Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

An Experimental Methodology for the Reconstruction of Three-Dimensional Acoustic Pressure Fields in Ducts

[+] Author and Article Information
Giovanni Ferrara

Department of Industrial Engineering of Florence,
University of Florence,
Via di Santa Marta 3,
Florence 50139, Italy
e-mail: giovanni.ferrara@unifi.it

Lorenzo Ferrari

National Council of Research of Italy,
Via Madonna del Piano 10, 50019,
Sesto Fiorentino,
Florence, Italy
e-mail: lorenzo.ferrari@iccom.cnr.it

Giulio Lenzi

Department of Industrial Engineering of Florence,
University of Florence,
Via di Santa Marta 3,
Florence 50139, Italy
e-mail: giulio.lenzi@unifi.it

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 1, 2013; final manuscript received August 9, 2013; published online October 22, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(1), 011505 (Oct 22, 2013) (11 pages) Paper No: GTP-13-1213; doi: 10.1115/1.4025348 History: Received July 01, 2013; Revised August 09, 2013

The claim for low emission engines, imposed by strict environmental legislation, has prompted the aeronautical industry to reduce both noise emission and pollution by using lean combustion technology. These engines are often affected by acoustic instabilities that can compromise their correct functioning. A 3D acoustic wave field investigation is increasingly relevant for a correct design and comprehension of this kind of phenomena. Numerical codes are widely used for this type of analysis but an experimental validation is still required due to the complexity of the real phenomena involved in acoustic generation and propagation. While the wall acoustic pressure can be easily measured, very few examples of radial measurement for a 3D analysis can be found in research on this subject. This paper presents an example of a radial measurement of a 3D acoustic pressure field by means of a waveguide probe based on a 1/4" pressure microphone. In particular, several probe geometries were designed and calibrated on a specialized test rig. In order to verify the adopted methodology, the acoustic 3D pressure fields of two simplified geometries were measured and compared with those from a theoretical model describing the actual conditions of the test rig.

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Fig. 1

Schematic shapes of acoustic modes of a cylindrical duct

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Fig. 2

Theoretical single modes at 4.2 kHz

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Fig. 3

First radial and tangential mode in annular duct

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Fig. 4

Microphone junction with the transmitting duct

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Fig. 5

Probe calibration test rig

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Fig. 6

Comparison of the microphone junction

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Fig. 7

Side branch configuration

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Fig. 8

Comparison of the ideal muffler with a generic single chamber and a dual camber

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Fig. 9

Schematic sketch of the reference single and double chamber mufflers

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Fig. 10

Developed mufflers

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Fig. 11

FRF of the three mufflers probes

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Fig. 12

Comparison of the predicted FRF of the probe with the experimental calibration

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Fig. 13

Mapping measurement section

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Fig. 14

Measurement point distribution for boundaries condition evaluation

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Fig. 15

Schematic of the test rig with the speaker acoustic source

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Fig. 16

Experimental pressure map of the wave field at 4.2 kHz

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Fig. 17

Theoretical pressure map of the wave field at 4.2 kHz

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Fig. 18

Schematic of the annular section with rotor

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Fig. 19

Decay of m=1, n=1 mode in the planar range of propagation

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Fig. 20

Reflection coefficient of the end of annular test rig

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Fig. 21

FFT spectrum of the flush mounted microphone

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Fig. 22

Experimental map of the fifth BPF

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Fig. 23

Theoretical wave field of the fifth BPF




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