D FVL RIFAAPropeller Noise Tests in theGerman-Dutch Wind Tunnel DNWExecutive Data Report OFVLR-IB 129-86/3

FAA Report No. AEE 86-3

4.- ve

jointly conducted by: - .itsve

- by Werner M. DobrzynskiI__ Hanno H. Heller

... ftS Eeotmn DetceLrcugn E C 1T ~ John 0. PowersLDEC 1j Deatmn 1986 n James E Densmore

of Transportajtion Versuchsanstalt fur 3E -01.

FdlAmiaton utudRmfh eVAdirinistaton Lutudufhte

Office of Environment Inst fur Entwurfsaerodynamik Aand Energy Atiteilung Technische Akustik

86 12 09 097

% N %p

DATA REPORT ON PROPELLER NOISE TESTS

1N THE GERMIAN-DUTCH WIND TUNNEL

4.

EXECUTIVE DATA REPORT

by

W. Dobrzynski*, H. Heller*and

J. Powers**, J. Densmore**

*DYVLR, Flughafen, 3300 Braunschwelg, W.-Germany

*FAA, 800 Independence Ave., S.W., Washington, D.C. 20591, USA

,.'7

Table of Content

Page

Symbols ..................................................... 5

1. Introduction ............................................. 7

2. Test Set-up .............................................. 82.1 Drive System ......................................... 82.2 Test-rig Installation ................................ 92.3 Test Propellers ...................................... 92.4 In-flow Microphone Arrangement .......................... 10

3. Acoustic Quality of Test Set-up ............................. 11

4. Data Acquisition ......................................... 13

4.1 Propeller Operational Data............................134.2 Wind Tunnel Data ..................................... 154.3 Acoustic Data ........................................ 15

5. Test Matrix .............................................. 16

6. Data Reduction ........................................... 176.1 Operational Data Processing ............................. 176.2 Acoustic Data Analysis ............................... 19

6.2.1 Quick-look Data ... ............................. 196.2.2 Energy Averaged Spectra.........................206.2.3 Enhanced Acoustic Wave Forms and Spectra ....... 21

7. Documentation of Test-data ............................... 24

8. Summary .................................................. 26

Acknowledgement ............................................. 26

°<.4.

'.' -,-

3

-- -m. - :, . . 4 . . - -' : L _ j ' -. . -: - , C' .,

Symbols

c m/s Speed of sound

PPC - Power coefficient

cT - Thrust coefficient

D m Propeller diameter

DF Hz Analysing frequency bandwidth F

F - Disturbance factor ..

L dB Pressure levelp ,I

M - Helical blade-tip Mach-numberH

n rpm Rotational speed

p Pa Absolute pressure

P Watt Power r -

T K Flow temperature

T F N Thrust

U m/s Propeller blade-tip rotational velocity

V m/s Axial flow velocity

% deg Apparent angle of attack (at 75% station)

deg Blade pitch angle (at 75% station)

A - Advance ratio (conforms to: J = 1 ) -

deg Attitude angle

kg/m3 Air density

' deg Blade azimuthal angle

V.

% '

'.F .-

1. Introduction

Within a joint effort; (and supported by the German Ministry of

Research and Technology/BMFT) between the Deutsche Forschungs-

und Versuchsanstalt fir Luft- und Raumfahrt (DFVLR), the US

Federal Aviation Administration (FAA), and the German Ministry

of Transportation (BMV), propeller noise tests were conducted in

the "Deutsch-Niederldndischer Windkanal/German Dutch Wind Tunnel

(DNW)"tto develop high quality propeller-acoustics data, which

could be used by manufacturers for acoustic design purposes, and

by researchers to validate established or newly developed theo-

retical noise prediction methods.

Specifically, the program addressed propeller Mach number and

disc;plane attitude effects as related to noise certification

test and evaluation procedures. Changes in Mach-number, as they

* affect acoustic data adjustments, were explored through indepen-

dent variation of tunnel flow velocity, propeller rotational

speed and ambient air temperature. The tests on the effect of

inflow angle on propeller noise also incorporated the influence

of a typical engine nacelle on the flow field and, hence, on the

propeller noise.

In this 4-!-cti-ve") report, acoustic and operational data-ac-

quisition and -reduction procedures are described. Only a selec-

tion of typical test results is presented, in order to illus-

trate the acoustic analysisktechniques. A complete collection of

as-measured noise data in terms of pressure-time-histories and

narrow-band spectra is documented in 6 Appendices to this re-

port, together with supplementary information necessary for fur-

ther data interpretation.

As a compliment to the propeller wind tunnel noise tests, the

FAA conducted comprehensive noise flight tests with the same mo-

del propeller as the "round-tip" propeller used in the wind tun-

nel. The test airplane also had the same engine cowling design

as that used in part of the wind tunnel tests. The flight tests,

conducted on September 25, 1984, encompassed a wide range of

7

acoustically-related parameters available within the a! piane

operating limitations. The results are being documentped' in a se-

parate report.

2. Test Set-up

Figs. 1 and 2 Drovide an overview of the set-up with the in-flow

microphone array and the drive system installed in the DNW8x6 M 2 open test section, approximately halfway between the

nozzle and the collector. The drive system is located 1.6 m to

the side of the tunnel axis to allow both the propeller and the

microphones to operate in the (low turbulence intensity) tunnel

coreflow region. This results in a distance between the propel-

ler axis and the ("reference") microphone (located in the plane

of rotation) of 4 m, corresponding to two propeller diameters.

Tests on the effect of engine-cowling installation on propeller

noise radiation were performed with a full-scale Piper Saratoga

engine-cowling. The installation of this cowling on the - other-

wise aerodynamcally clean - drive-unit is shown in Fig. 3.

2.1 Drive System

The drive-unit consists of two DC-electric motors (ir. tandem

arrangement) with a maximum combined power output of 360 k% -L a

rotational speed of 3000 rpm. The motors are cooled by externa'-

ly supplied air which is fed into the drive-unit through the

support pylon and emanates into the tunnel flow at the aft end

of the drive-unit nacelle. To avoid mechanically and aerodyna-

mically generated motor-noise ra',A.l :on into the farfield, the

interior surfaces of the (aerodynamically shaped) nacelle are

covered with sound-absorbtive material. The maximum nacelle

diameter is 0.' m. The 0.5 m diameter suoport pylon is located

2.6 m downstream of the propeller disc-pla.,.

8 -

I '.. -.- '.'- . .'.. .-. -'.'."." - -'' " -" " '" ' -. " ' """ -"v .' ''''''?- . . . . , q ' '

2.2 Test-rig Installation

The drive-system and the in-flow microphone support were aligned

in the flow direction by optical means (Theodolite). Angular de-

viations of the mean flow were within 0.2 degrees of the propel-

ler and the microphone axes. The horizontal distance of the pro-

peller axis to the reference in-flow microphone (located in the

plane of rotation) was held to 4 m with an accuracy of 0.01 m.

To establish different propeller disc-plane attitude angles re-

lative to the tunnel mean-flow direction, the drive system sup-

port was moved (on air-cushions) relative to a ground-fixed cen-

ter of rotation located directly underneath the propeller cen-

ter. By means of additional ground-fixed mechanical devices, any

predefined attitude angle could be exactly positioned. The actu-

al values of propeller disc-plane attitude angles, as realized

during th tests were as follows:

S= +7.3; +3.6; 0.0; -3.8 and -7.4 deg.

(the orientation of the angle 4 is defined in Fig. 1).

2.3 Test Propellers

Acoustic data were taken for two different 2-bladed propellers

of 2.03 m diameter each, manufactured by Hartzell (Fig. 4):

Design Tip-shape Rel. Thickness Blade Serial No.at 0.75 Radius

F 8475 D-4 Round 6.4 % F 52972F 52976

F 9684-14 Square 8.5 % F 55004F 55005

For margin of safety considerations, the maximUm power con-

sumption of each propeller had to be limited to approximately

9

250 kW. Propeller-tip geometries as well as the radial ". ri-

butions of rElative blade-thickness, -chord, and -t'. st angle

are shown in Figs. 5, 6 and 7 for both propel1--s. All of the

blade airfoil sections are essentially Clark Y sections.

Blade pitch-stetting was adjusted manually, as based on a cali-

bration-chart provided by Hartzell, giving the relationship

between pitch-angle and number of "turns" on a set-screw. The

pitch-angle sEtting was accurate to within ±0.2 deg.

2.4 In-flow Microphone Arrangement

A total of seven in-flow microphones were positioned in the ho-

rizontal plane at different streamwise locations corresponding

to particular geometric radiation angles from the propeller cen-

ter (Fig. 8). Since for non-zero disc-plane attitude angles, the

sound-radiation field was expected to be unsymmetric, two addi-

tional microphones were positioned in the plane of rotation (4 m

lateral distance to the propeller axis) at angles of ± 30 deg.

respectively agove and below the horizontal plane with reference

to the propeller center.

In order to avoid aerodynamic/acoustic interference zffects, all

microphones located in the horizontal plane were later- ', spac-

ed such that the connecting line between those microphones .;ild

exhibit an ang-e of 10 deg with respect to the mean flow dirt

tion. The indi-idual - aerodynamically shaped - microphone sup-

port struts were both inclined in the streamwise direction and

arranged in a "helical" manner around a streamwise-orientated

main carrier-tibe. This construct. - n concept (Fig. 9) was chosen

to minimize aetodyamic noise generatiun due to wake-strut inter-

actions, and at the same time to avoid acoustic interferences at

the measuring nicrophones due to sound reflections off the strut

surfaces. For the same reason, the main ca rier-tube as well as

the entire bas? structure (two vertically orientated st,.ts),

were aerodynariically shaped and acoustic, ly treated with a

50 mm thick foam cover.

.,

10.... . . . . . I

3. Acoustic Quality of Test Set-up

To determine whether the total set-up as installed in the open

test-section would give rise to any sound reflections which

could adulterate the propeller noise signature "bang-tests" werecarried out.

For this purpose, an explosive charge was attached to the blade-

tip which was ignited and pressure-time histories were obtained

at all microphone positions. These time histories were synchro-

nized with the ignition time and sources of reflections were

identified. This procedure was repeated for different blade azi-

muthal angles within a range of 90 deg 270 degrees under

wind-off conditions.

Typical pressure-time histories are plotted in Figs. 10 and i

for all in-flow microphones. If no reflections occur, then pres-

sure amplitudes are not expected for any point in time after

which the direct incident pressure-pulse (with a positive and

subsequent negative pressure amplitude) has passed the micro-

phone. This ideal situation was however only achieved for parti-

cular combinations of microphone position and location of the

explosive (blade azimuthal angle), such as microphone MP 8 in

Fig. 11, for example. In many other situations weak sound re-

flections were present.

Analysing the respective time-delays, it turned out, that for

microphones MP 5, 6 and 9 in particular, sound waves were re-

flected from the nearby (vertically orientated) microphone sup-

port struts; for microphone MP 7, a reflection occured at the

particular support strut of that microphone (Fig. 10). In the

latter case, however, the reflected amplitude was damped signi-

ficantly by covering this strut with damping material (10 mm

foam)

since the main support struts had already been treated with

damIing material and the pressure level difference between di-

rect incident and reflected sound signals turned out to be at

IC-

r

LII

least 14 dB, no further efforts were expended to furt ;r reduce

sound reflect.ion amplitudes. Later analyses of .- neasured pro-

peller noise signatures however showed, that r--maining reflected

amplitudes were still high enough to adulterate radiated propel-

ler noise to some extent. The example given in Fig. 12 illus-

trates the effect of such sound reflections.

Interpretaticn of measured propeller noise data requires know-

ledge of thE prevailing background-noise-level spectra. Back-

ground noise measurements were therefore conducted at different

tunnel flow-\elocities with the complete test set-up installed

in the test-section. During these measurements the propeller was

removed from the drive unit and replaced by a dummy-spinner.

Represens:ative measurement results are plotted in Fig. 13 in

terms of ("mznually smoothed") narrow-band spectra.* The upper

graph in Fig. 13 provides general information on the influence

of flow-velocity on measured background noise level-spectra for

the microphone? position MP 4 in the plane of rotation. The meas-

ured levels were confirmed to correspond to published background

noise caiibra-ion data.

The dotted line in this graph, corresponding 1-o zero tunnel-

wind-speed, indicates the noise floor as originating from the

drive-unit ruining at 2700 rpm (but for zero power outp, ) and

the cooling a .r unit operating.

In the lower (raph of Fig. 13 background noise levels as measur-

ed at different microphone positions are compared for the same

flow-velocity. Obviously, foL ncst of the microphones (MP 1

A complete original set of background ,i.se data is i-.,1uded

as an attachment to this report.

12

-~~~~~~~~~~~7 -_ - . --SwV ~ -- - -. .. ..- ,.

through 5* and 8) no additional noise contribution originating

from the flow around the microphones' support structures can be

detected. The microphone at MP 9 however suffers from additional"airfame-noise", since it is mounted very close to one of the

extended (vertically orientated) main support struts. For the

measurement point MP 7, a broadband level increase at a frequen-

cy around 2 kHz is observed. Since this particular microphone

is mounted on an extremely long support strut, it is - from the

experience gained during the tests - suspected that microphone

vibrations are the reason for this effect. Indeed, background

noise-levels as measured at this microphone position tend to ex-

hibit unsteady and rather intense level fluctuations with in-

creasing flow-velocity. For this reason, propeller noise signa-

tures as measured at MP 7 are heavily distorted in those cases

when the flow-velocity exceeds a value of about 50 m/s.

4. Data Acquisition

In this chapter information is provided on measurement techni-

ques and respective accuracies of measured operational and

acoustic data.

4.1 Propeller Operational Data

To correlate the acoustic data with propeller operational para-

meters, the drive system was instrumented with various sensors

in order to determine thrust and torque (strain-gauge technique)

as well as rotational speed (pulse generation 512/rev.) and the

* During the measurements the microphone at MP 6 dropped out,

so that no information on this particular sensor is availab-le. However, due to the position of MP 6, it may be safelyassumed, that respective background noise levels should com-pare to those measured at MP 5.

13

p instantaneous azimuthal p: ion of the propeller blar- with

respect to The measuread .:t ic pressure-time signature

(Fig . 14.

The follcwing listin_ irvI: in f)r :!a-ton on sensor-type and

respective meisurement ~ic~, (ieteririned within static ca-

libration, tes-.s:

Physical Sensor Sensor Measurement AccuracyQuantity Maniufacturer Type Range

Thrust Hottinger Ul (two sy- 0-4000 N _,20 NBaldwin stems acting

in a parallelcircuit)

Torque Philips MM S 9372 0-2000 Nm 110 Nm/020

Rotational Hibner OG 9 DN 0-9000 rpm +_1 rpm* Speed

During the te:;t-runs with the propeller installed, the steady-

state thrust Aas superimposed by unsteady compor-nts. Therefore,

both the maxinum and the minimum readings were taken from a di-

gital-voltmeter as analog values and averaged linE,Ai.'j after-

* wards .

J.

From measurement principles (see Fig.14) the experimentally de-

termined thrust values incluide the aerodynamic drag of the spin-

ner . For respective compari-,c-2- with theoretically determined

* thrust data (from the blades alonr' the aerodynamic drag of the

% spinner must be added to measured thrLoIt. To enable such a cor-

rection, the soinner drag was measured in the wind tunnel for a

* wide range of flow-velocities (however u i er static, non-rotat-

ing conditions). The determined drag fo s es are plotted i-

Fig. 15.

Synchronizatioi of -.he azimuthal pr opelIl- -blIade orientation

11

a..: 1................................................7 .-. *

with the acoustic-data recordings was attained by means of a

pulse-generator (1 pulse/revolution), mechanically coupled to

the drive-motor axis. Fig. 16 shows the angular position of the

propeller for the instant in time, when the trigger-pulse is re-

leased.

4.2 Wind Tunnel Data

During testing, all essential operational data such as wind-

speed and -temperature, absolute pressure and relative humidity

in the core-flow, were monitored and a print-out was obtained

for each run.

The measurement accuracy of these data as given by DNW are as

follows:

Velocity: ± ±0.1 %

Temperature: - !0.1 K

Absolute Pressure: , ±0.1 %

Relative Humidity: < ±2.0 %.

4.3 Acoustic Data

In-flow noise signatures were measured by means of nose-cone

protected 1/4" diam. condenser microphones (Briel&Kjaer, Type

4136). The microphone output signals were recorded via a multi-

channel preamplifier system on a 14-channel FM tape-recorder

(Ampex, Type PR 2230) together with the rotational trigger pulseand a time-code signal. The tape speed was set at 15 ips for all

measurements. Gains were adjusted manually by means of oscillos-

cope-type monitors installed in each preamplifier. Gain-factor

settings then were printed out automatically.

Each measuring channel was separately calibrated by recording a

p1istonphon reference-tone of 124 dB at 250 Hz. In addition, the

calibration was cross-checked at the beginning and the end of

15

each day. These cross-checks showed deviations of gener -iy less

than ±0.2 dB from the recorded pistonphon reference--one.N

5. Test Matr x

With respect to the scope of the test-program, the total data-

point matrix consists of five sub-matrices which could be attri-

buted tc the following sub-programs:

1. Basic Test Program

2. Effect of Flow Temperature

3. Effect of Propeller Disc-plane Attitude

4. Effect of Engine-cowling Installation

Within these sub-programs the so-called "Basic Program" contains

the basic data-point matrix. All other sub-programs refer to

particular parts of this basic data-point matrix with an addi-

tional variable (i.e. temperature, attitude-angle, or cowling-

installation) according to the sub-program's name.

The combination of individual operational test-parameters form-

ing the basic data-point matrix was triggered by the intention

to cover the typical operational ranges of General-Aiation air-

craft propellers. Therefore, the data matrix is compjbi.,j of four

individual sEts of data with different pitch-angle set 'ngs.

Each of these data-sets finally combines data-points with ca,

tant advance ratio, tunnel flow-velocity or rotational speed

respectively, at otherwise different operational conditions. For

each pitchset-ing, an additional "zero-power" condition was as-

signed.

To allow for better comparison of noise data from both propel-

lers, the res;ective basic data-point maC-rices contain the iden-tical values -:or flow-velocity and rotati nal speed, but sliqh) -

ly different pitch-angle settings to appr mately achi+-"x equal

power consump,.ion and thrust output.

16

The first measurements indicated that both the power consumption

and the thrust-output of the propellers were about 30% higher

than expected. Due to power limits, as defined by the propellerS manufacturer, data-points combining high rotational speeds and

low tunnel wind speeds therefore had to be reorganized and were

run at appropriately increased wind-speeds.

The actual matrices of all data-points acquired within the test-

period are listed in Tables I to VII.

6. Data Reduction

To thoroughly investigate the influence on propeller noise ra-

diation of flow temperature, propeller disc-plane attitude and

engine-cowling installation , measured noise data from all in-

flow microphones were analysed in terms of sound-pressure time-

histories and narrow-band spectra. Since these data at the same

Lime represent a good basis for many researchers to check the

validity of their individual noise prediction programs, propel-

ler noise signatures are presented 'as measured' together with

corresponding background information (such as operational para-

meters, geometric, and noise environmental data, etc).

6.1 Operational Data Processing

To determine the power- and thrust-coefficients for each data-point, the actual air density , as a function of pressure, tem-

perature and relative humidity, was calculated. A list of these"environmental parameters" is included in Tables I to VII for

all test-runs.

Since the relative humidity turned out to be fairly constant

- exhibiting a mean value of approximately 60% - and does not

have a significant influence on the air density anyway witnin a

range of 40% to 70%, calculations were based on a constant rela-

tive humidity of 60%.

17

For this rezson the density can be determined as a fa,,ction ofpressure anc temperature only and calculated h,- che following

approximation

(1) = 1.2524 + 1.2503 10 5 (p) - 0.0045 (T).

Calculated density values for all test-runs are listed ir TablesI to VIi. The characteristic propeller coefficients are thencalculated o.i the basis of the following equations:

P

(2) cp = 3

TF(3) CT F 2

p( (') D4

60

" Other characteristic parameters, such as advance-ratio and heli-cal tip Mach-number are determined by the following relations:

(4) U T[ D n / 60

(5) v / u

MH U2 + V 2

In addition, the apparent angle of attack for the propellerblade at the 75% station is calculated as

(7) CL = - arc tan (',/ 0.75)

ICorresponding results from Eqs. (2), (P, (5), (6), and (7) arelisted in Tatles I to VII together witf, measured data for each

test-run.

11 8 .

.. ... . ... ...... " ... ... -* - " . f' ",: " m . i " £ " - i .. : .. * . . .. N. N.

6.2 Acoustic Data Analysis

The acoustic data were analyzed in three stages. First, the data

on the analog tapes were processed using a BrUel & Kjaer (B&K)

measuring amplifier to determine quick-look values of the linear

overall sound pressure level (OASPL) and the A-weighted noise

S levels (L A). The second phase consisted of forming an energy

average of the spectra calculated with an FFT-algorithm to de-

termine the average sound-pressure radiation spectrum of all

sources measured by the microphones. The third phase consisted

of an acoustic wave form "enhancement" technique, which provided

spectra free of stochastic disturbances, and also included sup-

pression of propeller broadband noise.

.

%.5

6.2.1 Quick-look Data

The first phase of the acoustic data processing was designed to

provide an early view of the trends of the propeller noise as

measured in the wind tunnel. The tape recordings were processed

using a B&K Type 2636 Measuring Amplifier with a slow time cons-

tant. For the quick-look phase, the typical recorded sample of

60 seconds was divided into 10 samples each for the linear and

A-weighted noise levels. The mean OASPL and LA values were cal-

culated with the variation between the highest and lowest levels

noted as, and identified by, the value R. This value was taken

as an indicator of the quality of the measured noise signals. For

-i the majority of the data, the value of R did not exceed 0.5 dB

with a standard deviation less than 0.2 dB. Conversely, level

differences of R = 7 dB were found for some combinations of mi-

crophone position and high windspeed operating conditions which

resulted in vibrationally-induced disturbances.

fThe quick-look data values were divided into "good" and "dis-

turbed" data. The good data was defined as having a level dif-

ference R less than 1.3 dB together with a standard deviation of

less than 0.4 dB. Higher R values are considered as disturbed

data and are identified with an asterisk. All the data are pre-

19

7.

sented in tabular form in the Appendix reports listed .n Section

7 of the present document.

6.2.2 Energ; Averaged Spectra

For the nex- two phases of the acoustic data analysis the analog

tapes wer2 digitized to facilitate computer analysis. The

l/rev.-trigler pulse was used to start the digitization process

and the sanple rate was set to the 512 pulse/rev.-signal. To

provide a h-gh frequency resolution, four propeller revolutions

in sequence were digitized (Fig. 17). The next revolution was

omitted to provide time for data transfer and storage. The pro-

cess was repeated on the subsequent revolutions until 70 time-

dsequences of 4 revolutions each were digitized. Thus, 280 revol-

-* utions were digitized for each microphone for each test condi-

tion. As a result of the process, both the bandwidth and the up-

per-limiting frequency were a function of the rotational speed.

For the two-blade propellers tested, the bandwidth corresponds

to one-eighth of the blade-passage frequency. To avoid aliasing

effects, a low-pass filter was set at a frequency of 4 kHz.

For each data-point, the first quarter of the ime-sequence was

arbitrarily selected as the acoustic wave form for further ana-

lysis. A representative example is presented in the u1 U r graph

of Fig. 19 ind is labeled "INSTANTANEOUS TIME HISTORY". -hese

time histories were individually examined and where stochab 'c

disturbances were obviously present, that specific time history

was deleted from further data processing. By means of an FFT-

algorithm, sound pressure-lec: I spectra were calculated for the

first revolu-ion (i.e., first qu rLer) of each remaining digi-

tized time-squence set of acoustic pressure- time histories.

These spectri were energy averaged and are presented as the low-

er graph of lig. 19 for each data-point and are labled "AVERAGE

(xx) POWER S ECTRUM". The "xx" in the lhel denotes the n-,,er

of time hist(ries from which individual 'ectra wp . Iculated

and sub:3equently averaged in that part culat spectrum. This

spectrum contains all of the sound-pressur information includ-

20

- ..' ? d.' .. 2. .

ing propeller broadband noise radiation.

6.2.3 Enhanced Acoustic Wave Forms and Spectra

On further evaluation of the data analysis, it was evident that

it would be desirable to remove the unsteady pressure distur-

bances resulting from wind tunnel background noise and vibra-

tional induced noise which were superimposed on a number of the

propeller noise signatures. These stochastic disturbances were

particularly evident at certain microphone positions for several

flow velocities. To accomplish this objective, the DFVLR per-

formed a detailed acoustic data enhancement. Utilizing the repe-

titive character of the acoustic wave form, the data enhancement

methods employed retain the propeller tonal characteristics

while suppressing the random characteristics. The enhancement

method is detailed in the following.

For the data taken when low propeller rotational speeds were

combined with high wind tunnel flow velocities, it is possible

to increase the signal-to-noise ratio by averaging the pressure-

time histories using the i/rev.-trigger pulse. Through this pro-

cess, braodband noise (including propeller broadband noise) and

non-synchronous noise is suppressed due to cancellation effects

and the final pressure-time history contains acoustic informa-

tion from up to 280 propeller revolutions.

Since the propeller operational and environmental conditions in

the wind tunnel are fully controlled and the sound waves propa-

qate in a very low-turbulence flow-field, the rotational propel-

ler noise signature should inherently be very stationary for

each propeller revolution. It seemed reasonable, therefore, to

adopt the smallest peak-to-peak sound pressure amplitude occur-

ring within the large number of time-sequences as a reference

(or undisturbed signal) to define a limiting pressure amplitude

as an indicator of the presence of a stochastic disturbance

and then to delete all data with amplitudes above the limit

(Fig. 18). However, for statistical reasons it is desirable to

21

0 retain at least 50 time-sequences of four revolution, -dch. In

incorpcrating this procedure, it was necessary t- use a "self

adjusting" limiting pressure amplitde differ .nce to obtain a

sufficient number of time-sequences. Therefore, a "disturbance

factor F" was defined as

(8) (Pmax - Pmin ) - F(Pmax - Pmin )Minimum

Numerous aprropriate tests suggested that

F = L.25 (corresponding to a level difference of

20.iog(l.25) = 2 dB)

would be a reasonable value to start the analysis. As a conse-

quence all peak-to-peak pressures within 1.25 of the minimum

were retainEd. If this process resulted in fewer than 50 time-

sequences remaining, the factor F was multiplied by itself toincrease the limit and the selection process repeated. The pro-

cess was repeated as necessary to obtain 50 time-sequences up to

a value of ' f 6. For values of F > 6, none of the time-sequenc-

es were deleted, all of the time-sequences for that data-point

were pressure averaged in the time domain and the respective

data marked with a triple-star (***) to indicate that the data

are heavily distorted. For values of F = 6, tio difference be-

tween the ninimum and limiting peak-to-peak ampl ,des nP in

percent (e.•., AP - 144% corresponds to F4 = 1.25 4 4 minus

lxlOO) is listed on the graph to provide information on th. sag-

nitude of the stochastic disturbances for each data-point. i r

each data-point the number of time history sets of four revolu-

tions used in the analysis is listed.

% Careful inspection of averaged t. L histories showed the sound

pressure amplitudes at the beginning and the end of one revolu-

Stion may not be identical in each case as might be expected from

physical reasoning. This variation cou,,i be caused by low-fre-

quency distL rbances. Therefore the ave iiing of the i-3ustic

wave form was conducted in two steps. F, st thu Lime-sequences,

each containing four revolutions, were p: 'ssure averaged yield-

22.A•-

ing a single averaged time-sequence. Then the resulting four-re-

volution averaged time-sequence was pressure averaged in the

time domain to provide a final averaged time history for one re-

volution. This final pressure-time history contains the informa-

tion from at least 200 propeller revolutions.

Accordingly, for each data-point the upper graph example in

Fig. 20 presents the pressure averaged time history and is

labeled "AVERAGE (xx) TIME HISTORY". The lower graph in Fig. 20

resents the pressure-level spectrum calculated with the FFT-

algorithm from the average time history and is labeled "POWER

SPECTRUM OF AVERAGE TIME HISTORY".

* .esults from the Section 6.2.2 Energy Average Spectra analysis

procedure and thie above described process (to delete disturbed

pressure-time histories) were compared. No decrease in the amp-

litudes of the harmonics could be detected, as one should ex-

pect, if data had been arbitrarily removed at the upper end of a

statistical amplitude distribution.

Three examples of that data re(2uction technique are shown in

Figs. 19 to 24. From the analysis of the noise signature corres-

ponding to data-point AN-3 at microphone MP 4 (Figs. 19 and 20)

it is obvious that sophisticated procedures to enhance the sig-

nal-to-noise ratio are hardly necessary due to the high intensi-

ty of the propeller noise signature. Accordingly, the computer

averages all 70 time-sequences for the lowest disturbance factor

defined (F = 1.25) corresponding to a 25% amplitude variation as

indicated in the graph. However in case of a lower rotational

speed, the time-averaging procedure proves extremely useful, as

can be seen from Fig. 21 and 22. In this case (data- point AN-7,

microphone MP 4) low frequency pressure fluctuations obviously

distort the instantaneous pressure-time history. As a result the

computer needs a higher disturbance factor (F = 2.44 = 144 %)

for averaging at least 50 time-sequences and deletes 6 series in

this mode. The noise signature - as measured at microphone MP 7for the identical test-run (Fig. 23 and 24) - finally turns out

to be completely useless. In comparing the instantaneous pres-

23

, . < - * ,- - . -.. , .. , . ., .- -. ..- ,.-.. .-. .,..-_'.. . .. .. . •, .. ,.

sure-time listory with the averaged one (incorporatino jistur-

bance factor of F = 5.96 496%) the presence of *,umerous and

intense pressure disturbances is obvious. The pectrum as deter-

mined from the averaged time history (Fig. 24) does indeed not

exhibit an periodic noise components.

For every cata-point and microphone position* pressure-time his-

tories (instantaneous and averaged) as well as frequency spectra

as averaged in the frequency domain - and as calculated from theaveraged time history, resp., - are plotted and presented in the

corresoonding Data-Appendix to this report.

In additior, harmonic pressure levels were determined from all

spectra of averaged time histories (under the presupposition of

a 10 dB signal-to-noise ratio) and submitted to the A-weighting

function**. Both linear and A-weighted harmonic levels as well

as the respective overall pressure levels (calculated from the

energy sum of harmonic levels) are listed in the Data-Appendi-

ces. Fig. 23 provides an example of such a listing.

7.Documenta-ion of Test-data

Due to the overwhelming amount of data acquired ..,hin this pro-

peller-noise research program, the total data anal, :nnot be

documented -n one single volume. Accordingly test data . the

different pioblem areas investigated, for two geometricall, iif-

ferent prope±llers, are summarized in separate documents in

following appendices to this report:

* Data fron microphone MP 8 were only ?nalysed for the sub-pro-

gram "Attitude Effect" since otherwiL, no additional inf_- ,a-tion is [rovided.

** A-weighting was applied in terms of d icr ete (/ - ct ave

band) stepwise weighting curve.

24!~~~~~~~~~~................... ... ......................-.........-.....%....... ,?...... .,........ .... -.........

Appendix I : Results from the Basic Test-program

(Propeller 1: Thickness 6.4%, Round Tip-shape)

Appendix II : Results from the Basic Test-program

(Propeller 2: Thickness 8.5%, Square Tip-shape)

Appendix III: Test Results on the Effect of Flow Temperature

Appendix IV : Test Results on the Effect of Propeller Disc-plane

Attitude

(Propeller 1: Thickness 6.4%, Round Tip-shape)

Appendix V : Test Results on the Effect of Propeller Disc-

plane Attitude

(Propeller 2: Thickness 8.5%, Square Tip-shape)

Appendix VI : Test Results on the Effect of Engine-cowling

Installation.

In addition to acoustic data analyses each appendix provides

background information necessary for data interpretation accord-

ing to the following table of contents:

1. Introduction

2. Microphone Array

3. Environmental and Operational Test-data

4. Overall Noise Levels from Direct Analog Analysis

5. Acoustic Pressure-time Histories and Narrow-band Spectra

6. Propeller Rotational Harmonic Noise and Overall Noise Levels

7. Comments on Data-interpretation.

Background noise level spectra applicable for all appendices are

included as an attachment to the executive data report.

For completeness, all measured data have been analysed and are

documented regardless of occasional microphone drop-outs or the

occurrence of external pressure-disturbances which tended to

sometimes completely distort the propeller noise-signature as

has been discussed in Chapter 6.2. Under the heading "Comments

on Data-interpretation" therefore instructions are given on how

to detect data which should be interpreted with care or deleted

completely.

25

' 7. ' " '' ' ' ' . '_

¢.', ." ~~. ,'-. ... •.¢ . . .. ,. . . ,- , . . .. . .

8. Summary

Extensive :oise-tests have been conducted i i the German DutchWind Tunnel (DNW) on two full-scale 2m-diameter General Aviation

aircraft propellers of different geometry, to specifically de-

termine propeller Mach-number, disc-plane attitude and engine-

cowling installation effects as related to noise certification

test- and evaluation procedures. Radiated propeller noise was

measured b an array of in-flow microphones at a lateral dis-

tance Df aLout two propeller-diameters from the propeller axis.

Acoustic data are analysed in terms of pressure-time histories

and narrow-band level spectra. This report describes the data

acquisition and reduction procedure and provides background in-

formation iecessary for individual data interpretation. With

respec: to the different problem areas investigated acoustic

data are documented "as measured" within 6 Data-appendices to

this report together with respective operational and environ-

mental conditions.

Acknowiedgenent

The efforts and the results of this research '"riject could not

have been achieved without the help of numerous :eople inside

and outside of the DFVLR and the FAA. Special thunk_ to the

German Bun'esministerium fur Verkehr, Referat LRl5 "rman

Federal Min..stry of Transportation), Mr. Karl Hierl in par- i-

lar, to the German Bundesministerium fUr Forschung und Technu

logie, Referat 514 (German Federal Ministry of Research and

Technology), Dr. Horst HerL!:'h in particular. Further thanks go

to the excellent and extremeLy ',elpful management and crew of

the German-D)utch Wind Tunnel, Dr. i,>inrich Weyer, Mr. Hans van

Ditzhuizen, and Dr. Edzard Mercker in narticular. The members of

the German ind of the American test-r ws are to be commended

for their -- iterally - tireless effort, during the test- ilod

in the tunn~l.

26

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co 000 000 000 000 C (

I %Ot\ - ~ j '0 0 _r\

Z: C N~ co C' 0 1) O 'Or C'< a O OmN% Dm%

>- w 0 --.r0 -- 0 r\J0.r\ r- m

0 I- N('(' CsJ j LO(~i' \Ji

W \\ - a, Mo-~ --

0-::~ r*c'~-. 0' 00- o 'C\ 0'0

<.J 0

-O -- -1 -J - 0 -- - - - - --~ -) -00-- - - -0---- -- ---

T a o _'O _'0,r \'0 - \ (31,C

O 04

o z> -- ~ r0~ --- -- ' Q) 0l

_r . 0 000 'f0 \ 0010 Z 4-I

a-< I E-4

0 4 -)s

r- 4ZI

c3- c I '0L or - -1 R _ Jz J 4F _r

0n I 0~ NC- '.C'. cj j \ U 0-

LI) C\O C \J'.ONr C7\ O EE-a r rO)-j

- -- r -- -~ .- -

10 c.U E- "I

a.<a2~6M a

--.-- + - -- - - - - - -

1- - -I I- wPVo

Not

* 1;' T --- O

.. n the I .... .. .m O

3 4O

- - -h ' - : -t 7 . - .,

-' Ii \'l< t ,,I /

N p

-I ll

Fig. 1 Sc:hematic Representation of Test-riq Arrangemwent .w._thin the Core-flow Reqime of the DNW 8x6 m2 OpenTest Section

SN

4".

34 -

* .. -. N.--.',. N. . ,.? " ' *.*" .''..' * . '.*.'"*o'.. .' " " ':. ' " '. :"" -': . . ,-" . .-,N,. , . '- " - ,_,. _,- ' ' " ' ,

2-

-t

t

r

.1~

1t~z~

9. 1

I

Fig. 2 Test-rig installed in the DNW Open T K :1w.'t ICE

S.

qt.

-p

S.

S JS

.4

45

5.

C'

C'.

.5:

-S. A)

S%\.*...........t'..V. .%XX

41

Fig. 3 Drive-unit in its Basic Configuraltion(with the Piper-Saratoqa Engine-cowlimik

Fig. 4 The General Aviation Aircraft Propellers ofDifferent Tip-shapes and Thicknesses as Testedin the DNW

. . . ..... ...-...

-075.

Fi.5 Ti-emtr fbthTs-roelr

F3

3 ~~~~~~0.4 _ _ _ _ _ _ _ _ _ _ _

0.35

d. 0.3

0S 0.25

0.2

0.15

0.05

0.2 0.4 060.81

Radial Station e Radius0 Chord re R +t /C C' IwAt 100~

Fig. 6 Radial Distributions of Blade-chord, -thickness-4.. and -twist for the Round-tip Propeller (F8475D-4)

0.5

0.4-

0

83

* - 0.3 %

M8- 300 UpwardsM9 - 300 Downwards

- M2 M3

M 6

-750 -7504150 -200

-40 ,0 Radius 4 m

Plane otRotation

- -i- -Propeller-axis -

Fig. 8 In-flow Microphone Positioning

Fig. 9 Front-view of In-flow Microphone Arrangementin the Open Tunnel Cross Section

39

MP 1 MP 5

V 0 0--

HP 2 M

OP.0

Ln

a:a-

LU

LU

0 -- 0 -

00m

TIME - '

MPD 9Explosive

In -flow

- Microphone_______ 20 2 ms

Fig. 10 "Bang-test" Results for all In-flow MicrophonePositions with the Explosive Charge Fixed at thePropeller Blade-tip (Blade-axis at 90 deg to theHorizontal Plane)

40

-- - - -* ---

MP 1 NP 5

-S-

~MP 2 j MP 60 0- 0

MP23MI¢)-S-

LU

0D

Uf)LU

Ir

-0.

' 20 ms

" "" TIME MP4 MP 9

• Explosive,

'1500

In -flow... :Microphone

'"" 20 ms

TIM - TIME

"Fig. 1 1 "Bang-test" Results for all In-flow Mic"r,)p4i(,noPositions with the Explosive Chariv eix(,,! +Propeller Blade-tip (Blade-axis Jt I __ +______

Horizontal Plane)

44

41

-7 --. . -yW -- . . _. - - -

DATA FLA INT AN-- KI

2: .8 1H: .8088 r): 27,00 rprf v/u: .- 12 V.@ T:279 K

50

an-5 --

LI]

CL. 3.2 ms

150 MEASURED TIME-HISTORY1---- APPROXIMATE "CLEAN"

I TIME-HISTORY--200 - - - ------ - - _ _

120 - ~ -I- ~ - - -

lie MEAS URED HARMONIC LEVELS

ENELP OF"LENI HARMONIC LEVELS

Lf 10 1

GO AIi L!

Fig 12 Eapeo heDtietlEfeto on

Reflections (Mcohn oiinM )oa Mesue Pr re-im Hisor andth

CorrespondingNarrow-band evI_-s[Lct Lu

C ~.':;:42

110 I

d3MP 4 V= 0.0 rn/s100 A f 11.2 Hz 25.8

38.7

90 -... - 51.2

0.0

0 5

-J

> 30r

Ir 20 I

i-" 110U.]

a- dB V 51.2 rn/s MP 1

Z 10 Af 11.2 Hz -- MP 20 ~MP 3

90

MP 7

70

60

500 1 2 3 kHz

FREQUENCY

Fig. 13 "Background Noise" Narrow-band Spectra withPropel ler-blades Rem-,oved as Measured f or Di f ferentTunnel Flow-velocities (Top) and Microphone Po-sitions (Bottom)

43

'S ~~~~~~~'A * -*.rJ>...- 9

%~-- - ~ . r .. , - - -

A SugPP2.tPyLri

* Fig. 14 Schematic Representation of the MeasurementPrinciples for Operational Data

200 -- -1-- T

Spinner Dicmeter d 0 36. mAir-Oens~ty 1185 ky/ms

N

Crag -c, ? Tl'V

150 From Experiment ct 051

100

0

0

0 10 20 30 1.0 50 60 70 m/s 80TUNNEL FLOW-VELOCITY

Fig. 15 Test-results on the Aerodynamic Drag ofthe (Nonrotating) Propeller-spinner

44i

Square -tip Prop. F 55 0014I Rou'nd-tip Prop. F 52976

MPI.

Square -tip Prop. F 55 005Round -tip Prop. F 52 972

4 M

4S.

% Fig. 16 Propeller Azimuthal Position for Trigger-pulse Release (View in Flow-direction)

DIGITIZED TIME-SEOUENCE

Number of Samples:4. 512 2048

Trigger TriggerTrgeTrgrTrgeTrgr1/rev. 1/rev 1rv1rv1rv /e

LS

-S.

wrDt DAt. tO*1l t, 2 ~ t 0 .30 t..4 Kt.56

TIME

Fig. 17 Schematic Representation of the Digitization-procedure Applied to the Analog Data forComputer Analysis

45

...- ---- ... .--

~q.7 -. 77737

do

.4

%

UNDISTURBEDTIME -SEQUE NCE

man

____ 1 Time-Sequence ___

(4. RevolutionsJ

DISTURBEDTIM,~E -~ SEQUENCE

Lp Time -Sequence is

___________________________F =Disturbance Factor

Fig. 18 Selection-criteria to Delete Time-sequenceswith Obvious Pressure-disturbances Prior toSignal-averaging

J.t

46

P,'

IDATA POINT: AN-3 RUN: 65 SP: 4

P: 20.80 MH: .8688 n: 2700 rpm v/u: .242 €: .0" T: 287.9 K

INSTANTANEOUS TIME HISTORY

PMAX= 75.9

50

o_ 0

) -50n

Q_

PM]IN= -154.81

TIME - REV.

20AVERAGE (70) POWER SPECTRUM

20I y10

S@0~

0 10 .20 05U

HA,£rl~IyJ1C NUrE'[R

TIE .RV

0 1 2 KHz

F F,E UL rlL 1

Fig. 19 Example of an Instantaneous Pressure-time Historyand an Averaged Frequency Spectrum as Calculatedfrom all 70 Instantaneous Spectra in Case of aHigh Signal-to-noise Ratio

J 47110..

-

-" . . ""' '' ','* ,''' %" " '' " "" ''= - - , / " .. . 3 ,J. "Q' _'.

- - -,.W '.,. " -, . - .. . . . ... , , - - , % mll,100,,, ,,, i i .~

DATA PO IINT: AN'K P UN:C- J7 N]P:~20.80 [1H: .BGBS n: 27001 rpm v/u: .22 ):*p T: 287.9K

AVE AO 70) T I E H I 'T(PY <A P (25~

50

%CLU

-15

-2C I

-20 ____

cit

70 2%-

CNJ

(fo al]0isatnou iehsoisan h epc i( rqec ;pcrmPc ro

-Jtin OwIw ; a u ) ~i; ib rcrw ()

70 = l 1. 1 n(A a 1 q Si ni - O-i.-(

Ratio-

'I.i

k . . - I _. I. - -

.

DATA PO INT : AN-7 P L ..... }

p: 20.80 MH: .7174 n: "189 rpm. v,(u: .31 ¢: .0 1: 21 .-3 1

INSTANTANEOUS JTIME HISTORY_

IPMAX* 24.8

2O 101*0

10

w

-20 r

-30

-,q0

50PMIN= -43.6

.0 .5 1 .0".

T TI E - .EV.

AVERAGE (64) POWER SPECTRUI "120 I

OF= 9.1 Hz

110 %

IAA.

100

LL)

70

0 20 30

_j 2

Fig. 21 Example of an Instantaneous Pressure-timeHistory and an Averaged Frequency Spectrum

as Calculated from 64 Instantaneous Spectrain Case of a very Poor Signal-to-noise Ratio

49

%•. • . -. -. ., . . , - . . . . . . .--. _%.. . . .I . . ... -. . C,• ,- ' , " ' ,, ,- , ",", . " °,"% -. , ' . , . ",, , .,.C7_. " ,"

. .,*; I-,! . -. -

-DATA POIN T AN-- .I ,> _- .

_I: 20.80 IiD: .7174 n: IF v ' .v31 4: .0 T"

AVEFAGE ( I I 'F f I T I-. , ____ -14_,.

20

10md

-10

'Z -20

Z._-i ~ ~-..

"7 lIE - REV.

1002.2

--- 70

- ii

F~i r . 'r ;/

,_ Fig. 22 Example of an Averaged Pressure-time History~(from 64 Instantaneous Time-histories) and

11 the Respective Frequency Spectrum now exhibit- ,

ing an Adequate ("Enhanced") Siqnal-to-noise .'Ratio when Compared to Fiq. 21 (Due to Intense,Low-frequency Background Noise the D~isturbanceFactor Adopts the Value of F =2.44)

050

,.,, .,.... -.... ...- ,., ,-..,.'..-.,-.. .,...,...............',. ........ . . .,-.- .,, -,- ,.-;. . . S _,_

",-.-. /-. "-. "-" ,""" ,'' ', ' ", . "• -" """. a'' ,i,¢ ",d'; - ,70 -.a, f

JDATA P01iNT:. AN-7 R UN: f8 rHF 7

P: 20.80 NH: .7174 n: 2189 r-DM '//U: .331 .0: T: 291 .0 K

200 INSTANTANEOUS ITIME HISTORY MX12

100 -0 -

U, -100U)

wS-200

0. -300

Pr11N= -376.6

-500 I.0 .5 1.0

TIME - REV .

veAVERAGE (70) POWER SPECTRUM

DF= 9.1 Hz

130LL120

a110

100-j0.

90

A 800 10 20 30 1

HARMON IC NUMBER

-2 - - - - -_ _ KHzFPEGU[1jUC Y

Fig. 23 Example of an Instantaneous Pressure-time Historyand an Averaged Frequency Spectrum as Calculatedfrom all 70 Instantaneous Spectra in Case of aHighly Disturbed Propeller Noise Signature

51

.....................................................

-~*,y- I . -- - - -" - -

DATA PiNl A,-7 -K H : 7" 20.80 NH: .717-1 n: 218-9 r'i- v/u: .0j: "': .00 T: 79! .0

AVE A',F I : "Tr 1.c

20

10

LU/0:z -0 /_

-30

N FqN -2 .g

I .

T I E - REV.

120 1- , __. 9.* h

110 J

iiij80 p fJI Ji/, /''I

zjFig. 24 E p - PiL i so

(from ~ H r~f ( all 70Intntneu-F mehstr.s

1• r - .. ..- . .. . ..-- -- - - *--,-- - - -. . ] . . . ... . .

(from all 70 Instantaneous Coime-histlories)<"and the Respect irye F'rcqu ,nley Spcct t rm l ncr -", porating a Disturbance Factor of F :5.96

(Due to High Pressure-disturbances the Pro-~peller-noise Signature is Completely Distorted)

52

• . .. , ., ad.. . .

DNV PROPELLER NOISE TEST

MICROPHONE: HP 4 ( PITCH ANGLE: 20.8 DEG

+---------------------------------------------------------------------+

DATA-POINT / RUN

I AN-1 / 63 II AN-2 I 64 II AN-3 1 65 Ir+..---....... + ....-.+.....H- - -- .-.. .+- -. +

I HN II F I SPL I SPLA II F I SPL I SPLA II F I SPL I SPLAI...--....... +...-.+.- 4-+ .....----... +- + ...-...+ ....-.+....-..

I 1 11 70.0 1108.3 1 82.1 I 80.0 1112.9 1 90.4 1 90.0 1116.9 1 97.8 11 2 11 140.0 1104.3 1 88.2 11 160.0 1108.4 1 95.0 11 180.0 1114.9 1104.0 11 3 1 210.0 98.2 1 87.3 1 240.0 1108.7 1100.1 11 270.0 1116.9 1108.3 11 4 1 280.0 95.7 1 87.1 320.0 1106.1 1 99.5 360.0 1114.9 110.1 I1 5 1 350.0 92.7 86.1 1 400.0 1102.4 1 97.6 11 450.0 1114.1 1110.9 11 6 1I 420.0 89.0 1 84.2 1 480.0 1101.4 1 98.2 11 540.0 1112.4 1109.2 11 7 1 490.0 82.1 1 78.9 1 560.0 1100.3 1 97.1 1 630.0 1113.6 1111.7 11 8 1 560.0 80.5 1 77.3 1 640.0 1 98.3 1 96.4 1 720.0 1111.1 1110.3 11 9 1I 630.0 78.1 1 76.2 720.0 1 93.9 1 93.1 1I 810.0 1110.8 1110.0 1

I 10 11 700.0 67.8 1 65.9 11 800.0 1 92.8 1 92.0 900.0 1109.9 1109.9 111 770.0 68.1 1 67.3 11 880.0 1 90.7 1 89.9 11 990.0 1108.2 1108.2 1

1 12 11 840.0 63.3 1 62.5 11 960,0 1 86.2 1 86.2 111080.0 1107.4 1107.4 11 13 1I 910.0 1 0.0 1 0.0 111040.0 1 85.9 1 85.9 111170.0 1106.9 1107.5 11 14 1I 980.0 0.0 1 0.0 111120.0 1 83.3 1 83.3 111260.0 1103.4 1104.0 11 15 111050.0 1 0.0 1 0.0 111200,0 1 79.7 1 80.3 111350.0 1104.4 1105.0 11 16 111120.0 1 0.0 1 0.0 111280.0 75.1 1 75.7 111440.0 1102.5 1103.5 11 17 111190.0 1 0.0 1 0.0 111360.0 1 75.4 1 76.0 111530.0 1 99.9 1100.9 11 18 111260.0 1 0.0 1 0.0 111440.0 1 72.5 1 73.5 111620.0 1 98.7 1 99.7 11 19 111330.0 1 0.0 1 0.0 111520.0 1 68.1 1 69.1 111710.0 1 98.1 1 99.1 11 20 111400.0 1 0.0 1 0.0 111600.0 1 66.8 1 67.8 111800.0 1 96.7 1 97.9 11 21 111470.0 1 0.0 0.0 111680.0 1 64.9 1 65.9 111890.0 1 94.0 1 95.2 11 22 111540.0 1 0.0 1 0.0 111760.0 1 64.5 1 65.5 111980.0 1 92.6 1 93.8 11 23 111610.0 1 0.0 1 0.0 111840.0 1 61.1 1 62.3 112070.0 1 91.2 1 92.4 11 24 111680.0 1 0.0 1 0.0 111920.0 I 0.0 1 0.0 112160.0 1 89.6 1 90.8 11 25 111750.0 1 0.0 1 0.0 112000.0 1 0.0 1 0.0 112250.0 1 88.2 1 89.5 11 26 111820.0 1 0.0 1 0.0 112080.0 1 0.0 1 0.0 112340.0 1 87.3 1 88.6 11 27 111890.0 1 0.0 1 0.0 112160.0 1 0.0 1 0.0 112430.0 1 86.1 1 87.4 11 28 111960.0 1 0.0 1 0.0 112240.0 1 0.0 1 0.0 112520.0 1 85.2 1 86.5 1, 29 112030.0 1 0.0 1 0.0 112320.0 1 0.0 1 0.0 112610.0 1 84.7 1 86.0 11 30 112100.0 1 0.0 1 0.0 112400.0 0.0 1 0.0 112700.0 1 82.8 1 84.1 11 31 112170.0 1 0.0 1 0.0 112480.0 1 0.0 1 0.0 112790.0 1 81.4 1 82.7 11 32 112240.0 1 0.0 1 0.0 112560.0 1 0.0 1 0.0 112880.0 1 81.3 1 82.5 11 33 112310.0 1 0.0 1 0.0 112640.0 1 0.0 1 0.0 112970.0 1 79.0 1 80.2 11 34 112380.0 1 0.0 1 0.0 112720.0 1 0.0 1 0.0 113060.0 I 77.3 1 78.5 11 35 112450.0 1 0.0 1 0.0 112800.0 1 0.0 1 0.0 113150.0 1 78.1 1 79.3 11 36 112520.0 1 0.0 1 0.0 112880.0 1 0.0 1 0.0 113240.0 1 75.6 1 76.81 37 112590.0 1 0.0 1 0.0 112960.0 1 0.0 1 0.0 113330.0 1 73.7 1 74.9 11 38 112660.0 1 0.0 1 0.0 113040.0 1 0.0 1 0.0 113420.0 1 73.3 1 74.5 11 39 112730.0 1 0.0 1 0.0 113120.0 1 0.0 1 0.0 113510.0 1 71.9 1 73.1 11 40 112800.0 1 0.0 1 0.0 113200,0 1 0.0 1 0.0 113600.0 1 68.8 1 69.8 1

-44-----------------+---+. -------------- +- ------------+----4 -- +

------------------------- ----------- - 4----------4---- ------ -------I OASPL 1110.3 1 94.3 II 1116.4 1107.1 1i 1124.6 120.7 1

------------------------------------- 4----------+ ------- ----- - -

F - FREQUENCY HZSPL - SOUND PRESSURE LEVEL DB RE 2E-5 PASPLA - A-WEIGHTED SOUND PRESSURE LEVEL DBA RE 2E-5 PA

Fig. 25 List of Harmonic Levels (Linear and A-weighted)and Overall Rotational Noise Levels as Calcu-lated under the Presupposition of a MinimumSignal-to-noise Ratio of at Least 10 dB foreach Harmonic

53"-, "~~~~~~~~~~~~~~~~~~. ..'..".. .-..-..."......-................. .•. . ...... .... ...........-..-.....-.. ".. ."... .-..

ATTACHMENT

'3acSkgrouL~c Noise Leve 1 -spectra

To Interpr-cL "Averagee (xx) Power Spectra" (containing broadband

poiseinforn'ation) correspondinp bpckground noise spectrP are

* providee for all microphone positions and a frequency bandwidth

1, DF 11.2 Vv.' (background noise spectra as obtained at the mi-

- crophone position MP 6 should not he interpreted, since this mi-

crophone dropped out during the measureirents).

Since tI'e analysing bandwidth cf propeller noise signatures was

leifined as el function of rotationalI speed, background noise

* trpectra as obtained at mifcrophone positions NF I and MP 4 In ad-

dition arc presented for correspondingly different bandwidths.

NP

cAT wN v- v--.

4 AVERAH- (52' PGWEP SPECTP; f Il AP90 ----- __ _ _

80 -

I-

C, L -

4 o j~fIU

10 20 2

HAR1NNIC NtJM1FP~

L'tV~~A F i I

v i

0 21)

fM30 ~

Na <j 1

__DA T-A PG 0 1f N T G ,,7 PUN K,

-,w~ v o c tt v: .7 in, s

go AVERAI3E (53) P IOWER S3PECfTRUM A~P ' 5 )

30 ~~~~DF 5.0H

80

S70

w

40

K, HFREQFN]

F ow ~ 3 . .-

0 VF'.

.4.7

5 0iIl

.J..

AVERAC~~F P PCT'' 1F 5

l- . .. l- i .... . .

DATYAFN _1 N K

I7

.

1 -- P r : " ,r N ! !]- -

%,

U J

-. .L ....

-...

HAP.. -" ,[

D_ ATA _T .P -i -O : .r ......

FLow ve'oci t. v .0m

AVERAC-E (70 POWER SPECTRUM (JIP < 5)G %)707

i,1 i " IF= 6.3 Hz

60

I 2LH-I i i iij I io

3e-

20

10 I-- -_ _

0 0 20 30 ,

HARMONIC NUMER

~r12 tHz

FPEUENL

RtIAF!VtA.F ew vc

70 111

a IL

PI 't

P%

ri..jA _F FA P [0~ P4J I I~fJ~ b 1 7- k,,FI ow V. I Ic tj C iv .7 L- V 3

AVERAGL- (53) POWER SP[CTRUM JLP < %;/*

80

dn 70 ; H

a-

*Y 60

-40L

*1 ~30-4 --0 10 20 30 40

HARMiGNIC NUMBER

0 12 KHzF RE I] Er C'

-e-4. - r

T-

p ~DA! A :L

%

.O

.5

I.

uLJ

CL-

50

440

0 10 -4,

HF P F1 NCME,

FPE t Nic-

- DA lA 01H 3i 0 Fi:FLow votocity v:F .1 in;

10 AVEPRAGE e" 70 P I WEP SFECTRUM I ~P-< 144 %.)___

DF- 6.3 Hz

100

S90

J

80

70

so

50 ---- _ _

0 10 2 0 30HAPN'OtN1C NUMB~ER

0 2 KH:zFREQUENC t

4-

7- - -'AI .v7-r A

FLow ect .j

FD

04HAco JM3C

itI70 T

N5

.14

HAN ,1F

A0 AVE E R f 68 ) POWER SPEC TRUM JP (5G *

fsF 7.5 H-,

0

Q--0: Ln 50

10I

0 10 20 30 40

HARMONIC NUMB18LR

.1 KHzPREGUENC

%

.4. A- P

~ AV -')

70

tn- 7oII0U

Lii

20 A1Jj -

0 10 1.10

0

FRFC Ic'

FFF~i~ y F

.DM.... ....... . .. . . .". i1 .A. I

FL o,! veI oci 3i.t r, -/s

AVERAF. (70) POWER SPECTRUM ( P < I -1 -490 r [ -- --v..-_.. .

OF= 7.5 Hz

80

0-

o_70

4 .. . .. .

04

-~50

0 10 20 30 40HARIION C NUt1UFP'

1 2 KHzF RE UE NC'

-.,

.-'-S . .S.,- ". ' - - .- . - . , . . . . . . . . .. . : " - - -. , - , - . . . - . - - . - . . , . . . . . . . .- -. . . . . .

F Lo 0~~ i. v:v

N 100 T T ,<~

So

ci4 1

F~ P - -P

w Al

4.11

jA I A KTTI vr1

ftk'- '' I.1.1 . '1.''j V :

AVERAG-E (70) POWER SPECTRUM (AP < 141 %) DF7 z

110

00

0f 90

uJ IuJm 80rm

60

70

0 102 04

HARM1ONIC NUMIBER

-S 12 KHzFREQ(UE NCY

5-%

DNATA PO '~Nir T

FL w vL&.,oc i Ly 7

AY~f,A2j 579 'IF £FEF I [rl IP < 56. -

0

L 1 012 H

uii

DA~J A F101-11 ~ K-

90O UL1E.AFj - 70 1O V.--P CT LM (J ,4

"'IS..i

% 50 t

4'.3

3 -

1020304

HANO I iiPE

U. 2 K~z

FRII',C,

7AA P01 H 'I F- 2 1 -

FLow veLocity v: -. r,

AVERAGfF (70) PCWEP -PFCIRF cLIP I 1A 1

Or-=

8.7 Hz

80

nL70

,6 -.e 0 1

40 '

0 10 20 30 40

HARMONIC NUIDER

2 KH,-

FRE1LUENC "

0 o

F E3L ;C'J o . " . " , o " - " o % " I " , , , r " , . % " ! ' "" * c ,, ,..

LDATA PO INT B!N ."\oFtc' veLocity v: 51 .2 rn),;

A V E R A G E ( 7 0 ) P O W F R S P E C TR U M ( AP < 11 4 ) ___

OF= 8.7 Hz

90

S80

w 70 L

60 k

I ,

,.;

*..

I f.1050!"-

_ _ I _ _ _'

0 10 20 3a 10HARMONIC NUI1BLR

0KHz

FREQUENCY

r

-I.

p

'p%

I, II ~ .. . . . . . ..I '~ -

.... .. . . . . . . . . . . .

F L v c- c v. * --

DAT A VE AU i'j 70 PWRSFTKr .

r OP= 8.7 Hz

100

C5

N0-.- K 0

60 L ~ ~ i~

50 Yie..0 10 20 30 L

HA&'O UNIC NIUhBDY

2 2FRPIGUENC T

P P ' .7,j

[) [ \ f--11! , i Ijf_ ~ L~~-

AVERAGE (70) POWFR SPECTRUrM (P < 141f %)1 10 - ---------------DP= 8.7 Hz

100

Q-

0

LlL

LU)

60

50 I 1 10 10 20 30 "0

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0

0 020 '3n iHARMONIC NUMBER

0 -) KHzFPEQUENCY

7.

w v cC

-EFF :!PF.Pu-r t..-PE-~ <' -. 9

.. . . . . . . . .1.. ..H.

HA"CI _____ __ _

rjF= 1.2 r'

AF.r

AVA

=''RAGE 53 POWEP 3-PEC TR'jM AF 1 -4~

- 10

1001

HARMOIC NUMBY

4K-,

'p.QUNC

STA P7

'S - . r 70

110.

I Ij

wl DO0

p.. - K

o~rw vc~~~ n r-ff 11 t, n's

10AVERAGE (70) P !OWER Sr)ECTRUM I AP ( 496 %.) _______

DF=I 11.2 Hz

110

30

70 F-

v1 ~ t 10 20O t

HARM~ONIC NUMiBER

2 1 HzFPEQUEN[Y

'.%

-b%

F-ow VE<l~jcit 2.1 i'

VAv;AE 62) P OWER S-PEC-TRU JP <e 144

4 00

.1

a)i 'P 0T-

-IA4,

* AW7 AV 7;- - .- *

DATA POINT BGN- I J N_ 2-0 QP: 39Flow velocity v: .0 m,'s

AVERAGE (69) POWER SPECTRUM (JP < 56 %)70 F _ __

A., 60

L) 50

tu

.. J. 30 ~ 'J. -

A ~20 H0 10 20 30 40

HARMONIC NUMrBFR

A-.- - -- 7 . . . . .-

012 3FREOIFNI-

:.-

Z7Al

DATA p~L-'~ i':~F~low vo-oit<g v: 9',.' a

U.

AVERAGE (70) POWER S'ECTPUM (AP ( 49G % ____-

100- ----- VOF= 11.2 Hz

90 -,

Ln 80

Lii -- Ccli

w HI

-

_e[ - _ _ 1 !_.

O 0 2 30 40

HARMONIC NUIPEP

0 I 3 KHz

.

%- n

AN r- e

DAA P 0 P \J, F Q 7 KJ> 1I ~IL 7 1 3

FLow ve ocit. v: ..<:v.7 r/.

AVERAGE (70) POWER SPECTRUM (AP < 496 .)110 I"

OF:= 11 .2 Hz

100

t 90

. , a,-

Au02

HARMONIC NIJNBER

012 3 KHzFREOU[ N1 f

IDA TA PC) I NT : 'hiiK'- >iVK N 7 7 V

F L w ve L o,:'- v 5 1.2 m s

120 AVERAGE (70) P IOWER SPECTRUMI (AdP < 19FD ) OFF112

10

80

- 60 -

0 10 20 330aHAPMONI1C NUM 1B E R

0 12 3 KH::

* FRF OUF1II7Y

- AA- J -I tA Y. b(- -9 9 ~

IFLow vetociLy v 61 .l m/s

120 AVERAGE (65) POWER SPECTRUM (AP < 14- 1 )

DF-- 11 .2 Hz

110

oo

-Si

OL90

rn it70-

- I 1 L _ I i L ',+ ' ,,._ I 1_ _

10 20 34

HARM1NIC NLU- -

0 1 2 3 k HzFREOe ,e

i-s" .,.. , .•-.- ..- . . .

FLow veLocit ( *

O~F= 11.2 Hz

1 20

ci

cr

rr j

10 I

7C ~ LA ___