Effect of Grazing Flow on Grooved Over-the-Rotor Acoustic Casing Treatments

Bozak, Richard F.; Jones, Michael G.; Howerton, Brian M.; Brown, Martha C.

doi:10.2514/6.2019-2564

Cited by 8 publications

(5 citation statements)

References 10 publications

(22 reference statements)

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“…is the mode number, L is the cavity width, α = 0.25 is the empirical constant which increases as L/D increases, K c is the ratio of the vortex convection speed across the liner cavity face sheet to the free-stream velocity, and M is the free-stream Mach number. Unlike the case of Eq.3 proposed by Rossiter, Block [24] has shown that the self-sustained oscillation frequencies in deep cavities are also sensitive to the L/D ratio of the cavity in addition to the Mach number, and it is given by [25],…”

Section: Liner Self-noisementioning

confidence: 99%

Experimental and numerical assessment of novel acoustic liners for aero-engine applications

Palani

Murray

McAlpine

et al. 2022

28th AIAA/CEAS Aeroacoustics 2022 Conference

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In this paper the performance of two novel broadband liners for aero-engine applications is assessed in the presence of both high sound pressure level and grazing flow. The novel liner configurations include a slanted porous septum concept with varying percentage open areas, and a MultiFOCAL (MULTIple FOlded CAvity Liner) concept. In-duct liner insertion loss predictions and measurements for both downstream and upstream sound propagation are presented, with the results compared to an optimised conventional single-degree-of-freedom perforate liner. Both the novel liners are predicted and measured to provide improved broadband attenuation for downstream propagation, with excellent agreement seen between the measurement and prediction. For downstream sound propagation, a uniform flow model (convected wave equation) with the standard Ingard-Myers boundary condition is shown to predict the liner attenuation accurately, indicating that the boundary effects can be neglected for the downstream case. For upstream sound propagation, the insertion loss predictions and measurements highlight the importance of accounting for boundary-layer refraction in the numerical modelling. Thus, the linearised Euler equations are used to model the effect of the boundary layer on the predicted liner attenuation for upstream propagation.

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Section: Liner Self-noisementioning

confidence: 99%

Experimental and numerical assessment of novel acoustic liners for aero-engine applications

Palani

Murray

McAlpine

et al. 2022

28th AIAA/CEAS Aeroacoustics 2022 Conference

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“…3 Testing of the same OTR casing treatments in the NASA Grazing Flow Impedance Tube showed the generation of cavity noise at the same frequency range than when installed over a turbofan rotor. 14 The lengthwise tones caused by the feedback loop of the unstable shear layer over the cavity 15 cannot be predicted in the analytical groove impedance model nor the FEM solver due to the inviscid nature of the Helmholtz equation and it is out of the scope of this work.…”

Section: Application To Otr Liners: Multiple Grooves Excited By a Poimentioning

confidence: 99%

Impedance modelling of acoustically treated circumferential grooves for over-tip-rotor fan noise suppression

Palleja-Cabre

Tester

Astley

et al. 2020

International Journal of Aeroacoustics

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Experimental investigation of Over-Tip-Rotor circumferential groove liners has shown potential for fan noise suppression in turbofan engines whilst providing minimal penalty in fan aerodynamic performance. The validation of Over-Tip-Rotor liner analytical prediction models against published experimental data requires the modelling of an equivalent impedance for such acoustic treatments. This paper describes the formulation of two analytical groove impedance models as semi-locally reacting liners, that is locally reacting in the axial direction and non-locally reacting in the azimuthal direction. The models are cross-verified by comparison with high-order FEM simulations, and applied to a simplified Over-Tip-Rotor configuration consisting of multiple grooves excited by a monopole point source located close to the grooved surface.

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“…After testing grooved OTR acoustic casing treatments on a turbofan rotor (see next sections), a follow-on study was performed to investigate the effect of flow on grooved acoustic liners. 46 The experiment was performed to understand the scaling of acoustic liner absorption with grazing flow and to investigate the source of selfnoise due to the grooved liner. Six configurations were tested in the GFIT, matching those that were tested in the ANCF and W-8.…”

Section: Uniform-depth Concept With and Without Embedded Expansion Chambersmentioning

confidence: 99%

Investigations of three over-the-rotor liner concepts at various technology readiness levels

Sutliff

Bozak

Jones

et al. 2021

International Journal of Aeroacoustics

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The emphasis on increased turbofan fuel efficiency requires advanced turbofan designs that will integrate higher engine bypass ratios and shorter nacelles. The resulting acoustic signature of these designs will have a more broadband character as well as a smaller available area for liner installation. This two-fold impact compels a need for an improvement in the state of the art in liner technology. Increasing the acoustic absorption efficacy over a broader frequency range is a means to address this need. NASA investigated over-the-rotor acoustic liners for turbofan applications as a potential solution. This type of liner represents a significant advance over traditional liners due to placement in close proximity to the rotor. An advantage of placing treatment in this region is a modification of the acoustic near field, thereby inhibiting noise generation mechanisms. This can result in higher attenuation levels than could be achieved by the conventional sound absorption means. In addition, there is potential to integrate the liner with fan rub-strip and containment components, reducing engine components and thus weight, enabling a systematic enhancement in noise reduction and engine performance. This article reviews the development and evaluation process of three unique over-the-rotor concepts focusing on the discrete tests conducted across the Technology Readiness Level span.

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Effect of Grazing Flow on Grooved Over-the-Rotor Acoustic Casing Treatments

Cited by 8 publications

References 10 publications

Experimental and numerical assessment of novel acoustic liners for aero-engine applications

Experimental and numerical assessment of novel acoustic liners for aero-engine applications

Impedance modelling of acoustically treated circumferential grooves for over-tip-rotor fan noise suppression

Investigations of three over-the-rotor liner concepts at various technology readiness levels

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