Acoustic Resonance in an Axial Multistage Compressor Leading to Non-Synchronous Blade Vibration

2020 ◽  
Author(s):  
Anne-Lise Fiquet ◽  
Agathe Vercoutter ◽  
Nicolas Buffaz ◽  
Stéphane Aubert ◽  
Christoph Brandstetter
Keyword(s):  
Acoustic Waves ◽  
High Speed ◽  
Numerical Study ◽  
Acoustic Resonance ◽  
Structural Vibration ◽  
Wave Number ◽  
Blade Vibration ◽  
Acoustic Modes ◽  
Blade Vibrations ◽  
Circumferential Wave

Abstract Significant non-synchronous blade vibrations (NSV) have been observed in an experimental three-stage high-speed compressor at part-speed conditions. High amplitude acoustic modes, propagating around the circumference and originating in the highly loaded Stage-3 have been observed in coherence with the structural vibration mode. In order to understand the occurring phenomena, a detailed numerical study has been carried out to reproduce the mechanism. Unsteady full annulus RANS simulations of the whole setup have been performed using the solver elsA. The results revealed the development of propagating acoustic modes which are partially trapped in the annulus and are in resonance with an aerodynamic disturbance in Rotor-3. The aerodynamic disturbance is identified as an unsteady separation of the blade boundary layer in Rotor-3. The results indicate that the frequency and phase of the separation adapt to match those of the acoustic wave, and are therefore governed by acoustic propagation conditions. Furthermore, the simulations clearly show the modulation of the propagating wave with the rotor blades, leading to a change of circumferential wave numbers while passing the blade row. To analyze if the effect is self-induced by the blade vibration, a noncoherent structural mode has been imposed in the simulations. Even at high vibration amplitude the formerly observed acoustic mode did not change its circumferential wave number. This phenomenon is highly relevant to modern compressor designs, since the appearance of the axially propagating acoustic waves can excite blade vibrations if they coincide with a structural eigenmode, as observed in the presented experiments.

ACOUSTIC RESONANCE IN AN AXIAL MULTISTAGE COMPRESSOR LEADING TO NON-SYNCHRONOUS BLADE VIBRATION

2021 ◽  
pp. 1-12
Author(s):  
Anne Lise Fiquet ◽  
Stephane Aubert ◽  
Christoph Brandstetter ◽  
Nicolas Buffaz ◽  
Agathe Vercoutter
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Acoustic Resonance ◽  
High Amplitude ◽  
Acoustic Mode ◽  
Structural Vibration ◽  
Wave Number ◽  
Blade Vibration ◽  
Acoustic Modes ◽  
Circumferential Wave

Abstract Significant non-synchronous blade vibrations (NSV) have been observed in an experimental three-stage high-speed compressor at part-speed conditions. High amplitude acoustic modes, propagating around the circumference and originating in the highly loaded Stage-3 have been observed in coherence with the structural vibration mode. In order to understand the occurring phenomena, a detailed numerical study has been carried out to reproduce the mechanism. Unsteady full annulus RANS simulations of the whole setup have been performed using the solver elsA. The results revealed the development of propagating acoustic modes which are partially trapped in the annulus and are in resonance with an aerodynamic disturbance in Rotor-3. The aerodynamic disturbance is identified as an unsteady separation of the blade boundary layer in Rotor-3. The results indicate that the frequency and phase of the separation adapt to match those of the acoustic wave, and are therefore governed by acoustic propagation conditions. Furthermore, the simulations clearly show the modulation of the propagating wave with the rotor blades, leading to a change of circumferential wave numbers while passing the blade row. To analyze if the effect is self-induced by the blade vibration, a non-coherent structural mode has been imposed in the simulations. Even at high vibration amplitude the formerly observed acoustic mode did not change its circumferential wave number. This phenomenon is highly relevant to modern compressor designs as observed in the presented experiments.

Acoustic-Structural Coupling in Pipework

2007 ◽  
Author(s):  
Hugh Goyder
Keyword(s):  
Acoustic Waves ◽  
Alternative Assessment ◽  
Natural Frequencies ◽  
Assessment Tool ◽  
Acoustic Resonance ◽  
Assessment Method ◽  
Structural Vibration ◽  
Simple Method ◽  
Set Up ◽  
Two Degree Of Freedom

If an acoustic resonance is set up in a pipework system then it may cause structural vibration which can lead to a catastrophic fatigue failure. An investigation is made into the coupling between acoustic waves and pipework stress with the objective of developing a simple method for determining if stresses are excessive. The analysis of the coupled acoustic and structural vibration results in a two-degree-of-freedom model with two natural frequencies and two damping ratios. This model is impractical as an assessment tool because the natural frequencies and damping ratios are either not known at all or are only known imperfectly. The model is therefore manipulated to give the stress corresponding to the most unfavourable conditions for the natural frequencies. This results in a useful assessment equation which may be used in practical circumstances. Comparisons are made with an alternative assessment method based on uncoupled behaviour.

Mechanism of Nonsynchronous Blade Vibration in a Transonic Compressor Rig

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Daniel Möller ◽  
Maximilian Jüngst ◽  
Felix Holzinger ◽  
Christoph Brandstetter ◽  
Heinz-Peter Schiffer ◽  
...  
Keyword(s):  
Numerical Study ◽  
Stability Limit ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Structural Vibration ◽  
Blade Vibration ◽  
Tip Clearance Flow ◽  
Transonic Compressor ◽  
Clearance Flow ◽  
Fluctuation Pattern

This paper presents a numerical study on blade vibration for the transonic compressor rig at the Technische Universität Darmstadt (TUD), Darmstadt, Germany. The vibration was experimentally observed for the second eigenmode of the rotor blades at nonsynchronous frequencies and is simulated for two rotational speeds using a time-linearized approach. The numerical simulation results are in close agreement with the experiment in both cases. The vibration phenomenon shows similarities to flutter. Numerical simulations and comparison with the experimental observations showed that vibrations occur near the compressor stability limit due to interaction of the blade movement with a pressure fluctuation pattern originating from the tip clearance flow. The tip clearance flow pattern travels in the backward direction, seen from the rotating frame of reference, and causes a forward traveling structural vibration pattern with the same phase difference between blades. When decreasing the rotor tip gap size, the mechanism causing the vibration is alleviated.

Damping of Acoustic Waves in Pipelines due to End Conditions

2013 ◽  
Author(s):  
Hugh Goyder
Keyword(s):  
Acoustic Waves ◽  
Wave Amplitude ◽  
Acoustic Resonance ◽  
Resonant Mode ◽  
Structural Vibration ◽  
Acoustic Model ◽  
Simplified Models ◽  
Physical Behaviour ◽  
End Conditions ◽  
Simple Equations

Acoustic waves in pipelines are of concern because they can cause failure due to structural vibration and fatigue. The maximum wave amplitude that can be generated is limited by damping; a good understanding of damping is therefore vital. The damping considered here is due to the loss of energy from a resonant mode at a reflecting boundary. This type of damping is straightforward to analysis and consequently simple equations for damping are developed. A further aspect of damping is that it considerably modifies the description of acoustic resonance. The use of damped acoustic modes is shown to be problematic because they are complex and do not satisfy orthogonally conditions. A further and more significant observation is that damping prevents modes from being uncoupled and considered as independent. An uncoupled configuration is always found in undamped modes and is useful in forming simplified models however such uncoupling does not, in general, extend to damped modes. A condition for determining if modes can be uncoupled is derived. If a damped mode, which is not uncoupled, is used in an acoustic model it can generate energy as well as absorb energy. This non-physical behaviour greatly complicates the analysis of acoustic systems with damping.

scholarly journals Wavelet Analysis of Experimental Blade Vibrations During Interaction With an Abradable Coating

2014 ◽  
Vol 136 (3) ◽  
Author(s):  
Romain Mandard ◽  
Jean-François Witz ◽  
Yannick Desplanques ◽  
Jacky Fabis ◽  
Jean Meriaux
Keyword(s):  
Wavelet Transform ◽  
Continuous Wavelet Transform ◽  
High Speed ◽  
Continuous Wavelet ◽  
High Speed Imaging ◽  
Blade Vibration ◽  
Time Frequency ◽  
Abradable Coating ◽  
Blade Vibrations ◽  
Blade Tip

Minimizing the clearance between turbofan blades and the surrounding casing is a key factor to achieving compressor efficiency. The deposition of an abradable coating on casings is one of the technologies used to reduce this blade-casing clearance and ensure blade integrity in the event of blade-casing contact. Aircraft in-service conditions may lead to interactions between the blade tip and the coated casing, during which wear of the abradable coating, blade dynamics, and interacting force are critical yet little-understood issues. In order to study blade/abradable-coating interactions of a few tens of milliseconds, experiments were conducted on a dedicated test rig. The experimental data were analyzed with the aim of determining the friction-induced vibrational modes of the blade. This involved a time-frequency analysis of the experimental blade strain using continuous wavelet transform (CWT) combined with a modal analysis of the blade. The latter was carried out with two kinds of kinematic boundary conditions at the blade tip: free and modified, by imposing contact with the abradable coating. The interaction data show that the blade vibration modes identified during interactions correspond to the free boundary condition due to the transitional nature of the phenomena and the very short duration of contacts. The properties of the continuous wavelet transform were then used to identify the occurrence of blade-coating contact. Two kinds of blade/abradable-coating interactions were identified: bouncing of the blade over short time periods associated with loss of abradable material and isolated contacts capable of amplifying the blade vibrations without causing significant wear of the abradable coating. The results obtained were corroborated by high-speed imaging of the interactions.

The Influence of Neighboring Blade Rows on the Unsteady Aerodynamic Response of Cascades

1997 ◽  
Vol 119 (1) ◽  
pp. 85-93 ◽  
Author(s):  
K. C. Hall ◽  
P. D. Silkowski
Keyword(s):  
Linear Equations ◽  
Forced Response ◽  
Analytical Models ◽  
Wave Number ◽  
Computationally Efficient ◽  
Blade Vibration ◽  
Transmission Coefficients ◽  
Unsteady Aerodynamic ◽  
Blade Row ◽  
Circumferential Wave

In this paper, we present an analysis of the unsteady aerodynamic response of cascades due to incident gusts (the forced response problem) or blade vibration (the flutter problem) when the cascade is part of a multistage fan, compressor, or turbine. Most current unsteady aerodynamic models assume the cascade to be isolated in an infinitely long duct. This assumption, however, neglects the potentially important influence of neighboring blade rows. We present an elegant and computationally efficient method to model these neighboring blade row effects. In the present method, we model the unsteady aerodynamic response due to so-called spinning modes (pressure and vorticity waves), with each mode corresponding to a different circumferential wave number and frequency. Then, for each mode, we compute the reflection and transmission coefficients for each blade row. These coefficients can be obtained from any of the currently available unsteady linearized aerodynamic models of isolated cascades. A set of linear equations is then constructed that couples together the various spinning modes, and the linear equations are solved via LU decomposition. Numerical results are presented for both the gust response and blade vibration problems. To validate our model, we compare our results to other analytical models, and to a multistage vortex lattice model. We show that the effect of neighboring blade rows on the aerodynamic damping of vibrating cascades is significant, but nevertheless can be modeled with a small number of modes.

scholarly journals The Influence of Neighboring Blade Rows on the Unsteady Aerodynamic Response of Cascades

1995 ◽  
Author(s):  
Kenneth C. Hall ◽  
Peter D. Silkowski
Keyword(s):  
Linear Equations ◽  
Forced Response ◽  
Analytical Models ◽  
Wave Number ◽  
Computationally Efficient ◽  
Blade Vibration ◽  
Transmission Coefficients ◽  
Unsteady Aerodynamic ◽  
Blade Row ◽  
Circumferential Wave

In this paper, we present an analysis of the unsteady aerodynamic response of cascades due to incident gusts (the forced response problem) or blade vibration (the flutter problem) when the cascade is part of a multistage fan, compressor, or turbine. Most current unsteady aerodynamic models assume the cascade to be isolated in an infinitely long duct. This assumption, however, neglects the potentially important influence of neighboring blade rows. We present an elegant and computationally efficient method to model these neighboring blade row effects. In the present method, we model the unsteady aerodynamic response due to so-called spinning modes (pressure and vorticity waves), with each mode corresponding to a different circumferential wave number and frequency. Then, for each mode, we compute the reflection and transmission coefficients for each blade row. These coefficients can be obtained from any of the currently available unsteady linearized aerodynamic models of isolated cascades. A set of linear equations is then constructed that couples together the various spinning modes, and the linear equations are solved via LU decomposition. Numerical results are presented for both the gust response and blade vibration problems. To validate our model, we compare our results to other analytical models, and to a multistage vortex lattice model. We show that the effect of neighboring blade rows on the aerodynamic damping of vibrating cascades is significant, but nevertheless can be modeled with a small number of modes.

Non-Synchronous Aeroacoustic Interaction in an Axial Multi-Stage Compressor

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Anne-Lise Fiquet ◽  
Christoph Brandstetter ◽  
Stéphane Aubert ◽  
Mickael Philit
Keyword(s):  
Rotor Blade ◽  
High Speed ◽  
Acoustic Mode ◽  
Blade Vibration ◽  
Unsteady Pressure ◽  
Multi Stage ◽  
Engine Order ◽  
Major Interest ◽  
Blade Vibrations ◽  
Magnet Coil

Abstract Non-engine order rotor blade vibration is an aeroelastic phenomenon of major interest for compressor designers resulting from excitation of rotor blade modes through aerodynamic instabilities. Indicators for a comparable type of instability, caused by propagating acoustic modes, have been observed in an experimental multistage high-speed compressor by Safran Helicopter Engines. It is intended to understand the cause of these instabilities by combining experimental data and numerical simulations. Unsteady pressure measurements were carried out by case-mounted and stator-mounted transducers. Rotor tip-timing and magnet-coil sensor systems were installed to measure the blade vibrations. Experimental results show non-engine order signatures in the unsteady pressure signal coherent to the shifted frequency of blade vibrations. In the present paper, the waveform of these oscillations is analyzed in detail, showing a dominant propagating acoustic mode interacting with vibrations of rotor 2. The root cause for the non-synchronous oscillations is identified as an acoustic mode that is cutoff downstream of rotor 3. During the test, the mode changes its frequency and circumferential order, affecting the amplitude of associated blade vibrations.

Measurements of Radial Vortices, Spill Forward and Vortex Breakdown in a Transonic Compressor

2017 ◽  
Author(s):  
Christoph Brandstetter ◽  
Maximilian Jüngst ◽  
Heinz-Peter Schiffer
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Vortex Breakdown ◽  
Measurement Techniques ◽  
Leading Edge ◽  
Rotating Stall ◽  
Clear Correlation ◽  
Blade Vibration ◽  
Transonic Compressor ◽  
Blade Vibrations

The phenomena prior to rotating stall were investigated in a high-speed compressor test rig using optical and pneumatic measurement techniques. A number of throttling procedures was performed at transonic and subsonic speedlines with the aim to detect the unsteady effects initiating rotating stall or large amplitude blade vibrations. At transonic speed radial vortices traveling around the circumference were detected in the upstream part of the rotor using phase-locked PIV measurements above 92% span and unsteady wall pressure measurements. When these radial vortices impinge on a blade leading edge, they cause a forward spill of fluid around the leading edge. The effects are accompanied by a large-scale vortex breakdown in the blade passage leading to immense blockage in the endwall region. At subsonic speeds, the observed flow phenomena are similar but differ in intensity and structure. During the throttling procedure, blade vibration amplitudes were monitored using strain gauges and blade tip timing instrumentation. Non-synchronous blade vibrations in the first torsional eigenmode were measured as the rotor approached stall. Using the different types of instrumentation, it was possible to align the aerodynamic flow features with blade vibration levels. The results show a clear correlation between the occurrence of radial vortices and blade vibrations.

Numerical investigations on non-synchronous vibration and frequency lock-in of low-pressure steam turbine last stage

2021 ◽  
pp. 095765092110606
Author(s):  
Xiaocheng Zhu ◽  
Ping Hu ◽  
Tong Lin ◽  
Zhaohui Du
Keyword(s):  
Low Pressure ◽  
Wave Number ◽  
Global Maximum ◽  
Steam Turbines ◽  
Response Level ◽  
Blade Vibration ◽  
Pressure Steam ◽  
Blade Vibrations ◽  
Last Stage ◽  
Lock In

The flow phenomenon of rotating instability (RI) and its induced non-synchronous vibrations (NSV) in the last stage have gradually become a security problem that restricts the long-term flexible operations of modern large-scaled low-pressure steam turbines. Especially, if one structural mode of the last stage moving blade (LSMB) is excited, significant blade vibrations may potentially lead to high-cycle fatigue failure. A loosely coupled computational fluid dynamics reduced model with prescribed blade vibrations has been established to investigate NSV of the LSMB and the potential lock-in phenomenon under low-load conditions. Firstly, calculations with reduced multi-passage domain have been verified by comparing with the results of the full-annulus one, and an appropriate reduced domain is determined. Secondly, a set of calculations by controlling blade vibration parameters indicate that lock-in phenomenon between RI frequency and blade vibration frequency may occur when nodal diameters of cascade vibrations is coincident with the wave number of RI. Furthermore, dynamic modal decomposition technology has been employed to identify the unsteady pressure field around the blade surface and to reveal the interaction relationship between the flow modes of RI and vibration-induced pressure disturbance. Finally, the blade response evaluation based on harmonic analysis shows that in NSV, the global maximum dynamic response level of locked-in case is nearly 20 times than that of unlocked one.

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