The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Dara W Childs - One of the best experts on this subject based on the ideXlab platform.
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Predicted Rotordynamic Behavior of a Labyrinth Seal as Rotor Surface Speed Approaches Mach 1
Journal of Engineering for Gas Turbines and Power, 2010Co-Authors: Manish R. Thorat, Dara W ChildsAbstract:Prior one-control-volume (1CV) models for Rotor-fluid interaction in labyrinth seals pro- duce synchronously reduced (at running speed), frequency-independent stiffness and damping coefficients. The 1CV model, consisting of a leakage equation, a continuity equation, and a circumferential-momentum equation (for each cavity), was stated to be invalid for Rotor Surface speeds approaching the speed of sound. However, the present results show that while the 1CV fluid-mechanic model continues to be valid, the calcu- lated Rotordynamic coefficients become strongly dependent on the Rotor’s precession fre- quency. A solution is developed for the reaction-force components for a range of preces- sion frequencies, producing frequency-dependent stiffness and damping coefficients. They can be used to define a Laplace-domain transfer-function model for the reaction-force/ Rotor-motion components. Calculated results are presented for a simple Jeffcott Rotor model acted on by a labyrinth seal. The model’s undamped natural frequency is 7.6 krpm. The fluid properties, seal radius Rs, and running speed ? cause the Rotor Surface velocity Rs ? to equal the speed of sound c0 at ?? 58 krpm. Calculated synchronous-response results due to imbalance coincide for the synchronously reduced and the frequency- dependent models. For an inlet preswirl ratio of 0.5, both models predict the same log-dec out to ? ? 14.5 krpm. The synchronously reduced model predicts an onset speed of instability (OSI) at 10 krpm, but a return to stability at 48 krpm, with subsequent increases in log-dec out to 70 krpm. The frequency-dependent model predicts an OSI of 10 krpm and no return to stability out to 70 krpm. The frequency-dependent models predict small changes in the Rotor’s damped natural frequencies. The synchronously reduced model predicts large changes. The stability-analysis results show that a frequency-dependent labyrinth seal model should be used if the Rotor Surface speed approaches a significant fraction of the speed of sound. For the present example, observ- able discrepancies arose when Rs ?? 0.26c0.
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predicted Rotordynamic behavior of a labyrinth seal as Rotor Surface speed approaches mach 1
ASME Turbo Expo 2009: Power for Land Sea and Air, 2009Co-Authors: Manish R. Thorat, Dara W ChildsAbstract:Prior one-control-volume (1CV) models for Rotor-fluid interaction in labyrinth seals produce synchronously-reduced (at running-speed), frequency-independent stiffness and damping coefficients. The 1CV model, consisting of a leakage equation, a continuity equation, and a circumferential-momentum equation (for each cavity) was stated to be invalid for Rotor Surface speeds approaching the speed of sound. However, the present results show that, while the 1CV fluid-mechanic model continues to be valid, the calculated Rotordynamic coefficients become strongly frequency dependent. A solution is developed for the reaction-force components for a range of precession frequencies, producing frequency-dependent stiffness and damping coefficients. They can be used to define a Laplace-domain transfer-function model for the reaction-force/Rotor-motion components. Calculated Rotordynamic results are presented for a simple Jeffcott Rotor acted on by a labyrinth seal. The seal radius Rs and running speed ω cause the Rotor Surface velocity Rs ω to equal the speed of sound c0 at ω = 58 krpm. Calculated synchronous-response results due to imbalance coincide for the synchronously-reduced and the frequency-dependent models. For an inlet preswirl ratio of 0.5, both models predict the same log decs out to ω≈14.5 krpm. The synchronously-reduced model predicts an onset speed of instability (OSI) at 15 krpm, but a return to stability at 45 krpm, with subsequent increases in log dec out to 65 krpm. The frequency-dependent model predicts an OSI of 65 krpm. The frequency-dependent models predict small changes in the Rotor’s damped natural frequencies. The synchronously-reduced model predicts large changes. The stability-analysis results show that a frequency-dependent labyrinth seal model should be used if the Rotor Surface speed approaches a significant fraction of the speed of sound. For the present example, observable discrepancies arose when Rs ω = 0.26 c0 .© 2009 ASME
Juha Pyrhönen - One of the best experts on this subject based on the ideXlab platform.
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Rotor Surface Ferrite Permanent Magnets in Electrical Machines: Advantages and Limitations
IEEE Transactions on Industrial Electronics, 2017Co-Authors: Ilya Petrov, Markku Niemelä, Pavel Ponomarev, Juha PyrhönenAbstract:Permanent-magnet synchronous machines (PMSM) are gaining a foothold in a growing number of applications. However, the high cost of these machines compared with the prices of induction motors, whose production process is mature and material costs are low, limits the use of PMSMs with rare-earth permanent magnets in many potential cases. A viable design solution for a PMSM cost reduction is to use low-cost ferrite magnets instead of rare-earth ones. Nevertheless, it is challenging to apply ferrite magnets to a high-power Rotor Surface magnet PMSM because of their weaker magnetic properties compared with the rare-earth magnets and the risk of irreversible demagnetization. This paper aims to investigate the boundaries and limiting factors for achieving the maximum tangential stress and linear current density at a certain air gap diameter by using Rotor Surface ferrite magnets. The computed results are validated by a prototype, which was designed within the described boundaries.
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harmonic loss calculation in Rotor Surface permanent magnets new analytic approach
IEEE Transactions on Magnetics, 2012Co-Authors: Juha Pyrhönen, Hanne Jussila, Yuliya Alexandrova, Pavol Rafajdus, Janne NergAbstract:The paper introduces an analytic permanent-magnet eddy-current loss calculation method for Rotor Surface permanent magnets. The problem has been studied widely in the literature, yet many of the suggested methods are difficult to use. A straightforward analytic solution is needed to speed up the motor preliminary design as present day computational capabilities are not fast enough to be used for 3-D time-stepped finite element analysis (FEA) of permanent-magnet eddy-current losses in every day design problems. An analytic approach is suggested to calculate different-harmonics-caused eddy-current losses. The results are compared both with 3-D FEA and measurement results. A comparison between the theoretical and experimental results is reported for an axial-flux two-stator single-Rotor machine with no Rotor yoke. The method has, however, been used in evaluating permanent-magnet losses also in machines with narrow slot openings where the flux density dips do not penetrate through the whole magnet or in machines having a laminated Rotor yoke.
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Harmonic Loss Calculation in Rotor Surface Permanent Magnets—New Analytic Approach
IEEE Transactions on Magnetics, 2012Co-Authors: Juha Pyrhönen, Hanne Jussila, Yuliya Alexandrova, Pavol Rafajdus, Janne NergAbstract:The paper introduces an analytic permanent-magnet eddy-current loss calculation method for Rotor Surface permanent magnets. The problem has been studied widely in the literature, yet many of the suggested methods are difficult to use. A straightforward analytic solution is needed to speed up the motor preliminary design as present day computational capabilities are not fast enough to be used for 3-D time-stepped finite element analysis (FEA) of permanent-magnet eddy-current losses in every day design problems. An analytic approach is suggested to calculate different-harmonics-caused eddy-current losses. The results are compared both with 3-D FEA and measurement results. A comparison between the theoretical and experimental results is reported for an axial-flux two-stator single-Rotor machine with no Rotor yoke. The method has, however, been used in evaluating permanent-magnet losses also in machines with narrow slot openings where the flux density dips do not penetrate through the whole magnet or in machines having a laminated Rotor yoke.
M. V. Mironova - One of the best experts on this subject based on the ideXlab platform.
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Calculating the thermal state of steam-cooled high-temperature elements of a turbine flow path: An analysis of different approaches
Thermal Engineering, 2011Co-Authors: V. V. Nazarov, N. N. Kortikov, M. V. MironovaAbstract:We present the results from a 3D numerical calculation aimed at analyzing the thermal state of the steam-cooled segment of the flow path of a double-flow intermediate-pressure cylinder used in a steam turbine for ultrasupercritical steam conditions. It is shown that the circumferential nonuniformity of metal temperature on the end-face Surfaces of disks and on the Rotor Surface may be disregarded when the turbine runs at the nominal frequency of rotation.
Dale B. Taulbee - One of the best experts on this subject based on the ideXlab platform.
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Prediction of Unsteady Rotor-Surface Pressure and Heat Transfer From Wake Passings
Journal of Turbomachinery-transactions of The Asme, 1992Co-Authors: Le T. Tran, Dale B. TaulbeeAbstract:The research described in this paper is a numerical investigation of the effects of unsteady flow of gas turbine heat transfer, particularly of a Rotor blade Surface. The unsteady flow in a Rotor blade passage and the unsteady heat transfer of the blade Surface as a result of wake/blade interaction are modeled by the inviscid flow/boundary layer approach. The Euler equations that govern the inviscid flow are solved using a time-accurate marching scheme
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Prediction of Unsteady Rotor-Surface Pressure and Heat Transfer From Wake Passings
Volume 4: Heat Transfer; Electric Power; Industrial and Cogeneration, 1991Co-Authors: Le T. Tran, Dale B. TaulbeeAbstract:The research described in this paper is a numerical inves- tigation of the effects of unsteady flow on gas turbine heat transfer, particularly on a Rotor blade Surface. The un- steady flow in a Rotor blade passage and the unsteady heat transfer on the blade Surface as a result of wake/blade in- teraction are modeled by the inviscid flow/boundary laver approach. The Euler equations which govern the inviscid flow are solved using a time accurate marching scheme. The unsteady flow in the blade passage is induced by pe- riodically moving a wake model across the passage inlet. Unsteady flow solutions in the passage provide pressure gradients and boundary conditions for the boundary-layer equations which govern the viscous flow adjacent to the blade Surface. Numerical solutions of the unsteady turbu- lent boundary layer yield Surface heat flux values which can then be compared to experimental data. Comparisons with experimental data show that unsteady heat flux on the blade suction Surface is well predicted, but the predic- tions of unsteady heat flux on
Manish R. Thorat - One of the best experts on this subject based on the ideXlab platform.
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Predicted Rotordynamic Behavior of a Labyrinth Seal as Rotor Surface Speed Approaches Mach 1
Journal of Engineering for Gas Turbines and Power, 2010Co-Authors: Manish R. Thorat, Dara W ChildsAbstract:Prior one-control-volume (1CV) models for Rotor-fluid interaction in labyrinth seals pro- duce synchronously reduced (at running speed), frequency-independent stiffness and damping coefficients. The 1CV model, consisting of a leakage equation, a continuity equation, and a circumferential-momentum equation (for each cavity), was stated to be invalid for Rotor Surface speeds approaching the speed of sound. However, the present results show that while the 1CV fluid-mechanic model continues to be valid, the calcu- lated Rotordynamic coefficients become strongly dependent on the Rotor’s precession fre- quency. A solution is developed for the reaction-force components for a range of preces- sion frequencies, producing frequency-dependent stiffness and damping coefficients. They can be used to define a Laplace-domain transfer-function model for the reaction-force/ Rotor-motion components. Calculated results are presented for a simple Jeffcott Rotor model acted on by a labyrinth seal. The model’s undamped natural frequency is 7.6 krpm. The fluid properties, seal radius Rs, and running speed ? cause the Rotor Surface velocity Rs ? to equal the speed of sound c0 at ?? 58 krpm. Calculated synchronous-response results due to imbalance coincide for the synchronously reduced and the frequency- dependent models. For an inlet preswirl ratio of 0.5, both models predict the same log-dec out to ? ? 14.5 krpm. The synchronously reduced model predicts an onset speed of instability (OSI) at 10 krpm, but a return to stability at 48 krpm, with subsequent increases in log-dec out to 70 krpm. The frequency-dependent model predicts an OSI of 10 krpm and no return to stability out to 70 krpm. The frequency-dependent models predict small changes in the Rotor’s damped natural frequencies. The synchronously reduced model predicts large changes. The stability-analysis results show that a frequency-dependent labyrinth seal model should be used if the Rotor Surface speed approaches a significant fraction of the speed of sound. For the present example, observ- able discrepancies arose when Rs ?? 0.26c0.
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predicted Rotordynamic behavior of a labyrinth seal as Rotor Surface speed approaches mach 1
ASME Turbo Expo 2009: Power for Land Sea and Air, 2009Co-Authors: Manish R. Thorat, Dara W ChildsAbstract:Prior one-control-volume (1CV) models for Rotor-fluid interaction in labyrinth seals produce synchronously-reduced (at running-speed), frequency-independent stiffness and damping coefficients. The 1CV model, consisting of a leakage equation, a continuity equation, and a circumferential-momentum equation (for each cavity) was stated to be invalid for Rotor Surface speeds approaching the speed of sound. However, the present results show that, while the 1CV fluid-mechanic model continues to be valid, the calculated Rotordynamic coefficients become strongly frequency dependent. A solution is developed for the reaction-force components for a range of precession frequencies, producing frequency-dependent stiffness and damping coefficients. They can be used to define a Laplace-domain transfer-function model for the reaction-force/Rotor-motion components. Calculated Rotordynamic results are presented for a simple Jeffcott Rotor acted on by a labyrinth seal. The seal radius Rs and running speed ω cause the Rotor Surface velocity Rs ω to equal the speed of sound c0 at ω = 58 krpm. Calculated synchronous-response results due to imbalance coincide for the synchronously-reduced and the frequency-dependent models. For an inlet preswirl ratio of 0.5, both models predict the same log decs out to ω≈14.5 krpm. The synchronously-reduced model predicts an onset speed of instability (OSI) at 15 krpm, but a return to stability at 45 krpm, with subsequent increases in log dec out to 65 krpm. The frequency-dependent model predicts an OSI of 65 krpm. The frequency-dependent models predict small changes in the Rotor’s damped natural frequencies. The synchronously-reduced model predicts large changes. The stability-analysis results show that a frequency-dependent labyrinth seal model should be used if the Rotor Surface speed approaches a significant fraction of the speed of sound. For the present example, observable discrepancies arose when Rs ω = 0.26 c0 .© 2009 ASME
