Effects of Non-Axisymmetric Volute On Rotating Stall in the Vaneless Diffuser of Centrifugal Compressors

2022 ◽  
Author(s):  
Zitian Niu ◽  
Zhenzhong Sun ◽  
Baotong Wang ◽  
Xinqian Zheng
Keyword(s):  
Flow Field ◽  
Stability Boundary ◽  
Rotating Stall ◽  
Vaneless Diffuser ◽  
Unstable Flow ◽  
Centrifugal Compressors ◽  
Cfd Simulations ◽  
Specific Location ◽  
Stable Operating ◽  
The Stability

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 inducing non-axisymmetric flows in centrifugal compressors, which has an important effect on compressors' aerodynamic performance. However, the influence of volute on rotating stall is unclear. Therefore, the effects of volute on rotating stall behavior have been explored in this paper by experiments and numerical simulations. The frequency of the rotating stall captured by the experiments is 43.9% of the impeller passing frequency, while it is 44.7% of IPF calculated from the numerical results, which proves the accuracy and capability of the numerical method in this work to study the rotating stall behavior. The flow fields from CFD simulations further reveal that one stall cell initializing in a particular location deforms into several stall cells while rotating along the circumferential direction and becomes much smaller in a specific location during the evolution process, and finally, it is suppressed in another specific location as a result of the distorted flow field caused by the volute. By optimizing volute geometry to reduce the distortion of the flow field, it is expected that the rotating stall can be weakened or suppressed, which is helpful to extend the stable operating range of centrifugal compressors.

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.

Investigation of the instability mechanisms in a turbocharger centrifugal compressor with a vaneless diffuser by means of unsteady simulations

2016 ◽  
Vol 231 (11) ◽  
pp. 1558-1567 ◽  
Author(s):  
Xinqian Zheng ◽  
Anxiong Liu ◽  
Zhenzhong Sun
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
High Speed ◽  
Simulation Method ◽  
Great Accuracy ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Vaneless Diffuser ◽  
Unstable Flow ◽  
Low Velocity

The stable-flow range of a compressor is predominantly limited by surge and stall. In this paper, an unsteady simulation method was employed to investigate the instability mechanisms of a high-speed turbocharger centrifugal compressor with a vaneless diffuser. In comparison with the variation in the pressure obtained by dynamic experiments on the same compressor, unsteady simulations show a great accuracy in representing the stall behaviour. The predicted frequency of the rotating stall is 22.5% of the rotor frequency, which agrees with to the value for the high-frequency short-term rotating stall obtained experimentally. By investigating the instability of the flow field, it is found that the unstable flow of the turbocharger compressor at high rotational speeds is caused by the tip clearance leakage flow and the ‘backflow vortices’ originating from the interaction of the incoming flow and the backflow in the tip region of the passages. The asymmetric volute helps to induce the occurrence of stall in certain impeller passages because it generates an asymmetric flow field. The high-pressure low-velocity area from the 180° circumferential position to the 270° circumferential position is dominant and strengthens the backflow at the trailing edge of the impeller, finally triggering the stall.

Numerical Simulation of Surge in Turbocharger Centrifugal Compressor: Influences of Downstream Plenum

2011 ◽  
Author(s):  
Strong Guo ◽  
Hua Chen ◽  
Xiaocheng Zhu ◽  
Zhaohui Du
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Mass Flow ◽  
Centrifugal Compressor ◽  
Stokes Equations ◽  
Numerical Technique ◽  
Pressure Ratio ◽  
Rotating Stall ◽  
Vaneless Diffuser ◽  
Unstable Flow

Surge is an important instability seriously affecting compression systems. This paper presents a numerical simulation of surge flow phenomenon inside a turbocharger centrifugal compressor with a vaneless diffuser. The compressor was discharged into a plenum and the effect of the plenum on surge behavior of the compressor system was investigated. The entire geometry of the compressor, including the impeller, vaneless diffuser, volute housing and downstream plenum, were included in the simulation. Three-dimensional Reynolds averaged compressible Navier–Stokes equations were solved with the k–ε turbulence model using commercial software CFX and two different sizes of plenum were studied. A new plenum model is proposed which allows temporal variation of temperature inside the plenum. The numerical technique employed to set up CFD (computational fluid dynamics) with such an unstable flow system are described. The results show that when the plenum volume was nearly doubled, the dominating frequency of the system suddenly dropped from 72Hz to 23Hz. During the surge cycle, the compressor characteristic (pressure ratio ν mass flow curve) showed distinct differences. With the smaller plenum, the characteristic showed random traces with little global backflow at the compressor inlet, while with the larger plenum, clear surge cycles are displayed with strong global backflow at the inlet. The flow fields of the two systems are presented as functions of time and show distinct differences. In the case of the smaller plenum, the circumferential flow field inside the impeller is non uniform, showing influences of rotating stall, while in the case of the large plenum, the circumferential uniformity returns and the flow field behaves quasi-steadily during the surge cycle. With the larger plenum, the volute flow synchronises with the inlet mass flow oscillation in time and a completed vortex break down occurs at every volute cross section, but with the smaller plenum the synchronisation disappears and vortex break down only occurs partially at the centers of some volute cross sections.

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.

The Application of PIV in the Study of Impeller-Diffuser Interaction in Centrifugal Fan: Part I — Impeller-Vaneless Diffuser Interaction

2001 ◽  
Author(s):  
Tarek Mekhail ◽  
Zhang Li ◽  
Du Zhaohui ◽  
Willem Jansen ◽  
Chen Hanping
Keyword(s):  
Flow Field ◽  
Flow Rate ◽  
High Speed ◽  
Maximum Flow ◽  
Image Processing Technique ◽  
High Speed Photography ◽  
Centrifugal Fan ◽  
Performance Measurements ◽  
Vaneless Diffuser ◽  
Unstable Flow

Abstract The PIV (Particle Image Velocimetry) technology is a brand-new technique of measuring velocity. It started in the 1980’s with the development of high-speed photography and the image processing technique of computers. This article deals with PIV applied to the study of unsteady impeller-vaneless diffuser interaction in centrifugal fen. Experiments were carried out at The Turbomachinery Laboratory of Shanghai Jiaotong University. The test rig consists of a centrifugal, shrouded impeller, diffuser and volute casing all made of plexiglass. A series of performance measurements were carried out at different speeds and different vaneless diffuser widths. PIV measurements were applied to measure the unsteady flow at the exit part of the impeller and the inlet part of the diffuser for the case of the same width vaneless diffuser. The absolute flow field is measured at medium flow rate and at maximum flow rate. It is informative to capture the whole flow field at the same instant of time, and it might be more revealing to observe the unstable flow in real time.

Flow Behavior of a Centrifugal Compressor With Vaneless Diffuser at Design and Off Design Conditions

2012 ◽  
Author(s):  
Chuang Gao ◽  
Weiguang Huang ◽  
Haiqing Liu ◽  
Hongwu Zhang ◽  
Jundang Shi
Keyword(s):  
Centrifugal Compressor ◽  
Flow Behavior ◽  
Travelling Waves ◽  
Leading Edge ◽  
Pressure Oscillation ◽  
Rotating Stall ◽  
Vaneless Diffuser ◽  
Unstable Flow ◽  
Flow Recirculation ◽  
Static Performance

This paper concerns with the numerical and experimental aspects of both steady and unsteady flow behavior in a centrifugal compressor with vaneless diffuser and downstream collector. Specifically, the appearance of flow instabilities i.e., rotating stall and surge is investigated in great detail. As the first step, the static performance of both stage and component was analyzed and possible root cause of system surge was put forward based on the classic stability theory. Then the unsteady pressure data was utilized to find rotating stall and surge in frequency domain which could be classified as mild surge and deep surge. With the circumferentially installed transducers at impeller inlet, backward travelling waves during stall ramp could be observed. The modes of stall waves could be clearly identified which is caused by impeller leading edge flow recirculation at Mu = 0.96. However, for the unstable flow at Mu = 1.08, the system instability seems to be caused by reversal flow in vaneless diffuser where the pressure oscillation was strongest. Thus steady numerical simulation were performed and validated with the experimental performance data. With the help of numerical analysis, the conjectures are proved.

Criteria for the Stability Limit Prediction of High Speed Centrifugal Compressors With Vaneless Diffuser: Part I — Flow Structure Analysis

2020 ◽  
Author(s):  
Carlo Cravero ◽  
Davide Marsano
Keyword(s):  
Rotational Speed ◽  
High Speed ◽  
Stability Limit ◽  
Vaneless Diffuser ◽  
Centrifugal Compressors ◽  
Vaned Diffuser ◽  
High Rotational Speed ◽  
Lower Accuracy ◽  
The Stability ◽  
Computational Resources

Abstract High-speed centrifugal compressor requirements include a wide operating range between choking and stall especially for turbocharging applications. The prediction of the stability limit at different speeds is still challenging. In literature, several studies have been published on the phenomena that trigger the compressor instability. However, a comprehensive analysis of criteria that can be used in the first steps of centrifugal compressors design to predict the stability limit is still missing. In previous work the authors have already presented a criterion, so called “Stability Parameter”, to predict the surge line of centrifugal compressors based on a simplified CFD approach that does not require excessive computational resources and that can be efficiently used in the preliminary design phases. The above methodology has demonstrated its accuracy for centrifugal compressors with vaned diffuser, but a lower accuracy has been detected for vaneless diffusers. Before proceeding to identify additional criteria focused on compressors with vaneless diffuser, an in-depth fluid dynamics analysis has been necessary. This analysis has been also carried out through fully 3D unsteady simulations to allow identifying the real phenomena linked to the trigger of the instability of centrifugal compressors. It has been found how these phenomena are strongly related to the rotational speed, in particular have been shown the key role of the volute at high rotational speed.

scholarly journals An Investigation of Surge in a High-Speed Centrifugal Compressor Using Digital PIV

2000 ◽  
Vol 123 (2) ◽  
pp. 418-428 ◽  
Author(s):  
Mark P. Wernet ◽  
Michelle M. Bright ◽  
Gary J. Skoch
Keyword(s):  
Flow Field ◽  
Centrifugal Compressor ◽  
High Speed ◽  
Transient Flow ◽  
Dynamic Pressure ◽  
Rotating Stall ◽  
Transient Pressure ◽  
Pressure Transducers ◽  
Stable Operating ◽  
Particle Imaging

Compressor stall is a catastrophic breakdown of the flow in a compressor, which can lead to a loss of engine power, large pressure transients in the inlet/nacelle, and engine flameout. The implementation of active or passive strategies for controlling rotating stall and surge can significantly extend the stable operating range of a compressor without substantially sacrificing performance. It is crucial to identify the dynamic changes occurring in the flow field prior to rotating stall and surge in order to control these events successfully. Generally, pressure transducer measurements are made to capture the transient response of a compressor prior to rotating stall. In this investigation, Digital Particle Imaging Velocimetry (DPIV) is used in conjunction with dynamic pressure transducers to capture transient velocity and pressure measurements simultaneously in the nonstationary flow field during compressor surge. DPIV is an instantaneous, planar measurement technique that is ideally suited for studying transient flow phenomena in high-speed turbomachinery and has been used previously to map the stable operating point flow field in the diffuser of a high-speed centrifugal compressor. Through the acquisition of both DPIV images and transient pressure data, the time evolution of the unsteady flow during surge is revealed.

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.

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

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