Influence of Flow Coefficient, Stagger Angle, and Tip Clearance on Tip Vortex in Axial Compressors

2006 ◽  
Vol 128 (6) ◽  
pp. 1274-1280 ◽  
Author(s):  
Yong Sang Yoon ◽  
Seung Jin Song ◽  
Hyoun-Woo Shin
Keyword(s):  
Pressure Fluctuations ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Tip Vortex ◽  
Time Resolved ◽  
Pressure Transducers ◽  
High Frequency Response ◽  
Response Pressure ◽  
Casing Pressure ◽  
Stagger Angle

Experiments have been performed on the low speed research compressor (LSRC) at General Electric Aircraft Engines to investigate the effects of flow coefficient, stagger angle, and tip clearance on tip vortex. Time resolved casing pressure distributions over the third stage rotor have been acquired with high-frequency-response pressure transducers. Also, tip vortex strength and trajectory have been estimated from the casing pressure fluctuations which have been obtained simultaneously from various axial locations. As flow coefficient decreases, tip vortex gets strengthened and migrates upstream. The stagger angle increase weakens the tip vortex and moves it downstream slightly because the blade loading is decreased. However, tip leakage vortex is influenced mainly by tip clearance, and there exists a “critical” tip clearance which determines the type of tip vortex trajectory (“straight” or “kinked”). As predicted by others, tip vortex gets strengthened with increasing tip clearance. However, unlike the predictions, the tip vortex trajectory moves upstream with increasing tip clearance. Furthermore, with tip clearance above a “critical” value, the tip vortex trajectory is no longer straight but shows a kink in the passage.

Prestall Instability in Axial Flow Compressors

2020 ◽  
Vol 142 (7) ◽  
Author(s):  
Mario Eck ◽  
Roland Rückert ◽  
Dieter Peitsch ◽  
Marc Lehmann
Keyword(s):  
Pressure Fluctuations ◽  
Axial Compressor ◽  
Axial Flow ◽  
Leading Edge ◽  
Propagation Speed ◽  
Flow Coefficient ◽  
Spectral Signature ◽  
Time Resolved ◽  
Pressure Transducers ◽  
Flow Disturbances

Abstract The aim of the present paper is to improve the physical understanding of discrete prestall flow disturbances developing in the tip area of the compressor rotor. For this purpose, a complementary instrumentation was used in a single-stage axial compressor. A set of pressure transducers evenly distributed along the circumference surface mounted in the casing near the rotor tip leading edges measures the time-resolved wall pressures simultaneously to an array of transducers recording the chordwise static pressures. The latter allows for plotting quasi-instantaneous casing pressure contours. Any occurring flow disturbances can be properly classified using validated frequency analysis methods applied to the data from the circumferential sensors. While leaving the flow coefficient constant, a continuously changing number of prestall flow disturbances appears to be causing a unique spectral signature, which is known from investigations on rotating instability. Any arising number of disturbances is matching a specific mode order found within this signature. While the flow coefficient is reduced, the propagation speed of prestall disturbances increases linearly, and meanwhile, the speed seems to be independent from the clearance size. Casing contour plots phase-locked to the rotor additionally provide a strong hint on prestall disturbances clearly not to be caused by a leading edge separation. Data taken beyond the stalling limit demonstrate a complex superposition of stall cells and flow disturbances, which the title “prestall disturbance” therefore does not fit to precisely any more. Different convection speeds allow the phenomena to be clearly distinguished from each other. Furthermore, statistical analysis of the pressure fluctuations caused by the prestall disturbances offer the potential to use them as a stall precursor or to quantify the deterioration of the clearance height between the rotor blade tips and the casing wall during the lifetime of an engine.

Compressibility Effects in Turbulent Subsonic Jets

2003 ◽  
Author(s):  
Zhexuan Wang ◽  
Yiannis Andreopoulos
Keyword(s):  
Mach Number ◽  
Pressure Fluctuations ◽  
Turbulent Jets ◽  
Spreading Rate ◽  
Jet Flows ◽  
Mean Velocity ◽  
Pressure Transducers ◽  
High Frequency Response ◽  
Mach Numbers ◽  
Response Pressure

The behavior of compressible turbulent jets issuing in still air in the absence of shock waves has been investigated at three different subsonic Mach numbers, 0.3, 0.6 and 0.9. Helium, nitrogen and krypton gases were used to generate the jet flows and investigate the density effects on the structure of turbulence. Particle Image Velocimetry and high-frequency response pressure transducers were used to obtain velocity, Mach number inside the flow field. The decay of the Mach number at the centerline of the axisymmetric jets increases with increasing the initial Mach number at the exit of the flow for all jets. The decay of mean velocity at the centerline of the jets is also higher at higher exit Mach numbers. However, the velocity non-dimensionalized by the exit velocity seems to decrease faster at low exit Mach numbers suggesting a reduced mixing with increasing the exit flow Mach numbers. Helium jets were found to have the largest spreading rate among the three different gas jets used in the present investigation, while krypton had the lowest spreading rate. Total pressure fluctuations appear to decrease with increasing exit flow Mach numbers. Unusually high turbulence intensities were measured in helium jets issuing in still air.

The Effect of the Operating Point on the Pressure Fluctuations at the Blade Passage Frequency in the Volute of a Centrifugal Pump

2002 ◽  
Vol 124 (3) ◽  
pp. 784-790 ◽  
Author(s):  
Jorge L. Parrondo-Gayo ◽  
Jose´ Gonza´lez-Pe´rez ◽  
Joaquı´n Ferna´ndez-Francos
Keyword(s):  
Centrifugal Pump ◽  
Pressure Fluctuations ◽  
Fast Response ◽  
Strong Increase ◽  
Flow Rates ◽  
Blade Passage ◽  
Pressure Transducers ◽  
Leading Role ◽  
Dynamic Forces ◽  
Response Pressure

An experimental investigation is presented which analyzes the unsteady pressure distribution existing in the volute of a conventional centrifugal pump with a nondimensional specific speed of 0.48, for flow-rates from 0% to 160% of the best-efficiency point. For that purpose, pressure signals were obtained at 36 different locations along the volute casing by means of fast-response pressure transducers. Particular attention was paid to the pressure fluctuations at the blade passage frequency, regarding both amplitude and phase delay relative to the motion of the blades. Also, the experimental data obtained was used to adjust the parameters of a simple acoustic model for the volute of the pump. The results clearly show the leading role played by the tongue in the impeller-volute interaction and the strong increase in the magnitude of dynamic forces and dipole-like sound generation in off-design conditions.

Experimental Study of Interactions of Shock Wave With Free-Stream Turbulence

1994 ◽  
Vol 116 (4) ◽  
pp. 763-769 ◽  
Author(s):  
A. Honkan ◽  
C. B. Watkins ◽  
J. Andreopoulos
Keyword(s):  
Shock Wave ◽  
Free Stream ◽  
Length Scale ◽  
Pressure Transducers ◽  
Free Stream Turbulence ◽  
High Frequency Response ◽  
Reflected Shock ◽  
Response Pressure ◽  
Decaying Turbulence ◽  
Large Eddies

Phenomena related to turbulence interactions with shock waves have been studied in detail. The present investigation is focused on interactions of a normal shock wave with homogeneous/grid-generated turbulence. When a shock wave formed in a shock-tube is passed through a grid, the induced flow behind the shock has the features of a compressible flow with free-stream turbulence. The decaying turbulence is subjected to an interaction with the reflected shock traveling in the opposite direction. Data were sampled simultaneously from four channels of high frequency response pressure transducers and dual hot-wires probes. A cold-wire was used to provide instantaneous total temperature measurements while a single hot-wire provided instantaneous mass flux measurements. Amplification of velocity and temperature fluctuations and dissipative length scales has been found in all experiments. Velocity fluctuations of large eddies are amplified more than the fluctuations of small eddies. The dissipative length scale, however, of the large eddies is amplified less than the length scale of the small eddies.

scholarly journals Cavitation Inception in Spool Valves

1981 ◽  
Vol 103 (4) ◽  
pp. 564-575 ◽  
Author(s):  
C. Samuel Martin ◽  
H. Medlarz ◽  
D. C. Wiggert ◽  
C. Brennen
Keyword(s):  
Reynolds Number ◽  
Hydraulic Systems ◽  
Cavitation Inception ◽  
Pressure Transducers ◽  
High Frequency Response ◽  
Annular Jet ◽  
Directional Control ◽  
Valve Opening ◽  
Response Pressure ◽  
Spool Valves

Cavitation has been investigated in directional control valves in order to identify damage mechanisms characteristic of components of aircraft hydraulic systems. Tests have been conducted in a representative metal spool valve and in a model three times larger. Data taken under noncavitating conditions with both valves showed that the position of the high-velocity annular jet shifts orientation, depending upon valve opening and Reynolds number. By means of high-frequency response pressure transducers strategically placed in the valve chamber cavitation could be sensed by the correlation of noise with a cavitation index. The onset of cavitation can be detected by comparing energy spectra for a fixed valve opening and a constant discharge. Another sensitive indicator of cavitation inception is the ratio of cavitating to noncavitating spectral densities. The incipient cavitation number as defined in this investigation is correlated with the Reynolds number for both valves.

Wall-vorticity flux dynamics in a two-dimensional turbulent boundary layer

1996 ◽  
Vol 309 ◽  
pp. 45-84 ◽  
Author(s):  
J. Andreopoulos ◽  
J. H. Agui
Keyword(s):  
Boundary Layer ◽  
Viscous Force ◽  
Flux Dynamics ◽  
Pressure Transducers ◽  
High Frequency Response ◽  
Wall Structures ◽  
Response Pressure ◽  
Vorticity Flux ◽  
Low Amplitude ◽  
Physical Phenomena

Four high-frequency-response pressure transducers with 10 viscous units resolution each have been used to obtain simultaneously the fluctuating pressure gradients at the wall of a zero-pressure-gradient boundary layer and then to compute the vorticity flux away from the wall. Since the viscous force on an element of incompressible fluid is determined by the local vorticity gradients, understanding of their dynamical characteristics is essential in identifying the turbulent structure. Extremely high and low amplitudes of both vorticity gradients have been observed which contribute significantly to their statistics although they have low probability of appearance. The r.m.s. of the vorticity flux when scaled with inner wall variables depends very strongly on the Reynolds number, indicating a breakdown of this type of scaling. The application of a small threshold to the data indicated two preferential directions of the vorticity flux vector. An attempt has been made to identify these high- and low-amplitude signals with physical phenomena associated with bursting-sweep processes. Vortical structures carrying bipolar vorticity are the dominant wall structures which are associated with the violent events characterized by large fluctuations of vorticity flux.

Effect of Tip Clearance on the Performance of Forward Swept Subsonic Axial Compressor Rotors at High Stagger Angles

2011 ◽  
Author(s):  
P. V. Ramakrishna ◽  
M. Govardhan
Keyword(s):  
Axial Compressor ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Geometric Flow ◽  
Suction Surface ◽  
Local Flow ◽  
Vena Contracta ◽  
Flow Acceleration ◽  
Pressure Surface ◽  
Stagger Angle

Tip leakage phenomenon in axial compressors is sensitive to the flow incidence, flow coefficient, tip gap height and the pressure gradients. All these geometric/flow features are considerably altered by blade stagger angle. Literature on the stagger angle effects in compressors is scarce; and indeed, such studies for various tip gap heights have not been reported yet. The present paper reports the effect of rotor stagger angle on the performance of subsonic axial compressor rotor with different forward sweep configurations and for various rotor tip clearances. The computational model for the study utilizes finest hexahedral grids. A commercial CFD package ANSYS® CFX 11.0 was used with standard k-ω turbulence model for the simulations. CFD results were well validated with experiments. The following observations were made: At higher stagger angles, flow separates from upstream suction surface locations. Little tip clearance had a positive effect for certain stagger angle increments owing to beneficial interaction of leakage flows with the local flow field. However, severe performance loss was observed at higher stagger settings with large clearances. As the stagger angle was increased, vena contracta effect was highly reduced. At high stagger angles, the flow was observed to leak in a more “axially-reversed” fashion through the tip gap. The deep lowest pressure zones near the pressure surface of the tip are due to the effect of ‘vena contracta.’ Such zones near the suction surface edge of the tip are due to flow acceleration. This particular feature is directly correlated with the tip aerofoil loading and thickness-to-tip gap ratio.

scholarly journals Effect of Wind Tunnel Acoustic Modes on Linear Oscillating Cascade Aerodynamics

1993 ◽  
Author(s):  
Daniel H. Buffum ◽  
Sanford Fleeter
Keyword(s):  
Wind Tunnel ◽  
Unsteady Aerodynamics ◽  
Wave Mode ◽  
Influence Coefficient ◽  
Airfoil Surface ◽  
Pressure Transducers ◽  
Acoustic Modes ◽  
High Frequency Response ◽  
Response Pressure ◽  
Acoustic Treatment

The aerodynamics of a biconvex airfoil cascade oscillating in torsion is investigated using the unsteady aerodynamic influence coefficient technique. For subsonic flow and reduced frequencies as large as 0.9, airfoil surface unsteady pressures resulting from oscillation of one of the airfoils are measured using flush-mounted high-frequency-response pressure transducers. The influence coefficient data are examined in detail and then used to predict the unsteady aerodynamics of a cascade oscillating at various interblade phase angles. These results are correlated with experimental data obtained in the traveling-wave mode of oscillation and linearized analysis predictions. It is found that the unsteady pressure disturbances created by an oscillating airfoil excite wind tunnel acoustic modes which have detrimental effects on the experimental results. Acoustic treatment is proposed to rectify this problem.

Effect of Tip Vortex Reduction on Air-Cooled Condenser Axial Flow Fan Performance: An Experimental Investigation

2021 ◽  
Author(s):  
J. P. Pretorius ◽  
J. A. Erasmus
Keyword(s):  
Performance Test ◽  
Performance Enhancement ◽  
Large Diameter ◽  
Pressure Coefficient ◽  
Axial Flow ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Tip Vortex ◽  
Experimental Investigations ◽  
Fan Performance

Abstract Large diameter axial flow fans are used in Air-cooled Condenser (ACC) systems of modern power stations. Efficiency improvements on these fans can significantly reduce the ACC power consumption and increase the net sent-out power to the grid. This study targets fan performance enhancement through blade tip vortex reduction. Experimental investigations are performed on a representative ACC scale fan, where tests consider the effects of tip clearance and two new tip endplate designs on fan performance. Test results confirm the findings of previous studies, showing the negative effect of increasing tip clearance on performance. Despite testing limitations, results from tests incorporating endplates show fan static pressure coefficient and efficiency increases over large ranges of flow coefficient compared to the datum fan. These outcomes agree with observations from literature and warrants further exploration. Future work is recommended to provide confirmation on the presented trends.

scholarly journals Experimental Methods Applied in a Study of Stall Flutter in an Axial Flow Fan

2004 ◽  
Vol 11 (5-6) ◽  
pp. 597-613 ◽  
Author(s):  
John D. Gill ◽  
Vincent R. Capece ◽  
Ronald B. Fost
Keyword(s):  
Experimental Data ◽  
Dynamic Pressure ◽  
Axial Flow ◽  
Leading Edge ◽  
Axial Flow Fan ◽  
Pressure Transducers ◽  
High Frequency Response ◽  
Stall Flutter ◽  
Response Pressure ◽  
Flutter Testing

Flutter testing is an integral part of aircraft gas turbine engine development. In typical flutter testing blade mounted sensors in the form of strain gages and casing mounted sensors in the form of light probes (NSMS) are used. Casing mounted sensors have the advantage of being non-intrusive and can detect the vibratory response of each rotating blade. Other types of casing mounted sensors can also be used to detect flutter of rotating blades. In this investigation casing mounted high frequency response pressure transducers are used to characterize the part-speed stall flutter response of a single stage unshrouded axial-flow fan. These dynamic pressure transducers are evenly spaced around the circumference at a constant axial location upstream of the fan blade leading edge plane. The pre-recorded experimental data at 70% corrected speed is analyzed for the case where the fan is back-pressured into the stall flutter zone. The experimental data is analyzed using two probe and multi-probe techniques. The analysis techniques for each method are presented. Results from these two analysis methods indicate that flutter occurred at a frequency of 411 Hz with a dominant nodal diameter of 2. The multi-probe analysis technique is a valuable method that can be used to investigate the initiation of flutter in turbomachines.

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