scholarly journals Forced Response Analysis of an Aerodynamically Detuned Supersonic Turbomachine Rotor

1986 ◽  
Vol 108 (2) ◽  
pp. 117-124 ◽  
Author(s):  
D. Hoyniak ◽  
S. Fleeter
Keyword(s):  
High Performance ◽  
Maximum Amplitude ◽  
Aircraft Engine ◽  
Forced Response ◽  
Rotor Blades ◽  
Response Analysis ◽  
Axial Component ◽  
Compressor Blades ◽  
Response Characteristics ◽  
Influence Coefficients

High-performance aircraft engine fan and compressor blades are vulnerable to aerodynamically forced vibrations generated by inlet flow distortions due to wakes from upstream blade and vane rows, atmospheric gusts, and maldistributions in inlet ducts. In this paper, an analysis is developed to predict the flow-induced forced response behavior of an aerodynamically detuned rotor operating in a supersonic flow with a subsonic axial component. The aerodynamic detuning is achieved by alternating the circumferential spacing of adjacent rotor blades. The total unsteady aerodynamic loading acting on the blading, due to the convection of the transverse gust past the airfoil cascade and the resulting motion of the cascade, is developed in terms of influence coefficients. This analysis is then utilized to investigate the effect of aerodynamic detuning on the forced response characteristics of a 12-bladed rotor, with Verdon’s Cascade B flow geometry as a uniformly spaced baseline configuration. The results of this study indicate that for forward traveling wave gust excitations, aerodynamic detuning is generally very beneficial, resulting in significantly decreased maximum amplitude blade responses for many interblade phase angles.

Geometrical Variability Modelling of Axial Compressor Blisk Aerofoils and Evaluation of Impact on the Forced Response Problem

2020 ◽  
Author(s):  
Marco Gambitta ◽  
Arnold Kühhorn ◽  
Sven Schrape
Keyword(s):  
Computational Models ◽  
Axial Compressor ◽  
Principal Component ◽  
Forced Response ◽  
Rotor Blades ◽  
Civil Aviation ◽  
Mode Shapes ◽  
Stochastic Representation ◽  
Compressor Blades ◽  
Multiple Variable

Abstract The present work focuses on the effect of the manufacturing geometrical variability on the high-pressure compressor of a turbofan engine for civil aviation. The deviations of the geometry over the axial compressor blades are studied and modeled for the representation in the computational models. Such variability is of particular interest for the forced response problem, where small deviations of the geometry from the ideal nominal model can cause significant differences in the vibrational responses. The information regarding the geometrical mistuning is extracted from a set of manufactured components surface scans of a blade integrated disk (blisk) rotor. The optically measured geometries are parameterized, defining a set of opportune variables to describe the deviations. The dimension of the variables domain is reduced using the principal component analysis approach and a reconstruction of the modeled geometries is performed for the implementation in CFD and FEM solvers. The generated model allows a stochastic representation of the variability, providing an optimal set of variables to represent it. The aeroelastic analyses considering geometry based mistuning is carried out on a test-rig case, focusing on how such variability can affect the modal forcing generated on the blades. The force generated by the unsteady pressure field over the selected vibrational mode shapes of the rotor blades is computed through a validated CFD model. The uncertainty quantification of the geometrical variability effect on the modal forcing is performed employing Monte Carlo methods on a reduced model for the CFD solution, based on a single passage multi-blade row setup. The amplitude shift of the unsteady modal forcing is studied for different engine orders. In particular the scatter of the main engine orders forcing amplitudes for the manufactured blades can be compared with the nominal responses to predict the possible amplification due to the geometrical variability. Finally the results are compared to a full assembly computational model to assess the influence of multiple variable blades.

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.

Stator Blades Manufacturing Geometrical Variability in Axial Compressors and Impact on the Aeroelastic Excitation Forces

2021 ◽  
pp. 1-16
Author(s):  
Marco Gambitta ◽  
Arnold Kühhorn ◽  
Bernd Beirow ◽  
Sven Schrape
Keyword(s):  
Manufacturing Process ◽  
Axial Compressor ◽  
Reconstruction Algorithm ◽  
Forced Response ◽  
Rotor Blades ◽  
Compressor Blades ◽  
Input Uncertainty ◽  
Axial Compressors ◽  
Compressor Rotor ◽  
The Impact

Abstract The manufacturing geometrical variability is an unavoidable source of uncertainty in the realization of machinery components. Deviations of a part geometry from its nominal design are inevitably present due to the manufacturing process. In the aeroelastic forced response problem within axial compressors, these uncertainties may affect the vibration characteristics. Therefore, the impact of geometrical uncertainties due to the manufacturing process onto the modal forcing of axial compressor blades is investigated. The research focuses on the vibrational behavior of an axial compressor rotor blisk. In particular, the amplitude of the forces acting as source of excitation on the vibrating blades is studied. The geometrical variability of the upstream stator is investigated as input uncertainty. The variability is modeled starting from a series of optical surface scans. A stochastic model is created to represent the measured manufacturing geometrical deviations from the nominal model. A data reduction methodology is proposed to represent the uncertainty with a minimal set of variables. The manufacturing geometrical variability model allows to represent the input uncertainty and probabilistically evaluate its impact on the aeroelastic problem. An uncertainty quantification is performed in order to evaluate the resulting variability on the modal forcing acting on the vibrating rotor blades. Of particular interest is the possible rise of low engine orders due to the mistuned flow field along the annulus. A reconstruction algorithm allows the representation of the variability during one rotor revolution. The uncertainty on low harmonics of the modal rotor forcing can be therefore identified and quantified.

Experimentally Verified Study of Regeneration-Induced Forced Response in Axial Turbines

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Jens Aschenbruck ◽  
Joerg R. Seume
Keyword(s):  
Vibration Amplitude ◽  
Turbine Blades ◽  
Forced Response ◽  
Rotor Blades ◽  
Response Analysis ◽  
Reference Case ◽  
Angle Variation ◽  
Air Turbine ◽  
Axial Turbines ◽  
Stagger Angle

Geometrical variations occur in highly loaded turbine blades due to operation and regeneration. To determine the influence of such regeneration-induced variances of turbine blades on the aerodynamic excitation, a typical stagger angle variation of overhauled turbine blades is applied to stator vanes of an air turbine. This varied turbine stage is numerically and experimentally investigated. For the aerodynamic investigation of the vane wake, computational fluid dynamics (CFD) simulations are conducted. It is shown that the wake is changed due to the stagger angle variation. These results are confirmed by aerodynamic probe measurements in the air turbine. The vibration amplitude of the downstream rotor blades has been determined by a computational forced response analysis using a unidirectional fluid–structure interaction (FSI) approach and is experimentally verified here by tip-timing measurements. The results of the simulations and the measurements both show significantly higher amplitudes at certain operating points (OPs) due to the additional wake excitation. For typical regeneration-induced variations in stagger angle, the vibration amplitude is up to five times higher than in the reference case of uniform upstream stators. Based upon the present results, the influence of these variations and of the vane patterns on the vibration amplitude of the downstream rotor blade can and should be estimated in the regeneration process to minimize the dynamic stresses of the blades.

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.

Stator Blades Manufacturing Geometrical Variability in Axial Compressors and Impact on the Aeroelastic Excitation Forces

2021 ◽  
Author(s):  
Marco Gambitta ◽  
Arnold Kühhorn ◽  
Bernd Beirow ◽  
Sven Schrape
Keyword(s):  
Manufacturing Process ◽  
Axial Compressor ◽  
Reconstruction Algorithm ◽  
Forced Response ◽  
Rotor Blades ◽  
Compressor Blades ◽  
Input Uncertainty ◽  
Axial Compressors ◽  
Compressor Rotor ◽  
The Impact

Abstract The manufacturing geometrical variability is a source of uncertainty, which cannot be avoided in the realization of machinery components. Deviations of a part geometry from its nominal design are inevitably present due to the manufacturing process. In the case of the aeroelastic forced response problem within axial compressors, these uncertainties may affect the vibration characteristics. For this reason, the impact of geometrical uncertainties due to the manufacturing process onto the modal forcing of axial compressor blades is investigated in this study. The research focuses on the vibrational behavior of an axial compressor rotor blisk. In particular the amplitude of the forces acting as source of excitation on the vibrating blades is studied. The geometrical variability of the upstream stator is investigated as input uncertainty. The variability is modeled starting from a series of optical surface scans. A stochastic model is created to represent the measured manufacturing geometrical deviations from the nominal model. A data reduction methodology is proposed in order to represent the uncertainty with a minimal set of variables. The manufacturing geometrical variability model allows to represent the input uncertainty and probabilistically evaluate its impact on the aeroelastic problem. An uncertainty quantification is performed in order to evaluate the resulting variability on the modal forcing acting on the vibrating rotor blades. Of particular interest is the possible rise of low engine orders due to the mistuned flow field along the annulus. A reconstruction algorithm allows the representation of the variability during one rotor revolution. The uncertainty on low harmonics of the modal rotor forcing can be therefore identified and quantified.

Effect of Ni3Al Coating on Vibration Suppression of Beams of Various Thicknesses

2021 ◽  
Vol 875 ◽  
pp. 294-301
Author(s):  
Shoaib Nadeem ◽  
Hasan Aftab Saeed ◽  
Imran Aziz ◽  
Khalid Mehmood
Keyword(s):  
Vibration Suppression ◽  
Piezoelectric Materials ◽  
Damping Ratio ◽  
Aircraft Engine ◽  
Forced Response ◽  
Response Analysis ◽  
Sharp Change ◽  
Thin Structures ◽  
Thin Coatings ◽  
Mechanical Coating

High cycle fatigue (HCF) caused by the vibratory stresses is the main cause of failure in many machine components, e.g. aircraft engine and gas turbine components, which has caused loss of many lives and billions of dollars. To avoid these kind of failures, vibratory stresses should be attenuated to an acceptable level, especially at resonant frequencies. A lot of previous studies have shown that thin coatings of different materials significantly reduced these vibratory stresses by adding extra damping to the system. These include viscoelastic materials, plasma graded coatings, piezoelectric materials, and magneto-mechanical damping material coatings, but some of these had applicability and performance issues. Among these thin coatings, magneto-mechanical materials are very effective in reducing these vibratory stresses significantly.In this study, the effect of different beam structure thicknesses under same magneto-mechanical coating of 0.2mm was studied. For this purpose, Ni3Al was applied as magneto-mechanical coating. The natural frequencies, damping ratios and displacements of beams were calculated before and after applying magneto-mechanical coatings using forced response analysis and hammer tests. The results indicated a sharp change in vibration characteristics i.e. natural frequency, damping ratio and beam deflections, of all the beams used. The results showed that the magneto-mechanical coatings were more effective when applied to thin structures as compared to thick structures, because thin structures have higher strains, which enabled magneto-mechanical coatings to dissipate larger amounts of energy of applied loadings, because performance of these coatings is strain dependent.

Multi-Stage Coupled Forced Response of Aircraft Engine Compressor and Turbine Bladed Discs

2016 ◽  
Author(s):  
Romuald Rzadkowski ◽  
Artur Maurin
Keyword(s):  
Maximum Stress ◽  
Aircraft Engine ◽  
Forced Response ◽  
Rotor Blades ◽  
Mode Shapes ◽  
Finite Element Models ◽  
Free And Forced Vibrations ◽  
Multi Stage ◽  
Engine Compressor ◽  
Engine Rotor

Considered here is the effect of multistage coupling on the dynamics of an aircraft engine rotor with eight mistuned bladed discs on a drum-disc shaft during foreign object ingestion (FOI). In the dynamic model, each disc had a different number of rotor blades. Free and forced vibrations were examined using finite element models of single rotating blades, bladed discs and an entire rotor with bladed discs. Calculations of the mode shapes of flexible mistuned bladed disc-shaft assemblies took into account simultaneous excitations of the first and second stages of the compressor and the turbine bladed disc with 0EO, 1EO and 2EO. The thus obtained maximal stress values of all of the rotor blades were carefully examined and compared with a tuned system to discover resonance conditions and coupling effects. Our investigation has shown that mistuning changes the stress distribution in individual rotor blades and the level of maximum stress increases in relation to single or multiple bladed disc excitation.

Representation and Analysis of Geometric Uncertainties in Rotor Blades

2018 ◽  
Author(s):  
Luigi Carassale ◽  
Silvia Bruzzone ◽  
Andrea Cavicchi ◽  
Michela Marrè Brunenghi
Keyword(s):  
Natural Frequencies ◽  
Principal Component ◽  
Forced Response ◽  
Rotor Blades ◽  
Negative Effects ◽  
Sensitivity Matrix ◽  
Compressor Blades ◽  
Simplified Approach ◽  
Geometric Uncertainties

Geometric uncertainties involved in the rotor blade manufacturing process are a major concern for designers. The deviation of the produced components from their nominal geometry have an impact on the Natural Frequencies (NF) that, under certain circumstances, may have negative effects on the dynamic forced response in operative conditions. Geometric defects are usually limited by imposing dimensional tolerances based on empirical considerations, simplified approach that may lead to costly manufacturing requirements that still may not guarantee safe results. This paper proposes a probabilistic representation of the geometric uncertainties for rotor blades and defines a procedure to evaluate their effects on the blade NFs. The deviation from nominal geometry is represented through the Principal Component Analysis (PCA) where it is expressed as a sum of characteristic geometric shapes (GUMs) modulated by mutually uncorrelated random variables (Principal Components, PC). The effect of each GUM is then linearly propagated on the blade NFs and a sensitivity matrix is finally defined. The procedure is applied to a case-study that concerns a set of 50 nominally identical compressor blades and the ability of GUMs to represent the effects of geometric uncertainties is tested.

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