design and wind tunnel testing of cal poly's amelia 10

27TH

INTERNATIONAL CONGRESS OF THE AERONAUTICAL SCIENCES

DESIGN AND WIND TUNNEL TESTING OF CAL POLY’S AMELIA 10 FOOT SPAN HYBRID WINGBODY

LOW NOISE CESTOL AIRCRAFT

Kristina K. Jameson*, David D. Marshall*, Robert Ehrmann*, Eric Paciano*, Rory Golden*, and Dave Mason**

*California Polytechnic State University, San Luis Obispo, **PatersonLabs

Keywords: Poweredlift, Circulation Control, CFD database, NFAC

Abstract

California Polytechnic Corporation, Georgia Tech Research Institute (GTRI), and DHC Engineering collaborated on a NASA NRA to develop and validate predictive capabilities for the design and performance of Cruise Efficient, Short TakeOff and Landing (CESTOL) subsonic aircraft. In addition, a large scale wind tunnel effort to validate predictive capabilities for aerodynamic performance and noise during takeoff and landing has been undertaken.

The model, Advanced Model for Extreme Lift and Improved Aeroacoustics (AMELIA), was designed as a 100 passenger, N+2 generation, regional, CESTOL airliner with hybrid blended wingbody with circulation control. The model design was focused on fuelsavings and noise goals set out by the NASA N+2 definition. The AMELIA is 1/13 scale with a 10 ft wing span. PatersonLabs was chosen to build AMELIA and The National FullScale Aerodynamic Complex (NFAC) 40 ft by 80 ft wind tunnel was chosen to perform the nine week long large scale wind tunnel test in the summer of 2011.

1 Introduction

With the very recent advent of NASA’s

Environmentally Responsible Aviation Project

(ERA)[1], dedicated to designing aircraft that

will reduce the impact of aviation on the

environment, there is a need for research and

development of methodologies to minimize fuel

burn, emission, and a reduction in community

noise produced by regional airlines. ERA is

specifically concentrating in the areas of

airframe technology, propulsion technology,

and vehicle systems integration all in the time

frame for the aircraft to be at a Technology

Readiness Level (TRL) of 46 by the year of

2020 (deemed N+2). The proceeding project

looking into similar issues was led by NASA’s

Subsonic Fixed Wing Project and focused on

conducting research to improve prediction

methods and technologies that will produce

lower noise, lower emissions, and higher

performing subsonic aircraft for the Next

Generation Air Transportation System.

The work provided in this investigation was

an NRA funded by Subsonic Fixed Wing

Project starting in 2007 with a specific goal of

conducting a large scale wind tunnel test along

with the development of new and improved

predictive codes for the advanced poweredlift

concepts incorporated into the wind tunnel

model in conjunction with the verification of

these codes with the experimental data obtained

during the wind tunnel test. Poweredlift

concepts investigated are Circulation Control

(CC) wing in conjunction with over the wing

mounted engines to entrain the exhaust and

further increase the lift generated by CC

technologies alone.

There are a number of papers in the past

few years presenting computational studies of

CC technologies. Most of them have focus on

2D studies[211] While there are a number of

excellent 2D experimental datasets available for

such CFD validation[1215], the same is not

1

JAMESON, MARSHALL, EHRMANN, PACIANO, GOLDEN, MASON

true for 3D experimental data[16]. This effort

aims to address this short fall by creating a

comprehensive and relevant 3D database for

current and future 3D simulations. Experimental

measurements included in the database will

include forces and moments, surface pressure

distributions, local skin friction, boundary and

shear layer velocity profiles, farfield acoustic

data and noise signatures from turbofan

propulsion simulators. This paper focuses on

designing and developing a model with NASA’s

N+2 goals for less environmental impact as well

as the fabrication of a 10 foot span wind tunnel

model to be used to create the 3D validation

database for numerical simulations. The

resulting design is the Advanced Model for

Extreme Lift and Improved Aeroacoustics

(AMELIA) and is the subject of the rest of this

paper.

2 Advanced Model for Extreme Lift and Improved Aeroacoustics (AMELIA)

2.1 Summary of NASA’s N+2 Design Goals

NASA is committed to identify solutions that

meet improvements for noise, emissions, and

energy usage (fuel burn). They have classified

the N+2 design metrics as a 40% reduction in

fuel consumption, progress towards 42 dB

lower noise levels, a 70% decrease in emissions,

and a 50% reduction in field length performance

over current generation aircrafts. Theoretically

the aircraft should reach a Technology

Readiness Level (TRL) of 46 by the year 2020.

Dave Hall at DHC Engineering did the

conceptual design of four separate

configurations to address the N+2 goals with a

down selection to one favorable configuration.

This yielded the Advanced Model for Extreme

Lift and Improved Aeroacoustics (AMELIA).

2.2 Conceptual Designs Considered

Four CESTOL configurations were

developed for consideration for the large scale

wind tunnel test. The first concept,

Configuration 1, has a more conventional

appearance with a high aspect ratio wing, a tee

tail, and twin engines configured over the wing,

as can be seen in Fig. 1. The trailing edge wing

surface aft of the engine is designed for turning

the flow to create poweredlift.

Fig. 1. Conceputal design of Configuration 1 consisting of

a high aspect ratio wing, a teetail, and twin engines

configured over the wing.

The second concept, Configuration 2, is a

hybrid blendedwingbody. The design utilizes

circulation control at the leading and trailing

edges of the wing. This configuration utilizes

over the wing engine locations for noise

shielding and engine exhaust entrainment

purposes. A structural rudder and Vtail were

also employed in this design. Configuration 2 is

shown in Fig. 2.


circulation control wings and over the wing engine

mounting for enhanced powered lift.

The third aircraft configuration was inspired

by the extensive research now underway to

develop a true BlendedWingBody aircraft,

BWB, by the Boeing Company[17]. This

aircraft concept is a significant departure from

the first two aircraft designs. The turbofan

engines are embedded within the very thick

wing root as the wing blends into the fuselage,

as shown in Fig. 3. The exhaust discharges

2

SIGN AND WIND TUNN

OT SPAN HYBRID WIN

zle at the

tent is not

is nozzle

increased

generating

consisting of

termed the

may be

a vertical

aft wings

to improve

rmation at

se vertical

sails than

tr

aft wing

planform

ave a high

ystem is a

e mounted

consisting of

hannel wing

D

F STO

D no

trailing edge of the vehicle. The i

only to produce thrust through t

throughout the flight but to creat

flow circulation around the aircraft

3 Conceputal design of Configuration 3

The final design, seen in Fig. 4, is

. It

Wing with

member joining the fore an

at the outer span points. The intent is

local air flow and mitigate shock f

high subsonic Mach numbers. Th

members are more like wingtip

winglets and act structurally as

forward wing sweeps aft and th

sweeps forward forming a diamon

shape in the top view. Both wings

propulsion

sized geared turbofan engi

Conceputal design of Configuration 4

wing design with

AMELIA

ch design, it w

n 1

N+2 design.

r hand was too

thin an N+2 time

unnel test, being

A utilized a

y with circulation

uration

riate

tigations into this

span model based

st locations.

s project, it was

st suited for the

s a rendering of

ter many design

tion 2

s

Configuration 2

wind tunnel test

difications were

alteration to the

ng system of the

as chosen as the

odynamic forces

s ability to take

Direct mounting

ough the aft end

the flow around

ody mount was

ent location with

EL TESTING OF CAL P

BODY LOW NOISE C

2.3 Configuration 2 Become

After close consideration of e

apparent that Configurati

ntional to be an

Configuration 4 on the oth

advanced to be considered w

frame. A large scale wind

conducted by a competing N

model that was similar to

it was a blended wing bo

Confi

appro

inve

showed that a 10’

would n

our perspective t

consulting all involved in th

onfiguration

was b

5 sho

a

Configur

AMELIA Design Featur

In order to utilize the

geometry in a large scale

design m

needed. The most significan

geometry came in the mount

wind tunnel model. A sting

ideal method to measure ae

for i

intrusively

of the model to the sting th

raised concerns with disturbin

the beaver tail. An under

designed to provide an attach

DEESIGN AND WIND TUNNEL TESTING OF CAL PO OLY’S AMELIA 10 FO OOT SPAN HYBRID WINGBODY LOW NOISE CE ESTOL AIRCRAFT

through a high aspect ratio 2D nozzzle at the

trailing edge of the vehicle. The in ntent is not

only to produce thrust through thhis nozzle

throughout the flight but to create e increased

flow circulation around the aircraft generating

additional lift.

Fig.3 Conceputal design of Configuration 3 consisting of

a blended wing body and embeded engines.

The final design, seen in Fig. 4, is termed the

DiamondWingBody (DWB). It may be

thought of as a JoinedWing with a vertical

structural member joining the fore andd aft wings

at the outer span points. The intent is to improve

local air flow and mitigate shock fo ormation at

high subsonic Mach numbers. The ese vertical

members are more like wingtip sails than

winglets and act structurally as sstruts. The

forward wing sweeps aft and the e aft wing

sweeps forward forming a diamond d planform

shape in the top view. Both wings h have a high

aspect ratio. The chosen propulsion s system is a

mediumsized geared turbofan engin ne mounted

in a channel wing.


high aspect ratio diamondwing design with cchannel wing

mounted engines.

2.3 Configuration 2 Becomes s AMELIA

After close consideration of ea ach design, it was

apparent that Configuratio on 1 was too

conventional to be an N+2 design.

Configuration 4 on the othe er hand was too

advanced to be considered wi ithin an N+2 time

frame. A large scale wind ttunnel test, being

conducted by a competing NR RA utilized a test

model that was similar to CConfiguration 3 in

that it was a blended wing bod dy with circulation

control wings[18]. Config guration 2 was

considered to be at the approp priate level for the

N+2 time frame. Further inves stigations into this

design also showed that a 10’ span model based

on Configuration 2 would no ot exceed the load

limits of all our perspective te est locations. After

consulting all involved in thiis project, it was

decided that Configuration 2—the hybrid

blended wing body—was be est suited for the

AMELIA test. Figure 5 show ws a rendering of

Configuration 2 in flight af fter many design

iterations.

Fig. 5. Rendered image of Configura ation 2 the Hybrid

Blended Wing Body in flight.

2.4 AMELIA Design Feature es

In order to utilize the Configuration 2

geometry in a large scale wind tunnel test

setting, many design mo odifications were

needed. The most significant t alteration to the

geometry came in the mountiing system of the

wind tunnel model. A sting w was chosen as the

ideal method to measure aerrodynamic forces

and moments, mainly for it ts ability to take

measurements nonintrusively. . Direct mounting

of the model to the sting thr rough the aft end

raised concerns with disturbingg the flow around

the beaver tail. An underb body mount was

designed to provide an attachm ment location with

3

t

vertically

scussed in

e inverted

e negative

eded to be

s to extend

three view

the blade

oved and

mpennage

use

e majority

main focus

ustic and

strakes,

e previous

order to

d testing.

el via off

h

tilizes an

e see Ref.

radius flap

cost and

º, 60º and

to be

anical flap

e 90º flap

e to issues

he flaps of

modified

GOLDEN, MASO

minimal flow disturbance. The mou

with a clamshell blade that extend

from the sting tip. For purposes d

subsequent sections the model will

for a portion of the test, as a result t

angle of attack limit of the sting n

ded. The blade mount also serv

shows a

drawing of the model mounted to

attachment with empennage re

The tail

view bec

t

testing, due to the fact that the

of the testing is on aeroac

aerodynamic measurements. Th

in t

tured in

supplement subsequent research a

These surfaces attach to the mo

wi

The selected configuration

[plea

with a dual

2

order to minimize

complexity dual radius flaps of 0º, 3

propose

manufactured, as opposed to a mec

where deflection can be varied. T

deflection was later changed to 80º d

of the flap.

design were als

for each wing, in

flow disturbance

p surface.

the 80° flap,

showing the inter

attachment and tail

del.

low pressure air

pipe supplies the

ower the

units, while the

e low pressure air

ontrol slots at the

ed

ng, however two

in order to study

n entrainment of

trol flow. Height

ted using faired

rent heights [see

l engine height

act as pressure

pressure air is fed

n

experiment it’s

el be highly

re the maximum

instrumentation

t wing and was

ry CFD res

atic of the model

cement of the

ACIANO,

be a single continuous flap

order to reduce the amount o

from discontinuities of the fl

, wit

Cut away of the AMELIA

blad

empennage on the manufacturing m

supplies the necessary high an

to the model. The larger blue

ir required to

Propulsion Simulator (TPS)

pipe provides t

necessary for the circulation

piping systems will be discus

onfiguratio

will be mounted over the w

mounting heights will be teste

the effects of engine height

exhaust in the circulation co

adjustments will be compl

two diff

for the optim

These pylons als

vessels within which the high

A Instrumentati

As a CFD validation

imperative that the mo

instrumented in order to capt

amount of data. Almost al

placement occurs on the le

chosen based on prelimin

span sche

illustrating the relative pl


minimal flow disturbance. The moun nt is faired

with a clamshell blade that extends s vertically

from the sting tip. For purposes di iscussed in

subsequent sections the model will b be inverted

for a portion of the test, as a result th he negative

angle of attack limit of the sting ne eeded to be

extended. The blade mount also serve es to extend

this negative limit. Figure 6 shows a three view

drawing of the model mounted to the blade

attachment with empennage rem moved and

relevant dimensions shown. The tail e empennage

is not shown in the threeview beca ause it will

not be attached to the model during th he majority

of the testing, due to the fact that the main focus

of the testing is on aeroaco oustic and

aerodynamic measurements. The e strakes,

structural rudder and Vtail seen in th he previous

figure were manufactured in order to

supplement subsequent research an nd testing.

These surfaces attach to the mod del via off

blocks.

Fig. 6 Threeview drawing of AMELIA wit th stingblade

attachment with the tail surfaces removed.

The selected configuration uutilizes an

optimized supercritical airfoil [pleas se see Ref.

1920 for further details] with a dual radius flap

at the trailing edge[Please see Ref. 21 1 for further

details]. In order to minimize cost and

complexity dual radius flaps of 0º, 300º, 60º and

90º deflections were proposed d to be

manufactured, as opposed to a mech hanical flap

where deflection can be varied. Th he 90º flap

deflection was later changed to 80º du ue to issues

with the manufacturing of the flap. T The flaps of

the Configuration 2 design were alsoo modified

to be a single continuous flap for each wing, in

order to reduce the amount of f flow disturbance

from discontinuities of the flaap surface. A cut

away view of the model, withh the 80° flap, is

shown in Fig. 7.

Fig 7. Cut away of the AMELIA showing the internal

structure along with the stingblade e attachment and tail

empennage on the manufacturing mo odel.

The piping seen in Fig. 7 exiting the blade

supplies the necessary high andd low pressure air

to the model. The larger blue pipe supplies the

high pressure air required to p power the Turbine

Propulsion Simulator (TPS) units, while the

smaller amber pipe provides th he low pressure air

necessary for the circulation c control slots at the

leading and trailing edges. TThe details of the

piping systems will be discusssed in subsequent

sections.

As shown in Configuration n 2 the TPS units

will be mounted over the wi ing, however two

mounting heights will be tested d in order to study

the effects of engine height oon entrainment of

exhaust in the circulation con ntrol flow. Height

adjustments will be comple eted using faired

structural pylons of two diffe erent heights [see

Ref. 2223 for the optima al engine height

location]. These pylons also o act as pressure

vessels within which the high pressure air is fed

to the TPS units.

2.5 AMELIA Instrumentatio on

As a CFD validation experiment it’s

imperative that the moddel be highly

instrumented in order to captu ure the maximum

amount of data. Almost alll instrumentation

placement occurs on the lef ft wing and was

chosen based on prelimina ary CFD results.

Figure 8 is a halfspan schem matic of the model

illustrating the relative plaacement of the

4

DESIGN AND WIND TUNNEL TESTING OF CAL POLY’S AMELIA 10 FOOT SPAN HYBRID WINGBODY LOW NOISE CESTOL AIRCRAFT

pressure ports and unsteady pressure

transducers. The model is instrumented with

280 static pressure ports in five chordwise

groups and one spanwise group (highlighted in

red in Fig. 8). Five static pressure ports are

located on the right wing in order to verify

symmetry in the pressure distribution.

Eight unsteady pressure Kulites exist on

the model (shown as blue circles in Fig. 8). As

aeroacoustics is one of the main focuses of the

large scale test, five Kulites are located in line

with the engine assembly. The remaining three

Kulites are located at the estimated passengers

head level, on the wing blend to gain a better

understanding of the implications of over the

wing mounted engines and passenger comfort

level. Six stationary microphones will be placed

underneath model approximately 5 ft above the

tunnel floor (in order to be sufficiently out of

the boundary layer) to measure farfield noise

generated by the poweredlift design. A 70

element stationary microphone array will also

be placed directly underneath the wing below

one of the propulsion simulators to determine

the noise signature associated with TPS unit.

Fig. 8. Halfspan schematic of AMELIA illustrating the

relative location of the pressure ports and unsteady

pressure transducers on the left half of the model.

In order to monitor the health of the TPS

units, each unit is instrumented with seven

rakes, each consisting of 4 total pressure probes

and a thermocouple. The design and amount of

these rakes were based on discussions with

engineers from industry who have previous

experience with TPS units.

Each of the circulation control plenums is

instrumented with 3 total pressure probes (the

plenums can be seen in Fig. 7), while a cross

correlation rake measures boundary layer

interactions at the plenum exit or slot. Further

discussion of the design and theory behind the

cross correlation rake can be found in Section 5.

The majority of the right wing is free of

instrumentation in order for the local shear

stress measurements to be obtained. In order to

take high fidelity measurements, the surface

must be of number 2 finish (mirror like) or

better. For this reason the model will be painted

with a black Imron coating.[24] Further

discussion of the requirements of the technique

will be discussed in Section 4.

2.6 Internal Design of AMELIA

The model is supplied using two separate air

systems for the propulsion simulators and the

blown slots. Figure 9 shows a complete cut

away schematic of the model showing the

internal piping for both the high and low

pressure systems.

Fig. 9. A complete cutaway schematic of AMELIA

showing the 8 in flow thru balance and the internal piping

for both the high and low pressure systems.

The high pressure air system (600 psi

maximum determined by the limits of the flow

thru balance) is supplied thru the NASA

provided sting into the fabricated strut. The air

passes up the strut and through the 8in flow thru

balance. On the front of the balance is a flow

control system that controls the air flow to the

left and right hand TPS units. The airflow is

controlled using conical plugs that can be

remotely controlled while the tunnel is running.

The conical plugs are driven using MMP 24vdc

gear motors, and use linear potentiometers for

position feedback. The plugs can be positioned

5

. The TPS

steel pipes

at feed the

lete piping

the high

sting

air system

roximately

air to the

ading and

trol wing.

lled using

pots for

m can

trol room.

cts on the

d by a pipe

e pipe

for the low

for system

ment.

GOLDEN, MASO

100% mass flo

stainless

that attach to wing mounted pylons t

e 10 shows the com

and mass flow control plenum fo

pressure air system along with the

A schematic of the high pressur

(ap

supply th

at the l

trialing edges for the circulation co

The low pressure system is contr

, with rotary

feedback. The flow to each plen

controlled individually from the co

adverse eff

balance the low pressure plenum is f

that has bellows at each end of t

pressure system along with the bellows

blade attac

est

y

e Aerodynamic

0 ft win

e week long large

e NFAC offered

rge wind tunnels

with the most

model could be

llows for cleaner

ed aerodynamic

l could supply the

ow rate necessary

nd the turbofan

enough such that

he CCW wings

or of the tunnel

r

was acoustically

ic and acoustic

e performed

AC’s cost and

time frame and

cale schematic of

g in the 40 ft by

th the associated

mounted on the

ind tunnel model

nnel.

AMELIA in the

ounted and inverted

with the far

nary acoustic array.

ACIANO,

Large Scale Wind Tunnel

Wind Tunnel Test Facili

Sca

Complex (NFAC) 40 ft by

was chosen to perform the ni

scale wind tunnel test. T

several benefits over other l

,

significant being: the 10 foo

measurements of the produ

forces and moments, the tunn

high pressure air at the mass f

to operate the CCW slots

simulators, the tunnel is large

nwash created by

would not impinge on the fl

thus creating cleaner f

measurements, the tunnel

treated such that aerodyna

measurements could

e N

schedule fit within Cal Poly’

2 shows a

the model inverted on the sti

80 ft NFAC wind tunnel w

acoustic measurement device

r relative to the

placed in the center of the t

shows the relative scale of

12. A schematic of AMELIA

on the sting in the NFAC alon

es and the stati


to provide from 0100% mass flow w. The TPS

units are supplied through stainless steel pipes

that attach to wing mounted pylons th hat feed the

TPS units. Figure 10 shows the comp plete piping

and mass flow control plenum forr the high

pressure air system along with the stingblade

attachment.

Fig. 10. A schematic of the high pressuree air system

internal to AMELIA.

The low pressure system (app proximately

100 psi) will be used to supply the e air to the

plenums that feed the slots at the leeading and

trialing edges for the circulation con ntrol wing.

The low pressure system is contro olled using

24vdc gear motors, with rotary pots for

feedback. The flow to each plenu um can be

controlled individually from the con ntrol room.

To isolate and minimize adverse effeects on the

balance the low pressure plenum is fe ed by a pipe

that has bellows at each end of th he pipe, as

shown in Fig. 11.

Fig. 11. An internal schematic of the pipingg for the low

pressure system along with the bellows for system

isolation downstream of the stingblade attachhment.

3 Large Scale Wind Tunnel T Test NFAC

3.1 Wind Tunnel Test Facilit ty

The National FullScal le Aerodynamic

Complex (NFAC) 40 ft by 8 80 ft wind tunnel

was chosen to perform the nin ne week long large

scale wind tunnel test. Th he NFAC offered

several benefits over other la arge wind tunnels

across the United States, with the most

significant being: the 10 foott model could be

mounted on a sting which aallows for cleaner

measurements of the producced aerodynamic

forces and moments, the tunne el could supply the

high pressure air at the mass fl low rate necessary

to operate the CCW slots aand the turbofan

simulators, the tunnel is large enough such that

the downwash created by tthe CCW wings

would not impinge on the flooor of the tunnel

thus creating cleaner fa arfield acoustic

measurements, the tunnel was acoustically

treated such that aerodynam mic and acoustic

measurements could bbe performed

simultaneously, and the NFFAC’s cost and

schedule fit within Cal Poly’ss time frame and

budget. Figure 12 shows a s scale schematic of

the model inverted on the stin ng in the 40 ft by

80 ft NFAC wind tunnel wi ith the associated

acoustic measurement devices s mounted on the

tunnel floor relative to the w wind tunnel model

placed in the center of the tu unnel. Figure 13

shows the relative scale of AMELIA in the

NFAC.

Fig. 12. A schematic of AMELIA m mounted and inverted

on the sting in the NFAC along g with the farfield

stationary microphones and the statioonary acoustic array.

6


Fig. 13. Isometric view of AMELIA mounted on the sting

in the NFAC.

3.2 AMELIA Test Matrix

The proposed text matrix for the model includes

calibrations while mounted on the sting balance

of both model and acoustic instrumentation,

static tests of all blown features on the model, a

Reynolds number sweep, a dynamic pressure

sweep, a turbofan simulator sweep, and a CCW

sweep.

After the completion of the preliminary

sweeps, eight to ten critical tests points will be

identified from the experimental test data

obtained. During the critical tests points all

experimental instrumentation will be utilized.

Acoustically, the farfield measurements along

with a traversing 30 degree sideline

measurements will be made. Also the 70

element stationary array placed under one of the

turbofan simulators will be utilized to

characterize the noise signature beneath the

wing. The aerodynamic forces, moments, static

pressure measurements, and unsteady pressure

measurements will simultaneously be

conducted. Then the model will be inverted and

the same critical test points will be repeated.

Inverting the model offers several advantages in

obtaining experimental measurements. The oil

interferometry requires less lighting in the large

wind tunnel and high power lights can be shown

directly on the reflective surface. The 70

element stationary array can be utilized to

identify any hot spots created by the TPS units.

The cross correlation rake will also be utilized

while the model is inverted.

Once the critical test points have been

completed, the model will be returned to right

side up and alpha (up to +20 to 5 degrees) and

beta (+20 to 20 degrees) sweeps will be

conducted at three different tunnels speeds. The

majority of the tests will be conducted at lower

tunnel speeds in order to correctly match the

necessary design thrust coefficients (limited by

the TPS thrust output). Only farfield acoustic

measurements, aerodynamic forces and

moments, and static pressure measurements will

be conducted for this portion of the test

allowing a significant number of test points to

be investigated to create the database for current

and future CFD validation efforts.

4 Oil Interferometry

The FringeImage Skin Friction (FISF)

technique, also known as oil interferometry, was

chosen for the large scale wind tunnel test to

measure local skin friction because both

magnitude and direction can be determined

from a single image. The FISF technique has the

advantage of maturity and reliability which

becomes significant due to the difficulties of

obtaining measurements in the NFAC due to its

sheer size and the amount of time between

tunnel shut down and the point where

photographs of the model can be obtained.

4.1 FISF Technique

The FISF technique was developed by Monson

et al.[25] The theory behind the technique is that

a single relationship can relate the thickness of

the oil drop at a single location to the skin

friction magnitude and direction. The oil

thickness is measured via photographic

interferometry. Data reduction is completed

with CXWIN4GG, a PC application developed

by Zilliac.[26]

The FISF technique has a few key steps in its

process to obtain the crucial photographs

necessary to determine surface skin friction. The

process is as follows: A drop of silicone oil of

known viscosity is placed on the model surface.

Once the oil is applied to the surface, the air

flow begins, causing the oil to spread and thin.

The air continues to flow for a given time,

continually thinning the oil. When sufficient

time has elapsed (220 minutes, depending on

oil viscosity), the air flow is turned off. A quasi

monochromatic light source is then indirectly

applied to the surface by use of a large diffuse

7


reflector. Light is reflected from the surface of

the model and oil. Two specific light rays are

reflected and separated by the thickness of the

oil, shown in Fig. 14. Once the oil has thinned,

the oil height linearly varies where constructive

and destructive interference occurs, causing

light and dark fringes on the oil surface. Skin

friction is proportional to the spacing distance,

Δs, on the fringes which is directly related to the

thickness of the oil. The relationship for skin

friction is as follows:

C f = w

q

τ

∞ =

2 o o n s

q t

µ

λ

Δ

∞ ( )cos rθ

(1)

where Cf is the skin friction coefficient, τw is the

wall shear stress, q∞ is the freestream dynamic

pressure, no is the oil index of refraction, µo is

the oil viscosity, λ is the wavelength of the light

source, t is the duration of time the oil flow was

exposed to air flow, and θr is the light refraction

angle through the airoil interface. Eq. 1 holds

for zero pressure gradient and shear stress

gradients. Further details on the oil flow

technique and the theory behind it is covered by

Naughton and Sheplak.[27]

Fig. 14. A schematic of the basic FISF setup highlighting

the oil flow and fringe pattern on a droplet of oil[27].

4.2 Application of FISF to AMELIA

In order to successfully apply the FISF

technique, the fringes on a model need to be

clearly visible. Fringe visibility is based upon

the surface finish of the model. An ideal surface

is extremely smooth with consistent and durable

optical properties. Based on a study by

Zilliac[28] the best fringes appeared on high

flint content SF11 glass manufactured by Schott

Glass of Germany, which is an impractical

material for a wind tunnel model. A practical

surface finish for a model would be mirror like,

which can be achieved by nickel plating the

model surface. Acceptable substitutes have been

made utilizing polished stainless steel or black

Mylar sheets applied to the model surface.

Black Mylar sheets offer the most cost effective

solution for oil flow testing. However, at higher

speeds and long run times Mylar would begin to

peal along the edges, ruining any data

downstream. The continual Mylar reapplication

to the model would prove time consuming and

impractical due the model height in the NFAC

for the AMELIA test. Mylar is also difficult to

apply to a 3D surface, usually resulting in small

wrinkles in the Mylar distorting the skin friction

measurements. Polished stainless steel and

nickel plating have the durability that Mylar

lacks. Another alternative to nickel plated

aluminum is aluminum painted with black

Imron. Difficulties arose in the capability of

plating the fuselage of AMELA due to its sheer

size. For these reasons, the entire model will be

painted with Imron, also allowing future

experiments with AMELIA to investigate other

regions besides the wing.

In order to properly view the fringes, a

monochromatic light source must be reflected

off a diffuse reflector. In large wind tunnel

applications, the tunnel walls have been used as

the reflector.[29] Unfortunately, the NFAC

tunnels walls are composed of a matte metal

mesh covering a deep, perforated acoustic liner,

rendering the walls unable to sufficiently light

the tunnel. The next option is to build a reflector

which encompasses the portion of interest on

the model. A small hole would be cut in the

reflector allowing a camera to capture the fringe

spacings; a setup such as this is shown in Fig. 4.

AMELIA has a highly curved blended wing

which causes additional difficulty in the image

processing. Due to the models highly polished

and curved surfaces, the camera will see

reflections from a large area of the wind tunnel.

Therefore, if the wind tunnel is being used as

the diffuse reflector, large areas of the tunnel

need to be white. Since this would be costly in

the NFAC, it is necessary to use a curved

diffuse reflector. This will ensure the model is

uniformly lit allowing for accurate fringe

8


spacing identification and does so with fewer

lights. The type of diffuse reflector used on the

wing blend is also shown in Fig. 15.

The angle at which the light enters the

camera can greatly affect the skin friction

measurement, especially at large angles such as

leading edges or the blended wing portion of the

model. Zilliacs CXWIN4GG software utilizes

single camera photogrammetry to determine the

angle of the light reflecting off the oil on the

surface of the wind tunnel model. This is made

possible by using fiducial marks over the model

surface. The camera captures an image

encompassing the entire wing with several

fringes over the wing surface. Within that image

are multiple fiducial marks with known

locations on the model coordinate system.

Zilliacs software completes the photogrammetry

by matching the known fiducial marks locations

(both a pixel xy coordinate system as well as

the model coordinate) to a given set of model

points. This allows the software to calculate the

light incident angle at any visible point on the

model.

Due of the size of the NFAC, a special

procedure has been devised to ensure accurate

fringe production. Normally the tunnel

transients are short, resulting in little error from

the startup and shutdowns. However, the NFAC

requires a minimum of 5 minutes to startup and

shutdown which can introduce unacceptable

error into the skin friction measurements if the

incorrect viscosity of oil is chosen for the test.

In order to ensure recording accurate fringes, the

model will be at a high angle of attack during

the tunnel startup allowing separated flow (low

to no shear) over the wing. Once the tunnel

freestream has been reached, the model will be

positioned to the angle of attack of interest. At

this point, slot blowing and the turbine

simulators will be started as well. The model

will remain at this test condition for a minimum

of 20 minutes. Once the oil is sufficiently

spread, the slot blowing, turbine simulator, and

tunnel freestream will be turned off, while the

model is once again pitched upward to cause

separation over the wing allowing the fringes to

be unaffected by the shutdown procedure. Once

the flow has stopped, the diffuse reflector and

camera will be brought into the tunnel. The

model will be inverted for the skin friction

measurements, allowing for optical access to the

suction side of the airfoil without having to be

physically placed above the model. A diffuse

reflector will be held up to the model, lighting

it, while a second person will capture the fringe

spacings in two images. This process is time

consuming, but worthwhile to ensure quality

data for CFD validations to be made against.

For this reason, only eight to ten key test

conditions will be investigated with oil

interferometry for CFD validation. Please refer

to Ref. 30 for further investigation of the FISF

technique for the preparation of the AMELIA

test.

Fig. 15. The FISF solution used for the wing blend. The

dark spot is due to no light being reflected by the camera

lens.

5 Boundary and Shear Layer Velocity Profiles with a Micro Flow Measurement Device

5.1 Application of FISF to AMELIA

In 2001, NASA Glenn developed a

thermocouple boundary layer rake which has

the capability to measure 0.0025 inches from

the surface, four times closer than any state of

the art measurement before.[31] This was

achieved with the device shown in Fig. 16. This

device is constructed with a base made out of

aluminum, a constant thickness strut which

protrudes from the base, and the necessary

electrical wires corresponding to the number of

thermocouples present for a given design. The

strut is made of quartz, chosen for its insulative

9

. From the

re several

functions

en height

ual to the

e no strut

horseshoe

d at the

in NASA

ke.

undary layer

ctions and b)

a platinum

ture above

p, the air

difference

ownstream

n velocity

rake setup

xactly the

rve can be

calibration

ds number

Gustave

le rake’s

CCR) was

calibration

anticipated

conductive

er of the

mperature

tantaneous

ding edge

oltage ta

ons in the

the local

the loop

th velocity

correlation

e between

GOLDEN, MASO

and low thermal expansion propertie

re

pairs of thermocouples. The devic

based on the theory that for a gi

above the base, the velocity is e

velocity of the flow as if there we

present. It should be noted that no

found to be sh

intersection of the strut and base

r

Photographs of a thermocouple b

rake, a) shows the base and electrical conn

At the center of the strut, there is

loop which is heated to a temper

ambient. As air flows over the lo

downstream is heated. The voltage

between the upstream and

lated to kno

values obtained from a total pressur

next to the thermocouple rake at

same axial position. A calibration c

developed from this data. This

procedure is needed for every Reyno

Upon further discussions wit

Fralick, one of the thermocou

designers, a Cross Correlation Rake

suggested for use since an in situ

process would prove difficult in the

The CCR contains a

platinum loop located at the cen

substrate. This loop is heated to a t

above the ambient conditions. In

voltage differences on the loop’s le

and trailing edge are measured by

along the loop. The voltage fluctuat

loop are caused by fluctuations i

resistance. The resistance relates t

temperature, which relates directly w

Utilizing a cross

the ti

upstream and

n be calculated.

he upstream and

p is known, the

MELIA

both leading and

to vastly increase

effort will be to

ve the flap. The

shown in Fig.

his region is of

he jet’s boundary

er above the jet.

validation of the

ill be achieved

er detail

the CCR].

ay be tested to

ss on AMELIA.

at Cal Poly, with

bstrate at NASA

, then a trailing

ss Correlation Rake

the airfoil section is

ounting apparatus is

AMELIA test is

strate, platinum

voltage taps, as

ig. 18

IA flap and was

n

arge as possible

ACIANO,

voltage fluctuations on th

downstream voltage taps c

Since the distance between

downstream edges of the lo

flow velocity can be calculate

CCR to

The AMELIA model has

trailing edge blowing in order

the lift. Part of the validatio

acquire velocity profiles ab

CCR will be implemented as

chieve this.

particular interest because of

layer as well as the shear la

The design, construction, and

bsonic speeds

for furt

design and construction o

addition, transonic speeds

demonstrate the CCR readin

constructed

the platinum applied to the s

Glenn. The CCR will first b

plate for validation purpose

A rendering of the Cr

applied to the AMELIA flap wher

shown as in light blue and the

The CCR designed for th

composed of a quartz su

heating loop, and platinum

photograph in

was sized based on the AME

sized to 1.1 x 0.55 inches

thick. It needed to be as


and low thermal expansion properties s. From the

base to the top of the strut, there aare several

pairs of thermocouples. The device e functions

based on the theory that for a givven height

above the base, the velocity is eq qual to the

velocity of the flow as if there werre no strut

present. It should be noted that no horseshoe

vortices were found to be she ed at the

intersection of the strut and base in NASA

Glenn’s testing of the thermocouple raake.[32]

Fig. 16. Photographs of a thermocouple bo oundary layer

rake, a) shows the base and electrical conne ections and b)

detail of platinum and gold films.[32]

At the center of the strut, there is a platinum

loop which is heated to a tempera ature above

ambient. As air flows over the loo op, the air

downstream is heated. The voltage difference

between the upstream and ddownstream

thermocouples is then related to know wn velocity

values obtained from a total pressure e rake setup

next to the thermocouple rake at eexactly the

same axial position. A calibration cu urve can be

developed from this data. This calibration

procedure is needed for every Reynollds number

intended for testing.

Upon further discussions with h Gustave

Fralick, one of the thermocoup ple rake’s

designers, a Cross Correlation Rake ((CCR) was

suggested for use since an in situ calibration

process would prove difficult in the anticipated

application. The CCR contains a conductive

platinum loop located at the centter of the

substrate. This loop is heated to a teemperature

above the ambient conditions. Ins stantaneous

voltage differences on the loop’s leaading edge

and trailing edge are measured by v voltage taps

along the loop. The voltage fluctuatiions in the

loop are caused by fluctuations in n the local

resistance. The resistance relates to o the loop

temperature, which relates directly wiith velocity

at that location.[33] Utilizing a cross correlation

script from MATLAB[34], the tim me between

voltage fluctuations on the e upstream and

downstream voltage taps ca an be calculated.

Since the distance between tthe upstream and

downstream edges of the loo op is known, the

flow velocity can be calculated d.

5.2 Application of CCR to A AMELIA

The AMELIA model has both leading and

trailing edge blowing in order to vastly increase

the lift. Part of the validation n effort will be to

acquire velocity profiles abo ove the flap. The

CCR will be implemented as shown in Fig. 17

in order to achieve this. TThis region is of

particular interest because of t the jet’s boundary

layer as well as the shear lay yer above the jet.

The design, construction, and validation of the

CCR at subsonic speeds wwill be achieved

[please see Ref. 35 for furthher detail on the

design and construction of f the CCR]. In

addition, transonic speeds mmay be tested to

demonstrate the CCR readine ess on AMELIA.

The substrate was constructed at Cal Poly, with

the platinum applied to the su ubstrate at NASA

Glenn. The CCR will first be e applied to a flat

plate for validation purposes s, then a trailing

edge of an airfoil.

Fig. 17. A rendering of the Cro oss Correlation Rake

applied to the AMELIA flap where e the airfoil section is

shown as in light blue and the mmounting apparatus is

shown in lime green.

The CCR designed for the e AMELIA test is

composed of a quartz subbstrate, platinum

heating loop, and platinum voltage taps, as

shown in the photograph in F Fig. 18. The CCR

was sized based on the AMELLIA flap and was

sized to 1.1 x 0.55 inches aand 0.043 inches

thick. It needed to be as llarge as possible

10

SIGN AND WIND TUNN

OT SPAN HYBRID WIN

or trailing

inch. The

ight above

his height

The total

ith the top

lower half

lides from

substrate.

thickness

leted CCR

h only the

ires for the

Rake of the

Correlation

l model

gn g

n of the

completed

ete

te

scale wind

the NFAC

ese results

D

F STO

without being too near to the slot

edge. The resulting length was 1.0

height was based upon the desired h

the flap to measure velocity profiles.

termined to be 0.12 inches

height of the rake is 0.040 inches,

half above the flap and the remainin

below the flap. Quartz microscope

Ted Pella, Inc. were utilized as th

y sold at

Figure 19 shows a com

in the flat plate mounting device wi

exposed surface and the associated

Photograph of the Cross Correlatio

Cros

researchers have

a design for a large scale wind tunn

compliance of NASAs N+2 des

fabricati

and at the time this paper was

nearly 90% comp

a projected delivery d

Finally, large

ned for

T

and acoustic

and

acknowledge the

ent awar

with technical

Clif Horne, who

ork. The authors

ch Center’s Fluid

, Gregory Zilliac

ta

IA. The authors

NASA Glenn,

or his time and

A's

)

erence, Atlanta GA,

edaisch J. Evaluation

ediction of

ntrol and

ciences Meeting and

m A. Computational

foil using FLUENT.

ontrol Technology

. Jones, Vol. 214 of

eronautics, chap. 21,

ics and Astronautics,

, Xiao X

ng in

ls.

y,

214 of Progress in

chap. 19, America

stronautics, Inc., pp.

R. J., Ahuja, K. K.,

evaluation of steady

lation control airfoil.

ontrol Technology

. Jones, Vol. 214 of

eronautics, chap. 22,

ics and Astronautics,

EL TESTING OF CAL P

BODY LOW NOISE C

lift

current

The authors would like to

NASA Research Announce

#NNL07AA55C,

monitors Craig Hange and

provided funding for this

wish to thank the Ames Resea

Mechanics Lab, in particula

and David Driver for the assi

the FISF technique to AME

would also like to than

especially Gustave Fralick

Overview of NA

viation (ER

Fundamental Aeronautics Con

, Nagib H and K

46th AIAA Aerospace

, AIAA, Reno NV, AIA

McGowan G and Gopalarathn

study of circulation control ai

ions of Circulation

edited by R. D. Joslin and G.

Progress in Astronautics and

American Institute of Aeronau

McGowan G, Gopalarathnam

odel

control airfo

Circulation Control Technolo

Joslin and G. S. Jones, Vol.

Astronautics and Aeronautics,

Institute of Aeronautics and

Liu, Y., Sankar, L. N., Englar,

and Gaeta, R. J. Computationa

and pulsed set effects on a circ

tion

edited by R. D. Joslin and G.

Progress in Astronautics and

American Institute of Aeronau

DEESIGN AND WIND TUNNEL TESTING OF CAL PO OLY’S AMELIA 10 FO OOT SPAN HYBRID WINGBODY LOW NOISE CE ESTOL AIRCRAFT

without being too near to the slot or trailing

edge. The resulting length was 1.00 0 inch. The

height was based upon the desired he eight above

the flap to measure velocity profiles. TThis height

was determined to be 0.12 inches. . The total

height of the rake is 0.040 inches, w with the top

half above the flap and the remaining g lower half

below the flap. Quartz microscope s slides from

Ted Pella, Inc. were utilized as the e substrate.

Microscope slides were only sold at aa thickness

of 1.0 mm. Figure 19 shows a comp pleted CCR

in the flat plate mounting device witth only the

exposed surface and the associated w wires for the

rake.

Fig. 18. Photograph of the Cross Correlation n Rake of the

first batch of rakes delivered to Cal Poly.

Fig. 19. Photograph of the completed Crosss Correlation

Rake mounted in the flat plate apparatus.

6 Conclusions

Cal Poly and GTRI researchers have completed

a design for a large scale wind tunne el model in

compliance of NASAs N+2 i goals. design

PatersonLabs has started fabricatioon of the

model and at the time this paper was completed

AMELIA was nearly 90% compl lete. The

model has a projected delivery da ate of late

September of 2010. Finally, large scale wind

tunnel test activities are planned for the NFAC

starting in the summer of 2011. Th hese results

will provide poweredlift and acoustic

validation data for current and future 3D

modeling efforts.

6 Acknowledgements

The authors would like to acknowledge the

NASA Research Announcem ment award under

Contract i#NNL07AA55C, with technical

monitors Craig Hange and Clif Horne, who

provided funding for this wwork. The authors

wish to thank the Ames Researrch Center’s Fluid

Mechanics Lab, in particular r, Gregory Zilliac

and David Driver for the assis stance in applying

the FISF technique to AMEL LIA. The authors

would also like to thank k NASA Glenn,

especially Gustave Fralick ffor his time and

assistance.

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Copyright Statement

The authors confirm that they, and/or their company or

organization, hold copyright on all of the original material

included in this paper. The authors also confirm that they

have obtained permission, from the copyright holder of

any third party material included in this paper, to publish

it as part of their paper. The authors confirm that they

give permission, or have obtained permission from the

copyright holder of this paper, for the publication and

distribution of this paper as part of the ICAS2010

proceedings or as individual offprints from the

proceedings.

13

design and wind tunnel testing of cal poly's amelia 10

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