Unsteady Viscous Flow in a High-Speed Core Compressor

1992 ◽  
Vol 114 (2) ◽  
pp. 287-294 ◽  
Author(s):  
M. A. Cherrett ◽  
J. D. Bryce
Keyword(s):  
High Speed ◽  
Secondary Flows ◽  
Pressure Measurements ◽  
High Frequency Response ◽  
Unsteady Viscous Flow ◽  
Novel Method ◽  
Multistage Compressor ◽  
Response Pressure ◽  
Random Fluctuations ◽  
Unsteady Pressure Measurements

A probe incorporating a miniature high-frequency response pressure transducer has been traversed behind the first three stages of a high-speed multistage compressor operating at throttle settings corresponding to near choke, peak efficiency, and near surge. A novel method of compensating for transducer temperature sensitivity was employed. Consequently, time-averaged pressures derived from the transducer were found to be in good agreement with pneumatic pressure measurements. Analysis of the unsteady pressure measurements revealed both the periodic and random fluctuations in the flow field. This provided information on rotor-rotor interaction effects and the nature of viscous blade wake and secondary flows in each stage.

scholarly journals Unsteady Viscous Flow in a High Speed Core Compressor

1991 ◽  
Author(s):  
M. A. Cherrett ◽  
J. D. Bryce
Keyword(s):  
High Speed ◽  
Secondary Flows ◽  
Pressure Measurements ◽  
High Frequency Response ◽  
Unsteady Viscous Flow ◽  
Novel Method ◽  
Multistage Compressor ◽  
Response Pressure ◽  
Random Fluctuations ◽  
Unsteady Pressure Measurements

A probe incorporating a miniature high-frequency response pressure transducer has been traversed behind the first three stages of a high-speed multistage compressor operating at throttle settings corresponding to near choke, peak efficiency and near surge. A novel method of compensating for transducer temperature sensitivity was employed. Consequently, time-averaged pressures derived from the transducer were found to be in good agreement with pneumatic pressure measurements. Analysis of the unsteady pressure measurements revealed both the periodic and random fluctuations in the flowfield. This provided information on rotor-rotor interaction effects and the nature of viscous blade wake and secondary flows in each stage.

Experimental Study of Surge Precursors in a High-Speed Multistage Compressor

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Nicolas Courtiade ◽  
Xavier Ottavy
Keyword(s):  
High Frequency ◽  
High Speed ◽  
Rotation Speed ◽  
Characteristic Line ◽  
Pressure Measurements ◽  
High Frequency Response ◽  
Stable Operating ◽  
Variable Duration ◽  
Multistage Compressor ◽  
Operating Points

Pressure measurements using high frequency response sensors have been carried out on the third rotor of the 3.5-stage high speed compressor CREATE (rotation speed: 11,543 RPM, Rotor 1 tip speed: 313 m/s) over the complete characteristic line and during the surge transient. Precursors to the instabilities occurring near surge are observable at stable operating points. Just before surge, these precursors characterized as rotating disturbances grow in amplitude and provoke the onset a stall cell after a variable duration, which finally triggers surge. This paper presents a detailed analysis of the phenomena of rotating instabilities and surge transient and shows that it is possible to develop an antisurge active control system based on the early detection of the precursors.

scholarly journals Flow instability effects related to purge through a gas turbine chute seal

2021 ◽  
Vol 5 ◽  
pp. 111-125
Author(s):  
Arijit Roy ◽  
Jens Fridh ◽  
James Scobie ◽  
Carl Sangan ◽  
Gary Lock
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Flow Instability ◽  
Flow Coefficient ◽  
Flow Instabilities ◽  
Pressure Measurements ◽  
Flow Conditions ◽  
Seal Design ◽  
Purge Flow ◽  
Unsteady Pressure Measurements

This paper investigates flow instabilities inside the cavity formed between the stator and rotor disks of a high-speed turbine rig. The cavity rim seal is of chute seal design. The influence of flow coefficient on the sealing effectiveness at constant purge flow rate through the wheel-space is determined. The effectiveness at different radial positions over a range of purge flow conditions and flow coefficients is also studied. Unsteady pressure measurements have identified the frequency of instabilities that form within the rim seal, phenomena which have been observed in other studies. Frequencies of these disturbances, and their correlation in the circumferential direction have determined the strength and speed of rotation of the instabilities within the cavity. Large scale unsteady rotational structures have been identified, which show similarity to previous studies. These disturbances have been found to be weakly dependent on the purge flow and flow coefficients, although an increased purge reduced both the intensity and speed of rotation of the instabilities. Additionally, certain uncorrelated disturbances have been found to be inconsistent (discontinuous) with pitchwise variation.

scholarly journals Transient Behavior of a Radial Vaneless Diffuser

2011 ◽  
Author(s):  
Antoine Dazin ◽  
Patrick Dupont ◽  
Guy Caignaert ◽  
Ge´rard Bois
Keyword(s):  
Experimental Data ◽  
High Speed ◽  
Laser Sheet ◽  
High Repetition Rate ◽  
Optical Methods ◽  
Pressure Measurements ◽  
Vaneless Diffuser ◽  
Test Rig ◽  
Unsteady Pressure ◽  
Unsteady Pressure Measurements

The paper refers to the behavior of a radial flow pump vaneless diffuser during a starting period. Results obtained with a 1D numerical model are compared with some new experimental data which have been obtained using 2D/3C High repetition rate PIV within the diffuser coupled with unsteady pressure measurements. These tests have been performed on a test rig with a radial impeller matched with a vaneless diffuser. They have been made in air, on a test rig well adapted for studies on interactions between impeller and diffuser, as well as for the use of optical methods and especially Particle Image Velocimetry (PIV) as there is no volute downstream of the diffuser. The present study refers to new experiments combining pressure measurements and 2D/3C High Speed PIV at partial flow rates within a vaneless diffuser with a large outlet radius. Four Bru¨el & Kjaer condenser microphones are used for the unsteady pressure measurements. They were flush mounted on the shroud side of the diffuser wall and on the suction pipe of the pump. The sampling frequency was 2048 Hz. For PIV measurements, the laser sheet was generated by a Darwin PIV ND:YLF Laser at three heights within the diffuser. PIV snapshots have been recorded by two identical CMOS cameras. A home made software has been used for the images treatment. The results consist in fields of 80 × 120 mm2 and 81 × 125 velocity vectors with a temporal resolution of 250 velocity maps per second. For each flow rate and each laser sheet height in the diffuser, two acquisitions of about 1500 velocity maps have been realised. The experimental data are compared with the ones provided by a 1D transient model of the flow within the diffuser.

Spatial Correlation Based Stall Inception Analysis

2007 ◽  
Author(s):  
Joshua D. Cameron ◽  
Scott C. Morris
Keyword(s):  
Spatial Correlation ◽  
High Speed ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Fourier Decomposition ◽  
Stall Inception ◽  
Pressure Transducers ◽  
High Frequency Response ◽  
Wide Range ◽  
Response Pressure

Investigations of stall inception and compressor pre-stall behavior have used a variety of techniques to make inferences about the mechanisms of rotating stall inception. Many of these techniques utilized data from arrays of circumferentially spaced hot-wires or high frequency response pressure transducers. This paper presents results from the application of several typical analysis techniques to the interpretation of unsteady casing pressure measurements recorded during two representative stall event in a high-speed axial compressor stage. Results from visual pressure trace inspection, spatial Fourier decomposition, wavelet filtering, and traveling wave energy techniques are presented and compared. The effects of measurement and analysis parameters are also briefly discussed. A new analysis technique based on windowed two-point spatial correlation between adjacent stall inception sensors is described. The method was found to provide both spatial and temporal information about rotating features in the compressor flow and is insensitive to low pass filtering and parameter selection over a wide range of values. It was also found to be valuable for analysis of both pre-stall and stall inception behavior.

scholarly journals Time-resolved flow field investigation in an industrial centrifugal compressor application involving TR-PIV synchronized with unsteady pressure measurements

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Joachim Klinner ◽  
Melanie Voges ◽  
Michael Schroll ◽  
Alessandro Bassetti ◽  
Christian Willert
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Laser System ◽  
Power Spectra ◽  
Field Investigation ◽  
High Repetition Rate ◽  
Pressure Measurements ◽  
Time Resolved ◽  
Unsteady Pressure ◽  
Unsteady Pressure Measurements

We report on combined velocity and unsteady pressure measurements obtained on an radial compressor with vaneless diffuser and asymmetric volute. Time-resolved PIV recordings were acquired at 26 kHz both upstream of the impeller as well as within the vaneless diffusor at several rotation speeds at clean conditions and prior to the onset of instabilities within the rotor. The velocity data was acquired with a high-repetition rate, double-pulse laser system consisting of two combined DPSS lasers and a high-speed CMOS camera that was synchronized with multi-point unsteady pressure measurements. Details on the facility, the utilized instrumentation and data processing are provided with particular focus on the spectral and coherence analysis. Power spectra obtained from time records of the inlet velocity and unsteady pressure reveal an increase of low-frequency fluctuations below the blade passing frequency and the occurrence of a mode-locked behaviour indicating the presence of rotating instabilities. High levels of correlation between velocity and unsteady pressure signals not only confirm the temporal coherence of the acquired data but also reveal a direct coupling between flow field and pressure signature that is more prominent upstream of the rotor rather than in the diffusor.

scholarly journals A Parallel CFD Tool to Produce Faulty Blade Signatures for Diagnostic Purposes

1998 ◽  
Author(s):  
D. G. Koubogiannis ◽  
V. P. Iliadis ◽  
K. C. Giannakoglou
Keyword(s):  
High Speed ◽  
Unstructured Grids ◽  
Fast Response ◽  
Operating Conditions ◽  
Pressure Measurements ◽  
Diagnostic Systems ◽  
Compressor Cascade ◽  
Computational Fluid Dynamics Cfd ◽  
Response Pressure ◽  
The One

In the turbomachinery field, many diagnostic systems utilize databases with symptoms corresponding to the most frequent operation faults. Thanks to Computational Fluid Dynamics (CFD), databases can be created without costly experiments, whereas the use of unstructured grids in combination with parallel processing makes the whole task easy and fast to accomplish. In this paper, a procedure that builds up a database for gas-turbine fault diagnosis is demonstrated. Advanced CFD tools that operate concurrently on multi-processor platforms are used. The so-prepared database contributes to the identification of faults through the analysis of the unsteady pressure signals that correspond to hypothetical sensors located in the inter-blade region. The pressure signals are post-processed in a similar way to the one experimentalists employ for fast-response pressure measurements. Symptoms related to displaced and/or twisted blades in an industrial high-speed compressor cascade, at design and off-design operating conditions, are analyzed.

scholarly journals Multifrequency Instability of Cavitating Inducers

2006 ◽  
Vol 129 (6) ◽  
pp. 731-736 ◽  
Author(s):  
Christopher E. Brennen
Keyword(s):  
High Speed ◽  
Low Frequency ◽  
Performance Degradation ◽  
Cavitation Number ◽  
Pressure Measurements ◽  
Higher Harmonics ◽  
Unsteady Pressure ◽  
Arbitrary Frequency ◽  
Unsteady Pressure Measurements

Recent testing of high-speed cavitating turbopump inducers has revealed the existence of more complex instabilities than the previously recognized cavitating surge and rotating cavitation. This paper explores one such instability that is uncovered by considering the effect of a downstream asymmetry, such as a volute on a rotating disturbance similar to (but not identical to) that which occurs in rotating cavitation. The analysis uncovers a new instability that may be of particular concern because it occurs at cavitation numbers well above those at which conventional surge and rotating cavitation occur. This means that it will not necessarily be avoided by the conventional strategy of maintaining a cavitation number well above the performance degradation level. The analysis considers a general surge component at an arbitrary frequency ω present in a pump rotating at frequency Ω and shows that the existence of a discharge asymmetry gives rise not only to beat components at frequencies, Ω−ω and Ω+ω (as well as higher harmonics), but also to rotating as well as surge components at all these frequencies. In addition, these interactions between the frequencies and the surge and rotating modes lead to “coupling impedances” that effect the dynamics of each of the basic frequencies. We evaluate these coupling impedances and show not only that they can be negative (and thus promote instability) but also are most negative for surge frequencies just a little below Ω. This implies potential for an instability involving the coupling of a surge mode with a frequency around 0.9Ω and a low-frequency rotating mode about 0.1Ω. We also examine how such an instability would be manifest in unsteady pressure measurements at the inlet to and discharge from a cavitating pump and establish a “footprint” for the recognition of such an instability.

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