Time-resolved Rotating Instability Waves in an annular Cascade

2012 ◽  
Author(s):  
Benjamin Pardowitz ◽  
Ulf Tapken ◽  
Lars Enghardt
Keyword(s):  
Time Resolved ◽  
Instability Waves ◽  
Rotating Instability ◽  
Annular Cascade

Experiments on an Axial Fan Stage: Time-Resolved Analysis of Rotating Instability Modes

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Benjamin Pardowitz ◽  
Ulf Tapken ◽  
Lars Neuhaus ◽  
Lars Enghardt
Keyword(s):  
Leading Edge ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Axial Fan ◽  
Time Resolved ◽  
Instability Waves ◽  
Instability Modes ◽  
Mode Decomposition ◽  
Rotating Instability ◽  
Annular Cascade

Rotating instability (RI) occurs at off-design conditions in axial compressors, predominantly in rotor configurations with large tip clearances. Characteristic spectral signatures with side-by-side peaks below the blade passing frequency (BPF) are typically referred to RI located in the clearance region next to the leading edge (LE). Each peak can be assigned to a dominant circumferential mode. RI is the source of the clearance noise (CN) and an indicator for critical operating conditions. Earlier studies at an annular cascade pointed out that RI modes of different circumferential orders occur stochastically distributed in time and independently from each other, which is contradictory to existing explanations of RI. Purpose of the present study is to verify this generally with regard to axial rotor configurations. Experiments were conducted on a laboratory axial fan stage mainly using unsteady pressure measurements in a sensor ring near the rotor LE. A mode decomposition based on cross spectral matrices was used to analyze the spectral and modal RI patterns upstream of the rotor. Additionally, a time-resolved analysis based on a spatial discrete-Fourier-transform (DFT) was applied to clarify the temporal characteristics of the RI modes and their potential interrelations. The results and a comparison with the previous findings on the annular cascade corroborate a new hypothesis about the basic RI mechanism. This hypothesis implies that instability waves of different wavelengths are generated stochastically in a shear layer resulting from a backflow in the tip clearance region.

Experiments on an Axial Fan Stage: Time Resolved Analysis of Rotating Instability Modes

2014 ◽  
Author(s):  
Benjamin Pardowitz ◽  
Ulf Tapken ◽  
Lars Neuhaus ◽  
Lars Enghardt
Keyword(s):  
Leading Edge ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Axial Fan ◽  
Time Resolved ◽  
Instability Waves ◽  
Instability Modes ◽  
Mode Decomposition ◽  
Rotating Instability ◽  
Annular Cascade

Rotating Instability (RI) occurs at off-design conditions in axial compressors, predominantly in rotor configurations with large tip clearances. Characteristic spectral signatures with side-by-side peaks below the blade passing frequency are typically referred to RI located in the clearance region next to the leading edge (LE). Each peak can be assigned to a dominant circumferential mode. RI is the source of the clearance noise and an indicator for critical operating conditions. Earlier studies at an annular cascade pointed out that RI modes of different circumferential orders occur stochastically distributed in time and independently from each other, which is contradictory to existing explanations of the RI. Purpose of the present study is to verify the generality with regard to axial rotor configurations. Experiments were conducted on a laboratory axial fan stage mainly using unsteady pressure measurements in a sensor ring near the rotor LE. A mode decomposition based on cross spectral matrices was used to analyze the spectral and modal RI patterns upstream of the rotor. Additionally, a time-resolved analysis based on a spatial Discrete-Fourier-Transform was applied to clarify the temporal characteristics of the RI modes and their potential interrelations. The results and a comparison with the previous findings on the annular cascade corroborate a new hypothesis about the basic RI mechanism. This hypothesis implies that instability waves of different wavelengths are generated stochastically in a shear layer resulting from a backflow in the tip clearance region.

scholarly journals Time-Resolved Visualization of Instability Waves in a Hypersonic Boundary Layer

AIAA Journal ◽  
2012 ◽  
Vol 50 (1) ◽  
pp. 243-246 ◽  
Author(s):  
S. J. Laurence ◽  
A. Wagner ◽  
K. Hannemann ◽  
V. Wartemann ◽  
H. Lüdeke ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Hypersonic Boundary Layer ◽  
Time Resolved ◽  
Instability Waves

Rotating Instability in an Annular Cascade: Detailed Analysis of the Instationary Flow Phenomena

2013 ◽  
Vol 136 (6) ◽  
Author(s):  
Benjamin Pardowitz ◽  
Ulf Tapken ◽  
Robert Sorge ◽  
Paul Uwe Thamsen ◽  
Lars Enghardt
Keyword(s):  
Unsteady Flow ◽  
High Speed ◽  
Pressure Sensors ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Tip Vortex ◽  
Pressure Waves ◽  
Flow Profile ◽  
Rotating Instability ◽  
Annular Cascade

Rotating instability (RI) occurs at off-design conditions in compressors, predominantly in configurations with large tip or hub clearance ratios of s* ≥3%. RI is the source of the blade tip vortex noise and a potential indicator for critical operating conditions like rotating stall and surge. The objective of this paper is to give more physical insight into the RI phenomenon using the analysis results of combined near-field measurements with high-speed particle image velocimetry (PIV) and unsteady pressure sensors. The investigation was pursued on an annular cascade with hub clearance. Both the unsteady flow field next to the leading edge as well as the associated rotating pressure waves were captured. A special analysis method illustrates the characteristic pressure wave amplitude distribution, denoted as “modal events” of the RI. Moreover, the slightly adapted method reveals the unsteady flow structures corresponding to the RI. Correlations between the flow profile, the dominant vortex structures, and the rotating pressure waves were found. Results provide evidence to a new hypothesis, implying that shear layer instabilities constitute the basic mechanism of the RI.

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.

scholarly journals Advanced Stereo High-Speed PIV in an Annular Cascade without Clearance: Evidences of Rotating Instability

2017 ◽  
Author(s):  
Julija Peter ◽  
Benjamin Pardowitz ◽  
Mario Eck ◽  
Lars Enghardt ◽  
Dieter Peitsch ◽  
...  
Keyword(s):  
High Speed ◽  
Rotating Instability ◽  
Annular Cascade

Visualization of Three-Dimensional Flow Structures Caused by Rotating Instability

2019 ◽  
Author(s):  
Julija Peter ◽  
Paul Uwe Thamsen
Keyword(s):  
High Speed ◽  
Spectral Characteristics ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Flow Structures ◽  
Experimental Investigations ◽  
Flow Topology ◽  
Time Resolved ◽  
Characteristic Flow ◽  
Rotating Instability

Abstract The present study deals with the flow phenomenon Rotating Instability (RI), which is predominantly observed in axial compressors at off-design conditions e.g. near stall. It potentially induces noise and triggers blade vibrations. Despite numerous studies, the characteristics and the source of RI are not completely understood. The objective of this work is to identify and to visualize characteristic flow topology corresponding to RI by means of Stereo High Speed Particle Image Velocimetry (PIV). The experimental investigations were carried out in an annular compressor stator cascade with and without hub clearance at an inflow Mach number of Ma = 0.4 and the Reynolds number of Re = 300 000. The time-resolved 3C flow field is measured in a single blade passage in planes tangential to the hub. Additionally, the time-resolved pressure fluctuations are captured synchronously to the PIV system. By using combined correlation techniques the spectral characteristics, the spatial extension of the RI and the characteristic flow structures were identified and visualized in configurations with and without hub clearance. The investigations point out that the general flow mechanism of RI is similar in compressor cascades with and without hub clearance. Overall, this work gives important insights into the complex phenomenon Rotating Instability, which can be taken into account when developing compressors in the future.

Experimental Analysis of Rotating Instability Using Hot Wire Triggered PIV and Wavelet Transform

2014 ◽  
Author(s):  
Georg Hermle ◽  
Martin Lawerenz
Keyword(s):  
Wavelet Transform ◽  
Temporal Resolution ◽  
Sampling Rate ◽  
Hot Wire ◽  
Mean Flow ◽  
Compressor Cascade ◽  
Time Resolved ◽  
Piv Measurements ◽  
Rotating Instability ◽  
Phase Angles

The authors present initial results of hot wire anemometry triggered PIV measurements of periodic effects in an annular compressor cascade. The investigations are focused on the unsteady effect of a rotating instability (RI) and are based on PIV measurements performed within the passage of a highly loaded annular compressor cascade. Simultaneously, hot wire measurements were conducted within the same passage. Post-processing the hot wire signal by means of the wavelet transform obtained the time resolved frequency spectrum as well as the time resolved phase angles. Such spectra allow filtering the PIV results to select only the results that feature the investigated effect of PI. The corresponding phase angles of the wavelet transform enable grouping the selected PIV results in phase classes. The average of each class gives the statistical mean flow field for the corresponding phase angle. Afterwards, the statistical mean period of the RI can be displayed by discrete ensemble averaged PIV results. The presented method improves the possible temporal resolution of PIV systems beyond their technical sampling rate. In the case presented, the statistical method leads to a temporal resolution corresponding to a sampling rate of 1.5 kHz, whereas the effective sampling rate of the PIV system used is 4 Hz. The possible resolution in time is only limited by the number of phase classes and accordingly by the number of PIV measurements.

Rotating Instability in an Annular Cascade: Detailed Analysis of the Instationary Flow Phenomena

2013 ◽  
Author(s):  
Benjamin Pardowitz ◽  
Ulf Tapken ◽  
Robert Sorge ◽  
Paul Uwe Thamsen ◽  
Lars Enghardt
Keyword(s):  
Unsteady Flow ◽  
High Speed ◽  
Pressure Sensors ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Tip Vortex ◽  
Pressure Waves ◽  
Flow Profile ◽  
Rotating Instability ◽  
Annular Cascade

Rotating instability (RI) occurs at off-design conditions in compressors, predominantly in configurations with large tip or hub clearance ratios of s* ≥ 3% [1]. RI is the source of the blade tip vortex noise and a potential indicator for critical operating conditions like rotating stall and surge. The objective of this paper is to give more physical insight into the RI phenomenon using the analysis results of combined near-field measurements with High-Speed PIV and unsteady pressure sensors. The investigation was pursued on an annular cascade with hub clearance. Both the unsteady flow field next to the leading edge as well as the associated rotating pressure waves were captured. A special analysis method illustrates the characteristic pressure wave amplitude distribution, denoted as ‘Modal Events’ of the RI. Moreover, the slightly adapted method reveals the unsteady flow structures corresponding to the RI. Correlations between the flow profile, the dominant vortex structures and the rotating pressure waves were found. Results provide evidence to a new hypothesis, implying that shear layer instabilities constitute the basic mechanism of the RI.

Influence of Mach Number and Aerodynamic Loading on Rotating Instability in an Annular Compressor Cascade

2012 ◽  
Author(s):  
Christian Beselt ◽  
Dieter Peitsch
Keyword(s):  
Mach Number ◽  
Flow Field ◽  
Steady Flow ◽  
Field Measurements ◽  
Sudden Increase ◽  
Compressor Cascade ◽  
Time Resolved ◽  
Aerodynamic Loading ◽  
Rotating Instability ◽  
Time Resolved Measurements

An experimental study was conducted to investigate the influence of Mach number and aerodynamic loading on Rotating Instability (RI). Investigations were performed on an annular compressor cascade with radial clearance at the hub. In addition to steady flow field measurements, time resolved measurements of static wall-pressure at the hub, close to the tip clearance, were performed. For a specific range of incidence angles, RI could be detected at all flow speeds (Ma = 0.2–0.7). Shortly before the inception of RI, a sudden increase in pressure loss coefficient and outflow angle was detected by steady flow field measurements. The time resolved measurements showed an abruptly broadband increase of amplitude in the frequency range, in which RI occurs at higher loadings. RI propagates with 25–33% of the circumferential component of the upstream flow speed. Furthermore it is possible to scale the power spectral density function of the unsteady data with Strouhal number.

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