Prediction of Low-Engine-Order Excitation Due to a Nonsymmetrical Nozzle Ring in a Radial Turbine by Means of the Nonlinear Harmonic Approach

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Nikola Kovachev ◽  
Tobias R. Müller ◽  
Christian U. Waldherr ◽  
Damian M. Vogt
Keyword(s):  
Computational Cost ◽  
Forced Response ◽  
Response Analysis ◽  
Cfd Models ◽  
Engine Order ◽  
Throat Width ◽  
Time Marching ◽  
Computational Fluid Dynamics Cfd ◽  
Manufacturing Tolerances ◽  
Nozzle Guide

Abstract Low engine order (LEO) excitation in a turbomachine stage can be induced by nonuniform inflow conditions, manufacturing tolerances, or in-service wear. LEOs are known to excite significant forced response vibration amplitudes that can easily cause high cycle fatigue failure of blades. The accurate prediction of LEO excitation usually requires high-fidelity computational fluid dynamics (CFD) models of the full annulus of the machine due to the loss of symmetry leading to excessive computational cost. Previous investigation showed that the aerodynamic excitation stemming from the blade-passing-frequency in a vaned radial inflow turbine can be accurately predicted by using the nonlinear harmonic (NLH) method at highly reduced computational costs. In the current paper, the feasibility of the NLH method for the prediction of LEO excitation due to geometrical asymmetries is investigated for the same test object. An exact digital replica of the nozzle guide ring is created using measured throat width data. NLH simulations resolving different combinations of frequencies and a time-marching calculation are conducted with the new model involving this digital replica. The results show that a NLH model including small number of certain frequencies is able to predict the occurring LEO excitation sufficiently accurate. By comparing results from subsequent forced response analysis with measured vibration amplitudes, a satisfactory agreement was found confirming this conclusion.

Prediction of Low-Engine-Order Excitation due to a Non-Symmetrical Nozzle Ring in a Radial Turbine by Means of the Nonlinear Harmonic Approach

2019 ◽  
Author(s):  
Nikola Kovachev ◽  
Tobias R. Müller ◽  
Christian U. Waldherr ◽  
Damian M. Vogt
Keyword(s):  
Computational Cost ◽  
Forced Response ◽  
Response Analysis ◽  
Cfd Models ◽  
Engine Order ◽  
Throat Width ◽  
Time Marching ◽  
Manufacturing Tolerances ◽  
Nozzle Guide ◽  
Guide Ring

Abstract Low engine order (LEO) excitation in a turbomachine stage can be induced by non-uniform inflow conditions, manufacturing tolerances or in-service wear. LEOs are known to excite significant forced response vibration amplitudes that can easily cause High Cycle Fatigue (HCF) failure of blades. The accurate prediction of LEO excitation usually requires high-fidelity CFD models of the full annulus of the machine due to the loss of symmetry leading to excessive computational cost. Previous investigation showed that the aerodynamic excitation stemming from the blade-passing-frequency in a vaned radial inflow turbine can be accurately predicted by using the NonLinear Harmonic (NLH) method at highly reduced computational costs. In the current paper, the feasibility of the NLH method for the prediction of LEO excitation due to geometrical asymmetries is investigated for the same test object. An exact digital replica of the nozzle guide ring is created using measured throat width data. NLH simulations resolving different combinations of frequencies and a time-marching calculation are conducted with the new model involving this digital replica. The results show that a NLH model including small number of certain frequencies is able to predict the occurring LEO excitation sufficiently accurate. By comparing results from subsequent forced response analysis with measured vibration amplitudes, a satisfactory agreement was found confirming this conclusion.

Optimization-Aided Forced Response Analysis of a Mistuned Compressor Blisk

2014 ◽  
Author(s):  
Bernd Beirow ◽  
Arnold Kühhorn ◽  
Thomas Giersch ◽  
Jens Nipkau
Keyword(s):  
Young’S Modulus ◽  
Young's Modulus ◽  
Strong Dependence ◽  
Forced Response ◽  
Response Analysis ◽  
Influence Coefficient ◽  
Aerodynamic Damping ◽  
Design Variables ◽  
Engine Order ◽  
Main Driver

The forced response of the first rotor of an E3E-type high pressure compressor blisk is analyzed with regard to varying mistuning, varying engine order excitations and the consideration of aeroelastic effects. For that purpose, SNM-based reduced order models are used in which the disk remains unchanged while the Young’s modulus of each blade is used to define experimentally adjusted as well as intentional mistuning patterns. The aerodynamic influence coefficient technique is employed to model aeroelastic interactions. Furthermore, based on optimization analyses and depending on the exciting EO and aerodynamic influences it is searched for the worst as well as the best mistuning distributions with respect to the maximum blade displacement. Genetic algorithms using blade stiffness variations as vector of design variables and the maximum blade displacement as objective function are applied. An allowed limit of the blades’ Young’s modulus standard deviation is formulated as secondary condition. In particular, the question is addressed if and how far the aeroelastic impact, mainly causing aerodynamic damping, combined with mistuning can even yield a reduction of the forced response compared to the ideally tuned blisk. It is shown that the strong dependence of the aerodynamic damping on the inter-blade phase angle is the main driver for a possible response attenuation considering the fundamental blade mode. The results of the optimization analyses are compared to the forced response due to real, experimentally determined frequency mistuning as well as intentional mistuning.

Forced Response Analysis of a Mistuned Compressor Blisk Comparing Three Different Reduced Order Model Approaches

2016 ◽  
Author(s):  
Mauricio Gutierrez Salas ◽  
Ronnie Bladh ◽  
Hans Mårtensson ◽  
Paul Petrie-Repar ◽  
Torsten Fransson ◽  
...  
Keyword(s):  
Structural Modeling ◽  
Forced Response ◽  
Response Analysis ◽  
Reduced Order Models ◽  
Energy Localization ◽  
Order Model ◽  
Foreign Object Damage ◽  
Reduced Order ◽  
Manufacturing Tolerances ◽  
Blade Failure

Accurate structural modeling of blisk mistuning is critical for the analysis of forced response in turbomachinery. Apart from intentional mistuning, mistuning can be due to the manufacturing tolerances, corrosion, foreign object damage and in-service wear in general. It has been shown in past studies that mistuning can increase the risk of blade failure due to energy localization. For weak blade to blade coupling, this localization has been shown to be critical and higher amplitudes of vibration are expected in few blades. This paper presents a comparison of three reduced order models for the structural modeling of blisks. Two of the models assume cyclic symmetry while the third model is free of this assumption. The performance of the reduced order models for cases with small and large amount of mistuning will be examined. The benefits and drawbacks of each reduction method will be discussed.

Detection of Cracks in Mistuned Bladed Disks Using Reduced-Order Models and Vibration Data

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Chulwoo Jung ◽  
Akira Saito ◽  
Bogdan I. Epureanu
Keyword(s):  
Degrees Of Freedom ◽  
Dimensional Space ◽  
Equations Of Motion ◽  
Computational Cost ◽  
Three Dimensional ◽  
Cost Savings ◽  
Forced Response ◽  
Response Analysis ◽  
Reduced Order Models ◽  
Reduced Order

A novel methodology to detect the presence of a crack and to predict the nonlinear forced response of mistuned turbine engine rotors with a cracked blade and mistuning is developed. The combined effects of the crack and mistuning are modeled. First, a hybrid-interface method based on component mode synthesis is employed to develop reduced-order models (ROMs) of the tuned system with a cracked blade. Constraint modes are added to model the displacements due to the intermittent contact between the crack surfaces. The degrees of freedom (DOFs) on the crack surfaces are retained as active DOFs so that the physical forces due to the contact/interaction (in the three-dimensional space) can be accurately modeled. Next, the presence of mistuning in the tuned system with a cracked blade is modeled. Component mode mistuning is used to account for mistuning present in the uncracked blades while the cracked blade is considered as a reference (with no mistuning). Next, the resulting (reduced-order) nonlinear equations of motion are solved by applying an alternating frequency/time-domain method. Using these efficient ROMs in a forced response analysis, it is found that the new modeling approach provides significant computational cost savings, while ensuring good accuracy relative to full-order finite element analyses. Furthermore, the effects of the cracked blade on the mistuned system are investigated and used to detect statistically the presence of a crack and to identify which blade of a full bladed disk is cracked. In particular, it is shown that cracks can be distinguished from mistuning.

Forced Response Excitation of a Compressor Stator Owing to Shock Wave Induced by Adjacent Rotor Blade

2021 ◽  
Author(s):  
Toshimasa Miura ◽  
Naoto Sakai ◽  
Naoki Kanazawa ◽  
Kentaro Nakayama
Keyword(s):  
Flow Simulation ◽  
Strong Shock ◽  
Response Prediction ◽  
Forced Response ◽  
Rotor Blades ◽  
Response Analysis ◽  
Vibration Level ◽  
Fluid Force ◽  
Axial Compressors ◽  
Engine Order

Abstract The accurate prediction of high cycle fatigue (HCF) is becoming one of the key technologies in the design process of state-of-the-art axial compressors. If they are not properly designed, both rotor blades and stator vanes can be damaged. There are two main factors to cause HCF. One is low engine order (LEO) and the other is high engine order (HEO) excitation by fluid force associated with adjacent rotor-stator interaction. For the front stages of axial compressors for power generations and aero engines, the inlet Mach number of a rotor tip typically exceeds the speed of sound and strong shock waves tend to be induced. This can be the source of HEO excitation fluid force, and adjacent stator vanes are sometimes severely damaged. Thus, the aim of this study is to establish an efficient method for predicting the vibration response in this type of problem with high accuracy. To achieve this, numerical investigations are carried out by one-way fluid structure interaction (FSI) simulation. To validate the accuracy of FSI simulation, experiments are also conducted using a gas turbine engine for power generation. In the experiment, the vibration level is measured with strain gauges mounted on the surface of stator vanes and the data are compared with the predicted results. In the first part of the study, efficient prediction methods of excitation fluid force on the stator vane are investigated by time transformation (TT) and harmonic balance (HB) methods. Their accuracies are evaluated by comparing the results with those calculated by transient rotor stator (TRS) simulation whose pitch ratio is one between rotor and stator computational domains. It is found that the TT method can accurately predict the excitation fluid force with lower computation load even when there are pitch differences between rotor and stator regions. In the second part of the study, forced response analyses are carried out using the excitation fluid force obtained in the unsteady flow simulation. To obtain the total damping of the system, both hammering test and flutter simulations are carried out. Computed results are validated with experimental data and it is found that the predicted vibration level is in good agreement with experimental results. Through this study, the effectiveness of one-way FSI simulation is confirmed for this type of forced response prediction. By utilizing the combination of efficient unsteady computational fluid dynamics (CFD) methods and harmonic response analysis, vibration amplitude can be predicted accurately and efficiently.

Forced Response Analysis of a Mistuned Compressor Blisk

2013 ◽  
Author(s):  
Bernd Beirow ◽  
Arnold Kühhorn ◽  
Thomas Giersch ◽  
Jens Nipkau
Keyword(s):  
Strong Dependence ◽  
Forced Response ◽  
Response Analysis ◽  
Influence Coefficient ◽  
Aerodynamic Damping ◽  
Design Variables ◽  
Engine Order ◽  
Main Driver ◽  
Displacement Based ◽  
Blade Frequency

The forced response of an E3E-type HPC-blisk front rotor is analyzed with regard to varying mistuning and the consideration of the fluid-structure interaction (FSI). For that purpose, a reduced order model is used in which the disk remains unchanged and mechanical properties of the blades namely stiffness and damping are adjusted to measured as well as intentional blade frequency mistuning distributions. The aerodynamic influence coefficient technique is employed to model the aeroelastics. Depending on the blade mode, the exciting engine order and aerodynamic influences it is sought for the worst mistuning distributions with respect to the maximum blade displacement based on optimization analyses. Genetic algorithms using blade alone frequencies as design variables are applied. The validity of the Whitehead-limit is assessed in this context. In particular, the question is addressed if and how far aeroelastic effects, mainly caused by aerodynamic damping, combined with mistuning can even cause a reduction of the forced response compared to the ideally tuned blisk. It is shown that the strong dependence of the aerodynamic damping on the inter-blade phase angle is the main driver for a possible response attenuation considering the fundamental as well as a higher blade mode. Furthermore, the differences to the blisk vibration response without a consideration of the flow and an increase of the disk’s stiffness are discussed. Closing, the influence of pure damping mistuning is analyzed again using optimization.

Optimization-Aided Forced Response Analysis of a Mistuned Compressor Blisk

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Bernd Beirow ◽  
Thomas Giersch ◽  
Arnold Kühhorn ◽  
Jens Nipkau
Keyword(s):  
Young’S Modulus ◽  
Young's Modulus ◽  
Strong Dependence ◽  
Forced Response ◽  
Response Analysis ◽  
Influence Coefficient ◽  
Aerodynamic Damping ◽  
Design Variables ◽  
Engine Order ◽  
Main Driver

The forced response of the first rotor of an engine 3E (technology program) (E3E)-type high pressure compressor (HPC) blisk is analyzed with regard to varying mistuning, varying engine order (EO) excitations and the consideration of aero-elastic effects. For that purpose, subset of nominal system modes (SNM)-based reduced order models are used in which the disk remains unchanged while the Young's modulus of each blade is used to define experimentally adjusted as well as intentional mistuning patterns. The aerodynamic influence coefficient (AIC) technique is employed to model aero-elastic interactions. Furthermore, based on optimization analyses and depending on the exciting EO and aerodynamic influences it is searched for the worst as well as the best mistuning distributions with respect to the maximum blade displacement. Genetic algorithms using blade stiffness variations as vector of design variables and the maximum blade displacement as objective function are applied. An allowed limit of the blades' Young's modulus standard deviation is formulated as secondary condition. In particular, the question is addressed if and how far the aero-elastic impact, mainly causing aerodynamic damping, combined with mistuning can even yield a reduction of the forced response compared to the ideally tuned blisk. It is shown that the strong dependence of the aerodynamic damping on the interblade phase angle is the main driver for a possible response attenuation considering the fundamental blade mode. The results of the optimization analyses are compared to the forced response due to real, experimentally determined frequency mistuning as well as intentional mistuning.

Forced Response in Axial Turbines Under the Influence of Partial Admission

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Jens Fridh ◽  
Björn Laumert ◽  
Torsten Fransson
Keyword(s):  
High Speed ◽  
Pressure Ratio ◽  
Forced Response ◽  
Rotor Blades ◽  
Response Analysis ◽  
Validation Data ◽  
Pressure Transducers ◽  
Control Stage ◽  
Engine Order ◽  
Partial Admission

High cycle fatigue (HCF) due to unforeseen excitation frequencies, underestimated force magnitudes, or a combination of both causes control-stage failures for steam turbine stakeholders. This paper provides an extended design criteria toolbox, as well as validation data, for control-stage design based on experimental data to reduce HCF incidents in partial-admission turbines. The upstream rotor in a two-stage air test turbine is instrumented with pressure transducers and strain gauges. Admission degrees extend from 28.6% to 100%, as one or two admission arcs are simulated by blocking segmental arcs immediately upstream of the first stator vanes with aerodynamically shaped filling blocks. Sweeps across a speed range of 50%–105% of design speed are performed at a constant turbine pressure ratio during simultaneous high-speed acquisition. A forced-response analysis is performed and results presented in Campbell diagrams. Partial admission creates a large number of low-engine-order forced responses because of the blockage, pumping, loading, and unloading processes. Combinations of the number of rotor blades and low-engine-order excitations are the principal sources of forced-response vibrations for the turbine studied here. Altering the stator and/or rotor pitches changes the excitation pattern. We observed that a relationship between the circumferential lengths of the admitted and nonadmitted arcs dictates the excitation forces and may serve as a design parameter.

Forced Response in Axial Turbines Under the Influence of Partial Admission

2012 ◽  
Author(s):  
Jens Fridh ◽  
Björn Laumert ◽  
Torsten Fransson
Keyword(s):  
High Speed ◽  
Pressure Ratio ◽  
Forced Response ◽  
Rotor Blades ◽  
Response Analysis ◽  
Validation Data ◽  
Pressure Transducers ◽  
Control Stage ◽  
Engine Order ◽  
Partial Admission

High cycle fatigue (HCF) due to unforeseen excitation frequencies or due to under predicted force magnitudes, or a combination of both causes control stage failures for steam turbine stakeholders. The objectives of this paper is to provide an extended design criteria toolbox and validation data for control stage design based on experimental data, with the aim to decrease HCF incidents for partial admission turbines. The upstream rotor in a two stage air test turbine is instrumented with pressure transducers and strain gauges. Admission degrees stretching from 28.6% to 100% as one or two admission arcs are simulated by blocking segmental arcs immediately upstream of first stator vanes by aerodynamically shaped filling blocks. Sweeps across a speed range from 50 to 105% of design speed are performed at constant turbine pressure ratio during simultaneous high speed acquisition. A forced response analysis is performed and results presented in Campbell diagrams. Partial admission creates a large number of low engine order forced responses because of the blockage, pumping, loading and unloading processes. Combinations of the number of rotor blades and low engine order excitations are the principal sources of forced response vibrations for the turbine studied herein. Altering the stator and/or rotor pitches will change the excitation pattern. A relation between the circumferential lengths of the admitted and non-admitted arcs that dictates the excitation forces is observed that may serve as a design parameter.

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.

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