scholarly journals Blade Vibrations of a High Speed Compressor Blisk-Rotor: Numerical Resonance Tuning and Optical Measurements

1996 ◽  
Author(s):  
J. Frischbier ◽  
G. Schulze ◽  
M. Zielinski ◽  
G. Ziller ◽  
C. Blaha ◽  
...  
Keyword(s):  
Rotor Blade ◽  
High Speed ◽  
Mechanical Design ◽  
Optimization Technique ◽  
Optical Measurements ◽  
Vibration Measurement ◽  
Blade Vibration ◽  
Transonic Compressor ◽  
Resonance Tuning ◽  
Blade Vibrations

A major challenge during the design process of a modern low aspect ratio high speed axial compressor is to find rotor blade geometries that meet both, aerodynamic and mechanical requirements. This paper deals with the mechanical design of a transonic compressor blade. In order to meet the mechanical requirements in a short development time, new methods were used: A numerical optimization tool and an optical blade vibration measurement method: The numerical resonance tuning took advantage of a semi-automatic optimization technique, based on a Finite Element vibration anlysis tool. The intention was to find a geometry which has no critical resonances (with fundamental engine orders) within the operation range. To verify the calculated blade natural frequencies and eigen-values standard shaker tests using a laser holography system were carried out. Blades under g-load in the running compressor were investigated with an in-house developed vibration measurement system. This system is able to measure frequencies and amplitudes of the rotor blade vibrations without blade instrumentation but small optical probes, mounted in the compressor casing. The measured resonance points are in good agreement with the predictions. All amplitudes are far below the blade fatigue limits.

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.

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

2018 ◽  
Vol 140 (6) ◽  
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 were 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 particle-image-velocimetry (PIV) measurements above 92% span and unsteady wall pressure measurements. When these radial vortices impinge on a blade leading edge (LE), they cause a forward spill of fluid around the LE. 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 (SG) and blade tip timing instrumentation. Nonsynchronous 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.

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.

Mistuning Identification Approach With Focus on High-Speed Centrifugal Compressors

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
Robby Weber ◽  
Arnold Kühhorn
Keyword(s):  
Experimental Data ◽  
High Speed ◽  
Common Knowledge ◽  
Optical Measurements ◽  
Fe Model ◽  
Blade Vibration ◽  
Mode Localization ◽  
Characteristic Quantity ◽  
Calculation Results ◽  
Geometric Deviations

Blade vibrations are one of the main cost drivers in turbomachinery. Computational blade vibration analysis facilitates an enormous potential to increase the productivity in the design of bladed components. Increasing computing power as well as improved modeling and simulation methods leads to comprehensive calculation results. This allows for a more precise prediction and assessment of experimental data. Usually, in the field of turbomachinery, identical blades are assumed to lower the required computational resources. However, mistuning is unavoidable, since small deviations due to the manufacturing process will lead to slightly different blade behavior. Potential effects such as mode localization and amplification can be treated statistically and have been thoroughly studied in the past. Since then, several reduced order models (ROMs) have been invented in order to calculate the maximum vibration amplitude of a fleet of mistuned blisks. Most commonly, mistuning is thereby modeled by small material deviations from blade to blade, e.g., Young's modulus or density. Nowadays, it is common knowledge that the level of manufacturing imperfection (referred as level of mistuning) significantly influences mode localization as well as vibration amplification effects. Optical measurements of the geometric deviations of manufactured blades and converting to a high-fidelity finite element (FE) model make huge progress. However, to the knowledge of the authors, there is no reliable method that derives a characteristic quantity from the geometric mistuning, that fits into the mentioned statistically approaches. Therefore, experimental data are needed to quantify the level of mistuning. Several approaches, which isolate blade individual parameters, are used to identify the dynamic behavior of axial compressors and turbines. These methods can be applied to medium-speed centrifugal turbine wheels but tend to fail to evaluate high-speed compressor with splitter blades. This paper briefly presents the original approach and discusses the reasons for failure. Thereafter, a new approach is proposed. Finally, the level of mistuning and important quantities to perform a statistical evaluation of a high-speed compressor is shown.

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.

Analysis of an Axial Compressor Blade Vibration Based on Wave Reflection Theory

1984 ◽  
Vol 106 (1) ◽  
pp. 57-64 ◽  
Author(s):  
J. A. Owczarek
Keyword(s):  
Rotor Blade ◽  
Wave Reflection ◽  
Axial Compressor ◽  
Compressor Blade ◽  
Rotor Blades ◽  
Wave Reflections ◽  
Blade Vibration ◽  
Blade Vibrations ◽  
Reflection Theory ◽  
Prediction Techniques

The paper describes application of the theory of wave reflection in turbomachines to rotor blade vibrations measured in an axial compressor stage. The blade vibrations analyzed could not be explained using various flutter prediction techniques. The wave reflection theory, first advanced in 1966, is expanded, and more general equations for the rotor blade excitation frequencies are derived. The results of the analysis indicate that all examined rotor blade vibrations can be explained by forced excitations caused by reflecting waves (pressure pulses). Wave reflections between the rotor blades and both the upstream and downstream stator vanes had to be considered.

Analysis of a LPT Rotor Blade for a Geared Engine: Part I — Aero-Mechanical Design and Validation

2016 ◽  
Author(s):  
Matteo Giovannini ◽  
Filippo Rubechini ◽  
Michele Marconcini ◽  
Andrea Arnone ◽  
Francesco Bertini
Keyword(s):  
Turbine Blade ◽  
Turbulence Model ◽  
Rotor Blade ◽  
High Speed ◽  
Design Space Exploration ◽  
Mechanical Design ◽  
Incidence Angle ◽  
High Standard ◽  
Optimization Strategy ◽  
Geometrical Constraints

The rotational speed of low pressure turbines (LPT) for geared turbofan applications is significantly increased looking for potential benefit in performance, weight and overall dimensions. As a drawback, the high speed LPT are characterized by critical mechanical constraints due to the large centrifugal stresses in conjunction with the use of lightweight materials. The present activity was carried out in the framework of the Clean Sky European research project ITURB (Optimal High-Lift Turbine Blade Aero-Mechanical Design), aimed at designing and validating a turbine blade for a geared open rotor engine. This two-part paper presents the redesign and the analysis of an optimized rotor blade starting from a baseline configuration, representative of a state-of-the-art LPT rotor. In the redesign activity high standard of performance was required in conjunction with tight mechanical and geometrical constraints. The design strategy was based on an effective multi-objective optimization strategy. The aerodynamic performance was evaluated by means of 3D steady multi-row viscous computations using a two-equation k-ω turbulence model. At the same time, the mechanical integrity checks were mainly based on the evaluation of the maximum rotor tensile stress due to centrifugal forces. A simplified and very fast tool was developed in order to compute the centrifugal stress. Finally a response-surface approach based on neural-networks (ANNs) was adopted for the design space exploration. The design was validated by means of a comprehensive experimental campaign carried out in a low-speed turbine single-stage facility. A comparison between the numerical and experimental results is presented in terms of the main rotor performance for a fixed Reynolds number while varying the rotor incidence angle. Unsteady numerical analysis of both the baseline and the optimized blade were carried out by using a multi-equation, transition-sensitive, turbulence model and considering the boundary conditions measured on the test rig.

Effects of Flow Control on Forced Response and Performance of a Transonic Compressor

2002 ◽  
Author(s):  
S. Todd Bailie ◽  
Wing F. Ng ◽  
Alfred L. Wicks ◽  
William W. Copenhaver
Keyword(s):  
Flow Control ◽  
Rotor Blade ◽  
Forced Response ◽  
Strain Gages ◽  
Complex Flow ◽  
Compressor Blades ◽  
Transonic Compressor ◽  
Engine Order ◽  
Blade Vibrations ◽  
And Performance

The main contributor to the high-cycle fatigue of compressor blades is the response to aerodynamic forcing functions generated by an upstream row of stators or inlet guide vanes. Resonant response to engine order excitation at certain rotor speeds is especially damaging. Studies have shown that flow control by trailing edge blowing (TEB) can reduce stator wake strength and the amplitude of the downstream rotor blade vibrations generated by the unsteady stator-rotor interaction. In the present study, the effectiveness of TEB to reduce forced blade vibrations was evaluated in a modern transonic compressor rig. A row of wake generator (WG) vanes with TEB capability was installed upstream of the rotor, which was instrumented with strain gages. Data was collected with and without TEB at various rotor speeds involving resonance crossings. Using 0.8% of the compressor core flow for TEB along the full WG-span, rotor blade strain was reduced by 66% at the first torsional resonance crossing. Substantial reductions were also achieved with only partial span TEB. The results demonstrate the effectiveness of the TEB technique for reducing rotor vibrations in the complex flow environment of a closely-spaced transonic stage row. Moderate increases in stage performance were also measured.

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