Research Papers

A High-Resolution Continuous-Scan Acoustic Measurement Method for Turbofan Engine Applications

[+] Author and Article Information
Parthiv N. Shah

ATA Engineering, Inc.,
San Diego, CA 92128

Håvard Vold

ATA Engineering, Inc.,
Charleston, SC 29412

Dan Hensley

ATA Engineering, Inc.,
Lakewood, CO 80401

Edmane Envia, David Stephens

NASA Glenn Research Center,
Cleveland, OH 44135

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received April 6, 2015; final manuscript received August 10, 2015; published online September 23, 2015. Assoc. Editor: Ron Bunker.This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States. Approved for public release; distribution is unlimited.

J. Turbomach 137(12), 121002 (Sep 23, 2015) (11 pages) Paper No: TURBO-15-1064; doi: 10.1115/1.4031341 History: Received April 06, 2015; Revised August 10, 2015

Detailed mapping of the sound field produced by a modern turbofan engine, with its multitude of overlapping noise sources, often requires a large number of microphones to properly resolve the directivity patterns of the constituent tonal and broadband components. This is especially true at high frequencies where the acoustic wavelength is short, or when shielding, scattering, and reflection of the sound field may be present due to installation effects. This paper presents a novel method for measuring the harmonic and broadband content of complex noncompact noise sources using continuously moving (referred to here as continuous-scan (CS)) microphones in conjunction with a state-of-the-art phase-referencing technique. Because the microphones are moving through the sound field produced by the noise sources, they effectively provide infinite spatial resolution of the sound directivity over the scan path. In this method, harmonic (i.e., shaft-coherent) content at the integer multiples of the instantaneous shaft rotational frequency is first extracted from the time signal using a tachometer signal and the Vold-Kalman (VK) filter. The residual broadband signal is then filtered in the time domain in fractional octave bands. The broadband spectra of the signals from the moving microphones are then computed at arbitrary positions along their scan paths using weighted averages (based on Chebyshev polynomial zero-crossings) and the assumption of a complex envelope that varies slowly over a spatial scale whose lower bound is set by the acoustic wavenumber. A benefit of this method is that the decomposition of the total measured sound field into a stochastic superposition of components preserves a meaningful phase definition for each “partial field” associated with a given shaft order (SO). This preservation of phase data enables the forward or backward projection of each of these partial fields using acoustical holography (AH). The benefits of the CS method are demonstrated using acoustic data acquired for a 22-in. scale-model fan stage run at the NASA Glenn Research Center's 9-foot by 15-foot wind tunnel. Two key outcomes of the work include (1) significant improvement in the spatial resolution of the measured sound field and (2) reduction in the overall data acquisition time. Additionally, the methods described here lead to new opportunities for noise source diagnostics and visualization.

Copyright © 2015 by ASME
Your Session has timed out. Please sign back in to continue.


Williams, E. G. , 1999, Fourier Acoustics: Sound Radiation and Nearfield Acoustical Holography, 1st ed., Academic Press, London.
Wold, H. , 1938, “ A Study in the Analysis of Stationary Time Series,” Ph.D. thesis, University of Stockholm, Stockholm, Sweden.
Soeder, R. H. , 1993, “ NASA Lewis 9- by 15-Foot Low-Speed Wind Tunnel User Manual,” NASA Lewis Research Center, Cleveland, OH, Report No. NASA/TM-106247.
Woodward, R. P. , Dittmar, J. H. , Hall, D. G. , and Kee-Bowling, B. , 1995, “ Background Noise Levels Measured in the NASA Lewis 9- by 15-Foot Low-Speed Wind Tunnel,” AIAA Paper No. 95-0720.
Dahl, M. D. , and Woodward, R. P. , 1990, “ Comparison Between Design and Installed Acoustic Characteristics of NASA Lewis 9- by 15-Foot Low-Speed Wind Tunnel Acoustic Treatment,” NASA Lewis Research Center, Cleveland, OH, Report No. NASA/TP-2996.
Woodward, R. P. , Hughes, R. J. , Jeracki, R. J. , and Miller, C. J. , 2002, “ Fan Noise Source Diagnostic Test–Far-field Acoustic Results,” AIAA Paper No. 2002-2427.
Chellappa, B. , and Hoff, G. E. , 1993, “ Propulsion Simulator for High Bypass Turbofan Performance Evaluation,” SAE Technical Paper No. 931410.
Allen, C. , and Soderman, P. , 1993, “ Aeroacoustic Probe Design for Microphone to Reduce Flow-Induced Self-Noise,” AIAA Paper No. 93-4343.
Niemi, H. , 1980, “ On the Construction of the Wold Decomposition for Non-Stationary Stochastic Processes,” Prob. Math. Stat., 1(1), pp. 73–82.
Niemi, H. , 1979, “ On the Construction of Wold Decomposition for Multivariate Stationary Processes,” J. Multivariate Anal., 9(4), pp. 545–559. [CrossRef]
Vold, H. , and Leuridan, J. , 1993, “ High Resolution Order Tracking at Extreme Slew Rates, Using Kalman Tracking Filters,” SAE Technical Paper No. 931288.
Herlufsen, H. , Gade, S. , Konstantin-Hansen, H. , and Vold, H. , 2000, “ Characteristics of the Vold-Kalman Order Tracking Filter,” IEEE International Conference on Acoustics, Speech, and Signal Processing (ICASSP '00), Istanbul, Turkey, June 5–9, pp. 3895–3898.
Vold, H. , Mains, M. , and Blough, J. , 1997, “ Theoretical Foundations for High Performance Order Tracking With the Vold-Kalman Tracking Filter,” SAE Technical Paper No. 972007.
Vold, H. , Herlufsen, H. , Mains, M. , and Corwin-Renner, D. , 1997, “ Multi Axle Order Tracking With the Vold-Kalman Tracking Filter,” Sound Vib., 31(5), pp. 30–35.
Stephens, D. B. , and Vold, H. , 2013, “ Order Tracking Signal Processing for Open Rotor Acoustics,” J. Sound Vib., 333(16), pp. 3818–3830. [CrossRef]
Wang, K. , and Heyns, P. S. , 2011, “ The Combined Use of Order Tracking Techniques for Enhanced Fourier Analysis of Order Components,” Mech. Syst. Signal Process., 25(3), pp. 803–811. [CrossRef]
Wang, K. , and Heyns, P. S. , 2011, “ Application of Computed Order Tracking, Vold–Kalman Filtering and EMD in Rotating Machine Vibration,” Mech. Syst. Signal Process., 25(1), pp. 416–430. [CrossRef]
ANSI, 2009, “ Specification for Octave, Half-Octave, and Third Octave Band Filter Sets,” American National Standards Institute, Washington, DC, Standard No. S1.11.
Williams, E. G. , and Maynard, J. D. , 1980, “ Holographic Imaging Without the Wavelength Resolution Limit,” Phys. Rev. Lett., 45, pp. 554–557. [CrossRef]
Hildebrand, B. P. , and Brenden, B. B. , 1972, An Introduction to Acoustical Holography, Plenum Press, New York.
Shah, P. , Vold, H. , and Yang, M. , 2011, “ Reconstruction of Far-Field Noise Using Multireference Acoustical Holography Measurements of High-Speed Jets,” AIAA Paper No. 2011-2772.
Vold, H. , Shah, P. , Davis, J. , Bremner, P. , McLaughlin, D. , Morris, P. , Veltin, J. , and McKinley, R. , 2010, “ High-Resolution Continuous Scan Acoustical Holography Applied to High-Speed Jet Noise,” AIAA Paper No. 2010-3754.
Glauert, H. , 1928, “ The Effect of Compressibility on the Lift of an Aerofoil,” Proceedings of the Royal Society of London, Vol. CXVIII, pp. 113–119.
Vold, H. , Shah, P. , Morris, P. , Du, Y. , and Papamoschou, D. , 2012, “ Axisymmetry and Azimuthal Modes in Jet Noise,” AIAA Paper No. 2012-2214.


Grahic Jump Location
Fig. 2

Photograph of 22-inch SDT fan stage installed in the NASA Glenn 9 × 15 low-speed acoustic wind tunnel

Grahic Jump Location
Fig. 1

Top-view schematic of wind tunnel facility. Unless otherwise labeled, dimensions are in centimeters (inches in parentheses).

Grahic Jump Location
Fig. 3

FI Narrowband SPL spectrum from microphone 1 acquired at z = −1.02 m (θ = 114.5 deg (exhaust arc))

Grahic Jump Location
Fig. 4

FI Narrowband SPL spectrum from microphone 1 acquired at z = 1.38 m (θ = 58.5 deg (inlet arc))

Grahic Jump Location
Fig. 5

Shaft mechanical RPM time history during Fast CS (4in./s) acquisition

Grahic Jump Location
Fig. 6

Fast CS (4 in./s) Wold decomposition for microphone 1 signal

Grahic Jump Location
Fig. 17

One-third-octave directivities at 3981 Hz. See legend in Fig. 16.

Grahic Jump Location
Fig. 18

One-third-octave directivities at 15,849 Hz. See legend in Fig. 16.

Grahic Jump Location
Fig. 19

One-third-octave spectra at z = −1.02 m (i.e., 114.5 deg sideline angle). Refer to Fig. 20 for legend.

Grahic Jump Location
Fig. 20

One-third-octave spectra at z = +1.38 m (58.5 deg sideline angle)

Grahic Jump Location
Fig. 7

1BPF (SO 22) partial field (complex envelope magnitude) as a function of geometric (sideline) angle

Grahic Jump Location
Fig. 8

Same as Fig. 7, zoomed in over a 25-deg sideline angle

Grahic Jump Location
Fig. 9

4BPF (SO 88) partial field (complex envelope magnitude) as a function of geometric (sideline) angle

Grahic Jump Location
Fig. 10

Same as Fig. 9, zoomed in over a 25-deg sideline angle

Grahic Jump Location
Fig. 11

SO 86 partial field (complex envelope magnitude) as a function of geometric (sideline) angle. Two scan speeds and fixed index data are compared.

Grahic Jump Location
Fig. 12

Same as Fig. 11, zoomed in over a 25-deg sideline angle

Grahic Jump Location
Fig. 13

First 136 SOs at z = −1.02 m (i.e., at θ = 114.5 deg sideline angle)

Grahic Jump Location
Fig. 14

First 136 SOs at z = 1.38 m (i.e., at θ = 58.5 deg sideline angle)

Grahic Jump Location
Fig. 15

First six BPF harmonics compared at z = −1.02 m (θ = 114.5 deg) and z =+1.38 m (θ = 58.5 deg)

Grahic Jump Location
Fig. 16

One-third-octave directivities at 1000 Hz

Grahic Jump Location
Fig. 21

Wavenumber spectra of 1BPF and 4BPF partial fields, assuming n = 22 and 88, respectively

Grahic Jump Location
Fig. 22

AH sound-field reconstruction of 4BPF tone in near field. Blue asterisk shows assumed source origin at z = 0 m. Scan line shown in dashed black.

Grahic Jump Location
Fig. 23

Same as Fig. 22 with assumed source origin at z = 1.5 m

Grahic Jump Location
Fig. 24

Reconstruction of BPF 4 complex envelope along CS line using two different assumed source origins




Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In