Influence of Low-Solidity Cascade Diffuser on Spike Stall Inception in a Centrifugal Compressor

2012 ◽  
Author(s):  
Satoshi Joukou ◽  
Yasushi Shinkawa ◽  
Toshio Kanno ◽  
Hideo Nishida ◽  
Takahiro Nishioka ◽  
...  
Keyword(s):  
Flow Separation ◽  
Static Pressure ◽  
Rotating Stall ◽  
Short Length ◽  
Radius Ratio ◽  
Length Scale ◽  
Small Disturbance ◽  
Flow Angle ◽  
Stall Inception ◽  
Wing Section

Stall inception patterns for three low-solidity cascade diffusers were experimentally investigated to extend the operating range of centrifugal compressor. Pressure fluctuations on the wall and flow distributions at the diffuser inlet were measured, and static pressure-rises across the diffuser vane were also measured to clarify the mechanism of rotating stall inception. In the case of the original diffuser (LSD_O), which had the radius ratio between the impeller outlet and the diffuser vane inlet of 1.10 and a flat plate wing section, a short length-scale stall cell known as a spike first appeared in the positive slope of the diffuser static pressure-raise (after the flat slope was maintained), and then a surge occurred as flow-rate decreased. The propagation speed of short length-scale stall cell was about 13% of the impeller rotation speed. The measured flow distribution at the inlet of the LSD_O suggested that the flow separation occurred in the vaneless space and this separation influenced the rotating stall. In the case of the LSD_A, which had the radius ratio of 1.10 and the NACA 63 wing section, a short length-scale stall cell that was smaller than that of LSD_O was appeared in the positive slope of the diffuser static pressure-raise (without the flat slope). A surge also occurred as further flow-rate decreased. The propagation speed of short length-scale stall cell was about 13% just prior to surge point. In contrast, in the case of LSD_B, which had the radius ratio of 1.05 and the NACA 63 wing section, a small disturbance appeared without spike just prior to surge point and rotating stall did not occur. The small disturbance did not propagate in the circumferential direction. Moreover, the flow separation did not occur in the semi-vaneless space. At the stall inception point of LSD_O and LSD_A, the averaged absolute flow angle at the diffuser inlet agreed with the onset flow angel of rotating stall in vaneless diffuser predicted by Senoo. Therefore, it was considered that the flow separation also occurred in the vaneless space and this separation influenced the rotating stall in the case of LSD_A. Moreover, it was considered that the difference of two stall cell patterns between LSD_O and LSD_A depended on the static pressure-rise characteristic of diffuser determined by the design specifications in case of that the rotating stall occurred in the vaneless space. In contrast, at the point of the small disturbance appeared of LSD_B, the averaged absolute flow angle at the diffuser inlet is smaller than that predicted by Senoo. Therefore, in case of small the radius ratio, the reverse flow in vaneless diffuser is suppressed, and the rotating stall is also suppressed.

Short and Long Length-Scale Disturbances Leading to Rotating Stall in an Axial Compressor Stage With Different Stator/Rotor Gaps

2001 ◽  
Author(s):  
M. Inoue ◽  
M. Kuroumaru ◽  
S. Yoshida ◽  
M. Furukawa
Keyword(s):  
High Frequency ◽  
Wavelet Transforms ◽  
Wave Length ◽  
Axial Compressor ◽  
Leading Edge ◽  
Rotating Stall ◽  
Short Length ◽  
Length Scale ◽  
Compressor Stage ◽  
Stall Inception

The transient processes of rotating stall evolution have been investigated experimentally in a low-speed axial compressor stage with three stator-rotor gaps. The pressure traces at 8 circumferential locations on the casing wall near the rotor leading edge have been analyzed by the wavelet transforms. With the appropriate mother wavelets, the evolution of short and long length-scale disturbances leading to the stall can be captured clearly. Behavior of these disturbances is different depending on the stator-rotor gap. For the large and middle gap, the stall inception is detected by a spiky short length-scale disturbance, and the number of spiky waves increases to generate the high frequency waves. They becomes the short length-scale part-span stall cells at the mild stall for the large gap, while they turn into a big stall cell with growth of a long length-scale disturbance for the middle gap. In the latter case, therefore, the stalling process was identified with ‘high frequency stall inception’. For the small stator-rotor gap, the stalling process is identified with ‘long wave-length stall inception’, and supported the recent computational model for the short wave-length stall inception by showing that closing the rotor-stator gaps suppressed the growth of short length-scale disturbances. From the measurement of the pressure field traces on the casing wall, a hypothesis has been built up that the short length-scale disturbance should result from a separation vortex from a blade surface to reduce circulation. The processes of the stall evolution are discussed on this hypothesis.

Criteria for Spike Initiated Rotating Stall

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Huu Duc Vo ◽  
Choon S. Tan ◽  
Edward M. Greitzer
Keyword(s):  
Computational Study ◽  
Axial Compressor ◽  
Leading Edge ◽  
Rotating Stall ◽  
Short Length ◽  
Tip Clearance ◽  
Length Scale ◽  
Stall Inception ◽  
Tip Clearance Flow ◽  
Clearance Flow

A computational study to define the phenomena that lead to the onset of short length-scale (spike) rotating stall disturbances has been carried out. Based on unsteady simulations, we hypothesize there are two conditions necessary for the formation of spike disturbances, both of which are linked to the tip clearance flow. One is that the interface between the tip clearance and oncoming flows becomes parallel to the leading-edge plane. The second is the initiation of backflow, stemming from the fluid in adjacent passages, at the trailing-edge plane. The two criteria also imply a circumferential length scale for spike disturbances. The hypothesis and scenario developed are consistent with numerical simulations and experimental observations of axial compressor stall inception. A comparison of calculations for multiple blades with those for single passages also allows statements to be made about the utility of single passage computations as a descriptor of compressor stall.

Short and Long Length-Scale Disturbances Leading to Rotating Stall in an Axial Compressor Stage With Different Stator/Rotor Gaps

2002 ◽  
Vol 124 (3) ◽  
pp. 376-384 ◽  
Author(s):  
M. Inoue ◽  
M. Kuroumaru ◽  
S. Yoshida ◽  
M. Furukawa
Keyword(s):  
High Frequency ◽  
Wavelet Transforms ◽  
Axial Compressor ◽  
Leading Edge ◽  
Rotating Stall ◽  
Short Length ◽  
Length Scale ◽  
Compressor Stage ◽  
Stall Inception ◽  
High Frequency Waves

The transient processes of rotating stall evolution have been investigated experimentally in a low-speed axial compressor stage with three stator-rotor gaps. The pressure traces at eight circumferential locations on the casing wall near the rotor leading edge have been analyzed by the wavelet transforms. With the appropriate mother wavelets, the evolution of short and long length-scale disturbances leading to the stall can be captured clearly. Behavior of these disturbances is different depending on the stator-rotor gap. For the large and middle gap, the stall inception is detected by a spiky short length-scale disturbance, and the number of spiky waves increases to generate the high frequency waves. They become the short length-scale part-span stall cells at the mild stall for the large gap, while they turn into a big stall cell with growth of a long length-scale disturbance for the middle gap. In the latter case, therefore, the stalling process was identified with “high-frequency stall inception.” For the small stator-rotor gap, the stalling process is identified with “long wavelength stall inception” and supported the recent computational model for the short wavelength stall inception by showing that closing the rotor-stator gaps suppressed the growth of short length-scale disturbances. From the measurement of the pressure field traces on the casing wall, a hypothesis has been developed that the short length-scale disturbance should result from a separation vortex from a blade surface to reduce circulation. The processes of the stall evolution are discussed on this hypothesis.

Suppression of Short Length-Scale Rotating Stall Inception With Glow Discharge Actuation

2007 ◽  
Author(s):  
Huu Duc Vo
Keyword(s):  
Glow Discharge ◽  
Discharge Plasma ◽  
Input Voltage ◽  
Plasma Actuator ◽  
Rotating Stall ◽  
Short Length ◽  
Glow Discharge Plasma ◽  
Length Scale ◽  
Stall Inception ◽  
Plasma Actuation

This paper proposes and investigates the pioneering use of glow discharge (plasma) actuation to suppress short length-scale (spike) rotating stall inception. A single dielectric barrier discharge plasma actuator basically consists of two parallel offset thin electrodes separated by a dielectric material. The application of a high frequency AC voltage across the electrodes results in an induced body force on the flow adjacent to the surface. This simple, robust actuator may provide a practical low-power mean to positively alter the tip clearance flow dynamics responsible for spike stall inception. A computational study is carried out on a low-speed compressor rotor with the implementation of a published plasma actuation model in an established turbomachinery CFD code. The objective is to provide a preliminary assessment of the effectiveness of a casing circumferential plasma actuator, with varying actuator location, input voltage and frequency, in suppressing the two flow criteria associated with the formation of spike disturbances leading to stall. Results show that plasma actuation most effectively suppresses both of these flow criteria when placed near the rotor leading edge and delays the predicted stall point to a lower flow coefficient with minimal power input. The simulations also indicate that the effectiveness of the actuation decreases non-linearly with input voltage and frequency. In addition, results indicate that this technology could perhaps be used for suppression of both short and long-length scale stall inception in axial compressors.

Role of Blade Passage Flow Structurs in Axial Compressor Rotating Stall Inception

1999 ◽  
Vol 121 (4) ◽  
pp. 735-742 ◽  
Author(s):  
D. A. Hoying ◽  
C. S. Tan ◽  
Huu Duc Vo ◽  
E. M. Greitzer
Keyword(s):  
Leading Edge ◽  
Rotating Stall ◽  
Short Length ◽  
Tip Clearance ◽  
Length Scale ◽  
Central Feature ◽  
Local Flow ◽  
Stall Inception ◽  
Blade Passage ◽  
Tip Clearance Vortex

The influence of three-dimensional flow structures within a compressor blade passage has been examined computationally to determine their role in rotating stall inception. The computations displayed a short length-scale (or spike) type of stall inception similar to that seen in experiments; to the authors’ knowledge this is the first time such a feature has been simulated. A central feature observed during the rotating stall inception was the tip clearance vortex moving forward of the blade row leading edge. Vortex kinematic arguments are used to provide a physical explanation of this motion as well as to motivate the conditions for its occurrence. The resulting criterion for this type of stall inception (the movement of the tip clearance vortex forward of the leading edge) depends upon local flow phenomena related to the tip clearance with the implication that for this and possibly other stall mechanisms the flow structure within the blade passages must be addressed to explain the stability of an axial compression system that exhibits such short length-scale disturbances.

Stall Inception Mechanism in an Axial Flow Fan Under Clean and Distorted Inflows

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
Pramod B. Salunkhe ◽  
A. M. Pradeep
Keyword(s):  
Wavelet Transforms ◽  
Flow Characteristics ◽  
Axial Flow ◽  
Short Length ◽  
Flow Coefficient ◽  
Length Scale ◽  
Axial Flow Fan ◽  
Flow Angle ◽  
Stall Inception ◽  
Rotor Rotation

The present paper describes the use of Morlet wavelet transform in understanding the stall inception mechanism in a single stage axial flow fan. Unsteady pressure data from wall mounted sensors were used in the wavelet transforms. This paper was carried out under undistorted and distorted inflow conditions as well as for slow throttle closure and throttle ramping. It was observed from the wavelet transforms that the stall inception under clean inflow (undistorted) and counter-rotating inflow distortions (in the direction opposing the rotor rotation) incur through short length-scale disturbances and through long length-scale disturbances under static and co-rotating inflow distortions (in the same direction of rotor rotation). Modal activity was observed to be insignificant under clean inflow while under static inflow distortion, long length-scale disturbances evolved due to interaction between rotor blades and the distorted sector, especially near the trailing edge of the distortion screen. The presence of a strong mode was observed under both co- and counter-rotating inflow distortions. With throttle ramping, stall inception occurs through long and short length-scale disturbances under co- and counter-rotating inflow distortions, respectively. Some preliminary flow characteristics were studied using a seven hole probe. A significant increase in flow angle and decrease in axial flow coefficient close to the rotor tip were observed under co-rotating inflow distortion as compared with counter-rotating inflow distortion.

Performance and Short Length-Scale Disturbance Generation in an Axial Compressor With Non-Uniform Tip Clearance

2008 ◽  
Author(s):  
Scott C. Morris ◽  
Joshua D. Cameron ◽  
Matthew A. Bennington ◽  
G. Scott McNulty ◽  
Aspi Wadia
Keyword(s):  
Flow Field ◽  
Mass Flow ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Short Length ◽  
Tip Clearance ◽  
Length Scale ◽  
Stagnation Temperature ◽  
Local Flow ◽  
Stall Inception

The performance, efficiency, and stall inception of an axial compressor was investigated experimentally with small levels of rotor centerline offset. The measurements were acquired using a high-speed, single-stage compressor. The rotor was levitated magnetically during operation which allowed precise positioning of the rotor centerline within the circular casing. The offset magnitude used in this study was 0.23% of the rotor tip chord, equivalent to approximately 24% of the nominal gap value. The resulting asymmetry in the tip gap resulted in circumferential and radial variations in the measured stagnation pressure and stagnation temperature downstream of the stage. However, the spatially averaged performance of the compressor was not measurably different from that obtained with a concentric rotor. An array of unsteady (Kulite) pressure transducers was used to investigate the flow field during stall inception. These measurements were recorded during transient throttle movements which quickly decreased the mass flow in the compressor until the onset of rotating stall. A second set of measurements was acquired during quasi-transient throttling starting from a mass flow about 1% larger than the stalling mass flow. In both the symmetric and offset cases the flow breakdown was consistent with spike type inception. The measurements with offset indicated that the asymmetries in the local compressor flow field produced significant changes in the number of short-length scale rotating disturbances observed during throttling to stall. These disturbances appeared in the region of the annulus where the local flow coefficient was lowest and usually decayed upon rotating to the higher flow region. In this way, the addition of very small amounts of rotor offset tended to fix the disturbance generation location in the stationary reference frame. This was in contrast to the symmetric tip clearance case where the location of spike generation appeared stochastic.

Influence of Rotor Stagger Angle on Rotating Stall Inception in an Axial-Flow Fan

2003 ◽  
Author(s):  
Takahiro Nishioka ◽  
Shuuji Kuroda ◽  
Tadashi Kozu
Keyword(s):  
Flow Rate ◽  
Axial Flow ◽  
Rotating Stall ◽  
Short Length ◽  
Rotor Blades ◽  
Length Scale ◽  
Axial Flow Fan ◽  
Stall Inception ◽  
Stall Cells ◽  
Stagger Angle

Inception patterns of rotating stall in a low-speed axial flow fan have been investigated experimentally. Experiments have been carried out at two different stagger angle settings for rotor blades. Pressure and velocity fluctuations were measured to elucidate the features of the stall cells and the stall inception patterns. At the design stagger angle setting for the rotor blades, a short length-scale stall cell known as a “spike” and multiple short length-scale stall cells appear when the slope of pressure-rise characteristic is almost zero. These stall cells grow into a long length-scale stall cell as flow rate decreases. The spike and the multiple short length-scale stall cells do not make the slope of the characteristic positive. However, the long length-scale stall cell induces a full-span stall, and makes the slope of the characteristic positive. At the small stagger angle, a long length-scale disturbance known as a “modal oscillation” is observed first, when the slope of the characteristic is positive. Then the spikes appear together with the modal oscillation as flow rate decreases. The long length-scale stall cell is generated by the spikes without change in the size of the modal oscillation. Suction-tip corner stall occurs in the stator passage near the peak of the characteristic at both the design and the small stagger angle settings. At the design stagger angle, however, the corner stall does not induce the modal oscillation and does not make the characteristic positive. In contrast, the corner stall at the small stagger angle induces the modal oscillation and makes the characteristic positive because it is larger than that at the design stagger angle. It is concluded from these results that the rotating stall inception patterns depend on the rotor stagger angle, which influences blade loading and rotor-stator matching.

scholarly journals Role of Blade Passage Flow Structures in Axial Compressor Rotating Stall Inception

1998 ◽  
Author(s):  
Donald A. Hoying ◽  
Choon S. Tan ◽  
Huu Duc Vo ◽  
Edward M. Greitzer
Keyword(s):  
Leading Edge ◽  
Rotating Stall ◽  
Short Length ◽  
Tip Clearance ◽  
Flow Structures ◽  
Length Scale ◽  
Central Feature ◽  
Local Flow ◽  
Stall Inception ◽  
Blade Passage

The influence of three-dimensional flow structures within a compressor blade passage has been examined computationally to determine their role in rotating stall inception. The computations displayed a short length-scale (or spike) type of stall inception similar to that seen in experiments; to the authors’ knowledge this is the first time such a feature has been simulated. A central feature observed during the rotating stall inception was the tip clearance vortex moving forward of the blade row leading edge. Vortex kinematic arguments are used to provide a physical explanation of this motion as well as to motivate the conditions for its occurrence. The resulting criterion for this type of stall inception (which appears generic for axial compressors with tip-critical flow fields) depends upon local flow phenomena related to the tip clearance and it is thus concluded that the flow structure within the blade passages must be addressed to explain the stability of an axial compression system which exhibits such short length-scale disturbances.

Effects of Steady Tip Clearance Asymmetry and Rotor Whirl on Stall Inception in an Axial Compressor

2007 ◽  
Author(s):  
Joshua D. Cameron ◽  
Matthew A. Bennington ◽  
Mark H. Ross ◽  
Scott C. Morris ◽  
Thomas C. Corke
Keyword(s):  
Mass Flow ◽  
Axial Compressor ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Short Length ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Correlation Technique ◽  
Length Scale ◽  
Stall Inception

Effects of rotor centerline offset and whirl on the pre-stall and stall inception behavior of a high-speed tip-critical axial compressor were investigated. The observations were made using a circumferential array of unsteady pressure transducers. The maximum amount of rotor offset and whirl used in this investigation was 26% and 13% of the design axisymmetric tip clearance respectively. Measurements were conducted using transient throttle movements which quickly decreased the mass flow in the compressor until the onset of rotating stall. A second set of measurements used quasi-transient throttling starting from a mass flow about 0.5% larger than the stalling mass flow. These data were analyzed with the traveling wave energy method, visual inspection of the filtered pressure traces, and a two-point spatial correlation technique. For the uniform tip clearance case rotating stall occurred while the slope of the pressure rise characteristic was negative. As expected, the flow breakdown exhibited “spike” inception with no observable rotating disturbances in the pre-stall time period. The introduction of small levels of steady and unsteady tip clearance asymmetry did not significantly alter the time average performance of the stage; circumferential variations in pressure rise and flow coefficient were minimal and the stalling flow coefficient remained unchanged. However, significant short length-scale rotating disturbances were observed in both of these cases prior to stall inception. As in the symmetric tip clearance case, short length-scale disturbances initiated rotating stall in the non-uniform tip clearance experiments. The location of the generation of the incipient stall cells with respect to the non-uniform tip clearance was strongly effected by the rotor offset/whirl.

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