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Nicolas Rochuon - One of the best experts on this subject based on the ideXlab platform.

  • Effect of Unsteadiness on the Performance of a Transonic Centrifugal Compressor Stage
    Journal of Turbomachinery, 2009
    Co-Authors: Isabelle Trébinjac, Pascale Kulisa, Nicolas Bulot, Isabelle Trébinjac, Nicolas Rochuon
    Abstract:

    Numerical and experimental investigations were conducted in a transonic centrifugal Compressor Stage composed of a backswept splittered unshrouded impeller and a vaned diffuser. The characteristic curves of the Compressor Stage resulting from the unsteady simulations and the experiments show a good agreement over the whole operating range. On the contrary, the total pressure ratio resulting from the steady simulations is clearly overestimated. A detailed analysis of the flow field at design operating point led to identify the physical mechanisms involved in the blade row interaction that underlie the observed shift in performance. Attention was focused on the deformation in shape of the vane bow shock wave due its interaction with the jet and wake flow structure emerging from the impeller. An analytical model is proposed to quantify the time-averaged effects of the associated entropy increase. The model is based on the calculation of the losses across a shock wave at various inlet Mach numbers corresponding to the moving of the jet and wake flow in front of the shock wave. The model was applied to the Compressor Stage performance calculated with the steady simulations. The resulting curve of the overall pressure ratio as a function of the mass flow is clearly shifted towards the unsteady results. The model in particular enhances the prediction of the choked mass flow.

  • Effect of Unsteadiness on the Performance of a Transonic Centrifugal Compressor Stage
    Volume 6: Turbomachinery Parts A B and C, 2008
    Co-Authors: Isabelle Trébinjac, Pascale Kulisa, Nicolas Bulot, Nicolas Rochuon
    Abstract:

    Numerical and experimental investigations were conducted in a transonic centrifugal Compressor Stage composed of a backswept splittered unshrouded impeller and a vaned diffuser. The characteristic curves of the Compressor Stage resulting from the unsteady simulations and the experiments show a good agreement over the whole operating range. On the contrary, the total pressure ratio resulting from the steady simulations is clearly overestimated. A detailed analysis of the flow field at design operating point led to identify the physical mechanisms involved in the blade row interaction that underlie the observed shift in performance. Attention was focused on the deformation in shape of the vane bow shock wave due its interaction with the jet and wake flow structure emerging from the impeller. An analytical model is proposed to quantify the time-averaged effects of the associated entropy increase. The model is based on the calculation of the losses across a shock wave at various inlet Mach numbers corresponding to the moving of the jet and wake flow in front of the shock wave. The model was applied to the Compressor Stage performance calculated with the steady simulations. The resulting curve of the overall pressure ratio as a function of the mass flow is clearly shifted towards the unsteady results. The model in particular enhances the prediction of the choked mass flow.Copyright © 2008 by ASME

Masato Furukawa - One of the best experts on this subject based on the ideXlab platform.

  • effect of tip clearance on stall evolution process in a low speed axial Compressor Stage
    ASME Turbo Expo 2004: Power for Land Sea and Air, 2004
    Co-Authors: Masahiro Inoue, Motoo Kuroumaru, Shinichi Yoshida, Takahiro Minami, Kazutoyo Yamada, Masato Furukawa
    Abstract:

    Effect of the tip clearance on the transient process of rotating stall evolution has been studied experimentally in a low-speed axial Compressor Stage with various stator-rotor gaps. In the previous authors’ experiments for the small tip clearance, the stall evolution process of the rotor was sensitive to the gaps between the blade rows. For the large tip clearance, however, little difference is observed in the evolution processes independently of the blade row gap. In the first half process, it is characterized by gradual reduction of overall pressure-rise with flow rate decreasing, and the number of short length-scale disturbances is increasing with their amplitude increasing. In the latter half a long length-scale disturbance develops rapidly to result in deep stall. Just before the stall inception the spectral power density of the casing wall pressure reveals the existence of rotating disturbances with broadband high frequency near a quarter of the blade passing frequency. This is caused by the short length-scale disturbances occurring intermittently. A flow model is presented to explain mechanisms of the rotating short length-scale disturbance, which includes a tornado-like separation vortex and tip-leakage vortex breakdown. The model is supported by a result of a numerical unsteady flow simulation.Copyright © 2004 by ASME

  • short and long length scale disturbances leading to rotating stall in an axial Compressor Stage with different stator rotor gaps
    Journal of Turbomachinery-transactions of The Asme, 2002
    Co-Authors: Masahiro Inoue, Motoo Kuroumaru, Shinichi Yoshida, Masato Furukawa
    Abstract:

    The transient processes of rotating stall evolution have been investigated experimentally in a low-speed axial Compressor Stage with three stator-rotor gaps. The pressure traces at eight circumferential locations on the casing wall near the rotor leading edge have been analyzed by the wavelet transforms. With the appropriate mother wavelets, the evolution of short and long length-scale disturbances leading to the stall can be captured clearly. Behavior of these disturbances is different depending on the stator-rotor gap. For the large and middle gap, the stall inception is detected by a spiky short length-scale disturbance, and the number of spiky waves increases to generate the high frequency waves. They become the short length-scale part-span stall cells at the mild stall for the large gap, while they turn into a big stall cell with growth of a long length-scale disturbance for the middle gap. In the latter case, therefore, the stalling process was identified with highfrequency stall inception. For the small stator-rotor gap, the stalling process is identified with long wavelength stall inception and supported the recent computational model for the short wavelength stall inception by showing that closing the rotor-stator gaps suppressed the growth of short length-scale disturbances. From the measurement of the pressure field traces on the casing wall, a hypothesis has been developed that the short length-scale disturbance should result from a separation vortex from a blade surface to reduce circulation. The processes of the stall evolution are discussed on this hypothesis.

  • short and long length scale disturbances leading to rotating stall in an axial Compressor Stage with different stator rotor gaps
    Volume 1: Aircraft Engine; Marine; Turbomachinery; Microturbines and Small Turbomachinery, 2001
    Co-Authors: Masahiro Inoue, Motoo Kuroumaru, Shinichi Yoshida, Masato Furukawa
    Abstract:

    The transient processes of rotating stall evolution have been investigated experimentally in a low-speed axial Compressor Stage with three stator-rotor gaps. The pressure traces at 8 circumferential locations on the casing wall near the rotor leading edge have been analyzed by the wavelet transforms. With the appropriate mother wavelets, the evolution of short and long length-scale disturbances leading to the stall can be captured clearly.Behavior of these disturbances is different depending on the stator-rotor gap. For the large and middle gap, the stall inception is detected by a spiky short length-scale disturbance, and the number of spiky waves increases to generate the high frequency waves. They becomes the short length-scale part-span stall cells at the mild stall for the large gap, while they turn into a big stall cell with growth of a long length-scale disturbance for the middle gap. In the latter case, therefore, the stalling process was identified with ‘high frequency stall inception’. For the small stator-rotor gap, the stalling process is identified with ‘long wave-length stall inception’, and supported the recent computational model for the short wave-length stall inception by showing that closing the rotor-stator gaps suppressed the growth of short length-scale disturbances.From the measurement of the pressure field traces on the casing wall, a hypothesis has been built up that the short length-scale disturbance should result from a separation vortex from a blade surface to reduce circulation. The processes of the stall evolution are discussed on this hypothesis.Copyright © 2001 by ASME

Isabelle Trébinjac - One of the best experts on this subject based on the ideXlab platform.

  • Active Flow Control in a Radial Vaned Diffuser for Surge Margin Improvement: A Multislot Suction Strategy
    Hindawi Limited, 2017
    Co-Authors: Aurélien Marsan, Isabelle Trébinjac, Stéphane Moreau, Sylvain Coste
    Abstract:

    This work is the final step of a research project that aims at evaluating the possibility of delaying the surge of a centrifugal Compressor Stage using a boundary-layer suction technique. It is based on Reynolds-Averaged Navier-Stokes numerical simulations. Boundary-layer suction is applied within the radial vaned diffuser. Previous work has shown the necessity to take into account the unsteady behavior of the flow when designing the active flow control technique. In this paper, a multislot strategy is designed according to the characteristics of the unsteady pressure field. Its implementation results in a significant increase of the stable operating range predicted by the unsteady RANS numerical model. A hub-corner separation still exists further downstream in the diffuser passage but does not compromise the stability of the Compressor Stage

  • Description of the unsteady flow pattern from peak efficiency to near surge in subsonic centrifugal Compressor Stage
    2013
    Co-Authors: X. Carbonneau Y. Bousquet, Isabelle Trébinjac, M. Roumeas
    Abstract:

    This paper aims to describe the flow structure modifications when the operating point moves from peak efficiency to near stall condition in a moderate pressure ratio centrifugal Compressor Stage consisted of a splittered unshrouded impeller and a vaned diffuser. The investigations are based on three-dimensional U-RANS simulation results. The flow is described in the impeller and in the vaned diffuser through time-averaged flow quantities and unsteady fluctuations. Results show that at low mass flow rate, the effects of secondary flow in the impeller are more pronounced, inducing both, high time-averaged values and temporal fluctuations of the flow angle near the shroud at the diffuser inlet, leading to vane suction side boundary layer separation. Pressure waves due to impeller diffuser interaction spread through the vaned diffuser generating unsteadiness which intensifies at near surge condition.

  • Effect of Unsteadiness on the Performance of a Transonic Centrifugal Compressor Stage
    Journal of Turbomachinery, 2009
    Co-Authors: Isabelle Trébinjac, Pascale Kulisa, Nicolas Bulot, Isabelle Trébinjac, Nicolas Rochuon
    Abstract:

    Numerical and experimental investigations were conducted in a transonic centrifugal Compressor Stage composed of a backswept splittered unshrouded impeller and a vaned diffuser. The characteristic curves of the Compressor Stage resulting from the unsteady simulations and the experiments show a good agreement over the whole operating range. On the contrary, the total pressure ratio resulting from the steady simulations is clearly overestimated. A detailed analysis of the flow field at design operating point led to identify the physical mechanisms involved in the blade row interaction that underlie the observed shift in performance. Attention was focused on the deformation in shape of the vane bow shock wave due its interaction with the jet and wake flow structure emerging from the impeller. An analytical model is proposed to quantify the time-averaged effects of the associated entropy increase. The model is based on the calculation of the losses across a shock wave at various inlet Mach numbers corresponding to the moving of the jet and wake flow in front of the shock wave. The model was applied to the Compressor Stage performance calculated with the steady simulations. The resulting curve of the overall pressure ratio as a function of the mass flow is clearly shifted towards the unsteady results. The model in particular enhances the prediction of the choked mass flow.

  • Effect of Unsteadiness on the Performance of a Transonic Centrifugal Compressor Stage
    Volume 6: Turbomachinery Parts A B and C, 2008
    Co-Authors: Isabelle Trébinjac, Pascale Kulisa, Nicolas Bulot, Nicolas Rochuon
    Abstract:

    Numerical and experimental investigations were conducted in a transonic centrifugal Compressor Stage composed of a backswept splittered unshrouded impeller and a vaned diffuser. The characteristic curves of the Compressor Stage resulting from the unsteady simulations and the experiments show a good agreement over the whole operating range. On the contrary, the total pressure ratio resulting from the steady simulations is clearly overestimated. A detailed analysis of the flow field at design operating point led to identify the physical mechanisms involved in the blade row interaction that underlie the observed shift in performance. Attention was focused on the deformation in shape of the vane bow shock wave due its interaction with the jet and wake flow structure emerging from the impeller. An analytical model is proposed to quantify the time-averaged effects of the associated entropy increase. The model is based on the calculation of the losses across a shock wave at various inlet Mach numbers corresponding to the moving of the jet and wake flow in front of the shock wave. The model was applied to the Compressor Stage performance calculated with the steady simulations. The resulting curve of the overall pressure ratio as a function of the mass flow is clearly shifted towards the unsteady results. The model in particular enhances the prediction of the choked mass flow.Copyright © 2008 by ASME

Masanori Tanaka - One of the best experts on this subject based on the ideXlab platform.

  • effect of impeller blade loading on Compressor Stage performance in a high specific speed range
    Journal of Turbomachinery-transactions of The Asme, 2012
    Co-Authors: Takanori Shibata, Manabu Yagi, Hideo Nishida, Hiromi Kobayashi, Masanori Tanaka
    Abstract:

    The authors previously found that Compressor Stage efficiency in a high specific speed range was significantly improved by employing an increased relative velocity diffusion ratio coupled with a high backsweep angle (Shibata et al., "Performance Improvement of a Centrifugal Compressor Stage by Increasing Degree of Reaction Optimizing Blade Loading of a 3D-Impeller," ASME Paper No. GT2009-59588). In spite of such a high relative velocity diffusion ratio, the same surge margin as with a conventional design was able to be achieved by using a special front loading distribution with a lightly loaded inducer. In the present study, the blade loading distribution was further optimized in order to achieve a larger surge margin than previously. Four types of fully shrouded impellers were designed, manufactured, and tested to evaluate the effects of blade loading, backsweep angle, and relative velocity diffusion ratio on Compressor performance. The design suction flow coefficient was 0.125 and the machine Mach number was 0.87. Test results showed that the developed impeller achieved 3.8% higher Stage efficiency and 11% larger surge margin than the conventional design without reducing the pressure coefficient and choke margin. It was concluded that aft loading coupled with a high degree of reaction was a very effective way to improve surge margin as well as Stage efficiency. Stator matching was also investigated by changing the design incidence angle, which was shown to have a little influence on surge margin in the present test results.

  • performance improvement of a centrifugal Compressor Stage by increasing degree of reaction and optimizing blade loading of a 3d impeller
    Journal of Turbomachinery-transactions of The Asme, 2011
    Co-Authors: Takanori Shibata, Manabu Yagi, Hideo Nishida, Hiromi Kobayashi, Masanori Tanaka
    Abstract:

    Performance improvement of 3D impellers in a high specific speed range was investigated using computational fluid dynamics analyses and experimental tests. In order to reduce the loss production within the stator passages, the backsweep angle of the impellers was increased. At the same time, the inlet-to-exit relative velocity diffusion ratio was also increased by increasing the impeller exit width to prevent the reduction in the pressure ratio. Moreover, the blade loading distribution at the impeller shroud side was optimized to suppress the surge margin reduction caused by the increased relative velocity diffusion ratio. Five types of unshrouded impellers were designed, manufactured, and tested to evaluate the effects of blade loading, backsweep angle, and relative velocity diffusion ratio on the Compressor performance. The design suction flow coefficient was 0.125 and the machine Mach number was 0.87. Test results showed that the Compressor Stage efficiency was increased by 5% compared with the base design without reducing the pressure coefficient and surge margin. It was concluded that an increased relative velocity diffusion ratio coupled with large backsweep angle was a very effective way to improve the Compressor Stage efficiency. An appropriate blade loading distribution was also important in order to achieve a wide operating range as well as high efficiency.

  • effect of impeller blade loading on Compressor Stage performance in a high specific speed range
    ASME Turbo Expo 2010: Power for Land Sea and Air, 2010
    Co-Authors: Takanori Shibata, Manabu Yagi, Hideo Nishida, Hiromi Kobayashi, Masanori Tanaka
    Abstract:

    The authors previously found that Compressor Stage efficiency in a high specific speed range was significantly improved by employing an increased relative velocity diffusion ratio coupled with a high backsweep angle. In spite of such a high relative velocity diffusion ratio, the same surge margin as with a conventional design could be achieved by using a special front loading distribution with a lightly loaded inducer. In the present study, the blade loading distribution was further optimized in order to achieve a larger surge margin than previously. Four types of fully shrouded impellers were designed, manufactured and tested to evaluate the effects of blade loading, backsweep angle and relative velocity diffusion ratio on Compressor performance. The design suction flow coefficient was 0.125 and the machine Mach number was 0.87. Test results showed that the developed impeller achieved 3.8% higher Stage efficiency and 11% larger surge margin than the conventional design without reducing the pressure coefficient and choke margin. It was concluded that aft loading coupled with a high degree of reaction was a very effective way to improve surge margin as well as Stage efficiency. Stator matching was also investigated by changing the design incidence angle which was shown to have little influence on surge margin in the present test results.Copyright © 2010 by ASME

  • performance improvement of a centrifugal Compressor Stage by increasing degree of reaction and optimizing blade loading of a 3d impeller
    ASME Turbo Expo 2009: Power for Land Sea and Air, 2009
    Co-Authors: Takanori Shibata, Manabu Yagi, Hideo Nishida, Hiromi Kobayashi, Masanori Tanaka
    Abstract:

    Performance improvement of 3D impellers in a high specific speed range was investigated using computational fluid dynamics (CFD) analyses and experimental tests. In order to reduce the loss production within the stator passages, the backsweep angle of the impellers was increased. At the same time, the inlet-to-exit relative velocity diffusion ratio was also increased by increasing impeller exit width to prevent the reduction in pressure ratio. Moreover, the blade loading distribution at the impeller shroud side was optimized to suppress the surge margin reduction caused by the increased relative velocity diffusion ratio. Five types of unshrouded impellers were designed, manufactured and tested to evaluate the effects of blade loading, backsweep angle and relative velocity diffusion ratio on Compressor performance. The design suction flow coefficient was 0.125 and the machine Mach number was 0.87. Test results showed that Compressor Stage efficiency was increased by 5% compared to the base design without reducing the pressure coefficient and surge margin. It was concluded that an increased relative velocity diffusion ratio coupled with large backsweep angle was a very effective way to improve Compressor Stage efficiency. An appropriate blade loading distribution was also important in order to achieve a wide operating range as well as high efficiency.Copyright © 2009 by ASME

Masahiro Inoue - One of the best experts on this subject based on the ideXlab platform.

  • effect of tip clearance on stall evolution process in a low speed axial Compressor Stage
    ASME Turbo Expo 2004: Power for Land Sea and Air, 2004
    Co-Authors: Masahiro Inoue, Motoo Kuroumaru, Shinichi Yoshida, Takahiro Minami, Kazutoyo Yamada, Masato Furukawa
    Abstract:

    Effect of the tip clearance on the transient process of rotating stall evolution has been studied experimentally in a low-speed axial Compressor Stage with various stator-rotor gaps. In the previous authors’ experiments for the small tip clearance, the stall evolution process of the rotor was sensitive to the gaps between the blade rows. For the large tip clearance, however, little difference is observed in the evolution processes independently of the blade row gap. In the first half process, it is characterized by gradual reduction of overall pressure-rise with flow rate decreasing, and the number of short length-scale disturbances is increasing with their amplitude increasing. In the latter half a long length-scale disturbance develops rapidly to result in deep stall. Just before the stall inception the spectral power density of the casing wall pressure reveals the existence of rotating disturbances with broadband high frequency near a quarter of the blade passing frequency. This is caused by the short length-scale disturbances occurring intermittently. A flow model is presented to explain mechanisms of the rotating short length-scale disturbance, which includes a tornado-like separation vortex and tip-leakage vortex breakdown. The model is supported by a result of a numerical unsteady flow simulation.Copyright © 2004 by ASME

  • short and long length scale disturbances leading to rotating stall in an axial Compressor Stage with different stator rotor gaps
    Journal of Turbomachinery-transactions of The Asme, 2002
    Co-Authors: Masahiro Inoue, Motoo Kuroumaru, Shinichi Yoshida, Masato Furukawa
    Abstract:

    The transient processes of rotating stall evolution have been investigated experimentally in a low-speed axial Compressor Stage with three stator-rotor gaps. The pressure traces at eight circumferential locations on the casing wall near the rotor leading edge have been analyzed by the wavelet transforms. With the appropriate mother wavelets, the evolution of short and long length-scale disturbances leading to the stall can be captured clearly. Behavior of these disturbances is different depending on the stator-rotor gap. For the large and middle gap, the stall inception is detected by a spiky short length-scale disturbance, and the number of spiky waves increases to generate the high frequency waves. They become the short length-scale part-span stall cells at the mild stall for the large gap, while they turn into a big stall cell with growth of a long length-scale disturbance for the middle gap. In the latter case, therefore, the stalling process was identified with highfrequency stall inception. For the small stator-rotor gap, the stalling process is identified with long wavelength stall inception and supported the recent computational model for the short wavelength stall inception by showing that closing the rotor-stator gaps suppressed the growth of short length-scale disturbances. From the measurement of the pressure field traces on the casing wall, a hypothesis has been developed that the short length-scale disturbance should result from a separation vortex from a blade surface to reduce circulation. The processes of the stall evolution are discussed on this hypothesis.

  • short and long length scale disturbances leading to rotating stall in an axial Compressor Stage with different stator rotor gaps
    Volume 1: Aircraft Engine; Marine; Turbomachinery; Microturbines and Small Turbomachinery, 2001
    Co-Authors: Masahiro Inoue, Motoo Kuroumaru, Shinichi Yoshida, Masato Furukawa
    Abstract:

    The transient processes of rotating stall evolution have been investigated experimentally in a low-speed axial Compressor Stage with three stator-rotor gaps. The pressure traces at 8 circumferential locations on the casing wall near the rotor leading edge have been analyzed by the wavelet transforms. With the appropriate mother wavelets, the evolution of short and long length-scale disturbances leading to the stall can be captured clearly.Behavior of these disturbances is different depending on the stator-rotor gap. For the large and middle gap, the stall inception is detected by a spiky short length-scale disturbance, and the number of spiky waves increases to generate the high frequency waves. They becomes the short length-scale part-span stall cells at the mild stall for the large gap, while they turn into a big stall cell with growth of a long length-scale disturbance for the middle gap. In the latter case, therefore, the stalling process was identified with ‘high frequency stall inception’. For the small stator-rotor gap, the stalling process is identified with ‘long wave-length stall inception’, and supported the recent computational model for the short wave-length stall inception by showing that closing the rotor-stator gaps suppressed the growth of short length-scale disturbances.From the measurement of the pressure field traces on the casing wall, a hypothesis has been built up that the short length-scale disturbance should result from a separation vortex from a blade surface to reduce circulation. The processes of the stall evolution are discussed on this hypothesis.Copyright © 2001 by ASME