The Experts below are selected from a list of 198 Experts worldwide ranked by ideXlab platform
Reza S. Abhari - One of the best experts on this subject based on the ideXlab platform.
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Control of Rotor Tip Leakage Through Cooling Injection From the Casing in a High-Work Turbine
Journal of Turbomachinery-transactions of The Asme, 2008Co-Authors: Thomas Behr, Anestis I. Kalfas, Reza S. AbhariAbstract:This paper presents an experimental investigation of a novel approach for controlling the Rotor tip leakage and secondary flow by injecting cooling air from the stationary casing onto the Rotor tip. It contains a detailed analysis of the unsteady flow interaction between the injected air and the flow in the Rotor tip region and its impact on the Rotor secondary flow structures. The experimental investigation has been conducted on a one-and-1/2-stage, unshrouded turbine, which has been especially designed and built for the current investigation. The turbine test case models a highly loaded, high pressure gas turbine stage. Measurements conducted with a two-sensor fast-response aerodynamic probe have provided data describing the time-resolved behavior of flow angles and pressures, as well as turbulence intensity in the exit plane of the Rotor. Cooling air has been injected in the circumferential direction at a 30 deg angle from the casing tangent, opposing the Rotor turning direction through a circumferential array of ten equidistant holes per Rotor Pitch. Different cooling air injection configurations have been tested. Injection parameters such as mass flow, axial position, and size of the holes have been varied to see the effect on the Rotor tip secondary flows. The results of the current investigation show that with the injection, the size and the turbulence intensity of the Rotor tip leakage vortex and the Rotor tip passage vortex reduce. Both vortices move toward the tip suction side corner of the Rotor passage. With an appropriate combination of injection mass flow rate and axial injection position, the isentropic efficiency of the stage was improved by 0.55 percentage points.
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Control of Rotor Tip Leakage Through Cooling Injection From the Casing in a High-Work Turbine: Experimental Investigation
Volume 6: Turbo Expo 2007 Parts A and B, 2007Co-Authors: Thomas Behr, Anestis I. Kalfas, Reza S. AbhariAbstract:This paper presents an experimental investigation of a novel approach for controlling the Rotor tip secondary flow by injecting cooling air from the stationary casing onto the Rotor tip. It contains a detailed analysis of the unsteady flow interaction between the injected air and the flow in the Rotor tip region and its impact on the Rotor secondary flow structures. The experimental investigation has been conducted on a one-and-1/2-stage, unshrouded turbine, which has been especially designed and built for the current investigation. The turbine test case models a highly-loaded, high-pressure gas turbine stage. Measurements conducted with a two-sensor fast response pressure probe (FRAP) have provided data describing the time-resolved behavior of flow angles and pressures, as well as turbulence intensity in the exit plane of the Rotor. Cooling air has been injected in circumferential direction at a 30° angle from the casing tangent, opposing the Rotor turning direction through a circumferential array of 10 equidistant holes per Rotor Pitch. Different cooling air injection configurations have been tested. Injection parameters such as massflow, axial position and size of the holes have been varied to see the effect on the Rotor tip secondary flows. The results of the current investigation show that with the injection, the size and the turbulence intensity of the Rotor tip leakage vortex and the Rotor tip passage vortex reduce. Both vortices move towards the tip suction side corner of the Rotor passage. With an appropriate combination of injection massflow rate and axial injection position the isentropic efficiency of the stage was improved by 0.55 percent points.Copyright © 2007 by ASME
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Unsteady flow physics and performance of a one-and 1/2-stage unshrouded high work turbine
Journal of Turbomachinery-transactions of The Asme, 2006Co-Authors: Thomas Behr, Anestis I. Kalfas, Reza S. AbhariAbstract:This paper presents an experimental study of the flow mechanisms of tip leakage across a blade of an unshrouded turbine Rotor. It shows the design of a new one-and-1/2stage, unshrouded turbine configuration, which has been developed within the Turbomachinery Laboratory of ETH Zurich. This test case is a model of a high work (∆h/u 2 =2.36) axial turbine. The experimental investigation comprises data from unsteady and steady probe measurements, which has been acquired around all the bladerows of the one-and-1/2-stage, unshrouded turbine. A newly developed 2-sensor Fast Response Aerodynamic Probe (FRAP) technique has been used in the current measurement campaign. The paper contains a detailed analysis of the unsteady interaction between Rotor and stator blade rows, with particular attention paid on the flow in the blade tip region. It has been found that the pressure field of the second stator row has a influence on the development of the tip leakage vortex downstream of the Rotor. The vortex is modulated by the stator profiles and shows variation in size and relative position to the Rotor trailing edge when it stretches around the stator leading edge. Thereby a deflection of the tip leakage vortex has been observed, which expresses in a varying circumferential distance between two neighboring vortices of ±20% of a Rotor Pitch. Furthermore, a significant influence of quasi-stationary secondary flow features of the upstream stator row on the secondary flow of the Rotor has been detected. The geometry data of the one-and-1/2-stage turbine will be available to the public domain for validation and improvement of numerical tools. NOMENCLATURE c Absolute flow velocity
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Unsteady Flow Physics and Performance of a One-and-1/2-Stage Unshrouded High Work Turbine
Volume 6: Turbomachinery Parts A and B, 2006Co-Authors: Thomas Behr, Anestis I. Kalfas, Reza S. AbhariAbstract:This paper presents an experimental study of the flow mechanisms of tip leakage across a blade of an unshrouded turbine Rotor. It shows the design of a new one-and-1/2-stage, unshrouded turbine configuration, which has been developed within the Turbomachinery Laboratory of ETH Zurich. This test case is a model of a high work (Δh/u2 = 2.36) axial turbine. The experimental investigation comprises data from unsteady and steady probe measurements, which has been acquired around all the bladerows of the one-and-1/2-stage, unshrouded turbine. A newly developed 2-sensor Fast Response Aerodynamic Probe (FRAP) technique has been used in the current measurement campaign. The paper contains a detailed analysis of the unsteady interaction between Rotor and stator blade rows, with particular attention paid on the flow in the blade tip region. It has been found that the pressure field of the second stator row has a influence on the development of the tip leakage vortex downstream of the Rotor. The vortex is modulated by the stator profiles and shows variation in size and relative position to the Rotor trailing edge when it stretches around the stator leading edge. Thereby a deflection of the tip leakage vortex has been observed, which expresses in a varying circumferential distance between two neighboring vortices of ±20% of a Rotor Pitch. Furthermore, a significant influence of quasi-stationary secondary flow features of the upstream stator row on the secondary flow of the Rotor has been detected. The geometry data of the one-and-1/2-stage turbine will be available to the public domain for validation and improvement of numerical tools.Copyright © 2006 by ASME
Thomas Behr - One of the best experts on this subject based on the ideXlab platform.
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Control of Rotor Tip Leakage Through Cooling Injection From the Casing in a High-Work Turbine
Journal of Turbomachinery-transactions of The Asme, 2008Co-Authors: Thomas Behr, Anestis I. Kalfas, Reza S. AbhariAbstract:This paper presents an experimental investigation of a novel approach for controlling the Rotor tip leakage and secondary flow by injecting cooling air from the stationary casing onto the Rotor tip. It contains a detailed analysis of the unsteady flow interaction between the injected air and the flow in the Rotor tip region and its impact on the Rotor secondary flow structures. The experimental investigation has been conducted on a one-and-1/2-stage, unshrouded turbine, which has been especially designed and built for the current investigation. The turbine test case models a highly loaded, high pressure gas turbine stage. Measurements conducted with a two-sensor fast-response aerodynamic probe have provided data describing the time-resolved behavior of flow angles and pressures, as well as turbulence intensity in the exit plane of the Rotor. Cooling air has been injected in the circumferential direction at a 30 deg angle from the casing tangent, opposing the Rotor turning direction through a circumferential array of ten equidistant holes per Rotor Pitch. Different cooling air injection configurations have been tested. Injection parameters such as mass flow, axial position, and size of the holes have been varied to see the effect on the Rotor tip secondary flows. The results of the current investigation show that with the injection, the size and the turbulence intensity of the Rotor tip leakage vortex and the Rotor tip passage vortex reduce. Both vortices move toward the tip suction side corner of the Rotor passage. With an appropriate combination of injection mass flow rate and axial injection position, the isentropic efficiency of the stage was improved by 0.55 percentage points.
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Control of Rotor Tip Leakage Through Cooling Injection From the Casing in a High-Work Turbine: Experimental Investigation
Volume 6: Turbo Expo 2007 Parts A and B, 2007Co-Authors: Thomas Behr, Anestis I. Kalfas, Reza S. AbhariAbstract:This paper presents an experimental investigation of a novel approach for controlling the Rotor tip secondary flow by injecting cooling air from the stationary casing onto the Rotor tip. It contains a detailed analysis of the unsteady flow interaction between the injected air and the flow in the Rotor tip region and its impact on the Rotor secondary flow structures. The experimental investigation has been conducted on a one-and-1/2-stage, unshrouded turbine, which has been especially designed and built for the current investigation. The turbine test case models a highly-loaded, high-pressure gas turbine stage. Measurements conducted with a two-sensor fast response pressure probe (FRAP) have provided data describing the time-resolved behavior of flow angles and pressures, as well as turbulence intensity in the exit plane of the Rotor. Cooling air has been injected in circumferential direction at a 30° angle from the casing tangent, opposing the Rotor turning direction through a circumferential array of 10 equidistant holes per Rotor Pitch. Different cooling air injection configurations have been tested. Injection parameters such as massflow, axial position and size of the holes have been varied to see the effect on the Rotor tip secondary flows. The results of the current investigation show that with the injection, the size and the turbulence intensity of the Rotor tip leakage vortex and the Rotor tip passage vortex reduce. Both vortices move towards the tip suction side corner of the Rotor passage. With an appropriate combination of injection massflow rate and axial injection position the isentropic efficiency of the stage was improved by 0.55 percent points.Copyright © 2007 by ASME
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Unsteady flow physics and performance of a one-and 1/2-stage unshrouded high work turbine
Journal of Turbomachinery-transactions of The Asme, 2006Co-Authors: Thomas Behr, Anestis I. Kalfas, Reza S. AbhariAbstract:This paper presents an experimental study of the flow mechanisms of tip leakage across a blade of an unshrouded turbine Rotor. It shows the design of a new one-and-1/2stage, unshrouded turbine configuration, which has been developed within the Turbomachinery Laboratory of ETH Zurich. This test case is a model of a high work (∆h/u 2 =2.36) axial turbine. The experimental investigation comprises data from unsteady and steady probe measurements, which has been acquired around all the bladerows of the one-and-1/2-stage, unshrouded turbine. A newly developed 2-sensor Fast Response Aerodynamic Probe (FRAP) technique has been used in the current measurement campaign. The paper contains a detailed analysis of the unsteady interaction between Rotor and stator blade rows, with particular attention paid on the flow in the blade tip region. It has been found that the pressure field of the second stator row has a influence on the development of the tip leakage vortex downstream of the Rotor. The vortex is modulated by the stator profiles and shows variation in size and relative position to the Rotor trailing edge when it stretches around the stator leading edge. Thereby a deflection of the tip leakage vortex has been observed, which expresses in a varying circumferential distance between two neighboring vortices of ±20% of a Rotor Pitch. Furthermore, a significant influence of quasi-stationary secondary flow features of the upstream stator row on the secondary flow of the Rotor has been detected. The geometry data of the one-and-1/2-stage turbine will be available to the public domain for validation and improvement of numerical tools. NOMENCLATURE c Absolute flow velocity
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Unsteady Flow Physics and Performance of a One-and-1/2-Stage Unshrouded High Work Turbine
Volume 6: Turbomachinery Parts A and B, 2006Co-Authors: Thomas Behr, Anestis I. Kalfas, Reza S. AbhariAbstract:This paper presents an experimental study of the flow mechanisms of tip leakage across a blade of an unshrouded turbine Rotor. It shows the design of a new one-and-1/2-stage, unshrouded turbine configuration, which has been developed within the Turbomachinery Laboratory of ETH Zurich. This test case is a model of a high work (Δh/u2 = 2.36) axial turbine. The experimental investigation comprises data from unsteady and steady probe measurements, which has been acquired around all the bladerows of the one-and-1/2-stage, unshrouded turbine. A newly developed 2-sensor Fast Response Aerodynamic Probe (FRAP) technique has been used in the current measurement campaign. The paper contains a detailed analysis of the unsteady interaction between Rotor and stator blade rows, with particular attention paid on the flow in the blade tip region. It has been found that the pressure field of the second stator row has a influence on the development of the tip leakage vortex downstream of the Rotor. The vortex is modulated by the stator profiles and shows variation in size and relative position to the Rotor trailing edge when it stretches around the stator leading edge. Thereby a deflection of the tip leakage vortex has been observed, which expresses in a varying circumferential distance between two neighboring vortices of ±20% of a Rotor Pitch. Furthermore, a significant influence of quasi-stationary secondary flow features of the upstream stator row on the secondary flow of the Rotor has been detected. The geometry data of the one-and-1/2-stage turbine will be available to the public domain for validation and improvement of numerical tools.Copyright © 2006 by ASME
Anestis I. Kalfas - One of the best experts on this subject based on the ideXlab platform.
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Control of Rotor Tip Leakage Through Cooling Injection From the Casing in a High-Work Turbine
Journal of Turbomachinery-transactions of The Asme, 2008Co-Authors: Thomas Behr, Anestis I. Kalfas, Reza S. AbhariAbstract:This paper presents an experimental investigation of a novel approach for controlling the Rotor tip leakage and secondary flow by injecting cooling air from the stationary casing onto the Rotor tip. It contains a detailed analysis of the unsteady flow interaction between the injected air and the flow in the Rotor tip region and its impact on the Rotor secondary flow structures. The experimental investigation has been conducted on a one-and-1/2-stage, unshrouded turbine, which has been especially designed and built for the current investigation. The turbine test case models a highly loaded, high pressure gas turbine stage. Measurements conducted with a two-sensor fast-response aerodynamic probe have provided data describing the time-resolved behavior of flow angles and pressures, as well as turbulence intensity in the exit plane of the Rotor. Cooling air has been injected in the circumferential direction at a 30 deg angle from the casing tangent, opposing the Rotor turning direction through a circumferential array of ten equidistant holes per Rotor Pitch. Different cooling air injection configurations have been tested. Injection parameters such as mass flow, axial position, and size of the holes have been varied to see the effect on the Rotor tip secondary flows. The results of the current investigation show that with the injection, the size and the turbulence intensity of the Rotor tip leakage vortex and the Rotor tip passage vortex reduce. Both vortices move toward the tip suction side corner of the Rotor passage. With an appropriate combination of injection mass flow rate and axial injection position, the isentropic efficiency of the stage was improved by 0.55 percentage points.
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Control of Rotor Tip Leakage Through Cooling Injection From the Casing in a High-Work Turbine: Experimental Investigation
Volume 6: Turbo Expo 2007 Parts A and B, 2007Co-Authors: Thomas Behr, Anestis I. Kalfas, Reza S. AbhariAbstract:This paper presents an experimental investigation of a novel approach for controlling the Rotor tip secondary flow by injecting cooling air from the stationary casing onto the Rotor tip. It contains a detailed analysis of the unsteady flow interaction between the injected air and the flow in the Rotor tip region and its impact on the Rotor secondary flow structures. The experimental investigation has been conducted on a one-and-1/2-stage, unshrouded turbine, which has been especially designed and built for the current investigation. The turbine test case models a highly-loaded, high-pressure gas turbine stage. Measurements conducted with a two-sensor fast response pressure probe (FRAP) have provided data describing the time-resolved behavior of flow angles and pressures, as well as turbulence intensity in the exit plane of the Rotor. Cooling air has been injected in circumferential direction at a 30° angle from the casing tangent, opposing the Rotor turning direction through a circumferential array of 10 equidistant holes per Rotor Pitch. Different cooling air injection configurations have been tested. Injection parameters such as massflow, axial position and size of the holes have been varied to see the effect on the Rotor tip secondary flows. The results of the current investigation show that with the injection, the size and the turbulence intensity of the Rotor tip leakage vortex and the Rotor tip passage vortex reduce. Both vortices move towards the tip suction side corner of the Rotor passage. With an appropriate combination of injection massflow rate and axial injection position the isentropic efficiency of the stage was improved by 0.55 percent points.Copyright © 2007 by ASME
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Unsteady flow physics and performance of a one-and 1/2-stage unshrouded high work turbine
Journal of Turbomachinery-transactions of The Asme, 2006Co-Authors: Thomas Behr, Anestis I. Kalfas, Reza S. AbhariAbstract:This paper presents an experimental study of the flow mechanisms of tip leakage across a blade of an unshrouded turbine Rotor. It shows the design of a new one-and-1/2stage, unshrouded turbine configuration, which has been developed within the Turbomachinery Laboratory of ETH Zurich. This test case is a model of a high work (∆h/u 2 =2.36) axial turbine. The experimental investigation comprises data from unsteady and steady probe measurements, which has been acquired around all the bladerows of the one-and-1/2-stage, unshrouded turbine. A newly developed 2-sensor Fast Response Aerodynamic Probe (FRAP) technique has been used in the current measurement campaign. The paper contains a detailed analysis of the unsteady interaction between Rotor and stator blade rows, with particular attention paid on the flow in the blade tip region. It has been found that the pressure field of the second stator row has a influence on the development of the tip leakage vortex downstream of the Rotor. The vortex is modulated by the stator profiles and shows variation in size and relative position to the Rotor trailing edge when it stretches around the stator leading edge. Thereby a deflection of the tip leakage vortex has been observed, which expresses in a varying circumferential distance between two neighboring vortices of ±20% of a Rotor Pitch. Furthermore, a significant influence of quasi-stationary secondary flow features of the upstream stator row on the secondary flow of the Rotor has been detected. The geometry data of the one-and-1/2-stage turbine will be available to the public domain for validation and improvement of numerical tools. NOMENCLATURE c Absolute flow velocity
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Unsteady Flow Physics and Performance of a One-and-1/2-Stage Unshrouded High Work Turbine
Volume 6: Turbomachinery Parts A and B, 2006Co-Authors: Thomas Behr, Anestis I. Kalfas, Reza S. AbhariAbstract:This paper presents an experimental study of the flow mechanisms of tip leakage across a blade of an unshrouded turbine Rotor. It shows the design of a new one-and-1/2-stage, unshrouded turbine configuration, which has been developed within the Turbomachinery Laboratory of ETH Zurich. This test case is a model of a high work (Δh/u2 = 2.36) axial turbine. The experimental investigation comprises data from unsteady and steady probe measurements, which has been acquired around all the bladerows of the one-and-1/2-stage, unshrouded turbine. A newly developed 2-sensor Fast Response Aerodynamic Probe (FRAP) technique has been used in the current measurement campaign. The paper contains a detailed analysis of the unsteady interaction between Rotor and stator blade rows, with particular attention paid on the flow in the blade tip region. It has been found that the pressure field of the second stator row has a influence on the development of the tip leakage vortex downstream of the Rotor. The vortex is modulated by the stator profiles and shows variation in size and relative position to the Rotor trailing edge when it stretches around the stator leading edge. Thereby a deflection of the tip leakage vortex has been observed, which expresses in a varying circumferential distance between two neighboring vortices of ±20% of a Rotor Pitch. Furthermore, a significant influence of quasi-stationary secondary flow features of the upstream stator row on the secondary flow of the Rotor has been detected. The geometry data of the one-and-1/2-stage turbine will be available to the public domain for validation and improvement of numerical tools.Copyright © 2006 by ASME
Carsten Zscherp - One of the best experts on this subject based on the ideXlab platform.
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Investigation of Blade Tip Interaction With Casing Treatment in a Transonic Compressor—Part II: Numerical Results
Journal of Turbomachinery-transactions of The Asme, 2010Co-Authors: Rainer Schnell, Melanie Voges, Reinhard Mönig, Martin W. Müller, Carsten ZscherpAbstract:A single stage transonic axial compressor was equipped with a casing treatment consisting of 3.5 axial slots per Rotor Pitch in order to investigate its influence on stall margin characteristics, as well as on the Rotor near tip flow field, both numerically and experimentally. Contrary to most other studies, a generic casing treatment (CT) was designed to provide optimal optical access in the immediate vicinity of the CT, rather than for maximum benefit in terms of stall margin extension. The second part of this two-part paper deals with the numerical developments and their validation, carried out in order to efficiently perform time-accurate casing treatment simulations. The numerical developments focus on the extension of an existing coupling algorithm in order to carry out unsteady calculations with any exterior geometry coupled to the main flow passage (in this case a single slot), having an arbitrary Pitch. This extension is done by incorporating frequency domain, phase-lagged boundary conditions into this coupling procedure. Whereas the phase lag approach itself is well established and validated for standard Rotor-stator calculations, its application to casing treatment simulations is new Its capabilities and validation will be demonstrated on the given compressor configuration, making extensive use of the detailed particle image velocimetry flow field measurements near the Rotor tip. Instantaneous data at all measurement planes will be compared for different Rotor positions with respect to the stationary slots in order to evaluate the time-dependent interaction between the Rotor and the casing treatment.
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Investigation of Blade Tip Interaction With Casing Treatment in a Transonic Compressor—Part I: Particle Image Velocimetry
Journal of Turbomachinery-transactions of The Asme, 2010Co-Authors: Melanie Voges, Rainer Schnell, Reinhard Mönig, Martin W. Müller, Christian Willert, Carsten ZscherpAbstract:A single-stage transonic axial compressor was equipped with a casing treatment (CT), consisting of 3.5 axial slots per Rotor Pitch in order to investigate the predicted extension of the stall margin characteristics both numerically and experimentally. Contrary to most other studies the CT was designed especially accounting for an optimized optical access in the immediate vicinity of the CT, rather than giving maximum benefit in terms of stall margin extension. Part 1 of this two-part contribution describes the experi¬mental investigation of the blade tip interaction with casing treatment using Particle image velocimetry (PIV). The nearly rectangular geometry of the CT cavities allowed a portion of it to be made of quartz glass with curvatures matching the casing. Thus the flow phenomena could be observed with essentially no disturbance caused by the optical access. Two periscope light sheet probes were specifically designed for this application to allow for precise alignment of the laser light sheet at three different radial positions in the Rotor passage (87.5%, 95% and 99%). For the outermost radial position the light sheet probe was placed behind the Rotor and aligned to pass the light sheet through the blade tip clearance. It was demonstrated that the PIV technique is capable of providing velocity information of high quality even in the tip clearance region of the Rotor blades. The chosen type of smoke-based seeding with very small particles (about 0.5 µm in diameter) supported data evaluation with high spatial resolution, resulting in a final grid size of 0.5 x 0.5 mm. The PIV data base established in this project forms the basis for further detailed evaluations of the flow phenomena present in the transonic compressor stage with CT and allows validation of accompanying CFD calculations using the TRACE code. Based on the combined results of PIV measurements and CFD calculations of the same compressor and CT geometry a better understanding of the complex flow characteristics can be achieved, as detailed in Part 2 of this paper.
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PIV Application for Investigation of the Rotor Blade Tip Interaction with a Casing Treatment in a Transonic Compressor Stage
2008Co-Authors: Melanie Voges, Rainer Schnell, Christian Willert, M. Müller, Carsten ZscherpAbstract:This contribution describes the experimental investigation of the blade tip interaction with a casing treatment implemented to a transonic compressor stage using particle image velocimetry (PIV). The results obtained allowed for direct comparison with numerical simulations of the same compressor stage including the CT geometry, carried out using the DLR TRACE code following a new approach to efficiently perform time-accurate casing-treatment simulations. The single-stage transonic axial compressor was equipped with a casing treatment (CT), consisting of 3.5 axial slots per Rotor Pitch in order to investigate the predicted extension of the stall margin characteristics. Contrary to most other studies, the CT was designed especially accounting for an optimized optical access in the immediate vicinity of the CT, rather than giving maximum benefit in terms of stall margin extension. The nearly rectangular geometry of the CT cavities allowed one dividing bridge between two slots to be made of quartz glass with curvatures matching the casing. Thus the flow phenomena could be observed with essentially no disturbance caused by the optical access. Two periscope light sheet probes were specifically designed for this application to allow for precise alignment of the laser light sheet at three different radial positions in the Rotor tip region (at 87.5%, 95% and 99% blade height). For the outermost radial position the light sheet probe was placed behind the Rotor and aligned to pass the light sheet through the blade tip clearance. It was demonstrated that the PIV technique is capable of providing velocity information of high quality even in the tip clearance region of the Rotor blades. Phase-constant measurements were carried out with a resolution of 8 phase angles per blade Pitch in relation to the CT slots visible in the camera’s field of view. The chosen type of smoke-based seeding with very small particles (about 0.5 µm in diameter) supported data evaluation with high spatial resolution, resulting in a final grid size of 0.5 x 0.5 mm. The PIV data base established in this project forms the basis for further detailed evaluations of the flow phenomena present in the transonic compressor stage with CT and allows validation of accompanying CFD calculations using the DLR TRACE code. Based on the combined results of PIV measurements and CFD calculations of the same compressor and CT geometry a better understanding of the complex flow characteristics can be achieved.
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Investigation of Blade Tip Interaction With Casing Treatment in a Transonic Compressor: Part 2—Numerical Results
Volume 6: Turbomachinery Parts A B and C, 2008Co-Authors: Rainer Schnell, Melanie Voges, Reinhard Mönig, Martin W. Müller, Carsten ZscherpAbstract:A single-stage transonic axial compressor was equipped with a casing treatment, consisting of 3.5 axial slots per Rotor Pitch in order to investigate its influence on stall margin characteristics as well as on the Rotor near tip flowfield both numerically and experimentally. Contrary to most other studies a generic Casing Treatment was designed to provide optimal optical access in the immediate vicinity of the CT, rather than for maximum benefit in terms of stall margin extension. The second part of this two-part paper deals with the numerical developments, and their validation, carried out in order to efficiently perform time-accurate casing-treatment simulations. The numerical developments focus on the extension of an existing coupling algorithm in order to carry out unsteady calculations with any exterior geometry coupled to the main flow passage (in this case a single slot) having an arbitrary Pitch. This extension is done by incorporating frequency domain, phase-lagged boundary conditions into this coupling procedure. Whereas the phaselag approach itself is well established and validated for standard Rotor-stator calculations, its application to casing treatment simulations is new. Its capabilities and validation will be demonstrated on the given compressor configuration, making extensive use of the detailed PIV flowfield measurements near the Rotor tip. Instantaneous data at all measurement planes will be compared for different Rotor positions with respect to the stationary slots in order to evaluate the time-dependent interaction between the Rotor and the casing treatment.
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Investigation of Blade Tip Interaction With Casing Treatment in a Transonic Compressor: Part 1—Particle Image Velocimetry
Volume 6: Turbomachinery Parts A B and C, 2008Co-Authors: Melanie Voges, Rainer Schnell, Reinhard Mönig, Martin W. Müller, Christian Willert, Carsten ZscherpAbstract:A single-stage transonic axial compressor was equipped with a casing treatment (CT), consisting of 3.5 axial slots per Rotor Pitch in order to investigate the predicted extension of the stall margin characteristics both numerically and experimentally. Contrary to most other studies the CT was designed especially accounting for an optimized optical access in the immediate vicinity of the CT, rather than giving maximum benefit in terms of stall margin extension. Part 1 of this two-part contribution describes the experimental investigation of the blade tip interaction with casing treatment using Particle image velocimetry (PIV). The nearly rectangular geometry of the CT cavities allowed a portion of it to be made of quartz glass with curvatures matching the casing. Thus the flow phenomena could be observed with essentially no disturbance caused by the optical access. Two periscope light sheet probes were specifically designed for this application to allow for precise alignment of the laser light sheet at three different radial positions in the Rotor passage (87.5%, 95% and 99%). For the outermost radial position the light sheet probe was placed behind the Rotor and aligned to pass the light sheet through the blade tip clearance. It was demonstrated that the PIV technique is capable of providing velocity information of high quality even in the tip clearance region of the Rotor blades. The chosen type of smoke-based seeding with very small particles (about 0.5 μm in diameter) supported data evaluation with high spatial resolution, resulting in a final grid size of 0.5 × 0.5 mm. The PIV data base established in this project forms the basis for further detailed evaluations of the flow phenomena present in the transonic compressor stage with CT and allows validation of accompanying CFD calculations using the TRACE code. Based on the combined results of PIV measurements and CFD calculations of the same compressor and CT geometry a better understanding of the complex flow characteristics can be achieved, as detailed in Part 2 of this paper.Copyright © 2008 by ASME
Theodosios Korakianitis - One of the best experts on this subject based on the ideXlab platform.
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Blade-loading effects on the propagation of unsteady flow and on forcing functions in axial-turbine cascades
Journal De Physique Iii, 1992Co-Authors: Theodosios KorakianitisAbstract:This article investigates the effect of tangential blade loading on the propagation of time-dependent pressure disturbance due to potential-flow interaction ans viscous-wake interaction from upstream blade rows in axial-turbine-blade Rotor cascades. Results are obtained by modeling the effects of the stator viscous wake and tha stator-Rotor potential-flow field on the Rotor flow field. A computer program is used to calculate the unsteady flows in the Rotor passages. The amplitudes for the two types of interaction are based on a review of available experimental and computational data. We study the propagation of the isolated potential-flow interaction (no viscous-wake interaction), of the isolated viscous wake interaction (no potential-flow interaction), and of the combination of interactions. We examine the propagation of both interactions in three fRotor cascades of high, medium and low tangential-loading coefficient (1.2, 1.0 and 0.8 respectively) for typical values of reduced frequency. The discussion uses as example a stator-to-Rotor-Pitch ration R = 2. We investigate the differences when the stator-to-Rotor Pitch ratio is decreased (to R = 1) and increased (to R = 4). We offer new explanations of the mechanisms of generation of unsteady forces on the blades and study the effects of tangential blade and of axial gap between blade rows on th time-dependent forces acting on the blades. The potential-flow field of the Rotor-leading-edge region cuts the potential-flow field of the upstream stator, and distorts and cuts the wake centerlines. The potential-flow field cut into the Rotor passage propagates downstream as a potential-flow disturbance superimposed on the Rotor flow field. The direction and decay rate of this interaction are determined respectively by the stator-outlet flow angle and by the stator-cascade Pitch. The cut wake is sheared into the Rotor passage and it results in a region of increased unsteady pressure upstream of the wake centerline and a region of decreased unsteady pressure downstream of the wake centerline. The wake shearing is more pronounced in highly-loaded cascades, and for lower stator outlet-flow angles. The potential flow interaction dominates the unsteadiness for high values of R and the wake interaction dominates the unsteadiness for low values of R. The above explanations can be used to determine locations unsteady-pressure regions, and the shape of the unsteady forcing functions
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On the Prediction of Unsteady Forces on Gas Turbine Blades: Part 2—Analysis of the Results
Journal of Turbomachinery-transactions of The Asme, 1992Co-Authors: Theodosios KorakianitisAbstract:This article investigates the generation of unsteady forces on turbine blades due to potential-flow interaction and viscous-wake interaction from upstream blade rows. A computer program is used to calculate the unsteady forces on the Rotor blades. Results for typical stator-to-Rotor-Pitch ratios and stator outlet-flow angles show that the first spatial harmonic of the unsteady force may decrease for higher stator-to-Rotor-Pitch ratios, while the higher spatial harmonics increase. This (apparently counterintuitive) trend for the first harmonic, and other blade row interaction issues, are explained by considering the mechanisms by which the viscous wakes and the potential-flow interaction affect the flow field. The interaction mechanism is shown to vary with the stator-to-Rotor-Pitch ratio and with the outlet flow angle of the stator. It is also shown that varying the axial gap between Rotor and stator can minimize the magnitude of the unsteady part of the forces generated by the combined effects of the two interactions.
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On the Propagation of Viscous Wakes and Potential Flow in Axial-Turbine Cascades
Volume 5: Manufacturing Materials and Metallurgy; Ceramics; Structures and Dynamics; Controls Diagnostics and Instrumentation; Education; IGTI Scholar, 1991Co-Authors: Theodosios KorakianitisAbstract:This paper investigates the propagation of pressure disturbances due to potential-flow interaction and viscous-wake interaction from upstream blade rows in axial-turbine-blade Rotor cascades. Results are obtained by modeling the effects of the stator viscous wake and the stator potential-flow field on the Rotor flow field. A computer program is used to calculate the unsteady flow fields. The amplitudes for the two types of interaction are based on a review of available experimental and computational data. We study the propagation of the isolated potential-flow interaction (no viscous-wake interaction), of the isolated viscous wake interaction (no potential-flow interaction), and of the combination of interactions. The discussion uses as example a lightly-loaded cascade for a stator-to-Rotor-Pitch ratio R = 2. We examine the relative magnitudes of the unsteady forces for two different stator-exit angles. We also explain the expected differences when the stator-to-Rotor Pitch ratio is decreased (to R = 1) and increased (to R = 4). We offer new and previously unpublished explanations of the mechanisms of generation of unsteady forces on the blades. The potential flow field of the Rotor cuts into the potential flow field of the stator. After the potential-flow disturbance from the stator is cut into a Rotor cascade, it propagates into the relative flow field of the Rotor passage as a potential-flow disturbance. The potential flow field of the Rotor near the leading edge and the leading edge itself cut into the wake and generate two counter-rotating vortical patterns flanking the wake centerline in the passage. The vortical pattern upstream of the wake centerline generates an increase in the local pressure (and in the forces acting on the sides of the passage). The vortical pattern downstream of the wake centerline generates a decrease in the local pressure (and in the forces acting on the sides of the passage). The resulting unsteady forces on the blades are generated by the combined (additive) interaction of the two disturbances.Copyright © 1991 by ASME
