratio of Wind Turbine model, roughness of topography model surface for exact calculation.
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Koji Kikuyama, Yutaka Hasegawa, Hiroshi Imamura, Hitoshi Suzuki
Article type: Article
Pages
17-18
Published: July 31, 2000
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In order to introduce the wind turbine generator system (WTGS), an assessment of the wind energy resources is inevitable in a wind park. In the flat terrain such as in Europe and USA, the resource assessment can be easily performed by using a small number of anemometers. In a mountainous and complex terrain with rough surface, however, where a site proposed for a WTGS is often locates such as in Japan, contribution of local effects on the wind energy resources is quite large. Thus, in order to evaluate the wind energy resources accurately, enormous labor and money is necessary if the wind measurement with the anemometer is the only tool for the assessment. this paper describes an experimental and numerical analysis of a flow over simple shaped hill, in order to investigate the influence of the mountainous terrain on the atmospheric boundary layer flow.
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Hiroshi IMAMURA, Takahito BABA, Jun MATSUI, Junichi KUROKAWA
Article type: Article
Pages
19-20
Published: July 31, 2000
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This work is basic study to show the effect of terrain for the performance evaluation of a wind turbine generator system (WTGS) in complex terrain. Since the wind energy captured by the rotor of WTGS is proportional to the 3rd power of wind speed, the exact estimation of the wind speed at wind turbine constructed point are needed. However, the definitive method for the wind speed estimation in complex terrain has not yet been established. In this study, the effect of slope at the upwind of turbine has been investigated by means of numerical simulation using k-ε turbulent model. The results of simulation have shown that the wind energy obtained by rotor plane considerably depends on the position and hub height of the turbine for the incline angle of the slope.
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Toshiaki KANEMOTO, Daisuke TANAKA, Keiichi TOMINAGA
Article type: Article
Pages
21-22
Published: July 31, 2000
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To cope with the warming global environment, the renewable hydraulic power generation system composed of the counter-rotating type runners and generator was already proposed. This paper, continuously, clears the turbine characteristics under the variable operation conditions. The shaft output and efficiency decrease as the head decreases, because of the mechanical power losses. The characteristics can be unified with the head and the runner diameter as the same as those of usual turbines.
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Yukimaru SHIMIZU, Mitsuo KOBAYASHI
Article type: Article
Pages
23-24
Published: July 31, 2000
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Recently, ultra low-head hydropower in the small rivers is hardly utilized. Orthoptere water turbine has been developed for the purpose of generating electricity at ultra low head hydro energy. This paper describes performance improvement of Orthoptere water turbine with optimized cross-sectional area. In this study, the performance is evaluated by experimentally with change of water flow rate, water level, and aspect ratio about the type of triple blades. The test results of experiment show that the maximum power coefficient increases at same flow rate with optimized cross section.
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Kazuyoshi MIYAGAWA, Teruaki NAMBA, Yasutomo KANEKO, Hiroshi MATSUSHITA ...
Article type: Article
Pages
25-26
Published: July 31, 2000
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Analytical and experimental study has been carried out to verify the performance of pump-turbine runner with splitter blades for super high-head reversible pump-turbines, and the advantage of runner with splitter blades has been made clear from the view point of hydraulic performance. Besides the hydraulic performance, pump-turbine runners for super-high head pump turbines are required to have enough against severe operating condition generated under high pressure high peripheral speed. To evaluate the strength of pump-turbine runner with splitter blades, actual head test and numerical simulation was performed. In this paper, study of super high head pump-turbine runners with splitter blades from the view point of runner strength is described.
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Manabu TAKAO, Toshiaki SETOGUCHI, Tae Ho KIM, Kenji KANEKO, Masahiro I ...
Article type: Article
Pages
27-28
Published: July 31, 2000
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A number of self-rectifying air turbines for wave power conversion have been proposed over the last decade. However, noise characteristics of the turbines have not been presented so far. In order to clarify the noise characteristics of the turbines, the experimental investigations have been performed under steady flow conditions in this study. As a result, it is found that the noise characteristics of impulse type turbines are superior to the Wells type turbines. Moreover, the noise characteristics have been discussed from a viewpoint of a specific noise level.
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Masashi MIYAZAWA, Masami SUZUKI, Chuichi ARAKAWA
Article type: Article
Pages
29-30
Published: July 31, 2000
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Current PC-based computing systems can offer relatively inexpensive but powerful parallel distributed processing environment and it becomes reasonable to use a PC-cluster system for some heavy scientific computations which required an engineering workstation or a large parallel processing machine. In this paper, incompressible around a Wells turbine, which is commonly used for the wave power system, is computed with a small PC-cluster system. Speedup rate to single processor environment and the efficiency of parallel computation are presented, and some of the merits and demerits of the PC-cluster system are discussed.
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Hiroshi MUKAI, Akira MANABE
Article type: Article
Pages
31-32
Published: July 31, 2000
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Flow velocity was measured using laser doppler velocimetry at both the entrance and the exit of a mixed-flow pump to investigate an unstable flow pattern in the pump. The measurements revealed the following. 1) One factor leading to the unstable flow generated in the pump was that the flow rate is lower when the flow pattern around the impeller changes than when the impeller is stalled. 2) To stabilize the flow characteristics when the tangential flow velocity increases rapidly at the entrance side due to a stalled impeller, the flow pattern around the impeller should be changed to a centrifugal-flow pattern.
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Hiroshi TSUKAMOTO, Noriyasu TAKAHASHI, Tatsuhiro NAKAMOTO, Koji MIYAZA ...
Article type: Article
Pages
33-34
Published: July 31, 2000
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Experimental study was done to investigate the mechanism of the so-called drooping characteristics of Water Jet Pump. The flow-field was measured at the impeller inlet and outlet. The unsteady pressure on the casing wall was measured, and moreover, the inner flow at off design point was studied. As a result of the present study, the reason of this instability was found to be the secondary flow and the pre-rotation caused by the secondary flow.
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Tomotatsu NAGAFUJI, Akinori FURUKAWA, Eiji ASAKURA, Hideyuki KAWAJIRI
Article type: Article
Pages
35-36
Published: July 31, 2000
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3-D Navier-Stokes codes with the k-ε turbulence model and the wall function have been widely used for the flow simulation in turbomachinery with a high Reynolds number. Two centrifugal pumps of low specific speeds with vaneless diffusers were used in this study. The blade shape of these impellers is characterized by the large thickness at the outlet and results in the difficulty of grid generation on the computational model. In order to demonstrate the effects of the grid generation and boundary condition between stationary and rotational parts to the simulation results, some computational models are studied using the 3-D Navier-Stokes code. These simulation results are finally compared with experiments and the applicability of the Navier-Stokes code will be discussed.
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Jun MATSUI, Junichi KUROKAWA, Manabu HARA, Koji NAKAMURA, Hiroshi IMAM ...
Article type: Article
Pages
37-38
Published: July 31, 2000
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In the very low specific speed range especially at the specific speed less than 70,efficiency of volute pump becomes remarkably low. It seems that there is a complex inner flow even at the designed point, and we must understand flow pattern to improve the pump performance. However, it had been difficult to measure the volute pump inner flow by the conventional measuring method because of a rotating impeller. In this report, we wish to show the results of measuring the inner flow of the very low specific-speed volute pump by PTV-method. Comparing the measured inner flow to the normal specific-speed one, it has been cleared that there is a large difference between them.
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Hai HAN, Kazuhiro TANAKA, Toshio KOBAYASHI
Article type: Article
Pages
39-40
Published: July 31, 2000
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This paper describes a numerical simulation of screw-type centrifugal pump with tip clearance. A reliable commercial three-dimensional Navier-Stokes code with a standard k-ε turbulence model was used for this study. The influence of tip clearance is remarkable in this pump type. In the present study, to catch up the interaction effect between the impeller and volute casing, we have calculated the flow fields in a volute casing as well as in an impeller simultaneously by exchanging the calculated data between them at every time step. The simulation results show that the calculation considering the effect of the tip clearance can be predicted reasonably well. The measured pressure distributions are also compared.
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Akinori FURUKAWA, Yinchun CAO, Kusuo OKUMA, Satoshi WATANABE
Article type: Article
Pages
41-42
Published: July 31, 2000
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Demands for higher performance of axial flow pumps have led pump designers to consider the creative strategies for the new type. As a solution, contra-rotating rotors might be applied to a pump. Comparative experiment were conducted for two types, consisting of contra-rotating rotors and a rotor and a stator respectively, which were designed under the same specifications of pump head, flow rate and rotor specific speed. The measured pump performances and flow distributions are shown and the advantages of using contra-rotating type are clarified as follows. Contra-rotating type is superior in pump efficiency and cavitation performance in range of partial flow rates to conventional one though the specified pump head and maximum efficiency are not satisfied at design point in the case of contra-rotating test rotors. Results demonstrate that the rear rotor design is important to improve the pump efficiency.
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S. LIU, M. NISHI, K. YOSHIDA, H. TSUKAMOTO
Article type: Article
Pages
43-44
Published: July 31, 2000
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Downsizing is one of the considerations in various engineering technologies at present because of the energy and environmental problem in the future global society. To promote it in hydraulic machinery, we have been engaged in a basic study to develop a high performance mini-pump, the impeller of which diameter is 34mm. One of the design concepts for mini-impeller is to choose larger exit blade-angle. For the test impeller, we use 50°. The experimental result shows that the internal efficiency of more than 60% is achievable. But the unstable Q-H curve was observed in the low flow region. To improve this curve, we introduced the method to return some amount of flow bypassed from the pump exit to the suction pipe. From the experimental results so far, it is examined that the unstable performance can be improved to some extent by using the proposed method.
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Goh MORIMOTO, Hiroki NISHIDA, Yasunori TOKIMASA, Yoshiki YOSHIDA, Yosh ...
Article type: Article
Pages
45-46
Published: July 31, 2000
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This paper reports about experimental investigations of the effects of seal geometries on rotordynamic fluid forces in a whirling centrifugal impeller. It was found that, (1) At a certain whirling speed, the fluid forces has a peak caused by the coupling between the whirling motion and rotating stall in the vaneless diffuser. (2) The change of seal geometry (inside/outside seal) affects the direction of the fluid force, through the variation of the leakage flow due to the whirling motion.
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Chuichi Arakawa, Hideharu Matsumoto, Kosuke Kuriyama, Seiichi Ariga
Article type: Article
Pages
47-48
Published: July 31, 2000
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Recently, using wind power, especilly in Europe, is remarkably increasing and this shows wind turbine is reaching the stage of real use. Under this situation, to forecast the future of energy system, the authors use the energy simulation model of New Earth 21,in which the present wind power situation and introduction of wind turbines to offshore are taken into account. By using this simulation code, the wind power is predicted to be so popular in 50 years that the new kind of wind turbine with vernacular design is proposed.
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Tomoya TAWARA, Reishi OYA, Tomonobu GOTO, Yasunari TAKANO
Article type: Article
Pages
49-50
Published: July 31, 2000
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A large scale model is considered for a micro robot imitating the bacterium with a single flagellum such as Vibrio. In order to estimate the driving force exerted to a helical screw propella (flagella propella), we made a floating scale. By use of the floating scale and I-CCD camera, we measured the driving force and the rotation rate for sevral kinds of helical screw propella. The characterstics of driving force was compared to the drag coefficient of circular cylinder in a range of Reynolds number (10)^2∿(10)^3.
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Masakazu HIKICHI, Yutaka OHTA, Eisuke OUTA
Article type: Article
Pages
51-52
Published: July 31, 2000
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Based on the detailed investigation of the effective noise source distribution of blade-passing frequency (BPF) noise radiated from a centrifugal blower, active cancellation of noise sources is conducted. The extent of the effective noise sources of fundamental and higher-order BPF lies on the volute-side surface on the scroll relatively apart from each other, i.e., noise source of fundamental BPF exists on the vicinity of the cut off apex, while that of higher-order BPF lies relatively downstream area on the casing scroll. Therefore, simultaneous reduction of both fundamental and higher-order BPF can be possible. In the experiments, piezoelectric actuators are used to oscillate the casing wall directly. Noise level of fundamental and higher-order BPF can be reduced about 15 decibels, and discrete tones are almost disappeared from the power spectra of the blower radiated noise.
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Masato FURUKAWA, Choon Man JANG, Masahiro INOUE
Article type: Article
Pages
53-54
Published: July 31, 2000
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A vortical flow in a half-ducted propeller fan has been investigated by a large eddy simulation (LES) using the subgrid-scale model of Smagorinsky. The simulation shows that the tip vortex plays a major role in unsteady behavior of the vortical flow in the propeller fan. The tip vortex grows nearly in the tangential direction, thus impinging on the pressure surface of the adjacent blade. The spiral-type breakdown of the tip vortex occurs near the midpitch, so that the tip vortex twists and turns violently with time. The sound pressure radiated from the fan rotor blade is dominated by the pressure fluctuation caused by the breakdown of the tip vortex.
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Takashi SAIKA, Kouzou NAKAJIMA, Satoshi SETOYAMA, Hirotaka MURATOH, Ma ...
Article type: Article
Pages
55-56
Published: July 31, 2000
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Approximately over 1,500 Jet Fans are installed in the tunnels operated by Japan Highway Public Corporation. It is important to clearly grasp their performance and to use them for tunnel ventilation design, but this is still challenging task. It is the result of our research that the pressure raise equation based from jet fan thrust might be more suitable for designing and controlling on the conditions of the normal temperature, in comparison with the equation based from outlet air velocity. However, further study from various view points is necessary to conclude this issue.
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Akisato MIZUNO, Takashi SAIKA, Takahiro AZUMA, Atsushi ICHIKAWA, Hitor ...
Article type: Article
Pages
57-58
Published: July 31, 2000
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It is assumed that if jet fans are not installed at a certain interval, interference between their jets will harm their boosting capability. Experiments in an actual tunnel and numerical simulations were performed to study the relationship between the jet fan installation interval and their boosting capability in order to determine the adequate jet fan installation interval and the extent to which reducing their installation interval alters their boosting capability. This report introduces the results of this study.
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Motoo KUROUMARU, Tadakazu TANINO, Shinnichi YOSHIDA, Masahiro INOUE, M ...
Article type: Article
Pages
59-60
Published: July 31, 2000
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There are two types of stall inception in axial compressors. The first one is characterized by long length-scale disturbances called as "modal waves", and the second one is by a short length-scale distrubance known as "spike". In this paper, the development of rotating stall when varying the gap length between a rotor and an upstream stator is investigated by the wavelet analysis of the casing wall pressure signals. The route leading to stall switches from short to long wavelenghth with changing the gap length. In deep stall condition, these two disturbances are interfered with each other regardless of the gap length.
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Kimihiko MITSUDA, Yukiharu IWAMOTO, Kazuhiko YOKOTA, Yoshinobu TSUJIMO ...
Article type: Article
Pages
61-62
Published: July 31, 2000
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This paper presents the results of a two-dimensional stability analysis on supersonic flows using actuator disk methods. The relative flow is supersonic with subsonic axial component. The purpose of this study is to clarify the characteristics of the flow fluctuation which propagates slower than the cascade rotation. This flow fluctuation was found in CFD by Iwamoto, which suggested that this flow fluctuation is related with a detached shock oscillation and unstarted leak flow. The present actuator disk model involves these effects. The solution shows the possibility of the existence of the destabilizing mode in the supersonic cascade. The propagation velocity predicted by the present method agrees with that found in CFD.
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Chunqing TAN, Atsumasa YAMAMOTO
Article type: Article
Pages
63-64
Published: July 31, 2000
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With a low speed plane cascade tunnel, experiments were made for four kinds of turbine stator cascades with straight and positively curved blades of +10,+20,+30 degree lean angle (The positively curve means that the pressure surface forms acute angles with both endwalls). Flows were surveyed with a micro five-hole Pitot tube before and after the cascades in detail. The comparisons of each experimental result show that there are significant effects of blade curve on the cascade loss generation : The straight cascade has the lowest loss value; any positively curved blades could not reduce the loss which increased as the lean angle increased.
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Koji UENO, Masakazu OBATA, Koichiro TAGASIRA
Article type: Article
Pages
65-66
Published: July 31, 2000
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Static pressure measurements on the hub surface behind of a nozzle blade ring with rotating disc in a modeled air turbine stage were conducted with the objective of obtaining the effect of rotational speed on the pressure distribution characteristic. On the rotating disc, small cylindrical pins were mounted for simulating the leading-edge of rotor blades and the disc was driven by a VS motor. The effect of rotational speed was examined for several constant mainstream flow rates under a constant axial clearance without secondary flow injection. The hub static pressure distribution with disc rotations is presented for the blade pitch space and the axial space under comparison with without rotation.
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Katsuichi UCHIDA, Masakazu OBATA, Koichiro TAGASIRA
Article type: Article
Pages
67-68
Published: July 31, 2000
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Pressure measurements and surface flow visualization were conducted to obtain a detailed aerodynamic data base on the endwall, suction and pressure surfaces of two-dimensional scale turbine-blade cascade in a low speed wind-tunnel test equipment. The test blade is a typical turbine blade with a low aspect ratio and with a large turning angle. The experiments were conducted at the blade Reynolds number of 4.7×(10)^4 constant and a lamp-black method was applied for the flow visualization. The dominant change of the passage vortex at the endwall and at certain regions of the blade surface is illustrated and pressure distribution characteristics are shown for the blade passage.
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Tadateru ISHIDE, Nobuhide NISHIKAWA, Fumihiko MIKAMI
Article type: Article
Pages
69-70
Published: July 31, 2000
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The phenomenon of three-dimensional separation of the flow over a slender body at high angles of attack is difficult to model and still challenging problem. The singularity of the flow is caused by mutual intervention of three-dimensional separation and separated vortices. In this study, the flow in the cross-flow separation region of an axisymmetric paraboloid at 30,40,and 50 deg angle of attack has been investigated experimentally by hot wire anemometer. The growth of turbulence in separated vortices is discussed by r.m.s. and probability density function of velocity fluctuation in addition to Reynolds stress.
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Masanori MATSUMURA, Katsumi MIYAKOSHI, Yoichi SHIMIZUME
Article type: Article
Pages
71-72
Published: July 31, 2000
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Interactions between separation shear layers include vorticity cancellation are considered to be required for the periodic vortex shedding like a Karman vortex street. The purpose of this investigation is to understand the relation between the positions of interaction and the properties of vortex shedding. The measurements of vortex shedding properties were made in the wake of a normal plate with a long splitter plate which has a narrow slit. As the result, the positions of interaction necessary to the periodic vortex shedding were confirmed.
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Kazuhiro Miyazaki, Shinzaburo UMEDA, Wen Jei Yang, Shyunichi Sakanishi
Article type: Article
Pages
73-74
Published: July 31, 2000
Released on J-STAGE: August 01, 2017
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An oscillation of exit streams, called flip-flop phenomenon, is seen in bundles of cylinders of various cross sectional geometry. There is no thorough understanding of the flow characteristics which lead to flip-flop oscillation phenomenon. In the present work, flow visualization by means of a laser Doppler velocimetry(LDV) was performed inside diamond-shaped cylinder bundles and the oscillating characteristics of the flip-flop flow exiting downstream were investigated by varying the row number and the gap in the cross section of flow passages of the bundles. It is disclosed that the turbulence characteristics in the wake flow behind cylinder vary with the row number. The critical Reynolds number for the evolution of the flip-flop flow is clarified in each geometry of diamond-shaped cylinders. The oscillating frequency in term of the Strouhal number for different cross sections of bundles is clearly correlated with the Reynolds number.
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Yuichiro YOSHIDA, Takashi KUDO, Shinzaburo UMEDA, Wen Jei Yang
Article type: Article
Pages
75-76
Published: July 31, 2000
Released on J-STAGE: August 01, 2017
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A flip-flop phenomenon referring to flow oscillation phenomenon in a wake region behind obstacles was discovered in a flow network consisted of a family of mutually intersecting flow passages. Basic experiments were performed to apply the flip-flop flow to a fluid engineering of zincification. Results are obtained for oscillations of the flip-flop flow from bundles of diamond-shaped cylinders in five different viscous fluids. It is also disclosed that the amount of coating around tubes in a plating tank increases on the effect of the evolution of flip-flop flows.
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Masaki YAMAGISHI, Shinichi TASHIRO
Article type: Article
Pages
77-78
Published: July 31, 2000
Released on J-STAGE: August 01, 2017
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When the periodic velocity fluctuation is introduced in a mean flow, the separation flow changes in various manners. This report concerns with the "flapping" motion of the separation shear layer by means of the phase averaging of instantaneous velocity profiles over the separation region. In order to know the principal motion of the velocity profile precisely, wavelet transform is used. The shapes of profile are quite different at each phase and with the frequency of the fluctuation. When the suitable frequency was chosen, the phase averaged velocity profile is changing periodically between the profile of "inflection type" and "boundary layer type".
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Hisashi YAMAMOTO, Osamu MOCHIZUKI, Masaru KIYA, Hitoshi ISHIKAWA
Article type: Article
Pages
79-80
Published: July 31, 2000
Released on J-STAGE: August 01, 2017
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The transitional change of flow field at the beginning of separation on an NACA0020 airfoil with an angle of attack of 25 degree was investigated experimentally. The generation of separation was controlled by using a wall jet ejected from a thin slit near the leading edge of the airfoil. Velocity fluctuations near the surface were measured by using a split-film probe, so that the instantaneous separation could be determined an reverse flow was detected. It was found that the large vortical structure was formed at the beginning of separation and it induced a strong reverse flow with a value of a half of the free stream velocity.
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Yu FUKUNISHI, Yuzuru YOKOKAWA, Satoshi KIKUCHI
Article type: Article
Pages
81-82
Published: July 31, 2000
Released on J-STAGE: August 01, 2017
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In this paper, an attempt to control the spanwise phase of the velocity fluctuation in the flow over a cavity, utlizing the receptive nature of flow, is carried out. The final objective of this research is to suppress the aerodynamic noise generated from the separating flow. The active flow control technique with piezoelectric-devices is used and two types of actuator devices are tested. The first type is the uni-morph type actuator that expand or shrink parallel to the freestream, the other is the bi-morph type that would bend and vibrate its trailing edge vertically. Experimental results show that the flow field with a wavy structure 180 degree out of phase along the spanwise direction, can be formed using either type of the actuators. However, difference can be found in the yz-plane
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Shuya YOSHIOKA, Shinnosuke OBI, Shigeaki MASUDA
Article type: Article
Pages
83-84
Published: July 31, 2000
Released on J-STAGE: August 01, 2017
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The perturbation-frequency dependence of the vortical structures in the periodically perturbed separated shear layer is experimentally investigated. The turbulent flow over the backward-facing step is chosen for the test case, where the perturbation is introduced at the step edge. The perturbation with the most effective frequency on the reattachment promotion induces the highest number of vortices into the shear layer. On the other hand, the perturbation with the lower or the higher frequency than the most effective frequency introduces fewer vortices. The details of the vortical motion and its effect on the momentum transfer across the separated shear layer are discussed in this paper.
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Masaki FUCHIWAKI, Kazutaka NAGASHIMA, Kazuhiro TANAKA
Article type: Article
Pages
85-86
Published: July 31, 2000
Released on J-STAGE: August 01, 2017
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Recently, a few study on unsteady flow at low Reynolds number region have been developed by the interest in the micro-electro-mechnical systems (MEMS). However, the unsteady fluid forces acting on a moving airfoil have not been measured sufficiently and the relation between flow patterns and them has not been clarified. In the present study, the flow patterns around pitching airfoils such as five kinds of airfoils have been visualized by two kinds of dyes and dynamic fluid forces acting on them have been measured by a six-axes sensor in a water tunnel at low Reynolds number region. The separation from the leading edge began to reattach to the suction surface as the angle of attack in creased. The reattachment had little influences on the dynamic lift at low angle of attack and much influences at high angle of attack. The reattachment had little influences on the dynamic drag.
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Toshihiko SHAKOUCHI, Atsushi WATANABE
Article type: Article
Pages
87-88
Published: July 31, 2000
Released on J-STAGE: August 01, 2017
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Impinging jet has large heat and mass transfer rates at and near the stagnation point. Especially, at a very low nozzle-plate spacing they have considerably large rates, but the flow resitance of nozzle-plate system becomes very large. In this study, the flow and heat transfer characteristics of self-resonating free or impinging jet having very low nozzle-plate spacing are dissussed experimentally, and it is made clear that the self-resonating free or impinging jet has a small flow resistance at a certain volume of resonating room and using the self-resonating impinging jet the heat transfer characteristics can be also improved.
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Munenori UKAI, Dejan B. CVETINOVIC, Kazuyoshi NAKABE, Kenjiro SUZUKI
Article type: Article
Pages
89-90
Published: July 31, 2000
Released on J-STAGE: August 01, 2017
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Whistler nozzle has a simple geometry, consisting of a constant diameter straight pipe nozzle and the sudden expansion of a collar which can slide over the pipe nozzle. With a certain sliding length of the collar, audible self-oscillation can be generated in the jet flow. This oscillatory excitation can enhance the entrainment of the surroundings and disturb the potential core of the jet. In the previous flow visualization experiment, comparison between the excited and non-excited cases revealed that the oscillation drastically modifies the vortical structures of the jet, which results in the change of the distribution patterns of the impingement heat transfer. In the present study, more detail experiments were made to see how the effects of oscillation frequency, jet velocity and impingement distance on the heat transfer distributions are. It was found that the jet flow structure changes with Strouhal number, most dominant parameter based on the frequency, and has great influence on the distributions. The transition of the distribution pattern in the case of the excited case was changed more quickly with an increase in the impinging distance, compared with the non-excited case.
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Takashi HARIMA, Shigetaka FUJITA, Hideo OSAKA
Article type: Article
Pages
91-92
Published: July 31, 2000
Released on J-STAGE: August 01, 2017
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The mean flow properties of turbulent free jets issuing from twin circular nozzles with various nozzle spacing were investigated experimentally. The aim of this study is to clarify the effect of the difference in nozzle spacing on the mixing and diffusion processes. The nozzle spacing used in this study was 2,4 and 8 nozzle diameters. Reynolds number based on the nozzle diameter and the mean exit velocity, was kept constant 25,000 through this experiment. Measurements were made using an X-type hot wire probe and the linearized constant temperature anemometers. In this experiment, the quantity measured was longitudinal mean velocity. From the results, the effects of the difference in nozzle spacing on the streamwise variation of the velocity and the length scales were revealed, and the growth rate of volume flux of twin jets was smaller than that of the single circular jet.
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Kozo SUDO
Article type: Article
Pages
93-95
Published: July 31, 2000
Released on J-STAGE: August 01, 2017
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Waste water from industrial, agricultural or domestic sources usually flows into the environment in the form of turbulent jets. The diffusion of the waste water depends on the mean-flow and turbulence characteristics of the resulting jets and the environmental conditions. In order to control the jet behavior and reduce the environmental contamination, one needs to understand correctly the physical mechanisms of the jets and develop a detailed mathematical model. The presentation aims to introduce the configuration and characteristic of water jets under various conditions.
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