.:. .....
NASA Technical Memo_a:,dum 81470
'_ ANIMPROVEDPREDICTIONMETHOD
il FORTHENOISEGENERATEDIN
._ FLIGHTBYCIRCULARJETS l
.:.. (NASA-_,_-alq701 AN I_P_OVBD _REDICT_ON Nd0-22048
, ._ RETHOD £CR _E _OISE GB_ERATED IN FLIGH_ BX
CIRCULAR OET_ (_AS&) 33 _ liC A03_BF A01
r_ CSCL 20& Uncla_
_.. G3/71 qbSJ4
"j
James R. Stoneand FrancisJ. Monteganl
_' Lewis Research Center
:':_ _. Cleveland, Ohio
!.
!i i
l.! Prepared for' the _,l_; _ "_._'.,._ _"'..
' Ninety-ninth _,ieettngof the Acoustical Society of America i;,
_: Atlanta, Georgia, April 21-25, 198,9 l_: "%. _.
F
=_
1980013561
_.
: AN IMI_ROVEDPRED|CTION M_"FHODFOR THI_ N_ISE
'" GEN_RATED IN FLIGHT BY CIRCULAR JETS
by Jm_cs R. Stone and Francis J. Montcgani
[ .. National Aerommtics and 8paco Admhtistrat/ofl
Lewis Resear0h Center
Cleveland, Ohio 44135
I.
ABSTRACT
A son, t-empirical model for predicting the noise genor_lted by Jets ex-
haust/rig from titular nozzles is presented and compared with small-scale
static and simulated-flight data. The present method is an updated version of
; thllt part of the original NASA Aircraft Noise Predlctibh 1)rogranl (1974) rela-
ting to circular jet noise. The earlier method has been shown tOagree reason-
ably well with experimental static and flight data for Jet velocities up to ~520
" " m/see. The poorer agreement at higher jet velocities appeared to be due pri-
marily to the manner in whlvh supersonic convection effects wore formuhtted.
' The purely empirical supersonic convection formulation is replaced in the pre-
.- sent method by one based on theoretical considerations. Other improvements
of an empirical nature have been included based on model-jet/free-Jet simula-
• ted-flight tests. The effects of nozzle size, Jet velocity, jet temperature, and
l_'_ flight arc included.
. INTRODUCTION
i. Accurate noise prediction methods are now required-in order to predict
the environmental impact of airport operations on tee surrounding communi-
ties, as well as for the realistic design of new aircraft and the development of
noise reducing modifications to existing aircraft. The prediction method pre-
:: sented herein is an updated, more theoretically rinsed, version of that part of
the original NASA Aircraft Noise Prediction Program pertaining to circular
nozzles (ref. 1). This paper deals only with the noise generated by the ex-
hans! Jet mixing with the surrounding air and does not consider other noises
emanating from the engine such as narrow-band shock screech or internally-
generated noises.
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1980013561-TSA03
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': Al_mug_ the numereue aspects of.the mechanisms of Jet noise generation
ii are not fully understo_.the neoessity of pred!ot_ng J_ aoiseIres-ledtothede_ ,_Zt
" ve!opment of empt_cea proeedures. •The NASa interim _ediotlon method fo_
Jet norse {ref, 1) and an updated S0oisty_f ,4amzno£ive E_ineers (SA.E)metlmd-
.'- -- (ref, 2) are in m_rrenr_use, The SA]_ method shows reasonable alpmementwlth I
_:.. static experlment_ de[e, for jet veloo/t_es ep to about 8'/0 m/see., The-Ur, lksr
'.. NASA method (ref, I)-showsl _uonable agremnent._Vlth both _ and
. data at Jet-velocltles up to about 520 m/seo, HOwever, at higher velocities-
:' and at locations near the Jet axis (kngles _eate_ than about 1_0Owith respect
• to the inlet) the noise is overprectloted. The poo=e_ _reement at hiSh. Jet vel-
_"" ocities appeared to be due primarily tothe mannel' in whioli supersonic oon-
veotion effects were formulated, The htgltly empirical supersonic convection
formulstion _f reference 1 is replaced by one (ref. 3} based o_ theoretical" con-
slderations (_efs. 4 and 5). With these ohsages, the method presented herein
agreeg fairly well with the SAE method (ref. 2) under static conditions. The
same rel'sflonsIttpe are then used to pl_edict the noise in fligltt, in-oo,_l_ast to
• the SAE method, which uses a pureLy em_-ical approach for _ effects.
For mapersonio Jets not fully expanded'to ambient p_essure, sh6ok/turbu-
lent4 interaction noise must also be ootmldered. The purely empirical, shook
noise procedure of referenoe lie rel_ced hi the ourrent metiz3d by a semi-
.: empix4cal model based largely on the theory of Harper'Bourne and Fisher
:. (ref. e).
. SYM]_LS
(All symbols are in SI unJ.Lsunless noted.)
,a area
o speed of sound
D nozzle diameter
F functional relatio_ (eq. (i3))
f 1/3-oe_ave-hend center f_equency
I acoustic lz_msity
KI coefficient in equation (t)
k ratio of conVection velocity to Jet velooity
I charaeteristic length
M Math number, V/c
-T,
I:_""
- :!
,° ,_
. r_ convection factor exponent
.o
':" ' OASPL overatl sound pressure level, dB re 20 _/m 2
.: OASPL t predicted OASPL uncorrected for refraction, dB re 20/_N/m 2
:'_ p- presstire
I" : Pref roferenoe pressure, 20/JN/m l
. p mean-square acoustl_ pressure fluctuation
,I
R source-to-observer distance
• S -- effective Strouhal number (eq. (12))
SPL 1/3-0otave-band sound pressure level, dBre 20 _N/m 2
T total temperature
V velocity
t
X source position downstream of nozzle exit plane ('i
a turbulent length scale ratio
p effective angle of attack (fig. 1), deg 'i
A fl/ght level relative to static, dB
p density
0 polar .angle from inlet &x/s (fig. 1), deg
0' effective polar angle, 0(Vj/Ca)0" 1, deg
l.. OM Mach angle, sin-l(1/Mj), deg
oJ density exponent (eq. (4))
P..
•:- Subscripts:
f: a ambient or apparc,lt
_. C convection
_'. D dynamic
•.,-;.
e effective
; F flight
O
ISA international stm_ard atmosphere (288 K and 101. IIkN/m")
_. J folly-expanded jet
,.,% •
"....... -" "'" 1980013561-TSA05
!-'- 4
I_V'"
s ,t, io
_" - SO source alteration
m
" s shOck noi_e
¢ ." ....
:'" 90 ° parameter evaluated at O'= 90 °
0 aircraft
: FORMULATION OF PROCEDURE
The noise levels predicted are free-field _no reflections), far-fbeld and
lossless (1. e., the eff_sc_ of atmospheric-absorption are not included). The
geometric variables describing _ position of the observer relative to the en-
gtne are shOwn schematically in figtwe 1. The Jet mixing noise and shocknol'se
are assumed to by symmetric about the Jet axis. The results of the prediction
procedure are expressed in terms of S_L spectz.a at each an_le of interest.
(Acoustic power relations are not given explicitly, but power computations may
be nwtde by integrating the results numerically over all angles.)"
The prediction is first developed for shock-free Jet mixing noise with no
flight effects. Then, the effects of flight are considered, and static-to-flight
increments established. Finally, supersonic Jet shock noise effects (static and
flight) are incorporated into the prediction procedure.
Experimental aoise measurements are often made at a distance far enough
from the sources to be in the acoustic far field of each individual source, but
not far enough away to treat the entire Jet plume as a poi_lt source at the center
of the nozzle exit plane. When such is tlie case, comparisons between e._q_eri-
mental data and prediction must take source locations into account. The meth-
ods used to approximate these.sourc_e location effects are given in appendl× A.
Static Jet Mixing Noise
Lighthill's theoretical studies (refs. 7 and 8) established that the ncoustic
- 2
intensity of a shock-free Jet varies with pV_lca5jl . If the characteristic dimen-
sion m is taken to be the square root of the fully-cxp:mded Jet area Aj, the in-
tensity I at a distnnce R from the source would be given at 0 = 90 ° by
' ' 1980013561-TSA06