ROLE OF CFD IN MISSILE AERODYNAMIC DESIGN: A REVIEW OF RECENT ...

8/13/2019 ROLE OF CFD IN MISSILE AERODYNAMIC DESIGN: A REVIEW OF RECENT EFFORTS AT RAYTHEON

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ROLE OF CFD IN MISSILE AERODYNAMIC DESIGN: A REVIEW OF RECENT EFFORTS AT RAYTHEON

B. Srivastava, J. Furtek, A. Shelton, R. PaduanoRaytheon Systems Company

Systems Design LaboratoryTewksbury, MA 01876

USA

1. SUMMARYComputational Fluid Dynamics (CID) predictions forseveral supersonic missile models with wings, tails, divertjets, wire covers and strakes at several angles-of-attack andtail fin deflections of 10 and 20 deg are compared with themodel wind tunnel tests. The results show excellent com-parisons of all forces and moments with the measured data.Additional several example studies are discussed to showthat these predictive capabilities provide a powerful designand analysis tool that can be judiciously combined with thewind tunnel tests to reduce the overall system developmentcost and to enhance the system reliability for the current andfuture generation missiles.

2. INTRODUCTIONComputational Fluid Dynamics (CFD) is playing an everincreasing role in aerodynamic design for advanced flightvehicles either for performance improvement of the existingsystem for a new missions or for new concept developmentfor future missions. A cost effec tive design process is tojudiciously combine the wind tunnel tests and CFD studiesthat exploit the inherent strengths of each of these. This can

only be achieved through a focused program that providesthe necessary support and infrastructure needed for the task.At Raytheons System Design Laboratory, a CFD programthat was initiated a few years ago, is impacting the missileaerodynamic design process from eff iciency and costconsiderations. The subject matter o f this paper deals with abrief overview of the effor t in this area. It discusses theCFD aspects of software and hardware capabilities,validation results for generic missile systems with wings,tails and other relevant appendages, divert jet for missilecontrol, and fin deflections. Missile related designapplications are then discussed to outline the missile loaddistribution methodology, multibody interactions (such as

a/c mounted missile with pylon) and plume effect s.Relevant conclusions as well as our future efforts are brief lyenumerated.

A coupled wind tunnel and CFD based progressive designflowchart is shown in Fig. (1) which highlights the specif icrole of the CFD during missile design process. The rightbranches o f the flowchart are traditional past efforts that arebeing currently augmented with the left branches based onthe CFD technology. As shown in this chart, comributionsfrom validated CFD in the areas of missile load distribution,free-flight scaling, heat transfer ef fec ts, sensor opticalquality and captive loads are typical since the correspondingrepeat wind tunnel tests for achieving design iterations or

modifications are prohibitively expensive. An alternateapproach is to utilize the like data base for CFD validationstudies with subsequent design trade-off studies. Postflightanalysis using CFD are additional ways to supplement thequest of flight observed anomalies. However, emphasismust be placed on the cautious utilization of CFD within therealm of appropriate validation which highlights themodeling issues, boundary approaches and grid effect s for agiven application. Numerous considerations such as thosedepicted through Fig. (2) are the necessary ingredients of aCFD validation process. A design team must build theseover a substantial time period to make the needed impact onthe design and development environment.

3. COMPUTATIONAL CAPABILITIESFor most missile applications, a server with parallelcompute capability is a requirement to meet the neededchallenge in a design environment. Relevant pre and post-processing software/workstations as well as parallel CFDsolvers, complete the minimum requirement for a thrivingCFD design activity. The work reported here was done on aDIGITAL 8400 with six processors, GRIDGEN (Ref . 1) as a

preprocessor and TECPLOT (Ref. 2) as a postprocessor.Most of the computations were performed with 1-2 Milliongrid points with a turn-around time of approximately 6-10hours with dedicated 4-6 processors. Specific examplescontain the relevant details. Most of the computationsreported here were performed using the flow solver PARCHfor which additional details are available in Refs. (3-5).Details of many of the results presented here are alsoavailable through several other past presentations of thecurrent authors. These references are cited along with therelevant example cases. All reported CFD results are basedon appropriate convergence studies, grid accuracy effects ,boundary effects and the type of flow solver (Euler versus

Navier-Stokes, laminar versus turbulent) needed. In major-ity of the cases studied, it was determined that an Eulersolver is adequate to provide a good estimate of the forceand moment coefficients. Utilization of more complex flowmodels with turbulence did not yield any appreciable changein the predicted force and moment coefficients.

4. EXAMPLE STUDIES

4.1 Supersonic Missile with Wings and Tails

4.1.1 Symmetric CasesExtensive comparisons of wind tunnel data and CFDcomputations at angles-of-attack from 0 to 3.5 deg for

Paper presented at the RTO AVT Symposium on Missile Aerodynamics , held in Sorrento,Italy, II-14 May 1998, and published in RTO MP-5.


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symmetric supersonic flight configurations have been madeto demonstrate the validation aspects of our CFD methodol-ogy. A sample of 16 such cases at Mach Nos. of 2, 3,4, and5 with angles-of-attack going up to 30 deg with both x andI+ configurations of the missile is shown in Fig. (3) for awind tunnel missile model A. Additional cases of CFDcomparisons that go up to 40 deg angle-of-attack are shownin Fig. (4) where results are presented for Mach Nos. of 3,4and angles-of-attack 20, 30 and 40 deg for x and +missile configuration using a missile model B. Thesevalidations show the capability of CFD model to predict theoverall force and moments of a missile in supersonic flows.The right side of Fig. (4) also shows the procedure that wasutilized in the design process for computing the missileairframe load distribution. Essentially, the CFD basedpressure distribution is used to compute the overall axialload distribution and any differences between the windtunnel values and CFD are adjusted through a linear cor-rection term. Notice from this figure that the correcteddistribution is only marginally different from the CFD

derived distribution. Varying forms of this methodology isused to derive the component load distribution. All designload distributions are currently channeled throughcontrolled CFD/tunnel data bases.

41.2 Asymmetric CasesAll asymmetr ic cases in this category are presented with thedivert jet case that are presented below.

4.2 Supersonic Missile with Wings and Tails with Diver tJets

42.1 Symmetric Cases

Diver t jets promise missile agility. However, the aerody-namics of jet and free-stream interaction is very complex.We have developed a good understanding of the jetinteraction through utilization of CFD models. Extensivecomparisons of wind tunnel data and CFD computations atangles-of-attack from 0 to 25 deg for symmetric flightconfigurations with divert jets of thrust ratio (T/q.s, where Tis thrust, q is free-stream dynamic head and s is the missilecross-sectional area) of 0 (no jet), 1 and 4 are presented inFig. (5). Notice the excellent comparative agreements. Thisfigure also shows the cross-plane Mach number contoursalong the missile with a jet thrust ratio of 4, showingdominant supersonic flows. Details of these test cases areavailable in Ref . (3).

4.2.2 Asymmetric CasesFigs. (6, 7) show the computed results and their comparisonwith the wind tunnel data for missile model A inasymmetric configuration at a nominal Mach number o f 4and angles-of-attack going up to 20 deg with jet thrust ratioof 0, 1 and 4. Notice the excellent predictive capability ofCFD for all five force and moment coefficients whencompared to the wind tunnel data for a wide range of cases.These f igures show the deviation of the CFD predicted

coeff icien ts from the wind tunnel data along with the 45 degline that represents the ideal line for an exact match.Symbols falling on this line show an exact match with thewind tunnel data. The bar in these figures indicate the tipercent local deviation from the ideal line. There are somepredictions that compare better with the data than others.The specific ones that do not compare well are enumeratedin these figures. There is no specif ic trend in the enumer-ated cases for the observed deviations from the wind tunneldata. Also, notice from the roll moment comparisons in Fig.(7) that there is good amount of data scatter near zeroindicating the possibility of wind tunnel balance measure-ment errors for numerically small moment coef ficients.Further details of these results can be obtained from Ref .6).

4.3 Supersonic Missile with Wings and Deflected TailsMissile with fin deflections are fairly challenging tosimulate with CFD methods due to the stringent gridrequirements. We have made a significant progress in this

area using novel grid topologies. Extensive comparisons ofthe wind tunnel data and CFD computations at angles-of-attack from 0 to 50 deg for symmetric and asymmetr ic flightconfigurations with f in deflection of 10 and 20 deg havebeen recently performed. Some examples of these cases areshown in Figs. (8, 9). Fig. (8) shows the CFD computationfor a missile model A with 10 deg pitch fin deflection at aflight Mach number of 5.5 and at an angle-of-attack of 20deg. Notice that the coeff icien ts compare ve ry well with thewind tunnel data. Fig. (9) shows the results for a findeflection of 20 deg for the same missile in both thesymmetric x and I+ configurations with angles-of-attackgoing up to 50 deg. The results are now presented for

normal force coefficient and the center of pressure locationto eliminate the arbitrary choice o f a moment referencelocation associated with the longitudinal moments.

4.4 Supersonic Missile with AppendagesExternal wire cove rs are common appendages for missiles.Design of these appendages require aerodynamic loaddistribution along its length for attachment (pin) design,Wind tunnel tests have been used previously to reduce theassociated drag effects and provide the overall total forceand moments carried by these components. Uncerta inty,however, prevails over the distributive load that canoptimize the design process and thus reduce the overallmissile weight. Validations are needed for the overall CFDpredictions as well as for the load carried by these compo-nents. An example of this level of computation is shown inFig. (10) for a missile model C at a flight Mach number of5.5 and angle-of-attack of 20 and 24 deg. The overall CFDand wind tunnel force and moment coeffic ient comparisonsare excellent as shown in this figure. Fig. (11) shows theloads on the windward wire cover. Measured experimentaldata typically utilize a trapezoidal load variation, whichhave been compared with the CFD load distribution forthree flight conditions. Notice that the peak near the leading


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edge for critical design is significantly higher than estimatedby wind tunnel measurement. It was possible to modi fy thedesign using the CFD/wind tunnel coupled studies, in thisinstance.

4.5 Concept DevelopmentCFD methodology also provides a means for early conceptdevelopment without much associated cost. An example ofthis class of applications is the low, force amplificationfactor associated with a windward jet. Several conceptualstudies suggested that this low amplification factor cannotbe enhanced to one or more without making a major changein the missile design (Refs. 3, 6). Additional studies werethen conducted using CFD to demonstrate that wing tipmounted divert jets can alleviate this performance limitation(Ref. 7).

4.6 Plume EffectsEff ects of plume on missile airframe aerodynamics forsupersonic flows is discussed here very brie fly. At certain

altitudes, missile exhaust plume can interfere with thecontrol surfaces to warrant specific studies. Typicallyexpensive wind tunnel tests are needed to address airframe-plume interactions even with cold exhaust tests. Modelmounting, exhaust gas simulation and balance mounting inthe wind tunnel tests create many diff icul t issues. At times,a solid plume shape has been utilized to quant ify theseeffects. We have recently performed several studies toquantify these effec ts utilizing CFD studies. An example isshown in Fig. (12). The exhaust nozzle flow was simulatedby specifying the nozzle exit conditions (velocity distribu-tion etc.) with a single component hot gas. Afterburningand subsequent chemistry eff ects were not included in the

present computations. A full Navier-Stokes analysis wasperformed at a lower and a higher altitude of interest toassess the total changes in the force and moment coeffi-cients. For this case, the results show very marginalchanges in the overall force and moment coefficients.Similar studies were conducted to assess the influence of theplume on the control effectiveness.

4.7 Complex Missile GeometryMost of the results presented above show a typical missilegeometry with ogive cylinder forebody. This kind ofgeometry requires a grid topology that is fairly easilyconstructed. Complexity in missile geometry can compli-cate the grid construction process. It is critical that in suchcases appropriate effort is devoted to create a quality gridconsistent with the flow solver. An example is a missilewhich has a complex forebody, as well as a complex tailmounting in the rear of the missile as shown in Fig. (13).This missile consists of a fla t nose-window, a roll-controlnose strake, puffed-up side cheeks, a step down in diameterand later a fin assembly mounting at the rear end. Missilesurface pressure distribution obtained from the CFD compu-tations for a flight Mach number of 2.7, an angle-of-attack

of 26 deg with windward window is shown in this figure.All flow details are properly resolved. Fig. (14) shows theaxial load distribution on eve ry component of the missile aswell as a comparison of the overall force and momentcoeff icient with the wind tunnel data. Notice that thecomparison is good.

4.8 Multibody EffectsCaptive loads determination is an important design criteriafor air-to-air missiles. Current analytic/empirical methodsare inadequate to provide needed design data. Wind tunneltests can provide the needed interference eff ects. costconstraints, however, preclude these kind o f tests in theearly design phase. CFD can provide an adequate means tobridge the gap. For the missile discussed above, windtunnel tests were conducted to determine the torque requiredto rotate the nose for target observation at numerous flightconditions. However, during captive flight, nose-to-noseinterference can alter the projected torque requirements.CFD methodology was used to estimate these effects for two

missiles mounted on a simulated aircraf t (only winginterference) with pylons. CFD validation studies were firstconducted to predict the single model wind tunnel measurednose torque which established a basis for further designtrade-off studies. Further studies related to two missileswith wing and pylons as shown in Fig. (15). Captive flightconditions were at an angle-of-attack of 10 deg, a flightMach number of 1.2 and a side slip angle o f 45 deg. Theoverall results of the CFD computation is shown in Fig. (15)with surface pressure distribution and a cross-plane pressuredistribution. Using these types of studies, it was possible toestimate the interference eff ects for design applications.

5. SUMMARY AND CONCLUSIONSCFD technology has a vas t potential to contribute in adesign environment that can result in substantial programcost savings as well as enhanced product reliability. Theseare only a few of the vas t arena of CFD applicability. Theexamples cited in this paper have resulted in a betterquantification of the design parameters through a judiciousamalgamation of CFD and wind tunnel technology. A closecoupling of the wind tunnel test programs and CFD projectsare, thus, essential to exploit the most out of the twotechnology areas. For CFD to meet its challenges, an up-front focused technical effort is required in terms ofresources, infrastructure and personnel. It has been shownthat when that happens, the CFD technology can meet thedesired challenges of the design environment.

6. REFERENCES

(1) GRIDGEN, Software Licensed by Pointwise Inc.,P.O. Box 210698, Bedford, Texas 760957698, USA

(2) TECPLOT, Software Licensed by Amtec EngineeringInc., P.O. Box 3633, Bellevue, WA 98009-3633, USA


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(3)

(4)

(5)

Srivastava, B. N., Lateral Jet Control of SupersonicMissile: CFD Predictions and Comparisons to Forceand Moment Measurement, AIAA Paper No. 97-0639,35th Aerospace Sciences Meeting, Reno, Nevada,January 6-lo,1997

Srivastava, B. N., CID Analysis and Validation forLateral Jet Control of a Missile, AIAA Paper No. 96-0288, 34th Aerospace Sciences Meeting, Reno, Nevada,January, 1996. Also, Journal of Spacecrafts and Rock-ets, Vol. 34, No. 5, pp 584-592, September, 1997

Dash, S. M., York, B. J., Sinha, N., Lee, R. A.,Hosangadi, A. , and Kenzakowski, D. C., Recent De-velopments in the Simulation of Steady and TransientTransverse Jet Interactions for Missile, Rotorcraft and

(6)

(7)

Propulsive Applications, AGARD Meeting on Compu-tational and Experimental Assessments of Jets in aCross Flow, 1993, pp 29-1,29-21

Srivastava, B. N., Computation and Validation ofAsymmetric Force and Moment Coefficients for Lat-eral Jet Controlled Supersonic Missile, AIAA PaperNo. 98-2410-CP, 16th Applied Aerodynamics Confer-ence (AIAA), Alburquerque, NM, June, 1998

Srivastava, B. N., Lateral Jet Control of a SupersonicMissile: Computational Studies with Forward, RearBody and Wing Tip Mounted Jets, AIAA Paper No.97-2247, 15th Applied Aerodynamics Conference, At-lanta, June 23-25, 1997


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Design Overview

CFD Technology Traditional Desian

Engineering * EnsembleMethods Data Base

, SelectedVerification

l PackageValidated

CFDb

1

ValidatedCFD

AeroModel Wind Tunnel

Tests

l Load Distributionl Free Flight Scalingl Heat Transferl Window Optical Qualityl Captive Loads

High a, High aHigh M, Low M

ValidatedCFD

*4

w

Post FlightAnalysis

l Anomaly

Reduced Cost and Enhanced Performance / Reliability c

G3310478twk_001 MUA

Fig. 1). Role of CFD in Missile Design


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Check.-----------

Pictorial

bE?d Nose, Dorsal, Fin, etc.

IIIII -C_h_eckI- -------IIIII

C-Type, H-Type, O-TypeStructured/UnstructuredHybrid

II Check Euler, NS, Time Marching--------0-BI

Parabolic, etc.I

Turbulence ModelII

II

II Check------m---mIIII

and Data Base

Dedicated Trained Professionals Critical

G3310478twk 002MUA

Fig. (2). CFD Validation Methodology


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Symmetric Normal Force Coefficient

CFD Data

Symmetric PitchingMoment Coefficient . 5

3 5.00 45.0 20.04 2.00 45.0 30.05 3.00 45.0 30.0

CFD DataG3310478twk-003MUA

Fig. (3). CFD Validation for Missile Model A (Symmetric Confiiuration)[M = 2, 3, 4,&O < a < 35 deg, T/q.s = 0.0, 16 Cases]


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Flow Mach Number -3.4Angle of Attack -20,30,40 deg

X and + Configuration

Flow Mach Number -3.4Angle of Attack -20,30,40 deg

X and + Confiauration

Perfect Line

CFD Prediction andWind Tunnel Data forNormal Force Coefficient

CN (EXPT)

CFD and Wind TunnelPitching MomentCoefficient

CM (EXPT)

- UncorrectedUncorrected

Corrected and Uncorrected Values of TotalAirframe Loads vs. Missile Station

I I

M.S. (inches).S. (inches)

Fig. (4). CFD Validation for Missile Model B (Symmetric Configuration)[M = 2, 4, a = 20,30,40 deg, T/q.s = 0.0, 13 Cases]


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Mach Number Contours

Flow

FForce Coefficient

0

Moment Coefficient

Perfect Line

G3310478twk-005MUX

Fig. 5). CFD Validation for Missile Model A Symmetric Configuration)[M = 4.0, 0.0 I a 4 25 deg, IT/q.sj = 0, 1,4, Leeward/Windward, 17 Cases]


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CFD Data

0Asymmetric Side Force Coefficient

2 3.94 106.14 9.383 3.94 181.32 20.384 3.94 74.40 2.28

I I I I

CFD Data0

G3310478twkh006MUA

Fig. (6). CFD Validation for Missile Model A (Asymmetric Configuration)(M = 4.0, 0 5 a I20 deg, IT/q.sl = 0, 1,4,17 Cases)


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CFD Data0

_ Asymmetric Rolling MomentCoefficient

m

zizE; 0.0;:$ItI

II I I I I I I I I

0.0

CFD Data

Asymmetric Pitihing Momentsymmetric Pitihing MomentCoefficientoefficient

I

I I I I I

0CFD DataFD Data

M $1 3.94 181.32 20;82 3.94 74.40 2.283 3.94 76.17 9.114 3.94 74.85 18.98

M $1 3.94 76.80 19:82 3.94 76.17 9.113 3.94 75.90 9.694 3.94 134.10 2.965 3.94 110.60 9.776 3.94 136.14 19.74

M +1 3.94 134.10 2.:6

G3310478twk-007MUA

Fig. (7). CFD Validation for Missile Model A (Asymmetric Configuration)[M = 4.0, 0 5 a I20 deg, IT/q.sl = 0, 1,4]


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P / (gama*pinf)

Flow Mach Number -5.5Angle of Attack -20 deg, 6 = 10 deg

Y

z L X

+j 3.85

*Normalized with Experiment

I Deflection10 deg

Pressure Distribution on Missile Surface and Symmetry Plane

G3310478twkm008MU>

Fig. (8). CFD Simulation of a Missile Model A with Fin Deflection(Flow Mach Number -5.5, Angle-of-Attack -20 deg, 6 = 10 deg)


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X Configuration

20 Pitch Up Fin Deflection

I I I I I I0

cN CFD

a

+ Configuration

20 Pitch Up Fin Deflection

cN CFD

- - Xcp/d Experimental-+--- Xcp ld CFD

+ Configuration20 Pitch Up Fin Deflection

a

G3310478twk-009MUA

Fig. (9). CFD Validation with Fin Deflection for Missile Model A[M=4.0,6=20deg,O


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P / (gama*pi

4.003.833.653.473.303.132.952.772.602.422.252.081.901.731.551.381.201.020.850.680.50

nf)

Flow Mach Number -5.5Angle of Attack -19.8 deg

Flow Mach Number -5.5Angle of Attack -24.9 deg

I 1 .Cn* 1 Cm* 1

*Normalized with Experiment

Cn* Cm*

EXPT. 1 1.00 1 1.00 1

CFD 0.93 0.99

Normalized with Experiment

Pressure Distribution on Missile Surface Including Wire Covers

G3310478twkm01OMUX

Fig. (10). CFD Validation of a Missile C with Appendages (Strakes)[M = 5.5, a = 20, 26 deg]


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I + CFD* Expt. Trapezoid

Strake Length (in)

--D- CFD

* Expt. Trapezoid

Strake Length (in)

* CFD+ Expt. Trapezoid

Strake Length (in)

Strake Pin Design Modified

G3310478twk-011 MUP

Fig. (11). Comparison of CFD and Wind Tunnel Measurements Stake Load Distribution[M = 5.5, varying angle-of-attack]


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P / (gama*pinf)

4.003.83

3.653.473.30

f& 3.12-i2.952.772.602.422.252.081.901.731.551.381.201.020.850.680.50

F

Flow Mach Number -5.5Angle of Attack -20 deg

Cn* Cm*I I

1 .oo 1 oo

* Normalized Value

Y

120 KFT

(1*Normalized with Plume Value

Pressure Distribution on Symmetry Plane

G3310478hvk-012MUX

Fig. (12). CFD Simulation of a Missile With and Without Plume


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Window Windward

Nose

/

OVI

Z

:ins

Missile Surface Pressure Distribution for Geometry

G3310478twk-013MUX

Fig. (13). CFD Simulation of a Rotate-To-View Nose Missile(M = 2.7, a = 26 deg)


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Side Slip - 45 deg

P:: 0.30 0.37 0.44 0.51 0.58 0.65 0.72 0.79 0.86 0.93 1.00.30 0.37 0.44 0.51 0.58 0.65 0.72 0.79 0.86 0.93 1.00

Flow

Yk

X

z

Pressure Distribution Around Two Missiles withWing and Pylons at a Side Slip Angle

G3310478hkm015MUX

Fig. (14). CFD Load Distribution for a Rotate-To-View (RTV) Missile


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Window Winward

Appendages: Strake, Wire Cover, Fins, Fin Fairings

Fin Fairings\

Wire Cover

Distance from Nose (inch)

G3310478twk 014MUA

Fig. (15). CFD Simulation of RTV Missiles with Wing and Pylon


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