The Experts below are selected from a list of 219 Experts worldwide ranked by ideXlab platform

Pietro Giannattasio - One of the best experts on this subject based on the ideXlab platform.

  • Experimental study of the three-dimensional flow field in cross-flow fans
    Experimental Thermal and Fluid Science, 2011
    Co-Authors: L. Casarsa, Pietro Giannattasio
    Abstract:

    High-resolution PIV measurements of the flow field inside cross-flow fans have been performed in planes normal and parallel to the fan axis, both outside and inside the impeller. The well known difficulties in obtaining the optical access inside the impeller have been overcome by allowing the internal flow planes to be illuminated by the laser light sheet or shot by the CCD camera through the Moving Blade vanes. Measurements have been performed in two cross-flow fans having the same two-module impeller but casing geometries based on very different design concepts. PIV data in planes normal to the rotor axis show a strong correlation between vorticity distribution and turbulent shear stresses inside the eccentric vortex of each fan. Furthermore, they provide useful elements to explain the very different performance of the two fans evidenced by their characteristic curves. Measurements in planes parallel to the impeller axis show that wide three-dimensional recirculation structures develop near the casing end walls at the discharge of the fans. These mean flow structures are responsible for the backflow into the end portions of the impeller of part of the discharged fluid, which is then transported axially by the eccentric vortex towards the rotor central disc before being discharged once again outside the impeller. In the case of cross-flow fans including few rotor modules, the existence of significant axial velocity components inside the eccentric vortex can alter substantially the flow picture, common in the current literature, resulting from 2-D numerical models or measurements performed in a single transverse plane of the fan. ?? 2011 Elsevier Inc.

Benjamin Megerle - One of the best experts on this subject based on the ideXlab platform.

  • On the Prediction and Theory of the Temperature Increase of Low Pressure Last Stage Moving Blades During Low Volume Flow Conditions, and Limiting it Through Steam Extraction Methods
    Journal of Turbomachinery-transactions of The Asme, 2015
    Co-Authors: Adam Beevers, Said Havakechian, Benjamin Megerle
    Abstract:

    During extreme low volume flow conditions, the last stages of a low pressure steam turbine operate in ventilation conditions that can cause a significant temperature increase of critical regions of the last stage Moving Blade (LSB). Under some conditions, the Blade temperature may rise above a safe operating temperature, requiring the machine to be shut down. Limiting the heating effect on the LSB increases the allowable operating range of the low pressure turbine. One common method is to spray water droplets into the low pressure exhaust. As the length of LSBs continues to increase, this method reaches its limit of practical operating effectiveness due to the amount of water required and its impact on the erosion of the LSB. An investigation into complimentary solutions to limit the temperature increase was conducted using CFD. An appropriate CFD setup was chosen from a sensitivity study on the effects from geometry, mesh density, turbulence model, and time dependency. The CFD results were verified against steam turbine data from a scaled test facility. The proposed solutions include low temperature steam extraction, targeted for critical regions of the Moving Blade. From the test turbine and CFD results, the drivers of the temperature increase during ventilation conditions are identified and described.

  • On the Prediction and Theory of the Temperature Increase of Low Pressure Last Stage Moving Blades During Low Volume Flow Conditions, and Limiting it Through Steam Extraction Methods
    Volume 1B: Marine; Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2014
    Co-Authors: Adam Beevers, Said Havakechian, Benjamin Megerle
    Abstract:

    During extreme low volume flow conditions, the last stages of a low pressure steam turbine operate in ventilation conditions that can cause a significant temperature increase of critical regions of the last stage Moving Blade. Under some conditions, the Blade temperature may rise above a safe operating temperature, requiring the machine to be shut down. Limiting the heating effect on the last stage Moving Blade increases the allowable operating range of the low pressure turbine. One common method is to spray water droplets into the low pressure exhaust. As the length of last stage Moving Blades continues to increase, this method reaches its limit of practical operating effectiveness due to the amount of water required and its impact on the erosion of the LSB.An investigation into complimentary solutions to limit the temperature increase was conducted using CFD. An appropriate CFD setup was chosen from a sensitivity study on the effect of geometry, mesh density, turbulence model and time dependency. The CFD results were verified against steam turbine data from a test facility. The proposed complimentary solutions to limit the temperature increase include low temperature steam extraction, targeted for critical regions of the Moving Blade. From the test turbine and CFD results, the drivers of the temperature increase during ventilation conditions are identified and described.Copyright © 2014 by Alstom Technologie AG

Ben Zhao - One of the best experts on this subject based on the ideXlab platform.

  • Numerical investigation of the superimposed effects on stator wake oscillation in an axial-radial combined compressor
    Journal of Thermal Science, 2014
    Co-Authors: Ben Zhao, Liangjun Hu, Ce Yang, Mi Zhou, Jizhong Zhang
    Abstract:

    The superimposed influences of the Blade rows in a multistage compressor are important because different matches of upstream and downstream Blades can result in significant differences in the stator wake oscillation. Numerical investigation of the axial stator wake oscillation, which is affected upstream by the axial rotor and downstream by the radial rotor, was performed in an axial-radial combined compressor. Many configurations with different Blade numbers and locations, which influence axial stator wake oscillation were investigated. When rotors have equal Blade numbers, the axial stator wake oscillates periodically versus time within time T (Moving Blade passing 1/3 revolution). In contrast, stator wake oscillates irregularly within T when rotors have different Blade numbers. A model-split subtraction method is presented in order to separate the influences of the individual Blade rows on the wake oscillation of the axial stator. Analysis from the rotor-stator configuration showed that the unsteady flow angle fluctuation response is caused by the upstream rotor. For the rotor-stator-rotor configuration, the unsteady flow angle fluctuations are influenced by up- and downstream Blade rows. With the model-split subtraction method, the up- and downstream influences on the flow angle fluctuation could be clearly separated and quantified. Low amplitudes could be observed when the influences from up- and downstream Moving rows were superimposed with the "positive peak-negative peak" type wave. Clocking investigations were carried out to change the relative superimposed phase of influences from the surrounding Blade rows in order to modulate the amplitudes of the axial stator wake oscillation. However, the amplitudes did not reach the maximum when they were superimposed with "positive peak-positive peak" type wave due to the impact of the interaction between the two Moving Blade rows. © 2014 Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag Berlin Heidelberg.

  • Effects of Blade Counts and Clocking on the Unsteady Profile Pressure Distribution in an Axial-Radial Combined Compressor
    2013
    Co-Authors: Ben Zhao, Liangjun Hu, Ce Yang, Dazhong Lao
    Abstract:

    A new hypothesis is presented for the superimposed effects of the Blade pressure distribution in a multistage compressor. The effects of the unsteady pressure fluctuations on the Blade surface are separated into three groups. The influences of the upstream or downstream rotors can be obtained by numerical simulation for the R/S or S/R configuration; the data produced by all the influences can be obtained from the R/S/R configuration. The effects of the Blade counts and clocking on the superimposed effects, acting on the profile pressure distribution, are studied using a special data analysis method that had been previously developed by the authors. The results indicate that the Blade counts of the upstream and downstream rotors determine the periods of the unsteady pressure fluctuations on the stator surface. The clocking Moving Blade rows modulate the relative superimposed phases and interactions between two rotors such that the unsteady pressure fluctuates with different amplitudes on the surface of the stator Blade.

  • Superposition of influences from wake and potential field with equal and unequal frequency in an axial-radial combined compressor
    Tuijin Jishu Journal of Propulsion Technology, 2013
    Co-Authors: Ben Zhao, D.-z. Lao, Ce Yang, W.-z. Zhang
    Abstract:

    A numerical investigation in an axial-radial combined compressor was performed to study the superposition of rotor/stator and stator/rotor interaction and to indicate the variations of the flow angle at inlet of the downstream rotor. Three configurations, R/S/R rig with unequal Moving Blade numbers, R/S rig and R/S/R rig with identical Moving Blade numbers, were included in this research project. Efforts were focused on the superposed interaction in the stator channel, specifically the changes in the deterministic kinetic energy caused by changing Blade numbers and rotor clocking. Besides, a useful mathematical model for analyzing these changes was presented. Results show that, for the compressor with unequal Moving Blade numbers, the position of the excitation/suppression changes with time whereas it keeps fixed position for the rig with identical Moving Blade numbers. But the position can be modulated by clocking when the rotors have equal Blade numbers. In addition, the Blade numbers and clocking position also decide the inlet flow angle for downstream radial rotor.

  • The influence of frequency and clocking on stator wake in an axial-radial combined compressor
    Kung Cheng Je Wu Li Hsueh Pao Journal of Engineering Thermophysics, 2013
    Co-Authors: Ben Zhao, M.-x. Qi, Du Li, Ce Yang, J Z Zhang
    Abstract:

    The unsteady flow in a combined compressor, which consists of axial flow and radial impellers, was simulated numerically at mass flow of 1.15 kg/s and speed of 60 kr/min (design point), and an in-depth analysis of the related factors caused stator wake flow variability was performed. This paper explored the major factors decided stator wake unsteady flow, as well as found out a method to control the stator wake unsteady flow. The research results indicated that: the Blade passing frequencies of upstream and downstream Moving Blade rows decided the periodicity of stator wake unsteady flow; and when the upstream rotor had the same Blade passing frequency as downstream rotor, the clocking could modify stator wake unsteady flow and the relative flow angle at inlet of radial rotor.

L. Casarsa - One of the best experts on this subject based on the ideXlab platform.

  • Experimental study of the three-dimensional flow field in cross-flow fans
    Experimental Thermal and Fluid Science, 2011
    Co-Authors: L. Casarsa, Pietro Giannattasio
    Abstract:

    High-resolution PIV measurements of the flow field inside cross-flow fans have been performed in planes normal and parallel to the fan axis, both outside and inside the impeller. The well known difficulties in obtaining the optical access inside the impeller have been overcome by allowing the internal flow planes to be illuminated by the laser light sheet or shot by the CCD camera through the Moving Blade vanes. Measurements have been performed in two cross-flow fans having the same two-module impeller but casing geometries based on very different design concepts. PIV data in planes normal to the rotor axis show a strong correlation between vorticity distribution and turbulent shear stresses inside the eccentric vortex of each fan. Furthermore, they provide useful elements to explain the very different performance of the two fans evidenced by their characteristic curves. Measurements in planes parallel to the impeller axis show that wide three-dimensional recirculation structures develop near the casing end walls at the discharge of the fans. These mean flow structures are responsible for the backflow into the end portions of the impeller of part of the discharged fluid, which is then transported axially by the eccentric vortex towards the rotor central disc before being discharged once again outside the impeller. In the case of cross-flow fans including few rotor modules, the existence of significant axial velocity components inside the eccentric vortex can alter substantially the flow picture, common in the current literature, resulting from 2-D numerical models or measurements performed in a single transverse plane of the fan. ?? 2011 Elsevier Inc.

Adam Beevers - One of the best experts on this subject based on the ideXlab platform.

  • On the Prediction and Theory of the Temperature Increase of Low Pressure Last Stage Moving Blades During Low Volume Flow Conditions, and Limiting it Through Steam Extraction Methods
    Journal of Turbomachinery-transactions of The Asme, 2015
    Co-Authors: Adam Beevers, Said Havakechian, Benjamin Megerle
    Abstract:

    During extreme low volume flow conditions, the last stages of a low pressure steam turbine operate in ventilation conditions that can cause a significant temperature increase of critical regions of the last stage Moving Blade (LSB). Under some conditions, the Blade temperature may rise above a safe operating temperature, requiring the machine to be shut down. Limiting the heating effect on the LSB increases the allowable operating range of the low pressure turbine. One common method is to spray water droplets into the low pressure exhaust. As the length of LSBs continues to increase, this method reaches its limit of practical operating effectiveness due to the amount of water required and its impact on the erosion of the LSB. An investigation into complimentary solutions to limit the temperature increase was conducted using CFD. An appropriate CFD setup was chosen from a sensitivity study on the effects from geometry, mesh density, turbulence model, and time dependency. The CFD results were verified against steam turbine data from a scaled test facility. The proposed solutions include low temperature steam extraction, targeted for critical regions of the Moving Blade. From the test turbine and CFD results, the drivers of the temperature increase during ventilation conditions are identified and described.

  • On the Prediction and Theory of the Temperature Increase of Low Pressure Last Stage Moving Blades During Low Volume Flow Conditions, and Limiting it Through Steam Extraction Methods
    Volume 1B: Marine; Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2014
    Co-Authors: Adam Beevers, Said Havakechian, Benjamin Megerle
    Abstract:

    During extreme low volume flow conditions, the last stages of a low pressure steam turbine operate in ventilation conditions that can cause a significant temperature increase of critical regions of the last stage Moving Blade. Under some conditions, the Blade temperature may rise above a safe operating temperature, requiring the machine to be shut down. Limiting the heating effect on the last stage Moving Blade increases the allowable operating range of the low pressure turbine. One common method is to spray water droplets into the low pressure exhaust. As the length of last stage Moving Blades continues to increase, this method reaches its limit of practical operating effectiveness due to the amount of water required and its impact on the erosion of the LSB.An investigation into complimentary solutions to limit the temperature increase was conducted using CFD. An appropriate CFD setup was chosen from a sensitivity study on the effect of geometry, mesh density, turbulence model and time dependency. The CFD results were verified against steam turbine data from a test facility. The proposed complimentary solutions to limit the temperature increase include low temperature steam extraction, targeted for critical regions of the Moving Blade. From the test turbine and CFD results, the drivers of the temperature increase during ventilation conditions are identified and described.Copyright © 2014 by Alstom Technologie AG