A Parametric Study of the Effects of Inlet Distortion on Fan Aerodynamic Stability

2018 ◽  
Vol 141 (1) ◽  
Author(s):  
Wenqiang Zhang ◽  
Mehdi Vahdati
Keyword(s):  
Boundary Layer ◽  
Measured Data ◽  
Rotating Stall ◽  
Aerodynamic Stability ◽  
Stall Margin ◽  
Turbofan Engines ◽  
Inlet Distortion ◽  
Recent Trends ◽  
Fan Blade ◽  
The Stability

The performance and aerodynamic stability of fan blades operating in a circumferentially nonuniform inlet flow is a key concern in the design of turbofan engines. With the recent trends in the design of civil engines with shorter inlet ducts (such as low-speed fans), or boundary layer ingesting engines, quick and reliable modeling of rotor/distortion interactions is becoming very important. The aim of this paper is to study the effects of inlet distortions on the aerodynamic stability of a fan blade and to identify the parameters that have a major impact on the stability of the blade. NASA rotor 67, for which a significant amount of measured data is available, was used for this study. In the first part of this study, the behavior of the fan with inlet distortion at near stall (NS) condition is analyzed, and it is shown how rotating stall is triggered. In the second part of this study, unsteady simulations with inlet distortion were performed to study how exit duct length influences the stall margin of the blade.

A Parametric Study of the Effects of Inlet Distortion on Fan Aerodynamic Stability

2018 ◽  
Author(s):  
Wenqiang Zhang ◽  
Mehdi Vahdati
Keyword(s):  
Boundary Layer ◽  
Measured Data ◽  
Rotating Stall ◽  
Aerodynamic Stability ◽  
Stall Margin ◽  
Turbofan Engines ◽  
Inlet Distortion ◽  
Recent Trends ◽  
Fan Blade ◽  
The Stability

The performance and aerodynamic stability of fan blades operating in a circumferentially non-uniform inlet flow is a key concern in the design of turbofan engines. With the recent trends in the design of civil engines with shorter inlet ducts (such as low-speed fans), or boundary layer ingesting engines, quick and reliable modelling of rotor/distortion interactions is becoming very important. The aim of this paper is to study the effects of inlet distortions on the aerodynamic stability of a fan blade and to identify the parameters that have a major impact on the stability of the blade. NASA rotor 67, for which a significant amount of measured data is available, was used for this study. In the first part of this study, the behavior of the fan with inlet distortion at near stall condition is analyzed, and it is shown how rotating stall is triggered. In the second part of this study, unsteady simulations with inlet distortion were performed to study how parameters, such as exit duct length and distortion strength, influence the stall margin of the blade.

Effects of tip air injection on the aerodynamic stability of an axial flow compressor with total pressure distortion

2021 ◽  
pp. 095441002110375
Author(s):  
Baofeng Tu ◽  
Xinyu Zhang ◽  
Liang Li ◽  
Jun Hu
Keyword(s):  
Total Pressure ◽  
Critical Role ◽  
Axial Flow ◽  
Air Injection ◽  
Aerodynamic Stability ◽  
Insertion Depth ◽  
Stall Margin ◽  
Low Speed ◽  
Inlet Distortion ◽  
The Stability

The compressor is a critical component that determines the aerodynamic stability of an aero-engine. Total pressure inlet distortion decreases the thrust and shrinks the stability margin, thus inducing severe performance degradation or even flameout. Generally, tip air injection is used to reduce the adverse influence of total pressure inlet distortion on the aerodynamic stability. In the present work, an experimental investigation on the effects of tip air injection on the stability of a two-stage low-speed axial compressor with total pressure inlet distortion was carried out. A flat baffle generated the total pressure distortion at the inlet of the compressor. The stall margin of the compressor was reduced significantly by the total pressure distortion. When the dimensionless insertion depth of the flat baffle was 0.45, the stall margin decreased to 11.4%. Under the total pressure inlet distortion, tip air injection effectively improved the distortion resistance capability of the compressor. The circumferential layout of the nozzle played a critical role in the stability expansion effect of tip air injection under the inlet flow condition of the total pressure distortion. The modal wave disturbance was likely to occur in the distortion-affected region (the low-pressure region and the mixing region). Tip air injection did not inhibit the generation of the modal wave but restrained the development of the modal wave into the stall cell. It improved the low-speed compressor’s tolerance to the modal wave and allowed a higher amplitude modal wave to occur.

Impact of Exit Duct Dynamic Response on Compressor Stability

2019 ◽  
Author(s):  
Wenqiang Zhang ◽  
Mehdi Vahdati ◽  
Fanzhou Zhao
Keyword(s):  
Dynamic Response ◽  
Model Simulation ◽  
Stability Margin ◽  
Quantitative Relationship ◽  
Aerodynamic Stability ◽  
Stall Margin ◽  
Acoustic Reflection ◽  
Exit Nozzle ◽  
Fan Blade ◽  
The Stability

Abstract Abrupt distortions can appear as a result of transient crosswind or during rapid aircraft maneuvers. Such distortions are known to reduce the aerodynamic stability of engines and therefore present a major concern to all aero-engine manufacturers. To assess the aerodynamic stability of fan blades due to distortions, rig tests are usually carried out to establish the loss in stall margin. In such test campaigns, an exit duct (which is followed by a nozzle) is placed downstream of the fan blade and the operating condition of the fan is controlled by this nozzle. It is shown in this paper that in such rig tests the length of duct downstream of a fan has a significant impact on fan stall margin. The key contributor for such interaction is the dynamic response of the exit duct and the aerodynamic stability of the fan is affected by the acoustic reflection from the exit nozzle. To study the underlying physics, transient response in the exit duct downstream of a transonic fan stage was studied numerically using a simplified model. Simulation results, along with calculations based on analytical theories, confirmed the generation, propagation and reflection of waves induced by the inlet distortion. A quantitative relationship concerning the lengths of the compression system is introduced which determines whether a duct setup would have beneficial or detrimental influences on compressor aerodynamic stability. The findings of this research have great implications for the stability assessment of fans as the stability margin can be affected by the waves generated in bypass ducts.

IMPACT OF EXIT DUCT DYNAMIC RESPONSE ON COMPRESSOR STABILITY

2020 ◽  
pp. 1-11
Author(s):  
Wenqiang Zhang ◽  
Mehdi Vahdati ◽  
Fanzhou Zhao
Keyword(s):  
Dynamic Response ◽  
Model Simulation ◽  
Stability Margin ◽  
Quantitative Relationship ◽  
Aerodynamic Stability ◽  
Stall Margin ◽  
Acoustic Reflection ◽  
Exit Nozzle ◽  
Fan Blade ◽  
The Stability

Abstract Abrupt distortions can appear as a result of transient crosswind or during rapid aircraft maneuvers. Such distortions can reduce the aerodynamic stability of engines and therefore present a major concern to all aero-engine manufacturers. To assess the aerodynamic stability of fan blades due to distortions, rig tests are usually carried out to establish the loss in stall margin. In such test campaigns, an exit duct followed by a nozzle is placed downstream of the fan blade and the operating condition of the fan is controlled by this nozzle. It is shown in this paper that in such rig tests the length of duct downstream of a fan has a significant impact on fan stall margin. The key contributor for such interaction is the dynamic response of the exit duct and the aerodynamic stability of the fan is affected by the acoustic reflection from the exit nozzle. To study the underlying physics, transient response in the exit duct downstream of a transonic fan stage was studied numerically using a simplified model. Simulation results, along with calculations based on analytical theories, confirmed the generation, propagation and reflection of waves induced by the inlet distortion. A quantitative relationship concerning the lengths of the compression system is introduced which determines whether a duct setup would have beneficial or detrimental influences on compressor aerodynamic stability. The findings of this research have great implications for the stability assessment of fans as the stability margin can be affected by the waves generated in bypass ducts.

Numerical Investigation of Effect of Inlet Distortion on Compressor Flow Field and Stability

2017 ◽  
Author(s):  
HaoGuang Zhang ◽  
Kang An ◽  
Feng Tan ◽  
YanHui Wu ◽  
WuLi Chu
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Total Pressure ◽  
Tip Clearance ◽  
Numerical Work ◽  
Stall Margin ◽  
Numerical Investigations ◽  
Inlet Distortion ◽  
Compressor Rotor ◽  
The Stability

The compressor aerodynamic design is conducted under the condition of clean inlet in general, but a compressor often operates under the condition of inlet distortion in the practical application. It has been proven by a lot of experimental and numerical investigations that inlet distortion can decrease the performance and stability of compressors. The circumferential or radial distorted inlet in mostly numerical investigations is made by changing the total pressure and total temperature in the inlet ring surface of the compressors. In most of inlet distortion experiments, distorted inlets are usually created by using wire net, flashboards, barriers or the generator of rotating distortion. The fashion of generating distorted inlet for experiment is different from that for numerical simulation. Consequently, the flow mechanism of affecting the flow field and stability of a compressor with distorted inlet for experiment is partly different than that for numerical simulation. In the numerical work reported here, the inlet distortion is generated by setting some barriers in the inlet ring surface of an axial subsonic compressor rotor. Two kinds of distorted inlet are investigated to exploring the effect of distorted range on the flow field and stability of the compressor with ten-passage unsteady numerical method. The numerical results show that the inlet distortions not only degrade the total pressure and efficiency of the compressor rotor, but also decrease the stability of the rotor. The larger the range of distorted inlet is, the stronger the adverse effect is. The comprehensive stall margin for the inlet distortion of 24 degrees and 48 degrees of ten-passages is reduced about 3.35% and 5.88% respectively. The detailed analysis of the flow field in the compressor indicates that the blockage resulted from tip clearance leakage vortex (TLV) and the flow separation near the suction surfaces of some blades tip for distorted inlet is more serious than that resulted from TLV for clean inlet. Moreover, the larger the range of distorted inlet is, the larger the range of the blockage is. The analysis of unsteady flow shows that during this process, which is that one rotor blade passes through the region affected by the distorted inlet, the range of the blockage in the rotor passage increases first, then reduces, and increases last.

scholarly journals A 3D Rotating Stall Stability Model for Axial Flow Compressor

1997 ◽  
Author(s):  
Ren-Jing Cao ◽  
Sheng Zhou
Keyword(s):  
Axial Flow ◽  
Rotating Stall ◽  
3D Flow ◽  
Aerodynamic Stability ◽  
Stall Margin ◽  
Spatial Variables ◽  
Stability Behavior ◽  
Stability Model ◽  
Flow Effects ◽  
Flow Compressor

Rotating stall phenomenon is usually characterized by 3D aerodynamic stability behavior. The earlier models mainly considered the flow effects in terms of 1D and 2D spatial variables. In order to involve the characteristics of the 3D flow of the compressor, it is necessary to improve the existing rotating stall stability models and further develop the models to consider the effects of the 3D disturbance. In this paper, a new aerodynamic stability model concerning the effects of a radial disturbance produced by the compressor, and explaining more mechanisms about the aerodynamic stability of compressor is presented. Using the developed rotating stall stability model, the stall margins are calculated and compared to experimental data for two axial flow compressors. The calculated results show that the developed 3D rotating stall stability model gives better stall margin prediction than that by the 2D model.

Calculations of Effects of Rotating Inlet Distortion on Flow Instabilities in Compression Systems

1995 ◽  
Author(s):  
Jun Hu ◽  
Leonhard Fottner
Keyword(s):  
Propagation Speed ◽  
Transient Behavior ◽  
Rotating Stall ◽  
Flow Coefficient ◽  
Flow Instabilities ◽  
Resonant Response ◽  
Response Frequency ◽  
System Parameters ◽  
Inlet Distortion ◽  
The Stability

In the present paper calculations are presented to predict the post stall transient behavior and the onset of flow instabilities in axial compression systems with rotating inlet circumferential total pressure distortion. The effects of system parameters and the compressor characteristic are taken into account, and the effects on the boundaries of rotating stall and surge are investigated. It has been found that both the inlet distortion amplitude and rotating frequency have a strong effect on the stability and post stall transient behavior, and the rotating frequency has the same strong influence on the onset of surge as the influence on the onset of rotating stall. But the resonant response frequency (i.e., the rotating frequency of inlet distortion at which the greatest loss of stability occurs) strongly depends on the frequency at which the stall cell rotates. The study of the effects of system parameters shows that the loading and the flow coefficient of the compressor at the design point have a significant effect on the onset of instability, but they have little effect on the propagation speed of rotating stall and the resonant response frequency. The Greitzer B-parameter affects the onset of rotating stall, but it has little effect on the onset of surge. Some qualitative comparisons with available experimental results are made in this paper and show that the results are reliable.

The effect of inlet distortion on low bypass ratio turbofan engines

2020 ◽  
Vol 234 (8) ◽  
pp. 1395-1413
Author(s):  
Vishwas Verma ◽  
Gursharanjit Singh ◽  
AM Pradeep
Keyword(s):  
Total Pressure ◽  
Stability Margin ◽  
Leading Edge ◽  
Axial Fan ◽  
Turbofan Engines ◽  
Inlet Distortion ◽  
Pressure Profiles ◽  
History Of ◽  
The Stability ◽  
Bypass Ratio

Inlet flow non-uniformity, commonly known as inflow distortion, has been a long-standing problem in the history of gas turbine engines. Distortion can be present in the form of total pressure, total temperature or inflow incidence or any combinations of these. The search for better and robust performance requires engines that can sustain a large amount of inlet distortion without considerable loss in the thrust. In the present paper, the effect of total pressure distortion on a single-stage compressor and low bypass ratio fans are studied. Distortion near hub and tip in the form of step radial total pressure profiles is imposed at far upstream of the rotor leading edge. A systematic approach to qualitatively predict the performance maps in the presence of these distortions is discussed. Further, two extents of total pressure distortion are explored for constant inlet distortion intensity. Hub distortion is found to increase the stability margin, whereas tip distortion reduces it. On extending the distortion extent, hub distortion drastically reduces the stability margin, whereas a comparatively lower reduction in stability margin with tip distortion is observed. The critical distortion limit is observed by varying the inlet distortion extent. Also, it is found that downstream ducts in the bypass axial fan do not interact with the upstream fan. This can be exploited to perform independent simulations of the core engine from low bypass ratio fans. Hub distortion is found to drastically affect the duct performance owing to the presence of thicker upstream inlet boundary layer.

Effects of Rotating Inlet Distortion on Multisage Compressor Stability

1994 ◽  
Author(s):  
J. P. Longley ◽  
H.-W. Shin ◽  
R. E. Plumley ◽  
P. D. Silkowski ◽  
I. J. Day ◽  
...  
Keyword(s):  
Theoretical Model ◽  
Stability Margin ◽  
Rotating Stall ◽  
Forced Response ◽  
Single Peak ◽  
Rotor Speed ◽  
Stall Inception ◽  
Stall Margin ◽  
Inlet Distortion ◽  
Two Peaks

In multi-spool engines, rotating stall in an upstream compressor will impose a rotating distortion on the downstream compressor, thereby affecting its stability margin. In this paper experiments are described in which this effect was simulated by a rotating screen upstream of several multistage low-speed compressors. The measurements are complemented by, and compared with, a theoretical model of multistage compressor response to speed and direction of rotation of an inlet distortion. For co-rotating distortions (i.e., distortions rotating in the same direction as rotor rotation), experiments show that the compressors exhibited significant loss in stability margin and that they could be divided into two groups according to their response. The first group exhibited a single peak in stall margin degradation when the distortion speed corresponded to roughly 50% of rotor speed. The second group showed two peaks in stall margin degradation corresponding to distortion speeds of approximately 25–35% and 70–75% of rotor speed. These new results demonstrate that multistage compressors can have more than a single resonant response. Detailed measurements suggest that the two types of behavior are linked to differences between the stall inception processes observed for the two groups of compressors and that a direct connection thus exists between the observed forced response and the unsteady flow phenomena at stall onset. For counter-rotational distortions, all the compressors tested showed minimal loss of stability margin. The results imply that counter-rotation of the fan and core compressor, or LP and HP compressors, could be a worthwhile design choice. Calculations based on the two-dimensional theoretical model show excellent agreement for the compressors which had a single peak for stall margin degradation. We take this first-of-a-kind comparison as showing that the model, though simplified, captures the essential fluid dynamic features of the phenomena. Agreement is not good for compressors which had two peaks in the curve of stall margin shift versus distortion rotation speed. The discrepancy is attributed to the three-dimensional and short length scale nature of the stall inception process in these machines; this includes phenomena that have not yet been addressed in any model.

Inducer Stall in a Centrifugal Compressor With Inlet Distortion

1987 ◽  
Vol 109 (1) ◽  
pp. 27-35 ◽  
Author(s):  
I. Ariga ◽  
S. Masuda ◽  
A. Ookita
Keyword(s):  
Flow Rate ◽  
Centrifugal Compressor ◽  
Stability Margin ◽  
Rotating Stall ◽  
Characteristic Parameters ◽  
Inlet Distortion ◽  
Rate Region ◽  
Compressor Performance ◽  
The Stability ◽  
Lower Flow Rate

The effects of inlet distortion on the inducer stall in a centrifugal compressor are investigated. Cases of both radial and circumferential distortion are investigated. It is shown that the rotating stall onset is amplified by radial distortions, and restrained by circumferential distortions. These results are compared with calculations based on the small disturbance theory. The authors find that the stall onset is governed by the characteristic parameters related to the lower flow rate region for radial distortions, but affected by those of the higher flow rate region for circumferential distortion. It is shown that the process of stall is different for each distortion pattern. Existence of inlet distortion reduces compressor performance characteristics and strongly influences the stability margin.

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