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.

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.

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.

Aeroacoustics of a Low-Speed Free Tip Fan With a Complex Clearance Geometry

2014 ◽  
Author(s):  
Dominic Lallier-Daniels ◽  
Stephane Moreau ◽  
Marlene Sanjose
Keyword(s):  
Numerical Study ◽  
Axial Flow ◽  
Point Of View ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Low Speed ◽  
Tip Leakage ◽  
Flow Noise ◽  
Lattice Boltzmann Simulations ◽  
Axial Fans

The influence of tip leakage flow on the performance of turbomachinery, both from an aerodynamic and acoustic point of view, has been demonstrated by several authors. However, most studies present in the literature are focused on the effects of tip leakage from an aerodynamic point of view and often forgo the mechanisms associated with the acoustics effect. The effect of different tip geometries is also still ill understood. The current advancement of a numerical study delving into tip leakage flow noise in low-speed turbomachinery applications is presented in this paper. The study as a whole aims to investigate the mechanisms associated with tip leakage flow noise on different axial fans with varying tip configurations. The study is carried out using lattice-Boltzmann simulations that allow to obtain the aerodynamic and aeroacoustic field simultaneously. As a first step in this investigation of tip flow noise, this paper focuses on a free-tip axial flow fan with a complex tip geometry. The global aerodynamic and acoustic performance of the fan is evaluated numerically and compared to available experimental results. An investigation of the simulated flowfield with regards to the observed acoustics is then carried out.

scholarly journals Investigation of the Shear Flow Effect and Tip Clearance on a Low Speed Axial Flow Compressor Cascade

2013 ◽  
Vol 2013 ◽  
pp. 1-22
Author(s):  
Mahesh Varpe ◽  
A. M. Pradeep
Keyword(s):  
Shear Rate ◽  
Shear Flow ◽  
Axial Flow ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Compressor Cascade ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Flow Compressor ◽  
End Wall

This paper explores the effect of inlet shear flow on the tip leakage flow in an axial flow compressor cascade. A flow with a high shear rate is generated in the test section of an open circuit cascade wind tunnel by using a combination of screens with a prescribed solidity. It is observed that a stable shear flow of shear rate 1.33 is possible and has a gradual decay rate until 15 times the height of the shear flow generator downstream. The computational results obtained agree well with the available experimental data on the baseline configuration. The detailed numerical analysis shows that the tip clearance improves the blade loading near the tip through the promotion of favorable incidence by the tip leakage flow. The tip clearance shifts the centre of pressure on the blade surface towards the tip. It, however, has no effect on the distribution of end wall loss and deviation angle along the span up to 60% from the hub. In the presence of a shear inflow, the end wall effects are considerable. On the other hand, with a shear inflow, the effects of tip leakage flow are observed to be partly suppressed. The shear flow reduces the tip leakage losses substantially in terms of kinetic energy associated with it.

scholarly journals Discussion: “Criteria for Spike Initiated Rotating Stall” (Vo, H. D., Tan, C. S., Greitzer, E. M., 2008, ASME J. Turbomach., 130, p. 011023)

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
A. Deppe ◽  
H. Saathoff ◽  
U. Stark
Keyword(s):  
Computational Study ◽  
Axial Flow ◽  
Leading Edge ◽  
Rotating Stall ◽  
Experimental Results ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Trailing Edge ◽  
Stall Inception ◽  
Tip Leakage

The paper “Criteria for Spike Initiated Rotating Stall” by Vo et al. (2008, ASME J. Turbomach., 130, p. 011023) provides a very important contribution to the understanding of spike-type stall inception in axial-flow compressors by demonstrating that spike-type disturbances are directly linked to the tip leakage flow of the rotor. The computational study of Vo et al. leads to the conclusion that two conditions have to be fulfilled simultaneously for the formation of spike-type stall: (i) axial backflow at the leading edge plane and (ii) axial backflow at the trailing edge plane. The objective of the present technical brief is to support these findings by corresponding experimental results.

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.

Linear to Nonlinear Transition During the Spike Stall Process in a Low Speed Axial Flow Compressor Rotor

2016 ◽  
Author(s):  
Yuping Qian ◽  
Yuzhi Jin ◽  
Weilin Zhuge ◽  
Yangjun Zhang ◽  
Yajun Lu
Keyword(s):  
Axial Flow ◽  
Second Order ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Stall Inception ◽  
Compression System ◽  
Tip Leakage ◽  
Axial Flow Compressor ◽  
Compressor Rotor ◽  
Flow Compressor

A linear to nonlinear transition during the spike stall process of an axial flow compressor rotor is presented. Recently, some researchers thought that spike stall inception is directly induced by the tip leakage flow. However, the authors utilized unsteady full annular simulations and found that a second-order disturbance appeared two revolutions before the breakdown of the tip leakage flow in an axial rotor, associate with spike stall inception while the tip leakage flow is still stable. This second-order disturbance grew rapidly in the next two revolutions and the process was unlike the low order disturbance development in modal stall inception. The response of the compression system was still linear in this process. The rapidly developing second-order disturbance made the tip leakage flow unstable, leading to the start of spike stall inception. The response of the compression system became nonlinear in this process.

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.

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