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.

Stall Inception, Evolution and Control in a Low Speed Axial Fan With Variable Pitch in Motion

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
Stefano Bianchi ◽  
Alessandro Corsini ◽  
Luca Mazzucco ◽  
Lucilla Monteleone ◽  
Anthony G. Sheard
Keyword(s):  
Pressure Fluctuations ◽  
Axial Flow ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Variable Pitch ◽  
Stall Inception ◽  
Low Speed ◽  
Tip Leakage ◽  
End Wall ◽  
Stagger Angle

Obtaining the right pitch in turbomachinery blading is crucial to efficient and successful operations. Engineers adjust the rotor’s pitch angle to control the production or absorption of power. Even for low speed fans this is a promising tool. This paper focuses on the inception and the evolution of the flow instabilities in the tip region which drive the stall onset in low speed axial fans. The authors conducted an experimental study to investigate the inception patterns of rotating stall evolution at different rotor blade stagger-angle settings with the aim of speculating on stable operating margin. The authors drove the fan to stall at the design stagger-angle setting and then operated the variable pitch mechanism in order to recover the unstable operation. They measured pressure fluctuations in the tip region of the low-speed axial-flow fan fitted with a variable pitch in motion mechanism, with flush mounted probes. The authors studied the flow mechanisms for spike and modal stall inceptions in this low-speed axial-flow fan which showed relatively small tip clearance. The authors cross-correlated the pressure fluctuations and analyzed the cross-spectra in order to clarify blade pitch, end wall flow, and tip-leakage flow influences on stall inception during the transient at the rotor blades’ different stagger-angle settings. The authors observed a rotating instability near the maximum pressure-rise point at both design and low stagger-angle settings. The stall inception patterns were a spike type at the design stagger-angle setting as a result of the interaction between the incoming flow, tip-leakage flow and end wall backflow.

Characteristics of End-Wall Flow at Spike and Modal Stall Inceptions in a Variable-Pitch Axial-Flow Fan

2007 ◽  
Author(s):  
Takahiro Nishioka ◽  
Toshio Kanno ◽  
Hiroshi Hayami
Keyword(s):  
Rotor Blade ◽  
Axial Flow ◽  
Leading Edge ◽  
Leakage Flow ◽  
Incoming Flow ◽  
Tip Leakage Flow ◽  
Stall Inception ◽  
Tip Leakage ◽  
End Wall ◽  
Stagger Angle

The flow mechanisms for spike and modal stall inceptions in a low-speed axial-flow fan with a relatively large tip clearance were studied. The pressure and velocity fluctuations were measured to clarify the influences of blade loading, end-wall flow, and tip-leakage flow on stall inception at two stagger-angle settings for the rotor blade, which are the design and small stagger-angle settings. A rotating instability was observed near the maximum pressure-rise point at both design and small stagger-angle settings. This instability was induced by the interaction between the incoming flow, tip-leakage flow, and end-wall backflow. The stall inception patterns were a spike type at the design stagger-angle setting and a modal type at the small stagger-angle setting. At the design stagger-angle setting, the interface between the incoming flow, tip-leakage flow, and end-wall backflow became parallel to the rotor leading edge plane and reached the pressure side of adjacent blade. The interaction between these flows generated the large end-wall blockage in the rotor blade passage, and this blockage developed leading edge separation on the overloaded rotor blade at the tip. The leading edge separation that developed then grew into a spike, which traveled upstream of the rotor. At the small stagger-angle setting, the rotating instability and modal disturbance were also induced by the interaction between the incoming flow, tip-leakage flow, and end-wall backflow. However, the interface between the tip-leakage flow and end-wall backflow surrounded the suction surface of the rotor blade at the tip and neither became parallel to the leading edge plane nor reached the pressure side of the adjacent blade even though the rotor blade at the tip had stalled. Spikes did not therefore appear. The modal disturbance periodically decreased the inlet velocity and induced a long length-scale stall cell including a spike. It is concluded from these results that the stall inception patterns, which were characterized by the interaction between the incoming flow, tip-leakage flow, and end-wall backflow, depended on the stagger-angle settings for the rotor blades.

PIV Maps of Tip Leakage and Secondary Flow Fields on a Low-Speed Turbine Blade Cascade With Moving End Wall

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
P. Palafox ◽  
M. L. G. Oldfield ◽  
J. E. LaGraff ◽  
T. V. Jones
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Field Measurements ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Low Speed ◽  
Tip Leakage ◽  
End Wall

New, detailed flow field measurements are presented for a very large low-speed cascade representative of a high-pressure turbine rotor blade with turning of 110deg and blade chord of 1.0m. Data were obtained for tip leakage and passage secondary flow at a Reynolds number of 4.0×105, based on exit velocity and blade axial chord. Tip clearance levels ranged from 0% to 1.68% of blade span (0% to 3% of blade chord). Particle image velocimetry was used to obtain flow field maps of several planes parallel to the tip surface within the tip gap, and adjacent passage flow. Vector maps were also obtained for planes normal to the tip surface in the direction of the tip leakage flow. Secondary flow was measured at planes normal to the blade exit angle at locations upstream and downstream of the trailing edge. The interaction between the tip leakage vortex and passage vortex is clearly defined, revealing the dominant effect of the tip leakage flow on the tip end-wall secondary flow. The relative motion between the casing and the blade tip was simulated using a motor-driven moving belt system. A reduction in the magnitude of the undertip flow near the end wall due to the moving wall is observed and the effect on the tip leakage vortex examined.

The Effects on Stability, Performance, and Tip Leakage Flow of Recirculating Casing Treatment in a Subsonic Axial Flow Compressor

2016 ◽  
Author(s):  
Wei Wang ◽  
Wuli Chu ◽  
Haoguang Zhang ◽  
Yanhui Wu
Keyword(s):  
Axial Flow ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Stall Inception ◽  
Casing Treatment ◽  
Tip Leakage ◽  
Axial Flow Compressor ◽  
Overall Performance ◽  
Flow Compressor

Recirculating casing treatment (RCT) was studied in a subsonic axial flow compressor experimentally and numerically. The RCT was parameterized with the injector throat height and circumferential coverage percentage (ccp) to investigate its influence on compressor stability and on the overall performance in the experimentation. The injector throat height varied from 2 to 6 times the height of the rotor tip clearance, and the ccp ranged from 8.3% to 25% of the casing perimeter. Various RCT configurations were achieved with a modular design procedure. The rotor casing was instrumented with fast-response pressure transducers to detect the stall inception, rotational speed of stall cells, and pressure flow fields. Whole-passage unsteady simulations were also implemented for the RCT and solid casing to understand the flow details. Results indicate that both the compressor stability and overall performance can be improved through RCT with appropriate geometrical parameters. The effect of injector throat height on the stability depends on the choice of ccp, i.e., interaction effect exists. In general, the RCT with a moderate injector throat height and a large circumferential coverage is the optimal choice. Phase-locked pattern of the casing wall pressure reveals a weakened tip leakage vortex under the effect of RCT compared with the solid casing. The numerical results show that the RCT has a substantial effect on tip blockage even when the blade passages break away from the domain of RCT. The reduction of tip blockage induced by the tip leakage vortex is the main reason for the extension of stable operation range. The unsteadiness of double-leakage flow is detected both in the experiment and in numerical simulations. The pressure fluctuations caused by double-leakage flow are depressed with RCT. This observation indicates reduced losses related with the double-leakage flow. Although the stall inception is not changed by implementing RCT, the stall pattern is altered. The stall with two cells is detected in RCT compared with the solid casing with only one stall cell.

Effects of Stream Surface Inclination on Tip Leakage Flow Fields in Compressor Rotors

1998 ◽  
Vol 120 (4) ◽  
pp. 683-692 ◽  
Author(s):  
M. Furukawa ◽  
K. Saiki ◽  
K. Nagayoshi ◽  
M. Kuroumaru ◽  
M. Inoue
Keyword(s):  
Boundary Layer ◽  
Vortex Breakdown ◽  
Axial Flow ◽  
Flow Fields ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Wall Boundary Layer ◽  
Wall Boundary

Experimental and computational results of tip leakage flow fields in a diagonal flow rotor at the design flow rate are compared with those in an axial flow rotor. In the diagonal flow rotor, the casing and hub walls are inclined at 25 deg and 45 deg, respectively, to the axis of rotation, and the blade has airfoil sections with almost the same tip solidity as that of the axial flow rotor. It is found out that “breakdown” of the tip leakage vortex occurs at the aft part of the passage in the diagonal flow rotor. The “vortex breakdown” causes significant changes in the nature of the tip leakage vortex: disappearance of the vortex core, large expansion of the vortex, and appearance of low relative velocity region in the vortex. These changes result in a behavior of the tip leakage flow that is substantially different from that in the axial flow rotor: no rolling-up of the leakage vortex downstream of the rotor, disappearance of the casing pressure trough at the aft part of the rotor passage, large spread of the low-energy fluid due to the leakage flow, much larger growth of the casing wall boundary layer, and considerable increase in the absolute tangential velocity in the casing wall boundary layer. The vortex breakdown influences the overall performance, also: large reduction of efficiency with the tip clearance, and low level of noise.

Numerical Investigation of the Behavior of Tip Leakage Flow in a Low-Speed Axial Compressor Rotor at Near-Stall Condition

2012 ◽  
Author(s):  
Zhenzhen Duan ◽  
Yangwei Liu ◽  
Lipeng Lu
Keyword(s):  
Axial Compressor ◽  
Rotating Stall ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Stall Inception ◽  
Low Speed ◽  
Tip Leakage ◽  
Compressor Rotor ◽  
Corner Vortex

In the present work, time-accurate simulations were performed to investigate the unsteady flow fields in the tip region of a low-speed large-scale axial compressor rotor at near-stall condition. Firstly, the steady performance characteristic of the rotor was obtained by steady simulations. Secondly, a series of unsteady simulations were carried out to investigate the physical processes as the rotor approaching stall and the role of complex tip flow mechanism on flow instability in the rotor. The characteristics of tip leakage vortex were compared between design condition and near-stall condition. Detailed analyses were then employed to emphasize the development of stall inception and the comprehensions of the internal flow field. Two flow phenomena, spillage at the leading edge and backflow at the trailing edge, are found beyond the flow solution limit, which are both linked to the tip leakage flow. And the breakdown of the tip leakage vortex has been captured. The flow visualization and the quantification of passage blockage expose that the tip leakage vortex and corner vortex contribute most to the total passage blockage. Therefore, they are considered to be the key flow structures contributing to the rotating stall. Further analyses indicate that, in the current rotor, the interaction of the tip leakage flow and the corner vortex is clarified to be the key factor that leads to the rotating stall. In addition, the very initial disturbances of stall inception are discussed. And the interaction of the boundary layer migration on the blade suction side and the tip leakage vortex also plays a significant role in the stall inception.

Characteristics of Tip-Leakage Flow at High Stagger-Angle Setting for Rotor Blade in an Axial Flow Fan

2012 ◽  
Author(s):  
Takahiro Nishioka ◽  
Masayoshi Joko
Keyword(s):  
Pressure Loss ◽  
Total Pressure ◽  
Tip Clearance ◽  
Total Pressure Loss ◽  
Maximum Efficiency ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Stagger Angle

Rotor-tip flow fields at high stagger-angle setting were investigated to clarify the loss generation mechanism in a high specific-speed axial-flow fan. The tip clearance flow in the cases of large and small clearances, which are 2.0% and 1.0% of the rotor tip chord length respectively, are experimentally and numerically evaluated at the maximum efficiency point and the operating limit. At the maximum efficiency point, the tip leakage vortex reached to the rotor exit in both cases of large and small tip clearances. However, the leakage vortex in the case of large tip-clearance passed closer to the pressure side of the adjacent blade than that in the case of small one. Moreover, in the case of large tip clearance, the tip leakage vortex generated the large total pressure loss in the blade passage, and the interaction between the tip leakage vortex and the wake also generated the large total pressure loss at the rotor exit. Therefore, the maximum efficiency of the rotor and the fan was lower than that in the case of small tip clearance. At the operating limit, the tip-leakage vortex extended inside the blade passage and reached to the front part of the pressure side of the next blade in the case of small tip-clearance. Moreover, the double leakage flow occurred in the case of small tip clearance. In contrast, the leakage vortex reached to the leading edge of the next blade, and the spillage of the tip leakage flow from the leading edge occurred in the case of large tip clearance. The spillage of the tip leakage flow induced the larger total pressure loss than that induced by the double leakage flow. Therefore, the pressure rise in the case of large tip clearance is lower than that in the case of small tip clearance at the operating limit. It was concluded from the experimental and numerical results at the high stagger-angle setting for rotor blade that the loss generation mechanism depended on the behavior of tip-leakage vortex and that this behavior also depended on the tip-clearance.

Rotating Stall Inception From Spike and Rotating Instability in a Variable-Pitch Axial-Flow Fan

2008 ◽  
Author(s):  
Takahiro Nishioka ◽  
Toshio Kanno ◽  
Hiroshi Hayami
Keyword(s):  
Three Dimensional ◽  
Axial Flow ◽  
Rotating Stall ◽  
Tip Leakage Flow ◽  
Axial Flow Fan ◽  
Trailing Edge ◽  
Stall Inception ◽  
Tip Leakage ◽  
Rotating Instability ◽  
Stagger Angle

End wall flow fields at the two stagger-angle settings for the rotor blades in the low-speed axial-flow fan are experimentally and numerically investigated to elucidate the mechanism of stall inception. Rotating instability is confirmed near the maximum pressure-rise point at both design and large stagger-angle settings. This instability is induced by the interaction between the incoming flow, tip leakage flow, and backflow from the trailing edge. The stall-inception pattern, however, differs at the two stagger-angle settings. The stall inception from a spike is observed at the design stagger-angle setting, and the stall inception without the spike and modal disturbance is observed at the large stagger-angle setting. The rotating instability seems to influence the formation of stall cell at the large stagger-angle setting. Tip-leakage vortex breakdown occurs at both design and large stagger angle settings. This breakdown induces the three-dimensional separation on the suction surface of the rotor blade at the tip. Three-dimensional separation at the design stagger-angle setting is stronger than that at the large stagger-angle setting. The strong separation grows into a three-dimensional separation vortex, which crosses the blade passage near the trailing edge. This separation vortex seems to be one of the conditions for spike initiation.

Effects of Stream Surface Inclination on Tip Leakage Flow Fields in Compressor Rotors

1997 ◽  
Author(s):  
Masato Furukawa ◽  
Kazuhisa Saiki ◽  
Kenya Nagayoshi ◽  
Motoo Kuroumaru ◽  
Masahiro Inoue
Keyword(s):  
Boundary Layer ◽  
Vortex Breakdown ◽  
Axial Flow ◽  
Flow Fields ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Wall Boundary Layer ◽  
Wall Boundary

Experimental and computational results of tip leakage flow fields in a diagonal flow rotor at the design flow rate are compared with those in an axial flow rotor. In the diagonal flow rotor, the casing and hub walls are inclined at 25 degrees and 45 degrees, respectively, to the axis of rotation, and the blade has airfoil sections with almost the same tip solidity as that of the axial flow rotor. It is found out that “breakdown” of the tip leakage vortex occurs at the aft part of the passage in the diagonal flow rotor. The “vortex breakdown” causes significant changes in the nature of the tip leakage vortex: disappearance of the vortex core, large expansion of the vortex, and appearance of low relative velocity region in the vortex. These changes result in the behavior of the tip leakage flow substantially different from that in the axial flow rotor: no rolling-up of the leakage vortex downstream of the rotor, disappearance of the casing pressure trough at the aft part of the rotor passage, large spread of the low-energy fluid due to the leakage flow, much larger growth of the casing wall boundary layer, and considerable increase in the absolute tangential velocity in the casing wall boundary layer. The vortex breakdown influences the overall performance, also: large reduction of efficiency with the tip clearance, and low level of noise.

The Tip Leakage Vortex Breakdown and its Possible Relationship With Rotating Instability in a Subsonic Compressor Rotor

2021 ◽  
Author(s):  
Fan Yang ◽  
Yanhui Wu
Keyword(s):  
Unsteady Flow ◽  
Vortex Breakdown ◽  
Tangential Velocity ◽  
Leading Edge ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Back Flow ◽  
Tip Leakage ◽  
Rotating Instability ◽  
Flow Vortex

Abstract The unsteady flow in the compressor at small mass flow rate has an important impact on the safety and efficiency of the compressor. Rotating instability was found in the experiment at near stall condition. Through URANS simulation, the origin of unsteady flow in an isolated subsonic rotor is studied. And the relationship between unsteadiness of tip leakage flow and rotating instability is revealed. With the deepening of the throttle, the flow field in the rotor changes from steady to unsteady. The intermittent spiral type breakdown of tip leakage vortex is considered to be the origin of the unsteady flow. Quantitative analysis of the tip leakage vortex shows the breakdown cycle caused by the interaction of the tip leaked vortex with the adjacent blade. When the tangential velocity and axial velocity of the leakage vortex reach a critical value, the tip leakage vortex will break. A radial vortex called back flow vortex will appear periodically after breakdown happens, which plays an important in rotating instability. The back flow vortex at upstream causes an overflow at adjacent blade leading edge, which results the next breakdown happens at downstream. Due to such feedback, the tip leakage vortex breakdown at two location alternately. A possible cause of RI was proposed: The spiral breakdown of the tip leakage vortex at different positions resulted in a cross-passage structure, which propagates into circumferential direction.

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