Technical report project for MEC E 200 during my spring-summer term 2012. First tech. paper I have written. Primarily focused on the design and development of a new aircraft engine nozzle for quiet supersonic flight.

1. Improvements in Engine
Nozzle Design within the
Field of Supersonic Flight
Alaric Tomas
2nd year Mechanical Engineering student
June 18th, 2012
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2. Abstract:
NASA’s Fundamental Aeronautics Supersonics Project has revealed an interesting
development in the field of aeronautic engineering: an inverted velocity-profile nozzle. This is a
nozzle device to be fitted to end of new engines to improve efficiency and noise reduction.
Developed by GE Aviation, this device will sport supreme supersonic noise reduction potential
along with excellent aerodynamic performance. Utilizing a specialized flow arrangement with a
supplemental fluid shield, this new design will potentially allow for major improvements in the
future of commercial supersonic flight.
Introduction:
In late 2003 the last commercial supersonic passenger jet, the “Aérospatiale-BAC Concorde,”
was retired from service due in part to a dwindling economic interest and the ceaseless
complaints of noise pollution [1]. However, recent developments in advanced flow design tools
have allowed for a influx in development by NASA and industry. This research is primarily aimed
at creating a new supersonic passenger jets with specialized nozzles that will produce minimal
noise pollution, improve fuel efficiency, and as a result be more economically feasible [2]. Initial
developments in this field have been greatly aided with advancements in computational fluid
dynamics (CFD) for complex flow interaction. This allows for detailed modeling of the flow
through the aircrafts engine inlet flow and exhaust systems. As a result of these developments
GE Aviation has developed the inverted velocity-profile nozzle, a key component for the new
supersonic passenger jet project.
Methods:
One of the primary developments spawned from the advancements in CFD is the development
of the Adaptive Versatile Engine Technology (ADVENT) program by the Pentagon’s research
project, the Versatile Affordable Advanced Turbine Engines (Vaate). The primary result of this
project is new high efficient and adaptive jet engines that can vary airflow throughout the
different flow paths in the engine [3]. Traditionally, most jet engines have two flows, a hot inner
core and a cooler bypass. With the ADVENT engine, however, a new cool third stream flow has
been introduced. This allows for, among other things, a stream dedicated to noise reduction, a
feature well used by the inverted velocity profile nozzle.
In prospective normal operation, this new nozzle has an unorthodox method for the
arrangement of the two main stream flows. After passing through the engines and entering the
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3. nozzle, the cooler slower inner flow is directed through the center of the output flow whilst the
fast main hot flow is routed around the outside, this is opposite of traditional jet engines. Noise
from a jet engine is typically caused by faster exhaust violently shearing with slower ambient air
[4], hence this method seems counter-intuitive. However the placement of the fast hot flows on
the outside allows for faster mixing of the air resulting in a quick reduction of peak velocity. The
quicker shear time caused by the initial violent mixing causes an increase in high frequency
noise, but a reduction in the principal low frequency noise. This low frequency noise results in
the “rumbling” sound of typical commuting aircraft, a common public complaint.[5]
Fig 1. Prototype drawing of ADVENT engine showing stream routes and nozzle placement (circa 2007)
(Note: Figure shown for visualization purposes, does not show current design layout) [6].
To reduce the new high frequency noise, a fluid shield, which is a thin layer of flow underneath
the engine, was implemented with the design of the nozzle [7]. This fluid shield works by
offsetting some of the flow provided by the ADVENTs third stream, and directing it underneath
the output stream to reflect the high frequency noise caused by the initial inversion of the two
main flows. This development has many useful properties; one being that the fluid shields
position can be adjusted to direct the reflected noise. This allows for sideways noise reduction
at the airport and ground noise reduction when the aircraft is in aerial operation. An added
advantage of the fluid shield is that the flow can be toggled on, for noise sensitive areas, and off
in other areas, to reduce the losses caused by the changed direction of flow.
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4. Fig 2. Fluid shield vent design and placement on a previous generation jet engine (Circa 2005) [8].
Results:
The current results of the new inverted velocity-profile nozzle have been positive. Tests have
shown that the new nozzle has significant acoustic benefits, along with having excellent
aerodynamic performance. However, most of the numerical statistics of the nozzle itself are not
available to the public as of yet.
However, since the fluid shield has had the benefit of previous years or research, numerical
stats are available. The potential acoustic suppression of an engine equipped with a fluid shield
has been in the range of 4 to 8 effective perceived noise dB [9].
Conclusion:
The inverted velocity-profile nozzle has many valuable features that can be potentially utilized in
the future of supersonic air travel. It has a unique inverted flow design that allows for a major
cutback in low frequency noise, leaving only high frequency noise. This noise is then reflected
towards a less sound sensitive area via a thin fluid shield generated by the third stream in
ADVENTs new engine design. The active nature of the fluid shield allows for greater acoustic
flexibility in flight and on the tarmac. Overall, the further development and refinement of this
nozzle will be an asset that will pave the way for quieter, more efficient, and economical
supersonic travel.
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5. References:
[1] Robert M Allen, “Legal and Enviromental Ramifications of the Concorde”. Available from:
http://heinonline.org/HOL/LandingPage?collection=journals&handle=hein.journals/jalc42&div=2
8&id=&page= (Accessed on June18, 2012).
[2] Main stem article: Guy Norris, Graham Warwick, “NASA Focuses Supersonic Effort On Low-
Boom Propulsion”. Available from: http://www.aviationweek.com/Article.aspx?id=/article-
xml/AW_06_04_2012_p50-461842.xml&p=4(Accessed on June16, 2012).
[3] Unknown, “The ADVENT of a Better Jet Engine?” Available from:
http://www.defenseindustrydaily.com/the-advent-of-a-better-jet-engine-03623/ (Accessed on
June18, 2012).
[4] Ilan Kroo and Juan Alonso, “Noise”. Available from:
http://adg.stanford.edu/aa241/noise/noise.html (Accessed on June18, 2012).
[5] D. J. Bodony and S.K. Lele, Low frequency sound sources in high-speed turbulent jets.
Available from http://ctr.stanford.edu/ResBriefs06/23_bodony.pdf (Accessed June 27,2012).
[6] Bill Sweetman, Aviation Week article on B-2 engine improvements. Available from:
http://aviationweek.typepad.com/ares/2007/05/baby_b2.html (Accessed on June 27, 2012).
[7] Rudolph A. Mangiarotty , “Controlling jet noise with a fluid shield”. Available from:
http://asadl.org/jasa/resource/1/jasman/v69/iS1/pS117_s4?bypassSSO=1 (Accessed on
June18, 2012).
[8] Salikuddin, M.; Mengle, V. G.; Shin, H. W.; Majjigi, R. K., “Acoustic and Aero-Mixing
Experimental Results for Fluid Shield Scale Model Nozzles”. Page 16 Available from:
http://ntrs.nasa.gov/search.jsp?R=20050080678 (Accessed on June19, 2012).
[9] Salikuddin, M.; Mengle, V. G.; Shin, H. W.; Majjigi, R. K., “Acoustic and Aero-Mixing
Experimental Results for Fluid Shield Scale Model Nozzles”. Page 507, 6., Available from:
http://ntrs.nasa.gov/search.jsp?R=20050080678 (Accessed on June19, 2012).
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