Acoustic Resonance in Aeroengine Intake Ducts

2004 ◽  
Vol 126 (3) ◽  
pp. 432-441 ◽  
Author(s):  
A. J. Cooper ◽  
A. B. Parry ◽  
N. Peake
Keyword(s):  
Theoretical Model ◽  
Analytical Methods ◽  
Swirling Flow ◽  
Acoustic Resonance ◽  
Rotating Stall ◽  
Flow Conditions ◽  
Resonance Phenomena ◽  
Axial Variation ◽  
Acoustic Lining

A theoretical model is used to investigate the effect of geometry, flow conditions and acoustic lining on the occurrence of acoustic resonance within aeroengine ducts. Semi-analytical methods are used to demonstrate that two types of acoustic resonance can be excited. The first is an intake resonance arising due to axial variation of the intake shape and the presence of swirling flow downstream of the rotor. The second occurs as a result of mode trapping between the rotor and stator. Such resonance phenomena may be relevant to the destabilization of the fan and the onset of flutter and rotating stall.

Trapped acoustic modes in aeroengine intakes with swirling flow

2000 ◽  
Vol 419 ◽  
pp. 151-175 ◽  
Author(s):  
A. J. COOPER ◽  
N. PEAKE
Keyword(s):  
Swirling Flow ◽  
Aircraft Engine ◽  
Acoustic Resonance ◽  
Axial Fan ◽  
System Parameters ◽  
Acoustic Modes ◽  
Resonant States ◽  
Blade Row ◽  
Actuator Disc ◽  
Axial Variation

A theoretical model of an aeroengine intake–fan system is developed in order to show the existence of acoustic resonance in the intake. In general this phenomenon can be linked to instabilities in aircraft engine inlets.The model incorporates a slowly varying duct intake and accounts for the swirling flow downstream of the fan. The slow axial variation in cross-section gives rise to turning points where upstream-propagating acoustic modes are totally reflected into downstream-propagating modes. The effect of the swirling flow downstream can be to cut off a mode which is cut on upstream of the fan. It is shown that these two aspects of the flow, coupled with the effects of the fan (represented by an actuator disc), can lead to acoustic modes becoming trapped in the intake, thus giving rise to pure acoustic resonance.A whole range of system parameters, such as axial, fan and swirl Mach numbers, which satisfy the conditions for resonance are identified. The effects of a stationary blade row behind the fan are also considered leading to a second family of resonant states. In addition we find resonance due to reflection of acoustic modes at the open (inlet) end of the duct.

Noise Generation and Propagation Within Corrugated Pipes

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Hugh Goyder
Keyword(s):  
Differential Equation ◽  
Theoretical Model ◽  
Acoustic Wave ◽  
Standing Wave ◽  
Fatigue Damage ◽  
Acoustic Resonance ◽  
Noise Generation ◽  
Flow Conditions ◽  
Noise Levels ◽  
Acoustic Standing Wave

Corrugated pipes have the advantage of being flexible but the disadvantage of generating unacceptable levels of noise. The noise generated within these pipes is due to oscillation of vortices formed within the corrugations. The noise can induce vibration and unacceptable fatigue damage. Consequently, it is desirable to have a method for predicting the flow conditions that facilitate noise and the noise levels that are generated. This paper develops a theoretical model for the noise generation by considering the interaction of an acoustic wave with the vortices. The key issue that emerges is the delay or phase angle between vortex production in the corrugations and an acoustic standing wave. For the usual conditions, where there are many corrugations in a wavelength, it is possible to form a differential equation for the build-up and saturation of an acoustic resonance. The relative few parameters within this differential equation provide a good basis for modeling the occurrence and level of noise produced. It is anticipated that some experimental input will always be needed for particular corrugation geometries.

Laminar Swirling Pipe Flow

1954 ◽  
Vol 21 (1) ◽  
pp. 1-7
Author(s):  
L. Talbot
Keyword(s):  
Swirling Flow ◽  
Nonlinear Effects ◽  
Critical Conditions ◽  
Flow Conditions ◽  
Rotationally Symmetric ◽  
Rate Of Decay ◽  
Linearized Theory ◽  
The Stability ◽  
Experimental Values ◽  
Rates Of Decay

Abstract The problem of the decay of a rotationally symmetric steady swirl superimposed on Poiseuille flow in a round pipe was investigated theoretically and experimentally. The object was to determine the degree to which the rate of decay of the swirl as predicted by a linearized theory agreed with measured rates of decay at flow conditions near the critical conditions for swirl instability. The solution to the linearized equation of motion for the swirl was obtained. Swirling flow was produced experimentally by rotating a section of the test pipe. Swirl velocities were determined from motion-picture studies of colored oil droplets introduced in the flow. The stability of the swirl was investigated through visualization of a dye filament, and a critical curve for swirl instability was determined experimentally relating the angular velocity of the rotating section to the Reynolds number. The theoretical and experimental values for the decay parameter were found to agree closely, even at conditions of flow near the critical conditions for instability. It was concluded that in the problem under consideration the nonlinear effects are not appreciable for stable decay of the swirl.

Analysis of Local Flow Structure and Global Compressor Performance During Rotating Stall

2004 ◽  
Author(s):  
Chiara Palomba
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
Rotational Speed ◽  
Axial Flow ◽  
Rotating Stall ◽  
Performance Parameters ◽  
Flow Conditions ◽  
Local Flow ◽  
Flow Parameters ◽  
Compressor Performance

Rotating stall is an instability phenomenon that arises in axial flow compressors when the flow is reduced at constant rotational speed. It is characterised by the onset of rotating perturbations in the flow field accompanied by either an abrupt or gradual decrease of performances. Although the flow field is unsteady and non axisymmetric, the global operating point is stable and a stalled branch of performance curve may be experimentally determined. The number, rotational speed, circumferential extension of the rotating perturbed flow regions named rotating cells may vary from one compressor to another and may depend on the throttle position. The present work focuses on the interaction between local flow parameters and global compressor performance parameters with the aim of reaching a better understanding of the phenomenon. Starting from the Day, Greitzer and Cumpsty [1] model the detailed flow conditions during rotating stall are studied and related to the global performance parameters. This is done both to verify if the compressor under examination fits to the model and if the detailed flow structure may highlight the physics that in the simple model may hide behind the correlation’s used.

Distinctions Between Two Types of Self Excited Gas Oscillations in Vaneless Radial Diffusers

1979 ◽  
Author(s):  
A. N. Abdelhamid ◽  
J. Bertrand
Keyword(s):  
Static Pressure ◽  
Pressure Fluctuations ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Flow Coefficient ◽  
Width Ratio ◽  
Flow Conditions ◽  
Oscillating Flows ◽  
Frequency Domains ◽  
Order Of Magnitude

Experiments were conducted to determine the characteristics of oscillating flows in a centrifugal compression system with vaneless diffusers. The system was operated without a diffuser and with eight different diffuser configurations to determine the effects of diffuser diameter and width ratios on the unsteady behavior of the system. Mean and fluctuating velocity and static pressure measurements were carried out in the time and frequency domains. The system without a diffuser was found to be stable at all operating conditions. The installation of any of the eight diffusers resulted in the generation of self-excited oscillations at some operating conditions. It was found that the critical flow coefficient at which onset of oscillations was observed increased as the diffuser width ratio was decreased and as the diameter ratio was increased. Comparison between the characteristics of the oscillations observed in the present study and those observed by other investigators indicate that rotating stall in two geometrically similar diffusers can be an order of magnitude different in the non-dimensional rotational speed and level of unsteady pressure fluctuations. These differences point towards the possibility of existence of more than one set of flow conditions which could lead to the occurrence of the unsteady phenomena.

1101 Study of Acoustic Resonance Phenomena Including Sound Source Position

2013 ◽  
Vol 2013 (0) ◽  
pp. _1101-01_-_1101-04_
Author(s):  
Fumio SHIMIZU ◽  
Junichiro TAMAO ◽  
Kazuhiro TANAKA
Keyword(s):  
Sound Source ◽  
Acoustic Resonance ◽  
Source Position ◽  
Resonance Phenomena

Boundary-layer velocity profiles in a swirling convergent flow field

1972 ◽  
Vol 52 (2) ◽  
pp. 357-367 ◽  
Author(s):  
T. M. Houlihan ◽  
D. J. Hornstra
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Swirling Flow ◽  
Theoretical Calculations ◽  
Experimental Investigations ◽  
Conical Nozzle ◽  
Flow Conditions ◽  
Boundary Layer Flows ◽  
Layer Velocity ◽  
Convergent Flow

Velocity distributions within the boundary layer of a swirling flow of incompressible fluid in a convergent conical nozzle have been investigated. Theoretical calculations with boundary conditions more appropriate to physically existent situations discounted the existence of 'super-velocities’ within the boundary layer. Parallel experimental investigations demonstrated an interdependence of core and boundary-layer flows which precluded the maintenance of the flow conditions required by the analysis.

scholarly journals Investigation of Flow in a Radial Turbine Using Laser Anemometry

1993 ◽  
Author(s):  
Sohail Hamid Zaidi ◽  
Robin L. Elder
Keyword(s):  
Inner Core ◽  
Swirling Flow ◽  
Guide Vane ◽  
Flow Direction ◽  
Flow Region ◽  
Flow Conditions ◽  
Trailing Edge ◽  
Outer Flow ◽  
Laser Anemometry ◽  
Nozzle Guide

A lightweight, high pressure radial inflow turbine was tested and laser anemometry used to measure the flow at various positions within the nozzle guide vanes, immediately upstream of the rotor and at two axial stations downstream of the rotor. The laser anemometry results indicated flow conditions within the nozzle vanes which were largely two dimensional (blade-to-blade with little hub to shroud variation) except at the vane outlet. Unsteadiness due to rotor blade passing effects were detected at the nozzle guide vane trailing edge but had almost entirely decayed at the vane throat. The results also indicate significant variations in flow conditions across the pitch of the nozzles suggesting incidence variations on the rotor of approaching 30 degrees. The laser anemometry results downstream of the turbine show a swirling flow characterised by a turbulent inner core region, a ‘centre annulus’ region of uniform velocity and flow direction and an outer flow region with a similar flow direction but velocity which increases rapidly towards the outer wall. The blade passing unsteadiness (blade-to-blade) is hardly noticeable some 50mm downstream of the rotor trailing edge.

A turbulent bore on a beach

1984 ◽  
Vol 148 ◽  
pp. 73-96 ◽  
Author(s):  
I. A. Svendsen ◽  
P. A. Madsen
Keyword(s):  
Theoretical Model ◽  
Energy Dissipation ◽  
Shallow Water ◽  
Shallow Water Equations ◽  
Present Model ◽  
Finite Amplitude ◽  
Shear Stresses ◽  
Flow Conditions ◽  
Physical Conditions ◽  
Turbulent Bore

A theoretical model is developed giving a moderately detailed description of the flow in a turbulent bore, the velocity profiles, the shear stresses, the energy dissipation, etc. An analysis of the flow conditions at the toe of the turbulent front indicates significant differences from the usual description based on the finite-amplitude shallow-water equations, and it is shown that the present model gives a closer description of the actual physical conditions. Finally, numerical results are presented that illustrate how the model works, and test its validity on an example with known properties.

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