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Research ArticleTheoretical Analysis and Experimental Researches regardingthe Asymmetrical Fluid Flow Applied in Aeronautics
Ionics Cรฎrciu,1 Doru Luculescu,1 Vasile Prisacariu,1
Eduard Mihai,2 and Constantin Rotaru1
1Department of Aviation, โHenri Coandaฬโ Air Force Academy, 160 Mihai Viteazul Street, 500183 Brasฬงov, Romania2National Defence University โCarol Iโ, Panduri Street No. 68-72, sector 5, 050662 Bucharest, Romania
Correspondence should be addressed to Ionicaฬ Cฤฑฬrciu; [email protected]
Received 21 January 2015; Revised 27 March 2015; Accepted 30 March 2015
Academic Editor: Tang Xiaosheng
Copyright ยฉ 2015 Ionicaฬ Cฤฑฬrciu et al. This is an open access article distributed under the Creative Commons Attribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The current paper has been written in order to find the best solutions to replace the antitorque rotor of single-rotor helicopters,with removal of its disadvantages through the Coandaฬ Effect.This would significantly increase the flight performance.The researchmainly aims at obtaining a controlled lateral force due to Coandaฬ flows through the tail boom, a force which would be useful forthe stabilization needed because of the lifting rotor during the flight of single-rotor helicopters.
1. Introduction
The Coandaฬ effect is a classic phenomenon applied in fluidmechanics and one of the fundamental discoveries of theRomanian inventor Henri Coandaฬ (1886โ1972). He wasa Romanian inventor, an aerodynamics pioneer, and thedesigner and builder of the worldโs first jet powered aircraftin 1910, a revolutionary plane of the beginning of the 20thcentury.
The lateral pressure that urges the flame of a candletowards the stream of air from a blowpipe is probably exactlysimilar to that pressure which eases the inflection of a currentof air near an obstacle.
If you bring a convex body into contact with the side ofthe stream, the place of the dimplewill immediately show thatthe current is deflected towards the body; and if the body wasat liberty to move in every direction, it will be urged to movetowards the current.
A hundred years later, Henri Coandaฬ identified an appli-cation of the effect during experiments with his first aircraftwhich mounted an unusual engine designed by Coandaฬ. Themotor-driven turbine pushed hot air rearward, and Coandaฬnoticed that the airflow was attracted to nearby surfaces.
He discussed this matter with leading aerodynamicistTheodore von Kaฬrmaฬn who named it the Coandaฬ effect. In1934 Coandaฬ obtained a patent in France for a โMethod andapparatus for deviation of a fluid into another fluid.โThe effectwas described as the โDeviation of a plain jet of a fluid thatpenetrates another fluid in the vicinity of a convex wallโ [1, 2].
The Coandaฬ effect is a natural phenomenon with actionon the flow attached to a divergent wall (volet or airfoil)characterized by high asymmetry.
Figure 1 shows themain effect flowof a fluid characterizedby the following aspects:
(a) The depressurized zone that determines a flowacceleration upstream in the slot, without increasingupstream pressure or temperature and the displace-ment of the local fluid.
(b) Detaching and reattaching are characterized by hys-teresis (the reattaching is produced at smaller anglesthan the detaching).
(c) The global flow that results from the mixture betweenthe main flow and the displaced one is situated inthe depressurized zone and is characterized by lowertemperature.
Hindawi Publishing CorporationAdvances in Materials Science and EngineeringVolume 2015, Article ID 681284, 9 pageshttp://dx.doi.org/10.1155/2015/681284
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ab
c
Figure 1: Coandaฬ effect flow (2D).
2. Theoretical Aspects of the Coands Effect
In Figure 2, the primary flow is introduced in the inlet(section O-O), by compression, or acceleration, or throughabsorption, directly from the environment.
The absorption section, marked with (h-h), throughwhich the inflow only advances, may be described as havingthe property that the total enthalpy ๐โ of the inflow is equalwith that of the environment, ๐โ
๐ป. The place around A is
considered to be the longitudinal spot from the tail boom,where the loss of pressure of the flow is maximal. Section B-Bshows the end of the Coandaฬ profile (line OAB). Section C-Cis the place where the absorption section ends and themixingregion extends to both walls. D-D is the exit section from theair ejector and is characterized by the fact that the static pres-sure is equal with that of the environment static pressure ๐
๐ป.
The area h-O-C-B-h is considered to be the absorptionarea, where the total enthalpy, ๐โ, of the flow is ๐โ = ๐โ
๐ป. Area
O-ABC-C-O is considered to be that of the junction whereboth flows mix, where the entire generated flow is receivedthrough the permeable surface C-O.
Area C-D-D-C is the area of acquiring uniformity for theaero thermo gas dynamic parameters in section C-C and itusually has a divergent form, which favourably contributes tothe efficiency of the air ejector.
Its existence leads to the increase of the generated flow,but it does not necessarily mean an increase of the propulsionforce [3, 4].The research on the force increasewill have to takeinto consideration the entire geometry of the air ejector [5, 6].The known factors are
(i) geometry of the air ejector in its sections (Ah,AO, andAD),
(ii) the slot conditions (๐โ, ๐0),
(iii) environmental conditions (๐๐ป, ๐๐ป, ๐โ
๐ป).
Also, for this global analysis of the mixture in the air ejector,the values of the energetic performance (๐
๐ถ, ๐๐ท) on sections
OO-CC and OO-DD are considered to be known.
Letโs analyse a particular Coandaฬ ejector with nonuni-form and variable speed distribution, in exit section ๐ท.The static pressure ๐
๐ทequals the environment pressure ๐
๐ป.
The power transferred to the fluid in section๐ท is
๐0= ๐๐๐ท= โซ๐ด๐ท
๐๐ป๐๐ท(๐ฆ) (๐โ
๐ทโ ๐โ
๐ป) ๐๐ด๐ท. (1)
The gain in force is given by the difference between thetwo force distributions, with a maximal value correspondingto the angle.
We may describe a Coandaฬ flow by using two zones,the centrifugal zone and the suction zone, each havingspecial properties. The equations for the centrifugal zone,associated to themixing regionO-ABC-C-Owith thewallCOconsidered to be permeable, are
1
๐โ ๐ (๐ โ ๐ข
๐)
๐๐= 0,
โ๐ข2
๐
๐= โ
1
๐
๐๐
๐๐,
๐ข๐
๐๐ข๐
๐๐= โ
1
๐
๐๐
๐๐,
๐โ
= ๐โ
๐ป(๐
๐๐ป
)
(๐โ1)/๐
+๐ข2
๐
2.
(2)
For a small element of the jet flow (Figure 3), the radialmovement equation is
๐๐
๐ =๐๐
๐๐ข2๐
. (3)
For a point Bi on the profile Coandaฬ,
๐ข๐= ๐ข๐0๐๐ข(๐ ) ; ๐ข
๐0= ๐ข0๐๐ข0
(4)
and the total enthalpy is preserved:
๐โ
(๐ ) =[๐ข๐(๐ )]2
2+ โซ
[๐ข๐(๐ )]2
๐ ๐๐
๐
+ ๐โ
๐. (5)
The static pressure is expressed by
๐ (๐ ) = ๐๐ป(1 +
1
๐โ
๐ป
โซ[๐ข๐(๐ )]2
๐ ๐๐
๐
)
๐/(๐โ1)
(6)
and the static parameters, as density and temperature, are
๐ (๐ ) = ๐๐ป(1 +
1
๐โ
๐ป
โซ[๐ข๐(๐ )]2
๐ ๐๐
๐
)
๐/(๐โ1)
,
๐ (๐ ) = ๐๐ป(1 +
1
๐โ
๐ป
โซ[๐ข๐(๐ )]2
๐ ๐๐
๐
)
๐/(๐โ1)
.
(7)
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O
O
hh
ABB
C C
DD
(a)
O
O
h h
ABB
C C
D D
V0 Vh
Vc
VD
(b)
Figure 2: Coandaฬ ejector with (a) nonuniform speed distribution and (b) uniform speed distribution.
Vhb
Vh
p + dp
p
dR
R0
OR โ
V(R)
V0B
Figure 3: Jet flow elements.
The gain in force at Bi is
๐Bi =1
๐0
โซ
๐ 2
๐ 1
(1 +1
๐โ
๐ป
โซ[๐ข๐(๐ )]2
๐ ๐๐
๐
)
๐/(๐โ1)
โ ๐2
๐ข0
๐2
๐ข(๐ ) ๐๐ .
(8)
We may note that the attached flow is situated in thedepressurised zone (area defined by the slot exit frontier, O-O, B-B section, and D-D exit) having a maximal value in ๐ด[7, 8]. We assume that the section of the open slot ๐
0has
got the normal line perpendicular to the axis and due to
O
O
V0
pH
pH
pโ0
Figure 4: Free jet flow through the slot.
the Coandaฬ profile (Figure 4) on one of its sides, there is someflow asymmetry revealed by asymmetrical distribution of theexisting gas dynamic parameters within the section.
The speed๐0of the expansion from ๐โ
0at a pressure ๐
๐ปis
๐0= โ2 (๐
โ
0โ ๐๐ป) = โ2๐
โ
๐ป[(๐โ
0
๐๐ป
)
(๐โ1)/๐
โ 1]. (9)
Speed variation along the radius is assumed to be
๐ (๐ ) = ๐0(๐ 0+ ๐0
๐ )
๐
(10)
and we have ๐0= ๐(๐
0+ ๐0).
If the radius of curvature of the slot is big enoughcompared to the slot opening, we can approximate that thebrake enthalpy is constant on the radius and the asymmetryis caused only by the static pressure variation from ๐
๐ปin
the upper part of the slot to ๐0at the wall, in the lower part
(Figure 5).
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Table 1
Nr.crt Static pressure [N/m2] ๐๐[m/s] Force ๐น [N] ๐น๐ฆ [Nm] ๐น๐ง [Nm]
1 101237,4642 4,122222 2,26655 0,063376 โ0,0100042 101239,1528 4,178888 2,31825 0,068185 โ0,0121683 101240,7134 4,210001 2,40756 0,072684 โ0,0145054 101242,4722 4,290344 2,51815 0,076828 โ0,016535 101244,1634 4,340777 2,62753 0,080975 โ0,018276 101245,9927 4,386788 2,70147 0,085902 โ0,0184577 101248,1247 4,433453 2,74428 0,093680 โ0,0181688 101250,1457 4,532223 2,77195 0,102288 โ0,0171799 101252,0222 4,544555 2,80014 0,110612 โ0,01572210 101253,6918 4,666677 2,83484 0,116111 โ0,013897๐๐: the speed of the fluid through the tail boom.๐น: lateral force resulted from the Coandaฬ effect.๐น๐ฆ: torque on direction ๐ฆ, ๐น๐ง-torque on direction ๐ง.
Table 2
Nr.crt Static pressure [N/m2] ๐๐[m/s] Force ๐น [N] ๐น๐ฆ [Nm] ๐น๐ง [Nm]
1 101229,6367 4,122222 2,00683 0,03137 โ0,002612 101229,7828 4,178888 2,02760 0,033470 โ0,0024133 101229,9896 4,210001 2,07610 0,035853 โ0,0008934 101230,0755 4,290344 2,10305 0,037589 0,0008045 101230,3241 4,340777 2,13139 0,039402 0,000946 101230,7204 4,386788 2,15353 0,041249 0,001927 101231,0777 4,433453 2,17919 0,042487 0,002778 101231,4515 4,532223 2,21553 0,044657 0,003659 101232,0023 4,544555 2,22803 0,046067 0,00538
RR0 + b0
O
OR0
p0
p0
V0
V(R)
A
pโ0
Figure 5: Coandaฬ flow.
We write
๐ (๐ ) = ๐๐ป[๐โ
0
๐โ
๐ป
โ
๐2
(๐ )
2๐โ
๐ป
]
๐/(๐โ1)
= ๐๐ป{(๐โ
0
๐๐ป
)
๐/(๐โ1)
โ[(๐โ
0
๐๐ป
)
๐/(๐โ1)
โ 1](๐ 0+ ๐0
๐ )
2๐
}
๐/(๐โ1)
(11)
which under limiting conditions gives
๐ (๐ 0+ ๐0) = ๐๐ป, ๐
0= ๐ (๐
0) . (12)
The outflow mass rate through the slot isโ
๐0= ๐๐ป๐0๐ด0๐๐0, (13)
where ๐๐0
is the outflow increase coefficient; it is similar tothe coefficient for the increase of the expansion area from๐ด0to ๐๐0๐ด0having the constant speed ๐
0or similar to the
coefficient for the speed increase from ๐0to ๐๐0๐0, having
the same area as ๐ด0reference [9โ11].
3. Basic Modelling and Simulation Aspectsregarding the Coands Flow
The interest is to compute the flow characteristics aroundsome aerodynamic shapes with a particular focus on the tail(posterior fuselage) of IAR 316 B helicopter.
The results are presented in Figures 6 and 7.The numerical simulations were made with Fluent 6.1
software programwhich allowsmodelling of the flows arounda body.
Tables 1 and 2 show the values of the lateral force dueto the Coandaฬ effect at a vertical speed ๐
๐of the power
lines of 15m/s and ๐๐= 10m/s, respectively, depending on
the variation of the speed of the flow within the tail boom.
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(a)
(b)
(c)
Figure 6: Simulation of the flow around the tail of IAR 316 Bhelicopter.
Ten values have been selected for interpretation and graphicpresentation of force ๐น according to speed ๐
๐[6].
Table 1 shows the values of lateral force ๐น depending onthe variation of the speed of the fluid through the tail boom๐๐by maintaining the vertical air current at a constant speed
๐๐= 15m/s.Table 2 shows the values of lateral force ๐น depending on
the variation of the speed of the fluid through the tail boom๐๐ถby maintaining the vertical air current at a constant speed
๐๐ = 10m/s.The diagram in Figure 8 shows the increase of lateral
force F due to the Coandaฬ effect and depending on speed Vc,through rounding the values to two decimal digits.
There is a linear increase of force F, on small areas,compared to the mild increase of the speeds of the air streamthrough the tail boom, which makes us conclude that we canreach an increase of the lateral force F bymild variation of therotation speed of the fan.
(a)
(b)
(c)
Figure 7: A complete 3D view of the flow.
1.700
1.900
2.100
2.300
2.500
2.700
2.900
3.100
4.100 4.200 4.300 4.400 4.500 4.600 4.700
F(N
)
Vc (m/s)
VR = 15m/sVR = 10m/s
Figure 8: A comparative analysis of the variation of the lateral forcefor a constant ๐
๐ of 15m/s and 10m/s, respectively.
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3 4
5
6
7
8
9
10
Figure 9: Experimental device: 1: NOTAR helicopter blades carbon fiber, 2: hub pitch, 3: structure helicopter fiberglass, 4: Coandaฬ slots,5: device measuring dynamometer force ๐น, 6: tool kit with, 7: measuring and control equipment, 8: instruments for making measurements(timer, dynamometers, Anemometers electronic, mechanical comparator, and roulette), 9: dual source DC power, and 10: stabilized powersource and electronic oscilloscope.
4. Experimental Research on the Applicationof Coands Effect
The correct results regarding the Coandaฬ effect on the tailboom are reached by connecting the theoretical and compu-tational studies as well as by putting into practice the profilesthat need constant adjustments and they relate to
(i) the variation of the airflow generated by the mainrotor (there are two variables here: the pitch angle andthe rotation speed of the blades),
(ii) the variation of the air jet induced in the tail boomthrough the variable pitch fan,
(iii) the geometry of the profile (in our case being the tailboom),
(iv) the number of Coandaฬ slots and their geometry(including width ๐ฟ and length ๐).
It is to be noticed that appropriate, realistic results concerningthe fluid flow under the Coandaฬ effect have been reachedthrough practical experiments by means of hundreds ofconvenient adjustments and changes of the variables.
The experimental device, as observed in the workingprinciple schema and the physical schema in Figure 9, con-sists of I.A.R.316B helicopter model, at a scale of 1 : 10, pro-vided with the entrainment elements, namely, the measuringand control equipment. The experimental device (Figure 9)aims at gaining a lateral force๐น as strong as possible.The fluidflows along the tail boom and along the desired distance aswell as the variation of the lateral force ๐น due to the Coandaฬeffect having been analyzed. This was an attempt to createan adjustable, optimum Coandaฬ profile depending on theflows generated by the main rotor, the tail fan, and the slotgeometry and position.This optimization gives the possibility
to replace the antitorque rotor, removing its disadvantages,and creates the advantage of big (maximum) lateral forceswith low-energy consumption, which are found in helicopterperformance calculations. In order to obtain the biggestlateral force possible, the application of slots on the tail boomwas enlarged. This implies the modification of the force ofthe arm and the calculation of the application of the twoslots in such a manner that the addition of the first air jetfrom the first slot turns into a fluid entrainment mass forthe second slot. This entrainment of the fluid increases thesurface of the Coandaฬ profile. Thus, the entrainment of thefluid through the two slots generates a Coandaฬ flow andthe air mass that โattachesโ itself to the fuselage (tail boomsurface) becomes, in its turn, an adjustable surface of a newCoandaฬ profile through the vertical flow induced by themainrotor [6].This implies themodification of the force of the armand the calculation of the application of the two slots in sucha manner that the addition of the first air jet from the firstslot turns into a fluid entrainment mass for the second slot.Because of the use of new composite materials, particularlycarbon fiber, there is possibility to increase the beam of thegeometric elements of the queue, namely, the length and largediameter, thin-walled tube, and the complete construction(Figures 9 and 10).
The occurrence of any reinforcements placed inside theinner flow leads to lower system efficiency. Carbon fibres-reinforced composite laminate based on Huntsman XB3585epoxy resin presents excellent mechanical properties espe-cially along fibres direction. These properties are used asreplacement in the automotive and aeronautics industry [5].
Varied elements and measurements:
(i) the relief angle ๐ (formed by the null bearing axis andthe rotation plane) or the blade pitch ๐,
(ii) the rotation speed ๐๐ of the main rotor,
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Figure 10: A helicopter structure consists of two main components:a cabin and tail beams of composite materials.
(iii) the rotation speed๐๐of the intubated fan from the tail
boom,(iv) the entrainment power ๐ of the main rotor,(v) the entrainment power ๐
๐of the intubated fan from
the tail boom.
Calculated measurements and reference points:
(i) length of movement in time sequences (reaction tocontrols),
(ii) speed and flow of the air jet moving through the tailboom,
(iii) speed and flow of the air flux generated by the mainrotor,
(iv) speed of the fluid mixture around the slots.
Adjustment of the pitch is achieved through rotatingblade grips on the hub, measuring the angle, and blockingthem using a limiting screw. Angles are established with thehelp of a protractor and a pitch adjuster.
The rotation speed of the main rotor is achieved throughthree stages by manipulating the centre taps of the alter-nating current mains transformer as follows: 100 rot/min;144 rot/min; and 198 rot/min.
The rotation speed of the fan is achieved slowly as thefan is controlled through voltage, therefore by modifying thepower-supply voltage of direct current.
The opening of the slots and of the angle of inclination isreached with the help of the adjustable limiting screw.
Since their values were small, measurements of theCoandaฬ forces due to the air jet generated by the tail boomfan were interpreted with the help of a UMF 1/100. Variationof the power applied on the tail boom fan is reached withthe help of the adjustable direct current supply IEMI I 4102M2X40V 1,2A while the interpretation of the voltage andcurrent is according to the measurement scheme containingthe electronic multimeters. The phenomenon is highlightedby means of following the fine silk thread curves, whichis measurable with the help of the dynamometers and theelectronic anemometer.
Figures 11 and 12 show themodification of the lateral forcedue to the Coandaฬ effect depending on the modification of
0.000
0.500
1.000
1.500
6.00 7.20 8.40 9.60 10.60 12.00
F(N
)
Pc (W)
P = 70 (W)P = 95 (W)P = 145 (W)
Figure 11: Lateral force variation due to the Coandaฬ effect at con-stant values ๐ = 4โ and ๐ฟ = 2mm.
6.00 7.20 8.40 9.60 10.60 12.00
Pc (W)
P = 70 (W)P = 95 (W)P = 145 (W)
F(N
)
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1.80
2.00
Figure 12: Lateral force variation due to the Coandaฬ effect at con-stant values ๐ = 8โ and ๐ฟ = 2mm.
the useful power (three values: P = 70 [W]; 95 [W]; 145 [W])applied to the main rotor, while maintaining the constantwidth ๐ฟ = 2mm of the slots in accordance with the samevalues of the pitch angle of the blades 4โ and 8โ .
For each value of the useful power applied to the mainrotor, six power stages ๐
๐for the tail boom fan were used.
An approximately linear increase of the lateral force ๐น foreach value of power ๐ can be noticed, thus facilitating theestimation of a family of linear functions ๐
๐which can be
used to determine the relation force-applied powers.For ๐ = 95 [W] with constant pitch angle ๐ = 40 and
๐ฟ = 2mm, get the results shown in Figure 12.We obtain a linear function ๐
๐which can be used to find
the value of the lateral force๐น generated by the Coandaฬ effect:
๐๐โ1
100(8๐ + 9) . (14)
If the pitch angle ๐ = 80 changed, the measured valueswere interpreted graphically, the results obtained being likely
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0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
Efc(N
/W)
6.00 7.20 8.40 9.60 10.60 12.00
Pc (W)
P = 70 (W)P = 95 (W)P = 145 (W)
Figure 13: Variation of the tail boom efficiency ๐ธ๐๐
according tothe lateral force ๐น and the required power ๐
๐throughout the three
functioning stages of the main rotor at a pitch angle ๐ = 4โ.
to lead to the same initial conclusion related to the formationof the family of linear functions ๐
๐.
For ๐ = 95 [W] with constant ๐ = 80 and ๐ฟ = 2mm, weobtain the linear function ๐
๐which helps in determining the
lateral force ๐น due to the Coandaฬ effect:
๐
๐โ1
100(8,33๐ + 11) . (15)
The first conclusion is the increase of the value of lateralforce ๐น due to a greater mass of air being entrained and usedin the Coandaฬ flow, which is achieved throughmodifying thepitch angle of the main rotor.
Power ๐๐of the tail boom fan is the index variable๐.
We determine the efficiency ๐ธ๐of a propelling device
as the ratio of the propellerโs generated force to the powerrequired by it, ๐ธ
๐= ๐น/๐
0, in our case ๐น being the lateral force
generated by the Coandaฬ effect and ๐๐the power consumed
by the tail boom fan ๐๐.
We can therefore say that, in our case, index ๐ธ๐๐may be
the efficiency of the tail boom (Figures 13 and 14).
5. Conclusions
The values of the geometrical and input parameters wererespected and the experimental results were close to thecomputer-simulated ones.
Practically, in order to obtain a convenient force gen-erated by the Coandaฬ effect, a force which can be easilymodified, some directional adjustable elements need to beplaced on the length of the slots.
The force detected on the profile in each area of theCoandaฬ flow is the difference between two distinct forces:one on the upper side and one on the lower side, of differentstrengths, the same direction and opposing directions, which
6.00 7.20 8.40 9.60 10.60 12.00
Pc (W)
0.00
0.04
0.08
0.12
0.16
Efc(N
/W)
P = 70 (W)P = 95 (W)P = 145 (W)
Figure 14: Variation of the tail boom efficiency ๐ธ๐๐
according tothe lateral force ๐น and the required power ๐
๐throughout the three
functioning stages of the main rotor at a pitch angle ๐ = 8โ.
are significantly affected by the geometry of the chosen pro-file.
The computational simulation of the tail geometry basedon the optimal use of the two longitudinal Coandaฬ slotsfacilitates the achievement of a Coandaฬ flow, controllablevia the speed of induced jet and the flow resulted from themain rotor of the helicopter. The result is a lateral force inaccordance with the functioning requirements of the single-rotor helicopter.
Conflict of Interests
The authors declare that there is no conflict of interestsregarding the publication of this paper.
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