NASA Technical Reports Server (NTRS) 19970008122: Effect of In-Flight Ice Accretion on the Performance of a Multi-Element Airfoil

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by  NASA Technical Reports Server (NTRS)

Effect of In-Flight Ice Accretion on the Performance of a
Multi-Element Airfoil
Abdollah Khodadoust
Chat Dominik
McDonnell Douglas Aerospace
Lortg Beach, CA 90810-1864
Jaiwon Shin
Dean Miller
NASA Lewis Research Center
Cleveland, OH 4.4135
Abstract
loss in maximum lift coefficient
The effects of potential in-flight ice accretion on the

aerodynamic performance of a multi-element high- RN Reynolds number based on chord
lift nirfoil have been investigated at moderate-to-
high Reynolds numbers. The investigation was xlc nondimensional coordinate
conducted in the Low Turbulence Pressure Tunnel
(U PT) at NASA Langley Research Center. LTPT Low Turbulence Pressure TunneL
Simulated ice shapes obtained from eazlier testing
in the Icing Research Tunnel (IRT) at NASA Lewis IRT Icing Research Tunnel
Research Center were used on all three elements of
the multi-element configuration. Incremental
performance effects due to the ice accretion are INTRODUCTION
presented for both smooth and rough ice
accretions. Reynolds number effects on the High-lift system improvements on t
measured performance characteristics were also aircraft have been the subject of extensive
assessed. The present results confirm the for the past few years1'2. In order for the
importance of avoiding any ice accretions on th€ systems to achieve high levels of performa
forward element of a lifting configuration. new designs are often highly optimized for
overhang. As such, there was a conc
environmental contamination, such as in-f
NOMENCLATURE accretion, could cause a significant degrac
the high-lift system's performance.
angle of aftack degrees
Performance of airfoils and wir
slat deflection angle, degrees adverse weather conditions has been a sut
investigation in the past. Lynch et
flap deflection angle, degrees documented the effects of leading edge rou
on wings/airfoils in cruise and I
C pressure coefficient configurations. Their measurements in
values over 30% were possible
k/c ratio of roughness height to airfoil chord cruise configuration and over 10% for the I
configuration airfoils. The reduction in ar
M free stream Mach number attack margin to stall was as much as 5 degr
both cruise and landing configurations.
Presoived at Ue AH&SAE Intomaziorta/ IcLng Symposium 5, performance of a similar airfoil was tested
Mont,eai, Canada. S8pramhør 18-21, 1995. Copyngft by takeoff configuration by Bragg et. al.5 to ass
Uo Ama, w' H8iC*ptBr Soclaty, Inc. All nght
impact of underwing frost caused by cold-soaked ice shapes tested were slmulatiOnS of
fuel. Little change in the drag and maximum lift was measurements taken in the NASA Lewis' IRT on a
noted when the frost formation was simulated similar modeI9'°. Typical approach conditionS for a
downstream of the stagnation point (at maximum narrow body twin-jet transport aircraft were used to
lift) on the main element. The effect of frost simulate the flight-scale icing encounter in the IRT.
formation on the upper surface of an airfoil similar to
that used above was evaluated by Valarezo6. The The roughness associated with the iced
measurements indicated that in the takeoff surfaces was simulated by applying carborandum
configuration, maximum lift/stall-margin tosses were grit particles on top of the smooth ice shapes on the
most significant when the frost formation was slat, main element, and flap of the multi-element
high lift airfoil. The appropriate grit" size was
simulated on the slat.
estimated using a two-step process. First, the ice
Most recently, the performance of an roughness size was estimated for a similar 3-foot
advanced technology high-lift airfoil was evaluated chord mutti-element high-lift airfoil which was tested
in the presence of in-flight ice accretion at in the NASA Lewis' IRT9'10. Second, this ice
moderate-to-high Reynolds numbers at NASA roughness height was geometrically scaled to be
Langley's LTPT. The performance of the high-lift consistent with the LTPT high-lift airfoil. This scaled
system was evaluated to determine incremental value of roughness size was used to select the
effects of ice. The resuhs reported here are part of appropriate grit sizes for the ice shapes on the slat,
a cooperative experimental program conducted by main element, and flap of the LTPT airfoil.
McDonnell Douglas Aerospace, NASA Lewis
Research Center, and NASA Langley Research
Center to establish a data base of highlift airfoil ice
Acw
accretions and their effect on high-lift system
performance.
TEST FACILITY AND MODEL
Wek. SWV 5LdeU BLC .1
DESCRIPTION rake etrut vNw%9 5y8tIfl
9 Asutuitu*'ics
The Langley LTPT is a single return, dosed
throat wind tunnel that can be operated up to 10
Fig. 1. Schematic of Low Turbulence Pressi.ue
atmospheres thus allowing very high Reynolds
number capability7 (Fig. 1). The test section is 3 Tunnel (LTPT)
feet wide by 7.5 feet high by 7.5 feet long. A
sidewaii boundary layer control (BLC) system in the
/
test section is used to promote two-dimensional flow
over the model. The BLC system uses the
differential pressure between the test section and
the atmosphere to provide suction of the boundary
layer through porous endplates. The system
yielded good quality two-dimensional flew over the
model for the Reynolds numbers tested8.
The modal spanned the width of the test
section and had a stowed airfoil chord of 22 Inches.
The multi-element airfoil tested in the landing
configuration is shown in Fig. 2. The slat chord ratio
was 14.48% and the flap chord ratio was 30% for
both configurations tested. The slat and flap had
deflections of 30-degrees with respect to the main
element.
The multi-element airfoil was tested both in
the dean and iced configurations. The toed
Fig. 2. Airfoil Geometries Tested in the LTPT
configuration of the airfoil is shown in Fig. 2. The
icki performance degradation, C1 due tO
simulated Ice. The data shown indicate that the
Reynolds number effect is not large for this case.
Previous results, however, show that tests at RN <
5 x 1O are not representative of a flight-scale
article4. In order to obtain the correct assessment
of performance penalties in this complex flowfiald,
measurements should be obtained as near to the
flight Reynolds number as possible. Subsequent
results are shown for a Reynolds number of 9
million. This is representative of the full-scale
environment that a stall-critical section of a new
generation Wing on a narrow body twin-jet transport
aircraft is expected to experience.
Fig. 3. View of High-Lift Model Support Brackets
ã.3O
20
Instrumentation consisted of pressure
orifices located along the centerline of the model. 18
The clean and Iced slat each had 40 chordwise and
16
10 spanwise pressure orifices. The main element
had 43 chordwise and 10 spanwise pressure 14
orifices in each of the clean and iced configurations-
AQIIAX12
The clean flap had 62 chordwise and 20 spanwise
(Z)
pressure orifices. The iced flaps had 49 chotdwise 10
and 20 spartwLse pressure orifices. The spanwise
8
orifices were located along (or near) the trailing
edge of each airfoil element to monitor the two- 6
dimensionality of the flow at run time. Integration of 4
the pressure measurements yielded the forces
reported here. The data is corrected for the effects 2
of sidewall suction system on the tunnel 0
parameters. Four rows of streamned support 0 4 8 12 16 20
brackets for high-lift devices (Fig. 3) were required
REYNOLDS NUMBER (x106)
due to very high loads (up to 15000 pounds)
associated with the high free stream dynamic
Fig. 4. Reynolds Number Effect on Maximum Lift
pressure and lift coefficients obtained. Drag data
Loss Due to Simulated Ice Accretion
were computed by integration of static and total
pressures obtained from the LTPT wake survey
Iced Airfoil Results - Smooth and Rough
rake system.
The key objective of this investigation was
to assess the performance degradation of a high-lift
system in the presence of potential in-flight ice
RESULTS
accretions. The lift performance of the multi-
element airfoil with ice for RN 9 million is shown in
Unless otherwise noted, all data are
Fig. 5. The presence of smooth ice accretion on the
presented for free stream Mach number M = 0.20.
multi-element airfoil surfaces caused a small drop in
with little change in as+J However,
flyncds Number Effects
The effects of Reynolds number on lift, and addition of roughness to the ice surfaces caused a
maximum lift loss, have been repeatedly substantial loss in airfoil lift performance.
documented in the past12'. The Reynolds
number study conducted dunng this investigation Effects of roughness on airfoil
aerodynamics have been long recognize&.
reaffirms the necessity of obtaining measurements
These effects continue to be a source of
at flight-representative Reynolds numbers.
investigation in iced airfoil aerodynamics. The
effect of rough ice is also shown in Fig. 5. The ice
Figure 4 shows the effect of Reynolds
number on the multi-element airfoil maximum lift roughness was simulated to closely resemble the
appreciable change in the Location of the stagnation
measured ice roughness heights in the tAT during
icing tests on a similar a1rfoil910. Addition of point in the elements of the high lift system.
roughness to the simulated ice shape increased the a-30 6,-30
penalty to over 10%. with reduction of a =
ang(e-of-attack-margin to stall of nearly 4 degrees. -4 1 _________________________
The conthbulion to the lift deficit comes primarily
from the main element, but this is caused by the
effect of the slat ice accretion on the downstream
-3
elements. The disrupted flow on the slat affects the
performance of the main element and the flap. This
can be obsetved from pressure distributions on the
three elements of the high lift system. -2
[sm car1RRTtI1 I
a.
6 3O f cii 0
l-- stwmltX
5i 6 = 30 L-t- rx icc -1
4
0
3
-
Q2 0 4 8 12 16
x/c (%)
1 Fig. 6. Effect of Rough Ice on the Stat Surface
Pressures at a =8 degrees
6=3O 5,=3O
0
0 4 8 12 16 20 24
a
-6
cx (DEGREES) I sy ii- cwt. —ii;_.iii
Fig. 5. Effect of Ice on the Lift of a Three-Element - C..ERN 2.5159
Airfoil. -5 - - iGH IcE 2 .38_j
The effect of rough ice on the multi-element
-4
airfoil pressure distribution at representative
approach conditions Is shown in Figs. 6-8 for 9
million Reynolds number. Examination of the -3
pressure distributions indicates that the pressure
peaks are reduced on alLthree elements. - 0
-2
As expected, similar trends are observed
near stall. The pressure distributions for the airfoil
-1
at cz=20 degrees ,jé"hown in Figs. 9-11 for the slat,
main element and the flap. The drop in the peak
Cp's on the three elements is quite evident. There 0
is a pronounced collapse in the slat peak pressure.
The influence is felt downstream by the main 1 i , i i
element and the flap through a reduction in the
4 16 28 40 52 64 76 85
ability of these elements to maintain the same peak
pressures as their respective clean counterparts. x/c (%)
Note that the pressure measurements indicate that
Fig. 7. Effect of Rough Ice on the Main Element
the presence of rough ice shapes on the leading
edge of the elements did not produce an Surface Pressures at a = 8 degrees
5,=30 6,30
promoting premature growth of the mergrng wakes
a 8 and shear layers from the three elements.
6,=30 5,=3O
a = 20
—17
—16
—15
—14
—13
—2 - —12
0. —11
0 —10
—9
a-
(3 -
—7
—6
—5
—4
—3
1 11 . . , . . —2
70 76 82 88 94 100
0
x/c (7)
0 4 8 12 16
Fig. 8. Effect of Rough Ice on the Rap Surface
pressures at cz= 8 degrees x/c (%)
Fig.9 Effect of Rough Ice on the Slat Surface
The pressure distiibutlons in Figs. 6.11
Pressures at u = 20 degreeS
demonstrate the effect of rough ice on the peak
pressures from each elemenL The ability to sustain
5 3c? o,=3cr
high peak pressures relates directly to the multi-
a - 20'
element airfoil's capability to generate high lift. The —10
peak pressure coefficients for the multi-element
airfoil are shown in Fig. 12 for RN=9 million. Data —g
are shown for the dean, smooth ice and rough ice
—8
configurations. Cleajiy the rough ice had the most
dramatic impact on the peak pressure coefficients. —7
Near stall, growth of the wakes from the slat arid
main element cause the flap to unload. Unlike the —6
classical mechanisms of stall nvoMng flow
—5
separation), no separation has been observed on 0.
0
the flap at the high angles of attack typical of stall —4
(flap incidence - 50 degrees). The growth of the
wakes and merging shear layers from the slat and —3
the main element reduce the effective angle of
—2
attack experIenced by the flap which leads to the
flap unloading. This is somewhat analogous to a
—1
decambering effect of the airfoil. This in turn leads
to the unloading of the aft portion of the main 0
element, and subsequently the unloading of the slat,
which can be observed in the peak pressures, as I
well as the entire pressure distribution. 4 16 28 40 52 64 76 88
x/c (%)
Presence of ice on the elements of the
Fig. 10. Effect of Rough Ice on the Main Element
high-lift system hastens the staJi process, and
Surface Pressures at a =20 degrees
reduces the lift performance in general. by
6-30' 6,=30
RN = 9.0 X 10' M 0.20
a = 20
-j
L °"1. Sm C J1
p = 30 -- - O..Lf2
oir O.i37I -- 9WTh I
icr o . 3cvJ
- - - - RUL1 6, = 30 —ó— ROUGh iC_J
-2
0 e I 1 I
1 -f'M. . 0 0.02 0.04 0.06 0.08
70 76 82 88 94 100
Cd
x/c (%)
Fig. 13. Effect of Ice on the Drag Performance of a
Fig. 11. Effect of Rough Ice on the Flap Surface
Three-Element Airfoil
Pressures at a =20 degrees
62 = 30 a, = 30 ffct of Slat Anti-Ice Oceration
-20
The effect of slat anti-ice operation (i.e.,
-18 [Sm c(l6uRAhi0N keeping the slat free of any ice) on the multi-
l-e- Q1
-16 . Le- siwm icr SLAT element airfoil performance was also investigated.
Lt - This was carried out by testing the three-element
ROUGIILCE
-14
airfoil both with and without simulated ice on the
slat, with the main element and the flap in the iced
configuration. The lift performance of the multi-
-10
element airfoil in the landing configuration at RN = 9
-8 million is given in Fig. 14. Data is presented for the
-6 dean airfoil along with the following iced airfoil
configurations:
-4
-2 FLAP a) ice was simulated only on the flap,
0 . i • I I I I•I I I I b) ice was simulated only on the main element
0 2 4 6 8 10 12 14 16 18202224
and the flap, and
a (DEGREES)
Fig. 12. Effect of Ice on Peak Suction Pressure for a c) ice was simulated on all three elements.
Three-Element Airfoil
Recall that for the iced airfoil was
In addition to the lift penalty, the presence over 10% when all three elements were in the
of ice causes a significant penalty in parasite drag. rough-ice configuration. When the slat was kept
This is shown for the airfoil at RN=9 million in Fig. dean, the was approximately 4%.
13. The integrated wake rake data showed that the Examination of the lift performance data shown in
parasite drag nearly doubted at representative Fig. 14 indicates that contamination of the slat
approach conditions. All subsequent comparisons dearly has the Largest impact on the lift
with the clean model are presented for the performance of the high lift configuration tasted.
configuration with rough ice. This is not unlike the Mach number effect on the
Although no impact on the stall margin was
slat performance. where an increase in the tree
measured when the slat was clean, a noticeable
stream Mach number has led to a flow
increase in parasite drag was measured. This is
breakdown/limitation which in turn resulted in lift
shown in Fig. 15 where the drag polar for the clean
reductions. The toss in and astall
multi-element airfoil, as well as the iced
performance due to rough ice on the slat further
configurations, are presented. In general, presence
reinforces the conclusions made following
of ice on the multi-element airfoil caused a
measurements on single- and multi-element airfoils
substantial increase in drag.
with leading edge roughness.
= 30
Sm 9JAccs wiTh ic_
Incidentally, the role of the flap in
developing and maintaining lift can be observed 5 r3o' -a-
t IN OD(1 •
from the lift performance data shown in Fig. 14. At
-- SLAT • P1IN •
representative approach conditions (w-B°), the
4
degradation in lift is approximately the same for all
configurations shown in Fig. 14. When only the flap
was In the iced configuration, the lift increment was
3
somewhat tower than the other iced configurations
shown. This suggests that the wake from the flap is
altered due to the ice accretion on the flap, which in
turn leads to the flap unloading and a reduction in
the peak pressures sustained by the flap. As a
result, the aft part of the main element and
1
subsequently the slat also unload. Note that this
effect is not quite obvious near stall conditions.
Here ordy a small reduction in lift performance is
o
observed when only the flap is iced. Near stall, the 0 0.02 0.04 0.06 0.08
flap is mostly unloaded in the clean configuration-
Hence, addition of simulated ice to the flap did not Cd
result in the same magnitude of lift performance Fig. 15. Drag Performance of a Three-Element
degradation near stall (as it did at representative Airfoil with Clean and Iced Stat
approach conditions) with no change in angle-of-
attack-margin tO stall. A typical pressure distribution for the iced
It 9JFF1XS WiTh iIIII1 airfoil with a clean slat at representative approach
-a- conditions is shown in Fig. 16. Regardless of the
63 30 -a- CLAP presence of ice on the slat, none of the high lift
Pi!N ELDIENI • 1L11P elements exhibit the capability to sustain the same
& =30' -Q•.- SUIT * P1AN • FLRP
5 peak pressures as their respective clean
configuration. It is interesting to note that the drop
in slat peak pressure is approximately the same,
4
whether the slat is iced or clean. This cleazly
indicates the significance of the developing wakes
and merging shear layers from the main element
3
(and the flap as mentioned ea,iler). Regardless of
ice on the slat, the premature growth of the main
element wake causes the flap to unload, which in
turn cause the main element, and subsequently the
stat, to drop in peak pressures and normal force in
general. Near stall conditions (Fig. 17.), the flap in
the clean configuration is already unloaded due to
the growth of wakes from the main element and
slat. However, the developing wake from the iced
0
0 4 8 12 16 20 24
slat and the iced main element cause the flap to
further unload, thereby reducing the peak pressure
a (DEGREES)
sustained by the flap. As mentioned previously, this
FIg. 14. Lift Performance of a Three-Element Airfoil
leads to the main element (and the slat) unloading.
with Clean and Iced Slat
-7 - RN = 9.0 X 106 M = 0.20 SY?L SLZ11K3 WITh III c,
0€ 3.2524
ö=3O ô,30'
1 a r!N 1DD4T • ftN' 3.fl337
—61 RT • PVUN • n.p
—5
0 4 8 12 16 4 10 16 22 28 34 40 46 52 58 64 70 76 82 88 70 76 82 88 94100
x/c (%)
Fig. 16. Surface Pressure Distribution on a Multi-Element Airfoil with Clean and Iced Slat, a = 8 degrees.
. RN = 9.0 X i06 M = 0.20 siraL SullrFUS wiTh ICE C,
- 0 4.3518
—15 a=20' —0--- IIN ELDIENT • LRP 1.1664
A SUiT * lit1N * FLAP 3.7993
—13 -
—11
—9
U
—7
—5
—3
—1
III.,'
0 4 8 12 16 4 10 16 22 28 34 40 46 52 58 64 70 76 82 88 70 76 82 88 94100
x/c (%)
Fig. 17. Surface Pressure Distribution on a Multi-Element Airfoil with Clean and Iced Slat, a = 20 degrees.
coo 3t:''d m'i:i
CONCLUSIONS any reason to be concerned over losses in stall
margin with ice on the main element or the flap.
The aerodynamic performance of a multi-
Results reported in this paper detail the
element airtoil was evaluated in the presence of
performance losses of an advanced technology
simulated ice accretions. The test was conducted
multi-element airfoil in the presence of in-flight ice
at NASA Langleys LTPT at moderate-to-high
accretion. They represent the first set of
Reynolds numbers. The ice shapes used were
performance degradation data known to the
simulations of ice accretions grown on a similar
authors, in which simulations of realistic ice
model at the NASA Lewis' IRT. The conditions
accretions were tested on a high till system at flight-
simulated in the IRT were representative of typical
scale Reynolds numbers. This effort was a part of a
approach conditions for a narrow body twin-jet
cooperative experimental program cond
transport aircraft. Analysis of the results of this
McDonnell Douglas Aerospace, NAS
investigation has led to the following conclusions:
Research Center, and NASA Langley
1. Ice accretion on main element and flap Center to establish a data base of high-lift
leading edges does not have a significant impact on accretions and their effect on high-hf
maximum lift performance. There is no significant performance.
loss in angle-of-attack-margin to stall, but there is a
noticeable parasite drag increase. These results,
and those from prior measurements, point out the REFERENCES
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Configuration Development of a High-Lift Ai
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