Self-Excited Blade Vibration Experimentally Investigated in Transonic Compressors: Rotating Instabilities and Flutter

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
F. Holzinger ◽  
F. Wartzek ◽  
M. Jüngst ◽  
H.-P. Schiffer ◽  
S. Leichtfuss
Keyword(s):  
Stability Limit ◽  
Tip Clearance ◽  
Blade Vibration ◽  
Casing Treatment ◽  
Operating Range ◽  
Aerodynamic Damping ◽  
Torsion Mode ◽  
Experimental Campaign ◽  
Excited Vibration ◽  
Design Speed

This paper investigates the vibrations that occurred on the blisk rotor of a 1.5-stage transonic research compressor designed for aerodynamic performance validation and tested in various configurations at Technische Universität Darmstadt. During the experimental test campaign, self-excited blade vibrations were found near the aerodynamic stability limit of the compressor. The vibration was identified as flutter of the first torsion mode and occurred at design speed as well as in the part-speed region. Numerical investigations of the flutter event at design speed confirmed negative aerodynamic damping for the first torsion mode, but showed a strong dependency of aerodynamic damping on blade tip clearance (BTC). In order to experimentally validate the relation between BTC and aerodynamic damping, the compressor tests were repeated with enlarged BTC for which stability of the torsion mode was predicted. During this second experimental campaign, strong vibrations of a different mode limited compressor operation. An investigation of this second type of vibration found rotating instabilities to be the source of the vibration. The rotating instabilities first occur as an aerodynamic phenomenon and then develop into self-excited vibration of critical amplitude. In a third experimental campaign, the same compressor was tested with reference BTC and a nonaxisymmetric casing treatment (NASCT). Performance evaluation of this configuration repeatedly showed a significant gain in operating range and pressure ratio. The gain in operating range means that the casing treatment successfully suppresses the previously encountered flutter onset. The aeroelastic potential of the NASCT is validated by means of the unsteady compressor data. By giving a description of all of the above configurations and the corresponding vibratory behavior, this paper contains a comprehensive summary of the different types of blade vibration encountered with a single transonic compressor rotor. By investigating the mechanisms behind the vibrations, this paper contributes to the understanding of flow-induced blade vibration. It also gives evidence to the dominant role of the tip clearance vortex in the fluid–structure-interaction of tip critical transonic compressors. The aeroelastic evaluation of the NASCT is beneficial for the design of next generation casing treatments for vibration control.

Self-Excited Blade Vibration Experimentally Investigated in Transonic Compressors: Rotating Instabilities and Flutter

2015 ◽  
Author(s):  
F. Holzinger ◽  
F. Wartzek ◽  
M. Jüngst ◽  
H.-P. Schiffer ◽  
S. Leichtfuß
Keyword(s):  
Tip Clearance ◽  
Blade Vibration ◽  
Casing Treatment ◽  
Operating Range ◽  
Aerodynamic Damping ◽  
Torsion Mode ◽  
Experimental Campaign ◽  
Blade Tip ◽  
Design Speed ◽  
Blade Tip Clearance

This paper investigates the vibrations that occurred on the blisk rotor of a 1.5-stage transonic research compressor designed for aerodynamic performance validation and tested in various configurations at Technische Universität Darmstadt. During the experimental test campaign self-excited blade vibrations were found near the aerodynamic stability limit of the compressor. The vibration was identified as flutter of the first torsion mode and occurred at design speed as well as in the part-speed region. Numerical investigations of the flutter event at design speed confirmed negative aerodynamic damping for the first torsion mode, but showed a strong dependency of aerodynamic damping on blade tip clearance. In order to experimentally validate the relation between blade tip clearance and aerodynamic damping, the compressor tests were repeated with enlarged blade tip clearance for which stability of the torsion mode was predicted. During this second experimental campaign, strong vibrations of a different mode limited compressor operation. An investigation of this second type of vibration found rotating instabilities to be the source of the vibration. The rotating instabilities first occur as an aerodynamic phenomenon and then develop into self-excited vibration of critical amplitude. In a third experimental campaign, the same compressor was tested with reference blade tip clearance and a non-axisymmetric casing treatment. Performance evaluation of this configuration repeatedly showed a significant gain in operating range and pressure ratio. The gain in operating range means that the casing treatment successfully suppresses the previously encountered flutter onset. The aeroelastic potential of the non-axisymmetric casing treatment is validated by means of the unsteady compressor data. By giving a description of all of above configurations and the corresponding vibratory behavior, this paper contains a comprehensive summary of the different types of blade vibration encountered with a single transonic compressor rotor. By investigating the mechanisms behind the vibrations, this paper contributes to the understanding of flow induced blade vibration. It also gives evidence to the dominant role of the tip clearance vortex in the fluid-structure-interaction of tip critical transonic compressors. The aeroelastic evaluation of the non-axisymmetric casing treatment is beneficial for the design of next generation casing treatments for vibration control.

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.

Experimental Study on the Influence of Casing Treatment on Near-Stall Unsteady Behavior of a Mixed-Flow Compressor

2019 ◽  
Author(s):  
Juan Du ◽  
Felix Kauth ◽  
Jichao Li ◽  
Qianfeng Zhang ◽  
Joerg R. Seume
Keyword(s):  
Stability Limit ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Surprising Result ◽  
Mixed Flow ◽  
Stall Inception ◽  
Casing Treatment ◽  
Axial Compressors ◽  
Flow Compressor ◽  
Unsteady Behavior

Abstract This paper aims at experimentally demonstrating the effects of axial slot casing treatment and tip gap variation on compressor performance, unsteady tip clearance flow, and stall inception features in a highly-loaded mixed-flow compressor at partspeed. Two tip gaps (0.32% and 0.64% of rotor blade chord at mid-span) were tested at three rotational speeds. A semicircular axial slot casing treatment improves compressor stability. The experimental results show that this casing treatment significantly moves the stability limit at partial speeds towards lower mass flow for both tip gaps, compared to the reference case without casing treatment. In the case of the compressor with casing treatment, efficiency increases for the large tip gap and decreases for the small tip gap. Dynamic pressure transducers installed in the casing upstream and along the rotor tip chord direction are used to detect the unsteady behavior of tip region flow and stall inception signals of the compressor. The characteristic frequency in the tip region decreases, and the oscillating amplitude first decreases and then increases during the throttling process, regardless of tip gap size or casing treatment. For axial compressors, by contrast, the observation in previous work has been an increase of the oscillating amplitude with decreasing flow coefficient. This is a surprising result of our work. Neither experiment nor CFD so far was able to explain why the trend in this mixed-flow compressor is different from the trend expected from axial compressors. The compressor stalls through the spike stall inception both with and without casing treatment. This observation also differs from recent studies on axial compressors, which demonstrated that casing treatments could change the type of stall inception. The unstable disturbance indicating initial stall inception initially appears in the blade tip region from blade mid-chord to trailing edge, and then propagates upstream towards the leading edge. This disturbance might be generated by the reversed flow separation near mid-chord.

Analysis Method of NSV and Influence of Tip Clearance Flow Instabilities on NSV in an Axial Transonic Compressor Rotor

2021 ◽  
pp. 1-80
Author(s):  
Le Han ◽  
Dasheng Wei ◽  
Yanrong Wang ◽  
Xianghua Jiang ◽  
Xiaojie Zhang
Keyword(s):  
Maximum Amplitude ◽  
Tip Clearance ◽  
Modal Shape ◽  
Blade Vibration ◽  
Tip Clearance Flow ◽  
Unsteady Pressure ◽  
Aerodynamic Damping ◽  
Transonic Compressor ◽  
Clearance Flow ◽  
Negative Damping

Abstract The relationship between tip clearance flow (TCF) and blade vibration in locked-in region is numerically investigated on a transonic rotor. The numerical method is verified by citing references. The phase of TCF changes with the operating condition. A separation method of the unsteady pressure caused by TCF and blade vibration is developed. The unsteady pressure during NSV is separated into the TCF and vibration components under 1B and 8th modes. The unsteady pressure of TCF is similar with that of rigid blade. The unsteady pressure of blade vibration is larger at part span, and its distribution depends on the modal shape and vibrating amplitude. The unsteady pressure of TCF and blade vibration determine the aerodynamic damping in locked-in region. The aerodynamic damping of TCF changes with the TCF phase. TCF provides positive damping at some phases and negative damping at other phases. The aerodynamic work of TCF and blade vibration increases linearly and at the rate of square with the vibrating amplitude, respectively. TCF is dominant in the initial stage of vibration. With the vibrating amplitude increasing, the aerodynamic work of vibration catches up gradually. NSV occurs when TCF provides negative damping and the unsteady pressure of vibration provides positive damping. If the work of vibration is negative, vibration will be enlarged until failure. The maximum amplitude of NSV canbe obtained by calculating the balance of work. For the 8th mode, the limit amplitude under 0ND is 0.0926%C corresponding to vibration stress of 60MPa.

Near Stall Behavior of a Transonic Compressor Rotor With Casing Treatment

2016 ◽  
Author(s):  
Christoph Brandstetter ◽  
Felix Holzinger ◽  
Heinz-Peter Schiffer ◽  
Sina Stapelfeldt ◽  
Mehdi Vahdati
Keyword(s):  
Stability Limit ◽  
Rotating Stall ◽  
Rotor Blades ◽  
Transient Effects ◽  
Stability Range ◽  
Blade Vibration ◽  
Casing Treatment ◽  
Transonic Compressor ◽  
Compressor Rotor ◽  
Engine Order

The aerodynamic and aeroelastic performance of an advanced axial slot casing treatment (CT) was investigated on a modern one and a half stage transonic compressor test rig. It is generally accepted that a well designed CT can extend the aerodynamic stability range of a compressor to lower mass flows. The extension of stall margin of the compressor rotor blades by using CT has been the subject of numerous research articles but much less attention has been paid to the behavior of the compressor in direct vicinity of the stability limit. For the compressor investigated here, two different phenomena were repeatedly observed near stall: 1) self-excited blade vibration, and 2) low engine order fluctuations developing into rotating stall. The current investigation firstly aims to identify the triggers for each of these phenomena. It then focusses on the aerodynamic and aeromechanical mechanism which lead to the formation of low engine order fluctuations shortly before stall. In order to measure the unsteady and transient effects, the system was instrumented with unsteady wall pressure transducers, a capacitive tip-timing system and strain gauges on the rotor blades. The flow structure in the blade tip region was measured via Particle Image Velocimetry underneath the CT-Cavities. Measurements showed a strong correlation between CT activity and the development of the low frequency oscillations with associated blade vibrations. Using numerical simulations, presented and validated in this paper, this correlation was attributed to an aerodynamic coupling between rotor passages through the recirculation of fluid inside the cavities.

Numerical Study on the Effects of Casing Treatment on Unsteadiness of Tip Leakage Flow in an Axial Compressor

2012 ◽  
Author(s):  
Yoojun Hwang ◽  
Shin-Hyoung Kang
Keyword(s):  
Numerical Study ◽  
Axial Compressor ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Casing Treatment ◽  
Tip Leakage ◽  
Operating Range ◽  
Compressor Rotor ◽  
Flow Through

A low speed axial compressor with casing treatment of axial slots was numerically investigated. Time-accurate numerical calculations were performed to simulate unsteady flow in the rotor tip region and the effects of casing treatment on the flow. Since the compressor rotor had a large tip clearance, it was found that the tip leakage flow had an inherent unsteady feature that was not associated with rotor rotation. The unsteadiness of the tip leakage flow was induced by changes in the blade loading due to the pressure distribution formed by the tip leakage flow. This characteristic is called rotating instability or self-induced unsteadiness. The frequency of the flow oscillation was found to decrease as the flow rate was reduced. On the other hand, as expected, the operating range was improved by casing treatment, as shown by calculations in good agreement with the experimentally measured data. The unsteadiness of the tip leakage flow was alleviated by the casing treatment. The interaction between the flow in the tip region and the re-circulated flow through the axial slots was observed in detail. The removal and injection of flow through the axial slots were responsible not only for the extension of the operating range but also for the alleviation of the unsteadiness. Analyses of instantaneous flow fields explained the mechanism of the interaction between the casing treatment and the unsteady oscillation of the tip leakage flow. Furthermore, the effects of changes in the amount of re-circulation and the location of the removal and injection flow on the unsteadiness of the tip leakage flow were examined.

Self-Regulating Casing Treatment for Axial Compressor Stability Enhancement

2011 ◽  
Author(s):  
Stephanie Weichert ◽  
Ivor Day ◽  
Chris Freeman
Keyword(s):  
High Pressure ◽  
Treatment Effectiveness ◽  
Axial Compressor ◽  
Operating Conditions ◽  
Tip Clearance ◽  
The Self ◽  
Optimized Design ◽  
Stall Margin ◽  
Casing Treatment ◽  
Operating Range

The operating range of an axial compressor is often restricted by a safety imposed stall margin. One possible way of regaining operating range is with the application of casing treatment. Of particular interest here is the type of casing treatment which extracts air from a high pressure location in the compressor and re-injects it through discrete loops into the rotor tip region. Existing re-circulation systems have the disadvantage of reducing compressor efficiency at design conditions because worked flow is unnecessarily re-circulated at these operating conditions. Re-circulation is really only needed near stall. This paper proposes a self-regulating casing treatment in which the re-circulated flow is minimized at compressor design conditions and maximized near stall. The self-regulating capability is achieved by taking advantage of changes which occur in the tip clearance velocity and pressure fields as the compressor is throttled toward stall. In the proof-of-concept work reported here, flow is extracted from the high pressure region over the rotor tips and re-injected just upstream of the same blade row. Parametric studies are reported in which the flow extraction and re-injection ports are optimized for location, shape and orientation. The optimized design is shown to compare favorably with a circumferential groove tested in the same compressor. The relationship between stall inception type and casing treatment effectiveness is also investigated. The self-regulating aspect of the new design works well: stall margin improvements from 2.2 to 6.0% are achieved for just 0.25% total air re-circulated near stall and half that near design conditions. The self-regulating capability is achieved by the selective location and orientation of the extraction hole; a simple model is discussed which predicts the optimum axial location.

scholarly journals Investigation of Performance and Rotor Tip Flow Field in a Low Speed Research Compressor with Circumferential Groove Casing Treatment at Varying Tip Clearance

2017 ◽  
Vol 2017 ◽  
pp. 1-14 ◽  
Author(s):  
Matthias Rolfes ◽  
Martin Lange ◽  
Ronald Mailach
Keyword(s):  
Flow Field ◽  
Operating Conditions ◽  
Single Stage ◽  
Tip Clearance ◽  
Experimental Investigations ◽  
Low Speed ◽  
Pressure Transducers ◽  
Casing Treatment ◽  
Operating Range ◽  
Circumferential Groove

Experimental investigations in a single-stage low speed axial research compressor are presented. The influence of four different rotor tip clearances on the overall compressor performance and on the rotor tip flow field is investigated in configurations with and without circumferential groove casing treatments. Piezo-resistive pressure transducers are used to capture the unsteady flow field in the rotor tip region. The investigated casing groove is effectively working at the three largest investigated tip clearance sizes. The largest achieved operating range increase by the groove is 6.9%. The groove can delay the upstream movement of the flow interface between leakage flow and main flow and thus increase the stable operating range. Rotating instabilities are shown to exist at large tip clearance sizes in throttled operating conditions. Their amplitudes can be damped by the casing groove. No modal activities could be detected in the current single-stage compressor build.

Experimental and Numerical Investigation of a Circumferential Groove Casing Treatment in a Low Speed Axial Research Compressor at Different Tip Clearances

2017 ◽  
Author(s):  
Matthias Rolfes ◽  
Martin Lange ◽  
Konrad Vogeler ◽  
Ronald Mailach
Keyword(s):  
Total Pressure ◽  
Solid Wall ◽  
Pressure Ratio ◽  
Axial Compressor ◽  
Chord Length ◽  
Single Stage ◽  
Tip Clearance ◽  
Low Speed ◽  
Operating Range ◽  
Circumferential Groove

The demand of increasing pressure ratios for modern high pressure compressors leads to decreasing blade heights in the last stages. As tip clearances cannot be reduced to any amount and minimum values might be necessary for safety reasons, the tip clearance ratios of the last stages can reach values notably higher than current norms. This can be intensified by a compressor running in transient operations where thermal differences can lead to further growing clearances. For decades, the detrimental effects of large clearances on an axial compressor’s operating range and efficiency are known and investigated. The ability of circumferential casing grooves in the rotor casing to improve the compressor’s operating range has also been in the focus of research for many years. Their simplicity and ease of installation are one reason for their continuing popularity nowadays, where advanced methods to increase the operating range of an axial compressor are known. In a previous paper [1], three different circumferential groove casing treatments were investigated in a single stage environment in the Low Speed Axial Research Compressor at TU Dresden. One of these grooves was able to notably improve the operating range and the efficiency of the single stage compressor at very large rotor tip clearances (5% of chord length). In this paper, the results of tests with this particular groove type in a three stage environment in the Low Speed Axial Research Compressor are presented. Two different rotor tip clearance sizes of 1.2% and 5% of tip chord length were investigated. At the small tip clearance, the grooves are almost neutral. Only small reductions in total pressure ratio and efficiency compared to the solid wall can be observed. If the compressor runs with large tip clearances it notably benefits from the casing grooves. Both, total pressure and efficiency can be improved by the grooves in a similar extent as in single stage tests. Five-hole probe measurements and unsteady wall pressure measurements show the influence of the groove on the flow field. With the help of numerical investigations the different behavior of the grooves at the two tip clearance sizes will be discussed.

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