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Coexisting Phenomena of Surge and Rotating Stall in an Axial Flow Compressor

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Journal of Thermal Science 2013年第6期22卷 547-554页

作者： Takuya ABE Hiroaki MITSUI Yutaka ohta Graduate Student Graduate School of Science and EngineeringWaseda University Department of Applied Mechanics and Aerospace Engineering Waseda University

The unsteady inner flow structure of a single-stage axial flow compressor under the coexisting conditions of surge and rotating stall was experimentally investigated via detailed measurements of the unsteady characteristics and the internal flow velocity fluctuations. The main relevant feature of the tested compressor is a shock tube with a capacity tank connected in series to the compressor outlet through slits and a concentric duplex pipe: surge and rotating stall can both be generated by connecting the shock tube. Research attention is focused on the unsteady behavior of a rotating stall during the surge cycle. The size of the rotating stall cell during the recovery process of an irregular surge cycle was experimentally determined by the circumferential flow velocity fluctuations ahead of the rotor blade. The results suggested that the size of the rotating stall cell at the switching point of the performance curve between large and small cycles is considered to be the key parameter in determining the following surge cycle. In addition, the surge cycle is largely influenced by the unsteady behavior of the rotating stall cell.

关键词： Axial flow compressor Surge Rotating stall Coexisting state of surge and rotating stall

Unsteady Behavior of Leading-edge Vortex and Diffuser Stall in a Centrifugal Compressor with Vaned Diffuser

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Journal of Thermal Science 2016年第1期25卷 13-21页

作者： Nobumichi FUJISAWA Shotaro HARA Yutaka ohta Graduate Student Graduate School of Fundamental Science and EngineeringWaseda University 3-4-10kuboShinjukuTokyo 169-8555Japan Department of Applied Mechanics and Aerospace Engineering Waseda University 3-4-1 OkuboShinjukuTokyo 169-8555Japan

The characteristics of a rotating stall of an impeller and diffuser and the evolution of a vortex generated at the diffuser leading-edge(i.e., the leading-edge vortex(LEV)) in a centrifugal compressor were investigated by experiments and numerical analysis. The results of the experiments revealed that both the impeller and diffuser rotating stalls occurred at 55 and 25 Hz during off-design flow operation. For both, stall cells existed only on the shroud side of the flow passages, which is very close to the source location of the LEV. According to the CFD results, the LEV is made up of multiple vortices. The LEV is a combination of a separated vortex near the leading-edge and a longitudinal vortex generated by the extended tip-leakage flow from the impeller. Therefore, the LEV is generated by the accumulation of vorticity caused by the velocity gradient of the impeller discharge flow. In partial-flow operation, the spanwise extent and the position of the LEV origin are temporarily transmuted. The LEV develops with a drop in the velocity in the diffuser passage and forms a significant blockage within the diffuser passage. Therefore, the LEV may be regarded as being one of the causes of a diffuser stall in a centrifugal compressor.

关键词： Centrifugal Compressor Vaned Diffuser Rotating Stall Leading-edge Vortex CFD DES

Unsteady Behavior of Surge and Rotating Stall in an Axial Flow Compressor

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Journal of Thermal Science 2012年第4期21卷 302-310页

作者： Yutaka ohta Yutaka FUJITA Daisuke MORITA Department of Applied Mechanics and Aerospace Engineering Waseda University 3-4-1 Okubo Shinjuku Graduate Student Graduate School of Science and Engineering Waseda University 3-4-1 Okubo Shinjuku

Unsteady behaviors as well as unsteady cascade flow fields of a single-stage axial flow compressor were experi- mentally investigated by detail measurements of unsteady performance characteristics and casing wall pressure and internal flow velocity fluctuations. The main feature of the test compressor is a capacity tank connected di- rectly to the compressor outlet in series through slits and a concentric duplex pipe, and also jet nozzles in order to inject compressed air toward the rotor tip region. Research attention is focused on the post-stall characteristics of surge and rotating stall which occur simultaneously. When the compressor was connected to the capacity tank, surge was generated with rotating stall in accordance with the capacitance increment of whole compressor system The surge behavior changed irregularly with throttling valve installed behind the compressor, and several types of surge cycles were observed. In addition, the surge cycle changed by jet injection to the rotor tip region. The re- suits suggested that the blockages of the cascade flow which were generated by a stall cell play an important role in deciding the surge behaviors.

关键词： Axial flow compressor Surge Rotating stall Stall cell Jet injection

Gd-EOB-DTPA-enhanced magnetic resonance imaging features of hepatic hemangioma compared with enhanced computed tomography

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World Journal of Gastroenterology 2012年第43期18卷 6269-6276页

作者： Akihiro Tateyama Yoshihiko Fukukura Koji Takumi Toshikazu Shindo Yuichi Kumagae kiyohisa Kamimura Masayuki Nakajo Department of Radiology Kagoshima University Graduate School of Medical and Dental Sciences Kagoshima 890-8544 Japan

AIM:To clarify features of hepatic hemangiomas on gadolinium-ethoxybenzyl-diethylenetriaminpentaacetic acid (Gd-EOB-DTPA)-enhanced magnetic resonance imaging (MRI) compared with enhanced computed tomography (CT). METHODS:Twenty-six patients with 61 hepatic hem- angiomas who underwent both Gd-EOB-DTPA-enhanced MRI and enhanced CT were retrospectively reviewed. Hemangioma appearances (presence of peripheral nodular enhancement, central nodular enhancement, diffuse homogenous enhancement, and arterioportal shunt during the arterial phase, fill-in enhancement during the portal venous phase, and prolonged enhancement during the equilibrium phase) on Gd-EOB-DTPA-enhanced MRI and enhanced CT were *** degree of contrast enhancement at the enhancing portion within the hemangioma was visually assessed using a five-point scale during each phase. For quantitative analysis, the tumor-muscle signal intensity ratio (SIR), the liver-muscle SIR, and the attenuation value of the tumor and liver parenchyma were calculated. The McNemar test and the Wilcoxon's signed rank test were used to assess the significance of differences in the appearances of hemangiomas and in the visual grade of tumor contrast enhancement between Gd-EOB-DTPA-enhanced MRI and enhanced CT. RESULTS:There was no significant difference between Gd-EOB-DTPA-enhanced MRI and enhanced CT in the presence of peripheral nodular enhancement (85% vs 82%), central nodular enhancement (3% vs 3%), diffuse enhancement (11% vs 16%), or arterioportal shunt (23% vs 34%) during arterial phase, or fill-in enhancement (79% vs 80%) during portal venous phase. Prolonged enhancement during equilibrium phase was observed less frequently on Gd-EOB-DTPA-enhanced MRI than on enhanced CT (52% vs 100%, P < 0.001). On visual inspection, there was significantly less contrast enhancement of the enhancing portion on Gd-EOB-DTPA-enhanced MRI than on enhanced CT during the arterial (3.94 ± 0.98 vs 4.57 ± 0.64, respectively, P < 0.001), por

关键词： Liver Hemangioma Magnetic resonance imaging Gadolinium-ethoxybenzyl-diethylenetriamin-pentaacetic acid Multidetector-row computed tomography

Unsteady Flow Field under Surge and Rotating Stall in a Three-stage Axial Flow Compressor

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Journal of Thermal Science 2011年第1期20卷 6-12页

作者： Takayuki HARA Daisuke MORITA Yutaka ohta Eisuke OUTA Graduate Student Graduate school of Science and EngineeringWaseda University3-4-1 OkuboShinjukuTokyo 169-8555Japan Department of Applied Mechanics and Aerospace Engineering Waseda University3-4-1 OkuboShinjukuTokyo 169-8555Japan

The unsteady flow structure between rotor blade-to-blade passages in a three-stage axial flow compressor is experimentally investigated by detailed measurements of unsteady performance characteristics,casing wall pressure fluctuations and their wavelet *** main feature of the test compressor is a capacity tank facility connected in series to the compressor outlet in order to supply compression and/or expansion waves from downstream of the *** attention is focused on the post-stall characteristics of the surge and rotating stall which occur *** influence of the compressor operating point on the unsteady performance curve shows that the surge cycle changes irregularly depending on the steady-state resistance characteristics,and the results of the wavelet analyses of the wall pressure fluctuations suggest that the surge cycle may selectively be determined by the rotating stall cell structure within the rotor cascade.

关键词： Axial flow compressor Surge Rotating stall Stall cell Wavelet analysis.

Effects of Diffuser Vane Geometry on Interaction Noise Generated from a Centrifugal Compressor

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Journal of Thermal Science 2005年第4期14卷 321-328页

作者： Yutaka ohta Naho TAKEHARA Yasuhiko OKUTSU Eisuke OUTA Department of Mechanical Engineering Waseda University 3-4-1 Okubo ShinjukuTokyo 169-8555Japan

The characteristics of interaction tone noise radiated from a centrifugal compressor with a vaned diffuser are discussed by experiments, including visualization techniques using the oil-film method. Research attention is paid to the leading edge geometries of the diffuser vanes that are deeply related to the generation mechanism of the interaction tone noise. The compressor-radiated noise can be reduced by several decibels by setting some clearances in both the hub and shroud surfaces of the diffuser wall along with some decline in the pressure-rise coefficient. Since the decline turned out to be caused by the flow impingement and also by the secondary flow within the diffuser passages, several new types of diffuser vane geometries which do not detract from both the performance and noise level are developed and utilized for the experiments. The presented diffuser vane geometries will offer a few basic guidelines for the diffuser vane design.

关键词： centrifugal compressor vaned diffuser interaction noise noise reduction.

Stall Inception Process and Prospects for Active Hub-Flap Control in Three-Stage Axial Flow Compressor

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Journal of Thermal Science 2008年第4期17卷 324-330页

作者： Tomoya OKADA Atsushi KAWAJIRI Yutaka ohta Eisuke OUTA Graduate school of Science and Engineering Waseda University Department of Applied Mechanics and Aerospace Engineering Waseda University

The possibility to apply the active hub-flap control method, which is a proven rotating stall control method for a single-stage compressor, to a 3-stage axial compressor is experimentally discussed, where complex rotating stall inception processes are observed. The research compressor is a 3-stage one and could change the stagger angle settings for rotor blades and stator vanes. Sixteen rotor blade/stator vane configuration patterns were tested by changing stagger angle for the stator vanes. By measurement of surface-pressure fluctuation, stall inception proc- esses are investigated and the measured pressure fluctuation data is used as a predictive signal for rotating stall. The experimental results show that the stall detection system applied to active hub-flap control in a single-stage compressor could be usefully applied to that in a 3-stage compressor with a more complex stall inception process.

关键词： axial flow compressor rotating stall active stall control stall inception stall precursor.

Surge Control of a Centrifugal Compression System by Using a Bouncing Ball

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Journal of Thermal Science 2008年第2期17卷 141-146页

作者： Yuichiro Asaga Shimpei Mizuki Hoshio Tsujita Shinsuke ohta Department of Mechanical Engineering Faculty of EngineeringHosei University Mitsubishi Heavy Industries Ltd.

The purpose of this study is to suppress the fluctuations of surge by a simple passive control method. A bouncing ball system with different weight of the balls was tested. As a result, the bouncing ball system suppressed mild surge without the deterioration of the performance characteristics, and moved the initiation point of surge toward the lower flow rate when the steel ball of 15mm outer diameter was used. The present system was effective to suppress the surge and to widen the stable operating range of a centrifugal compressor when the ball was chosen appropriately.

关键词： centrifugal compressor surge passive control bouncing ball

Development of Several New Reactions and Their Application to the Total Synthesis of Biologically Active Natural Products:Synthesis of Linderol A and Determination of Its Absolute Configuration

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复旦学报（自然科学版） 2005年第5期44卷 783-784页

作者： Shunsaku ohta Department of Functional Molecular Chemistry Kyoto Pharmaceutical University Misasagi Yamashinaku Kyoto 607-8412 Japan

Linderol A (1), a monoterpene-polyketide, was isolated in 1995 from the fresh bark of Lindera umbellata (Lauraceae), and its absolute structure was not determined[1]. It was also reported potent inhibitory activity of 1 on the melanin biosynthesis of the cultured B-16 melanoma cells[1]. See Fig. 1. On the other hand,we reported in 1995 an interesting multi-tandem reaction of coumarin derivatives (2; W = electron withdrawing group) by treatment with CH2 = S(O)Me2 to yield stereoselectively a tricyclic 2-substituted cyclopenta [ b ] benzofuran-3-ol derivative (4) via a cyclopropane intermediate (3) (Scheme 1)[2].

关键词：烯酸自然产物合成方法硫磺立体收敛