2024/05/22 更新

写真a

フジサワ ノブミチ
藤澤 信道
所属
理工学術院 基幹理工学部
職名
准教授
学位
工学博士 ( 早稲田大学 )

所属学協会

  •  
     
     

    ターボ機械協会

  •  
     
     

    ガスタービン学会

  •  
     
     

    日本機械学会

研究分野

  • 流体工学

研究キーワード

  • 数値流体力学

  • ターボ機械

  • 流体工学

受賞

  • 2021年度日本機械学会賞(論文)

    2022年03月  

  • 2018 ASME Turbo Expo Best Paper

    2019年06月  

  • ターボ機械協会第76回北見講演会 若手優秀講演賞

    2016年09月  

  • 日本機械学会三浦賞

    2015年03月  

  • 第42回日本ガスタービン学会学生優秀講演賞

    2014年10月  

  • 日本機械学会畠山賞

    2013年03月  

▼全件表示

 

論文

  • Unsteady Pre-Stall Behavior in a Centrifugal Compressor With Vaned Diffuser

    Yutaro Suzuki, Nobumichi Fujisawa, Yutaka Ohta

    Journal of Turbomachinery   146 ( 4 )  2024年04月

     概要を見る

    Unsteady pre-stall behavior in a centrifugal compressor with a vaned diffuser was investigated by experimental and numerical analysis. The pre-stall disturbances occurred at a slightly higher flow coefficient at the stall point in the diffuser region. Five disturbances occurred in the circumferential direction, and each rotated at approximately 1.7%N at this flow coefficient. Numerical analysis showed that five stall cells rotated at approximately 2.0%N within the diffuser passage. To understand this pre-stall phenomenon, we focused on the rotation mechanism and initiation process of the five-cell rotating stalls. Each of the fivecell stalls was found to rotate by the following mechanism. When the preceding low-velocity region moved to an adjacent passage, the high-velocity region was circumferentially pushed by the low-velocity area and reached the following passage. The incoming flow collided with the backflow around the throat area, and the flow bent at the diffuser inlet of the passage. Consequently, the incidence angle toward the adjacent passage increased, and a separation was induced at the leading edge of the succeeding diffuser vane. Subsequently, the mass flowrate of the succeeding passage started to decrease. These phenomena occurred sequentially, causing the five-cell stalls to rotate. Five stationary low-velocity regions that did not rotate were observed before the initiation of the five-cell rotating stalls. When the outlet mass flowrate decreased, a one-cell rotating stall appeared within the diffuser passage. It provided a low-energy fluid to the diffuser passages where the low-velocity regions existed. Subsequently, five low-velocity regions were clearly formed, which started rotating according to the rotating mechanism explained above.

    DOI

    Scopus

  • 突極形タービン発電機の内部流動と冷却構造に関する研究

    浅沼拓真, 藤澤信道, 太田有, 武藤琢真, 小澤明, 佐藤和雄, 増田光

    日本ガスタービン学会定期講演会講演論文集(CD-ROM)   51st  2023年

    J-GLOBAL

  • UNSTEADY PRE-STALL BEHAVIOR IN A CENTRIFUGAL COMPRESSOR

    Yutaro Suzuki, Nobumichi Fujisawa, Yutaka Ohta

    Proceedings of the ASME Turbo Expo   13D  2023年

     概要を見る

    Unsteady pre-stall behavior in a centrifugal compressor with a vaned diffuser was investigated by experimental and numerical analysis. The pre-stall disturbances occurred at a slightly higher flow coefficient at the stall point in the diffuser region. Five disturbances occurred in the circumferential direction, and each rotated at approximately 1.7%N at this flow coefficient. Numerical analysis showed that five stall cells rotated at approximately 2.0%N within the diffuser passage. To understand this pre-stall phenomenon, we focused on the rotation mechanism and initiation process of the five-cell rotating stalls. Each of the five-cell stalls was found to rotate by the following mechanism. When the preceding low-velocity region moved to an adjacent passage, the high-velocity region was circumferentially pushed by the low-velocity area and reached the following passage. The incoming flow collided with the back flow around the throat area, and the flow bent at the diffuser inlet of the passage. Consequently, the incidence angle toward the adjacent passage increased, and a separation was induced at the leading edge of the succeeding diffuser vane. Subsequently, the mass flow rate of the succeeding passage started to decrease. These phenomena occurred sequentially, causing the five-cell stalls to rotate. Five stationary low-velocity regions that did not rotate were observed before the initiation of the five-cell rotating stalls. When the outlet mass flow rate decreased, a one-cell rotating stall appeared within the diffuser passage. It provided a low-energy fluid to the diffuser passages where the low-velocity regions existed. Subsequently, five low-lowvelocity regions were clearly formed, which started rotating according to the rotating mechanism explained above.

    DOI

    Scopus

  • DIFFUSER STALL INCEPTION IN A HIGH-PRESSURE RATIO CENTRIFUGAL COMPRESSOR WITH FISHTAIL PIPE DIFFUSER

    Atsushi Ogino, Nobumichi Fujisawa, Ryo Nakayama, Satoshi Aoyama, Eijiro Kitamura, Yutaka Ohta

    Proceedings of the ASME Turbo Expo   13D  2023年

     概要を見る

    This paper presents the stall inception of fishtail pipe diffuser investigated by both unsteady and steady numerical analyses. Fishtail pipe diffuser decelerates the air flow from impeller and induces the flow to the combustor by changing the flow direction from radial to axial. Each unsteady numerical simulation with full annulus model and steady simulation with 1 passage model was performed to investigate the stall inception of the fishtail pipe diffuser attached on the transonic centrifugal compressor stage by commercial code for the design speed, where the flow at the diffuser inlet is supersonic. The numerical simulations were well validated by experimental results. The characteristics of speed-lines and stall points by the numerical simulations matched the surge line of the experimental result. In near stall condition, the separation flow was observed on the suction side wall at the bend section of diffuser. The separation extended upstream by further increase of back pressure of diffuser. When the separation affected the boundary layer on throat wall, diffuser stall occurred. To confirm the effect of the bend, the numerical analysis of the straight shape diffuser was also performed. Straight diffuser was confirmed more stable than the diffuser with bend. From these observations, it was concluded that stall inception was the suction side boundary layer separation promoted by the secondary flow due to the bend.

    DOI

    Scopus

  • 遠心圧縮機に発生する羽根車失速と羽根なしディフューザ失速の相互作用

    鈴木祐太郎, 岸隼冬, 内藤桃子, 藤澤信道, 太田有

    日本機械学会年次大会講演論文集(CD-ROM)   2022  2022年

    J-GLOBAL

  • 羽根なしディフューザを有する遠心圧縮機の旋回失速に関する実験的調査

    藤澤信道, 山尾佳史, 内藤桃子, 太田有

    ターボ機械   50 ( 6 ) 36 - 44  2022年

    DOI

  • EFFECTS OF TIP CLEARANCE ON INTERNAL FLOW AND LOSS GENERATION MECHANISM IN AN AXIAL COMPRESSOR AT WINDMILLING CONDITIONS

    Tomohiro Inada, Ryousuke Sekino, Nobumichi Fujisawa, Yutaka Ohta

    American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FEDSM   1  2022年

     概要を見る

    The internal flow structure and loss generation mechanism of a single-stage compressor during windmilling were investigated through experimental and computational analyses. The windmilling state occurs when the air flowing through an unlit engine drives the compressor rotor blades, similar to a turbine. This study focused on the effect of tip clearance size on the internal flow during windmilling operations. Therefore, detached eddy simulations were conducted at three tip clearance conditions: without clearance, design clearance, and wide clearance. Consequently, the total pressure loss decreased when the size of the tip clearance was expanded under windmilling conditions. In the windmilling state, separation on the pressure side due to the high negative incidence was generated, which was the main reason for the total pressure loss. When the size of the clearance increased, the size of the separation decreased because of the tip leakage flow. According to the detailed numerical results for the windmilling state, the leakage flow held the separation to the blade surface near the tip area. In addition, the tip leakage flow formed a blockage in the midchord, so the tip side of the separation vortex was moved to the midchord and formed a significant loss region. Thus, the tip leakage flow reduced the loss region, and the overall loss was reduced.

    DOI

    Scopus

    1
    被引用数
    (Scopus)
  • INTERACTION MECHANISM OF IMPELLER AND DIFFUSER STALL IN A CENTRIFUGAL COMPRESSOR

    Nobumichi Fujisawa, Momoko Naitou, Yutaka Ohta

    Proceedings of the ASME Turbo Expo   10-D  2022年

     概要を見る

    The interaction mechanism of impeller and diffuser stall in a centrifugal compressor with a vaneless diffuser was investigated by experimental and computational analyses. This study focuses on the effect of impeller stall on the diffuser stall behavior. Impeller stall rotated at 58% of the impeller rotational speed was generated inside the impeller. Two-cell diffuser stalls (with each of the cells rotating at 25%-30% of the impeller rotational speed) were generated inside the diffuser. The diffuser stall fluctuations were observed at 180° from the cutoff. The magnitudes of the diffuser stall fluctuations gradually increased near the volute tongue. The diffuser stall fluctuations were generated near both the shroud and hub sides. Finally, the diffuser stall cell vanishes when it passes the cutoff because mass flow recovery occurs. The numerical results revealed that boundary layer separation occurred near the hub side at 45°-90° of the diffuser because of the circumferential adverse pressure gradient. Subsequently, the low-velocity region discharged from the impeller caused by impeller stall merged into the boundary layer separation, which was generated near the hub side at 45°- 90°. Diffuser stall was initiated by the hub-side boundary layer separations, which were caused by the impeller stall. The diffuser stall cell was then further developed by the boundary layer separation accumulation and the induced low-velocity area. The boundary separation was further developed by merging the wake from the impeller stall passage.

    DOI

    Scopus

    2
    被引用数
    (Scopus)
  • Behavior of Vaneless Diffuser Stall in a Centrifugal Compressor

    Yuki Agari, Yoshifumi Yamao, Nobumichi Fujisawa, Yutaka Ohta

    Journal of Thermal Science   31 ( 1 ) 3 - 12  2022年01月

     概要を見る

    The rotating stall in a centrifugal compressor with a vaneless diffuser was investigated both experimentally and numerically with focus on the effect of the internal flow field within the impeller on the diffuser stall. Through numerical analysis, the boundary layer separation at the impeller outlet was found to play an important role in the expansion and rotation processes of the diffuser stall. In particular, the expanded boundary layer separation near the hub side at the outlet of the main blade (M.B.) suction surface passage was considered to be the main cause of the expansion and rotation processes. A longitudinal vortex existed at the throat of the M.B. passage, and the mass flow rate in the M.B. passage was significantly reduced by the blockage effect. In addition, the longitudinal vortex induced the rolling up flow near the hub side at the impeller exit. Thus, the boundary layer separation expanded.

    DOI

    Scopus

    2
    被引用数
    (Scopus)
  • The effect of unsteady vortex behavior on noise characteristics in a centrifugal compressor

    Kenta Tajima, Hiroshi Miida, Nobumichi Fujisawa, Yutaka Ohta

    Journal of Physics: Conference Series   1909 ( 1 ) 012021 - 012021  2021年05月

     概要を見る

    Abstract

    The effect of diffuser width on the noise level of a centrifugal compressor equipped with vaneless diffusers was investigated through experiments and numerical techniques. In this regard, two diffusers with different widths were installed in the compressor. In case the wider diffuser was used, there was the bandwidth (800 to 900 Hz) noise and pressure fluctuation which was closed to 1/2BPF (700 Hz). This fluctuation occurred because the leakage vortices were of two different frequencies. Type 1 vortices are the ones that were discharged from the main blade and covered Passage 1. Type 2 vortices had the same length as Type 1, but they were discharged from the splitter blade. Type 3 vortices covered both Passages 1 and 2; these were discharged from the main blade. Type 3 vortices were generated predominantly at 270°, and their frequency was approximately 700 Hz at 1/2 BPF frequency. The former two types of vortices occurred occasionally, and their frequency was approximately 1400 Hz. Type 3 vortices grew with the wider diffuser because of the higher pressure-recovery, which caused the serous loading to the impeller blades. The broadband noise fluctuation occurred by the coexistence of the two frequency vortices.

    DOI

    Scopus

  • Rotating mechanism of diffuser stall in a centrifugal compressor with vaneless diffuser

    Nobumichi Fujisawa, Yuki Agari, Yoshifumi Yamao, Yutaka Ohta

    Proceedings of the ASME Turbo Expo   2D-2021  2021年

     概要を見る

    The rotating mechanism of diffuser stall in a centrifugal compressor with a vaneless diffuser is investigated via experimental and computational analyses. Diffuser stall is generated as the mass flow rate decreases, and it rotates at 25%-30% of the impeller rotational speed. First, a diffuser stall cell emerges at 180° from the cutoff by the hub-side boundary layer separation. Subsequently, the diffuser stall cell develops further owing to boundary layer separation accumulation and an induced low-velocity area. The low-velocity region forms a blockage across the diffuser passage span. The diffuser stall cell expands owing to the boundary layer separations that occurred on the shroud and hub wall by turns. Finally, the diffuser stall cell vanishes when it passes the cutoff because mass flow recovery occurred. Furthermore, the static pressure ahead of the rotating stall decreases because of the merging of the impeller discharge flow and the reverse flow from the casing. Accordingly, a reverse flow occurred owing to the evolution of the separation vortex at the diffuser exit. In addition, the flow angle decreases by the merging of the impeller discharge flow and reverse flow from the casing. Therefore, boundary layer separations start occurring on the shroud and hub wall ahead of the stall cell. The rotating mechanism of the diffuser stall is induced by the reverse flow development and a decrease in the flow angle ahead of the stall cell.

    DOI

    Scopus

    5
    被引用数
    (Scopus)
  • Generation Mechanism of Diffuser Stall in a Centrifugal Compressor with Vaneless Diffuser

    Nobumichi Fujisawa, Kenta Tajima, Hiroshi Miida, Yutaka Ohta

    Journal of the Global Power and Propulsion Society   4   190 - 201  2020年12月

     概要を見る

    The generation mechanism of a diffuser stall in a centrifugal compressor with a vaneless diffuser was investigated by experimental and computational analyses. The diffuser stall generated as the mass flow rate decreased. The diffuser stall cell rotated at 25-30 % of the impeller rotational speed, with diffuser stall fluctuations observed at 180° from the cutoff. The diffuser stall fluctuation magnitude gradually increased near the cutoff. According to the CFD analysis, the mass flow fluctuations at the diffuser exit showed a low mass flow region, rotating at approximately 25% of the impeller rotational speed. They began at 180° from the cutoff and developed as this region approached the cutoff. Therefore, the diffuser stall could be simulated by CFD analysis. First, the diffuser stall cell originated at 180° from the cutoff by interaction with boundary separation and impeller discharge vortex. Then, the diffuser stall cell further developed by boundary separation accumulation and the induced low velocity area The low velocity region formed a blockage across the diffuser passage span. The diffuser stall cell expanded due to boundary separation caused by a positive flow angle. Finally, the diffuser stall cell vanished when it passed the cutoff, because mass flow recovery occurred.

    DOI

  • The Unsteady Behavior of Diffuser Stall in a Centrifugal Compressor With Vaneless Diffuser

    Hiroshi Miida, Kenta Tajima, Nobumichi Fujisawa, Yutaka Ohta

    Volume 1: Fluid Applications and Systems; Fluid Measurement and Instrumentation   1  2020年07月

     概要を見る

    <title>Abstract</title>
    The unsteady diffuser stall behavior in a centrifugal compressor with a vaneless diffuser was investigated by experimental and computational analyses. The diffuser stall generated as the mass flow rate decreased. The diffuser stall cell rotated at 25–30% of the impeller rotational speed, with diffuser stall fluctuations observed at 180° from the cutoff. The diffuser stall fluctuation magnitude gradually increased near the cutoff. Based on diffuser inlet velocity measurements, the diffuser stall fluctuations generated near both the shroud and hub sides, and the diffuser stall appeared at 180° and 240° from the cutoff. According to the CFD analysis, the mass flow fluctuations at the diffuser exit showed a low mass flow region, rotating at approximately 25% of the impeller rotational speed. They began at 180° from the cutoff and developed as this region approached the cutoff. Therefore, the diffuser stall could be simulated by CFD analysis. First, the diffuser stall cell originated at 180° from the cutoff by interaction with boundary separation and impeller discharge vortex. Then, the diffuser stall cell further developed by boundary separation accumulation and the induced low velocity area, located at the stall cell center. The low velocity region formed a blockage across the diffuser passage span. The diffuser stall cell expanded in the impeller rotational direction due to boundary separation caused by a positive flow angle. Finally, the diffuser stall cell vanished when it passed the cutoff, because mass flow recovery occurred.

    DOI

  • Effect of Forward-Swept Rotor on Stall Margin in an Axial Flow Compressor at Distorted Inflow Condition

    Kyonosuke Hamaguchi, Yuu Sakata, Nobumichi Fujisawa, Yutaka Ohta, Dai Kato

    International Journal of Gas Turbine, Propulsion and Power Systems   11 ( 4 ) 13 - 21  2020年

     概要を見る

    In this study, we aim to elucidate the effect of a forward-swept rotor on the stall margin and flow field at the distorted inflow conditions. The rig in this research is a low-speed, single-stage axial compressor, which has two types of rotor blades: The radially stacked blade (Radial) and the forward-swept blade (Sweep). The distortion screen that circumferentially generates distorted inflow is located upstream of the rotor. The stall margin of Sweep was found to be larger than that of Radial. Sweep was considered to improve the flow fields at the distorted inflow conditions. From the results of the study, it was observed that Sweep suppressed the circumferential expansion of the high-load regions and the spike-type disturbances generated at the distorted sector. Therefore, Sweep enlarged the stall margin more than to Radial.

    DOI

  • Rotor Performance of an Axial Flow Compressor at Free and Highly Loaded Windmilling Conditions

    Wenbo Zhang, Nobumichi Fujisawa, Yutaka Ohta, Takashi Goto, Dai Kato

    International Journal of Gas Turbine, Propulsion and Power Systems   11 ( 2 ) 17 - 26  2020年

     概要を見る

    The work characteristics and loss-generation mechanism of a single-stage axial flow compressor in windmilling operation were investigated via experiments and computational fluid dynamics analyses. The windmilling state occurs when air flowing through an unlit engine drives the compressor rotor blades, similar to a turbine. This phenomenon applies mostly to aircraft engines, where it is caused by ram pressure. When the inlet flow coefficient is gradually increased in the design, the rotor blades gradually enters the windmilling operation from the tip toward the hub. This research has focused on two windmilling operations: free windmilling (FW) and highly loaded (HL) windmilling. In the case of FW, the net work performed by the rotor blades to the fluid is canceled out (zero), and the rotor is in an idle state. In the HL windmilling condition, the work performed to the rotor blades by the fluid increases, the compressor acts as a turbine, and power is generated. According to the detailed numerical results, the total-pressure loss under the free and HL windmilling conditions was mainly caused by three flow structures: (1) tip leakage flow from the suction surface (SS) to the pressure surface (PS) near the leading edge and that from the PS to the SS near the trailing edge; (2) the interaction of leading-edge separation vortices due to the highly negative incidence and the rotor leading-edge vortex; and (3) the boundary- layer separation near the hub wall. Surface-pressure measurement on a rotating rotor blade revealed that the distribution of the rotor operating mode existed not only in the spanwise direction but also in the chordwise direction under the windmilling operations. The turbine mode region was observed near the leading edge, while the compressor mode region was observed near the trailing edge, even in the HL windmilling condition. Therefore, the driving force of the windmilling was dominated not by the area of the turbine mode on the rotor surface but by the strength of the operating mode, i.e., the static-pressure difference between the SS and PS on the rotor. Finally, the unsteady flow field within blade-to-blades passages was investigated via an unsteady detached eddy simulation, and the differences in the loss-generation mechanism between the FW and HL windmilling conditions were examined.

    DOI

  • Development of Rotating Stall Cell Under Coexisting Phenomena of Surge and Rotating Stall in an Axial-Flow Compressor

    Yuu Sakata, Shuji Ando, Nobumichi Fujisawa, Yutaka Ohta

    Volume 3A: Fluid Applications and Systems   3A-2019  2019年07月

     概要を見る

    <title>Abstract</title>
    The relationship between the growth of the stall cell and variation in the surge behavior was experimentally investigated. The aim of this study was to reveal the effect of the stall cell on the surge behavior from the viewpoint of the inner flow structure. In the experiment, the unsteady compressor characteristics during the surge and rotating stall were obtained by using a precision pressure transducer and a one-dimensional single hotwire anemometer. Under the coexisting states of surge and rotating stall, various surge behaviors were observed by throttling the mass flow rate. When the flow rate was set such that the surge behavior switched, an irregular surge was observed. During the irregular cycle, two different cycles were selected randomly corresponding to the stall behavior. When the amplitude of the plenum pressure is relatively large among the measurement results, the absolute value of the time-change rate in the flow coefficient and the static pressure-rise coefficient tend to be high. This shows that the flow field during stable operation near the peak point of the unsteady characteristics changes rapidly. In this case, an auto-correlation function of the wall-pressure fluctuation data showed that the stall inception of the compressor was induced earlier in the large cycle compared with the case of the top cycle. When studying the growth of the stall cell during the stalling process of the large cycle, the wall-pressure fluctuation data showed that the stall cell rapidly grew by gathering more than one spike-type disturbance into one stall cell. In this case, the stall cell fully expanded along the circumferential direction and developed into a deep stall. Therefore, the key factors that determine the surge behavior are the sudden change in the flow field near the peak point of the unsteady characteristics and the rapid growth in the stall cell during the stalling process.

    DOI

  • Transient Analysis of Rotating Stall Development in a Centrifugal Compressor With Vaned Diffuser

    Nobumichi Fujisawa, Masaki Takahashi, Yutaka Ohta

    Volume 2A: Turbomachinery   2A-2019  2019年06月

     概要を見る

    <title>Abstract</title>
    The transient process of the rotating stall development in a centrifugal compressor with a vaned diffuser was investigated by experimental and numerical analyses. Previous studies show that a diffuser stall triggers a stage stall, which rotates through rotor and stator passages. The vortex evolution at the diffuser throat represents the key factor in diffuser stall development. The developed diffuser stall cell blocked the impeller exit, causing an impeller passage stall. This paper focused on two aspects regarding the transient process of the diffuser stall development. The first aspect is the process by which the vortex at the diffuser throat near the hub side, develops in the circumferential direction. Secondly, we investigated the mechanism of the diffuser stall expansion into impeller passages. The transient analysis of the diffuser stall development was conducted experimentally and numerically by closing the throttle valve abruptly. The hub side blockage was initiated near the cutoff by the strong adverse pressure gradient in the diffuser throat area. Therefore, the key factor in the diffuser stall evolution was the development of a throat blockage near the cutoff, obtained from both experimental and computational fluid dynamics results. Furthermore, the transient stall cell blocked the impeller passages and induced a hub side blockage at the throat of the impeller passages and the impeller leading edge separation. The pressure surface separation of the impeller at the trailing edge had a great impact on the development of the stall cell within impeller passages.

    DOI

  • Evolution Process of Diffuser Stall in a Centrifugal Compressor With Vaned Diffuser

    Nobumichi Fujisawa, Tetsuya Inui, Yutaka Ohta

    Journal of Turbomachinery   141 ( 4 )  2019年04月

     概要を見る

    This paper describes in detailed flow field in a centrifugal compressor with a vaned diffuser at off design point. Especially, we conducted both the experimental and numerical analysis in order to investigate the evolution process of a diffuser stall. At the stall point, the diffuser stall was initiated and rotated near the shroud side in the vaneless space. Furthermore, the diffuser stall was developed to a stage stall cell, as the mass flow was decreased. The developed stall cell was rotated within both the impeller and diffuser passages. The evolution process of the diffuser stall had three stall forms. First, the diffuser stall was rotating near the shroud side. Then, the diffuser stall shifted to the hub side and moved into the impeller passages. Finally, a stage stall was generated. From computational fluid dynamics (CFD) analysis, a tornado-type vortex was generated first, near the hub side of the diffuser leading edge, when the diffuser stall was shifted to the hub side. Next, a throat area blockage was formed near the hub side because of the boundary layer separation in the vaneless space. Finally, the blockage within the diffuser passages expanded to the impeller passages and developed into a stage stall. From the pressure measurements along the impeller and diffuser passages, the magnitude of pressure fluctuation on the casing wall of the diffuser throat area also suddenly increased when the diffuser stall shifted to the hub side. Therefore, the evolution area of the diffuser stall was caused by the evolution of the blockage near the throat area of the diffuser passage.

    DOI

    Scopus

    29
    被引用数
    (Scopus)
  • Interaction Between Surge Behavior and Internal Flow Field in an Axial-Flow Compressor

    Yuu Sakata, Nobumichi Fujisawa, Yutaka Ohta

    Volume 3: Fluid Machinery; Erosion, Slurry, Sedimentation; Experimental, Multiscale, and Numerical Methods for Multiphase Flows; Gas-Liquid, Gas-Solid, and Liquid-Solid Flows; Performance of Multiphase Flow Systems; Micro/Nano-Fluidics   3  2018年07月

     概要を見る

    Interaction between surge behavior and internal flow field under coexisting phenomena of surge and rotating stall was experimentally investigated. In the experiment, the tank pressure of the compressor during surge was measured to detect the effect of the back-pressure fluctuation on the change in the internal flow field. Furthermore, the rotating stall in the compressor was investigated to define the influence of an unsteady internal flow field change on the surge behavior. From the tank pressure measurements, the amplitude of the tank pressure fluctuation was found to vary depending on the cycle. A larger maximal value for the tank pressure fluctuation led to a higher flow rate where the stall inception occurred. This difference in the flow rate indicated that the stall was induced by a severe adverse pressure gradient in the compressor. Then, the absolute rate of change in the flow coefficient was increased by both a large decrease in the compressor back pressure and performance degradation from stalling. In a case where the rate of decline in the flow rate was large, the scale of the stall cell developed up to a deep stall according to the movement of the operating point. Thus, a large trajectory for the surge cycle was selected, where the unsteady operating point went through the deep stall region. This development in the scale of the stall cell suggested to be influenced by the instability of the inner flow field caused by the rapid change in the flow rate.

    DOI

  • Evolution Process of Diffuser Stall in a Centrifugal Compressor with Vaned Diffuser

    Nobumichi Fujisawa, Tetusya Inui, Yutaka Ohta

    Proceedings of ASME Turbo Expo 2018   2A-2018  2018年06月

    DOI

    Scopus

    11
    被引用数
    (Scopus)
  • 遠心圧縮機ディフューザ前縁形状が騒音・失速特性に与える影響

    藤澤信道, 太田 有

    ターボ機械   2017 ( 45 ) 11 - 19  2017年11月

  • Unsteady Behavior of Diffuser Stall in a Centrifugal Compressor With Vaned Diffuser

    Nobumichi Fujisawa, Daiki Ema, Yutaka Ohta

    Volume 2D: Turbomachinery    2017年06月

     概要を見る

    In this study, the unsteady behavior of a diffuser rotating stall in a centrifugal compressor with a vaned diffuser was investigated through experiments and numerical analyses. From the casing static pressure measurements, it was determined that the diffuser stall propagated at 25% of impeller rotational speed in the vaneless space. The numerical results revealed the presence of a typical vortical structure on the diffuser’s leading edge. Under partial flow condition, a tornado-type vortex was generated on the diffuser’s leading edge. Furthermore, a longitudinal vortex at the shroud/suction surface corner (i.e., leading edge vortex (LEV)) was induced by the rolling-up flow on the diffuser suction surface. As the velocity was decreased, the development of the tornado-type vortex and LEV forms a substantial flow blockage within the diffuser passages. Furthermore, the diffuser stall cell was caused by the systematic vortical structure which consisted of the tornado-type vortex, LEV, and vortex in the throat area of diffuser passages. In addition to this, the developed LEV interacted with the next diffuser leading edge and formed the throat area blockage with the passage of time. Then, the tornado-type vortex and LEV developed by the throat area blockage and diffuser stall cell, which was caused by the systematic vortical structure, propagated to the succeeding diffuser vane. Therefore, the diffuser stall in the centrifugal compressor was caused by the evolution of the tornado-type vortex and LEV.

    DOI

  • Transition Process from Diffuser Stall to Stage Stall in a Centrifugal Compressor with a Vaned Diffuser

    Nobumichi Fujisawa, Yutaka Ohta

    International Journal of Rotating Machinery   2017 ( 2861257 )  2017年

     概要を見る

    The transition process from a diffuser rotating stall to a stage stall in a centrifugal compressor with a vaned diffuser was investigated by experimental and numerical analyses. From the velocity measurements, it was found that the rotating stall existed on the shroud side of the diffuser passage in the off-design flow condition. The numerical results revealed the typical vortical structure of the diffuser stall. The diffuser stall cell was caused by the systematic vortical structure which consisted of the tornado-type vortex, the longitudinal vortex at the shroud/suction surface corner (i.e., leading edge vortex (LEV)), and the vortex in the throat area of the diffuser passages. Furthermore, the stage stall, which rotated within both the impeller and diffuser passages, occurred instead of the diffuser stall as the mass flow rate was decreased. According to the velocity measurements at the diffuser inlet, the diffuser stall which rotated on the shroud side was shifted to the hub side. Then, the diffuser stall moved into the impeller passages and formed the stage stall. Therefore, the stage stall was caused by the development of the diffuser stall, which transferred from the shroud side to the hub side in the vaneless space and expanded to the impeller passages.

    DOI

    Scopus

    13
    被引用数
    (Scopus)
  • Unsteady Behavior of Leading-edge Vortex and Diffuser Stall in a Centrifugal Compressor with Vaned Diffuser

    Nobumichi Fujisawa, Shotaro Hara, Yutaka Ohta

    JOURNAL OF THERMAL SCIENCE   25 ( 1 ) 13 - 21  2016年02月  [査読有り]

     概要を見る

    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.

    DOI

    Scopus

    21
    被引用数
    (Scopus)
  • STRUCTURE OF DIFFUSER STALL AND UNSTEADY VORTICES IN A CENTRIFUGAL COMPRESSOR WITH VANED DIFFUSER

    Nobumichi Fujisawa, Sota Ikezu, Yutaka Ohta

    PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2016, VOL 2D   2D-2016  2016年  [査読有り]

     概要を見る

    The characteristics of a diffuser rotating stall and the evolution of a vortex generated on the diffuser leading edge (i.e., leading-edge vortex (LEV)) in a centrifugal compressor were investigated using experiments and numerical analyses. The experimental results showed that both impeller and diffuser rotating stalls occurred at 55 and 25 Hz during off-design flow operation. Both the stall cells existed only on the shroud side of the flow passages, which is in close proximity to the source location of the LEV. The numerical results showed that the LEV is a combination of a separated vortex near the leading edge and the extended tip-leakage flow from the impeller. In the partial flow operation, the LEV develops as the velocity decreases in the diffuser passages and forms a huge flow blockage within the diffuser passages. Therefore, the LEV may be considered to be one of the causes of diffuser stall in the centrifugal compressor.

    DOI

    Scopus

    9
    被引用数
    (Scopus)
  • 遠心圧縮機の羽根車翼端隙間が内部流れに及ぼす影響

    黒田 未来, 池津 聡太, 藤澤 信道, 太田 有

    流体工学部門講演会講演論文集   2015   "1615 - 1"-"1615-3"  2015年11月

  • 羽根付ディフューザを有する遠心圧縮機に発生する失速と前縁渦の関係

    Fujisawa, Nobumichi, Hara, Shotaro, Ohta, Yutaka

    日本機械学会論文集   81 ( 829 ) 15 - 00194-15-00194  2015年09月

     概要を見る

    The experimental and CFD analysis were conducted to investigate the relationship between stall and leading-edge vortex (LEV) in a centrifugal compressor with vaned diffuser. The LEV is distinct from the separating vortex of the diffuser leading-edge and passage vortex of the diffuser. The LEV is made up of two longitudinal vortices. It is produced by the accumulation of vortices caused by the velocity gradient of the impeller-discharge flow. According to the experimental results, both the impeller and diffuser rotating stalls occurred at 55 and 25 Hz during off-design flow operation. Both stall cells were existed only on the shroud side of the flow passages, which is very close to the source location of the LEV. Additionally, the intensity and scale of the diffuser stall fluctuation are much larger than those of the impeller stall fluctuation. Therefore, the unsteady behavior of the LEV may play an important role in the inception of the rotating stall. According to the CFD results, the size of the LEV doesn't change, and the LEV is comparatively stable in the designed flow operation. On the other hand, the LEV develops and forms a huge flow blockage within the diffuser passages during off-design operation. Therefore, the LEV may be considered to be one of the causes of the diffuser stall in the centrifugal compressor.

    DOI CiNii

  • Unsteady Behavior and Control of Vortices in Centrifugal Compressor

    Yutaka Ohta, Nobumichi Fujisawa

    JOURNAL OF THERMAL SCIENCE   23 ( 5 ) 401 - 411  2014年10月  [査読有り]

     概要を見る

    Two examples of the use of vortex control to reduce noise and enhance the stable operating range of a centrifugal compressor are presented in this paper. In the case of high-flow operation of a centrifugal compressor with a vaned diffuser, a discrete frequency noise induced by interaction between the impeller-discharge flow and the diffuser vane, which appears most notably in the power spectra of the radiated noise, can be reduced using a tapered diffuser vane (TDV) without affecting the performance of the compressor. Twin longitudinal vortices produced by leakage flow passing through the tapered portion of the diffuser vane induce secondary flow in the direction of the blade surface and prevent flow separation from the leading edge of the diffuser. The use of a TDV can effectively reduce both the discrete frequency noise generated by the interaction between the impeller-discharge flow and the diffuser surface and the broadband turbulent noise component. In the case of low-flow operation:a leading-edge vortex (LEV) that forms on the shroud side of the suction surface near the leading edge of the diffuser increases significantly in size and blocks flow in the diffuser passage. The formation of an LEV may adversely affect the performance of the compressor and may cause the diffuser to stall. Using a one-side tapered diffuser vane to suppress the evolution of an LEV, the stable operating range of the compressor can be increased by more than 12 percent, and the pressure-rise characteristics of the compressor can be improved. The results of a supplementary examination of the structure and unsteady behavior of LEVs, conducted by means of detailed numerical simulations, are also presented.

    DOI

    Scopus

    14
    被引用数
    (Scopus)
  • EFFECTS OF DIFFUSER VANE GEOMETRIES ON COMPRESSOR PERFORMANCE AND NOISE CHARACTERISTICS IN A CENTRIFUGAL COMPRESSOR

    Yohei Morita, Nobumichi Fujisawa, Takashi Goto, Yutaka Ohta

    PROCEEDINGS OF THE ASME FLUIDS ENGINEERING DIVISION SUMMER MEETING, 2013, VOL 1B: SYMPOSIA   1 B  2014年  [査読有り]

     概要を見る

    The effects of the diffuser vane geometries on the compressor performance and noise characteristics of a centrifugal compressor equipped with vaned diffusers were investigated by experiments and numerical techniques. Because we were focusing attention on the geometries of the diffuser vane's leading edge, diffuser vanes with various leading edge geometries were installed in a vaned diffuser. A tapered diffuser vane with the tapered portion near the leading-edge of the diffuser's hub-side could remarkably reduce both the discrete frequency noise level and broadband noise level. In particular, a hub-side tapered diffuser vane with a taper on only the hub-side could suppress the development of the leading edge vortex (LEV) near the shroud side of the diffuser vane and effectively enhanced the compressor performance.

    DOI

    Scopus

    2
    被引用数
    (Scopus)
  • UNSTEADY BEHAVIOR OF LEADING EDGE VORTEX AND DIFFUSER STALL INCEPTION IN A CENTRIFUGAL COMPRESSOR WITH VANED DIFFUSER

    Nobumichi Fujisawa, Shotaro Hara, Yutaka Ohta, Takashi Goto

    PROCEEDINGS OF THE ASME FLUIDS ENGINEERING DIVISION SUMMER MEETING - 2014, VOL 1B: SYMPOSIA   FEDSM2014-21242  2014年  [査読有り]

     概要を見る

    Experiments and numerical analyses were used to investigate the unsteady behavior of a vortex generated on the leading-edge of a diffuser (i.e., leading-edge vortex (LEV)) and the diffuser stall inception in a centrifugal compressor equipped with vaned diffusers. The LEV is distinct from the separation vortex of the diffuser's leading edge and passage vortex of the diffuser; it is generated by the accumulation of vortices caused by the velocity gradient of the impeller discharge flow. The LEV increases with decreasing velocity in the diffuser passage and forms a huge flow blockage within the diffuser passage. Therefore, the LEV may help cause the diffuser stall inception in the centrifugal compressor. A diffuser vane, that was tapered only on the hub side was designed and used in the experiment. The results of the computational fluid dynamics analysis and experiments showed that the tapered diffuser vane can suppress LEV evolution during off-design operations. Therefore, the tapered diffuser vane may control the diffuser stall inception in a centrifugal compressor by suppressing LEV evolution.

    DOI

    Scopus

    6
    被引用数
    (Scopus)

▼全件表示

書籍等出版物

  • 流体の力学

    太田 有, 藤澤 信道

    共立出版  2020年03月 ISBN: 4320082230

    ASIN

講演・口頭発表等

  • Effect of Circumferential Groove Casing Treatment on Internal Flow in a Centrifugal Compressor with Vaneless Diffuser

    Koshiro Tokuda, Nobumichi Fujisawa, Yutaka Ohta

    9th Asian Joint Workshop on Thermophysics and Fluid Science  

    発表年月: 2022年11月

  • Effect of Rotating Stall Development on Surge Behavior in an Axial Compressor

    Yuki Nishii, Nobumichi Fujisawa, Yutaka Oht

    9th Asian Joint Workshop on Thermophysics and Fluid Science  

    発表年月: 2022年11月

  • Flow Fields on Development Process of Diffuser Rotating Stall in a Centrifugal Compressor with Vaned Diffuser

    Momoko Naito, Yutaro Suzuki, Nobumichi Fujisawa, Yutaka Ohta

    9th Asian Joint Workshop on Thermophysics and Fluid Science  

    発表年月: 2022年11月

  • 軸流圧縮機における動翼翼端隙間感度の改善

    山上舞, 若林祥, 佐藤大佑, 加藤大, 藤澤信道, 太田有

    第50回日本ガスタービン学会定期講演会  

    発表年月: 2022年10月

  • 航空エンジン用遠心圧縮機における羽根車旋回失速の挙動

    青山慧士, 藤澤信道, 太田有, 中山亮, 荻野敦, 北村英二郎

    第50回日本ガスタービン学会定期講演会  

    発表年月: 2022年10月

  • 軸流圧縮機における旋回不安定擾乱発生時の非定常動翼特性

    中村圭吾, 谷口恵太, 藤澤信道, 太田有, 山上舞, 後藤尚志, 加藤大

    第50回日本ガスタービン学会定期講演会  

    発表年月: 2022年10月

  • 遠心圧縮機に発生する羽根車失速と羽根なしディフューザ失速の相互作用

    鈴木祐太郎, 岸隼冬, 内藤桃子, 藤澤信道, 太田有

    日本機械学会2022年度年次大会  

    発表年月: 2022年09月

  • Unsteady Behavior of Tip Leakage Vortex on the Formation of Rotating Instability in an Axial Compressor

    Keita Taniguchi, Keigo Nakamura, Nobumichi Fujisawa, Yutaka Ohta, Mai Yamagami, Takashi Goto, Dai Kato

    Asian Congress on Gas Turbines 2022  

    発表年月: 2022年08月

  • 遠心圧縮機の羽根なしディフューザ失速における羽根車内部流れ場の影響

    上利雄貴, 山尾佳史, 藤澤信道, 太田有

    第49回 ガスタービン学会 定期講演会  

    発表年月: 2021年10月

  • Vortical Structure of Vaneless Diffuser Stall in a Centrifugal Compressor

    Yoshifumi Yamao, Yuki Agari, Nobumichi Fujisawa, Yutaka Ohta

    The 16th Asian International Conference on Fluid Machinery  

    発表年月: 2021年09月

  • Behavior of Vaneless Diffuser Stall in a Centrifugal Compressor

    Yuki Agari, Yoshifumi Yamao, Nobumichi Fujisawa, Yutaka Ohta

    Asian Congress on Gas Turbine 2020  

    発表年月: 2021年08月

  • Rotating Mechanism of Diffuser Stall in a Centrifugal Compressor with Vaneless Diffuser

    Nobumichi Fujisawa, Yuki Agari, Yoshifumi Yamao, Yutaka Ohta

    ASME 2021 Turbo Expo  

    発表年月: 2021年06月

  • 軸流圧縮機のウインドミル条件における非定常流れに翼端隙間が及ぼす影響

    関野諒輔, 藤澤信道, 太田有

    第34回数値流体力学シンポジウム  

    発表年月: 2020年11月

  • 軸流圧縮機の流入条件および翼蛋隙間の大きさの違いによる失速初生形態への影響

    荒田康太朗, 藤澤信道, 太田有, 加藤大

    日本機械学会第98期流体工学部門講演会  

    発表年月: 2020年11月

  • Effect of Unsteady Vortex Behavior on Noise Characteristics in a Centrifugal Compressor

    Kenta Tajima, Hiroshi Miida, Nobumichi Fujisawa, Yutaka Ohta

    ISROMAC 2020  

    発表年月: 2020年11月

  • 羽根なしディフューザを有する遠心圧縮機におけるディフューザ失速の構造

    田島健太, 三井田弘, 藤澤信道, 太田有

    第48回 ガスタービン学会 定期講演会  

    発表年月: 2020年10月

  • 遠心圧縮機の羽根なしディフューザ内部で発生する旋回失速の構造

    藤澤信道, 太田有

    第14回 送風機・圧縮機の騒音と性能研究分科会  

    発表年月: 2020年09月

  • 羽根なしディフューザを有する遠心圧縮機における失速セルの旋回挙動

    上利祐貴, 三井田弘, 田島健太, 藤澤信道, 太田有

    第84回 ターボ機械協会講演会  

    発表年月: 2020年09月

  • AEセンサを用いた軸流圧縮機作動状態の計測

    高橋一颯, 藤澤信道, 太田有, 鈴木武志, 梅沢修一, 大森修一

    日本機械学会2020年度年次大会  

    発表年月: 2020年09月

  • Generation Meachanism of Diffuser Stall in a Centrifugal Compressor With Vaneless Diffuser

    Nobumichi Fujisawa, Kenta Tajima, Hiroshi Miida, Yutaka Ohta

    GPPS Chania20  

    発表年月: 2020年09月

  • The Unsteady Behavior of Diffuser Stall in a Centrifugal Compressor With Vaneless Diffuser

    Hiroshi Miida, Kenta Tajima, Nobumichi Fujisawa, Yutaka Ohta

    ASME 2020 Fluids Engineering Division Summer Meeting  

    発表年月: 2020年07月

  • 非一様流入条件下で前方スイープ動翼が内部流れに及ぼす影響の数値的調査

    市川友喜, 坂田友, 藤澤信道, 太田有

    日本機械学会 関東支部 第26期総会・講演会  

    発表年月: 2020年03月

  • 遠心圧縮機の羽根無しディフューザ流路幅が発生騒音に与える影響

    三井田弘, 田島健太, 藤澤信道, 太田有

    日本機械学会 関東支部 第26期総会・講演会  

    発表年月: 2020年03月

  • 遠心圧縮機の羽根無しディフューザに発生する旋回失速セルの非定常挙動

    上利祐貴, 三井田弘, 田島健太, 藤澤信道, 太田有

    日本機械学会 関東支部 第26期総会・講演会  

    発表年月: 2020年03月

  • 航空エンジン用軸流圧縮機のウインドミル状態における内部流れ場の数値解析

    関野諒輔, 藤澤信道, 太田有

    日本機械学会 関東支部 第26期総会・講演会  

    発表年月: 2020年03月

  • 軸流圧縮機の動翼形状および流入条件の違いによる失速初生形態への影響

    荒田康太朗, 坂田友, 藤澤信道, 太田有

    日本機械学会 関東支部 第26期総会・講演会  

    発表年月: 2020年03月

  • 数値解析を用いた突極形同期発電機の複雑内部流れ場の調査

    武藤琢真, 小澤明, 生田哲平, 伊藤匠, 藤澤信道, 太田有

    発表年月: 2020年03月

  • Rotor Performance of an Axial Flow Compressor at Free and Highly Loaded Windmilling Conditions

    Wenbo Zhang, Nobumichi Fujisawa, Yutaka Ohta, Takashi Goto, Dai Kato

    International Gas Turbine Congress 2019  

    発表年月: 2019年11月

  • Effect of Forward-Swept Rotor on Stall Margin in an Axial Flow Compressor at Distorted Inflow Condition

    Kyonosuke Hamaguchi, Yuu Sakata, Nobumichi Fujisawa, Yutaka Ohta, Dai Kato

    International Gas Turbine Congress 2019  

    発表年月: 2019年11月

  • Numerical Analysis of Rotating Stall Development in a Centrifugal Compressor with Vaned Diffuser

    Hiroshi Miida, Masaki Takahashi, Nobumichi Fujisawa, Yutaka Ohta

    7th Korea-Japan Joint Workshop on Fans and Compressors  

    発表年月: 2019年10月

  • 軸流圧縮機の失速初生形態に及ぼす前方スイープ動翼の影響

    濵口京之介, 藤澤信道, 太田有, 加藤大

    第47回 ガスタービン学会 定期講演会  

    発表年月: 2019年09月

  • Development of rotating stall cell under coexisting phenomena of surge and rotating stall in an axial-flow compressor

    Yuu Sakata, Nobumichi Fujisawa, Yutaka Ohta

    ASME-JSME-KSME Joint Fluids Engineering Conference 2019  

    発表年月: 2019年08月

  • Development of Diffuser Stall and Flow Structures in a Centrifugal Compressor with Vaned Diffuser

    Masaki Takahashi, Nobumichi Fujisawa, Yutaka Ohta

    14th International Symposium on Experimental and Computational Aerothermodynamics of Internal Flows  

    発表年月: 2019年07月

  • Transient Analysis of Rotating Stall Development in a Centrifugal Compressor with Vaned Diffuser

    Nobumichi Fujisawa, Masaki Takahashi, Yutaka Ohta

    ASME 2019 Turbo Expo  

    発表年月: 2019年06月

  • 突極形同期発電機内部の複雑内部流動と損失発生機構

    生田哲平, 藤澤信道, 太田有, 武藤琢真, 小澤明

    第81回 ターボ機械協会 総会講演会  

    発表年月: 2019年05月

  • 遠心圧縮機低流量域でのディフューザ旋回失速の挙動と内部流動調査

    渡邉紗貴, 乾哲也, 藤澤信道, 太田有

    第46回日本ガスタービン学会定期講演会  

    発表年月: 2018年10月

  • Diffuser Rotating Stall Development in a Centrifugal Compressor with Vaned Diffuser

    Tetusya Inui, Saki Watanebe, Nobumichi Fujisawa, Yutaka Ohta

    発表年月: 2018年08月

  • Interaction between Surge Behavior and Internal Flow Field in an Axial-Flow Compressor

    Yuu Sakata, Nobumichi Fujisawa, Yutaka Ohta

    ASME FEDSM 2018  

    発表年月: 2018年07月

  • Evolution Process of Diffuser Stall in a Centrifugal Compressor with Vaned Diffuser

    Nobumichi Fujisawa, Tetusya Inui, Yutaka Ohta

    ASME Turbo Expo 2018  

    発表年月: 2018年06月

  • 遠心圧縮機内部に発生するディフューザ失速の流量低下に伴う拡大メカニズム

    乾哲也, 藤澤信道, 太田有

    第45回日本ガスタービン学会定期講演会  

    発表年月: 2017年10月

  • 羽根付ディフューザを有する遠心圧縮機に発生する失速の成長過程

    江間大輝, 藤澤信道, 太田有

    日本流体力学会年会 2017  

    発表年月: 2017年08月

  • Unsteady Behavior of Diffuser Stall in a Centrifugal Compressor with Vaned Diffuser

    Nobumichi Fujisawa, Ema Daiki, Yutaka Ohta

    ASME Turbo Expo 2017,  

    発表年月: 2017年06月

  • 遠心圧縮機内部に発生する旋回失速の流量低下に伴う過渡特性

    江間大輝, 池津聡太, 藤澤信道, 太田有

    日本機械学会 第94期 流体工学部門 講演会  

    発表年月: 2016年11月

  • Investigation of Unsteady Flow Field under Developed Rotating Stall in a Centrifugal Compressor with Vaned Diffuser

    Sota Ikezu, Nobumichi Fujisawa, Yutaka Ohta

    The 5th Korea-Japan Joint Workshop on Fans and Compressors  

    発表年月: 2016年11月

  • 羽根付ディフューザを有する遠心圧縮機に発生するディフューザ失速の旋回構造

    池津聡太, 江間大輝, 藤澤信道, 太田有

    第44回 日本ガスタービン学会定期講演会  

    発表年月: 2016年10月

  • 遠心圧縮機ディフューザに発生する失速の非定常挙動

    藤澤信道, 池津聡太, 太田有

    ターボ機械協会 第76回北見講演会  

    発表年月: 2016年09月

  • Stall Characteristics of a Centrifugal Compressor with Vaned Diffuser

    Sota Ikezu, Nobumichi Fujisawa, Yutaka Ohta

    6th Asian Joint Workshop on Thermophysics and Fluid Science  

    発表年月: 2016年09月

  • 過給機用遠心圧縮機内部に発生するディフューザ失速の構造と非定常挙動

    藤澤信道, 池津聡太, 太田有

    第9回 送風機・圧縮機の騒音と性能研究文科会  

    発表年月: 2016年07月

  • Characteristics of Diffuser Stall and Diffuser Leading-edge Vortex in a Centrifugal Compressor

    Nobumichi Fujisawa, Shotaro hara, Yutaka Ohta

    発表年月: 2015年11月

  • 遠心圧縮機の羽根車翼端隙間が内部流れに及ぼす影響

    黒田 未来, 池津 聡太, 藤澤 信道, 太田 有

    流体工学部門講演会  

    発表年月: 2015年11月

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

    Nobumichi Fujisawa, Sota Ikezu, Yutaka Ohta

    The 4th Japan Korea Joint Workshop on Fans and Compressor  

    発表年月: 2015年10月

  • 遠心圧縮機内部に発生する旋回失速と非定常渦の構造

    池津聡太, 藤澤信道, 太田有

    第43回 日本ガスタービン学会定期講演会  

    発表年月: 2015年09月

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

    Nobumichi Fujisawa, Shotaro hara, Yutaka Ohta

    12th International Symposium on Experimental Computational Aerothermodynamics of Internal Flows  

    発表年月: 2015年07月

  • 遠心圧縮機ディフューザ前縁部に発生する非定常渦の構造

    藤澤信道, 原昇太郎, 太田有

    第8回 送風機・圧縮機の騒音と性能研究文科会  

    発表年月: 2015年05月

  • 羽根付ディフューザを有する遠心圧縮機に発生する失速と前縁渦の関係

    日本ガスタービン学会定期講演会  

    発表年月: 2014年10月

  • Experiments Investigation of Three-dimensional Structure of Rotating Instability Vortex in a Centrifugal Compressor

    Yasuyuki Fukuda, Yuta Itagaki, Nobumichi Fujisawa, Yutaka Ohta

    Asian Congress on Gas Turbine  

    発表年月: 2014年08月

  • Unsteady Behavior of Leading Edge Vortex and Diffuser Stall Inception in a Centrifugal Compressor

    Nobumichi Fujisawa, Shotaro hara, Yutaka Ohta, Takashi Goto

    ASME 2014 4th Joint US-Europian Fluids Engineering Division Summer Meeting  

    発表年月: 2014年08月

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共同研究・競争的資金等の研究課題

  • 遠心圧縮機の非軸対称性により発生する旋回失速の発生機構の解明と実験的検証

    日本学術振興会  科学研究費助成事業

    研究期間:

    2019年04月
    -
    2023年03月
     

    藤澤 信道

     概要を見る

    本研究では、遠心圧縮機の幾何形状および流入条件がもたらす非軸対称性により発生する旋回失速の発生機構を解明し、失速の初生構造を実験により検証することを目的とする。研究計画を以下に示す。1.実機試験により、渦型室により形成される不均一な圧力場および非一様流入条件が旋回失速の初生に与える基本特性を調査する。さらに、2.数値解析により、失速の初生位置およびその発生構造を明らかにし、遠心圧縮機特有の非軸対称条件下での汎用的な失速形成モデルを提案する。3.新たに壁面境界層内のせん断応力を測定する手法を確立・導入し、圧力計測と組み合わせることで、解析により明らかにした失速形成モデルを実験により検証する。本研究では、遠心圧縮機の幾何形状および流入条件がもたらす非軸対称性により発生する旋回失速の発生機構を解明し、失速の初生構造を実験により検証することを目的とする。羽根車下流に渦型室を持つ遠心圧縮機は本質的に非軸対称であり、さらに実用下では、圧縮機入口で偏流・乱れなど非一様な流入となることも少なくない。このため、作動範囲を制限する旋回失速の発生予測は困難であり、発生構造の普遍的な理解も無い。そこで、1.実機試験により、渦型室により形成される不均一な圧力場および非一様流入条件が旋回失速の初生に与える基本特性を調査する。さらに、2.数値解析により、失速の初生位置およびその発生構造を明らかにし、遠心圧縮機特有の非軸対称条件下での汎用的な失速形成モデルを提案する。3.新たに壁面境界層内のせん断応力を測定する手法を確立・導入し、圧力計測と組み合わせることで、解析により明らかにした失速形成モデルを実験により検証する。本年度は,遠心圧縮機全周を対象とした大規模DES解析の結果より、失速点に陥ると舌部を起点とした時計回りに90°離れた位置において、ディフューザ壁面ハブ側からの境界層剥離に起因して、ディフューザ失速が初生していることを明らかにした。さらに、失速セルが旋回するにつれてディフューザ内部の逆圧力勾配の影響により、ハブおよびシュラウドの交互に発生する境界層剥離とともに失速セルは大きく拡大する。最終的に、失速セルは舌部近傍における逆圧力勾配が低下するため、失速セルは縮小および消滅することが分かった。さらに実機試験からも、数値解析と同様に舌部を起点とした時計回りに90°離れた位置においてディフューザ失速がハブ側で初生し、羽根車回転方向に拡大するとともに規模が大きくなることを確かめた。加えて、ディフューザ失速は渦型室の圧力分布により旋回速度を少しずつ変化させながら旋回していることが分かった。数値解析においては、ケーシング領域を含めた大規模解析の数値コストが高く失速セルの発現には時間を要すると予想していたが、比較的順調にデータを取得できた。実機試験では、流速孔および圧力孔の追加加工が順調に進み、予定を上回るスピードでデータ取得が実行できた。一方で、新しくせん断応力計測のための熱戦流速計を購入したが、検定手法の確立に時間を要している。実験および数値解析の結果、当初の予想通りディフューザ失速は壁面境界層により初生していることが明らかとなり、特に舌部付近のディフューザ流路におけるハブ、シュラウド側で交互に発達する境界層剥離が失速セル拡大の重要な役割を果たしていることが分かった。さらに、ディフューザ失速は渦型室の非軸対称な圧力分布の影響により旋回速度や規模が大きく異なることが確認された。そこで、ディフューザ流路周方向での失速挙動の変化を同定するため、周方向の圧力多点計測による空間フーリエ解析手法を導入し、ディフューザ流路における圧力変動の測定実験を新たに研究計画に加えた。1.一様流入条件下の旋回失速の初生機構の解明・失速形成モデルの提案本圧縮機では、流量低下時に羽無しディフューザ流路の舌部を起点とした時計回りに90°離れた位置の境界層剥離から旋回失速が形成されるという知見を得られた。そこで失速初生・発達の形態変化の発生箇所を捉えるために、ディフューザ流路壁面で周方向8点の壁面圧力同時計測を行い、得られた波形に対して空間フーリエ解析を応用した手法により、失速に起因するモード分布を算出する。この解析より、煩雑な波形から失速初生のような微弱な変動を捉え、その旋回速度および規模の拡大を可視化できる。また、本年度と引き続きディフューザ失速の初生から発達する過程での非定常的な渦構造を調査するために、スクロールも含めた圧縮機系全体を対象としたDES解析を用いた数値解析を行う。特に、ディフューザ失速セルの拡大の要因であるハブ、シュラウド側で交互に発達する境界層剥離の発生構造を理解するため、ディフューザ流路内部の渦構造を明らかにする。以上より、ディフューザ流路内での逆圧力勾配の大きさと境界層剥離との関係を調査し、失速の形成モデルを提案する。2.せん断応力計測技術の確立・導入、失速形成モデルの実験的検証本項目は1より提案した失速の形成モデルを検証するため、新たにせん断応力計測技術を確立・導入し、圧力計測と組み合わせることでディフューザ壁面での非定常のせん断応力分布を得るものである。せん断応力計測技術の導入のために、1年目に境界層内流速計の校正技術を確立する。また、複雑な内部流動が非定常的に変化する失速機構を実験的に検証するため、圧力測定による空間フーリエ解析に加え、流速測定を用いた二重位相固定平均法を導入し。失速セルの実験的可視化を行う

  • 遠心圧縮機内部に発生する旋回失速の過渡的特性の解明と失速制御手法の確立

    日本学術振興会  科学研究費助成事業

    研究期間:

    2016年08月
    -
    2018年03月
     

    藤澤 信道

     概要を見る

    圧縮機を実際に運転する際、不安定現象を避けるため、流量マージンを取り運転されている。そのため、不安定現象を制御し作動範囲を広げることで、より高性能な点で運転可能となる。しかし、不安定現象の制御方法は、未だ経験的な手法が多いのが現状である。そこで、本研究は不安定現象の抑制および制御手法を明確に提案するために、遠心圧縮機において、部分流量運転時に発生する旋回失速の発生構造を実機計測および数値解析の両面から調査したものである。その結果、ディフューザに発生する旋回失速の詳細な渦構造およびディフューザ失速が拡大する際の流動現象を解明し、ディフューザ失速の制御手法を明確にした

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  • 理工学術院   大学院基幹理工学研究科

学内研究所・附属機関兼任歴

  • 2022年
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    2024年

    理工学術院総合研究所   兼任研究員

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  • 遠心圧縮の羽根付ディフューザ内部で発生する失速予兆現象に関する調査

    2023年  

     概要を見る

    本研究では、遠心圧縮機の幾何形状がもたらす非軸対称性により発生するディフューザ旋回失速発生前の失速予兆現象の流動構造を解明することを目的とする。試験と数値解析を組み合わせ失速予兆現象の非定常的な挙動を分析することで失速セルおよび予兆現象の形成過程を調査した。失速予兆現象発生時の内部流れ場の特徴を捉えるために、非定常の数値流体解析を実施する。また、ディフューザ流路壁面の壁面圧力計測およびディフューザ流路内での流速の同時多点測定を行い、その非定常現象の特性を解析結果と比較検証する。ディフューザ流路壁面の圧力測定および非定常数値解析より、サージ形成前に5つの旋回失速セルが発生することが明らかになった。この失速セルは、5つの流路内部の失速域が流量低下とともに旋回し始めることで、形成していることが分かった。また、渦型室による非軸対象の圧力場の影響を排除するために、渦型室を無くした非定常解析を実施した。この解析結果より、旋回失速発生前にディフューザにて5つの静止した失速域が形成していることが分かった。このため、この5つの静止した低速域は渦型室の影響で発生したのではなく、ディフューザ流路にて発生するモードであることが分かった。次年度は、周方向の多点圧力測定より、静止した5つの低速域を試験において確認する。

  • 軸流圧縮機のサージ・旋回失速共存形態における内部流動把握

    2023年  

     概要を見る

    本研究では、軸流圧縮機のサージ・旋回失速共存形態での複雑流動を解明・検証し、サージの発生構造を明らかにすることを目的とする。軸流圧縮機の作動範囲を縮小するサージ・旋回失速発生時の内部流れは非常に複雑であり、両者の関連性の普遍的な理解は未だ無い。また、数値解析により予測された失速の詳細な渦構造を試験で解明した例は無く、解析の妥当性も検証されていない。そこで、1.実機試験・数値解析により、翼端隙間の変化および圧縮波入射による内部流動構造の違いがサージサイクルの切り替わりに与える影響を調査する。さらに、2.圧縮波入射時の動翼前後の圧力変動を検証する。本年度は、多段圧縮機に圧縮波を入射した際に内部流れ場の影響を調査するために、まずは単段形態での基礎的なデータを取得する。軸流圧縮機の作動範囲を縮小するサージ・旋回失速発生時の内部流れを調査する前段階として、高精度の数値解析コードの作成を行った。サージ点の予測精度が未だ不十分であるが、次年度にて非定常解析を導入しサージ点の予測精度を向上する。その後、数値解析により、旋回失速の流動構造の違いがサージサイクルの切り替わりに与える影響を調査する。また、圧縮機入射によるサージサイクルの挙動変化を調査した。動翼前後の非定常圧力変動を調査し、圧縮波入射による動翼前後の圧力変動の位相差を明らかにした。次年度以降は、多段圧縮機に形態を変更し、圧縮波入射の影響が上流に伝播することによる内部流れ場に与える影響を調査する.

  • 軸流圧縮機内部で発生するサージ・旋回失速の共存状態における内部流れ構造の調査

    2022年  

     概要を見る

    本研究では、軸流圧縮機のサージ・旋回失速共存形態での複雑流動を解明・検証し、サージの発生構造を明らかにすることを目的とする。軸流圧縮機の作動範囲を縮小するサージ・旋回失速発生時の内部流れは非常に複雑であり、両者の関連性の普遍的な理解は未だ少ない。また、数値解析により予測された失速の詳細な渦構造を試験で解明した例は無く、解析の妥当性も検証されていない。そこで、実機試験・数値解析により、温度による過渡的な翼端隙間の変化およびその変化に伴う旋回失速の流動構造の違いがサージサイクルの切り替わりに与える影響を調査する。

  • 羽根なしディフューザ部において発生する旋回失速の発生構造の調査と試験による検証

    2021年  

     概要を見る

    本研究では、遠心圧縮機の幾何形状がもたらす非軸対称性により発生するディフューザ旋回失速の初生機構を解明し、汎用的な失速形成モデルを提案することを目的とする。特に、解析により得られた失速周りの流れを、壁面の圧力測定や流速測定により検証した。失速セル前後の内部流れ場の特徴を捉えるために、ディフューザ流路壁面の壁面圧力計測および流速測定を行い、失速セルの周波数に同期させた渦位相平均手法を導入した。数値解析より得られた旋回失速周りの流動構造と同様に、失速前縁において流れが加速することによる低圧域、失速後縁にて低速域に主流が衝突することによる高圧域が生じることを試験にて明らかにした。

  • 遠心圧縮機の羽根無しディフューザ部に発生する旋回失速の発生機構の実験的調査

    2020年  

     概要を見る

    本研究では、遠心圧縮機の幾何形状がもたらす非軸対称性により羽根無しディフューザ部で発生するディフューザ旋回失速の初生機構およびその内部構造を実機計測より解明することを目的とした。ディフューザ流路壁面での壁面圧力測定と流路内での流速測定の同時計測を行い、得られた波形に対して失速セルの旋回周波数にてアンサンブル平均を施した。失速セル前縁にて発達するハブ・シュラウド交互に形成される境界層剥離とケーシングからの逆流が干渉することにより、ディフューザ失速は初生・成長することが明らかとなった。また、数値解析より得られた旋回失速周りの流動構造と同様な傾向が得られることも合わせて確認された。

  • 遠心圧縮機においてサージ点近傍で発生する失速過渡現象の構造解明とその制御

    2018年  

     概要を見る

    本研究は遠心圧縮機において,サージ点近傍で発生する失速過渡現象の構造解明およびその制御を目的とし,数値解析の観点から調査したものである.特に,失速セルがディフューザ流路から羽根車流路側へと拡大していく過渡現象を調査した.非定常DES解析の結果,舌部近傍での圧力上昇によりディフューザ流路スロート部で発生したブロッケージを起点として,羽根車流路への強い逆圧力勾配が形成されることが分かった.また,その逆圧力勾配により,羽根車正圧面後縁において剥離渦および羽根車スロート部での縦渦が成長し失速セルを構成する.以上の結果より,旋回失速の過渡状態における成長過程を明らかにした.

  • 遠心圧縮機においてサージ点近傍にて発生する旋回失速の拡大機構の解明

    2018年  

     概要を見る

    本研究は遠心圧縮機において,サージ点近傍にて発生する旋回失速の拡大機構を実機計測から調査したものである.特に,渦型室が形成する非軸対称の圧力場が旋回失速の初生位置に与える影響を調査した.ディフューザ壁面圧力を周方向に複数流路で測定した結果,運転点に関わらず舌部近傍でディフューザ出口において静圧が上昇することが分かった.失速点において,舌部における静圧上昇の影響により舌部に近いディフューザ流路スロート部にてブロッケージの形成による局所的な圧力上昇が確認できた.以上の結果より,旋回失速の初生箇所と渦型室の非軸対称の圧力場との関係が明らかとなった.

  • 遠心圧縮機ディフューザに発生する旋回失速の構造調査

    2017年  

     概要を見る

    本研究は遠心圧縮機において,部分流量運転時に発生する旋回失速の発生機構を実機計測および数値解析の両面から調査したものである.ディフューザ案内羽根前縁部シュラウド側で発生する竜巻型の渦および負圧面コーナー部での縦渦からなるディフューザ失速は,ディフューザ流路スロート部で発生するブロッケージと干渉し拡大した後に,段失速へと成長する.また,圧縮機子午面方向の壁面圧力測定より,案内羽根スロート部で段失速の初生が確認された後にディフューザ入口部から上流側での圧力上昇を伴いながら,圧縮機全体へと拡大していくことを明らかにした.以上の結果より,旋回失速の初生箇所およびその拡大機構が明らかとなった.

  • 遠心圧縮機において部分流量運転時に発生する非定常流動現象の解明

    2016年  

     概要を見る

    本研究は遠心圧縮機において,部分流量運転時に発生する旋回失速の発生構造を実機計測および数値解析の両面から調査したものである.ディフューザ案内羽根前縁部シュラウド側で発生する竜巻型の渦が,負圧面コーナー部で渦を誘起し,隣接翼へと干渉しながら旋回する.以上の規則的な渦群の旋回が,ディフューザ失速の発生要因であることを明らかにした.さらに流量を減じると,案内羽根前縁部シュラウド側で旋回していたディフューザ失速がハブ側へと移行し,羽根車流路へと拡大し,段全体での失速へと陥る過渡現象を見出した.また,案内羽根スロート部の渦がハブ側にて拡大することが,上記の過渡現象の一要因であることを示唆した.

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