HCF Optimization of a High Speed Variable Geometry Turbine

2021 ◽  
Author(s):  
Alister Simpson ◽  
Sung in Kim ◽  
Jongyoon Park ◽  
Seong Kwon ◽  
Sejong Yoo
Keyword(s):  
High Speed ◽  
Forced Response ◽  
Variable Geometry ◽  
Blade Vibration ◽  
Operating Cycle ◽  
Turbine Wheel ◽  
Aerodynamic Loads ◽  
Radial Turbine ◽  
Wide Range ◽  
Variable Geometry Turbine

Abstract This paper describes the structural optimization of a high speed, 35mm tip diameter radial turbine wheel in a Variable Geometry Turbine (VGT) system, subjected to the wide range of aerodynamic loads experienced during the full operating cycle. VGTs exhibit a wide range of unsteady flow features, which vary as the nozzle vanes rotate through different positions during operation, as do the magnitudes and frequencies of the resulting pressure fluctuations experienced by the downstream turbine blades. The turbine wheel typically passes through a number of blade natural frequencies over their operating cycle, and there are a number of potential conditions where these unsteady aerodynamic loads can lead to resonant blade vibration. The focus of this work is on the development of a pragmatic design approach to improve the structural characteristics of a radial turbine blade with respect to High Cycle Fatigue (HCF), informed by detailed time-accurate Computational Fluid Dynamics (CFD) prediction of the unsteady pressure loads, coupled with FE vibration analysis to quantify the resulting blade vibration magnitudes. Unsteady CFD simulations are performed to determine the time-accurate pressure loads on the blades, and the results are used as input to forced response analysis to determine the peak alternating stress amplitudes. The detailed analysis results are then used to guide a subsequent parametric study in order to investigate the influence of key geometric parameters on the structural performance of the blade, with the optimum design identified through the use of a Goodman Diagram. The results quantify the influence of both blade thickness distribution and hub fillet details on the vibration characteristics of radial turbines.

Influence of Aerodynamic Mistuning and Aerodynamic Coupling on Vibration Behavior of Mistuned Small Radial Turbine Wheels

2017 ◽  
Author(s):  
David Hemberger ◽  
Dietmar Filsinger ◽  
Hans-Jörg Bauer
Keyword(s):  
Forced Response ◽  
Laser Vibrometer ◽  
Fe Model ◽  
Blade Vibration ◽  
Turbine Wheel ◽  
Vibration Measurements ◽  
Guide Vanes ◽  
Vibration Behavior ◽  
Operation Conditions ◽  
Radial Turbine

The study at hand analyzes the influence of aerodynamic mistuning and aerodynamic coupling on the vibration behavior of mistuned small radial turbine wheels. The aerodynamic mistuning is caused by angular non uniformity of the variable turbine guide vanes. Variable turbine guide vanes are state of the art in exhaust gas turbochargers for automotive diesel engines. Aerodynamic coupling describes the coupling of the turbine blades through the flow. It can influence the mistuned vibration behavior of the turbine wheel due to varying operation conditions, in which the turbine pressure ratio and the pressure distribution over the turbine wheel surface is changed. It was analyzed whether the aerodynamic mistuning and aerodynamic coupling must be considered for small radial turbine wheel designs. The basis for this investigation were blade vibration measurements under standstill conditions with a laser vibrometer as well as blade vibration measurements during operation with a tip timing system. The mistuned turbine eigenforms were analyzed and compared at various ambient conditions using these measurement results. By means of forced response calculations — unsteady 3D CFD and 3D FEA —, the influence of aerodynamic mistuning on the ideal tuned turbine was examined to be able to separate the aerodynamic mistuning from the mistuning of the structure. Furthermore, the superimposed effect of the aerodynamic mistuning and the mistuning of the structure on the turbine eigenforms and the amplitude amplification was analyzed using a mistuned 3D FE model and a population of samples with varying aerodynamic mistuning. It was found, that the aerodynamic coupling and aerodynamic mistuning have a negligible effect on the mistuned vibration behavior for a small radial turbine with variable turbine guide vanes. These two parameters must not be considered when designing such a turbine wheel.

Numerical Investigation of a Novel Approach for Mitigation of Forced Response of a Variable Geometry Turbine During Exhaust Braking Mode

2016 ◽  
Author(s):  
Ben Zhao ◽  
Leon Hu ◽  
Harold Sun ◽  
Ce Yang ◽  
Xin Shi ◽  
...  
Keyword(s):  
Shock Wave ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Forced Response ◽  
Aerodynamic Load ◽  
Variable Geometry ◽  
Original Design ◽  
Turbine Wheel ◽  
Nozzle Vane ◽  
Variable Geometry Turbine

One of critical concerns in a variable geometry turbine (VGT) design program is shock wave generated from nozzle exit at small open conditions with high inlet pressure condition, which may potentially lead to forced response of turbine wheel, even high-cycle fatigue issues and damage of inducer or exducer. Though modern turbine design programs have been well developed, it is difficult to eliminate the shock wave and all the resonant crossings that may occur within the wide operating range of a VGT turbine for automotive applications. This paper presents an option to mitigate intensity of the shock wave induced excitation using grooves on nozzle vane surface before the shock wave. Two kinds of turbines in which nozzle vanes with and without grooves were numerically simulated to obtain a three-dimensional flow field inside the turbine. The predicted performances from steady simulations were compared with test data to validate computational mesh and the unsteady simulation results were analyzed in detail to predict the responses of both shock wave and aerodynamic load acting on turbine blade surface. Compared with the original design, an introduction of grooves on nozzle vane surface mitigates the shock wave while also obviously reduces the amplitudes of alternating aerodynamic load on the turbine blades.

Aerodynamic Design of Fixed and Variable Geometry Nozzleless Turbine Casings

1980 ◽  
Vol 102 (1) ◽  
pp. 141-147 ◽  
Author(s):  
P. M. Chappie ◽  
P. F. Flynn ◽  
J. M. Mulloy
Keyword(s):  
Design Method ◽  
Pressure Ratio ◽  
Wall Friction ◽  
Variable Geometry ◽  
Aerodynamic Design ◽  
Blade Vibration ◽  
Turbine Wheel ◽  
Design Constraints ◽  
Variable Geometry Turbine ◽  
Turbine Casing

A design method has been developed to produce nozzleless turbine casings which provide a centrifugal turbine wheel with a uniform inlet state. The analysis includes the effect of wall friction and has been found to accurately predict the mass flow versus pressure ratio characteristics of nozzleless casings. The uniform inlet state provided by this design approach provides turbine wheel/casing configurations with near optimum efficiency and a very low aerodynamic blade vibration excitation level. The model has been extended to produce variable area casings to simulate a simplified variable casing geometry. Testing has verified the accuracy of the approach both in the design point and variable geometry cases. Also depicted are new insights into turbine wheel design constraints discovered when using a variable geometry turbine casing.

Mistuning and Damping of a Radial Turbine Wheel. Part 1: Fundamental Analyses and Design of Intentional Mistuning Pattern

2021 ◽  
Author(s):  
Alex Nakos ◽  
Bernd Beirow ◽  
Arthur Zobel
Keyword(s):  
High Stress ◽  
Forced Response ◽  
Experimental Investigations ◽  
Detailed Knowledge ◽  
Turbine Wheel ◽  
Operation Conditions ◽  
Radial Turbine ◽  
Influence Coefficients ◽  
Modes Of Vibration ◽  
The Impact

Abstract The radial turbine impeller of an exhaust turbocharger is analyzed in view of both free vibration and forced response. Due to random blade mistuning resulting from unavoidable inaccuracies in manufacture or material inhomogeneities, localized modes of vibration may arise, which involve the risk of severely magnified blade displacements and inadmissibly high stress levels compared to the tuned counterpart. Contrary, the use of intentional mistuning (IM) has proved to be an efficient measure to mitigate the forced response. Independently, the presence of aerodynamic damping is significant with respect to limit the forced response since structural damping ratios of integrally bladed rotors typically take extremely low values. Hence, a detailed knowledge of respective damping ratios would be desirable while developing a robust rotor design. For this, far-reaching experimental investigations are carried out to determine the damping of a comparative wheel within a wide pressure range by simulating operation conditions in a pressure tank. Reduced order models are built up for designing suitable intentional mistuning patterns by using the subset of nominal system modes (SNM) approach introduced by Yang and Griffin [1], which conveniently allows for accounting both differing mistuning patterns and the impact of aeroelastic interaction by means of aerodynamic influence coefficients (AIC). Further, finite element analyses are carried out in order to identify appropriate measures how to implement intentional mistuning patterns, which are featuring only two different blade designs. In detail, the impact of specific geometric modifications on blade natural frequencies is investigated.

Behavior of a Variable Geometry Turbine Wheel to High Cycle Fatigue

2020 ◽  
Author(s):  
Calogero Avola ◽  
Alberto Racca ◽  
Angelo Montanino ◽  
Carnell E. Williams ◽  
Alfonso Renella ◽  
...  
Keyword(s):  
High Cycle Fatigue ◽  
Combustion Engine ◽  
Turbine Blades ◽  
Variable Geometry ◽  
Cycle Fatigue ◽  
Turbine Stage ◽  
Turbine Wheel ◽  
Variable Geometry Turbine ◽  
Turbine Design ◽  
Mechanical Optimization

Abstract Maximization of the turbocharger efficiency is fundamental to the reduction of the internal combustion engine back-pressure. Specifically, in turbochargers with a variable geometry turbine (VGT), energy losses can be induced by the aerodynamic profile of both the nozzle vanes and the turbine blades. Although appropriate considerations on material limits and structural performance of the turbine wheel are monitored in the design and aero-mechanical optimization phases, in these stages, fatigue phenomena might be ignored. Fatigue occurrence in VGT wheels can be categorized into low and high cycle behaviors. The former would be induced by the change in turbine rotational speed in time, while the latter would be caused by the interaction between the aerodynamic excitation and blades resonating modes. In this paper, an optimized turbine stage, including unique nozzle vanes design and turbine blades profile, has been assessed for high cycle fatigue (HCF) behavior. To estimate the robustness of the turbine wheel under several powertrain operations, a procedure to evaluate HCF behavior has been developed. Specifically, the HCF procedure tries to identify the possible resonances between the turbine blades frequency of vibrations and the excitation order induced by the number of variable vanes. Moreover, the method evaluates the turbine design robustness by checking the stress levels in the component against the limits imposed by the Goodman law of the material selected for the turbine wheel. In conclusion, both the VGT design and the HCF approach are experimentally assessed.

Forced Response Analyses of Mistuned Radial Inflow Turbines

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Thomas Giersch ◽  
Peter Hönisch ◽  
Bernd Beirow ◽  
Arnold Kühhorn
Keyword(s):  
Numerical Method ◽  
Fluid Structure Interaction ◽  
Industrial Applications ◽  
Forced Response ◽  
Blade Vibration ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Aerodynamic Damping ◽  
Radial Turbine ◽  
Spiral Casing

Radial turbine wheels designed as blade integrated disks (blisk) are widely used in various industrial applications. However, related to the introduction of exhaust gas turbochargers in the field of small and medium sized engines, a sustainable demand for radial turbine wheels has come along. Despite those blisks being state of the art, a number of fundamental problems, mainly referring to fluid-structure-interaction and, therefore, to the vibration behavior, have been reported. Aiming to achieve an enhanced understanding of fluid-structure-interaction in radial turbine wheels, a numerical method, able to predict forced responses of mistuned blisks due to aerodynamic excitation, is presented. In a first step, the unsteady aerodynamic forcing is determined by modeling the spiral casing, the stator vanes, and the rotor blades of the entire turbine stage. In a second step, the aerodynamic damping induced by blade vibration is computed using a harmonic balance technique. The structure itself is represented by a reduced order model being extended by aerodynamic damping effects and aerodynamic forcings. Mistuning is introduced by adjusting the modal stiffness matrix based on results of blade by blade measurements that have been performed at rest. In order to verify the numerical method, the results are compared with strain-gauge data obtained during rig-tests. As a result, a measured low engine order excitation was found by modeling the spiral casing. Furthermore, a localization phenomenon due to frequency mistuning could be proven. The predicted amplitudes are close to the measured data.

Forced Response Analyses of Mistuned Radial Inflow Turbines

2012 ◽  
Author(s):  
Thomas Giersch ◽  
Peter Hönisch ◽  
Bernd Beirow ◽  
Arnold Kühhorn
Keyword(s):  
Numerical Method ◽  
Fluid Structure Interaction ◽  
Industrial Applications ◽  
Forced Response ◽  
Blade Vibration ◽  
Fluid Structure ◽  
Structure Interaction ◽  
Aerodynamic Damping ◽  
Radial Turbine ◽  
Spiral Casing

Radial turbine wheels designed as blade integrated disks (blisk) are widely used in various industrial applications. However, related to the introduction of exhaust gas turbochargers in the field of small and medium sized engines a sustainable demand for radial turbine wheels has come along. Despite those blisks are state of the art, a number of fundamental problems, mainly referred to fluid-structure-interaction and therefore to the vibration behavior, have been reported. Aiming to achieve an enhanced understanding of fluid-structure-interaction in radial turbine wheels a numerical method, able to predict forced responses of mistuned blisks due to aerodynamic excitation, is presented. In a first step the unsteady aerodynamic forcing is determined by modeling the spiral casing, the stator vanes and the rotor blades of the entire turbine stage. In a second step the aerodynamic damping induced by blade vibration is computed using a harmonic balance technique. The structure itself is represented by a reduced order model being extended by aerodynamic damping effects and aerodynamic forcings. Mistuning is introduced by adjusting the modal stiffness matrix based on results of blade by blade measurements that have been performed at rest. In order to verify the numerical method, the results are compared with strain-gauge data obtained during rig-tests. As a result a measured low engine order excitation was found by modeling the spiral casing. Furthermore a localization phenomenon due to frequency mistuning could be proven. The predicted amplitudes are close to measured data.

Forced Response Analysis of a Radial Turbine With Different Modelling Methods

2019 ◽  
Author(s):  
Yang Gao ◽  
Mauricio Gutierrez Salas ◽  
Paul Petrie-Repar ◽  
Tobias Gezork
Keyword(s):  
Periodic Boundary ◽  
Computational Cost ◽  
Computational Effort ◽  
Forced Response ◽  
Response Analysis ◽  
Phase Lag ◽  
Blade Vibration ◽  
Radial Turbine ◽  
High Level ◽  
Key Aspects

Abstract Forced response analysis is a critical part in the radial turbine design process. It estimates the vibration mode and level due to aerodynamic excitations and then enables the analysis of high-cycle fatigue (HCF) to determine the life span of the turbine stage. Two key aspects of the forced response analysis are the determination of the aerodynamic forcing and damping which can be calculated from unsteady 3D computational fluid dynamics (CFD) simulations. These simulations are problematic due to the high level of complexity in the simulations (multi-row, full annular, tip gap, etc.) and the consequent high-computational cost. The aim of this paper is to investigate and compare different CFD methods applied to the forced response analysis of a radial turbine. Full annular simulations are performed for the prediction of the excitation force. This method is taken as the baseline and is usually the most time-consuming one. One method of reducing the computational effort is to use Phase-lag periodic boundary conditions. A further reduction can be obtained by using a frequency-based method called nonlinear harmonic. For the prediction of aero-damping, the Phase -lag periodic boundary condition method is also available. Moreover, a frequency-based method called harmonic balance can further accelerate the aero-damping calculation. In this paper, these CFD methods will be applied to the simulations of an open-geometry radial turbine with a vaned volute. A comparison of unsteady results from different methods will be presented. These unsteady results will also be implemented to a tuned forced response analysis in order to directly compare the corresponding maximum blade vibration amplitudes.

Mistuning and Damping of a Radial Turbine Wheel. Part 1: Fundamental Analyses and Design of Intentional Mistuning Pattern

2021 ◽  
Author(s):  
Alex Nakos ◽  
Bernd Beirow ◽  
Arthur Zobel
Keyword(s):  
High Stress ◽  
Forced Response ◽  
Experimental Investigations ◽  
Detailed Knowledge ◽  
Turbine Wheel ◽  
Operation Conditions ◽  
Radial Turbine ◽  
Influence Coefficients ◽  
Modes Of Vibration ◽  
The Impact

Abstract The radial turbine impeller of an exhaust turbocharger is analyzed in view of both free vibration and forced response. Due to random blade mistuning resulting from unavoidable inaccuracies in manufacture or material inhomogeneities, localized modes of vibration may arise, which involve the risk of severely magnified blade displacements and inadmissibly high stress levels compared to the tuned counterpart. Contrary, the use of intentional mistuning (IM) has proved to be an efficient measure to mitigate the forced response. Independently, the presence of aerodynamic damping is significant with respect to limit the forced response since structural damping ratios of integrally bladed rotors typically take extremely low values. Hence, a detailed knowledge of respective damping ratios would be desirable while developing a robust rotor design. For this, far-reaching experimental investigations are carried out to determine the damping of a comparative wheel within a wide pressure range by simulating operation conditions in a pressure tank. Reduced order models are built up for designing suitable intentional mistuning patterns by using the subset of nominal system modes (SNM) approach introduced by Yang and Griffin [1], which conveniently allows for accounting both differing mistuning patterns and the impact of aeroelastic interaction by means of aerodynamic influence coefficients (AIC). Further, finite element analyses are carried out in order to identify appropriate measures how to implement intentional mistuning patterns, which are featuring only two different blade designs. In detail, the impact of specific geometric modifications on blade natural frequencies is investigated. The first part of this three-part paper is focused on designing the IM pattern. The second and third part following later on will address the topics (i) experimental validation after implementation of the IM pattern at rest and under rotation, and (ii) the development of an approach for fast estimating damping ratios in the design phase.

A Radial Inflow Turbine Impeller for Improved Off-Design Performance

1982 ◽  
Author(s):  
J. M. Mulloy ◽  
H. G. Weber
Keyword(s):  
Operating Conditions ◽  
Shape Design ◽  
Variable Geometry ◽  
Turbine Wheel ◽  
Final Design ◽  
Variable Geometry Turbine ◽  
Turbine Casing ◽  
Radial Inflow Turbine ◽  
Inlet Conditions ◽  
Turbine Impeller

Given the instantaneous operating conditions of the radial inflow turbine on a diesel engine and the possible requirement of a variable geometry turbine casing, an alternate approach was used to design an impeller which could accommodate the large variations in inlet states. Several impeller designs were generated and tested. Each was found to give a performance advantage in some portion of the turbine map. A blunt inlet shape design was found to give the best performance at all suspected inlet conditions. A final design turbine wheel was generated to cover the operating range of a variable geometry turbine casing. It was found that this impeller gave improved efficiencies at all operating conditions.

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