Dale E. Van Zante and Mark P. Wernet

Glenn Research Center, Cleveland, Ohio

Tip Vortex and Wake Characteristics of a

Counterrotating Open Rotor

NASA/TM—2012-217713

October 2012

AIAA–2012–4039
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Dale E. Van Zante and Mark P. Wernet

Glenn Research Center, Cleveland, Ohio

Tip Vortex and Wake Characteristics of a

Counterrotating Open Rotor

NASA/TM—2012-217713

October 2012

AIAA–2012–4039

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

48th Joint Propulsion Conference and Exhibit

cosponsored by AIAA, ASME, SAE, and ASEE

Atlanta, Georgia, July 30 to August 1, 2012
Acknowledgments

This work was sponsored by the NASA Environmentally Responsible Aviation Project of the Integrated Systems

Research Program. The PIV measurement team included Randy Locke, Adam Wroblewski, and Gary Clayo. Csaba

Horvath assisted with the fi gures presenting the PIV data.

Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

5301 Shawnee Road

Alexandria, VA 22312

Available electronically at http://www.sti.nasa.gov

Trade names and trademarks are used in this report for identifi cation 

only. Their usage does not constitute an offi cial endorsement, 

either expressed or implied, by the National Aeronautics and 

Space Administration.

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2012-217713 1 

Tip Vortex and Wake Characteristics of a 

Counterrotating Open Rotor 

Dale E. Van Zante and Mark P. Wernet 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

One of the primary noise sources for Open Rotor systems is the interaction of the forward rotor tip 

vortex and blade wake with the aft rotor. NASA has collaborated with General Electric on the testing of a 

new generation of low noise, counterrotating Open Rotor systems. Three-dimensional particle image 

velocimetry measurements were acquired in the intra-rotor gap of the Historical Baseline blade set. The 

velocity measurements are of sufficient resolution to characterize the tip vortex size and trajectory as well 

as the rotor wake decay and turbulence character. The tip clearance vortex trajectory is compared to 

results from previously developed models. Forward rotor wake velocity profiles are shown. Results are 

presented in a form as to assist numerical modeling of Open Rotor system aerodynamics and acoustics. 

Nomenclature 

X,Y Cartesian PIV coordinates, inches 

Z Axial PIV coordinate, inches 

MSTA Model Station axial coordinate, inches 

U,V Velocity components in X and Y directions, ft/s 

W Velocity component (axial) in Z direction, ft/s 

Vr Radial velocity, ft/s 

Vtheta Tangential velocity, ft/s 

ORPR Open Rotor Propulsion Rig 

Introduction 

The Open Rotor based propulsion system offers the potential for substantial fuel burn reductions, 

greater than 20 percent, compared to contemporary turbofan based propulsion systems. The increase in 

fuel costs and greater emphasis on reducing carbon emmisions have both contributed to the renewed 

interest in Open Rotors. 

Open Rotor concepts, previously called propfans, were studied extensively in the 1980s as a result of 

the oil price shocks of the 1970s. Development advanced as far as flight test engines. For example, the 

General Electric (GE) Unducted Fan (UDF) engine flew on both MD-80 and 727 airframes. Oil prices 

stabilized and interest in these radical new engine concepts waned. The UDF program at GE ended in 

1989. 

The 1980s demonstrator engines were memorable for their unique, scimitar shaped blades, their fuel 

burn reduction, and their noise levels. Design systems of the time were limited in their ability to optimize 

for both performance and acoustics simultaneously. The current generation of open rotors have been 

designed with both three-dimensional aerodynamics tools and computational aeroacoustics tools. This has 

enabled the new designs to match the best aero performance of the 1980s but with much improved noise 

characteristics. The goal of the current work is to achieve 15 to 17 EPNdB cumulative margin to the 

Chapter 4 noise regulations. 
NASA/TM

A 198

current wi

Propulsio

acoustic d

previous f

from Stere

a phased a

proprietar

for Open 

totality of

and analy

The H

methodolo

1980s wit

the origin

blade and

acoustics.

M—2012-21771

80s design bla

ind tunnel tes

n Rig (ORPR

data from this

flowfield data

eo Particle Im

array. In addi

ry and thus pr

Rotors. Detai

f these measur

ysis tools for O

Historical Bas

ogy. The orig

th some result

nal blade coor

d ‘A’ refers to 

 Table 1 show

13 

ade set, the H

st campaign in

R). Some deta

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a are in Refer

mage Velocim

tion, the geom

rovides a data

ils of the Hist

rements and g

Open Rotors c

The

seline blading

ginal F31/A31

ts reported in 

dinates. Figur

the aft blade

ws some gene

Figure

blad

TAB

Numbe

Nomina

Diamet

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tip spee

Historical Base

n the NASA G

ils of the 91

ovides a valid

ence 2. The c

metry (SPIV) m

metry and dat

aset for valida

torical Baselin

geometry deta

can be validat

e Historica

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Reference 3.

re 1 shows th

. The bladese

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2 

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PARAMETERS 

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mance without

s part of the 

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ormance and 

Details of 

led flow field

measurements 

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from which d

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M—2012-21771

he Open Roto

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Figure 2.—

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M—2012-21771

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NASA/TM

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M—2012-21771

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M—2012-21771

Figure

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ounted for in t

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ns at all of the

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was perform

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13 

e 5.—Sample P

p vortex. Valid 

ereo PIV tech

vector maps 

rsing a calibra

mm in 1.0 m

t vector maps 

a separate tran

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ons for each m

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unnel. A meta

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he light sheet 

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maps could be

g unique calib

ed to ensure t

calibration v

alibrations. Th

PIV image show

PIV correlation

Stereo P

hnique, a calib

computed fro

ation target o

mm increment

collected in t

nslation stage

erfectly aligne

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ion was acqui

measurement

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ng a calibratio

l plate with a

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locations use

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that the plane

verification op

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6 

wing level of flo

ns were obtaine

PIV Calibr

bration is requ

om the two ste

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s (Ref. 4). Th

the test progra

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ed in the sam

bration would 

ired for each 

t plane insured

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on jig which w

grid of 10 m

on stage to tra

d during the a

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ach measurem

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d suffice. Sinc

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performed by

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anslate the tar

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ommon coord

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ment plane, a

sheet coincide

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were then used

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ns of the image

onstructing the

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bration is the

r, in the ORPR

plane through

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asurement pla

riations in the

y yawing the m

ed from the la

ined into the 

rget ensured t

rements. The 

dinate grid so

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nent 
NASA/TM—2012-217713 7 

Stereo PIV Data Processing 

The collected SPIV image data were processed using an in-house developed SPIV cross-correlation 

processing program called PIVPROC (Ref. 6). The correlation based processing software program 

supports subregion image shifting and multi-pass correlation to improve the spatial resolution of the 

resultant velocity vector maps. In addition, PIVPROC also supports subregion distortion processing 

(Ref. 7). In multipass-correlation mode, the correlation processing grid is initially coarse (typically 

6464 pixel subregions), followed by a higher resolution 2nd pass (typically 3232 pixel subregions) in 

order to improve the spatial resolution of the resulting vector field. The objective of the multi-pass 

approach is to keep the correlation peak at the center of the correlation plane, which mitigates higher 

order errors in the correlation peak detection process (Ref. 8). In each pass, PIVPROC uses a spurious 

peak removal algorithm which removes any vector lying more than three standard deviations from its 

surrounding 8 neighbors and replaces it with an interpolated value. The estimates for the subregion offsets 

used in each pass are computed from the previous pass vector map. The offsets are computed from a 

spatially weighted average of the vector field. PIVPROC uses a simulated annealing approach in the 2nd

pass of the multi-pass correlation operation. For example, the first pass correlations were performed at 

6464 pixel subregions on a 3232 pixel grid followed by 2nd pass operations on 3232 pixel subregions 

on a 1616 pixel grid. In PIVPROC, a total of 6 passes at the higher grid density can be used, where in 

each successive pass the region on the correlation plane that is examined for correlation peaks is reduced. 

In the 6th pass, the correlation plane search region may only be 1/3 of the initial size. Since the subregion 

image shifting keeps the correlation peak at the center of the correlation plane, this simulated annealing 

approach reduces the number of spurious vectors by limiting where on the correlation plane that the 

correlation peaks can be detected. The offsets are computed from the surrounding flow field, so the local 

flow directs the correlation operation on where to find the correlation peak. 

In addition to multi-pass correlation processing, PIVPROC also employs subregion distortion 

processing (Ref. 7). Subregion distortion processing is used to correct for velocity gradients across the 

subregion and to minimize the “peak-locking” effect, which is the tendency for the estimated particle 

displacements to preferentially concentrate at integer values. In the subregion distortion technique, the 

local velocity gradients surrounding the current correlation subregion are used to distort the subregion 

before the cross-correlation processing operation. Distorting the subregion yields correlation subregions 

with uniform particle displacements, and hence, reduces any bias caused by the velocity gradients. 

Typically, two additional passes after the multi-pass processing are used with subregion distortion applied 

to refine the correlation peak estimates. 

The data were collected to maximize the information content with respect to the tip vortices from the 

blade tips and also provide blade wake trajectories down to the hub. In the near hub measurements, flare 

light scattering off of the hub corrupted the PIV image data. Hence, Symmetric Phase Only Filtering 

(SPOF) correlation processing was used to minimize the data corruption from flare light scattered off of 

the model (Ref. 9). SPOF is a modification of the traditional cross-correlation processing used in PIV, 

where the phase information in the frequency domain is emphasized and the image amplitude (flare light) 

information is suppressed. Combining all of these processing strategies yielded the high quality data sets 

presented here. 

Sequences of 400 velocity vector maps were acquired at each measurement station and ensemble 

averaged to provide first and second order statistics over the entire measurement plane. Chauvenet’s 

criteria was used to eliminate any outliers in the ensemble averaging process (Ref. 10). All of the 

processed PIV data were placed in the model coordinate system to facilitate comparison with CFD 

predictions. The final processed velocity vector maps had an in-plane spatial resolution of 1.43 mm in 

both the x- and y-directions. 
NASA/TM

The a

we try to m

oil based 

Small aero

2 nsec jitt

influencin

ensures th

processing

subregion

closer to s

peaks can

displacem

as 1 perc

displacem

Verificati

400 measu

statistical 

presented 

M—2012-21771

accuracy of th

minimize any

seeders produ

odynamic dia

ter in the laser

ng the measur

hat we are obt

g further ensu

ns or any peak

surfaces than 

n be nominally

ments were 16

cent of full sc

ments. The use

on helps to av

urements whi

outliers are r

here are 1 p

F

13 

P

he PIV measur

y bias errors, l

uced the smal

ameter equate

r pulse timing

rement accura

taining high q

ures that we a

k-locking effe

would otherw

y estimated to

6 pixels. Henc

cale. Smaller d

e of calibratio

void any bias 

ich are then e

removed using

percent of full

igure 6.—Repr

with the tip vo

PIV Measu

rement is dep

leaving only t

llest aerodyna

es to minimal/

g, making this

acy is the part

quality estima

are minimizin

ects. Use of SP

wise be possib

o 0.1 pixel. F

ce, the instant

displacement

ons for each m

errors in the 

ensemble aver

g Chauvenet’

l scale. 

resentative me

ortex highlighte

8 

urement A

pendent on sev

the random e

amic diameter

/no particle la

s error source

ticle displacem

ates of the par

ng any biases 

POF processi

ble. With all o

For the proce

aneous PIV m

s will have lo

measurement p

estimated vel

raged to comp

s Criteria. He

easurement vol

ed as an isosurf

Accuracy

veral factors. 

rror of the me

r particles ava

ag effects. Th

e negligible. H

ment estimate

rticle displace

caused by gra

ing ensures th

of these preca

ssing subregi

measurement 

ower accuracy

plane and app

locities. Final

pute the 1st an

ence, the PIV

ume shaded b

face of velocity

 In a well des

easurement. U

ailable for an

he Nd:YAG la

Hence, the ma

e. Using mult

ements. Subre

adients across

hat we can ma

autions, the cr

ions used here

accuracy is ty

y than the larg

plication of C

lly, we collec

nd 2nd order st

V measuremen

y velocity 

y. 

signed experim

Use of the mi

ny PIV experim

aser has less t

ain factor 

ti-pass proces

egion distortio

s the processi

ake measurem

ross-correlati

e, the maximu

ypically descr

gest 

Calibration 

ct data sets of

tatistics. Any

nt accuracy 

ment, 

neral 

ment. 

than 

ssing 

on 

ing 

ments 

on 

um 

ribed 

f

y
NASA/TM—2012-217713 9 

Results 

PIV flowfield measurements were acquired for multiple operating conditions and forward rotor phase 

positions for the Historical Baseline blade set. Table 2 lists the data conditions and repeat measurement 

(23Aug10e). Figure 6 shows a representative data volume at one phase step. Two phase steps of the 

forward rotor were acquired for each operating condition so that the tip vortex would be captured in the 

higher radial resolution portion of the measurement grid for the entire axial extent of the vortex. This is a 

consequence of slicing a helical shaped flow feature with flat planes. Results from both phase steps are 

used to determine the vortex core trajectory. The resolution of the forward blade wake does not change 

with phase step so representative results are shown for one phase step only. 

TABLE 2.—GENERAL TEST CONDITIONS 

PIV data set 

name 

Blade set Model 

config 

Blade pitch 

angle, 

Front/Aft 

Front 

rotor, 

rpm 

#PIV measurement 

planes 

Front rotor PIV 

delay phase step 

23Aug10a F31/A31 Take Off 40.1/40.8 6444 30 0

23Aug10b F31/A31 Take Off 40.1/40.8 6453 30 14.7

23Aug10c F31/A31 Take Off 40.1/40.8 5680 30 0

23Aug10d F31/A31 Take Off 40.1/40.8 5684 30 16.7

23Aug10e F31/A31 Take Off 40.1/40.8 6452 24 0

25Aug10a F31/A31 Approach 33.5/35.7 5704 30 0

25Aug10b F31/A31 Approach 33.5/35.7 5707 30 18.1

Tip Vortex Behavior 

The size, strength, trajectory and decay rate of the forward rotor tip vortex are all key parameters in 

assessing the acoustic influence of this flow feature on the system. For example, aft rotor clipping is a 

possible noise mitigation strategy in which the aft rotor is shortened sufficiently so that the tip vortex does 

not interact with the blade. However, aft clipping can have a negative impact on system efficiency so a 

minimal amount of clipping is desired to obtain the acoustic benefit without a substantial efficiency loss. 

Several models for the tip vortex interaction have been developed. See Majjigi, et al. (Ref. 11) for one 

example of a model developed at GE. The GE model was developed based on analytical assumptions 

about the vortex and some limited experimental data. The data available at the time consisted of 1) 

helicopter rotor in hover data for the tip vortex trajectory and 2) data from finite span airfoils at angle of 

attack in a wind tunnel (for vortex decay). Neither of these data are necessarily representative of the 

vortex character and flow conditions experienced by counter rotating open rotors. Majjigi, et al. noted 

many times that the accuracy, completeness, and sophistication of the model can be extended with the 

inclusion of more representative data. 

The tip vortex trajectory has been extracted from the current PIV data sets. The vortex core location 

was determined by looking at in-plane velocity vectors and in-plane streamlines as shown in Figure 7 for 

a specific axial location. The vortex core radial location is easily determined from this graphical view of 

the data. The process is repeated for additional axial planes until the vortex has moved outside of the PIV 

measurement volume. The accuracy of the location is assumed to be the spacing of the PIV measurement 

planes, either 0.1 or 0.2 in. at these locations. The geometric relationship between the PIV measurement 

coordinate system (shown in Fig. 10) and the open rotor model station coordinates is given in Table 3. 
NASA/TM

Figure

plan

radi

The v

of the vor

best fit lin

asymptote

both the N

in Figure 

The vo

radial mov

that are re

dataset un

data scatte

helicopter

open rotor

M—2012-21771

e 7.—Vortex co

ne velocity vect

al location wou

vortex trajecto

rtex core is no

ne shows that 

es. Figure 9 sh

Nominal Take

8 using the p

ortex core traj

vement of the

epresentative 

nambiguously

er). The chara

r rotor data an

rs. 

13 

ore radial locatio

tor plots at con

uld be the cente

TABL

MO

Mo

Forebody no

F31 trailing 

Rtip = 12.90

ory from Majj

ormalized by 

the vortex co

hows the traje

eoff and Appr

arameters list

jectory has a 

e core is nearl

of typical rot

y defines the v

acter and beha

nd the current

on can be dete

stant axial loca

er of rotation of

LE 3.—RELATI

ODEL STATIO

odel location 

ose 

edge tip 

053 in. 

jigi, et al. is re

the rotor tip r

ore moves inw

ectory of the 

roach pitch an

ted in Table 3

substantially 

ly linear with

or spacings. T

vortex trajecto

avior of the ti

t dataset is im

10 

ermined from a

ation slices thro

f the velocity ve

IONSHIP BETW

N (MSTA) COO

MST

in

166.

194.

194.

195.

-----

eproduced he

radius. Note th

ward radially 

tip vortex as 

ngle settings. 

3. 

different char

h axial distanc

The asymptot

ory with grea

ip vortex is no

mportant in est

a combination o

ough the PIV d

ectors. 

WEEN PIV AND

ORDINATES 

TA, 

n. 

Z

i

943 0.

254 –27

943 –28

943 –29

----- ----

ere in Figure 8

that there is m

quickly and t

extracted from

The data is n

racter than th

ce downstream

tic behavior is

ater certainty i

ot well repres

tablishing a c

of in-plane strea

data volume. Th

D

Z, 

in. 

.00 

7.31 

8.00 

9.00 

------ 

8. The radial 

much scatter in

then its radial

m the PIV me

normalized in 

hat shown in F

m, at least at t

s not present.

in vortex core

sented by the 

canonical vort

amlines and in

he vortex core 

and axial loca

n the data and

l motion 

easurements f

the same way

Figure 8. The 

the axial dista

 The current P

e location (les

model based 

tex trajectory 

-

ation 

d a 

for 

y as 

ances 

PIV 

ss 

d on 

for 
NASA/TM—2012-21771

Figure 8.—

the refe

Figure 9

13 

—Normalized v

erence). 

9.—Normalized

vortex core rad

 vortex core ra

11 

ial location fro

dius determin

m Reference 1

ed from the PIV

1 (Figure 10 w

 measuremen

ithin 

ts. 
NASA/TM

Additi

measurem

improve t

guiding d

advanced 

The sh

wake gene

caused by

and 13. A

profiles ar

Figure

system. T

maintain t

X = 11.03

Figure

tangential

forward ro

apparent a

less negat

character;

Velocity p

of the tip 

Fi

M—2012-21771

onal informat

ments. This ad

the models de

esign decision

blades in the

hape, strength

erated tone an

y a combinatio

A full assessm

re extracted to

e 10 shows the

The wake prof

the best spatia

3 in. The carte

es 11 to 16 sho

l velocity. Th

otor wake cle

as a uniform n

tive radial vel

; a deficit in a

profiles in the

vortex and th

igure 10.—Spa

maintain the b

13 

tion such as v

dditional analy

eveloped in th

ns. The curren

 current test c

h and turbulen

nd broadband

on of viscous 

ent of these e

o show the qu

e location of t

files are not al

al resolution. 

esian velocity

ow the wake 

e ~50 percent

early. The stre

negative radia

locity. The ax

axial velocity 

e ~75 percent 

he velocity pro

atial location of 

best spatial res

vortex core siz

ysis is beyond

he 1980s with

nt data has be

campaign. 

Wa

nce character 

d noise signatu

effects, press

effects is beyo

uality of the d

the extracted 

long a consta

In the PIV co

y components

profiles at the

t span wake p

eamtube contr

al velocity. Th

xial and tange

and an increa

span location

ofiles do not s

wake velocity 

olution. 

12 

ze and circula

d the scope of

 the intent of 

een used to va

ake Decay

of the forwar

ure of open ro

sure gradient 

ond the scope 

data set. 

wake profiles

nt radius but 

oordinate syst

 have been tra

e two span lo

profiles (X = 9

raction caused

he outward m

ential velocity

ase in tangent

ns (X = 11.03

show the clas

traces. Note th

ation can be d

f the current p

f developing a

alidate the de

y

rd rotor wakes

otors. Wake d

effects and w

 of this paper

s and the orie

rather follow

tem the wake

ansformed to

cations in term

9.13 in.), Figu

d by the thrus

migration of w

y profiles show

tial velocity w

3 in.) are heav

ssical behavio

hese are along

determined fr

paper. Furthe

a more robust 

esign philosop

s are key para

decay in turbo

wake stretchin

r, however rep

entation of the

w a PIV measu

e profiles are a

o cylindrical. 

rms of axial, r

ures 11, 13, a

st of the forw

wake fluid is r

w the typical 

within the wak

vily influence

or. 

 a constant X l

rom the PIV 

er analysis cou

model suitab

phy used for t

ameters in the

omachines is 

ng, Reference

presentative w

e PIV coordin

urement plane

at X = 9.13 in

radial and 

and 15, show 

ward rotor is 

represented by

turbomachine

ke region. 

ed by the pres

ocation to 

uld 

ble for 

the 

e

es 12 

wake 

nate 

e to 

n. and 

the 

y a 

ery 

ence 
NASA/TM

Figure 11

forward

Figure 12

forward

M—2012-21771

.—Axial velocit

d blade. 

.—Axial velocit

d blade. 

13 

ty wake profiles

ty wake profiles

 at the ~50 pe

 at the ~75 pe

13 

rcent span loc

rcent span loc

ation for three 

ation for three 

axial locations

axial locations

 downstream o

 downstream o

f the 

f the 
NASA/TM

Figure 

the fo

Figure 

the fo

M—2012-21771

13.—Radial ve

orward blade. 

14.—Radial ve

orward blade. 

13 

elocity wake pro

elocity wake pro

files at the ~5

files at the ~7

14 

0 percent span

5 percent span

 location for th

 location for th

ree axial locat

ree axial locat

ions downstrea

ions downstrea

m of 

m of 
NASA/TM

Figure 

of the

Figure 1

of the 

M—2012-21771

15.—Tangentia

e forward blade

6.—Tangential

forward blade.

13 

al velocity wake

e. 

l velocity wake 

e profiles at the

profiles at the 

15 

 ~50 percent s

~75 percent sp

pan location f

an location fo

or three axial l

r three axial lo

ocations down

ocations downs

stream 

tream 
NASA/TM—2012-217713 16 

The PIV data could be analyzed further to determine the relative importance of the sometimes 

competing effects of viscous decay and wake stretching. The turbulence character of the wake could also 

be analyzed to help guide broadband noise assessments. 

Summary 

A high quality, three dimensional velocity data set for counterrotating open rotors has been analyzed 

for tip vortex trajectory and rotor wake velocity profile characteristics. The tip vortex trajectory shows a 

linear character with axial distance. This is substantially different than the hyperbolic character derived 

from helicopter rotor measurements in the 1980s. The forward rotor wake profiles show the classical 

turbomachinery wake character for the more inboard span locations. The wake velocity character is 

heavily influenced by the tip vortex at the outer span locations and does not exhibit a classical wake 

behavior. 

The data set is of sufficient resolution and quality that further analysis is warranted to determine the 

vortex core diameter and wake turbulence characteristics. 

References 

1. Woodward,, Richard P. and Hughes, Christopher E., “Acoustic Performance of the GEAE UPS 

Research Fan in the NASA Glenn 9- by 15-Foot Low-Speed Wind Tunnel,” NASA/TM—2012-

217450, May 2012. 

2. Podboy, Gary G. and Krupar, Martin J., “Laser velocimeter measurements of the flow field 

generated by a forward-swept propfan during flutter,” NASA TM-106195, 1994 

3. Woodward, R.P., Hall, D.G., Podboy, G.G., and Jeraki, R.J., “Takeoff/Approach Noise for a Model 

Counterrotation Propeller with a Forward-Swept Upstream Rotor,” AIAA-93-0596, presented at the 

31st Aerospace Sciences Meeting & Exhibit, Reno, NV, January 11-14, 1993. 

4. Soloff, S.M., Adrian, R.J., and Liu, Z-C, “Distortion Compensation for Generalized Stereoscopic 

Particle Image Velocimetry,” Measurement Science and Technology, Vol. 8, No. 12, pp. 1441-1454, 

1997. 

5. Bjorkquist, D.C., “Design and Calibration of a Stereoscopic PIV System,” Proc. 9th International 

Symposium on Applications of Laser Techniques to Fluid Mechanics, Vol. 1, pp. 6.5.1-6.5.8, 

Lisbon, Portugal, 1998. 

6. Wernet, M. P., “Fuzzy Logic Enhanced Digital PIV Processing Software,” Proceedings of the 18th

International Congress on Instrumentation for Aerospace Simulation Facilities (ICIASF), Toulouse, 

France, June, 1999. 

7. Gui, L., Werely, S.T., “A Correlation-Based Continuous Window-Shift Technique to Reduce The 

Peak-Locking Effect in Digital PIV Image Evaluation,” Exper. In Fluids, Vol. 32, pp. 506–517, 

2002. 

8. Westerweel, J., “Fundamentals of Digital Particle Image Velocimetry,” Meas. Sci. Technol., Vol. 8, 

pp. 1379-1392, 1997 

9. Wernet, M.P., “Symmetric Phase Only Filtering: a New Paradigm for DPIV Data Processing,” 

Meas. Sci. Technology, Vol. 16, pp. 601-618, 2005. 

10. Taylor, J.R., An Introduction to Error Analysis, University Science Books, Oxford University Press, 

Mill Valley, CA., 1982. 

11. Majjigi, R.K., Uenishi, K. and Gliebe, P.R., “An Investigation of Counterrotating Tip Vortex 

Interaction,” NASA CR-185135, 1989. 

12. Hill, P.G., Schaub, U.W., and Senoo, Y., “Turbulent Wakes in Pressure Gradients,” ASME Journal 

of Applied Mechanics, Vol. 85, pp. 518-524, 1963. 

13. Kool, P. and Hirsch, Ch., “A Prediction Scheme for the Decay of a Turbomachine Blade Wake,” 

ASME Paper No. 82-GT-273, 1982. 

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4. TITLE AND SUBTITLE

Tip Vortex and Wake Characteristics of a Counterrotating Open Rotor 

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Van Zante, Dale, E.; Wernet, Mark, P. 

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WBS 699959.02.09.03.05 

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John H. Glenn Research Center at Lewis Field 

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13. SUPPLEMENTARY NOTES

14. ABSTRACT

One of the primary noise sources for Open Rotor systems is the interaction of the forward rotor tip vortex and blade wake with the aft rotor. 

NASA has collaborated with General Electric on the testing of a new generation of low noise, counterrotating Open Rotor systems. Threedimensional particle image velocimetry measurements were acquired in the intra-rotor gap of the Historical Baseline blade set. The velocity 

measurements are of sufficient resolution to characterize the tip vortex size and trajectory as well as the rotor wake decay and turbulence 

character. The tip clearance vortex trajectory is compared to results from previously developed models. Forward rotor wake velocity profiles 

are shown. Results are presented in a form as to assist numerical modeling of Open Rotor system aerodynamics and acoustics.

15. SUBJECT TERMS

Aeroacoustics; Propeller noise; Noise reduction 

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