Editorial

It is a distinct honor and a pleasure to serve as Guest Editor for this special edition of the International Journal of Aeroacoustics in honor of Professor Philip J Morris. His research encompasses several topics: turbulence modeling, hydrodynamic stability, jet noise, theoretical and computational studies of fluid mechanics and aeroacoustics, wind turbine noise, helicopter noise, fan noise, and thermoacoustics. He has excelled in both teaching and research, inspiring numerous students for over forty years and making substantial advancements in fluid dynamics. With a solid grounding in fundamental and applied research learnt from Phil, many of his students have achieved distinction and have made significant contributions in industry, government laboratories, and academia. Phil pioneered the incorporation of large-scale structures observed in free shear flows for the modeling of turbulent mixing. His approach related the inherent growth/decay of the hydrodynamic instability waves in the mean flow with the evolution of the large-scale structures and provided the means for computing the spreading of turbulent free jets without empiricism. The importance of these structures in the generation and radiation of noise in supersonic jets was already recognized and Phil was instrumental in the development of methods based on his approach for the computation of farfield noise. His scientific contributions are internationally recognized and he is a leading authority on aeroacoustics, as exemplified by his prolific publications and technical presentations. Phil received the prestigious Aeroacoustics Award in 1999 from the American Institute of Aeronautics and Astronautics (AIAA), “for major contributions to jet noise prediction, turbulence modeling, and computational aeroacoustics.” He became a Fellow of the American Physical Society in 1995 and an AIAA Fellow in 2002. Phil has served as the Boeing/A. D. Welliver Professor of Aerospace Engineering at Penn State since 1992. He has received numerous teaching and research awards at Penn State, including the Outstanding Teaching Award and Penn State Engineering Society's Premier Research Award, the highest recognition for research from the Penn State College of Engineering. Phil has lent his expertise and collaborated with industry and government laboratories on the reduction of airplane noise. He has been an active participant in AIAA activities and was a past chair of the Aeroacoustics Technical Committee.

Phil was the Advisor for my Doctoral Dissertation and fostered my research interests in fluid dynamics and aeroacoustics of jet flows. I was fortunate to select my dissertation research on “Turbulent Mixing in Supersonic Jets,” at the time when Phil was making seminal contributions on this topic. When I started my doctoral studies, little did I know that Professor Dennis K McLaughlin was moving to Penn State and taking over as the Head of the Department of Aerospace Engineering at the same time. Dennis was immediately added to my doctoral committee and I have had the privilege of learning from them first, and collaborating with them for the last ∼25 years. I served as a Teaching Assistant under Dennis, who put me in charge of the Aerodynamics Laboratory course. These early interactions with both Phil and Dennis strengthened my background and interests in analytical, computational, and experimental approaches. Phil instilled in me the importance and value of preparation, clear formulation of the technical problem, familiarization of past research, and then exploration of various approaches that would lead to a solution. I have been privileged to observe his teaching and research methods and have endeavored to adopt his erudite and scholarly delivery in my own technical presentations. The many compliments that I have received reflect Phil’s enormous influence on my career. Phil’s emphasis on appropriate preparation, together with the legendary “planning meetings” which Dennis used to spearhead, has enabled me to lead, plan, and successfully conduct detailed and complex experimental programs at Boeing’s Low Speed Aeroacoustics Facility. The three of us have collaborated, along with numerous graduate students advised by Phil and Dennis, on several research projects: experimental and computational investigations of nonlinear jet noise propagation, acoustic waveform analysis techniques, prediction of supersonic jet noise, refurbishment of the six-component force balance at Penn State, effects of jet temperature on broadband shock-associated noise, reduction of jet noise from tactical fighter aircraft, space–time correlation measurements, analyses and interpretation of nearfield pressure characteristics, and many other innovative projects. In addition to technical interactions, our social get-togethers with our spouses Bing Morris, Connie McLaughlin, and Nancy Gonlin at conference sites and at State College have led to lasting family friendships, which all of us will cherish forever.

Many colleagues and former graduate students have enthusiastically contributed articles to this special issue. The solicited articles, preceded by a prosopography by McLaughlin, Viswanathan and Karen Morris, address varied research topics, a testament to Phil’s wide range of interests: prediction of jet noise and airplane noise by Viswanathan; nuances of phased-array analyses by Brian Tester and Stewart Glegg; grid-sensitivity of flow and noise in computational jet simulations by Christophe Bogey; unsteady disturbances in micro Rayleigh-Bénard flows by Whai-Wai Liou; surface roughness effects on rotor broadband noise by Ken Brentner et al.; large-eddy simulations of a noise reduction concept for supersonic jets by Tasos et al.; modern infinitesimals and entropy jump across a shock wave by Roy Baty; experimental investigation of the turbulent density —far field sound correlations by Christophe Bailly; and radiation from large-scale structures in a turbulent shear layer by Steve Miller. Gratitude is due to Professor Ganesh Raman for supporting and expediting the publication of this special issue.