Technical Report on NASA's Mixer-ejector nozzle concept

1. Mixer-Ejector Nozzle Advancements
By: Peter Derks
2nd Year Mechanical Engineering Student Co-op
June 20, 2012

2. Peter Derks Mixer-Ejector Nozzle Advancements 1
1.Abstract
Low sonic boom propulsion will allow for supersonic commercial flight over residential areas.
The current constraints are due to FAA regulations which restrict stage 3 flight, meaning flight
with a noise levelunder 104EPNdB (Effective perceived noise level) [1]. Lockheed Martin in
association with Rolls Royce and NASA has designed a mixer-ejector nozzle to allow for a great
deal of noise reduction without sacrificing performance, which up until nowwas mutually
exclusive. The nozzle operates by mixing ambient atmospheric air with high velocity core flow
from the engine.This is done by using a two stage suppressor that brings in ambient air through
arcuate gaps and lobes. The result is a velocity profile capable of reducing noise levels up to22
EPNdB below FAA regulations [2]. This means a functional low sonic boom jet could be
commercially available as early as 2022 [3].
2. Introduction
The key to commercially available supersonic flight is noise reduction and creation of low sonic
boom airliners. The obvious advantage of supersonic flight is to rapidly transport passengers.
The drawback is the high decibel sonic boom generated over residential areas, which must be
less than 104EPNdB for stage 3 flight with 3 engines [1], according to Federal Aviation
Administration (FAA) regulations. A solution is to modify the velocity profile resulting from the
exhaust of traditional variable-cycle engines (typical supersonic jet engine, i.e. Rolls Royce
Liberty Works) by altering the design of the nozzle at the nacelle’s rear end (aerodynamic
casing for engines and gearbox). Originally high performance and low sonic boom propulsion
were mutually exclusive [2]. Lockheed Martin in partnership with NASA has performed noise
level tests on two concepts, the GE Aviation inverted velocity-profile Nozzle and the Rolls Royce
mixer-ejector nozzle; which is the nozzle discussed in
this report. New advancement in computation fluid
dynamics (CFD) has allowed for accurate wind tunnel
tests, showing noise reduction of scaled models [2].
The mixer-ejector nozzle is part of the Liberty Works
engine and limits shear velocity generated between
ambient air and exhaust streams while maintaining
supersonic flight. The purpose of this report is to
examine the operation of the mixer-ejector nozzle.
3. Theory
Mixer-ejector nozzlesutilize the multi-stage mixer-
ejector suppressor concept. Typical flow
around/through the nacelle of the jet consists of core
flow through the centre of the engine, bypass flow
which is internal flow that bypasses the engine, ejector Figure 1: Two stage suppressor nozzle
highlighting divergent/convergent lobes [4]

3. Peter Derks Mixer-Ejector Nozzle Advancements
2
flow through the nozzle, and outer third stream flow. Suppressors mix the core flow from the
variable-cycle engine and ambient atmospheric air. This is done by using a lobed mixer with
divergent and convergent lobes known as curved stator vanes as shown in figure 1(22, 24).The
Two Stage Mixer-Ejector Concept (TSMEC) consists of two stator vane segments, which are
aligned to complement each other and maximize airflow mixing. Between the stages are arcuate
gaps that allow air flow to enter the suppressor [4]. In the Rolls Royce model, ejector doors on
the exterior of the nacelle allow for slow stream ambient air to enter the nozzle and mix with the
high velocity jet exhaust (core stream). These doors pivot between 5˚-15˚, while diverter flaps
on the interior of the nozzle pivot from 8˚-12˚ [2]. Diverter flaps are used to allow outer streams
of air to enter the main flow during take-off. When the jet is at cruise speed, the doors and flaps
are closed. The subsequent mixing allow for a unique velocity profile, minimizing noise.
4. Methods
Testing at NASA Glenn's Aero-Acoustic Propulsion Laboratory showed how the use of the
mixer-ejector suppressor leads to noise reduction to within FAA regulations.Tests were carriedat
take-off speeds (Mach 0.3), using convergent door and divergent flaps at various angles.The
results from testsproved the mixing of ambient air with core main flow would result innoticeable
noise reduction. Flow distributed between core flow, bypass flow, ejector flow and third stream
flow at 15%, 58% 18%, 9%, respectively [2]. The
resulting velocity profile gave a noise reduction
within the 104EPNdB for stage 3 flight with 3
engines, by surpassing it by 22 EPNdB [2].
5. Results and Discussion
The nozzle was effective at reducing noise limits
below FAA regulations for supersonic jets as
predicted, meaning the mixer-ejector nozzle is
suitable for commercial use on the N+1 jet, as
shown in figure 2. Another 1-1.5 dB may be Figure 2: Lockheed Martin low sonic boom jet concept [1]
reduced further by eliminating high frequency
tones caused by the 9% third stream flow [3]. The next task is to reduce noise level to 30
EPNdB below Stage 3 noise levels, to allow the supersonic jets to operate at commercial
airports. Other requirements that need to be met by the jet are less than 5 grams NOx/Kg fuel
emission at cruise speed and fuel consumption between 3.5-4.5 passengers miles/pounds fuel.
[5]. If these criteria were met, itmean low sonic boom propulsion may be available as early as
2022 [3].

4. Peter Derks Mixer-Ejector Nozzle Advancements 3
6. Conclusion
The mixer-ejector nozzle is designed to act as a two stage suppressor and allow for ambient air
to be mixed with core flow from the variable-cycle engine; resulting in an altered velocity profile.
From tests done at NASA Glenn’s Laboratory, the resulting flow reduced noise levels by up to
22 EPNdB below FAA regulations. The Rolls Royce Liberty Works engine combined with the
mixer-ejector nozzle have shown great promise in low boom sonic propulsion.
7. References
[1]. Electronic Code of Federal Regulations. “Noise Standard: Aircraft Type and Airworthiness
Certification.” Internet: http://ecfr.gpoaccess.gov/cgi/t/text/text-
idx?c=ecfr;sid=c24987ac17489454f64a368b36db2909;rgn=div5;view=text;node=14%3A1.0.1.3.
19;idno=14;cc=ecfr June 19, 2012 [June 19, 2012].
[2. G. Norris and G. Warwick. (2012, June). “NASA Focuses Supersonic Effort on Low Boom
Propulsion.” Aviation Week and Space Technology. [On-line]
Available:http://www.aviationweek.com/Article.aspx?id=/article-xml/AW_06_04_2012_p50-
461842.xml&p=4# [June 18, 2012].
[3].J. Banke. “Sonic Boom Heads for a Thump.” Internet:
http://www.nasa.gov/topics/aeronautics/features/sonic_boom_thump.htmlMay 8, 2012 [June 16,
2012].
[4]. W.M. Presz, Jr. “Two Stage Mixer-Ejector Suppressor.” US Patent 5 761 900, June 9, 1998.
[5]. J.J. Alonso and M.R. Colonno. (2011, Nov. 2). Multidisciplinary Optimization with
Applications to Sonic-Boom Minimization. [On-line]. Vol 44. Available:
http://www.annualreviews.org.login.ezproxy.library.ualberta.ca/doi/full/10.1146/annurev-fluid-
120710-101133 [June 18, 2012].