Separation of Up and Downstream Forced Response Excitations of an Embedded Compressor Rotor

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
Shreyas Hegde ◽  
Zhiping Mao ◽  
Tianyu Pan ◽  
Laith Zori ◽  
Rubens Campregher ◽  
...  
Keyword(s):  
Forced Response ◽  
Response Analysis ◽  
Wave Reflections ◽  
Compressor Rotor ◽  
Forcing Function ◽  
Engine Order ◽  
Aerodynamic Interaction ◽  
Stator Vane ◽  
Modal Force ◽  
The Individual

The aerodynamic interaction of upstream and downstream blade rows can have a significant impact on the forced response of the compressor. Previously, the authors carried out the forced response analysis of a three-row stator-rotor-stator (S1-R2-S2) configuration from a 3.5-stage compressor. However, since the stator vane counts in both the stators (S1 and S2) were the same, it was not possible to separate the excitations from both the rows as they excited the rotor at the same frequency. Hence, a new configuration was developed and tested in which the stator 1 blade count was changed to 38 and stator 2 blade count was maintained at 44 in order to study the individual influences of the stator on the embedded rotor. By using this method, the excitations from both rows can be determined, and the excitations can be quantified to determine the row having the maximum influence on the overall forcing. To achieve this, two sets of simulations were carried out. The three-row stator-rotor (S1-R2-S2) simulation was carried out at both the 38EO (engine order) and 44EO crossings at the peak efficiency (PE) operating condition. The two-row stator-rotor analysis (S1-R2) was carried out at the 38EO crossing, and the other two-Row (R2-S2) analyses were carried out at the 44EO crossing. The steady aerodynamics was preserved in both the cases. A study was done to determine the contribution of wave reflections from the stator inlet and exit planes to the forcing function. Two conclusions drawn from this study are as follows: (1) the modal force value decreased after the upstream stator was removed, which proved that wave reflections from this stator were significant and (2) the increase in modal force was in-line with experimental observations.

Forced Response Sensitivity of a Mistuned Rotor From an Embedded Compressor Stage

2015 ◽  
Author(s):  
Fanny M. Besem ◽  
Robert E. Kielb ◽  
Nicole L. Key
Keyword(s):  
Experimental Data ◽  
Forced Response ◽  
Symmetric System ◽  
Response Analysis ◽  
Cfd Simulations ◽  
Forcing Function ◽  
Wear And Tear ◽  
The Individual ◽  
The Impact ◽  
Interblade Phase Angle

The frequency mistuning that occurs due to manufacturing variations and wear and tear of the blades can have a significant effect on the flutter and forced response behavior of a blade row. Similarly, asymmetries in the aerodynamic or excitation forces can tremendously affect the blade responses. When conducting CFD simulations, all blades are assumed to be tuned (i.e. to have the same natural frequency) and the aerodynamic forces are assumed to be the same on each blade except for a shift in interblade phase angle. The blades are thus predicted to vibrate at the same amplitude. However, when the system is mistuned or when asymmetries are present, some blades can vibrate with a much higher amplitude than the tuned, symmetric system. In this research, we first conduct a deterministic forced response analysis of a mistuned rotor and compare the results to experimental data from a compressor rig. It is shown that tuned CFD results cannot be compared directly with experimental data because of the impact of frequency mistuning on forced response predictions. Moreover, the individual impact of frequency, aerodynamic, and forcing function perturbations on the predictions is assessed, leading to the conclusion that a mistuned system has to be studied probabilistically. Finally, all perturbations are combined and Monte-Carlo simulations are conducted to obtain the range of blade response amplitudes that a designer could expect.

Impact of Multi-Row Aerodynamic Interaction on the Forced Response Behaviour of an Embedded Compressor Rotor

2020 ◽  
Author(s):  
Shreyas Hegde ◽  
Robert Kielb ◽  
Laith Zori ◽  
Rubens Campregher
Keyword(s):  
Higher Order ◽  
Forced Response ◽  
Operating Conditions ◽  
High Loading ◽  
Response Behavior ◽  
Wave Reflections ◽  
Peak Efficiency ◽  
Compressor Rotor ◽  
Higher Order Modes ◽  
Modal Force

Abstract This paper focuses on the impact of multi-row interaction on the forced response behavior of an embedded compressor rotor at higher order modes. The authors in previous papers have discussed about the multi-row influence at the torsional mode resonant crossing and this paper extends the study to higher order modes. The paper talks about both the steady and unsteady influence of having additional rows in the configuration. It makes use of the time transformation (TT) method available in CFX to reduce the number of passages required in each row. Since the number of vanes from both the stators and the inlet guide vanes (IGV) is the same, the excitations from upstream rows and the potential field influence of the downstream row all contribute to the forcing, which is quantified both in terms of modal force and individual blade response. This paper describes the multi-row influence on the chordwise bending modes at both the peak efficiency (PE) and the high loading (HL) operating condition. To ascertain this influence, a 3-row case with just the two neighboring stators (S1, R2, S2 a 4-row case with the downstream rotor as well (S1, R2, S2, R3) and a 5-row with the upstream IGV were considered. While the 3-row case helped to determine the influence of neighboring stators on the forcing, the 4-row case provided the influence of the downstream rotor on the forced response behavior. Since the number of IGV vanes was the same as the neighboring stators the nature of interference between the stator and IGV wakes was determined as well. The 4-row case helped investigate physical wave reflections off a downstream rotating row, which had a significant influence on the modal force. The final section of the paper focuses on the mistuning response, which essentially couples frequency variations with the structural and aerodynamic aspects to predict individual blade responses, which are compared to experimental data. A mistuning analysis was carried out with the frequency mistuning present in the experimental facility Some of the key conclusions from this investigation are: 1) The interference of the IGV with the downstream stator (S1) is destructive at peak efficiency and constructive at high loading in line with the previous observation at torsional modes; 2) Physical wave reflections are constructive at all operating conditions at higher order modes unlike torsional modes where it was destructive; 3) The 3-row case gives the most accurate prediction in terms of average blade response and the 5-row case in terms of maximum blade response. Hence one of the significant findings is that, the aeromechanical behavior can be ascertained to a great deal of accuracy using just 3-rows at higher order modes crossings.

Influence of Disc Modes and Sideband Excitations on the Mistuned Forced Response Behaviour of an Embedded Compressor Rotor

2021 ◽  
Author(s):  
Shreyas Hegde ◽  
Andrew Madden ◽  
Robert Kielb
Keyword(s):  
Computational Cost ◽  
Axial Compressor ◽  
Travelling Wave ◽  
Forced Response ◽  
Operating Conditions ◽  
Operating Condition ◽  
Compressor Rotor ◽  
Forcing Function ◽  
Highly Sensitive ◽  
The Individual

Abstract This paper focusses on predicting the mistuned forced response behavior of an embedded compressor rotor blade row in a 3.5 stage axial compressor. The authors in previous papers studied the multi-row influence on the forcing function for multiple operating conditions. For these investigations CFX was utilized to predict the forcing However, in the mistuned predictions a consistent underprediction of the amplification factor was noted A previous investigation by the authors [32] considered an isolated mode family. The current work considers the same configuration but looks at a non-isolated mode family which is in a frequency “veering” region. Also, since the mistuning code was formulated on the lines of the fundamental mistuning model (FMM) the model only included a single DOF per ND and hence modes in the veering region were not modeled. The current paper addresses both these shortcomings and talks about the influence of sideband travelling wave excitations at the HL operating condition (the details of the mistuned predictions at the PE operating condition can be found in [32]). The paper also talks in detail about the effect of modelling the disc modes individually using the FMM model as well as together using the component mistuning model (CMM) as present in ANSYS Mechanical. Key conclusions are: 1) The mistuned response tends to be amplified by all cases including the sideband excitations, 2) The coupled influence of including a disc mode in the FMM model and sideband excitations is dependent on the proximity of the mode to the blade alone frequency, 3) Although the CMM model predicts the peak of the response accurately, it does not offer any substantial advantage over the FMM model given the computational cost required for the CMM prediction. Also, the prediction is highly sensitive to the frequency of the individual modes that can differ between codes.

Influence of Rotor-Stator Interaction and Reflecting Boundary Conditions on Compressor Forced Response

2018 ◽  
Author(s):  
Zhiping Mao ◽  
Shreyas Hegde ◽  
Tianyu Pan ◽  
Robert E. Kielb ◽  
Laith Zori ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Wave Reflection ◽  
Computational Effort ◽  
Forced Response ◽  
Response Analysis ◽  
Forcing Function ◽  
Modal Force ◽  
Rotor Stator Interaction ◽  
Unsteady Simulation ◽  
Response Modeling

This paper focuses on the rotor forced response behavior in a 3.5-stage compressor rig. The aim is to provide an accurate prediction of forced response with the less computational effort. Previous research indicates that by reducing the computation domain from 7-row to a 3-row stator-rotor-stator (S1-R2-S2) configuration, the forcing function is over-predicted by 60%. To address this over prediction, an investigation of boundary conditions and a study with additional rows are conducted. The influence of reflecting boundary conditions on the blade modal force is studied by preventing wave reflection. Additionally, a 5-row simulation is studied to take an extra source of excitation force, the IGV row with the same blade count as the other stators, into consideration. Three conclusions were drawn from this study: 1) boundary reflection has a significant influence on unsteady simulation and the modal force, thus should be avoided by using mesh treatment up and down stream; 2) the IGV wake contributes to the forcing function and cannot be ignored; 3) the clocking feature of IGV, S1, and S2 leads to a transfer of energy from 1st harmonic to other higher harmonics. This research provides a guidance of forced response modeling and can be employed for industrial forced response analysis.

Piezoelectric Networks for Vibration Suppression of Mistuned Bladed Disks

2007 ◽  
Vol 129 (5) ◽  
pp. 559-566 ◽  
Author(s):  
Hongbiao Yu ◽  
K. W. Wang
Keyword(s):  
Vibration Suppression ◽  
Periodic Structures ◽  
Electric Circuit ◽  
Forced Response ◽  
Bladed Disks ◽  
Vibration Localization ◽  
Network Concept ◽  
Engine Order ◽  
The Individual ◽  
Local Circuits

Extensive investigations have been conducted to study the vibration localization phenomenon and the excessive forced response that can be caused by mistuning in bladed disks. Most previous researches have focused on analyzing∕predicting localization or attacking the mistuning issue via mechanical tailoring. Few have focused on developing effective vibration control methods for such systems. This study extends the piezoelectric network concept, which has been utilized for mode delocalization in periodic structures, to the control of mistuned bladed disks under engine order excitation. A piezoelectric network is synthesized and optimized to effectively suppress vibration in bladed disks. One of the merits of such an approach is that the optimum design is independent of the number of spatial harmonics, or engine orders. Local circuits are first formulated by connecting inductors and resistors with piezoelectric patches on the individual blades. Although these local circuits can function as conventional damped absorber when properly tuned, they do not perform well for bladed disks under all engine order excitations. To address this issue, capacitors are introduced to couple the individual local circuitries. Through such networking, an absorber system that is independent of the engine order can be achieved. Monte Carlo simulation is performed to investigate the effectiveness of the network for a bladed disk with a range of mistuning level of its mechanical properties. The robustness issue of the network in terms of detuning of the electric circuit parameters is also studied. Finally, negative capacitance is introduced and its effect on the performance and robustness of the network is investigated.

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.

Analysis of mistuned forced response in an axial high-pressure compressor rig with focus on Tyler–Sofrin modes

2019 ◽  
Vol 123 (1261) ◽  
pp. 356-377
Author(s):  
F. Figaschewsky ◽  
A. Kühhorn ◽  
B. Beirow ◽  
T. Giersch ◽  
S. Schrape
Keyword(s):  
Axial Compressor ◽  
Maximum Amplitude ◽  
Forced Response ◽  
Operating Conditions ◽  
Cfd Simulations ◽  
High Pressure Compressor ◽  
Engine Order ◽  
Stator Vane ◽  
Vibration Responses ◽  
The Impact

ABSTRACTThis paper aims at contributing to a better understanding of the effect of Tyler–Sofrin Modes (TSMs) on forced vibration responses by analysing a 4.5-stage research axial compressor rig. The first part starts with a brief review of the involved physical mechanisms and necessary prerequisites for the generation of TSMs in multistage engines. This review is supported by unsteady CFD simulations of a quasi 2D section of the studied engine. It is shown that the amplitude increasing effect due to mistuning can be further amplified by the presence of TSMs. Furthermore, the sensitivity with respect to the structural coupling of the blades and the damping as well as the shape of the expected envelope is analysed.The second part deals with the Rotor 2 blisk of the research compressor rig. The resonance of a higher blade mode with the engine order of the upstream stator is studied in two different flow conditions realised by different variable stator vane (VSV) schedules which allows to separate the influence of TSMs from the impact of mistuning. A subset of nominal system modes representation of the rotor is used to describe its mistuned vibration behaviour, and unsteady CFD simulations are used to characterise the present strength of the TSMs in the particular operating conditions. Measured maximum amplitude vs blade pattern and frequency response functions are compared against the predictions of the aeromechanical models in order to assess the strength of the TSMs as well as its influence on vibration levels.

Forced Response Analysis of a Transonic Fan

2012 ◽  
Author(s):  
Parthasarathy Vasanthakumar ◽  
Paul-Benjamin Ebel
Keyword(s):  
Finite Element ◽  
Flow Field ◽  
Forced Response ◽  
Navier Stokes ◽  
Response Analysis ◽  
Aerodynamic Damping ◽  
Forcing Function ◽  
Transonic Fan ◽  
Work Done ◽  
Highly Loaded

The forced response of turbomachinery blades is a primary source of high cycle fatigue (HCF) failure. This paper deals with the computational prediction of blade forced response of a transonic fan stage that consists of a highly loaded rotor along with a tandem stator. In the case of a transonic fan, the forced response of the rotor due to the downstream stator assumes significance because of the transonic flow field. The objective of the present work is to determine the forced response of the rotor induced as a result of the unsteady flow field due to the downstream stator vanes. Three dimensional, Navier-Stokes flow solver TRACE is used to numerically analyse the forced response of the fan. A total of 11 resonant crossings as identified in the Campbell diagram are examined and the corresponding modeshapes are obtained from finite element modal analysis. The interaction between fluid and structure is dealt with in a loosely coupled manner based on the assumption of linear aerodynamic damping. The aerodynamic forcing is obtained by a nonlinear unsteady Navier-Stokes computation and the aerodynamic damping is obtained by a time-linearized Navier-Stokes computation. The forced response solution is obtained by the energy method allowing calculations to be performed directly in physical space. Using the modal forcing and damping, the forced response amplitude can be directly computed at the resonance crossings. For forced response solution, the equilibrium amplitude is reached when the work done on the blade by the external forcing function is equal to the work done by the system damping (aerodynamic and structural) force. A comprehensive analysis of unsteady aerodynamic forces on the rotor blade surface as a result of forced response of a highly loaded transonic fan is carried out. In addition, the correspondence between the location of high stress zones identified from the finite element analysis and the regions of high modal force identified from the CFD analysis is also discussed.

A Discrete Model to Consider the Influence of the Air Flow on Blade Vibrations of an Integral Blisk Compressor Rotor

2008 ◽  
Author(s):  
Bernd Beirow ◽  
Arnold Ku¨hhorn ◽  
Sven Schrape
Keyword(s):  
Air Flow ◽  
Forced Response ◽  
Response Analysis ◽  
Element Analysis ◽  
Compressor Rotor ◽  
Aerodynamic Properties ◽  
Cascade Arrangement ◽  
Simple Mass ◽  
Mass Spring ◽  
Elastically Supported

The influence of the aerodynamic coupling in the forced response analysis of a HPC test-blisk is studied by means of a reduced order mechanical model. In the first step this equivalent blisk model (EBM) is derived based on a finite element analysis of the disk from design and an adjustment to experimentally determined blade alone frequencies in order to consider the real blade mistuning. Applying the EBM — so far not considering the air flow influence — to carry out forced response analyses due to a rotating excitation acting on the stationary blisk, a maximum blade displacement amplification of more than 50% has been calculated comparing the tuned and the mistuned blisk. Aiming at an additional consideration of the air flow, fully coupled computations of the fluid structure interaction (FSI) are exemplarily carried out for elastically supported blades in a cascade arrangement. The results are used to calibrate simple mass-spring-damper models from which quantities of additional aerodynamic elements in terms of a consideration of co-vibrating air masses, air stiffening and aerodynamic damping are derived. Based on this information the EBM is extended to a so called advanced EBM. Aerodynamic influences are considered assigning the aerodynamic properties to each blade in dependence on the inter blade phase angle (IBPA). Forced response analyses, now including all aerodynamic influences, show that for an extreme application of a rear blisk close to the combustion chamber and under MTO conditions a strong smoothing of originally localized vibration modes occurs. The maximum blade displacement amplification due to mistuning is decreased from more than 50% to below 12% for the first blade flap mode.

Forced Response Sensitivity of a Mistuned Rotor From an Embedded Compressor Stage

2015 ◽  
Vol 138 (3) ◽  
Author(s):  
Fanny M. Besem ◽  
Robert E. Kielb ◽  
Nicole L. Key
Keyword(s):  
Axial Compressor ◽  
Forced Response ◽  
Fast Method ◽  
Forcing Function ◽  
Timing Data ◽  
Wear And Tear ◽  
Computational Fluid Dynamics Cfd ◽  
Cfd Analyses ◽  
The Individual ◽  
Wave Coordinates

The frequency mistuning that occurs due to manufacturing variations and wear and tear of the blades has been shown to significantly affect the flutter and forced response behavior of a blade row. While tuned computational fluid dynamics (CFD) analyses are now an integral part of the design process, designers need a fast method to evaluate the localized high blade responses due to mistuning. In this research, steady and unsteady analyses are conducted on the second-stage rotor of an axial compressor, excited at the first torsion vibratory mode. A deterministic mistuning analysis is conducted using the numerical modal forces and the individual blade frequencies obtained experimentally by tip timing data. The mistuned blade responses are compared in the physical and traveling wave coordinates to the experimental data. The individual and combined impacts of frequency, aerodynamic, and forcing function perturbations on the predictions are assessed, highlighting the need to study mistuned systems probabilistically.

Sign in / Sign up

Export Citation Format

Share Document