Some Guidelines for the Experimental Characterization of Vaneless Diffuser Rotating Stall in Stages of Industrial Centrifugal Compressors

2014 ◽  
Author(s):  
Alessandro Bianchini ◽  
Davide Biliotti ◽  
Marco Giachi ◽  
Elisabetta Belardini ◽  
Libero Tapinassi ◽  
...  
Keyword(s):  
Dynamic Pressure ◽  
Industrial Test ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Design Parameters ◽  
Accurate Estimation ◽  
Pressure Measurements ◽  
Vaneless Diffuser ◽  
Centrifugal Compressors ◽  
Test Models

An accurate estimation of rotating stall is one of the key technologies for high-pressure centrifugal compressors, as it is often connected with the onset of detrimental subsynchronous vibrations which can prevent the machine from operating beyond this limit. With particular reference to the vaneless diffuser stall, much research has been directed at investigating the physics of the phenomenon, the influence of the main design parameters and the prediction of the stall inception. Few of them, however, focused attention on the evaluation of the aerodynamic unbalance due to the induced pressure field in the diffuser, which, however, could provide a valuable contribution to both the identification of the actual operating conditions and the enhancement of the compressor operating range by a suitable choice of the control strategy. Although advanced experimental techniques have been successfully applied to the recognition of the stall pattern in a vaneless diffuser, the most suitable solution for a wider application in industrial test-models is based on dynamic pressure measurements by means of a reduced number of probes. Within this context, a procedure to transpose pressure measurements into the spatial pressure distribution was developed and validated on a wide set of industrial test-models. In this work, the main guidelines of the procedure are presented and discussed, with particular reference to signals analysis and manipulation as well as sensors positioning. Moreover, the prospects of using a higher number of sensors is analyzed and compared to standard solutions using a limited probes number.

A Systematic Approach to Estimate the Impact of the Aerodynamic Force Induced by Rotating Stall in a Vaneless Diffuser on the Rotordynamic Behavior of Centrifugal Compressors

2013 ◽  
Author(s):  
Alessandro Bianchini ◽  
Davide Biliotti ◽  
Giovanni Ferrara ◽  
Lorenzo Ferrari ◽  
Elisabetta Belardini ◽  
...  
Keyword(s):  
Aerodynamic Force ◽  
Dynamic Pressure ◽  
Journal Bearings ◽  
Rotating Stall ◽  
Squeeze Film ◽  
Accurate Estimation ◽  
Vaneless Diffuser ◽  
Test Rig ◽  
Centrifugal Compressors ◽  
The Impact

One of the main challenges of the present industrial research on centrifugal compressors is the need of extending the left margin of the operating range of the machines. As a result, interest is being paid in accurately evaluating the amplitude of the pressure fluctuations caused by rotating stall, which usually occurs prior to surge. The related aerodynamic force acting on the rotor can produce subsynchronous vibrations, which can prevent the machine to further operate, in case their amplitude is too high. These vibrations are often contained thanks to the stiffness of the oil journals. Centrifugal compressors design is, however, going towards alternative journal solutions having lower stiffness levels (e.g. Active Magnetic Bearings or Squeeze Film Dampers), which hence will be more sensitive to this kind of excitation: consequently, a more accurate estimation of the expected forces in presence of dynamic external forces like those connected to an aerodynamically unstable condition is needed to predict the vibration level and the compressor operability in similar conditions. Within this scenario, experimental tests were carried out on an industrial impeller operating at high peripheral Mach number. The dedicated test rig was equipped with several dynamic pressure probes that were inserted in the gas flow path; moreover, the rotor vibrations were constantly monitored with typical vibration probes located near the journal bearings. The pressure field induced by the rotating stall in the vaneless diffuser was reconstructed by means of an ensemble average approach, defining the amplitude and frequency of the external force acting on the impeller. The calculated force value was then included in the rotordynamic model of the test rig: the predicted vibrations on the bearings were compared with the measurements, showing satisfactory agreement. Finally, the prospects of the proposed approach are discussed by investigating the response of a real machine in high-pressure functioning when different choices of journal bearings are made.

A Systematic Approach to Estimate the Impact of the Aerodynamic Force Induced by Rotating Stall in a Vaneless Diffuser on the Rotordynamic Behavior of Centrifugal Compressors

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Alessandro Bianchini ◽  
Davide Biliotti ◽  
Giovanni Ferrara ◽  
Lorenzo Ferrari ◽  
Elisabetta Belardini ◽  
...  
Keyword(s):  
Aerodynamic Force ◽  
Dynamic Pressure ◽  
Journal Bearings ◽  
Rotating Stall ◽  
Squeeze Film ◽  
Accurate Estimation ◽  
Vaneless Diffuser ◽  
Test Rig ◽  
Centrifugal Compressors ◽  
The Impact

One of the main challenges of the present industrial research on centrifugal compressors is the need for extending the left margin of the operating range of the machines. As a result, interest is being paid to accurately evaluating the amplitude of the pressure fluctuations caused by rotating stall, which usually occurs prior to surge. The related aerodynamic force acting on the rotor can produce subsynchronous vibrations, which can prevent the machine's further operation, in case their amplitude is too high. These vibrations are often contained due to the stiffness of the oil journals. Centrifugal compressor design is, however, going towards alternative journal solutions having lower stiffness levels (e.g., active magnetic bearings or squeeze film dampers), which will be more sensitive to this kind of excitation: consequently, a more accurate estimation of the expected forces in the presence of dynamic external forces such as those connected to an aerodynamically unstable condition is needed to predict the vibration level and the compressor operability in similar conditions. Within this scenario, experimental tests were carried out on industrial impellers operating at high peripheral Mach numbers. The dedicated test rig was equipped with several dynamic pressure probes that were inserted in the gas flow path; moreover, the rotor vibrations were constantly monitored with typical vibration probes located near the journal bearings. The pressure field induced by the rotating stall in the vaneless diffuser was reconstructed by means of an ensemble average approach, thus defining the amplitude and frequency of the external force acting on the impeller. The calculated force value was then included in the rotordynamic model of the test rig: the predicted vibrations on the bearings were compared with the measurements, showing satisfactory agreement. Moreover, the procedure was applied to two real multistage compressors, showing notable prediction capabilities in the description of rotating stall effects on the machine rotordynamics. Finally, the prospects of the proposed approach are discussed by investigating the response of a real machine in high-pressure functioning when different choices of journal bearings are made.

Experimental Determination of Mechanical Stress Induced by Rotating Stall in Unshrouded Impellers of Centrifugal Compressors

2016 ◽  
Author(s):  
Philipp Jenny ◽  
Yves Bidaut
Keyword(s):  
High Cycle Fatigue ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Design Phase ◽  
Cycle Fatigue ◽  
Centrifugal Compressors ◽  
Impeller Blade ◽  
Pressure Transducers

Unshrouded centrifugal compressor impellers typically operate at high rotational speeds and volume flow rates. The resulting high mean stress levels leave little margin for dynamic excitations that can cause high cycle fatigue. In addition to the well-established high frequency impeller blade excitations of centrifugal compressors caused by the stationary parts, such as vaned diffusers or inlet guide vanes, the presented study addresses an unsteady rotating flow feature (rotating stall) which should be taken into account when addressing high cycle fatigue during the design phase. The unsteady fluid-structure interaction between rotating stall and unshrouded impellers was experimentally described and quantified during two different measurement campaigns with two full-size compression units operating under real conditions. In both campaigns dynamic strain gauges and pressure transducers were mounted at various locations on the impeller of the first compression stage. The casing was also equipped with a set of dynamic pressure transducers to complement the study. Rotating pressure fluctuations were found to form an additional impeller excitation at a frequency that is not a multiple of the shaft speed. The measurements show that the excitation amplitude and frequency caused by the rotating pressure fluctuations depend on the operating conditions and are therefore challenging to predict and consider during the design phase. Furthermore, the excitation mechanism presented was found to cause resonant impeller blade response under specific operating conditions. For the experimentally investigated impeller geometries a rotating pressure fluctuation caused approximately 1.5 MPa of additional dynamic stress in the structure per 1 mbar of dynamic pressure amplitude when exciting the first bending mode of the impeller. The induced dynamic mechanical stresses due to rotating stall are in the order of 10% of the endurance limit of the material for the tested impeller geometries, therefore they are not critical and confirm a robust and reliable design.

Experimental Analysis of the Pressure Field Inside a Vaneless Diffuser From Rotating Stall Inception to Surge

2015 ◽  
Author(s):  
Alessandro Bianchini ◽  
Davide Biliotti ◽  
Dante Tommaso Rubino ◽  
Lorenzo Ferrari ◽  
Giovanni Ferrara
Keyword(s):  
Transient Analysis ◽  
Pressure Field ◽  
Dynamic Pressure ◽  
Rotating Stall ◽  
Accurate Estimation ◽  
Vaneless Diffuser ◽  
Ensemble Averaging ◽  
Stall Inception ◽  
Key Points ◽  
Real Time Visualization

An accurate estimation of rotating stall is one of the key points for high-pressure centrifugal compressors, as it is often connected with the onset of detrimental subsynchronous vibrations which can prevent the machine from operating beyond this limit. With particular reference to vaneless diffuser rotating stall, the most common practice in industrial machines is to make use of a limited number of dynamic pressure probes to reconstruct the stall characteristics after an ensemble averaging approach. In this study, a 1:1 model of an industrial compressor stage was tested in a dedicated test rig and equipped with 24 pressure probes properly distributed along the diffuser circumference with the scope of providing a real-time visualization of the spatial pressure distribution within the diffuser. The results allowed the assessment of some important characteristics of the stall cells that were historically supposed based on averaged data, e.g. the cells rigidity. Moreover, the present study confirmed the existence of a stall pattern with two almost axisymmetric lobes. Finally, the transient analysis of both the stall inception and the surge onset was carried out, highlighting the flow field evolution in the diffuser under these conditions.

Experimental Determination of Mechanical Stress Induced by Rotating Stall in Unshrouded Impellers of Centrifugal Compressors

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Philipp Jenny ◽  
Yves Bidaut
Keyword(s):  
High Cycle Fatigue ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Design Phase ◽  
Cycle Fatigue ◽  
Centrifugal Compressors ◽  
Impeller Blade ◽  
Pressure Transducers

Unshrouded centrifugal compressor impellers typically operate at high rotational speeds and volume flow rates. The resulting high mean stress levels leave little margin for dynamic excitations that can cause high-cycle fatigue. In addition to the well-established high-frequency impeller blade excitations of centrifugal compressors caused by the stationary parts, such as vaned diffusers or inlet guide vanes (IGVs), the presented study addresses an unsteady rotating flow feature (rotating stall) which should be taken into account when addressing the high-cycle fatigue during the design phase. The unsteady fluid–structure interaction between rotating stall and unshrouded impellers was experimentally described and quantified during two different measurement campaigns with two full-size compression units operating under real conditions. In both campaigns, dynamic strain gauges and pressure transducers were mounted at various locations on the impeller of the first compression stage. The casing was also equipped with a set of dynamic pressure transducers to complement the study. Rotating pressure fluctuations were found to form an additional impeller excitation at a frequency that is not a multiple of the shaft speed. The measurements show that the excitation amplitude and frequency caused by the rotating pressure fluctuations depend on the operating conditions and are therefore challenging to predict and consider during the design phase. Furthermore, the excitation mechanism presented was found to cause resonant impeller blade response under specific operating conditions. For the experimentally investigated impeller geometries, a rotating pressure fluctuation caused approximately 1.5 MPa of additional dynamic stress in the structure per 1 mbar of dynamic pressure amplitude when exciting the first bending mode of the impeller. The induced dynamic mechanical stresses due to rotating stall are in the order of 10% of the endurance limit of the material for the tested impeller geometries; therefore, they are not critical and confirm a robust and reliable design.

Experimental Analysis of the Pressure Field Inside a Vaneless Diffuser From Rotating Stall Inception to Surge

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
Alessandro Bianchini ◽  
Davide Biliotti ◽  
Dante Tommaso Rubino ◽  
Lorenzo Ferrari ◽  
Giovanni Ferrara
Keyword(s):  
Transient Analysis ◽  
Pressure Field ◽  
Dynamic Pressure ◽  
Rotating Stall ◽  
Accurate Estimation ◽  
Vaneless Diffuser ◽  
Ensemble Averaging ◽  
Stall Inception ◽  
Key Points ◽  
Real Time Visualization

An accurate estimation of rotating stall is one of the key points for high-pressure centrifugal compressors, as it is often connected with the onset of detrimental subsynchronous vibrations which can prevent the machine from operating beyond this limit. With particular reference to vaneless diffuser rotating stall, the most common practice in industrial machines is to make use of a limited number of dynamic pressure probes to reconstruct the stall characteristics after an ensemble averaging approach. In this study, a 1:1 model of an industrial compressor stage was tested in a dedicated test rig and equipped with 24 pressure probes properly distributed along the diffuser circumference with the scope of providing a real-time visualization of the spatial pressure distribution within the diffuser. The results allowed the assessment of some important characteristics of the stall cells that were historically supposed based on averaged data, e.g., the cells rigidity. Moreover, the present study confirmed the existence of a stall pattern with two almost axisymmetric lobes. Finally, the transient analysis of both the stall inception (SI) and the surge onset (SO) was carried out, highlighting the flow field evolution in the diffuser under these conditions.

scholarly journals Detection of vaneless diffuser rotating stall by means of dynamic pressure sensors and acoustic measurements

2021 ◽  
Vol 312 ◽  
pp. 11007
Author(s):  
Luca Romani ◽  
Lorenzo Bosi ◽  
Alberto Baroni ◽  
Lorenzo Toni ◽  
Davide Biliotti ◽  
...  
Keyword(s):  
Dynamic Pressure ◽  
Pressure Sensors ◽  
Experimental Tests ◽  
Rotating Stall ◽  
Accurate Estimation ◽  
Sufficient Information ◽  
Acoustic Measurements ◽  
Vaneless Diffuser ◽  
Test Rig ◽  
Ensemble Averaging

An accurate estimation of rotating stall is one of the key technologies for high-pressure centrifugal compressors. Several techniques have been proposed to detect the stall onset; inter alia, few dynamic pressure probes have been shown to not only properly detect the phenomenon, but also reconstruct the stall characteristics after an ensemble averaging approach. The massive use of this technique in the field is, however, not a common practice yet. In the present study, the use of dynamic pressure probes has been combined with that of an environmental microphone to evaluate the prospects of this latter for a possible stall onset detection. To this end, experimental tests have been carried out in the experimental test rig of the Department of Industrial Engineering (DIEF) of Università degli Studi di Firenze. Results show that the microphone was able to distinguish the onset of rotating stall accurately and promptly, even though – differently from dynamic pressure sensors - it does not provide sufficient information to determine the characteristics of the stall pattern. On this basis, the use of acoustic measurements could find room for automatic detection of rotating stall onset.

Roles of vanes in diffuser on stability of centrifugal compressor

2019 ◽  
Vol 233 (14) ◽  
pp. 5380-5392
Author(s):  
Wangzhi Zou ◽  
Xiao He ◽  
Wenchao Zhang ◽  
Zitian Niu ◽  
Xinqian Zheng
Keyword(s):  
High Pressure ◽  
Centrifugal Compressor ◽  
Dynamic Pressure ◽  
Pressure Ratio ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Centrifugal Compressors ◽  
Compression System ◽  
The Stability ◽  
Rotating Instability

The stability considerations of centrifugal compressors become increasingly severe with the high pressure ratios, especially in aero-engines. Diffuser is the major subcomponent of centrifugal compressor, and its performance greatly influences the stability of compressor. This paper experimentally investigates the roles of vanes in diffuser on component instability and compression system instability. High pressure ratio centrifugal compressors with and without vanes in diffuser are tested and analyzed. Rig tests are carried out to obtain the compressor performance map. Dynamic pressure measurements and relevant Fourier analysis are performed to identify complex instability phenomena in the time domain and frequency domain, including rotating instability, stall, and surge. For component instability, vanes in diffuser are capable of suppressing the emergence of rotating stall in the diffuser at full speeds, but barely affect the characteristics of rotating instability in the impeller at low and middle speeds. For compression system instability, it is shown that the use of vanes in diffuser can effectively postpone the occurrence of compression system surge at full speeds. According to the experimental results and the one-dimensional flow theory, vanes in diffuser turn the diffuser pressure rise slope more negative and thus improve the stability of compressor stage, which means lower surge mass flow rate.

Effects of Non-Axisymmetric Volute on Rotating Stall in the Vaneless Diffuser of a Centrifugal Compressor

2020 ◽  
Author(s):  
Zitian Niu ◽  
Zhenzhong Sun ◽  
Baotong Wang ◽  
Xinqian Zheng
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Centrifugal Compressor ◽  
Stability Boundary ◽  
Rotating Stall ◽  
Evolution Process ◽  
Vaneless Diffuser ◽  
Unstable Flow ◽  
Centrifugal Compressors ◽  
Specific Location

Abstract Rotating stall is an important unstable flow phenomenon that leads to performance degradation and limits the stability boundary in centrifugal compressors. The volute is one of the sources to induce the non-axisymmetric flow in a centrifugal compressor, which has an important effect on the performance of compressors. However, the influence of volute on rotating stall is not clear. Therefore, the effects of volute on rotating stall by experimental and numerical simulation have been explored in this paper. It’s shown that one rotating stall cell generates in a specific location and disappears in another specific location of the vaneless diffuser as a result of the distorted flow field caused by the volute. Also, the cells cannot stably rotate in a whole circle. The frequency related to rotating stall captured in the experiment is 43.9% of the impeller passing frequency (IPF), while it is 44.7% of IPF captured by three-dimensional unsteady numerical simulation, which proves the accuracy of the numerical method in this study. The numerical simulation further reveals that the stall cell initialized in a specific location can be split into several cells during the evolution process. The reason for this is that the blockage in the vaneless diffuser induced by rotating stall is weakened by the mainstream from the impeller exit to make one initialized cell disperse into several ones. The volute has an important influence on the generation and evolution process of the rotating stall cells of compressors. By optimizing volute geometry to reduce the distortion of the flow field, it is expected that rotating stall can be weakened or suppressed, which is helpful to widen the operating range of centrifugal compressors.

scholarly journals Rotating Stall in Centrifugal Compressor Vaneless Diffuser: Experimental Analysis of Geometrical Parameters Influence on Phenomenon Evolution

2004 ◽  
Vol 10 (6) ◽  
pp. 433-442 ◽  
Author(s):  
Giovanni Ferrara ◽  
Lorenzo Ferrari ◽  
Leonardo Baldassarre
Keyword(s):  
Centrifugal Compressor ◽  
Dynamic Pressure ◽  
Pressure Sensors ◽  
Experimental Tests ◽  
Fast Response ◽  
Rotating Stall ◽  
Geometrical Parameters ◽  
Vaneless Diffuser ◽  
Response Dynamic ◽  
Frequency Domains

The rotating stall is a key problem for achieving a good working range of a centrifugal compressor and a detailed understanding of the phenomenon is very important to anticipate and avoid it. Many experimental tests have been planned by the authors to investigate the influence on stall behavior of different geometrical configurations. A stage with a backward channel upstream, a 2-D impeller with a vaneless diffuser and a constant cross-section volute downstream, constitute the basic configuration. Several diffuser types with different widths, pinch shapes, and diffusion ratios were tested. The stage was instrumented with many fast response dynamic pressure sensors so as to characterize inception and evolution of the rotating stall. This kind of analysis was carried out both in time and in frequency domains. The methodology used and the results on phenomenon evolution will be presented and discussed in this article.

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