Experimental and Numerical Quantification of the Aerodynamic Damping of a Turbine Blisk

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
Christopher E. Meinzer ◽  
Joerg R. Seume
Keyword(s):  
Cfd Simulation ◽  
Excitation Frequency ◽  
Sweep Rate ◽  
Accurate Estimate ◽  
Rotational Frequency ◽  
Forced Response ◽  
Operating Conditions ◽  
Friction Damping ◽  
Aerodynamic Damping ◽  
Turbine Blisk

Abstract Aerodynamic damping is the key parameter to determine the stability of vibrating blade rows in turbomachinery design. Both, the assessments of flutter and forced response vibrations need an accurate estimate of the aerodynamic damping to reduce the risk of high cycle fatigue that may result in blade loss. However, only very few attempts have been made to measure the aerodynamic damping of rotating blade rows experimentally under realistic operating conditions, but always with friction damping being present. This study closes the gap by providing an experiment in which a turbine blisk is used to eliminate friction damping at the blade roots and thereby isolate aerodynamic damping. The blades are excited acoustically and the resulting nodal diameter modes are measured using an optical tip-timing system in order to realize a fully non-intrusive setup. The measured vibration data are fitted to a single degree-of-freedom model (SDOF) to determine the aerodynamic damping. The results are in good accordance with the time-linearized CFD simulation. It is observed, however, that not only the sweep rate of the acoustic excitation but also the variation of the rotational frequency during the sweep excitation, and the excitation frequency influence the apparent damping.

Experimental and Analytical Investigations of a Low Pressure Model Turbine During Forced Response Excitation

2010 ◽  
Author(s):  
Christoph Heinz ◽  
Markus Schatz ◽  
Michael V. Casey ◽  
Heinrich Stu¨er
Keyword(s):  
Degrees Of Freedom ◽  
Timing Analysis ◽  
Dynamic Performance ◽  
Amplitude Distribution ◽  
Low Pressure ◽  
Forced Response ◽  
Operating Conditions ◽  
Linear Regression Method ◽  
Rotor Shaft ◽  
Aerodynamic Damping

To guarantee a faultless operation of a turbine it is necessary to know the dynamic performance of the machine especially during start-up and shut-down. In this paper the vibration behaviour of a low pressure model steam turbine which has been intentionally mistuned is investigated at the resonance point of an eigenfrequency crossing an engine order. Strain gauge measurements as well as tip timing analysis have been used, whereby a very good agreement is found between the methods. To enhance the interpretation of the data measured, an analytical mass-spring-model, which incorporates degrees of freedom for the blades as well as for the rotor shaft, is presented. The vibration amplitude varies strongly from blade to blade. This is caused by the mistuning parameters and the coupling through the rotor shaft. This circumferential blade amplitude distribution is investigated at different operating conditions. The results show an increasing aerodynamic coupling with increasing fluid density, which becomes visible in a changing circumferential blade amplitude distribution. Furthermore the blade amplitudes rise non-linearly with increasing flow velocity, while the amplitude distribution is almost independent. Additionally, the mechanical and aerodynamic damping parameters are calculated by means of a non-linear regression method. Based on measurements at different density conditions, it is possible to extrapolate the damping parameters down to vacuum conditions, where aerodynamic damping is absent. Hence the material damping parameter can be determined.

Damping Behavior of Blades From Small Radial Turbines

2015 ◽  
Author(s):  
David Hemberger ◽  
Dietmar Filsinger ◽  
Hans-Jörg Bauer
Keyword(s):  
Numerical Analysis ◽  
Dynamic Properties ◽  
Forced Response ◽  
Operating Conditions ◽  
Fe Model ◽  
Structural Damping ◽  
Aerodynamic Damping ◽  
Damping Behavior ◽  
Aerodynamic Properties ◽  
Radial Turbines

Next to excitation forces and the dynamic properties of mistuned structures the damping behavior is a key feature to evaluate the dynamic turbine blade response and thus the HCF life of a bladed disk (blisk). Just as the determination of the mistuning properties and the assessment of the vibration excitation, the evaluation of damping is also subject to uncertainty especially considering the wide operating range of a small radial turbine of a turbocharger. Since the total damping is composed of material damping, structural damping and aerodynamic damping, which are affected by parameters, like the eigenform of the vibration, the magnitude of the vibration amplitude and aerodynamic properties, the total damping can be strongly dependent on the operating conditions. The study at hand provides results from investigations that allow estimating the contribution of aerodynamic damping on the total damping. Experimental and numerical analysis of radial turbines from turbochargers for vehicular engines with variable turbine inlet vanes were performed. Measurements under different environmental conditions such as at rest and during operation, as well as unsteady CFD calculations and, coupled flow and structural calculations were carried out. A change in total damping could be found depending on the density of the surrounding gas by vibration measurements in operation on the hot gas test bench. But it was also shown that the total damping is decisively influenced by the mistuning of the structure. On one side the structural damping is varied by the variation in mistuned blade vibration amplitudes and otherwise the aerodynamic damping is influenced by the different inter blade phase angles (IBPA ) due to the mistuning, which is a symptom of geometric differences and material inhomogeneity in the wheels. Finally, the estimated total damping values were utilized in forced response calculations using a mistuned FE-model of a real turbine and excitation forces from unsteady CFD calculation. The magnitudes of the measured vibration amplitudes were compared with results from numerical analysis to validate the numerical model with focus on the investigation about the total damping. The deviation between the results was ±10% for different eigenforms and excitation orders.

Modal Analyses of an Axial Turbine Blisk With Intentional Mistuning

2017 ◽  
Author(s):  
Bernd Beirow ◽  
Felix Figaschewsky ◽  
Arnold Kühhorn ◽  
Alfons Bornhorn
Keyword(s):  
Aerodynamic Performance ◽  
Forced Response ◽  
Mode Shapes ◽  
Axial Turbine ◽  
The Real ◽  
Operational Conditions ◽  
Aerodynamic Damping ◽  
Optimization Study ◽  
Engine Order ◽  
Turbine Blisk

The potential of intentional mistuning to reduce the maximum forced response is analyzed within the development of an axial turbine blisk for ship diesel engine turbocharger applications. The basic idea of the approach is to provide an increased aerodynamic damping level for particular engine order excitations and mode shapes without any significant distortions of the aerodynamic performance. The mistuning pattern intended to yield a mitigation of the forced response is derived from an optimization study applying genetic algorithms. Two blisk prototypes have been manufactured a first one with and another one without employing intentional mistuning. Hence, the differences regarding the real mistuning and other modal properties can be experimentally determined and evaluated as well. In addition, the experimental data basis allows for updating structural models which are well suited to compute the forced response under operational conditions. In this way, the real benefit achieved with the application of intentional mistuning is demonstrated.

Modal Analyses of an Axial Turbine Blisk With Intentional Mistuning

2017 ◽  
Vol 140 (1) ◽  
Author(s):  
Bernd Beirow ◽  
Felix Figaschewsky ◽  
Arnold Kühhorn ◽  
Alfons Bornhorn
Keyword(s):  
Aerodynamic Performance ◽  
Forced Response ◽  
Mode Shapes ◽  
Axial Turbine ◽  
The Real ◽  
Operational Conditions ◽  
Aerodynamic Damping ◽  
Optimization Study ◽  
Engine Order ◽  
Turbine Blisk

The potential of intentional mistuning to reduce the maximum forced response is analyzed within the development of an axial turbine blisk for ship diesel engine turbocharger applications. The basic idea of the approach is to provide an increased aerodynamic damping level for particular engine order (EO) excitations and mode shapes without any significant distortions of the aerodynamic performance. The mistuning pattern intended to yield a mitigation of the forced response is derived from an optimization study applying genetic algorithms. Two blisk prototypes have been manufactured a first one with and another one without employing intentional mistuning. Hence, the differences regarding the real mistuning and other modal properties can be experimentally determined and evaluated as well. In addition, the experimental data basis allows for updating structural models which are well suited to compute the forced response under operational conditions. In this way, the real benefit achieved with the application of intentional mistuning is demonstrated.

Interaction of Concurrent Forced Response and Flutter Phenomena in a Compressor Stage

2017 ◽  
Author(s):  
Zhiping Mao ◽  
Robert E. Kielb
Keyword(s):  
Excitation Frequency ◽  
Harmonic Balance Method ◽  
Forced Response ◽  
Rotor Blades ◽  
Single Frequency ◽  
Response Frequency ◽  
Unsteady Pressure ◽  
Aerodynamic Damping ◽  
Frequency Domain Methods ◽  
The Impact

This paper studies a subsonic compressor case with concurrent forced response and flutter by using the Harmonic Balance method, and was inspired by historical experimental data. Forced response was observed when the rotating speed was approaching a crossing on the Campbell diagram, where flutter appeared to be suppressed. CFD simulations are conducted by using a quasi-3D configuration at the mid-span of one stage of a 3.5-stage compressor. Due to the constraint of frequency domain methods, the research is conducted in the vicinity of the 1T-44EO crossing with a small frequency shift between flutter frequency and external excitation frequency. The influence from flutter to forced response is observed: a one-way crosstalk at forced response frequency is observed, presented as the anomaly of unsteady velocity and unsteady pressure near the rear section of rotor blades and in the rotor wake region. The anomaly is speculated as the presence of increasing intensity of shedding vortices induced by the vibration of the blade. To further prove the impact of this viscous effect, a numerical experiment was performed with inviscid rotor blades. In contrast to the crosstalk at forced response frequency, no obvious influence on the unsteady behavior is detected at the flutter frequency, and this observation is confirmed at multiple vibration amplitudes. Considering the relationship between unsteady pressure at flutter frequency and aerodynamic damping, we conclude the influence of forced response on the aerodynamic damping is negligible. In addition, a linearity of unsteady pressure at the flutter frequency vs. vibration amplitude is uncovered. The discoveries provide a proof to linearity assumption and single-frequency simplification widely adopted by industry in flutter simulations.

A Methodology to Predicting Total Damping of Axial Compressor Shrouded Stator Vanes

2009 ◽  
Author(s):  
Caetano Peng ◽  
Andrea Zilli
Keyword(s):  
Strain Gauge ◽  
Forced Response ◽  
Vibration Modes ◽  
Friction Damping ◽  
Normal Contact ◽  
Aerodynamic Damping ◽  
Wide Range ◽  
Numerical Tools ◽  
Phase Angles ◽  
Q Values

The main objective of this paper is to evaluate the capability of existing numerical tools to predict the total damping Q values of axial core compressor shrouded stator vanes with a view to use them in the forced response simulations. Here, the aerodynamic damping is calculated for a wide range of vane vibration modes and nodal diameters (inter-blade-phase angles) using a CFD based aeroelasticity program. The mechanical friction damping of vane vibration modes is computed by using a multi-harmonic balance forced response code. These calculations take into account the effects of normal contact forces, friction coefficients, contact stiffness and excitation (forcing) loads. A pragmatic methodology has been developed to calculate the aerodynamic and mechanical friction damping values and hence predicting total Q values of stator vanes. Sensitivity studies are performed to assess the effects of mass flow and inter-blade-phase angles on aerodynamic damping. Moreover, the analyses allowed to identify the modeshapes associated with either high aerodynamic or mechanical damping or both. The numerical results are correlated with experimentally measured total Q values from strain gauge engine tests. This work shows that the current numerical tools have the capability to predict not only the aerodynamic forcing but also aerodynamic and mechanical friction damping values. Therefore, the analysis tools and methodologies close the stator vane forced response prediction capability loop. It means the vane force responses can be predicted as measured from strain gauge engine tests. This constitutes an important step in the development of axial compressors test-to-simulations, as more efforts are being placed towards the development of whole engines test-to-simulations.

Forced Response Analysis of Supercritical CO2 Radial Inflow Turbine Designed for Concentrating Solar Power

2016 ◽  
Author(s):  
Mohsen Modir Shanechi ◽  
Martin Veidt ◽  
Kamel Hooman
Keyword(s):  
High Pressure ◽  
Rotational Speed ◽  
Forced Response ◽  
Subcritical State ◽  
Fe Model ◽  
Brayton Cycle ◽  
Concentrating Solar Power ◽  
Aerodynamic Damping ◽  
Radial Inflow Turbine ◽  
Turbine Blisk

The forced response of high-pressure sCO2 radial-inflow turbine blisk is studied with regards to internal mistuning and inherent characteristics of supercritical Brayton cycle. A novel preliminary meanline analysis led to the generation of turbine designs for the sCO2 Brayton cycle with respect to concentrating solar power (CSP) applications. Details of mentioned study are published in a separate paper. The sCO2 turbine with a pressure ratio of 2.2 and the mild inlet temperature of 560 C is studied for rotational speed ranging between 75000 and 125000 RPM. Aiming to achieve an enhanced understanding of the fluid-structure-interaction in sCO2 radial-inflow turbine, a numerical method capable of predicting the forced responses of tuned and intentionally mistuned blisks due to aerodynamic excitation is presented. The numerical work involves the simulation of the transient flow field, and then the unsteady aerodynamic excitation forces on the blades are determined by modelling various resonance condition, including the influence of the operating condition and stator number. Performing the forced response of the structure, the transient and spatially resolved pressure distribution is used as a boundary condition in an FE model. As a result, the response amplifications of sCO2 turbines are eventually compared. The similar geometrical turbine was designed and manufactured to be operated in subcritical state for the sake of validation. The results of the subcritical turbine are derived by means of experimental and numerical analyses. To update the effect of mistuning in the FE model, blade by blade measurements using the example of a subcritical turbine blisk is performed and results of well correlated FRFs are used as inputs to adjust the blade individual Young’s modulus. The tendency of results is approved by previous works done in subcritical state. The structural damping information to be considered in the update process is taken from results of an experimental modal analysis and the aerodynamic damping induced by blade vibration is computed using an energy balance technique. It has been found that increase of the maximum forced response beyond that of the sCO2 turbine with higher rotational speed is not significant due to the existence of high pressure-density sCO2. This implies an occurrence of high aerodynamic damping which would cause a low vibrational amplitude in case of a mistuned blisk. Considering aeroelastic coupling, in supercritical turbine with small mistuning, no change of maximum response magnitudes is achieved for the fundamental bending mode; however, with large mistuning pattern, aerodynamic damping can cause significantly better response level. This result indicates considerable contrast with responses obtained from subcritical model which would be expressed by either characteristic or state of working fluid.

scholarly journals Stereo-DIC Measurements of a Vibrating Bladed Disk: In-Depth Analysis of Full-Field Deformed Shapes

2021 ◽  
Vol 11 (12) ◽  
pp. 5430
Author(s):  
Paolo Neri ◽  
Alessandro Paoli ◽  
Ciro Santus
Keyword(s):  
Single Point ◽  
Excitation Frequency ◽  
Phase Variation ◽  
Operating Conditions ◽  
Image Correlation ◽  
Response Analysis ◽  
Full Field ◽  
Low Speed ◽  
Bladed Disk ◽  
Depth Analysis

Vibration measurements of turbomachinery components are of utmost importance to characterize the dynamic behavior of rotating machines, thus preventing undesired operating conditions. Local techniques such as strain gauges or laser Doppler vibrometers are usually adopted to collect vibration data. However, these approaches provide single-point and generally 1D measurements. The present work proposes an optical technique, which uses two low-speed cameras, a multimedia projector, and three-dimensional digital image correlation (3D-DIC) to provide full-field measurements of a bladed disk undergoing harmonic response analysis (i.e., pure sinusoidal excitation) in the kHz range. The proposed approach exploits a downsampling strategy to overcome the limitations introduced by low-speed cameras. The developed experimental setup was used to measure the response of a bladed disk subjected to an excitation frequency above 6 kHz, providing a deep insight in the deformed shapes, in terms of amplitude and phase distributions, which could not be feasible with single-point sensors. Results demonstrated the system’s effectiveness in measuring amplitudes of few microns, also evidencing blade mistuning effects. A deeper insight into the deformed shape analysis was provided by considering the phase maps on the entire blisk geometry, and phase variation lines were observed on the blades for high excitation frequency.

Energy Harvesting From the Vibrations of Rotating Systems

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Christopher G. Cooley ◽  
Tan Chai
Keyword(s):  
Rotation Speed ◽  
Excitation Frequency ◽  
Average Power ◽  
Local Maximum ◽  
Operating Conditions ◽  
Centripetal Acceleration ◽  
Local Maxima ◽  
Closed Form Solutions ◽  
Energy Harvesters ◽  
Wide Range

This study investigates the vibration of and power harvested by typical electromagnetic and piezoelectric vibration energy harvesters when applied to vibrating host systems that rotate at constant speed. The governing equations for these electromechanically coupled devices are derived using Newtonian mechanics and Kirchhoff's voltage law. The natural frequency for these devices is speed-dependent due to the centripetal acceleration from their constant rotation. Resonance diagrams are used to identify excitation frequencies and speeds where these energy harvesters have large amplitude vibration and power harvested. Closed-form solutions are derived for the steady-state response and power harvested. These devices have multifrequency dynamic response due to the combined vibration and rotation of the host system. Multiple resonances are possible. The average power harvested over one oscillation cycle is calculated for a wide range of operating conditions. Electromagnetic devices have a local maximum in average harvested power that occurs near a specific excitation frequency and rotation speed. Piezoelectric devices, depending on their mechanical damping, can have two local maxima of average power harvested. Although these maxima are sensitive to small changes in the excitation frequency, they are much less sensitive to small changes in rotation speed.

CFD Simulation of a Co-rotating Twin-screw Extruder: Validation of a Rheological Model for a Starch-Based Dough for Snack Food

2017 ◽  
Vol 14 (2) ◽  
Author(s):  
Giorgia Tagliavini ◽  
Federico Solari ◽  
Roberto Montanari
Keyword(s):  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Operating Conditions ◽  
Second Phase ◽  
Snack Food ◽  
Suitable Model ◽  
Twin Screw Extruder ◽  
Parallel Plates ◽  
Screw Extruder ◽  
Twin Screw

AbstractThe extrusion of starch-based products has been a matter of interest, especially for the pasta and the snack food production. In recent years, twin-screw extruders for snack food have been studied from both structural and fluid dynamics viewpoints. This project started from the rheological characterization of a starch-based dough (corn 34 wt%, tapioca 32 wt%), comparing viscosity values acquired in laboratory with different theoretical models found in literature. A computational fluid dynamic (CFD) simulation recreating the simple case of a fluid flow between two parallel plates was carried out to validate the former comparison. After the rheological validation was completed, the second phase of this work covered a 3D CFD simulation of the first part of the twin-screw extruder (feeding zone). The objective was to find a suitable model for describing the dough rheological behavior and the operating conditions of a co-rotating intermeshing twin-screw extruder. Once the model would be defined, it would allow to investigate several working conditions and different screws geometries of the machine, predicting the evolution of the product rheological properties.

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