Page 46 - Winter Issue 2018
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Fl-am Sputnik no Spacex
ing a model-scale static-fire test (Gely et al., 2000). However, the engines come to full power (see Figure 5, c, d and e), it
the first time a ground-based beamforming experiment was may prove to be a significant source of launch noise. Thus,
conducted during an actual launch was not until the 2013 recent work focuses on applying results obtained previously
launch of Orbital ATK Antares rocket from the NASA Wal- concerning turbulent Coanda jet flows (Lubert, 2008, 2017)
lops Flight Facility in Virginia (Panda et al., 2013). Results to modeling the noise generated within this deflector.
from these experiments provided unprecedented and unex-
pected insights into rocket launch noise sources (see Figure The Future
5). In contrast to previous static-fire tests, they indicate that EXPehdah1e lauheh Vehicles have heeh used in the Vast me‘
the primary noise source changes with time and that the j°rhY 0f the aPPr°Xhhate1Y 5-700 iahheh attemPt5 Sihee
source distribution is actually very different from the tradi- SP11thik~ NOW. h0W€V€I3 the trend i5 1:01‘ 1611581716 I‘0Ck€'ES
tional model assumption of the plume as the primary noise (K103: 2017)- Indeed: the U5 Ail‘ F0156 and NASA) the ‘(W0
Source throughout launch (Eldred and Ionest 1971). biggest customers for US launch services, both predict using
. _ _ reusable rockets in the near future. For example, SpaceX’s
Figure 5’ left’ shews the souhd seuiees’ with hghtei e°i°is Falcon 9 rocket is designed to have a recoverable and reus-
ihuieutihg higher h°ise ieveis’ as idehtihed by the heath" able first stage. See]q9EjT for the historic first land-
forming experiments. Figure 5, right, shows selected frames ing of a Falcon 9 first Stage on December 21) 2015. Much
from it high‘sPeeti etuheia ahd are eouttesy tit the NASA of this effort is cost driven because typically about 70% of
KSC iihagihg group‘ Fiuih Figure 5’ u uhu h’ it is eietu that the cost of the rocket is related to the first stage. It should
uuiihg ihititu ehgihe ighitiuh’ the Piiihiity huise suuiee be noted that this is not the first attempt at reusability. The
(le-ft’ bright yeuuw/white Wehsi was the iauheh iheuht ahu Space Shuttle (see had reusable parts,
its aeeuihpahyihg giuuhu teheeti°h' Howevei’ uhee the eh" the three main engines, which were removed between flights
gihes eoihe t° tuu Puwei uutihg h°iu'u°wh’ the hut exhaust for extensive checking. This process was expensive and took
Piuihe exits the ueheetoi ahd the FD exit heeoihes the Pii' several months, whereas SpaceX’s current goal is to go from
ihaiy soutee (see Figure 5’ e ahd ti)‘ This eiteet is mitigated recovery to relaunch in 24 hours. However, as yet very little
to some uegiee by the duet wateh The TEL theh ieiesses the is known about how the launch acoustics change when reus-
iuuheh vehieie uhu Pitehes away from it White the iuuheh ing hardware or how the vibroacoustics might potentially be
vehicle simultaneously fires at a slight angle to the vertical more damaging to hardware that has already been used and
away from it. This so-called “TEL avoidance maneuver” structurally Stresseth
causes the hot exhaust plume to spill out from the FD inlet _ _ ’
and Spread across the launch Pad) causing a large area on Finally, rockets are getting larger and louder.tNASAs latest
the surface of the pad to become a loud, distributed acous- meket’ the SL8 (See g°‘heSe'g°v{23eeV9K)’ wih he the thest
tie Source’ in addition to the FD exit (See Figure 5, e and powerful they have ever built, with 20% more thrust at liftoff
f). Thus, contrary to assumptions made in many traditional theh the Sathrh V‘ That is’ at hheth the SL5 wih geherete
rocket noise models, it is not until the plume finally emerges more theh 30 thhes the total ththsttpmdheedhy e 747 hue
fully from the duct (see Figure 5, g and h) that it becomes Piehei Sueh extremely high flhethehhg eeoushe toads are a
the primary noise Source. principal source of structural vibration, and this vibroacous-
tic interaction critically affects the correct operation of the
These data indicate that, contrary to the traditional model rocket and its environs, including the vehicle components
assumptions, a thorough understanding of the changes in and supporting structures. Even relatively small reductions
acoustic source location with launch phase (time) is of fun- in the rocket launch noise level can result in substantial sav-
damental importance in accurate launch noise modeling. ings by reducing unexpected repairs, operating costs, and
For example, within the Antares flame trench, the Coanda system failures. These benefits are spurring the develop-
effect is present. In the Coanda effect, a jet of fluid passing ment of novel and effective acoustic suppression methods,
over a curved (Coanda) surface bends to follow that surface, new experimental data-gathering techniques such as acous-
simultaneously entraining large amounts of air as it does so. tic beamforming, and a plethora of mathematical modeling
Because this flame deflector is the primary noise source as tools aimed at accurate noise prediction.
44 | Acnustics Thday | Winter 2018

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