Updated on 2022/05/21

写真a

 
FUJISAWA, Nobumichi
 
Affiliation
Faculty of Science and Engineering, School of Fundamental Science and Engineering
Job title
Assistant Professor

Concurrent Post

  • Faculty of Science and Engineering   Graduate School of Fundamental Science and Engineering

Degree

  • Waseda University   Doctor of engineering

Professional Memberships

  •  
     
     

    ガスタービン学会

  •  
     
     

    日本機械学会

 

Research Areas

  • Fluid engineering

Research Interests

  • Fluid Engineering

Papers

  • Unsteady behavior and mechanism of a rotating stall in a centrifugal compressor with vaneless diffuser

    Nobumichi FUJISAWA, Hiroshi MIIDA, Kenta TAJIMA, Yutaka OHTA

    Transactions of the JSME (in Japanese)   87 ( 894 ) 20 - 00364  2021

    DOI

  • 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  2020.12

     View Summary

    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    2020.07

     View Summary

    <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

    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

    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    2019.07

     View Summary

    <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    2019.06

     View Summary

    <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 )  2019.04

     View Summary

    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

  • Rotor work characteristics and loss generation mechanism of an axial flow compressor at windmill operation

    Nobumichi FUJISAWA, Naomichi NISHIYAMA, Yutaka OHTA, Takashi GOTO, Dai KATO

    Transactions of the JSME (in Japanese)   85 ( 872 ) 18 - 00493  2019

    DOI

  • 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    2018.07

     View Summary

    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    2018.06

    DOI

  • Effects of Diffuser Leading-Edge Geometries on Noise and Stall Characteristics of a Centrifugal Compressor

    Nobumichi Fujisawa, Yutaka Ohta

      2017 ( 45 ) 11 - 19  2017.11

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

    Nobumichi Fujisawa, Daiki Ema, Yutaka Ohta

    Volume 2D: Turbomachinery    2017.06

     View Summary

    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

     View Summary

    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

  • 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  2016.02  [Refereed]

     View Summary

    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

  • 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  [Refereed]

     View Summary

    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

  • The Effects of Impeller Tip Clearance on Internal Flow Characteristics in a Centrifugal Compressor

    KURODA Miku, IKEZU Sota, FUJISAWA Nobumichi, OHTA Yutaka

    Fluids engineering conference ...   2015   "1615 - 1"-"1615-3"  2015.11

  • Stall and leading-edge vortex in a centrifugal compressor with vaned diffuser

    Fujisawa, Nobumichi, Hara, Shotaro, Ohta, Yutaka

    Transactions of the Japan Society of Mechanical Engineers   81 ( 829 )  2015.09

     View Summary

    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

  • Unsteady Behavior and Control of Vortices in Centrifugal Compressor

    Yutaka Ohta, Nobumichi Fujisawa

    JOURNAL OF THERMAL SCIENCE   23 ( 5 ) 401 - 411  2014.10  [Refereed]

     View Summary

    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

  • 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    2014  [Refereed]

     View Summary

    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

  • 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  [Refereed]

     View Summary

    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

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Books and Other Publications

  • 流体の力学

    太田 有, 藤澤 信道

    共立出版  2020.03 ISBN: 4320082230

    ASIN

Awards

  • 2018 ASME Turbo Expo Best Paper

    2019.06  

  • ターボ機械協会第76回北見講演会 若手優秀講演賞

    2016.09  

  • 日本機械学会三浦賞

    2015.03  

  • 第42回日本ガスタービン学会学生優秀講演賞

    2014.10  

  • 日本機械学会畠山賞

    2013.03  

Research Projects

  • The influence of non-axisymmetric geometry on the generation mechanism of rotating stall in a centrifugal compressor and the experimental validation

    Project Year :

    2019.04
    -
    2023.03
     

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

    Project Year :

    2016.08
    -
    2018.03
     

     View Summary

    The centrifugal compressors with vaned diffusers, compared to vaneless diffusers, are prone to unstable phenomena, such as surges and rotating stalls. The operating range of centrifugal compressors with vaned diffuser is limited by surges and rotating stalls, which can potentially cause serious accidents. Especially, the rotating stall can be recognized as a precursor of surge in the impeller or diffuser passage. Therefore, a better understanding of the physics of the rotating stalls leading to a surge is important in predicting of the surge and for the improvement of the stall margin and the control of rotating stall.This study investigates the evolution process of the diffuser rotating stall in a vaned diffuser of a centrifugal compressor during off-design operation by both experimental and numerical analysis. We revealed the transition characteristics of rotating stalls and the detailed vertical structure of the diffuser stall evolution

Presentations

  • Behavior of Vaneless Diffuser Stall in a Centrifugal Compressor

    Yuki Agari, Yoshifumi Yamao, Nobumichi Fujisawa, Yutaka Ohta

    Asian Congress on Gas Turbine 2020 

    Presentation date: 2021.08

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

    Nobumichi Fujisawa, Yuki Agari, Yoshifumi Yamao, Yutaka Ohta

    ASME 2021 Turbo Expo 

    Presentation date: 2021.06

  • 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 

    Presentation date: 2020.11

  • 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 

    Presentation date: 2020.11

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

    Kenta Tajima, Hiroshi Miida, Nobumichi Fujisawa, Yutaka Ohta

    ISROMAC 2020 

    Presentation date: 2020.11

  • 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 

    Presentation date: 2020.10

  • 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 

    Presentation date: 2020.09

  • 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 

    Presentation date: 2020.09

  • 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 

    Presentation date: 2020.09

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

    Nobumichi Fujisawa, Kenta Tajima, Hiroshi Miida, Yutaka Ohta

    GPPS Chania20 

    Presentation date: 2020.09

  • 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 

    Presentation date: 2020.07

  • 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 

    Presentation date: 2020.03

  • 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 

    Presentation date: 2020.03

  • 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 

    Presentation date: 2020.03

  • 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 

    Presentation date: 2020.03

  • 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 

    Presentation date: 2020.03

  • 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

    Presentation date: 2020.03

  • 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 

    Presentation date: 2019.11

  • 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 

    Presentation date: 2019.11

  • 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 

    Presentation date: 2019.10

  • 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 

    Presentation date: 2019.09

  • 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 

    Presentation date: 2019.08

  • 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 

    Presentation date: 2019.07

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

    Nobumichi Fujisawa, Masaki Takahashi, Yutaka Ohta

    ASME 2019 Turbo Expo 

    Presentation date: 2019.06

  • 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 

    Presentation date: 2019.05

  • 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 

    Presentation date: 2018.10

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

    Tetusya Inui, Saki Watanebe, Nobumichi Fujisawa, Yutaka Ohta

    Presentation date: 2018.08

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

    Yuu Sakata, Nobumichi Fujisawa, Yutaka Ohta

    ASME FEDSM 2018 

    Presentation date: 2018.07

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

    Nobumichi Fujisawa, Tetusya Inui, Yutaka Ohta

    ASME Turbo Expo 2018 

    Presentation date: 2018.06

  • 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 

    Presentation date: 2017.10

  • 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 

    Presentation date: 2017.08

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

    Nobumichi Fujisawa, Ema Daiki, Yutaka Ohta

    ASME Turbo Expo 2017, 

    Presentation date: 2017.06

  • 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 

    Presentation date: 2016.11

  • 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 

    Presentation date: 2016.11

  • 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 

    Presentation date: 2016.10

  • 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 

    Presentation date: 2016.09

  • Stall Characteristics of a Centrifugal Compressor with Vaned Diffuser

    Sota Ikezu, Nobumichi Fujisawa, Yutaka Ohta

    6th Asian Joint Workshop on Thermophysics and Fluid Science 

    Presentation date: 2016.09

  • 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 

    Presentation date: 2016.07

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

    Nobumichi Fujisawa, Shotaro hara, Yutaka Ohta

    Presentation date: 2015.11

  • The Effects of Impeller Tip Clearance on Internal Flow Characteristics in a Centrifugal Compressor

    KURODA Miku, IKEZU Sota, FUJISAWA Nobumichi, OHTA Yutaka

    Presentation date: 2015.11

  • 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 

    Presentation date: 2015.10

  • 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 

    Presentation date: 2015.09

  • 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 

    Presentation date: 2015.07

  • 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 

    Presentation date: 2015.05

  • 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 

    Presentation date: 2014.10

  • 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 

    Presentation date: 2014.08

  • 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 

    Presentation date: 2014.08

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Specific Research

  • 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  

     View Summary

    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  

     View Summary

    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  

     View Summary

    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  

     View Summary

    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  

     View Summary

    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  

     View Summary

    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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Syllabus

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