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.

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.

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.

scholarly journals Flow instability effects related to purge through a gas turbine chute seal

2021 ◽  
Vol 5 ◽  
pp. 111-125
Author(s):  
Arijit Roy ◽  
Jens Fridh ◽  
James Scobie ◽  
Carl Sangan ◽  
Gary Lock
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Flow Instability ◽  
Flow Coefficient ◽  
Flow Instabilities ◽  
Pressure Measurements ◽  
Flow Conditions ◽  
Seal Design ◽  
Purge Flow ◽  
Unsteady Pressure Measurements

This paper investigates flow instabilities inside the cavity formed between the stator and rotor disks of a high-speed turbine rig. The cavity rim seal is of chute seal design. The influence of flow coefficient on the sealing effectiveness at constant purge flow rate through the wheel-space is determined. The effectiveness at different radial positions over a range of purge flow conditions and flow coefficients is also studied. Unsteady pressure measurements have identified the frequency of instabilities that form within the rim seal, phenomena which have been observed in other studies. Frequencies of these disturbances, and their correlation in the circumferential direction have determined the strength and speed of rotation of the instabilities within the cavity. Large scale unsteady rotational structures have been identified, which show similarity to previous studies. These disturbances have been found to be weakly dependent on the purge flow and flow coefficients, although an increased purge reduced both the intensity and speed of rotation of the instabilities. Additionally, certain uncorrelated disturbances have been found to be inconsistent (discontinuous) with pitchwise variation.

scholarly journals Optimization Design and Experimental Study of Low-Pressure Axial Fan with Forward-Skewed Blades

2007 ◽  
Vol 2007 ◽  
pp. 1-10 ◽  
Author(s):  
Li Yang ◽  
Ouyang Hua ◽  
Du Zhao-Hui
Keyword(s):  
Experimental Study ◽  
Pressure Loss ◽  
Total Pressure ◽  
Optimization Design ◽  
Pressure Ratio ◽  
Low Pressure ◽  
Broadband Noise ◽  
Total Pressure Loss ◽  
Aerodynamic Noise ◽  
Axial Fan

This paper presents an experimental study of the optimization of blade skew in low pressure axial fan. Using back propagation (BP) neural network and genetic algorithm (GA), the optimization was performed for a radial blade. An optimized blade is obtained through blade forward skew. Measurement of the two blades was carried out in aerodynamic and aeroacoustic performance. Compared to the radial blade, the optimized blade demonstrated improvements in efficiency, total pressure ratio, stable operating range, and aerodynamic noise. Detailed flow measurement was performed in outlet flow field for investigating the responsible flow mechanisms. The optimized blade can cause a spanwise redistribution of flow toward the blade midspan and reduce tip loading. This results in reduced significantly total pressure loss near hub and shroud endwall region, despite the slight increase of total pressure loss at midspan. In addition, the measured spectrums show that the broadband noise of the impeller is dominant.

An Experimental Investigation of Stator Clocking Effects in a Two-Stage Low-Speed Axial Compressor

2011 ◽  
Author(s):  
J. Sta¨ding ◽  
D. Wulff ◽  
G. Kosyna ◽  
B. Becker ◽  
V. Gu¨mmer
Keyword(s):  
Total Pressure ◽  
Axial Compressor ◽  
Axial Flow ◽  
Leading Edge ◽  
Global Scale ◽  
Flow Coefficient ◽  
Maximum Efficiency ◽  
Pressure Measurements ◽  
Low Speed ◽  
The Impact

The impact of stator clocking on performance and flow of a 2.5-stage axial compressor has been investigated. Stator clocking, the circumferential indexing of adjacent stator rows with equal blade counts, is known as a potential means to modify the flow field in multistage turbomachinery and increase overall efficiencies of both turbines and compressors. These potential effects on turbomachine performance are due to wake-airfoil interactions and primarily depend on the alignment of the downstream stator row with the upstream stator wake path. The present survey describes and discusses the experimental research on stator clocking effects in a low-speed 2.5-stage axial flow compressor, using front loaded CDA blade sections and cantilevered stator rows with identical blade counts. Conventional static pressure tappings were used to locate global peaks in compressor performance for varying Stator 2 clocking positions at different flow coefficients. Results of unsteady total pressure measurements obtained by means of a high-frequency pressure transducer, embedded in the Stator 2 leading edge, give information on Stator 1 wake propagation. Traverse data from pneumatic 5-hole probes show the impact of stator indexing on Stator 2 exit total pressure at different blade spans. Regardless of flow coefficient, the variations of overall compressor efficiency due to Stator 2 clocking are around 0.2% and are exhibiting a near-sinusoidal trend over the clocking angle. It is shown that total pressure measurements at mid-span of Stator 2 leading edge suggest best overall performances for design and low loading conditions, if the Stator 1 wakes pass through mid-passage of Stator 2. At high loading, however, maximum efficiency locates the wake path directly at the leading edge. Due to a considerable span-wise skewness of the upstream stator wake, the aerodynamic clocking position for Stator 2 varies from hub to tip. While it is shown again that this effect weakens the advantages of airfoil indexing on a global scale, stator clocking shows much more potential if only a single blade section is considered.

Unsteady Pressure Measurements in a Single Stage Low Pressure Axial Compressor: Tip Vortex Flow and Stall Inception

2009 ◽  
Author(s):  
J. F. Brouckaert ◽  
N. Van de Wyer ◽  
B. Farkas ◽  
F. Ullmann ◽  
J. Desset ◽  
...  
Keyword(s):  
Flow Field ◽  
Axial Compressor ◽  
Low Pressure ◽  
Fast Response ◽  
Single Stage ◽  
Pressure Probe ◽  
Pressure Measurements ◽  
Stall Inception ◽  
Unsteady Pressure ◽  
Unsteady Pressure Measurements

The experimental investigation of the unsteady flow field in a single stage low pressure axial compressor designed for a counter-rotating turbofan engine architecture is presented in this paper. The rotor casing was instrumented with fast response pressure transducers to perform a detailed survey of the tip flow features during stable operation, near stall and during stall. Tests were performed at two different Reynolds numbers representative of cruise and take-off conditions in the VKI-R4 closed loop compressor test rig. Simultaneous time-resolved measurements with a miniature fast response total pressure probe were performed by radial traverses at the rotor exit to support the tip flow field investigation. The casing measurements allow to map the direction and extension of the tip leakage vortex. The flow path measurements show its extension at the exit of the rotor blade passage and its evolution as throttling is increased towards the compressor stability limit. These experimental results are discussed and compared to CFD simulations, showing good agreement. Stall inception and rotating stall patterns are investigated as well and described in this paper. They are based both on hot wire measurements and on the casing unsteady pressure measurements.

Effect of aft wall slope on cavity pressure oscillations in supersonic flows

2009 ◽  
Vol 113 (1143) ◽  
pp. 291-300 ◽  
Author(s):  
N. S. Vikramaditya ◽  
J. Kurian
Keyword(s):  
Experimental Study ◽  
Data Analysis ◽  
Acoustic Wave ◽  
Mode Switching ◽  
Pressure Measurements ◽  
Cavity Pressure ◽  
Pressure Oscillations ◽  
Stable Mode ◽  
Unsteady Pressure Measurements ◽  
Wall Slope

Abstract An experimental study of supersonic flow over wall mounted cavities with different aft wall angles is carried out. Unsteady pressure measurements were made on the walls and floor of the cavity. Data analysis was performed on the experimental results using statistical methods. In the case of higher angled cavities, the presence of an upstream traveling acoustic wave could be confirmed. For lower angled cavities (60 degrees and less) where the acoustic wave could not be identified, the flow inside the cavity was more or less stable. Mode switching occurring in higher angled cavities was confirmed by spectrogram studies.

scholarly journals Experimental study of water droplet break up in water in oil dispersions using an apparatus that produces localized pressure drops

2019 ◽  
Vol 74 ◽  
pp. 1 ◽  
Author(s):  
Fabricio S. Silva ◽  
Ricardo A. Medronho ◽  
Luiz Fernando Barca
Keyword(s):  
Experimental Study ◽  
Droplet Size Distribution ◽  
Energy Dissipation Rate ◽  
Experimental Results ◽  
Good Prediction ◽  
Pressure Drops ◽  
Turbulence Suppression ◽  
Kolmogorov Length Scale ◽  
Control Production ◽  
Break Up

Oil production facilities have choke/control valves to control production and protect downstream equipment against over pressurization. This process is responsible for droplets break up and the formation of emulsions which are difficult to treat. An experimental study of water in oil dispersion droplets break up in localized pressure drop is presented. To accomplish that, an apparatus simulating a gate valve was constructed. Droplet Size Distribution (DSD) was measured by laser light scattering. Oil physical properties were controlled and three different break up models were compared with the experimental results. All experimental maximum diameters (dmax) were above Kolmogorov length scale. The results show that dmax decreases with increase of energy dissipation rate (ε) according to the relation dmax ∝ ε−0.42. The Hinze (1955, AIChE J.1, 3, 289–295) model failed to predict the experimental results, although, it was able to adjust reasonably well those points when the original proportional constant was changed. It was observed that increasing the dispersed phase concentration increases dmax due to turbulence suppression and/or coalescence phenomenon. Turbulent viscous break up model gave fairly good prediction.

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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