On the modification of tip leakage noise sources by over-tip liners
On the modification of tip leakage noise sources by over-tip liners
Over-Tip-Rotor (OTR) liners have been investigated over the last decades as a technology to further reduce fan broadband noise in turbofan engines. The suppression of noise with OTR liners is attributed to conventional attenuation of acoustic waves and source modification effects. This paper describes a fundamental experiment to gain a better understanding of the source modification effects and establish whether they are purely due to acoustic back-reactions or also due to hydrodynamic changes on the source. The OTR liner configuration is approximated by a static airfoil with its tip located over a flat plate containing a flush-mounted liner insert and separated from the airfoil tip by a small gap. Synchronous measurements of the far-field noise and wall pressure fluctuations on the airfoil tip have shown that the reduction of wall pressure at the airfoil tip by the liner is the dominant mechanism of noise reduction. The reduction in unsteady pressure fluctuations on the airfoil tip by the liner is mainly caused by back-reaction effects at high frequencies and hydrodynamic modifications at low- and mid-frequencies. Over-tip liners are found to alter the unsteady flow field in the gap region and weaken the flow structures responsible for the generation of tip noise. This study has shown that far-field noise predictions based on analytical models are useful to estimate the performance of over-tip liners, but a complete assessment should also include the impact of the liner on the tip-leakage flow, and, consequently, the sources of tip noise.
Palleja-Cabre, Sergi
b841a96c-05d1-4f08-a197-8693cb3a3f90
Saraceno, Ivan
9c74b5c9-b834-43cc-b26d-9408b0534304
Chaitanya, Paruchuri
5c1def64-6347-4be3-ac2d-b9f6a314b81d
1 February 2024
Palleja-Cabre, Sergi
b841a96c-05d1-4f08-a197-8693cb3a3f90
Saraceno, Ivan
9c74b5c9-b834-43cc-b26d-9408b0534304
Chaitanya, Paruchuri
5c1def64-6347-4be3-ac2d-b9f6a314b81d
Palleja-Cabre, Sergi, Saraceno, Ivan and Chaitanya, Paruchuri
(2024)
On the modification of tip leakage noise sources by over-tip liners.
Physics of Fluids, 36 (2), [026114].
(doi:10.1063/5.0187951).
Abstract
Over-Tip-Rotor (OTR) liners have been investigated over the last decades as a technology to further reduce fan broadband noise in turbofan engines. The suppression of noise with OTR liners is attributed to conventional attenuation of acoustic waves and source modification effects. This paper describes a fundamental experiment to gain a better understanding of the source modification effects and establish whether they are purely due to acoustic back-reactions or also due to hydrodynamic changes on the source. The OTR liner configuration is approximated by a static airfoil with its tip located over a flat plate containing a flush-mounted liner insert and separated from the airfoil tip by a small gap. Synchronous measurements of the far-field noise and wall pressure fluctuations on the airfoil tip have shown that the reduction of wall pressure at the airfoil tip by the liner is the dominant mechanism of noise reduction. The reduction in unsteady pressure fluctuations on the airfoil tip by the liner is mainly caused by back-reaction effects at high frequencies and hydrodynamic modifications at low- and mid-frequencies. Over-tip liners are found to alter the unsteady flow field in the gap region and weaken the flow structures responsible for the generation of tip noise. This study has shown that far-field noise predictions based on analytical models are useful to estimate the performance of over-tip liners, but a complete assessment should also include the impact of the liner on the tip-leakage flow, and, consequently, the sources of tip noise.
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026114_1_5.0187951
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Accepted/In Press date: 22 January 2024
Published date: 1 February 2024
Additional Information:
Funding Information:
This work was funded by the Royal Academy of Engineering (RF ∖ 201819 ∖ 18 ∖ 194 ) and by the Engineering and Physical Sciences Research Council (EP/V00686X/1). The authors would like to thank Professor Phil Joseph for his insight on the acoustic power of tip-leakage noise presented in Sec. III B. The authors would also like to thank Dr. Paul Murray for measuring the liner impedance, Dr. Suresh Palani for valuable discussions, and Rolls-Royce for technical support.
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Local EPrints ID: 487736
URI: http://eprints.soton.ac.uk/id/eprint/487736
ISSN: 1070-6631
PURE UUID: 6802a92f-eb03-48e3-92a3-e436101bb808
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Date deposited: 04 Mar 2024 17:33
Last modified: 18 Mar 2024 03:42
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Author:
Ivan Saraceno
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