TY - JOUR
T1 - Low-frequency sound sources in high-speed turbulent jets
AU - Bodony, Daniel J.
AU - Lele, Sanjiva K.
N1 - Funding Information:
This work is funded, in part, by the Aeroacoustics Research Consortium and the Center for Turbulence Research. Computer resources were provided by the U.S. Department of Defense through contract AFOSR F49620-01-1-0138. The authors thank Professor J. Freund, of the University of Illinois at Urbana-Champaign, for access to his data. An earlier, limited version of this article appeared as conference paper AIAA-2005-3041 and was presented at the AIAA/CEAS Aeroacoustics Conference and Exhibit in Monterey, CA, 22–25 May 2005.
PY - 2008
Y1 - 2008
N2 - An analysis of the sound radiated by three turbulent, high-speed jets is conducted using Lighthill's acoustic analogy ( Proc. R. Soc. Lond. A, vol. 211, 1952, p. 564). Computed by large eddy simulation the three jets operate at different conditions: a Mach 0.9 cold jet, a Mach 2.0 cold jet and a Mach 1.0 heated jet. The last two jets have the same jet velocity and differ only by temperature. None of the jets exhibit Mach wave characteristics. For these jets the comparison between the Lighthill-predicted sound and the directly computed sound is favourable for all jets and for the two angles (30° and 90°, measured from the downstream jet axis) considered. The momentum (ρui uj) and the so-called entropy [p - p∞ - a∞2(ρ - ρ∞)] contributions are examined in the acoustic far field. It is found that significant phase cancellation exists between the momentum and entropy components. It is observed that for high-speed jets one cannot consider ρuiuj and (p′ - a∞ 2ρ′)δij as independent sources. In particular the ρ′ūxūx component of ρuiuj is strongly coupled with the entropy term as a consequence of compressibility and the high jet velocity and not because of a linear sound-generation mechanism. Further, in more usefully decoupling the momentum and entropic contributions, the decomposition of Tij due to Lilley (Tech. Rep. AGARD CP-131 1974) is preferred. Connections are made between the present results and the quieting of high-speed jets with heating.
AB - An analysis of the sound radiated by three turbulent, high-speed jets is conducted using Lighthill's acoustic analogy ( Proc. R. Soc. Lond. A, vol. 211, 1952, p. 564). Computed by large eddy simulation the three jets operate at different conditions: a Mach 0.9 cold jet, a Mach 2.0 cold jet and a Mach 1.0 heated jet. The last two jets have the same jet velocity and differ only by temperature. None of the jets exhibit Mach wave characteristics. For these jets the comparison between the Lighthill-predicted sound and the directly computed sound is favourable for all jets and for the two angles (30° and 90°, measured from the downstream jet axis) considered. The momentum (ρui uj) and the so-called entropy [p - p∞ - a∞2(ρ - ρ∞)] contributions are examined in the acoustic far field. It is found that significant phase cancellation exists between the momentum and entropy components. It is observed that for high-speed jets one cannot consider ρuiuj and (p′ - a∞ 2ρ′)δij as independent sources. In particular the ρ′ūxūx component of ρuiuj is strongly coupled with the entropy term as a consequence of compressibility and the high jet velocity and not because of a linear sound-generation mechanism. Further, in more usefully decoupling the momentum and entropic contributions, the decomposition of Tij due to Lilley (Tech. Rep. AGARD CP-131 1974) is preferred. Connections are made between the present results and the quieting of high-speed jets with heating.
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U2 - 10.1017/S0022112008004096
DO - 10.1017/S0022112008004096
M3 - Article
AN - SCOPUS:57049167625
SN - 0022-1120
VL - 617
SP - 231
EP - 253
JO - Journal of Fluid Mechanics
JF - Journal of Fluid Mechanics
ER -