The Experts below are selected from a list of 2055 Experts worldwide ranked by ideXlab platform
Tom Heuer - One of the best experts on this subject based on the ideXlab platform.
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Thermomechanical Analysis of Transient Temperatures in a Radial Turbine Wheel
Journal of Turbomachinery, 2017Co-Authors: Mathias Diefenthal, Christian Rakut, Manfred Wirsum, Piotr Łuczyński, Tom HeuerAbstract:In turbomachinery design, the accurate prediction of the life cycle is one of the most challenging issues. Traditionally, life cycle calculations for radial Turbine Wheels of turbochargers focus on mechanical loads such as centrifugal and vibration forces. Due to the increase of exhaust gas temperatures in the last years, thermomechanical fatigue in the Turbine Wheel came more into focus. In order to account for the thermally induced stresses in the Turbine Wheel as a part of the standard design process, a fast method is required for predicting metal temperatures. In order to develop a suitable method, the mechanisms that cause the thermal stresses have to be understood. Thus, in a first step, a detailed analysis of the temperature fields is conducted in the present paper. Extensive numerical simulations of a thermal shock process are carried out and validated by experimental data from a test rig. Based on the results, the main heat transfer mechanisms are identified, which are crucial for the critical thermal stresses in transient operation. It is shown that these critical stresses mainly depend on local 3D flow structures. With this understanding, two fast methods to calculate the transient temperatures in a radial Turbine were developed. The first method is based on a standard method for transient fluid/solid heat transfer. In this standard method, heat transfer coefficients are derived from steady-state computational fluid dynamics (CFD)/conjugate heat transfer (CHT) calculations and are linearly interpolated over the duration of the transient heating or cooling process. In the new method, this interpolation procedure was modified to achieve an exponential behavior of the heat transfer coefficients over the transient process in order to enable a sufficient accuracy. Additionally, a second method was developed. In this method, the specific heat capacity of the solid state is reduced by a “speed up factor” to shorten the duration of the transient heating or cooling process. With the shortened processes, the computing times can be reduced significantly. After the calculations, the resulting times are transferred into realistic heating or cooling times by multiplying them with the speed up factor. The results of both methods are evaluated against experimental data and against the results of a numerical method known from literature. The methods show a good agreement with those data.
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Analysis of Heat Transfer in a Radial Turbine Wheel of Turbochargers and Prediction of Heat Transfer Coefficients With an Empirical Method
Volume 8: Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2016Co-Authors: Christian Rakut, Mathias Diefenthal, Manfred Wirsum, Tom HeuerAbstract:The accurate prediction of the life cycle is one of the most challenging issues in turbomachinery design. Nowadays life cycle calculations for radial Turbines focus on mechanical loads such as centrifugal and vibration forces. Because of enhanced Turbine inlet temperatures with inevitably increasing thermal stress, the requirements in the design process of Turbine Wheels become higher. Therefore, it is desirable to know the temperature profile and thus the thermal stress in the Turbine Wheel as early as possible in the design process for steady state operating points and transient operation. This paper reports the development of a fast empirical method to calculate the heat transfer coefficients on the surface of a radial Turbine Wheel for steady state operating points. In order to do this, steady state Conjugate Heat Transfer (CHT) investigations of a turbocharger Turbine Wheel for commercial application were performed to model the heat transfer between the fluid and the solid state. These investigations provide a basis for the analysis and characterization of the heat transfer distribution at the Turbine Wheel and the flow phenomena that cause these. The empirical method for determining heat transfer coefficients of a Turbine Wheel is developed based on the numerical results. To model the local different heat transfer coefficients the Turbine Wheel is divided in several surface segments which correspond to the geometry of a radial Turbine Wheel. To validate the method the heat transfer coefficients from the empirical model are used as boundary conditions for a subsequent Finite Element Analysis (FEA). The calculated temperatures of the FEA results are compared to those of the CHT simulation and to the experimental data. For operating points with a circumferential velocity of u ≤ 0.75 u0 a good agreement are reached. The deviations increase for higher circumferential velocities. Furthermore the number of surface segments is varied to show the influence of the segmentation level to the temperature profile. It is also possible to reach a good agreement for operating points of u ≥ 0.75 u0 if the blade is segmented over its height. With the presented method a fast prediction of the heat transfer coefficients and the steady state temperature field of the Turbine Wheel are possible for steady state operating points.
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Thermomechanical Analysis of Transient Temperatures in a Radial Turbine Wheel
Volume 8: Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2016Co-Authors: Mathias Diefenthal, Christian Rakut, Manfred Wirsum, Michael Hopfinger, Tom HeuerAbstract:In turbomachinery design the accurate prediction of the life cycle is one of the most challenging issues. Traditionally, life cycle calculations for radial Turbine Wheels of turbochargers focus on mechanical loads such as centrifugal and vibration forces. Due to the increase in exhaust gas temperatures in the last years, thermomechanical fatigue in the Turbine Wheel came more into focus. In order to account for the thermally induced stresses in the Turbine Wheel as a part of the standard design process, a fast method is required for predicting metal temperatures.In order to develop a suitable method, the mechanisms have to be understood that cause the thermal stresses. Thus, in a first step a detailed analysis of the temperature fields is conducted in the present paper. Extensive numerical simulations of a thermal shock process are carried out and validated by experimental data from a test rig. Based on the results the main heat transfer mechanisms are identified, that are crucial for the critical thermal stresses in transient operation. It is shown that these critical stresses mainly depend on local 3D flow structures.With this understanding, a fast method to calculate the transient temperatures in a radial Turbine was developed. It is based on a standard method for transient fluid/solid heat transfer. This standard method was modified in order to achieve a sufficient accuracy in the calculation of the investigated heat transfer processes. The results show a good agreement with experimental data and with the results of the extensive numerical calculations.© 2016 ASME
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Experimental Investigation of Steady State and Transient Heat Transfer in a Radial Turbine Wheel of a Turbocharger
Volume 8: Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2015Co-Authors: Hailu Tadesse, Mathias Diefenthal, Christian Rakut, Manfred Wirsum, Tom HeuerAbstract:Turbochargers make an essential contribution to the development of efficient combustion engines by increasing the boost pressure. In recent years, there has been a trend towards enhanced Turbine inlet temperatures, which cause heat fluxes within the turbocharger. Due to the high rotational speed, the centrifugal force and thermal stress of the Turbine components rise inevitably. In addition to the enhanced temperature level, due to the variation of the load and speed of the engine in cold start, acceleration and deceleration periods, the Turbine inlet temperature is changing permanently, which leads to higher thermal loads. The flow state and thus the heat transfer in the turbocharger are constantly changing within a single cycle. This induces an unsteady temperature profile, which is essential for the thermal stress and thus the prediction of the component life cycle.The present study reports about the results of the experimental steady state and transient heat transfer investigations of a turbocharger which are conducted at a hot gas test rig. The investigations are performed transiently between different steady state operating points. In order to simulate the real driving conditions, the Turbine inlet temperature is changed between a high and low temperature level abruptly (thermal shock) or cyclically at an approximately constant mass flow. The flow parameters at the inlet and outlet of the Turbine as well as material and surface temperatures of the Turbine Wheel and casing are recorded. Additionally the compressor as well as the bearing housing inlet and outlet conditions are measured. The heat flux between the components is analyzed by means of the measured data.Copyright © 2015 by ASME
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Experimental and Numerical Investigation of Temperature Fields in a Radial Turbine Wheel
Volume 1B: Marine; Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2014Co-Authors: Mathias Diefenthal, Christian Rakut, Manfred Wirsum, Hailu Tadesse, Tom HeuerAbstract:Due to increasing demands on the efficiency of modern Otto and Diesel engines, turbochargers are subjected to higher temperatures. In consequence rotor speed and temperature gradients in transient operations are more severe and therefore thermal and centrifugal stresses increase.To determine the life cycle of turbochargers more precisely, the exact knowledge of the transient temperature distribution in the Turbine Wheel is essential.To assess these temperature distributions, experimental and numerical investigations on a turbocharger of a commercial vehicle were performed. For this purpose, four thermocouples were applied on the shaft and the Turbine Wheel. The measured temperatures are used to determine the boundary conditions for the numerical calculations and to validate the results.In the numerical investigations three methods are used to determine and to analyse the transient solid body temperature distribution in respect of the fluid. The methods are compared and evaluated using the measured data. Based on the calculations the transient temperature field is discussed and conclusions concerning to the thermal stresses are drawn.Copyright © 2014 by ASME
Mathias Diefenthal - One of the best experts on this subject based on the ideXlab platform.
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Thermomechanical Analysis of Transient Temperatures in a Radial Turbine Wheel
Journal of Turbomachinery, 2017Co-Authors: Mathias Diefenthal, Christian Rakut, Manfred Wirsum, Piotr Łuczyński, Tom HeuerAbstract:In turbomachinery design, the accurate prediction of the life cycle is one of the most challenging issues. Traditionally, life cycle calculations for radial Turbine Wheels of turbochargers focus on mechanical loads such as centrifugal and vibration forces. Due to the increase of exhaust gas temperatures in the last years, thermomechanical fatigue in the Turbine Wheel came more into focus. In order to account for the thermally induced stresses in the Turbine Wheel as a part of the standard design process, a fast method is required for predicting metal temperatures. In order to develop a suitable method, the mechanisms that cause the thermal stresses have to be understood. Thus, in a first step, a detailed analysis of the temperature fields is conducted in the present paper. Extensive numerical simulations of a thermal shock process are carried out and validated by experimental data from a test rig. Based on the results, the main heat transfer mechanisms are identified, which are crucial for the critical thermal stresses in transient operation. It is shown that these critical stresses mainly depend on local 3D flow structures. With this understanding, two fast methods to calculate the transient temperatures in a radial Turbine were developed. The first method is based on a standard method for transient fluid/solid heat transfer. In this standard method, heat transfer coefficients are derived from steady-state computational fluid dynamics (CFD)/conjugate heat transfer (CHT) calculations and are linearly interpolated over the duration of the transient heating or cooling process. In the new method, this interpolation procedure was modified to achieve an exponential behavior of the heat transfer coefficients over the transient process in order to enable a sufficient accuracy. Additionally, a second method was developed. In this method, the specific heat capacity of the solid state is reduced by a “speed up factor” to shorten the duration of the transient heating or cooling process. With the shortened processes, the computing times can be reduced significantly. After the calculations, the resulting times are transferred into realistic heating or cooling times by multiplying them with the speed up factor. The results of both methods are evaluated against experimental data and against the results of a numerical method known from literature. The methods show a good agreement with those data.
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Analysis of Heat Transfer in a Radial Turbine Wheel of Turbochargers and Prediction of Heat Transfer Coefficients With an Empirical Method
Volume 8: Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2016Co-Authors: Christian Rakut, Mathias Diefenthal, Manfred Wirsum, Tom HeuerAbstract:The accurate prediction of the life cycle is one of the most challenging issues in turbomachinery design. Nowadays life cycle calculations for radial Turbines focus on mechanical loads such as centrifugal and vibration forces. Because of enhanced Turbine inlet temperatures with inevitably increasing thermal stress, the requirements in the design process of Turbine Wheels become higher. Therefore, it is desirable to know the temperature profile and thus the thermal stress in the Turbine Wheel as early as possible in the design process for steady state operating points and transient operation. This paper reports the development of a fast empirical method to calculate the heat transfer coefficients on the surface of a radial Turbine Wheel for steady state operating points. In order to do this, steady state Conjugate Heat Transfer (CHT) investigations of a turbocharger Turbine Wheel for commercial application were performed to model the heat transfer between the fluid and the solid state. These investigations provide a basis for the analysis and characterization of the heat transfer distribution at the Turbine Wheel and the flow phenomena that cause these. The empirical method for determining heat transfer coefficients of a Turbine Wheel is developed based on the numerical results. To model the local different heat transfer coefficients the Turbine Wheel is divided in several surface segments which correspond to the geometry of a radial Turbine Wheel. To validate the method the heat transfer coefficients from the empirical model are used as boundary conditions for a subsequent Finite Element Analysis (FEA). The calculated temperatures of the FEA results are compared to those of the CHT simulation and to the experimental data. For operating points with a circumferential velocity of u ≤ 0.75 u0 a good agreement are reached. The deviations increase for higher circumferential velocities. Furthermore the number of surface segments is varied to show the influence of the segmentation level to the temperature profile. It is also possible to reach a good agreement for operating points of u ≥ 0.75 u0 if the blade is segmented over its height. With the presented method a fast prediction of the heat transfer coefficients and the steady state temperature field of the Turbine Wheel are possible for steady state operating points.
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Thermomechanical Analysis of Transient Temperatures in a Radial Turbine Wheel
Volume 8: Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2016Co-Authors: Mathias Diefenthal, Christian Rakut, Manfred Wirsum, Michael Hopfinger, Tom HeuerAbstract:In turbomachinery design the accurate prediction of the life cycle is one of the most challenging issues. Traditionally, life cycle calculations for radial Turbine Wheels of turbochargers focus on mechanical loads such as centrifugal and vibration forces. Due to the increase in exhaust gas temperatures in the last years, thermomechanical fatigue in the Turbine Wheel came more into focus. In order to account for the thermally induced stresses in the Turbine Wheel as a part of the standard design process, a fast method is required for predicting metal temperatures.In order to develop a suitable method, the mechanisms have to be understood that cause the thermal stresses. Thus, in a first step a detailed analysis of the temperature fields is conducted in the present paper. Extensive numerical simulations of a thermal shock process are carried out and validated by experimental data from a test rig. Based on the results the main heat transfer mechanisms are identified, that are crucial for the critical thermal stresses in transient operation. It is shown that these critical stresses mainly depend on local 3D flow structures.With this understanding, a fast method to calculate the transient temperatures in a radial Turbine was developed. It is based on a standard method for transient fluid/solid heat transfer. This standard method was modified in order to achieve a sufficient accuracy in the calculation of the investigated heat transfer processes. The results show a good agreement with experimental data and with the results of the extensive numerical calculations.© 2016 ASME
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Experimental Investigation of Steady State and Transient Heat Transfer in a Radial Turbine Wheel of a Turbocharger
Volume 8: Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2015Co-Authors: Hailu Tadesse, Mathias Diefenthal, Christian Rakut, Manfred Wirsum, Tom HeuerAbstract:Turbochargers make an essential contribution to the development of efficient combustion engines by increasing the boost pressure. In recent years, there has been a trend towards enhanced Turbine inlet temperatures, which cause heat fluxes within the turbocharger. Due to the high rotational speed, the centrifugal force and thermal stress of the Turbine components rise inevitably. In addition to the enhanced temperature level, due to the variation of the load and speed of the engine in cold start, acceleration and deceleration periods, the Turbine inlet temperature is changing permanently, which leads to higher thermal loads. The flow state and thus the heat transfer in the turbocharger are constantly changing within a single cycle. This induces an unsteady temperature profile, which is essential for the thermal stress and thus the prediction of the component life cycle.The present study reports about the results of the experimental steady state and transient heat transfer investigations of a turbocharger which are conducted at a hot gas test rig. The investigations are performed transiently between different steady state operating points. In order to simulate the real driving conditions, the Turbine inlet temperature is changed between a high and low temperature level abruptly (thermal shock) or cyclically at an approximately constant mass flow. The flow parameters at the inlet and outlet of the Turbine as well as material and surface temperatures of the Turbine Wheel and casing are recorded. Additionally the compressor as well as the bearing housing inlet and outlet conditions are measured. The heat flux between the components is analyzed by means of the measured data.Copyright © 2015 by ASME
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Experimental and Numerical Investigation of Temperature Fields in a Radial Turbine Wheel
Volume 1B: Marine; Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2014Co-Authors: Mathias Diefenthal, Christian Rakut, Manfred Wirsum, Hailu Tadesse, Tom HeuerAbstract:Due to increasing demands on the efficiency of modern Otto and Diesel engines, turbochargers are subjected to higher temperatures. In consequence rotor speed and temperature gradients in transient operations are more severe and therefore thermal and centrifugal stresses increase.To determine the life cycle of turbochargers more precisely, the exact knowledge of the transient temperature distribution in the Turbine Wheel is essential.To assess these temperature distributions, experimental and numerical investigations on a turbocharger of a commercial vehicle were performed. For this purpose, four thermocouples were applied on the shaft and the Turbine Wheel. The measured temperatures are used to determine the boundary conditions for the numerical calculations and to validate the results.In the numerical investigations three methods are used to determine and to analyse the transient solid body temperature distribution in respect of the fluid. The methods are compared and evaluated using the measured data. Based on the calculations the transient temperature field is discussed and conclusions concerning to the thermal stresses are drawn.Copyright © 2014 by ASME
Christian Rakut - One of the best experts on this subject based on the ideXlab platform.
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Thermomechanical Analysis of Transient Temperatures in a Radial Turbine Wheel
Journal of Turbomachinery, 2017Co-Authors: Mathias Diefenthal, Christian Rakut, Manfred Wirsum, Piotr Łuczyński, Tom HeuerAbstract:In turbomachinery design, the accurate prediction of the life cycle is one of the most challenging issues. Traditionally, life cycle calculations for radial Turbine Wheels of turbochargers focus on mechanical loads such as centrifugal and vibration forces. Due to the increase of exhaust gas temperatures in the last years, thermomechanical fatigue in the Turbine Wheel came more into focus. In order to account for the thermally induced stresses in the Turbine Wheel as a part of the standard design process, a fast method is required for predicting metal temperatures. In order to develop a suitable method, the mechanisms that cause the thermal stresses have to be understood. Thus, in a first step, a detailed analysis of the temperature fields is conducted in the present paper. Extensive numerical simulations of a thermal shock process are carried out and validated by experimental data from a test rig. Based on the results, the main heat transfer mechanisms are identified, which are crucial for the critical thermal stresses in transient operation. It is shown that these critical stresses mainly depend on local 3D flow structures. With this understanding, two fast methods to calculate the transient temperatures in a radial Turbine were developed. The first method is based on a standard method for transient fluid/solid heat transfer. In this standard method, heat transfer coefficients are derived from steady-state computational fluid dynamics (CFD)/conjugate heat transfer (CHT) calculations and are linearly interpolated over the duration of the transient heating or cooling process. In the new method, this interpolation procedure was modified to achieve an exponential behavior of the heat transfer coefficients over the transient process in order to enable a sufficient accuracy. Additionally, a second method was developed. In this method, the specific heat capacity of the solid state is reduced by a “speed up factor” to shorten the duration of the transient heating or cooling process. With the shortened processes, the computing times can be reduced significantly. After the calculations, the resulting times are transferred into realistic heating or cooling times by multiplying them with the speed up factor. The results of both methods are evaluated against experimental data and against the results of a numerical method known from literature. The methods show a good agreement with those data.
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Analysis of Heat Transfer in a Radial Turbine Wheel of Turbochargers and Prediction of Heat Transfer Coefficients With an Empirical Method
Volume 8: Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2016Co-Authors: Christian Rakut, Mathias Diefenthal, Manfred Wirsum, Tom HeuerAbstract:The accurate prediction of the life cycle is one of the most challenging issues in turbomachinery design. Nowadays life cycle calculations for radial Turbines focus on mechanical loads such as centrifugal and vibration forces. Because of enhanced Turbine inlet temperatures with inevitably increasing thermal stress, the requirements in the design process of Turbine Wheels become higher. Therefore, it is desirable to know the temperature profile and thus the thermal stress in the Turbine Wheel as early as possible in the design process for steady state operating points and transient operation. This paper reports the development of a fast empirical method to calculate the heat transfer coefficients on the surface of a radial Turbine Wheel for steady state operating points. In order to do this, steady state Conjugate Heat Transfer (CHT) investigations of a turbocharger Turbine Wheel for commercial application were performed to model the heat transfer between the fluid and the solid state. These investigations provide a basis for the analysis and characterization of the heat transfer distribution at the Turbine Wheel and the flow phenomena that cause these. The empirical method for determining heat transfer coefficients of a Turbine Wheel is developed based on the numerical results. To model the local different heat transfer coefficients the Turbine Wheel is divided in several surface segments which correspond to the geometry of a radial Turbine Wheel. To validate the method the heat transfer coefficients from the empirical model are used as boundary conditions for a subsequent Finite Element Analysis (FEA). The calculated temperatures of the FEA results are compared to those of the CHT simulation and to the experimental data. For operating points with a circumferential velocity of u ≤ 0.75 u0 a good agreement are reached. The deviations increase for higher circumferential velocities. Furthermore the number of surface segments is varied to show the influence of the segmentation level to the temperature profile. It is also possible to reach a good agreement for operating points of u ≥ 0.75 u0 if the blade is segmented over its height. With the presented method a fast prediction of the heat transfer coefficients and the steady state temperature field of the Turbine Wheel are possible for steady state operating points.
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Thermomechanical Analysis of Transient Temperatures in a Radial Turbine Wheel
Volume 8: Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2016Co-Authors: Mathias Diefenthal, Christian Rakut, Manfred Wirsum, Michael Hopfinger, Tom HeuerAbstract:In turbomachinery design the accurate prediction of the life cycle is one of the most challenging issues. Traditionally, life cycle calculations for radial Turbine Wheels of turbochargers focus on mechanical loads such as centrifugal and vibration forces. Due to the increase in exhaust gas temperatures in the last years, thermomechanical fatigue in the Turbine Wheel came more into focus. In order to account for the thermally induced stresses in the Turbine Wheel as a part of the standard design process, a fast method is required for predicting metal temperatures.In order to develop a suitable method, the mechanisms have to be understood that cause the thermal stresses. Thus, in a first step a detailed analysis of the temperature fields is conducted in the present paper. Extensive numerical simulations of a thermal shock process are carried out and validated by experimental data from a test rig. Based on the results the main heat transfer mechanisms are identified, that are crucial for the critical thermal stresses in transient operation. It is shown that these critical stresses mainly depend on local 3D flow structures.With this understanding, a fast method to calculate the transient temperatures in a radial Turbine was developed. It is based on a standard method for transient fluid/solid heat transfer. This standard method was modified in order to achieve a sufficient accuracy in the calculation of the investigated heat transfer processes. The results show a good agreement with experimental data and with the results of the extensive numerical calculations.© 2016 ASME
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Experimental Investigation of Steady State and Transient Heat Transfer in a Radial Turbine Wheel of a Turbocharger
Volume 8: Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2015Co-Authors: Hailu Tadesse, Mathias Diefenthal, Christian Rakut, Manfred Wirsum, Tom HeuerAbstract:Turbochargers make an essential contribution to the development of efficient combustion engines by increasing the boost pressure. In recent years, there has been a trend towards enhanced Turbine inlet temperatures, which cause heat fluxes within the turbocharger. Due to the high rotational speed, the centrifugal force and thermal stress of the Turbine components rise inevitably. In addition to the enhanced temperature level, due to the variation of the load and speed of the engine in cold start, acceleration and deceleration periods, the Turbine inlet temperature is changing permanently, which leads to higher thermal loads. The flow state and thus the heat transfer in the turbocharger are constantly changing within a single cycle. This induces an unsteady temperature profile, which is essential for the thermal stress and thus the prediction of the component life cycle.The present study reports about the results of the experimental steady state and transient heat transfer investigations of a turbocharger which are conducted at a hot gas test rig. The investigations are performed transiently between different steady state operating points. In order to simulate the real driving conditions, the Turbine inlet temperature is changed between a high and low temperature level abruptly (thermal shock) or cyclically at an approximately constant mass flow. The flow parameters at the inlet and outlet of the Turbine as well as material and surface temperatures of the Turbine Wheel and casing are recorded. Additionally the compressor as well as the bearing housing inlet and outlet conditions are measured. The heat flux between the components is analyzed by means of the measured data.Copyright © 2015 by ASME
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Experimental and Numerical Investigation of Temperature Fields in a Radial Turbine Wheel
Volume 1B: Marine; Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2014Co-Authors: Mathias Diefenthal, Christian Rakut, Manfred Wirsum, Hailu Tadesse, Tom HeuerAbstract:Due to increasing demands on the efficiency of modern Otto and Diesel engines, turbochargers are subjected to higher temperatures. In consequence rotor speed and temperature gradients in transient operations are more severe and therefore thermal and centrifugal stresses increase.To determine the life cycle of turbochargers more precisely, the exact knowledge of the transient temperature distribution in the Turbine Wheel is essential.To assess these temperature distributions, experimental and numerical investigations on a turbocharger of a commercial vehicle were performed. For this purpose, four thermocouples were applied on the shaft and the Turbine Wheel. The measured temperatures are used to determine the boundary conditions for the numerical calculations and to validate the results.In the numerical investigations three methods are used to determine and to analyse the transient solid body temperature distribution in respect of the fluid. The methods are compared and evaluated using the measured data. Based on the calculations the transient temperature field is discussed and conclusions concerning to the thermal stresses are drawn.Copyright © 2014 by ASME
Manfred Wirsum - One of the best experts on this subject based on the ideXlab platform.
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Thermomechanical Analysis of Transient Temperatures in a Radial Turbine Wheel
Journal of Turbomachinery, 2017Co-Authors: Mathias Diefenthal, Christian Rakut, Manfred Wirsum, Piotr Łuczyński, Tom HeuerAbstract:In turbomachinery design, the accurate prediction of the life cycle is one of the most challenging issues. Traditionally, life cycle calculations for radial Turbine Wheels of turbochargers focus on mechanical loads such as centrifugal and vibration forces. Due to the increase of exhaust gas temperatures in the last years, thermomechanical fatigue in the Turbine Wheel came more into focus. In order to account for the thermally induced stresses in the Turbine Wheel as a part of the standard design process, a fast method is required for predicting metal temperatures. In order to develop a suitable method, the mechanisms that cause the thermal stresses have to be understood. Thus, in a first step, a detailed analysis of the temperature fields is conducted in the present paper. Extensive numerical simulations of a thermal shock process are carried out and validated by experimental data from a test rig. Based on the results, the main heat transfer mechanisms are identified, which are crucial for the critical thermal stresses in transient operation. It is shown that these critical stresses mainly depend on local 3D flow structures. With this understanding, two fast methods to calculate the transient temperatures in a radial Turbine were developed. The first method is based on a standard method for transient fluid/solid heat transfer. In this standard method, heat transfer coefficients are derived from steady-state computational fluid dynamics (CFD)/conjugate heat transfer (CHT) calculations and are linearly interpolated over the duration of the transient heating or cooling process. In the new method, this interpolation procedure was modified to achieve an exponential behavior of the heat transfer coefficients over the transient process in order to enable a sufficient accuracy. Additionally, a second method was developed. In this method, the specific heat capacity of the solid state is reduced by a “speed up factor” to shorten the duration of the transient heating or cooling process. With the shortened processes, the computing times can be reduced significantly. After the calculations, the resulting times are transferred into realistic heating or cooling times by multiplying them with the speed up factor. The results of both methods are evaluated against experimental data and against the results of a numerical method known from literature. The methods show a good agreement with those data.
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Analysis of Heat Transfer in a Radial Turbine Wheel of Turbochargers and Prediction of Heat Transfer Coefficients With an Empirical Method
Volume 8: Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2016Co-Authors: Christian Rakut, Mathias Diefenthal, Manfred Wirsum, Tom HeuerAbstract:The accurate prediction of the life cycle is one of the most challenging issues in turbomachinery design. Nowadays life cycle calculations for radial Turbines focus on mechanical loads such as centrifugal and vibration forces. Because of enhanced Turbine inlet temperatures with inevitably increasing thermal stress, the requirements in the design process of Turbine Wheels become higher. Therefore, it is desirable to know the temperature profile and thus the thermal stress in the Turbine Wheel as early as possible in the design process for steady state operating points and transient operation. This paper reports the development of a fast empirical method to calculate the heat transfer coefficients on the surface of a radial Turbine Wheel for steady state operating points. In order to do this, steady state Conjugate Heat Transfer (CHT) investigations of a turbocharger Turbine Wheel for commercial application were performed to model the heat transfer between the fluid and the solid state. These investigations provide a basis for the analysis and characterization of the heat transfer distribution at the Turbine Wheel and the flow phenomena that cause these. The empirical method for determining heat transfer coefficients of a Turbine Wheel is developed based on the numerical results. To model the local different heat transfer coefficients the Turbine Wheel is divided in several surface segments which correspond to the geometry of a radial Turbine Wheel. To validate the method the heat transfer coefficients from the empirical model are used as boundary conditions for a subsequent Finite Element Analysis (FEA). The calculated temperatures of the FEA results are compared to those of the CHT simulation and to the experimental data. For operating points with a circumferential velocity of u ≤ 0.75 u0 a good agreement are reached. The deviations increase for higher circumferential velocities. Furthermore the number of surface segments is varied to show the influence of the segmentation level to the temperature profile. It is also possible to reach a good agreement for operating points of u ≥ 0.75 u0 if the blade is segmented over its height. With the presented method a fast prediction of the heat transfer coefficients and the steady state temperature field of the Turbine Wheel are possible for steady state operating points.
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Thermomechanical Analysis of Transient Temperatures in a Radial Turbine Wheel
Volume 8: Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2016Co-Authors: Mathias Diefenthal, Christian Rakut, Manfred Wirsum, Michael Hopfinger, Tom HeuerAbstract:In turbomachinery design the accurate prediction of the life cycle is one of the most challenging issues. Traditionally, life cycle calculations for radial Turbine Wheels of turbochargers focus on mechanical loads such as centrifugal and vibration forces. Due to the increase in exhaust gas temperatures in the last years, thermomechanical fatigue in the Turbine Wheel came more into focus. In order to account for the thermally induced stresses in the Turbine Wheel as a part of the standard design process, a fast method is required for predicting metal temperatures.In order to develop a suitable method, the mechanisms have to be understood that cause the thermal stresses. Thus, in a first step a detailed analysis of the temperature fields is conducted in the present paper. Extensive numerical simulations of a thermal shock process are carried out and validated by experimental data from a test rig. Based on the results the main heat transfer mechanisms are identified, that are crucial for the critical thermal stresses in transient operation. It is shown that these critical stresses mainly depend on local 3D flow structures.With this understanding, a fast method to calculate the transient temperatures in a radial Turbine was developed. It is based on a standard method for transient fluid/solid heat transfer. This standard method was modified in order to achieve a sufficient accuracy in the calculation of the investigated heat transfer processes. The results show a good agreement with experimental data and with the results of the extensive numerical calculations.© 2016 ASME
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Experimental Investigation of Steady State and Transient Heat Transfer in a Radial Turbine Wheel of a Turbocharger
Volume 8: Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2015Co-Authors: Hailu Tadesse, Mathias Diefenthal, Christian Rakut, Manfred Wirsum, Tom HeuerAbstract:Turbochargers make an essential contribution to the development of efficient combustion engines by increasing the boost pressure. In recent years, there has been a trend towards enhanced Turbine inlet temperatures, which cause heat fluxes within the turbocharger. Due to the high rotational speed, the centrifugal force and thermal stress of the Turbine components rise inevitably. In addition to the enhanced temperature level, due to the variation of the load and speed of the engine in cold start, acceleration and deceleration periods, the Turbine inlet temperature is changing permanently, which leads to higher thermal loads. The flow state and thus the heat transfer in the turbocharger are constantly changing within a single cycle. This induces an unsteady temperature profile, which is essential for the thermal stress and thus the prediction of the component life cycle.The present study reports about the results of the experimental steady state and transient heat transfer investigations of a turbocharger which are conducted at a hot gas test rig. The investigations are performed transiently between different steady state operating points. In order to simulate the real driving conditions, the Turbine inlet temperature is changed between a high and low temperature level abruptly (thermal shock) or cyclically at an approximately constant mass flow. The flow parameters at the inlet and outlet of the Turbine as well as material and surface temperatures of the Turbine Wheel and casing are recorded. Additionally the compressor as well as the bearing housing inlet and outlet conditions are measured. The heat flux between the components is analyzed by means of the measured data.Copyright © 2015 by ASME
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Experimental and Numerical Investigation of Temperature Fields in a Radial Turbine Wheel
Volume 1B: Marine; Microturbines Turbochargers and Small Turbomachines; Steam Turbines, 2014Co-Authors: Mathias Diefenthal, Christian Rakut, Manfred Wirsum, Hailu Tadesse, Tom HeuerAbstract:Due to increasing demands on the efficiency of modern Otto and Diesel engines, turbochargers are subjected to higher temperatures. In consequence rotor speed and temperature gradients in transient operations are more severe and therefore thermal and centrifugal stresses increase.To determine the life cycle of turbochargers more precisely, the exact knowledge of the transient temperature distribution in the Turbine Wheel is essential.To assess these temperature distributions, experimental and numerical investigations on a turbocharger of a commercial vehicle were performed. For this purpose, four thermocouples were applied on the shaft and the Turbine Wheel. The measured temperatures are used to determine the boundary conditions for the numerical calculations and to validate the results.In the numerical investigations three methods are used to determine and to analyse the transient solid body temperature distribution in respect of the fluid. The methods are compared and evaluated using the measured data. Based on the calculations the transient temperature field is discussed and conclusions concerning to the thermal stresses are drawn.Copyright © 2014 by ASME
M C Zhang - One of the best experts on this subject based on the ideXlab platform.
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Solidification characteristics and hot tearing susceptibility of Ni-based superalloys for turbocharger Turbine Wheel
Transactions of Nonferrous Metals Society of China, 2014Co-Authors: Z.-x. Shi, J. X. Dong, M C Zhang, Lei ZhengAbstract:Abstract The solidification characteristics and the hot tearing susceptibility were investigated on two Ni-based superalloys for turbocharger Turbine Wheel, K418 and K419. The segregation behaviors of the alloying elements and the precipitation phases were also studied. The results show that the solidification behavior of K419 alloy is complicated when compared with K418 due to the interdendritic segregation of many kinds of strong interdendritic partitioning elements in the remaining liquid at the final stage of solidification. The segregation of multiple elements in interdendritic liquid results in an extremely low solidus in K419. A long residual liquid stage is found during the solidification of K419, giving rise to reduced cohesion strength of dendrites and increased sensitivity to hot tearing. A hot tearing susceptibility coefficient (HTS) criterion is proposed based on a hot tearing sensitive model. The HTS value of K419 alloy is larger than that of K418 alloy.
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Microstructure and Hot Tearing Susceptibility of K418 and K419 Superalloy for Auto Turbocharger Turbine Wheel
Materials Science Forum, 2013Co-Authors: Z.-x. Shi, J. X. Dong, M C ZhangAbstract:K419 superalloy Turbine Wheel was more susceptible to hot tearing than K418 one when they were used for auto turbocharger Turbine Wheel. The fracture and microstructure characteristics in the K418 and K419 Turbine Wheel blades were analyzed. The segregation of alloying elements was analyzed by EDS. The probable equilibrium phases in the two kinds of superalloys, the effects of aluminum, titanium and niobium contents on the precipitation of γ and γ/γ eutectic phase and the segregation of alloying elements were studied by Thermo-Calc software. The results show that the hot tearing in the K418 and K419 superalloy Turbine Wheel blades is caused by the fracture of dendrites structures, while the amount of γ/γ eutectic in K419 is more than that in K418, resulting in K419 being more susceptible to hot tearing. Titanium and niobium, the strong positive segregation elements promote the formation of γ/γ eutectic, which lead to severe hot tearing susceptibility of the superalloy.
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Development of hot tearing on cast superalloys used for auto turbocharger Turbine Wheel
Cailiao Gongcheng Journal of Materials Engineering, 2012Co-Authors: Z.-x. Shi, J. X. Dong, M C ZhangAbstract:Hot tearing tended to occur in the Turbine Wheel blade when superalloys were used for auto turbocharger Turbine Wheel, which affected the application of cast superalloys used in turbocharger Turbine Wheel. Several cast superalloys which were currently widely used in auto turbocharger Turbine Wheel were introduced. The hot tearing mechanisms for castings were reviewed. Effects of the elements, such as Al, Ti, C, Zr and Hf on hot tearing susceptibility of cast superalloys were emphatically analyzed. Effects of solidification mode of superalloys and casting process parameters, such as characteristics of moulds, pouring conditions, constructions of castings and pouring system on hot tearing were also reviewed. In addition, measures to prevent hot tearing were proposed.
