A Novel Stall Warning Indicator: Part II — Underlying Flow Mechanism

2019 ◽  
Author(s):  
Mario Eck ◽  
Roland Rückert ◽  
Marc Lehmann ◽  
Dieter Peitsch
Keyword(s):  
Axial Compressor ◽  
Propagation Speed ◽  
Flow Coefficient ◽  
Spectral Signature ◽  
The Novel ◽  
Time Resolved ◽  
Pressure Transducers ◽  
Flow Disturbances ◽  
Stall Warning ◽  
Rotating Instability

Abstract The aim of the present paper is to improve the physical understanding of flow irregularities in the blade passing signal of turbomachinery rotors, since the novel stall warning method presented in part I is based upon those irregularities. For this purpose, a complementary instrumentation was used in a single stage axial compressor. A set of pressure transducers evenly distributed along the circumference surface mounted in the casing near the rotor tip leading edges is measuring the time-resolved wall pressures simultaneously to an array of transducers recording the chord-wise static pressures. The latter allows for plotting quasi-instantaneous 2D-pressure contours. Any occurring flow disturbances causing the before mentioned irregularity can later be classified using validated frequency analysis methods being applied to the data from the circumferential sensors. While leaving the flow coefficient constant, a continuously changing number of prestall flow disturbances appears to be causing the very spectral signature which is known from investigations on Rotating Instability. Any arising number of disturbances is matching a specific mode order to be found within the spectral signature. While the flow coefficient is reduced the propagation speed of prestall disturbances increases linearly as the speed seems to be independent from the clearance size. Data taken beyond the stalling limit demonstrate a complex superposition of stall cells and flow disturbances which the title “prestall disturbance” therefore doesn’t fit to precisely any more. Different convection speeds allow the phenomena to be clearly distinguished from each other.

Prestall Instability in Axial Flow Compressors

2020 ◽  
Vol 142 (7) ◽  
Author(s):  
Mario Eck ◽  
Roland Rückert ◽  
Dieter Peitsch ◽  
Marc Lehmann
Keyword(s):  
Pressure Fluctuations ◽  
Axial Compressor ◽  
Axial Flow ◽  
Leading Edge ◽  
Propagation Speed ◽  
Flow Coefficient ◽  
Spectral Signature ◽  
Time Resolved ◽  
Pressure Transducers ◽  
Flow Disturbances

Abstract The aim of the present paper is to improve the physical understanding of discrete prestall flow disturbances developing in the tip area of the compressor rotor. For this purpose, a complementary instrumentation was used in a single-stage axial compressor. A set of pressure transducers evenly distributed along the circumference surface mounted in the casing near the rotor tip leading edges measures the time-resolved wall pressures simultaneously to an array of transducers recording the chordwise static pressures. The latter allows for plotting quasi-instantaneous casing pressure contours. Any occurring flow disturbances can be properly classified using validated frequency analysis methods applied to the data from the circumferential sensors. While leaving the flow coefficient constant, a continuously changing number of prestall flow disturbances appears to be causing a unique spectral signature, which is known from investigations on rotating instability. Any arising number of disturbances is matching a specific mode order found within this signature. While the flow coefficient is reduced, the propagation speed of prestall disturbances increases linearly, and meanwhile, the speed seems to be independent from the clearance size. Casing contour plots phase-locked to the rotor additionally provide a strong hint on prestall disturbances clearly not to be caused by a leading edge separation. Data taken beyond the stalling limit demonstrate a complex superposition of stall cells and flow disturbances, which the title “prestall disturbance” therefore does not fit to precisely any more. Different convection speeds allow the phenomena to be clearly distinguished from each other. Furthermore, statistical analysis of the pressure fluctuations caused by the prestall disturbances offer the potential to use them as a stall precursor or to quantify the deterioration of the clearance height between the rotor blade tips and the casing wall during the lifetime of an engine.

Experimental Investigation of a Stall Prediction System Using a Transonic Multistage Compressor

2007 ◽  
Author(s):  
Tomofumi Nakakita ◽  
Masahiro Kurosaki ◽  
Yukio Kamiyoshihara
Keyword(s):  
Axial Compressor ◽  
Prediction System ◽  
Test Results ◽  
Stall Margin ◽  
Pressure Transducers ◽  
Stator Vane ◽  
Multistage Compressor ◽  
Stall Warning ◽  
Stall Control ◽  
Multistage Axial Compressor

This paper describes the test results of a stall prediction system using a transonic multistage axial compressor. The test results show that there is a clear relationship between the stall margin and the stall-warning index measured at the first stage. The stall warning index is derived from auto correlation of casing wall pressure signals above the rotor tip. In the tests, the compressor installed with pressure transducers on the casing wall near the leading edges of the first three rotors was forced to stall while operating at a constant speed by closing the discharge valve. The test results where the stator vane settings of the first three stages were changed show that load distribution among stages does not have significant effects on the stall margin vs. stall-warning index relationship. Using some smoothing technique, undesired time variation of the stall-warning index can be reduced to the level necessary for practical active stall control with allowable response time delay.

A Novel Stall Warning Indicator: Part I — Applications and Limitations

2019 ◽  
Author(s):  
Roland Rückert ◽  
Mario Eck ◽  
Dieter Peitsch ◽  
Marc Lehmann
Keyword(s):  
High Speed ◽  
Axial Compressor ◽  
Leading Edge ◽  
Experimental Tests ◽  
Axial Direction ◽  
Time Resolved ◽  
Compressor Rotor ◽  
Flight Operations ◽  
Stall Warning ◽  
The Impact

Abstract The present work is the first of two papers investigating the operation principle of stall warning quantities. It discusses the use and implementation of novel stall warning techniques based on experimental tests. Each of the addressed techniques is based upon integral statistical analysis of time-resolved wall pressures in close proximity to the leading edge of a compressor rotor. The experiments were conducted on a low speed axial compressor test rig at the Chair of Aeroengines at the Technische Universität Berlin. The compressor suffers from a specific type of pre-stall instability. The signature within the frequency spectrum of this semi-stable operating point is in itself unique and was observed by many within the scientific community on numerous occasions and various axial compressor types, both low and high speed. Strong evidence has been elaborated which indicate that each of those so called stall warning indicator’s functionality is based upon the existence of this prestall phenomena. The first of two indicators is time-dependent as it evaluates the as-is state against surrounding operating points during transient manoeuvres. Furthermore, the impact of varying geometrical boundary conditions, which are known to regularly arise in flight operations, were taken into account. The functionality of the indicator is assured if the instrumentation is adjusted accordingly. The second indicator is mainly a location-dependent quantity as it evaluates the pressure signature along the axial direction within the rotor passage at various aerodynamic loadings. The latter also gave rise to some fundamental and preliminary understanding of the physics behind so called prestall disturbances.

Influence of Flow Coefficient, Stagger Angle, and Tip Clearance on Tip Vortex in Axial Compressors

2006 ◽  
Vol 128 (6) ◽  
pp. 1274-1280 ◽  
Author(s):  
Yong Sang Yoon ◽  
Seung Jin Song ◽  
Hyoun-Woo Shin
Keyword(s):  
Pressure Fluctuations ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Tip Vortex ◽  
Time Resolved ◽  
Pressure Transducers ◽  
High Frequency Response ◽  
Response Pressure ◽  
Casing Pressure ◽  
Stagger Angle

Experiments have been performed on the low speed research compressor (LSRC) at General Electric Aircraft Engines to investigate the effects of flow coefficient, stagger angle, and tip clearance on tip vortex. Time resolved casing pressure distributions over the third stage rotor have been acquired with high-frequency-response pressure transducers. Also, tip vortex strength and trajectory have been estimated from the casing pressure fluctuations which have been obtained simultaneously from various axial locations. As flow coefficient decreases, tip vortex gets strengthened and migrates upstream. The stagger angle increase weakens the tip vortex and moves it downstream slightly because the blade loading is decreased. However, tip leakage vortex is influenced mainly by tip clearance, and there exists a “critical” tip clearance which determines the type of tip vortex trajectory (“straight” or “kinked”). As predicted by others, tip vortex gets strengthened with increasing tip clearance. However, unlike the predictions, the tip vortex trajectory moves upstream with increasing tip clearance. Furthermore, with tip clearance above a “critical” value, the tip vortex trajectory is no longer straight but shows a kink in the passage.

Casing Pressure Measurements and Numerical Simulations of a 1.5 Stage Axial Compressor: Tip Leakage Flow and Rotating Instability

2014 ◽  
Author(s):  
Hao Wang ◽  
Yadong Wu ◽  
Hua Ouyang ◽  
Jie Tian ◽  
Zhaohui Du
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
Axial Compressor ◽  
Fast Response ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Pressure Transducers ◽  
Tip Leakage ◽  
Response Pressure ◽  
Rotating Instability

Experimental and numerical investigations on the unsteady casing flow field in a one-and-half stage low speed axial compressor have been carried out. By using fast response pressure transducers instrumented on the rotor casing, the pressure time series were acquired at different operation points from throttle wide open to near-stall operation point. The pseudo-spatial pressure contours, phase-locked averaged and root-mean-square pressure contours and power spectrums of unsteady pressure signal have been achieved. The CFD simulations were conducted to help understanding the features of tip leakage vortex. The rotating instability has been detected throughout an operation range from small flow rate point to near stall point. The frequency characteristic of rotating instability according flow rate was discussed. Based on the pattern of RIF varying with flow rate, the developing process of rotating instability according to flow rate could be divided into two stages, referred as early-developing stage and fully-developed stage. By analyzing the correlation between rotating instability and casing flow field, it was discovered that the origination and development of rotating instability was closely related to the fluctuation induced by tip leakage vortex.

Event-Locked Time-Resolved Fourier Spectroscopy

1997 ◽  
Vol 51 (8) ◽  
pp. 1106-1112 ◽  
Author(s):  
H. Weidner ◽  
R. E. Peale
Keyword(s):  
Signal To Noise Ratio ◽  
Low Cost ◽  
Michelson Interferometer ◽  
Far Infrared ◽  
Time Base ◽  
The Novel ◽  
Time Resolved ◽  
Mathematical Algorithm ◽  
Scan Time ◽  
Recorded Data

A low-cost method of adding time-resolving capability to commercial Fourier transform spectrometers with a continuously scanning Michelson interferometer has been developed. This method is specifically designed to eliminate noise and artifacts caused by mirror-speed variations in the interferometer. The method exists of two parts: (1) a novel timing scheme for synchronizing the transient events under study and the digitizing of the interferogram and (2) a mathematical algorithm for extracting the spectral information from the recorded data. The novel timing scheme is a modification of the well-known interleaved, or stroboscopic, method. It achieves the same timing accuracy, signal-to-noise ratio, and freedom from artifacts as step-scan time-resolving Fourier spectrometers by locking the sampling of the interferogram to a stable time base rather than to the occurrences of the HeNe fringes. The necessary pathlength-difference information at which samples are taken is obtained from a record of the mirror speed. The resulting interferograms with uneven pathlength-difference spacings are transformed into wavenumber space by least-squares fits of periodic functions. Spectra from the far-infrared to the upper visible at resolutions up to 0.2 cm−1 are used to demonstrate the utility of this method.

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

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.

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

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

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.

Characteristics of Stable Rotating Stall Cells in an Axial Compressor

2017 ◽  
Author(s):  
Adam R. Hickman ◽  
Scott C. Morris
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Pressure Ratio ◽  
Pressure Sensors ◽  
Axial Compressor ◽  
Field Measurements ◽  
Rotating Stall ◽  
Flow Coefficient ◽  
Stable Operation ◽  
Double Phase

Flow field measurements of a high-speed axial compressor are presented during pre-stall and post-stall conditions. The paper provides an analysis of measurements from a circumferential array of unsteady shroud static pressure sensors during stall cell development. At low-speed, the stall cell approached a stable size in approximately two rotor revolutions. At higher speeds, the stall cell developed within a short amount of time after stall inception, but then fluctuated in circumferential extent as the compressor transiently approached a stable post-stall operating point. The size of the stall cell was found to be related to the annulus average flow coefficient. A discussion of Phase-Locked Average (PLA) statistics on flow field measurements during stable operation is also included. In conditions where rotating stall is present, flow field measurements can be Double Phase-Locked Averaged (DPLA) using a once-per-revolution (1/Rev) pulse and the period of the stall cell. The DPLA method provides greater detail and understanding into the structure of the stall cell. DPLA data indicated that a stalled compressor annulus can be considered to contained three main regions: over-pressurized passages, stalled passages, and recovering passages. Within the over-pressured region, rotor passages exhibited increased blade loading and pressure ratio compared to pre-stall values.

Stall Warning Using the Rotor Tip Pressure in a Transonic Axial Compressor With Circumferential Grooves

2018 ◽  
Author(s):  
Byeung Jun Lim ◽  
Tae Choon Park ◽  
Young Seok Kang
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Single Stage ◽  
Stall Inception ◽  
Casing Treatment ◽  
Stall Warning ◽  
Transonic Axial Compressor

In this study, characteristics of stall inception in a single-stage transonic axial compressor with circumferential grooves casing treatment were investigated experimentally. Additionally, the characteristic of increasing irregularity in the pressure inside circumferential grooves as the compressor approaches the stall limit was applied to the stall warning method. Spike-type rotating stall was observed in the single-stage transonic axial compressor with smooth casing. When circumferential grooves were applied, the stall inception was suppressed and the operating point of the compressor moved to lower flow rate than the stall limit. A spike-like disturbance was developed into a rotating stall cell and then the Helmholtz perturbation was overlapped on it at N = 80%. At N = 70 %, the Helmholtz perturbation was observed first and the amplitude of the wave gradually increased as mass flow rate decreased. At N = 60%, spike type stall inceptions were observed intermittently and then developed into continuous rotating stall at lower mass flow rate. Pressure measured at the bottom of circumferential grooves showed that the level of irregularity of pressure increased as flow rate decreased. Based on the characteristic of increasing irregularity of the pressure signals inside the circumferential grooves as stall approaches, an autocorrelation technique was applied to the stall warning. This technique could be used to provide warning against stall and estimate real-time stall margins in compressors with casing treatments.

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