Structural Dynamic Behavior of Axial Compressor Rotor

The vibrations involved in a typical axial compressor rotor in an aircraft engine are complex. Generally, the compressor blades are arranged in a cantilever type configuration. It is also known that the amplitude of vibration is highest near the tip section of the shroudless blade. Compressors are limited by aerodynamic instabilities such as rotating stall and surge. Rotating stall generally initiates near the tip region of the compressor. Blade vibrations coupled with aerodynamic instabilities will lead to a catastrophic scenario of flutter that is asynchronous to the rotor speed. This aeroelastic interaction is detrimental if not taken into consideration. Knowledge of vibration characteristics of the compressor rotor will help in mapping the flutter zone for safe operation. The modal characteristics of the transonic axial compressor rotor available at the Axial Flow Compressor Research (AFCR) facility of National Aerospace Laboratories (NAL) are established in this study. A cyclic-symmetric pre-stressed modal analysis is performed on a single sector of the compressor rotor consisting of a shroudless blade connected to the disk with a pin type dovetail arrangement for different speeds. The main diagnostic charts for turbomachinery vibration i.e., Campbell and Interference diagrams are generated for various speeds and harmonic indices/ nodal diameters of the compressor rotor. The critical crossings of the engine order excitation lines over the natural frequencies of the blade are highlighted. Experimental modal investigations and analysis are carried out on the compressor rotor at the stationary condition and for two different boundary conditions. First, the blade alone modal characteristics under the free-free condition are established. Later, the complete blade-disk assembly mounted on a base test-stand is used to investigate the cantilever fixed-free boundary condition of the chosen blade. The modal characteristics are established by performing impact hammer experiments. Blade excitation is provided by a calibrated Dytran make impact hammer and the response is measured using a calibrated accelerometer. The structural dynamic data acquisition hardware and software from OROS is used for determining the natural frequencies, mode shapes and structural damping for each mode of the compressor rotor. There is a good agreement in the natural frequencies and mode shapes established using experiment and numerical methods for the first three modes investigated. Modal Assurance Criteria (MAC) analysis is carried out for two different modal identification algorithms to compare the mode shapes.

Download Full-text

Theoretical and Experimental Determination of Pressure Losses in a Single-Stage Axial Flow Compressor

Journal of Engineering for Power ◽

10.1115/1.3445371 ◽

1970 ◽

Vol 92 (4) ◽

pp. 407-414 ◽

Cited By ~ 1

Author(s):

Y. Le Bot ◽

J. Paulon ◽

P. Belaygue

Keyword(s):

Mass Flow ◽

Axial Compressor ◽

Axial Flow ◽

Pressure Profile ◽

Rotating Stall ◽

Pressure Losses ◽

Compressor Rotor ◽

Mass Flow Rates ◽

Flow Compressor

A single, isolated, test axial compressor rotor in a constant section annular duct is used for determination of off-design pressure losses. The results obtained are interpreted by means of loss coefficients and description of the flow field is deduced from a simplified actuator theory that takes into account pressure losses. Rotor stall limit is interpreted as that limit mass flow rate for which no continuous solution of the equations can be obtained. Unstable operations that take place for mass flow rates smaller than the stall limit are shown to be either rotating stall or wall separation, according to the shape of the downstream pressure profile. Experiments on the rotor confirm validity of these assumptions.

Download Full-text

Spatially Resolved Experimental Modal Analysis on High-Speed Composite Rotors Using a Non-Contact, Non-Rotating Sensor

Sensors ◽

10.3390/s21144705 ◽

2021 ◽

Vol 21 (14) ◽

pp. 4705

Author(s):

Julian Lich ◽

Tino Wollmann ◽

Angelos Filippatos ◽

Maik Gude ◽

Juergen Czarske ◽

...

Keyword(s):

High Speed ◽

Natural Frequencies ◽

Mode Shapes ◽

Fiber Reinforced ◽

Structural Dynamic ◽

Spatially Resolved ◽

Glass Fiber Reinforced ◽

Vibration Responses ◽

And Performance

Due to their lightweight properties, fiber-reinforced composites are well suited for large and fast rotating structures, such as fan blades in turbomachines. To investigate rotor safety and performance, in situ measurements of the structural dynamic behaviour must be performed during rotating conditions. An approach to measuring spatially resolved vibration responses of a rotating structure with a non-contact, non-rotating sensor is investigated here. The resulting spectra can be assigned to specific locations on the structure and have similar properties to the spectra measured with co-rotating sensors, such as strain gauges. The sampling frequency is increased by performing consecutive measurements with a constant excitation function and varying time delays. The method allows for a paradigm shift to unambiguous identification of natural frequencies and mode shapes with arbitrary rotor shapes and excitation functions without the need for co-rotating sensors. Deflection measurements on a glass fiber-reinforced polymer disk were performed with a diffraction grating-based sensor system at 40 measurement points with an uncertainty below 15 μrad and a commercial triangulation sensor at 200 measurement points at surface speeds up to 300 m/s. A rotation-induced increase of two natural frequencies was measured, and their mode shapes were derived at the corresponding rotational speeds. A strain gauge was used for validation.

Download Full-text

INVESTIGATION ON MODE CHARACTERISTICS OF ROTATING INSTABILITY AND ROTATING STALL IN AN AXIAL COMPRESSOR

Journal of Turbomachinery ◽

10.1115/1.4053238 ◽

2021 ◽

pp. 1-24

Author(s):

Zeyuan Yang ◽

Yadong Wu ◽

Hua Ouyang

Keyword(s):

Axial Compressor ◽

Calibration Method ◽

Acoustic Mode ◽

Rotating Stall ◽

Frequency Spectra ◽

Compressor Rotor ◽

Mode Decomposition ◽

Aerodynamic Instability ◽

Rotating Instability ◽

Mode Order

Abstract Rotating instability (RI) and rotating stall (RS) are two types of aerodynamic instability in axial compressors. The former features the side-by-side peaks below the blade passing frequency (BPF) in frequency spectra, and the latter represents one or more stall cells rotating in the compressor. This paper presents an experimental on the nearfield pressure and farfield acoustic characteristics of RI phenomenon in a low-speed axial compressor rotor, which endures both RI and RS at several working conditions. In order to obtain the high-order modes of RI and other aerodynamic instability, a total of 9 or 20 Kulites are circumferentially mounted on the casing wall to measure the nearfield pressure fluctuation using a mode order calibration method. Meantime in the farfield 16 microphones are planted to measure the acoustic mode order using the compressive sensing method. Through calibration the experiments acquire the mode orders generated by RI and the interaction between RI and BPF, which is higher than the number of transducers. As for RS, the mode decomposition shows a mode order of 1, indicating one single stall cell rotating in the compressor. This experiment also shows that amplitude of RI modes is decreased when RS occurs, but RS modes and RI modes will both be enhanced if the flow rate is further reduced. This experiment reveals that RI experiences three stages of “strengthen-weaken-strengthen”, and hence RI may not be regarded only as “prestall” disturbance.

Download Full-text

Investigation on Mode Characteristics of Rotating Instability and Rotating Stall in an Axial Compressor

10.1115/gt2021-58929 ◽

2021 ◽

Author(s):

Zeyuan Yang ◽

Yadong Wu ◽

Hua Ouyang

Keyword(s):

Axial Compressor ◽

Calibration Method ◽

Acoustic Mode ◽

Rotating Stall ◽

Frequency Spectra ◽

Compressor Rotor ◽

Mode Decomposition ◽

Aerodynamic Instability ◽

Rotating Instability ◽

Mode Order

Download Full-text

Vibration-Based Damage Assessment in Gravity-Based Wind Turbine Tower under Various Waves

Shock and Vibration ◽

10.1155/2019/1406861 ◽

2019 ◽

Vol 2019 ◽

pp. 1-17 ◽

Cited By ~ 2

Author(s):

Cong-Uy Nguyen ◽

So-Young Lee ◽

Heon-Tae Kim ◽

Jeong-Tae Kim

Keyword(s):

Wind Turbine ◽

Damage Assessment ◽

Natural Frequencies ◽

Modal Identification ◽

Mode Shapes ◽

Modal Parameters ◽

Damage Scenarios ◽

Wind Turbine Tower ◽

Induced Variation ◽

Wave Induced

In this study, the feasibility of vibration-based damage assessment in a wind turbine tower (WTT) with gravity-based foundation (GBF) under various waves is numerically investigated. Firstly, a finite element model is constructed for the GBF WTT which consists of a tower, caisson, and foundation bed. Eigenvalue analysis is performed to identify a few vibration modes of interest, which represent complex behaviors of a flexible tower, rigid caisson, and deformable foundation. Secondly, wave-induced dynamic pressures are analyzed for a few selected wave conditions and damage scenarios are also designed to simulate the main components of the target GBF WTT. Thirdly, forced vibration responses of the GBF WTT are analyzed for the wave-induced excitation. Then modal parameters (i.e., natural frequencies and mode shapes) are extracted by using a combined use of time-domain and frequency-domain modal identification methods. Finally, the variation of modal parameters is estimated by measuring relative changes in natural frequencies and mode shapes in order to quantify the damage-induced effects. Also, the wave-induced variation of modal parameters is estimated to relatively assess the effect of various wave actions on the damage-induced variation of modal parameters.

Download Full-text

3D Flow Field Measurement Around a Rotating Stall Cell

Volume 1: Turbomachinery ◽

10.1115/98-gt-594 ◽

1998 ◽

Cited By ~ 1

Author(s):

C. Palomba ◽

P. Puddu ◽

F. Nurzia

Keyword(s):

Flow Field ◽

Axial Flow ◽

Rotating Stall ◽

Operating Conditions ◽

Field Pattern ◽

Mean Flow ◽

Axial Section ◽

Average Technique ◽

Compressor Rotor ◽

Flow Compressor

Rotating stall is an unsteady phenomenon that arises in axial and radial flow compressors. Under certain operating conditions a more or less regular cell of turbulent flow develops and propagates around the annulus at a speed lower than rotor speed. Recently little work has been devoted to the understanding of the flow field pattern inside a rotating cell. However, this knowledge could be of help in the understanding of the interaction between the cell and the surrounding flow. Such information could be extremely important during the modelling process when some hypothesis have to be made about the cell behaviour. A detailed experimental investigation has been conducted during one cell operation of an isolated low-speed axial flow compressor rotor using a slanted hot wire and an ensemble average technique based on the cell revolution time. The three flow field components have been measured on 9 axial section for 800 circumferential points and on 21 radial stations to give a complete description of the flow field upstream and downstream of the rotor. Interpretation of data can give a description of the mean flow field patterns inside and around the rotating cell.

Download Full-text

A Model for Dynamic Loss Response in Axial-Flow Compressors

Volume 1: Aircraft Engine; Marine; Turbomachinery; Microturbines and Small Turbomachinery ◽

10.1115/81-gt-154 ◽

1981 ◽

Author(s):

M. R. Sexton ◽

W. F. O’Brien

Keyword(s):

Response Function ◽

Fourier Transforms ◽

Axial Flow ◽

Rotating Stall ◽

Mathematical Representation ◽

Physical Mechanisms ◽

Compressor Rotor ◽

Disc Model ◽

Actuator Disc ◽

Dynamic Loss

An experimentally-determined dynamic loss response function was developed and incorporated in a model to predict the rotating stall behavior of an experimental compressor. The loss response model was developed employing Fourier transforms. The basis of the compressor model is a mathematical representation of the flow fields upstream and downstream of the compressor rotor. The compressor rotor is represented in the model by a semi-actuator disc. The results of the investigation show that the physical mechanisms which control the onset and propagation velocity of rotating stall in a single-stage compressor can be modeled with the use of the loss response function in a semi-actuator disc model of the compressor. The function represents the dynamic loss characteristics of the compressor rotor row, and provides important advantages over previous techniques.

Download Full-text

Surge and Rotating Stall in Axial Flow Compressors—Part II: Experimental Results and Comparison With Theory

Journal of Engineering for Power ◽

10.1115/1.3446139 ◽

1976 ◽

Vol 98 (2) ◽

pp. 199-211 ◽

Cited By ~ 152

Author(s):

E. M. Greitzer

Keyword(s):

Quantitative Description ◽

Axial Compressor ◽

Axial Flow ◽

Rotating Stall ◽

Experimental Results ◽

System Response ◽

Physical Parameters ◽

Geometrical Parameters ◽

Compression System ◽

Transient System

This paper reports an experimental study of axial compressor surge and rotating stall. The experiments were carried out using a three stage axial flow compressor. With the experimental facility the physical parameters of the compression system could be independently varied so that their influence on the transient system behavior can be clearly seen. In addition, a new data analysis procedure has been developed, using a plenum mass balance, which enables the instantaneous compressor mass flow to be accurately calculated. This information is coupled to the unsteady pressure measurements to provide the first detailed quantitative picture of instantaneous compressor operation during both surge and rotating stall transients. The experimental results are compared to a theoretical model of the transient system response. The theoretical criterion for predicting which mode of compression system instability, rotating stall or surge, will occur is in good accord with the data. The basic scaling concepts that have been developed for relating transient data at different corrected speeds and geometrical parameters are also verified. Finally, the model is shown to provide an adequate quantitative description of the motion of the compression system operating point during the transients that occur subsequent to the onset of axial compressor stall.

Download Full-text

Dynamic Total Head Loss Characteristic for an Axial Compressor Rotor

Journal of Mechanical Engineering Science ◽

10.1243/jmes_jour_1980_022_052_02 ◽

1980 ◽

Vol 22 (6) ◽

pp. 269-276 ◽

Cited By ~ 2

Author(s):

P. B. Sharma ◽

J. W. Railly

Keyword(s):

Time Delay ◽

Time Lag ◽

Axial Compressor ◽

Numerical Procedure ◽

Head Loss ◽

Rotating Stall ◽

Phase Lock ◽

Compressor Rotor ◽

Total Head ◽

Loss Characteristic

Detailed flow field and pressure measurements during rotating stall operation have been carried out at inlet to and exit from an axial compressor rotor using hot wire anemometers and probes incorporating fast response pressure transducers. An on-line data-acquisition system which employs a phase-lock sampling and averaging technique has been used to obtain ‘phase-lock averaged’ values of flow quantities and pressures. The dynamic total head loss/incidence characteristic for the rotor section at mean diameter has been computed from the above data. The dynamic characteristic exhibits a loop in the stalled region. A simple numerical procedure has been used to obtain the steady-state loss characteristic and the time-lag of this loss. It has been found that the loss time-lag of boundary layer time delay corresponds to a value equal to 1.8 times the time delay due to inertia of fluid in a blade passage. A simple theory for the prediction of this loss time-lag is also presented which shows reasonable agreement with the value determined from measurements.

Download Full-text