Influence of distorted inflows on the performance of a contra-rotating fan

2020 ◽  
pp. 1-18
Author(s):  
M.P. Manas ◽  
A.M. Pradeep
Keyword(s):  
Pressure Rise ◽  
Aircraft Engine ◽  
High Flow ◽  
Flow Coefficient ◽  
Potential Candidate ◽  
Blade Surface ◽  
Axial Fan ◽  
Stall Inception ◽  
Relative Contribution ◽  
Inflow Conditions

ABSTRACT A contra-rotating fan offers several aerodynamic advantages that make it a potential candidate for future aircraft engine configurations. Stall in a contra-rotating axial fan is interesting since instabilities could arise from either or both of the rotors. In this experimental study, a contra-rotating axial fan is analysed under clean or distorted inflow conditions to understand its performance and stall inception characteristics. The steady and unsteady measurements identified the relative contribution of each rotor towards the performance of the stage. The tip of rotor-1 is identified to be the most critical region of the contra-rotating fan. The contribution of rotor-2 to the overall loading of the stage is observed to be relatively less than rotor-1. The penalty due to distortion in the stage pressure rise is mostly felt by rotor-1, while rotor-2 also shows a reduction in performance for distorted inflows. Rotor-2 stalls at a high flow coefficient marking the initiation of partial stall of the stage, and the stall of the whole stage occurs once rotor-1 stalls. A fluid phenomenon that is attached to the blade surface marks the stall of rotor-1, and this fluid phenomenon initially rotates at a speed close to the speed of rotation of the blade. As the stage moves towards the fully developed stall, this fluid phenomenon sheds from the blade surface. The fluid phenomenon thus propagates at a speed much lower than the rotational speed of the blade during fully developed stall.

Correlation and Prediction of Rotating Stall Inception by Divergence Method

1985 ◽  
Vol 107 (2) ◽  
pp. 191-196
Author(s):  
V. J. Zika
Keyword(s):  
Pressure Rise ◽  
Area Ratio ◽  
Rotating Stall ◽  
Compressor Blade ◽  
Flow Coefficient ◽  
Geometric Form ◽  
Form Parameter ◽  
Stall Inception ◽  
Multi Stage ◽  
Stall Angle

An empirical correlation of rotating stall inception points of elementary compressors (isolated rotors, stages without prerotation, complete single stages, and multi-stage machines with repeating stages), modeled as equivalent diffusers, is presented. From it, two inception criteria for self-induced rotating stall are derived. Compressor blade rows are classified according to a geometric form parameter, (L/A∞)cor, into two groups, subcritical and supercritical. The subcritical geometries stall at a constant kinematic area ratio AE/A∞, in what appears to be a pure rotating stall mode, which occurs before the airfoil stalls. In supercritical geometries, the rotating stall is delayed until it is triggered by the airfoil stall. Thus, for the latter geometries, the airfoil stall and rotating stall are coincident. In contrast to other diffuser-analog methods, the divergence method determines the stall angle and the stalled flow coefficient rather than the stalled pressure rise.

A Transonic Mixed Flow Compressor for an Extreme Duty

2014 ◽  
Author(s):  
Hamid Hazby ◽  
Michael Casey ◽  
Ryusuke Numakura ◽  
Hideaki Tamaki
Keyword(s):  
Test Data ◽  
Pressure Rise ◽  
High Flow ◽  
Flow Coefficient ◽  
Compressor Stage ◽  
Aerodynamic Optimization ◽  
Mixed Flow ◽  
Axial Compressors ◽  
Blade Shape ◽  
Flow Compressor

This paper describes the design of a transonic mixed flow compressor stage for an extreme duty, with an extremely high flow coefficient (Φ) of 0.25 and a high isentropic pressure rise coefficient (ψ) of 0.56. The impeller design makes use of modern aerodynamic practice from radial and transonic axial compressors, whereby the aerodynamic blade shape involved arbitrary surfaces on several spanwise sections. Some aspects of the aerodynamic optimization of the design were limited by mechanical considerations, but nevertheless the test data obtained on a prototype stage demonstrates that acceptable performance levels can be achieved at these extreme design conditions, although map width enhancement devices were needed to obtain an acceptable operating range. The test data is compared with CFD predictions to demonstrate the validity of the design methods used.

Clearance Effects on Centrifugal Compressor Characteristic and Stability

2007 ◽  
Author(s):  
Yong Sang Yoon ◽  
Shin Hyung Kang ◽  
Seung Jin Song
Keyword(s):  
Centrifugal Compressor ◽  
Rotational Speed ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Component Level ◽  
Stall Inception ◽  
Stability Model ◽  
Number Of Cells

The effects of impeller inlet tip clearance and diffuser width on centrifugal compressor characteristic and stability have been experimentally investigated in a centrifugal compressor with a vaneless diffuser. An increase in the impeller inlet tip clearance decreases the overall pressure rise across the compressor, mainly due to the tip clearance loss in the impeller. However, the effect of inlet tip clearance on diffuser pressure rise or compressor stability is weak. A decrease in the diffuser width significantly lowers the compressor pressure rise, especially at hight flow rates. At the component level, the impeller is insensitive to the diffuser width variation, and the pressure rise across the diffuser actually increases as diffuser width is decreased. Upon further investigation, it has been found that the overall compressor characteristic is strongly influenced by the region between the impeller exit and the diffuser inlet. Also, a decrease in the diffuser width delays stall inception by increasing the radial velocity of the flow in the diffuser. Thus, the stalling flow coefficient is more sensitive to the variation in the diffuser than the inlet tip clearance. In all cases, rotating stall consists of two or three cells rotating at about approximately one tenth of the compressor rotational speed. When the number of cells changes from three to two, the rotational speed drops. However, when the number of cells remains constant, the cells’ rotational speed increases as flow coefficient is lowered. All of these trends agree well with predictions from a new stability model developed by the first author.

A Transonic Mixed Flow Compressor for an Extreme Duty

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Hamid Hazby ◽  
Michael Casey ◽  
Ryusuke Numakura ◽  
Hideaki Tamaki
Keyword(s):  
Test Data ◽  
Pressure Rise ◽  
High Flow ◽  
Flow Coefficient ◽  
Aerodynamic Optimization ◽  
Mixed Flow ◽  
Axial Compressors ◽  
Blade Shape ◽  
Computational Fluid Dynamics Cfd ◽  
Flow Compressor

This paper describes the design of a transonic mixed flow compressor stage for an extreme duty, with an extremely high flow coefficient (φ) of 0.25 and a high isentropic pressure rise coefficient (ψ) of 0.56. The impeller design makes use of modern aerodynamic practice from radial and transonic axial compressors, whereby the aerodynamic blade shape involved arbitrary surfaces on several spanwise sections. Some aspects of the aerodynamic optimization of the design were limited by mechanical considerations, but nevertheless the test data obtained on a prototype stage demonstrates that acceptable performance levels can be achieved at these extreme design conditions, although map width enhancement (MWE) devices were needed to obtain an acceptable operating range. The test data are compared with computational fluid dynamics (CFD) predictions to demonstrate the validity of the design methods used.

Windmilling Characteristics of a Contra-Rotating Fan

2020 ◽  
Author(s):  
Manas Madasseri Payyappalli ◽  
Arghya Karmakar ◽  
A. M. Pradeep
Keyword(s):  
Total Pressure ◽  
Flow Coefficient ◽  
Pressure Measurements ◽  
Axial Fan ◽  
Stall Inception ◽  
Pressure Drops ◽  
Low Aspect Ratio ◽  
Significant Parameter ◽  
Flow Development ◽  
Unsteady Pressure Measurements

Abstract In the present experimental study, a low aspect ratio, low hub-tip ratio contra-rotating axial fan is investigated to understand its performance under windmilling conditions. Two configurations are tested; in the first configuration (event A), the front rotor of the contra-rotating fan is powered and the rear rotor is allowed to windmill; in the second configuration (event B), the rear rotor of the contra-rotating fan is powered and the front rotor is allowed to windmill. The spanwise distribution of the loading coefficient and the flow angles at different streamwise positions reveal the details of the flow development across the rotors. The performances of event A and event B are nearly similar; however, event A stalls earlier than event B. Though the average total pressure drops across the windmilling rotor for both the events, a small spanwise region behaves as a fan or a stirrer. Thus, a “neutral radius” on the windmilling rotor is identified for both events A and B. The neutral radius appears close to the tip for event A and it appears close to the hub for event B. On the windmilling rotor in either events, the span regions close to the tip for event A behaves as a fan and the span regions close to the hub for event B behaves as a stirrer. It is also observed that the neutral radius shifts its position to a lower span location as the flow coefficient reduces. Thus, the flow coefficient is a significant parameter that decides the position of the neutral radius. Further, the unsteady pressure measurements recorded at the casing captures the fundamental phenomena during the stall inception. The paper thus relates the similarities and unveils the contrasting features of the windmilling events A and B. In summary, this paper discusses the performance, flow physics and stall inception characteristics of a contra-rotating axial fan under windmilling conditions.

Investigation on stall inception of axial compressor under inlet rotating distortion

2015 ◽  
Vol 231 (10) ◽  
pp. 1859-1870 ◽  
Author(s):  
Mingming Zhang ◽  
Anping Hou
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Numerical Approach ◽  
Flow Coefficient ◽  
Stall Inception ◽  
Stall Margin ◽  
Inlet Distortion ◽  
Flow Through ◽  
Inflow Conditions

This paper applies a numerical approach to improve the understanding of reaction to various inflow conditions for the compressor system and the mechanism of stall inception under rotating inflow distortions. Full annulus, unsteady, three-dimensional computational fluid dynamics has been used to simulate an axial low-speed compressor operating under rotating distorted inflow conditions. The development of the flow through the rotor is then explained in terms of the redistribution of the flow field and the process of stall inception. The results suggest that the increased flow incidence close to the tip region under co-rotating inflow distortion plays an important role on the stall inception process. The presence of a strong modal wave is observed under co-rotating inflow distortions. This leads to a significant impact on the loss of stall margin, as compared with other distorted inflow conditions. There is a significant peak in the flow coefficient at stall for co-rotating inlet distortion. It can be interpreted as a resonant behavior of the compressor under a strong interaction between the flow field and inlet distortion. It indicates that the stall inception is triggered by the perturbation of the rotating distorted inflow through the long 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.

Windmilling Characteristics of a Contra-Rotating Fan

2020 ◽  
Author(s):  
Manas MP ◽  
Arghya Karmakar ◽  
Pradeep A M
Keyword(s):  
Experimental Study ◽  
Total Pressure ◽  
Flow Coefficient ◽  
Pressure Measurements ◽  
Axial Fan ◽  
Stall Inception ◽  
Pressure Drops ◽  
Low Aspect Ratio ◽  
Flow Development ◽  
Unsteady Pressure Measurements

Abstract In the present experimental study, a low aspect ratio, low hub-tip ratio contra-rotating axial fan is investigated to understand its performance under windmilling conditions. Two configurations are tested; in the first configuration (event A), the front rotor of the contra-rotating fan is powered and the rear rotor is allowed to windmill; in the second configuration (event B), the rear rotor of the contra-rotating fan is powered and the front rotor is allowed to windmill. The spanwise distribution of the loading coefficient and the flow angles at different streamwise positions reveal the details of the flow development across the rotors. Though the average total pressure drops across the windmilling rotor for both the events, a small spanwise region behaves as a fan or a stirrer. Thus, a "neutral radius" on the windmilling rotor is identified for both events A and B. The neutral radius appears close to the tip for event A and it appears close to the hub for event B and the neutral radius shifts its position to a lower span location as the flow coefficient reduces. On the windmilling rotor, the span regions close to the tip for event A behaves as a fan and the span regions close to the hub for event B behaves as a stirrer. Further, the unsteady pressure measurements recorded at the casing captures the fundamental phenomena during the stall inception. The paper thus relates the similarities and unveils the contrasting features of the windmilling events A and B.

Surge in a Low-Speed Radial Compressor

1998 ◽  
Author(s):  
Corine Meuleman ◽  
Frank Willems ◽  
Rick de Lange ◽  
Bram de Jager
Keyword(s):  
Flow Rate ◽  
Pressure Rise ◽  
Flow Coefficient ◽  
Lumped Parameter Model ◽  
Pressure Oscillations ◽  
Vaned Diffuser ◽  
Flow Angle ◽  
Radial Compressor ◽  
Low Speed ◽  
Lumped Parameter

Surge is measured in a low-speed radial compressor with a vaned diffuser. For this system, the flow coefficient at surge is determined. This coefficient is a measure for the inducer inlet flow angle and is found to increase with increasing rotational speed. Moreover, the frequency and amplitude of the pressure oscillations during fully-developed surge are compared with results obtained with the Greitzer lumped parameter model. The measured surge frequency increases when the compressor mass flow is throttled to a smaller flow rate. Simulations show that the Greitzer model describes this relation reasonably well except for low rotational speeds. The predicted amplitude of the pressure rise oscillations is approximately two times too small when deep surge is met in the simulations. For classic surge, the agreement is worse. The amplitude is found to depend strongly on the shape of the compressor and throttle characteristic, which are not accurately known.

Fan Performance Scaling With Inlet Distortions

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
J. J. Defoe ◽  
M. Etemadi ◽  
D. K. Hall
Keyword(s):  
Design Flow ◽  
Flow Coefficient ◽  
Axial Fan ◽  
Fan Performance ◽  
Physical Mechanisms ◽  
Viscous Losses ◽  
Performance Scaling ◽  
Large Distortion ◽  
Stator Blade ◽  
Primary Focus

Applications such as boundary-layer-ingesting (BLI) fans and compressors in turboprop engines require continuous operation with distorted inflow. A low-speed axial fan with incompressible flow is studied in this paper. The objectives are to (1) identify the physical mechanisms which govern the fan response to inflow distortions and (2) determine how fan performance scales as the type and severity of inlet distortion varies at the design flow coefficient. A distributed source term approach to modeling the rotor and stator blade rows is used in numerical simulations in this paper. The model does not include viscous losses so that changes in diffusion factor are the primary focus. Distortions in stagnation pressure and temperature as well as swirl are considered. The key findings are that unless sharp pitchwise gradients in the diffusion response, strong radial flows, or very large distortion magnitudes are present, the response of the blade rows for strong distortions can be predicted by scaling up the response to a weaker distortion. In addition, the response to distortions which are composed of nonuniformities in several inlet quantities can be predicted by summing up the responses to the constituent distortions.

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