I have recently published an article in honor of the late NASA Senior Theoretical Aeroacoustician Dr. Fereidoun `Feri’ Farassat.
During the first week I worked at NASA, while I was sending a fax, Dr. Farassat literally screamed from the other end of building 1208, Is this how NASA researchers spend their time?‘ I was surprised and confused at the time, but now this question remains in my mind everyday. The French impressionist painter Camille Pissarro wrote,everyday a line,’ I might write, `everyday an equation.’ Doing so honors those who have come before us at this prestigious organization and allows us to stand on their shoulders, especially so during this 100th Anniversary of NACA!
The article citation is
Miller, S. A. E., “The Scaling of Broadband Shock-Associated Noise with Increasing Temperature,” International Journal of Aeroacoustics, Vol. 14, Num. 1-2, 2015, pp. 305-326. DOI: 10.1260/1475-472X.14.1-2.327 [Link via DOI] [PDF Preprint]
More important than the technical contribution of the article are the lessons we learned from the person the article honors. The article contains a personal introduction,
It is a privilege to contribute an article to this special edition in honor of Dr. Fereidoun ‘Feri’ Farassat. The present article involves the use of an acoustic analogy and a Green’s function for its solution. Dr. Farassat’s career was heavily involved with both of these fundamental methods in aeroacoustics since his Ph.D. [1] work at Cornell (under advisement of Professor William R. Sears) based on the work of J. E. Ffowcs Williams and D. L. Hawkings [2]. His Ph.D. work laid the foundation for the rest of his career at NASA Langley Research Center (LaRC) within the Aeroacoustics Branch. Dr. Farassat’s developments such as Formulation 1 (Farassat [3]), Formulation 1A (Farassat and Succi [4]), the use of generalized functions (Farassat and Myers [5]), and countless others, were extremely important for the field. Some of these contributions are available on the NASA Technical Reports Server, where Dr. Farassat has over 130 publications available to the public on a wide range of topics.
Dr. Farassat, during his mid- to late-career, was undoubtedly the theoretical backbone of the Aeroacoustics Branch at NASA Langley. He had influenced the technical direction of many researchers within both the branch and NASA as a whole, and had a considerable influence throughout the community, all of which are still being felt today.
Dr. Farassat had a long history of imparting his knowledge to new researchers at NASA Langley. Some of my first and most memorable interactions with Dr. Farassat had started with these teachings. I enjoyed many technical discussions in his office and his guidance changed my technical view-point, especially relating to the acoustic analogy. These discussions saved me large amounts of time and helped me avoid many possible technical failures. He also was not afraid to offer advice, technical or personal, and was genuinely interested in the well-being of everyone he interacted with. He was an unwavering advocate within NASA for the importance of research and was extremely supportive of junior researchers.
I am proud to call Dr. Farassat my colleague and friend. Thank you Feri for the time we had together.
Abstract
A physical explanation for the saturation of broadband shock-associated noise (BBSAN) intensity with increasing jet stagnation temperature has eluded investigators. An explanation is proposed for this phenomenon with the use of an acoustic analogy. To isolate the relevant physics, the scaling of BBSAN peak intensity level at the sideline observer location is examined. The equivalent source within the framework of an acoustic analogy for BBSAN is based on local field quantities at shock wave – shear layer interactions. Propagation of sound through the jet shear layer is predicted with an adjoint vector Green’s function solver of the linearized Euler equations. The combination of the equivalent source and adjoint vector Green’s function allows for correct predictions of the saturation of BBSAN with increasing stagnation pressure and stagnation temperature. The sources and vector Green’s function have arguments involving the steady Reynolds-Averaged Navier-Stokes solution of the jet. It is proposed that saturation of BBSAN with increasing jet temperature occurs due to a balance between the amplification of the sound propagation through the shear layer and the source term scaling.
Acknowledgements
The author benefited greatly from discussions with Boeing/A. D. Welliver Professor Philip J. Morris of the Pennsylvania State University. The availability of experimental data from Professor Dennis K. McLaughlin of the Pennsylvania State University, Dr. James Bridges of NASA Glenn Research Center at Lewis Field, and Dr. Viswanathan of the Boeing Company made this work possible. The author is grateful for continuous support from The National Aeronautics and Space Administration Fundamental Aeronautics Program High Speed Project.
Some References
[1] Farassat, F., “The Sound from Rigid Bodies in Arbitrary Motion,” Cornell University Ph.D. Dissertation, January 1973.
[2] Ffowcs Williams, J. E. and Hawkings, D. L., “Sound Generation by Turbulence and Surfaces in Arbitrary Motion,” Phil. Trans. R. Soc. Lond. A, Vol. 264, No. 1151, 1969, pp. 321–342. doi:10.1098/rsta.1969.0031.
[3] Farassat, F., “Linear Acoustic Formulas for Calculation of Rotating Blade Noise,” AIAA Journal, Vol. 19, No. 9, 1981, pp. 1122-1130. doi:10.2514/3.60051.
[4] Farassat, F. and Succi, G. P., “A Review of Propeller Discrete Frequency Noise Prediction Technology with Emphasis on Two Current Methods for Time Domain Calculations,” Journal of Sound and Vibration, Vol. 71, No. 3, 1980, pp. 399–419. doi:10.1016/0022–460X(80)90422-8.
[5] Farassat, F. and Myers, M. K., “Multidimensional Generalized Functions in Aeroacoustics and Fluid Mechanics-Part 1: Basic Concepts and Operations,” International Journal of Aeroacoustics, Vol. 10, No. 2–3, June 2011, pp. 161–200. doi:10.1260/1475–472X.10.2-3.161.