Investigation of tip leakage flow unsteadiness and rotating instability in a centrifugal compressor impeller

2021 ◽  
pp. 095440702110259
Author(s):  
Wenli Wang ◽  
Ce Yang ◽  
Chenxing Hu ◽  
Hang Zhang
Keyword(s):  
Centrifugal Compressor ◽  
Pressure Fluctuation ◽  
Wave Number ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Operating Condition ◽  
Tip Leakage ◽  
Flow Unsteadiness ◽  
Compressor Impeller ◽  
Rotating Instability

A phenomenon called rotating instability was rarely reported in a centrifugal compressor, although some associated discussions can be found in axial compressors. This paper presents a numerical investigation on the unsteadiness of the tip leakage flow and rotating instability in an isolated centrifugal compressor impeller. A three-dimensional, unsteady full annuls simulation is performed under three different operating conditions. The tip leakage flow unsteadiness at the impeller inlet and inside the impeller passage is detected by the pressure fluctuation. During the throttling process, the temporal and spatial propagation characteristic of the tip leakage flow unsteadiness under the near stall operating condition is revealed based on the wavelet analysis, Fourier transform, and dynamic mode decomposition. Furthermore, the relationship between the tip leakage flow unsteadiness and the rotating instability is also discussed. The results show that the pressure fluctuation mainly concentrates in the tip region at the near stall operating condition, which indicates the occurrence and circumferential propagation of tip leakage flow unsteadiness. The circumferential propagation of the tip leakage flow unsteadiness induces a significant circumferential rotating pressure wave with a wave number of 9 and approximately 48.2% of the rotational speed of the impeller. The characteristic frequency of the tip leakage flow unsteadiness agrees well with the dominant mode frequency of rotating instability. Therefore, the tip leakage flow unsteadiness is assumed to be responsible for the rotating instability. During the throttling process, the formation and development of the rotating instability at near stall operating condition can be divided into three stages based on signal analysis: prior to rotating instability, generation and development, and rotating instability.

Tip Leakage Flow Instability in a Centrifugal Compressor

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Teng Cao ◽  
Tadashi Kanzaka ◽  
Liping Xu ◽  
Tobias Brandvik
Keyword(s):  
Shear Layer ◽  
Centrifugal Compressor ◽  
Large Scale ◽  
Flow Instability ◽  
Leading Edge ◽  
Main Stream ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Unstable Flow ◽  
Tip Leakage

Abstract In this paper, an unsteady tip leakage flow phenomenon is identified and investigated in a centrifugal compressor with a vaneless diffuser at near-stall conditions. This phenomenon is associated with the inception of a rotating instability in the compressor. The study is based on numerical simulations that are supported by experimental measurements. The study confirms that the unstable flow is governed by a Kelvin–Helmholtz type instability of the shear layer formed between the main-stream flow and the tip leakage flow. The shear layer instability induces large-scale vortex roll-up and forms vortex tubes, which propagate circumferentially, resulting in measured pressure fluctuations with short wavelength and high amplitude which rotate at about half of the blade speed. The 3D vortex tube is also found to interact with the main blade leading edge, causing the reduction of the blade loading identified in the experiment. The paper also reveals that the downstream volute imposes a once-per-rev circumferential nonuniform back pressure at the impeller exit, inducing circumferential loading variation at the impeller inducer, and causing circumferential variation in the unsteady tip leakage flow.

Circumferential Propagation Characteristic of Unsteady Flow in a Subsonic Axial Flow Compressor Rotor at Different Reynolds Numbers

2019 ◽  
Author(s):  
Zhiyang Chen ◽  
Yanhui Wu ◽  
Yanwen Zhang ◽  
Junwen Gan ◽  
Jinhuaiyuan An
Keyword(s):  
Unsteady Flow ◽  
Frequency Band ◽  
Radial Flow ◽  
Propagation Characteristic ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Characteristic Frequencies ◽  
Tip Leakage ◽  
Flow Unsteadiness ◽  
Compressor Rotor

Abstract This paper studies the circumferential propagation characteristic of unsteady flow that occurs close to stall in a subsonic axial compressor rotor at different Reynolds number (Re). Experimental measurements are first conducted at high Re on the ground, and numerical investigations are carried out at two altitudes to explore the mechanism of circumferential propagation characteristic at different Re. The stability operating range of the compressor rotor gets small with the decrease of Re. Rotating instability (RI) is observed in the blade passage near the stall limit of the test rotor at high Re on the ground, which is characterized by a hump frequency band in the spectrum. Characteristic frequencies of numerical pressure signals at fixed frame are limited in the frequency band of RI at high Re. The cross power spectrums of numerical pressure signals detected in the neighboring passages suggest that circumferential disturbances rotates in the flow fields at different Re. Characteristic frequencies of the flow unsteadiness change with the decrease of Re. At high Re, the circumferential propagation of tip leakage flow unsteadiness is controlled by the interaction of the tip leakage flow and incoming flow, which is linked to RI. When the Re is reduced, the tip leakage flow gets weak and the radial flow from the hub to tip induced by the suction surface flow separation is dominant in the tip region. Thereafter, both the tip leakage flow and radial flow are associated with the blade tip loading, which changes the flow mechanism of RI.

Evolution of Pressure Signature Dominated by Unsteady Tip Leakage Flow

2013 ◽  
Author(s):  
Shaojuan Geng ◽  
Xiaoyu Zhang ◽  
Jichao Li ◽  
Long Zhao ◽  
Hongwu Zhang ◽  
...  
Keyword(s):  
Reference Frames ◽  
Fluid Dynamic ◽  
Critical Mass ◽  
Leakage Flow ◽  
Band Pass Filter ◽  
Tip Leakage Flow ◽  
Initiation Mechanism ◽  
Pass Filter ◽  
Tip Leakage ◽  
Flow Unsteadiness

This paper deals with the detailed numerical analyses of diverse manifestations of unsteady features induced by periodical oscillation of tip leakage flow under different operating points for the cases with uniform and hub distorted inlet conditions. The characteristics evolutions of pressure signature near rotor tip region during compressor throttling process are studied and compared with the experimental results. Monitors circumferentially arranged and aligned with blade chord are imposed to collect static pressure signals. Analysis methods of coordinate transformation between the rotor relative and absolute stationary reference frames, fast Fourier transform and frequency band pass filter are used. The modulated frequency features along blade chord in two reference frames are analyzed. Typically for the dominated frequency components, the circumferential propagation characteristics are studied, such as propagation speed and mode orders. And the unified evolution trends of modulated frequency relation for dominant components between two reference frames and circumferential propagation features during throttling process are summarized. A critical mass flow point is found to distinguish the different change trend of the characteristics of tip leakage flow unsteadiness. Based on the different speeds between circumferential propagation of tip leakage flow unsteadiness and revolution of compressor rotor, the fluid dynamic reason for the decrease of autocorrelation coefficient of pressure signals from transducer mounted on compressor casing is elucidated. All the results are helpful to further unveil the initiation mechanism of stall inception.

Numerical Study on Tip Clearance Effect on Performance of a Centrifugal Compressor

2002 ◽  
Author(s):  
Hark-Jin Eum ◽  
Shin-Hyoung Kang
Keyword(s):  
Centrifugal Compressor ◽  
Numerical Study ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Specific Work ◽  
Tip Leakage Flow ◽  
Viscous Effects ◽  
Tip Leakage ◽  
Performance Reduction ◽  
Viscous Loss

Effects of tip clearance on through flows and performance of a centrifugal compressor impeller with six different tip clearances were numerically studied using CFX-TASCflow. The flow structures inside the impeller of a centrifugal compressor were visualized observing streamlines starting the leading edge of blade tips. The calculated results at the impeller exit were circumferential averaged for quantitative discussion. Flow, pressure and entropy contours at the impeller exit were largely influenced by the tip leakage flow. Tip clearance effect on the performance was decomposed into inviscid and viscous components using one-dimensional relations expressed in terms of the specific work reduction and the additional entropy generation. Both inviscid and viscous effects affected performance to similar extent, while efficiency drop was mainly influenced by viscous loss of the tip leakage flow. Performance reduction and efficiency drop due to tip clearance was proportional to the ratio of tip clearance to blade height. A simple model suggested in the present study predicts performance and efficiency drop quite successfully.

Nonaxisymmetric Study of Tip Leakage Flow in a Centrifugal Compressor With a Volute During Stall Process

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Ce Yang ◽  
Botai Su ◽  
Li Fu ◽  
Hang Zhang
Keyword(s):  
Centrifugal Compressor ◽  
Static Pressure ◽  
Leading Edge ◽  
Work Capacity ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
High Static Pressure ◽  
Circumferential Nonuniformity

Abstract Tip leakage flow (TLF) patterns, which affect compressor performance, are closely related to compressor stability. To date, minimal attention has been given to circumferential nonuniformity of the TLF in a centrifugal compressor with a nonaxisymmetric volute structure. In this study, the circumferential difference of the TLF in a centrifugal compressor with a volute during the stall process is analyzed. The circumferential nonuniformity of tip leakage vortex (TLV) trajectories, loading distribution near the tip, and distance between the TLV core and the leading edge (LE) of splitter blades were also investigated. It is shown that in the circumferential direction, there are two peaks associated with the angle (α) between the TLV trajectory of the seven main blades and the axial direction. As the stall process progresses, the blade whose LE is affected by the high static pressure band (PP) induced by the volute tongue (VT) loses its work capacity first and the α difference between this blade and the other blades increases. In addition, the tip loading and TLF velocity of the blade whose LE is affected by the high static pressure band induced by the VT are at a minimum, and the flow loss in the tip clearance is higher. There is a phenomenon of the TLV breakdown. When the blade trailing edge (TE) is located in the low static pressure region, TLV streamlines appear as a significant turn at the breakdown point. However, the TLV streamlines at other circumferential positions do not exhibit this phenomenon.

Numerical Study on the Response of Tip Leakage Flow Unsteadiness to Micro Tip Injection in a Low-Speed Isolated Compressor Rotor

2007 ◽  
Author(s):  
Shaojuan Geng ◽  
Hongwu Zhang ◽  
Jingyi Chen ◽  
Weiguang Huang
Keyword(s):  
Numerical Study ◽  
The Self ◽  
Axial Position ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Low Speed ◽  
Tip Leakage ◽  
Flow Unsteadiness ◽  
Compressor Rotor ◽  
Tip Injection

A numerical study on the unsteady tip leakage flow with discrete micro tip injection from casing shroud in a low-speed isolated axial compressor rotor is presented. The main target is to clarify the flow mechanism of how the stall control measures act on the tip leakage flow typified by its self-induced unsteady flow characteristics. At operating condition near stall point, a series of calculations have been carried out for different axial position of injector and different injected mass flow rate. The computation results of flow field near rotor tip region show that under the influence of injected flow, the transient pressure distribution fluctuates along blade chord on both pressure and suction sides with respect to the relative position of injector and rotor. The pressure difference across the pressure and suction sides of compressor blade changes correspondingly, thus introduces a forced flow unsteadiness interacting with the unsteady tip leakage flow. When the injection is relatively strong and able to meet the tip leakage flow at its origination, the self-induced unsteadiness of tip leakage flow can be suppressed completely. In most cases, both frequency components of the self-induced unsteadiness and forced-induced unsteadiness are co-existing. The corresponding transient flow contours show that a local high pressure spot appears near blade pressure side, which moves downstream and shifts the tip leakage flow trajectory with less or without touching the neighboring pressure surface of the blade. Based on this understanding of discrete tip injection as force-induced flow unsteadiness, the numerical results are also analyzed to optimize the effect of injection in changing the route of tip leakage flow trajectories and therefore the chance of stability improvement of the compressor rotor.

Effect of Recirculation Device on Performance of High Pressure Ratio Centrifugal Compressor

2010 ◽  
Author(s):  
Hideaki Tamaki
Keyword(s):  
High Pressure ◽  
Centrifugal Compressor ◽  
Flow Behavior ◽  
Pressure Ratio ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Operating Range ◽  
High Pressure Ratio

Centrifugal compressors used for turbochargers need to achieve a wide operating range. A recirculation device, which consists of a bleed slot, an upstream slot and an annular cavity connecting both slots, is often applied to them. The author developed a high pressure ratio centrifugal compressor with pressure ratio 5.7 for a marine use turbocharger. In order to enhance operating range, a recirculation device was applied, the benefits of its application ensuring. This paper discusses how the recirculation device affects the flow field in the above transonic centrifugal compressor by using steady 3D calculations. It is reported that the interaction between shock and tip leakage vortex is one of the primary causes of stall inception in the impeller. Analysis of shock and tip leakage flow behavior leads to an understanding of the basic mechanism of the enhancement of operating range by the recirculation device. Hence this study focuses on the effect of the recirculation devices on the shock and tip leakage flow. Steady 3D calculations were performed and the effect of the recirculation device was clarified. The bleed slot of the recirculation device works in a similar way to circumferential grooves applied to axial compressors. It reduces the blade loading in the impeller tip region. And hence the velocity of tip leakage flow exiting the bleed slot becomes lower compared with that without the recirculation device. The flow through the bleed slot impinges on the tip leakage flow originated upstream and blocks the extension of the tip leakage flow. It also deflects the trajectory of the tip leakage vortex. In addition to these effects, the bleed slot removes the fluid near the casing. The shock moves downstream due to the reduction of the blockage. All these effects induced by the recirculation device are considered to lead to the suppression of the extension of blockage and to contribute to the enhancement of the compressor operating range.

Rotor-Tip Flow Fields Near Inception Point of Rotating Instability in an Axial-Flow Fan

2011 ◽  
Author(s):  
Takahiro Nishioka ◽  
Toshio Kanno ◽  
Kiyotaka Hiradate
Keyword(s):  
Vortex Breakdown ◽  
Rotor Blades ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Stall Inception ◽  
Tip Leakage ◽  
Rotating Instability ◽  
End Wall ◽  
Stagger Angle

Stall inception patterns at three stagger-angle settings for the highly loaded rotor blades were experimentally investigated in a low-speed axial-flow fan. Rotor-tip flow fields were also numerically investigated to clarify the mechanism behind the stall inception from a rotating instability. The rotating instability is confirmed near stall condition at the high stagger-angle settings for the highly loaded rotor blades as same as that for the moderate loaded rotor blades. The rotating instability is induced by an interaction between the incoming flow, the reversed tip-leakage flow, and the end-wall backflow from the trailing edge. At the high stagger-angle settings for the rotor blades, the interface between the incoming flow and the reversed tip leakage flow becomes parallel to the leading edge plane near and at the stall condition. Moreover, the tip leakage flow spills from the leading edge of the adjacent blade at the stall condition. The changes in the end-wall flow at the rotor tip are consistent with the criteria for the spike initiation suggested by Vo et al. and Hah et al. However, the short length-scale stall cell is not observed at the high stagger-angle settings. The tip-leakage vortex breakdown is confirmed at the three stagger-angle settings. The end-wall blockage induced by the tip-leakage vortex breakdown influences the development of the stall cell. Moreover, the development of the three-dimensional separation vortex induced by the tip-leakage vortex breakdown seems to be one of the criteria for spike-type stall inception.

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