Forced Response Prediction of Turbine Blades with Flexible Dampers: The Impact of Engineering Modelling Choices

This paper summarizes the results of an investigation to establish the impact of mistuning on the performance and design of blade-to-blade friction dampers of the type used to control the resonant response of turbine blades in gas turbine engines. In addition, it discusses the importance of friction slip force variations on the dynamic response of shrouded fan blades.

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The Impact of Excitation and Mode Shape on Non-Linear Blade Vibrations

Volume 11: Structures and Dynamics: Structural Mechanics, Vibration, and Damping; Supercritical CO2 ◽

10.1115/gt2020-14670 ◽

2020 ◽

Author(s):

Johannes Linhard ◽

Andreas Hartung ◽

Stefan Schwarz ◽

Hans-Peter Hackenberg ◽

Mateusz Sienko

Keyword(s):

Mode Shape ◽

Optical Measurement ◽

Turbine Blades ◽

Harmonic Balance Method ◽

Forced Response ◽

Vibration Measurement ◽

Numerical Predictions ◽

Non Linear ◽

Strain Gauge Measurements ◽

The Impact

Abstract Recently, reliable non-linear dynamic solvers for the analysis of frictionally coupled turbine blades have been developed which are based on either Higher Harmonic Balance Method or Non-linear Modal Analysis. One of these tools is OrAgL which was developed by Institute of Dynamics of Vibrations (Leibniz University of Hannover) and Institute of Aircraft Propulsion Systems (University of Stuttgart). In [1], the rig and engine validation results of with OrAgL performed forced response analyses have been published: The main aim of this paper was the comparison of non-linear numerical predictions (amplitude, frequencies) with the blade-to-blade averaged values of optical measurement results obtained using MTU’s non-contact vibration measurement system for shrouded turbine blades (BSSM-T). Detailed analyses and validations performed over the last two years showed several novel aspects of validation such as the comparison with strain gauge measurements. Moreover, a better understanding of the impact of excitation (magnitude and load distribution over the airfoil) as well as of the impact of the mode shape on the formation of saturation regimes is now possible. The results obtained from the analyses of real turbine blades are presented in this work.

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Regeneration-Induced Forced Response in Axial Turbines

Volume 7B: Structures and Dynamics ◽

10.1115/gt2013-95431 ◽

2013 ◽

Cited By ~ 5

Author(s):

Jens Aschenbruck ◽

Christopher E. Meinzer ◽

Linus Pohle ◽

Lars Panning-von Scheidt ◽

Joerg R. Seume

Keyword(s):

Turbine Blades ◽

Forced Response ◽

Response Analysis ◽

Geometrical Parameters ◽

Turbine Stage ◽

Structural Dynamic ◽

Air Turbine ◽

Axial Turbines ◽

Interaction Approach ◽

Stagger Angle

The regeneration of highly loaded turbine blades causes small variations of their geometrical parameters. To determine the influence of such regeneration-induced variances of turbine blades on the nozzle excitation, an existing air turbine is extended by a newly designed stage. The aerodynamic and the structural dynamic behavior of the new turbine stage are analyzed. The calculated eigenfrequencies are verified by an experimental modal analysis and are found to be in good agreement. Typical geometric variances of overhauled turbine blades are then applied to stator vanes of the newly designed turbine stage. A forced response analysis of these vanes is conducted using a uni-directional fluid-structure interaction approach. The effects of geometric variances on the forced response of the rotor blade are evaluated. It is shown that the vibration amplitudes of the response are significantly higher for some modes due to the additional wake excitation that is introduced by the geometrical variances e.g. 56 times higher for typical MRO-induced variations in stagger-angle.

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

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4052201 ◽

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.

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Aeroelastic Analysis of NREL Wind Turbine

Volume 9: Oil and Gas Applications; Supercritical CO2 Power Cycles; Wind Energy ◽

10.1115/gt2017-63161 ◽

2017 ◽

Author(s):

Yaozhi Lu ◽

Fanzhou Zhao ◽

Loic Salles ◽

Mehdi Vahdati

Keyword(s):

Numerical Model ◽

Wind Turbine ◽

Wind Turbines ◽

Gas Turbines ◽

High Cycle Fatigue ◽

Turbine Blades ◽

Measured Data ◽

Forced Response ◽

Cycle Fatigue ◽

Aeroelastic Analysis

The current development of wind turbines is moving toward larger and more flexible units, which can make them prone to fatigue damage induced by aeroelastic vibrations. The estimation of the total life of the composite components in a wind turbine requires the knowledge of both low and high cycle fatigue (LCF and HCF) data. The first aim of this study is to produce a validated numerical model, which can be used for aeroelastic analysis of wind turbines and is capable of estimating the LCF and HCF loads on the blade. The second aim of this work is to use the validated numerical model to assess the effects of extreme environmental conditions (such as high wind speeds) and rotor over-speed on low and high cycle fatigue. Numerical modelling of this project is carried out using the Computational Fluid Dynamics (CFD) & aeroelasticity code AU3D, which is written at Imperial College and developed over many years with the support from Rolls-Royce. This code has been validated extensively for unsteady aerodynamic and aeroelastic analysis of high-speed flows in gas turbines, yet, has not been used for low-speed flows around wind turbine blades. Therefore, in the first place the capability of this code for predicting steady and unsteady flows over wind turbines is studied. The test case used for this purpose is the Phase VI wind turbine from the National Renewable Energy Laboratory (NREL), which has extensive steady, unsteady and mechanical measured data. From the aerodynamic viewpoint of this study, AU3D results correlated well with the measured data for both steady and unsteady flow variables, which indicated that the code is capable of calculating the correct flow at low speeds for wind turbines. The aeroelastic results showed that increase in crosswind and shaft speed would result in an increase of unsteady loading on the blade which could decrease the lifespan of a wind turbine due to HCF. Shaft overspeed leads to significant increase in steady loading which affects the LCF behaviour. Moreover, the introduction of crosswind could result in significant dynamic vibration due to forced response at resonance.

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Experimental Validation of Forced Response Methods in a Multi-Stage Axial Turbine

Volume 7C: Structures and Dynamics ◽

10.1115/gt2018-75390 ◽

2018 ◽

Author(s):

Thomas Hauptmann ◽

Christopher E. Meinzer ◽

Joerg R. Seume

Keyword(s):

Experimental Data ◽

Vibration Amplitude ◽

Turbine Blades ◽

Service Condition ◽

Sensitivity Study ◽

Forced Response ◽

Tip Clearance ◽

Computational Time ◽

Reference Case ◽

Axial Turbine

Depending on the in service condition of jet engines, turbine blades may have to be replaced, refurbished, or repaired in the course of an engine overhaul. Thus, significant changes of the turbine blade geometry can be introduced due to regeneration and overhaul processes. Such geometric variances can affect the aerodynamic and aeroelastic behavior of turbine blades. One goal in the development of the regeneration process is to estimate the aerodynamic excitation of turbine blades depending on these geometric variances caused during the regeneration. Therefore, this study presents an experimentally validated comparison of two methods for the prediction of forced response in a multistage axial turbine. Two unidirectional fluid structure interaction (FSI) methods, a time-linearized and a time-accurate with a subsequent linear harmonic analysis, are employed and the results validated against experimental data. The results show that the vibration amplitude of the time-linearized method is in good agreement with the experimental data and, also requires lower computational time than the time-accurate FSI. Based on this result, the time-linearized method is used to perform a sensitivity study of the tip clearance size of the last rotor blade row of the five stage axial turbine. The results show that an increasing tip clearances size causes an up to 1.35 higher vibration amplitude compared to the reference case, due to increased forcing and decreased damping work.

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The Effect of Non-Uniform Aerodynamic Loading on the Blade Responses

ASME 2007 Power Conference ◽

10.1115/power2007-22048 ◽

2007 ◽

Cited By ~ 1

Author(s):

Abdelgadir M. Mahmoud ◽

Mohd S. Leong

Keyword(s):

Turbine Blades ◽

Forced Response ◽

Flow Section ◽

Flow Distortion ◽

Inlet Flow ◽

Bladed Disk ◽

Aerodynamic Loading ◽

Bladed Disk Assembly ◽

Flow Generator ◽

Inlet Flow Distortion

Turbine blades are always subjected to severe aerodynamic loading. The aerodynamic loading is uniform and Of harmonic nature. The harmonic nature depends on the rotor speed and number of nozzles (vanes counts). This harmonic loading is the main sources responsible for blade excitation. In some circumstances, the aerodynamic loading is not uniform and varies circumferentially. This paper discussed the effect of the non-uniform aerodynamic loading on the blade vibrational responses. The work involved the experimental study of forced response amplitude of model blades due to inlet flow distortion in the presence of airflow. This controlled inlet flow distortion therefore represents a nearly realistic environment involving rotating blades in the presence of airflow. A test rig was fabricated consisting of a rotating bladed disk assembly, an inlet flow section (where flow could be controlled or distorted in an incremental manner), flow conditioning module and an aerodynamic flow generator (air suction module with an intake fan) for investigations under laboratory conditions. Tests were undertaken for a combination of different air-flow velocities and blade rotational speeds. The experimental results showed that when the blades were subjected to unsteady aerodynamic loading, the responses of the blades increased and new frequencies were excited. The magnitude of the responses and the responses that corresponding to these new excited frequencies increased with the increase in the airflow velocity. Moreover, as the flow velocity increased the number of the newly excited frequency increased.

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Eco-friendly technology of manufacturing complex products made of composites

E3S Web of Conferences ◽

10.1051/e3sconf/201914002004 ◽

2019 ◽

Vol 140 ◽

pp. 02004

Author(s):

Aleksey Ignatov ◽

Rustam Subkhankulov

Keyword(s):

Composite Materials ◽

Cross Section ◽

Manufacturing Process ◽

Volume Fraction ◽

Turbine Blades ◽

Variable Cross Section ◽

Variable Cross ◽

Technological Parameters ◽

Technological Support ◽

The Impact

Numerous studies in application of modern composite materials show that their advantages can be successfully implemented in manufacturing «smart» products. This study proposes an improved technological method of manufacturing multilayer environmentally friendly products with a variable cross section, which allows us to expand the possibilities of using modern polymer composite materials (PCM). The technology allows manufacturing products of the most complex geometric shapes, such as wind turbine blades. The aim of the study is the technological support of engineering production in the manufacture of multilayer products of variable cross section made from PCM. Scientific novelty consists in identifying the patterns of implementation and management of the manufacturing process of multilayer products of variable cross-section, and establishing the influence of structural and technological parameters of the manufacturing process on their operational characteristics. The relationship between the pressure of a hot directed air stream and the volume fraction of pores in the hardened material of a multilayer composite product with a variable cross section during layer-by-layer application is investigated. During the study, fundamental and applied principles of mechanical engineering technology, material resistance, adhesion theory, mathematical statistics tools and software were used to process the results of the experiment. Based on the results of laboratory studies, a methodology has been developed for effective prediction of pore content in the manufacturing of composite products. The introduction of the presented technology and the corresponding original methodology into production will reduce the complexity and energy costs of manufacturing composite products, improve their quality and reduce the impact of toxic components from composite materials on workers.

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Study on the Formation of Stray Grains during Directional Solidification of Nickel-Based Superalloys

Materials Science Forum ◽

10.4028/www.scientific.net/msf.879.1582 ◽

2016 ◽

Vol 879 ◽

pp. 1582-1587 ◽

Cited By ~ 3

Author(s):

Maria Rita Ridolfi ◽

Oriana Tassa ◽

Giovanni de Rosa

Keyword(s):

Directional Solidification ◽

Gas Turbines ◽

Complex Geometry ◽

Turbine Blades ◽

Columnar Dendrite ◽

Affecting Factors ◽

Stray Grains ◽

Geometrical Factors ◽

Stray Grain ◽

The Impact

Ni-based superalloy single-crystal turbine blades are widely used in gas turbines for aircraft propulsion and power generation as they can be subjected to high service temperature and show high mechanical properties due to the almost total elimination of grain boundaries. Particularly in presence of complex geometry shapes, rare grains nucleating apart from the primary grain, become a serious problem in directional solidification, when characterized by high-angle boundaries with the primary grain, extremely brittle due the elevated amount of highly segregating elements and the absence of grain boundary strengthening elements. It is of fundamental importance analyzing the physical mechanisms of formation of stray grains, to understand which thermo-physical and geometrical factors highly influence their formation and to find possible ways to reduce the impact of the problem. In this paper, constrained dendrite growth and heterogeneous grain nucleation theories have been used to model the formation of stray grains in directional solidification of Ni-base superalloys. The study allows to derive the preferred locations of stray grains formation and the role played by the most affecting factors: (i) geometrical: angle of primary grain dendrites with withdrawal direction and orientation of the primary grain with respect to the side walls, responsible for the formation of volumes where the stray grain undercooling is lower than the undercooling of the columnar dendrite tip; (ii) process and alloy: thermal gradient ahead to the solidification front and alloy composition, influencing the columnar dendrite tip undercooling; (iii) wettability of foreign substrates, on which the stray grain undercooling strongly depends.

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A High Fidelity Quality Assessment of High Pressure Turbine Blades Using Surface Curvature and Gradient-Based Adjoint

Volume 2B: Turbomachinery ◽

10.1115/gt2018-75157 ◽

2018 ◽

Author(s):

Akhil Mulloth ◽

Gabriel Banks ◽

Giulio Zamboni ◽

Simon Bather

Keyword(s):

Quality Assessment ◽

Turbine Blades ◽

Three Dimensional ◽

Surface Curvature ◽

Assessment Process ◽

Screening Process ◽

Profile Tolerance ◽

Gradient Based ◽

Parts Manufacturing ◽

The Impact

Gas turbine performance is highly dependent on the quality of the manufactured parts. Manufacturing variations in the parts can significantly alter the performance, especially efficiency and thus SFC. The legacy process is to accept variations within predefined profile tolerance limits and a few other qualitative parameters, mostly at a few, key two-dimensional aerofoil sections. With the widespread use of White light scans and other similar three-dimensional scans, this has improved to include the three-dimensional profile. The future however may lie with performance based quality assessment of manufactured parts, combined with quantitative surface quality assessment to implement an intelligent screening process for the parts. The adjoint method, typically used for shape optimization is adapted to provide a prediction of the impact on performance due to manufacturing variations. The work presented outlines a three stage quality assessment process for manufactured parts, involving three-dimensional profile tolerance based screening, followed by a surface curvature based screening and finally an Adjoint based performance prediction.

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