Unstable Flows in the Vaneless Diffuser of a Centrifugal Compressor at Low Flow Rates

1985 ◽  
Author(s):  
S. Mizuki ◽  
C. W. Park ◽  
B. E. L. Deckker
Keyword(s):  
Low Frequency ◽  
Adverse Pressure Gradient ◽  
Rotating Stall ◽  
Low Flow ◽  
Vaneless Diffuser ◽  
Frequency Spectra ◽  
Flow Rates ◽  
Wave Amplification ◽  
Disturbance Waves ◽  
Small Flow

Time-averaged and time-dependent velocity distributions have been measured in the the vaneless diffuser of an experimental compressor. Changes in these distributions have been identified with the onset of rotating stall and fully developed stall. At very small flow rates, an approach to equilibrium has been observed. Frequency spectra analyses have revealed the existence of low frequency disturbance waves which, together with the large adverse pressure gradient prevailing in the diffuser, could lead to selective wave amplification and surging.

scholarly journals Vibration Characteristics Induced by Cavitation in a Centrifugal Pump with Slope Volute

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Ning Zhang ◽  
Minguan Yang ◽  
Bo Gao ◽  
Zhong Li
Keyword(s):  
Centrifugal Pump ◽  
High Frequency ◽  
Low Frequency ◽  
Local Maximum ◽  
Rotating Stall ◽  
Low Flow ◽  
Vibration Level ◽  
Flow Rates ◽  
Frequency Bands ◽  
Cavitation Process

Cavitation is one of the instability sources in centrifugal pump, which would cause some unexpected results. The goal of this paper was to analyze the influence of cavitation process on different frequency bands in a centrifugal pump with slope volute. And special attention was paid to low frequency signals, which were often filtered in the reported researches. Results show that at noncavitation condition, vibration level is closely related to flow structure interior pump. At partial flow rates, especially low flow rates, vibration level increases rapidly with the onset of rotating stall. At cavitation condition, it is proved that cavitation process has a significant impact on low frequency signals. With cavitation number decreasing, vibration level first rises to a local maximum, then it drops to a local minimum, and finally it rises again. At different flow rates, vibration trends in variable frequency bands differ obviously. Critical point inferred from vibration level is much larger than that from 3% head drop, which indicates that cavitation occurs much earlier than that reflected in head curve. Also, it is noted that high frequency signals almost increase simultaneously with cavitation occurring, which can be used to detect cavitation in centrifugal pump.

Spreadsheet as a Data Acquisition Tool in Turbomachinery

2010 ◽  
Author(s):  
Abraham Engeda
Keyword(s):  
Data Acquisition ◽  
Rotating Stall ◽  
Relative Speed ◽  
Vaneless Diffuser ◽  
Flow Rates ◽  
One Dimensional ◽  
Measurement And Analysis ◽  
Different Types ◽  
Unsteady Characteristics ◽  
The One

This paper shows the power of spreadsheets as a strong tool in engineering teaching and research labs. In applied thermo-fluid education, even the one dimensional design or simple experimental measurement and analysis becomes a very complex exercise unless the procedure is programmed. Due to lengthy calculations and iterations, simple solutions are not possible. Exercises have therefore been limited in the classroom. But recent advances in powerful spreadsheets have opened a simple and fast way of performing design and advanced measurements. In recent times due to the introduction of a variety of mathematical soft wares, students have been relived from unnecessary time consuming chores; and therefore, complex measurements can now be carried out more comprehensively and easily. This paper reports on an experimental investigation to determine the effect of the vaneless diffuser width on the unsteady flow performance of a centrifugal compressor stage, where the whole data processing was carried out using a spreadsheet both for the steady and unsteady characteristics. Two compressor configurations with different vaneless diffuser width were investigated at four different impeller speeds and compared in the frequency and time domain. Only one diffuser rotating stall but different types of impeller rotating stalls were detected. The experiments show that the diffuser has a strong influence on the flow in the impeller including in areas way upstream. Analysis of the results indicated: • With increasing diffuser width the onset of impeller rotating stall was shifted to lower flow rates. • With increasing diffuser width the frequencies of the rotating stalls decreased. • There is a common tendency in most of the experiments to lower numbers of rotating cells with increasing relative speed. The whole data acquisition, processing and presentation are carried out using Excel.

Effects of Seal Geometry on Dynamic Impeller Fluid Forces and Moments

2003 ◽  
Vol 125 (5) ◽  
pp. 786-795 ◽  
Author(s):  
Yoshiki Yoshida ◽  
Yoshinobu Tsujimoto ◽  
Goh Morimoto ◽  
Hiroki Nishida ◽  
Shigeki Morii
Keyword(s):  
Force Sensor ◽  
Rotating Stall ◽  
Low Flow ◽  
Centrifugal Impeller ◽  
Face Seal ◽  
Vaneless Diffuser ◽  
Fluid Force ◽  
Fluid Forces ◽  
Whirling Motion ◽  
Force Moment

This paper reports an experimental investigation of the rotordynamic fluid force and moment on a centrifugal impeller with three types of wear-ring seals; i.e., a face seal and two types of toothed seals. The impeller is equipped with a vaneless diffuser. Rotordynamic fluid forces and moments on the impeller in whirling motion were measured directly by using four-axis force sensor. Unsteady pressures were measured at several locations in the diffuser. It was found that, (1) at low flow rate, the fluid force and fluid force moment become maximum at a certain whirling speed caused by a coupling between the whirl motion and vaneless diffuser rotating stall and (2) the seal geometry with axial seal affects the direction of the coupled fluid force relative to the direction of eccentricity through the change in the unsteady leakage flow due to the whirl.

Control of Self-Excited Flow Oscillations in Vaneless Diffuser of Centrifugal Compression Systems

1982 ◽  
Author(s):  
A. N. Abdelhamid
Keyword(s):  
Flow Field ◽  
Performance Improvement ◽  
High Flow ◽  
Low Flow ◽  
Flow Oscillation ◽  
Vaneless Diffuser ◽  
Flow Area ◽  
Flow Measurements ◽  
Flow Rates ◽  
Flow Oscillations

Experiments were conducted to evaluate the effectiveness of axisymmetric diffuser exit throttle in delaying the occurrence of self-excited flow oscillation in vaneless diffusers. Sharp edge rings were installed at diffuser exit in order to change the exit flow area. Tests were carried out with the rings attached to one or both of the diffuser walls. Steady and unsteady flow measurements were used to determine the flow field in the diffuser at the onset of the flow oscillations. Results showed that the occurrence of flow oscillation was continuously delayed as the diffuser exit flow area was reduced for all these configurations and impeller speeds. Comparison between the performance of the compression system with and without diffuser exit blockage indicated that although large losses occur at high flow rates, the use of diffuser exit rings resulted in overall diffuser performance improvement at low flow rates. Retractable diffuser exit rings would therefore be ideal for centrifugal compression systems with vaneless diffuser.

scholarly journals ЗБІЛЬШЕННЯ ДІАПАЗОНУ СТІЙКОЇ РОБОТИ СТУПЕНЯ ВІДЦЕНТРОВОГО КОМПРЕСОРА З БЕЗЛОПАТКОВИМ ДИФУЗОРОМ

2019 ◽  
pp. 4-9
Author(s):  
Микола Васильович Калінкевич ◽  
Микола Іванович Радченко
Keyword(s):  
Mathematical Model ◽  
Gas Injection ◽  
Rotating Stall ◽  
Low Flow ◽  
Stable Operation ◽  
Vaneless Diffuser ◽  
Centrifugal Compressors ◽  
Flow Separation Control ◽  
Flow Part ◽  
Vaneless Diffusers

Centrifugal compressors often operate at different capacities, so it is important to ensure their stable operation over a wide flow range. Stages with vaneless diffusers have several advantages compared to stages with other types of diffusers: they are more technologically advanced to manufacture, and more uniform pressure distribution behind the impeller improves the dynamics of the rotor. At low flows, due to the occurrence of a rotating stall and surge, the efficiency of stages with vaneless diffusers rapidly decreases. The occurrence of unstable operating modes of centrifugal compressor stages at low flow rates is associated with the appearance of developed backflows in the flow part. To expand the range of stable operation of the stages, it is necessary to use methods of flow separation control. Separation of the flow can be controlled either by special profiling the flow part channels or by actively influencing the flow, for example, by injecting gas. To solve this problem, a mathematical model of the gas flow in a vaneless diffuser with gas injection is developed. The characteristics and parameters of the flow in the vaneless diffusers with various meridional profiles with and without injecting gas were calculated. A comparison of the calculated and experimental characteristics of the vaneless diffusers and flow parameters in diffusers with different geometries and with different injection modes confirms the adequacy of the mathematical model. Investigations have confirmed the possibility of improving the characteristics of the stages of centrifugal compressors through the use of vaneless diffusers and diffusers with gas injection. Gas injection diffusers extend the stable operation range of the stages. The use of gas injection in a vaneless diffuser allows reducing the power consumption during antisurge control in comparison with the widespread bypass suction system at the entrance to the impeller

A Distinction Between Different Types of Stall in a Centrifugal Compressor Stage

1986 ◽  
Vol 108 (1) ◽  
pp. 83-92 ◽  
Author(s):  
N. Ka¨mmer ◽  
M. Rautenberg
Keyword(s):  
Energy Transfer ◽  
Centrifugal Compressor ◽  
High Frequency ◽  
Low Frequency ◽  
Rotating Stall ◽  
Compressor Stage ◽  
Vaneless Diffuser ◽  
Pressure Transducers ◽  
Different Types ◽  
Probe Measurements

The flow at the stall line of a centrifugal compressor with vaneless diffuser was investigated at different speeds. A distinction between three kinds of stall phenomena could be made. One type of stall with regurgitation of fluid at the impeller inlet was of a nonperiodic character, whereas two different types of periodic stall appeared at higher speeds. The rotating nature of these two types of stall was verified from a comparison of signals of peripherally spaced pressure transducers. The low-frequency rotating stall exhibited features of diffuser generated stall and a lobe number of three was measured. From a detailed investigation of the high-frequency rotating stall, which included unsteady probe measurements upstream and downstream of the impeller, it can be shown that this type of rotating stall is generated in the impeller by a periodic breakdown of energy transfer from the rotor to the flow. This conclusion is supported by the distribution of shroud static pressures.

Rotating Stall Induced in Vaneless Diffusers of Very Low Specific Speed Centrifugal Blowers

1985 ◽  
Vol 107 (2) ◽  
pp. 514-519 ◽  
Author(s):  
Y. Kinoshita ◽  
Y. Senoo
Keyword(s):  
Flow Analysis ◽  
Rotating Stall ◽  
Experimental Results ◽  
Flow Coefficient ◽  
Critical Flow ◽  
Flow Rates ◽  
Small Flow ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Vaneless Diffusers

The limit of rotating stall was experimentally determined for three very small specific speed centrifugal blowers. The impellers were specially designed for stall-free at very small flow rates, so that the cause of rotating stall could be attributed to the vaneless diffusers. Experimental results demonstrated that the blowers did not stall until the flow coefficient was reduced to very small values, which had never been reported in the literature. The critical flow coefficient for rotating stall agreed very well with the prediction based on a flow analysis and a criterion for rotating stall in vaneless diffusers developed by the authors.

Experimental Investigation and Performance Analysis of Six Low Flow Coefficient Centrifugal Compressor Stages

1995 ◽  
Vol 117 (4) ◽  
pp. 585-592 ◽  
Author(s):  
J. Paroubek ◽  
V. Cyrus ◽  
J. Kyncˇl
Keyword(s):  
Development Program ◽  
Rotating Stall ◽  
Flow Coefficient ◽  
Low Flow ◽  
Vaneless Diffuser ◽  
Test Rig ◽  
Disk Friction ◽  
Return Channel ◽  
And Performance ◽  
Low Flow Coefficient

Some results of a research and development program for centrifugal compressors are presented. Six-stage configurations with low flow coefficient were tested. The stages had channel width parameter b2/D2 = 0.01 and 0.03. For each value of the width parameter, three different impellers with inlet hub to outlet diameter ratio do/D2 = 0.3, 0.4, and 0.5 were designed. Test rig, instrumentation, and data analysis are described. Special attention was devoted to probe calibrations and to evaluation of the leakage, bearing, and disk friction losses. Aerodynamic performance of all tested stages is presented. Slip factors of impellers obtained experimentally and theoretically are compared. Losses in both vaneless diffuser and return channel with deswirl vanes are discussed. Rotating stall was also investigated. Criteria for stall limit were tested.

scholarly journals Experimental Investigation and Performance Analysis of Six Low Flow Coefficient Centrifugal Compressor Stages

1994 ◽  
Author(s):  
J. Paroubek ◽  
V. Cyrus ◽  
J. Kyncl
Keyword(s):  
Rotating Stall ◽  
Development Programme ◽  
Diameter Ratio ◽  
Flow Coefficient ◽  
Low Flow ◽  
Vaneless Diffuser ◽  
Test Rig ◽  
Return Channel ◽  
And Performance ◽  
Low Flow Coefficient

Some results of a research and development programme for centrifugal compressors are presented. Six stage configurations with low flow coefficient were tested. The stages had channel width parameter bo/D2=0.01 and 0.03. For each value of the width parameter three different impellers with inlet hub to outlet diameter ratio do/D2=0.3, 0.4 and 0.5 were designed. Test rig, instrumentation and data analysis are described. Special attention was devoted to probe calibrations and to evaluation of the leakage, bearing and disc friction losses. Aerodynamic performance of all tested stages is presented. Slip factors of impellers obtained experimentally and theoretically are compared. Losses in both vaneless diffuser and return channel with de-swirl vanes are discussed. Rotating stall was also investigated. Criteria for stall limit were tested.

Predictability of Rotating Stall and Surge in a Centrifugal Compressor Stage With Dynamic Simulations

2014 ◽  
Author(s):  
Néstor González Díez ◽  
Jan P. M. Smeulers ◽  
Libero Tapinassi ◽  
Alberto Scotti Del Greco ◽  
Lorenzo Toni
Keyword(s):  
Centrifugal Compressor ◽  
Rotating Stall ◽  
Low Flow ◽  
Stable Region ◽  
Stable Operation ◽  
Performance Curve ◽  
Dynamic Simulations ◽  
Cycle Frequency ◽  
Flow Rates ◽  
Test Loop

A testing campaign performed on a centrifugal compressor test-loop showed that multiple areas of stable operation existed that were not expected. It was shown during the tests that after a first region of instability at low flow rates, a second stable region would appear at even lower flow rates. Dynamic simulations based on a modified Greitzer’s model have been performed in order to assess the predictability of these unsteady phenomena. The study is focused on matching the dynamic simulations and the experimental results, concerning the different stable and unstable regions. It was of particular interest to verify the simulation results for the first region of instability, where rotating stall is suspected to occur. In this region the time-averaged performance curve showed a positive, i.e. unstable, slope. The performance curve presents then two regions with negative, stable, slope. The model shows good agreement with the measured pressure fluctuations when operated in surge conditions, both in terms of fundamental surge cycle frequency and pulsation amplitude. Capturing the pressure variations for the rotating stall range proved more difficult and subject to the implemented performance curve, which is considered uncertain in this range. By tuning the performance curve in the corresponding range of flow rates, a satisfactory match with the test results could be achieved. The second range of stability was correctly captured by also modifying the compressor performance curve.

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