Military jet noise source imaging using multisource statistically optimized near-field acoustical holography.
The identification of acoustic sources is critical to targeted noise reduction efforts for jets on high-performance tactical aircraft. This paper describes the imaging of acoustic sources from a tactical jet using near-field acoustical holography techniques. The measurement consists of a series of scans over the hologram with a dense microphone array. Partial field decomposition methods are performed to generate coherent holograms. Numerical extrapolation of data beyond the measurement aperture mitigates artifacts near the aperture edges. A multisource equivalent wave model is used that includes the effects of the ground reflection on the measurement. Multisource statistically optimized near-field acoustical holography (M-SONAH) is used to reconstruct apparent source distributions between 20 and 1250 Hz at four engine powers. It is shown that M-SONAH produces accurate field reconstructions for both inward and outward propagation in the region spanned by the physical hologram measurement. Reconstructions across the set of engine powers and frequencies suggests that directivity depends mainly on estimated source location; sources farther downstream radiate at a higher angle relative to the inlet axis. At some frequencies and engine powers, reconstructed fields exhibit multiple radiation lobes originating from overlapped source regions, which is a phenomenon relatively recently reported for full-scale jets.
Air Force Research Laboratory, Battlespace Acoustics Branch, Wright-Patterson Air Force Base, Dayton, Ohio 45433, USA.
Alan T
AT
Wall
Department of Physics and Astronomy, N283 ESC, Brigham Young University, Provo, Utah 84602, USA.
Kent L
KL
Gee
Department of Physics and Astronomy, N283 ESC, Brigham Young University, Provo, Utah 84602, USA.
Tracianne B
TB
Neilsen
Air Force Research Laboratory, Battlespace Acoustics Branch, Wright-Patterson Air Force Base, Dayton, Ohio 45433, USA.
Richard L
RL
McKinley
Blue Ridge Research and Consulting, LLC, Asheville, North Carolina 28801, USA.
Michael M
MM
James