Experimental Investigation of Jet Noise Shielding
Dimitri Papamoschou
Professor of Mechanical and Aerospace Engineering
Henry Samueli School of Engineering
University of California, Irvine

 

Abstract：This study is motivated by the desire to develop ultra-quiet aircraft whose noise footprint will be confined to the airport perimeter.  Roughly speaking, a reduction of about 20 decibels, over the quietest airplanes flying today, is needed to achieve this target.  Whether the aircraft are powered by turbofan or open-rotor engines, this noise goal is unlikely to be met without propulsion-airframe integration.  The advent of the Hybrid Wing-Body (HWB) airplane, where the engines are mounted over the wing, has reinvigorated the engine over-the-wing concept for noise shielding, an area of active research in the 1970s.  The potential of jet noise shielding from the HWB is investigated here in subscale experiments using helium-air mixture jets.  The jet nozzle simulated the exhaust of a turbofan engine with bypass ratio of 10. The shield, fabricated from a thin flat plate, had the generic shape of the HWB planform.  Acoustic measurements utilized a microphone array that provided far-field sound measurements and enabled mapping of the noise source location.  Experimental parameters included the axial location of the nozzle and the installation of inboard vertical fins. The noise source of the jet exhausting from the unmodified nozzle is too long for the shield to produce substantial noise reduction.  Installing chevrons on the nozzle reduced the noise source length and therefore improves significantly the shielding.   Axial movement of the nozzle upstream of its nominal location provides an additional but small benefit.  The vertical fins are very important for suppressing noise in the sideline direction.  Examination of high-definition noise source maps shows a direct link between the noise reduction due to shielding and the axial location of the peak noise source.   Using the effective perceived noise level (EPNL) as a noise metric, the combination of chevrons and shield reduced noise by an average of 6 decibels.  While this is a very significant reduction, it is well short of the aforementioned goal.   The study underscores the importance of noise source compaction for effective shielding, and illustrates the challenges of meeting the goal of a “silent airplane”.   Some comments on predictive schemes will be included in the lecture.   

 

告人介绍：

Dimitri Papamoschou, Ph.D.
Professor
Department of Mechanical and Aerospace Engineering
University of California at Irvine
Irvine, California 92697-3975

 CITIZENSHIP: U.S.
RESEARCH AREAS
Compressible turbulence; jet noise; mixing enhancement; microphone phased array techniques;
advanced optical diagnostics.
EMPLOYMENT
2010-2011 Interim Dean,  The Henry SamueliSchool of Engineering University of California, Irvine
2007-2010 Associate Dean for Academic
Affairs,  The Henry SamueliSchool of Engineering University of California, Irvine
2002-2005 Chair, Department of Mechanical
and Aerospace Engineering University of California, Irvine
1998-present Professor University of California, Irvine
1994-1998 Associate Professor University of California, Irvine
1988-1994 Assistant Professor University of California, Irvine
1987-1988 Research Fellow California Institute of Technology
1982-1987 Graduate Research Assistant California Institute of Technology

 PROFESSIONAL ACTIVITIES
Reviewer National Science Foundation, Journal of Fluid Mechanics, Physics of Fluids, AIAA Journal, AIAA Journal of Propulsion and Power, ASME Journal of Fluids Engineering, Theoretical and Computational Fluid Dynamics, Experiments in Fluids, Combustion Science & Technology, Journal of Biomechanics.
Consultant Parker Hannifin Corporation; Radiant Technology Corporation;
Ultrasystems Engineers & Contractors
Member American Institute of Aeronautics and Astronautics
American Physical Society

 HONORS AND AWARDS
Fellow, AIAA, 2009.
Associate Fellow, AIAA, 2002.
Discover Awards Finalist in the area of Sound for the invention Virtual Shroud, 1998.
Invited Lecture at the 48th American Physical Society / Division of Fluid Dynamics Meeting, 1995.
Stanford University Center of Turbulence Research Summer Fellowship, 1992
UCI School of Engineering Teaching Award for 1991-92
Honorary Member, Pi Tau Sigma National Honorary Mechanical Engineering Fraternity, 1990.
Associate Member, Sigma Xi Scientific Research Society, 1986.
Donald Wills Douglas Fellowship, Caltech, 1981.
Fellow, Tau Beta Pi Association, 1981.