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AIAA 2001-0249

Advanced Aerodynamic Design ofPassive Porosity Control Effectors

C.A. Hunter, S.A. Viken, R.M. Wood,NASA Langley Research CenterHampton, Virginia

and S.X.S. Bauer

39th AIAA Aerospace SciencesMeeting & Exhibit

8-11 January 2001 / Reno, NV

For permission to copy or republish, contact the American Institute of Aeronautics and Astronautics1801 Alexander Bell Drive, Suite 500, Reston, VA 20191

https://ntrs.nasa.gov/search.jsp?R=20010013824 2018-06-22T17:00:23+00:00Z

AIAA 2001-0249

ADVANCED AERODYNAMIC DESIGN OF PASSIVE POROSITY CONTROL EFFECTORS

Craig A. Hunter', Sally A. Viken _, Richard M. W_×)d, and Steven X.S. BaueF t

NASA Langley Research CenterHampton, Virginia

Abstract

This paper describes aerodynamic design work aimed atdeveloping a passive porosit3 control effector systemfor a generic tailless fighter aircraft. As part of this

work, a computational design tool was developed andused to layout passive porosity effector systems forlongitudinal and lateral-directional control at a low-speed, high angle of attack condition. Aerodynamicanalysis was conducted using the NASA Langleycomputational fluid dynamics code USM3D, inconjunction with a newly formulated surface boundary'condition for passive porosity,. Results indicate thatpassive porosity effectors can provide maneuver controlincrements that equal and exceed those of con_ entionalaerodynamic effectors for low-speed, high-alpha flight,with control levels that are a linear function of porousarea. This work demonstrates the tremendous potentialof passive porosity to yield simple control effectorsystems that have no external moving parts and willpreserve an aircraft's fixed outer moldline.

Introduction

Since 1990, the aeronautics research community hasexplored novel concepts for aircraft shaping andaerodynamic control 11-9]. These concepts seek toincrease aerodynamic performance, improvesurvivability, and reduce weight and complexity byeliminating the breaks, gaps, hinges, and mechanicalcomponents found in conventional aircraft controleffector designs and replacing them with a combinationof blended control surfaces, smart materials, and flowcontrol actuators. The result of this design approach isa continuous or even fixed outer moldline aircraft that

is able to morph its effective aerodynamic shape andprovide maneuver control in a smooth, continuous,organic manner, similar to the methods birds and fishuse in nature. While promising, much of the recentresearch in this area has focused on fundamental flow

physics and material/actuator development, and manycontrol effector concepts remain unproven at realisticfull scale flight conditions at this time II0-131.

One exception in this area is the passive porosityconcept, which was originally developed in the early1980s as a means of shock - boundary layer interaction

control 114-191. Based on the initial control cffector

research reported b3 Bauer [171, passive porosity hasevolved into an extensively tested and well provenaercv,Jynamic 1"1o_ control technology with a _vidc rangeof capabilities and applications 11,20-231. The passivcporosity concept consists of a porous outer surface, aplenum, and a solid inner surface, as shown in Figure 1.Pressure differences between high- and low-pressureregions on the outer surface "'communicate" through theplenum, thereby modifying the pressure loading on theouter surface. In concert with this pressurecommunication, there is a small amount of mass

transfer into and out of the plenum that changes theeffective aerodynamic shape of the outer surface.

When regions with a large pressure difference areconnected by a passive porosity, system, it has thepotential to act as a control effector. For example,connecting a low-pressure region on the upper surfaceof an aircraft with a corresponding high-pressure regionon the lower surface of the aircraft would reduce the

pressure difference between the two regions, decreasingthe local normal force and translating the center ofpressure. Applied strategically to different areas of anaircraft, as shown in Figure 2, this can result in anextremely powerful control effector system capable ofgenerating a variety of forces and moments. Thegeneral idea would be to equip an aircraft with anumber of porous cavities and interconnected plenumsthat could be controlled and actuated by valves or othersimple devices, as illustrated in Figure 3. Compared toa traditional control effector such as a trailing edge flap,passive porosity has no external moving parts, itpreserves the vehicle outer moldline, and it shouldprovide better performance by generating a control

force that varies linearly with vehicle lift in apredictable manner [1 I.

In the past, passive porosity has been applied to existingaircraft configurations, working within the limitationsand constraints of aircraft designed to use conventionalcontrol effectors. While much of this work has been

successful, the full potential of passive porosity controleffectors can best be explored with a clean-sheetapproach - one using an aircraft design that is suitablefor advanced aerodynamic control effectors and can beconfigured to exploit the working principles of passive

* Configuration Aerodynamics Branch** Flow Physics and Control Branch5" Associate Fellow AIAA

Copyright c'_ 2001 by the American Institute of Aeronautics andAstronautics. Inc. No copyright is asserted in the tlnited States underTitle 17. US Code. The US Government has a royalty-free license toexercise all rights under the copyright claimed herein for government

purposes. All other rights are reserved b_ the copyright ov,,ner.

American Institute of Aeronautics and Astronautics

AIAA 2001-0249

porosity. This paper describes aerodynamic designwork aimed at developing a passive porosity control

effector system for such an aircraft, based on a simpletailless fighter concept. In the current investigation, thefocus has been narrowed to address longitudinal andlateral-directional maneuver control at low-speed, high

angle of attack conditions. Future studies will extendthis design work to more general maneuvering in otherregimes.

Nomenclature

_t, AOABL, 2_c

Ct,CDCyCiCmC,CG

CpFS, x

m

MR

Ro

WL, z

Angle of Attack, degreesButt Line (spanwise) Coordinate, inchesAerodynamic Chord (local), inchesLift Coefficient

Drag CoefficientSideforce Coefficient

Rolling Moment CoefficientPitching Moment CoefficientYawing Moment CoefficientCenter of GravityPressure Coefficient

Fuselage Station (axial) Coordinate, inchesForebody Polar Angle, degreesPorous Surface Net Mass Flux, slug/secMach Number

Computation ResidualInitial Computation ResidualWater Line (vertical) Coordinate, inches

Aircraft Configuration

The aircraft used in this investigation is based onfighter configurations developed under the Air ForceWright Lab "Aero Configuration/Weapons FighterTechnology" (ACWFF) program 1241. The goal of thisprogram was to develop multi-mission fighter aircraftconfigurations with advanced technologies andperformance characteristics capable of addressing post-year-2000 needs and threats. Special emphasis was

placed on the design and performance of advancedaerodynamic control effectors for tailless or reduced-tail concepts. Through a combination of wind-tunneltesting, performance analyses, and trade studies, aconcept was selected for design refinement, resulting inthe ACWFr 1204 configuration shown in Figure 4.

For the current study, a simplified aircraftconfiguration, dubbed "S1204"', was developed byextracting salient features of the basic 1204 planformand outer mold line to form an analytically definedgeometry (required for future studies involvingreshaping). To reduce complexity, the 1204's cockpitand engine inlets were removed, and the exhaust nozzlewas faired over. In addition, the 1204"s NACA

6-1--series airfoil shape was replaced with a simpler 4%

thick bi-convex airfoil. The resulting S!204configuration is shown in Figure 5. As developed, theS1204 configuration preserves the relevantcharacteristics of the ACWFT 1204 and is a good

generic testbed for advanced aerodynamic controleffector concepts, making it well suited for the presentinvestigation. Prior to the work discussed in this report,preliminary CFD analysis was conducted on the S1204configuration at a variety of flow conditions to verifythat its aerodynamic performance was consistent withthe original ACWFI' 1204.

Computational Fluid Dynamics Simulation

The NASA Langley unstructured computational fluiddynamics code "'USM3D" 1251 was used for Navier-Stokes analysis in this study. Within the tetrahedralcell-centered, finite volume flow solver, inviscid flux

quantities are computed across each cell face usingRoe's flux-difference splitting scheme. A novelreconstruction process is used for spatial discretization.based on an analytical formulation for computinggradients within tetrahedral cells. Solutions arcadvanced to a steady state condition using an implicitbackward-Euler time-stepping scheme.

Within USM3D, turbulence closure is given by theSpalart-AIImaras one-equation model I261. This modelsolves a single local transport equation for the turbulentviscosity. The turbulence model can be integrateddown to the wall, or can be coupled with a turbulentboundary layer wall function to reduce the number ofcells in the sublayer region of the boundary layer. Thelatter approach was used here.

Computational Model

The VGRID/GridTool software system 127,281 was

used to generate the unstructured grids for this studt.VGRID uses an advancing-front method for generatingEuler tetrahedral grids, and an advancing-layer methodfor thin-layer tetrahedral viscous grids required forNavier-Stokes analysis. In defining the computationaldomain, boundaries are represented by bi-linear surface

patches that are constructed in GridTool based on user-specified geometries. Grid characteristics like cellspacing and stretching are also specified in GridTool bxthe placement of cell "'sources".

A surface mesh is generated in VGRID by triangulatingeach surface patch with a two-dimensional (2D) versionof the advancing-front method. Triangulated surfacepatches then form the initial "'front" for the generationof three-dimensional (3D) tetrahedral volume cells by

the advancing-layer and advancing-front methods.Smooth variation of grid spacing is achieved by solvinga Poisson equation on a cartesian background grid,using the GridTool-defined cell sources as inputs.

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AI AA 2001-0249

T_vo grids were developed for this study: a semi-spangrid suitable for longitudinal control analysis, and afull-span grid intended for lateral-directional controlanalysis. The semi-span grid with symmetry plane isshown in Figure 6, and the full-span surface mesh isshown in Figure 7. In both cases, the computational

domain extended roughly 10-14 mean aerodynamicchord lengths from the aircraft CG in all directions.The semi-span grid contained a total of 961481tetrahedral cells and 168390 nodes, and the full span

grid contained twice that amount.

Boundary Conditions

Outer boundaries of the computational domain weretreated as characteristic inflo_v/outflo_v surfaces with

freestream conditions specified by Mach number,Reynolds Number, flow angle, and static temperature(the semi-span case used a reflection boundarycondition at the symmetry plane). For comparison withthe ACWFT database, Io_v-speed high angle of attackconditions of M = 0.14 and et = 28 ° were selected for

analysis. Reynolds number was chosen to match theI x 10'Tft - 2x 10"/ft conditions of the various ACWFI"wind tunnel tests.

Aircraft surfaces were treated as no-slip viscousboundaries. In cases involving the application ofpassive porosity control effectors, selected patches onthe aircraft surface were treated as porous surfacesusing the newly implemented porosity boundarycondition in USM3D. The boundary condition isstructured to allow any number of surface patches tocommunicate through a common plenum, withprovisions for up to eight independent plenums.Specific details of this boundary condition will be given

in a forthcoming paper [291, so onl 5 a basic overviewwill be given here.

The USM3D porous boundaD' condition is an extensionof the theory developed by Bush 130] to model flowthrough a screen. Bush's original model was derived topass information across a coterminous boundaryseparating an external flow and an internal plenum. Inthe revised approach used in USM3D, the Bush modelwas re-formulated as a surface boundary condition forthe external flow, thus eliminating the need to grid andcompute flow within a plenum. Conservation lawsfrom steady, one-dimensional (ID), isentropic, andadiabatic gas dynamics are used to model flow throughthe porous surface, in conjunction with the assumptionof a constant plenum pressure and the requirement ofzero net mass flow through the porous surface. Part ofthe solution procedure involves a feedback iteration toupdate the plenum pressure and drive net mass flow tozero. Because of the 1D equations used in theboundar) condition, only the surface porosity level isspecified, not the actual porous hole geometry (circular

holes of 0.020-0.050 inch diameter are typicall_ used in

wind tunnel and flight applications of passive porosity).Based on previous aerodynamic testing [1,17,22], aporosit 5 level of 22c_ openness was used in this study.

The porous boundary condition has been validated b_comparing computational results to experimental dataobtained for a GA(W)-I wing _vith leading-edgeporosit3 111 and a 5 caliber, tangent-ogive forebodywith circumferential porosit3 1221. In both cases,computational results sho_ved remarkable agreementwith experimental force and pressure data 1291.

Solution Procedure

All solutions presented in this paper were obtained byrunning USM3D on the "'Von Neumann'" Cra\ (7-90 atNASA Ames, using 10 processors in multi-task mode.

Typical cases needed 6000-8000 c3cles for fullconvergence. Semi-span computations required about175 megawords of memory and 60-85 hours ofcomputer time. Full span cases required double thoseamounts. During the computation, global CFL numberranged from 5 to approximatel_ 30.

Convergence was judged by several methods. The firstinvolved tracking the solution residual until it droppedseveral orders of magnitude and leveled out, as shownin Figure 8(a). Integrated aerodynamic performancecoefficients shown in Figure 8(b) were also used toverify convergence. Finall 3. in cases using the passiveporosity boundary condition, average porous surfacepressure, plenum pressure, and porous surface net massflow were tracked. Typical histories of theseparameters are shown in Figures 8(c) and 8(d).

Baseline Results

Results for the baseline S1204 configuration at

M = 0.14 and a = 28 ° are given in Figures 9 and 10.Figure 9 shows pressure coefficient (Cp) contours overthe upper and lower surface of the aircraft, and Figure10 uses particle traces to illustrate the vortical flowfield about the upper surface of the aircraft. Theseresults are typical for a chined body at high angle ofattack, and are in excellent agreement with the ACWFq"flow visualization results obtained b_ McGrath, et al[31 ]. Two large vortices track along the upper surfaceof the forebody (red and green traces), and wing flow ischaracterized by a spanwise vortex originating fromeach leading-edge wing-body junction (blue traces).These vortical flows create significant low-pressureregions along the aircraft's upper surface, with a typical(Tp level of about -2. As expected, the lower surface ofthe aircraft is dominated by high-pressure, with Cpranging from approximately 0 to 1. This combinationof Io_- and high-pressure regions is ideal for theapplication of passive porosity.

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AIAA 2001-0249

Control Effector Design

As discussed in the introduction, the basic premise of a

passive porosity control effector system involvesconnecting low- and high-pressure regions of an aircraftto alter surface loading and generate maneuver control.This can be accomplished by allowing pressure to alterthe surface loading directly, or by controlling asecondary flow (such as a vortex) which in turn alterssurface loading. In general, connecting low-pressure

upper surface regions with high-pressure lower surfaceregions tends to have the largest effect on flow in thelow-pressure (upper surface) region. The high-pressure(lower surface) region typically shows little or no

change, and basically acts as an unlimited high-pressuresource 11,17,20,221. Thus, the design of a passive

porosity control effector system involves two basicsteps: (1) identifying _'target'" regions on the aircraft'supper surface where the application of high-pressurewill generate a desired force or moment, and(2) identifying corresponding high-pressure "'source"

regions on the aircraft's lower surface. In the case ofthe S1204, where the entire lower surface contains

high-pressure at high angle of attack, source regionscan be chosen to simplify overall systems integration.

Design Tool

For a particular target region on an aircraft's uppersurface, the effect of applying passive porosity willdepend on several factors: the pressure distribution, thelocal surface geometry, and the location and momentarm relative to the aircraft CG. While the effect of

these factors is easy to visualize in simple cases, it canpose a significant design challenge for complexgeometries and arbitrary surface shapes. In order tostreamline the design process, a simple computationaltool was developed to help identify target areas for theapplication of passive porosity on an aircraft uppersurface. Using USM3D solution and grid files asinputs, the tool surveys the surface geometry andconfiguration layout of low-pressure, upper-surfaceregions and calculates the potential forces and momentsthat would be generated if the local surface pressurecoefficient were raised to a specified target level. For

the present investigation, Cp = 0 ffreestream pressure)was deemed a suitable target _,alue.

Results from the design tool are shown in Figure 1 l(a)and 11(b), for nose-down pitch and yaw, respectively(moments referenced to the stability axes). In eachplot, potential increments in moment are plotted perunit area over the aircraft upper surface. It is importantto note that results from the design tool do not indicatethe direct effects of applying passive porosity; rather,

they indicate the effect of raising local pressure on theupper surface. Passive porosity is simply one methodof accomplishing this, either by direct loading orthrough the control of secondaD _flows.

Results in Figure 1 I(a) indicate that target areas for

nose-down pitch control are the forebody and leading-edge wing-body junction regions (forward of theaircraft CG). Low-pressure in these regions is due tovortical flows, and control of these flows is key to

obtaining nose-down pitch. Potential yaw controlincrements in Figure l l(b) show a similar result, and

indicate that "asymmetric" control of the vortical flowsis required for yaw generation. At the et =28 °condition, stability-axes yaw depends heavily on bothyaw and roll about the body axes. Raising pressure onone side of the forebody will effect bods-axes yaw.

while raising pressure on the upper surface of one wingwill effect body-axes roll. Combined, these momentswill contribute to yaw in the stability-axes.

Control Effector Cot_gurations

Based on the design analysis, ten passive porosit)configurations were developed to effect pitch and ya_control. Target regions on the aircraft upper surfacewere mated with corresponding source regions on thelower surface (i.e., lower surface porosity was a direct

projection of upper surface porosity). From a systemsstandpoint, this approach would minimize the amountof complexity involved in connecting upper and lowersurface regions by a common plenum, making it a goodstarting point for design.

Five proposed pitch control configurations are shown inthe top row of Figure 12. Configurations PI and P2apply porosity to the forebody region, starting at thenose and going back to FS = 147 (covering 33% of theforebody area) and FS = 298 (covering 100%),respectively. Configuration P3 applies porosity to theleading-edge wing-body junction region, forward of theaircraft CG at FS = 365. Configurations P4 and P5 arecombinations of the PI, t_2, and P3 designs.

Five proposed yaw control configurations are shown inthe bottom row of Figure 12. Configurations Y1 andY2 are asymmetric counterparts of the P! and P2configurations, covering 17% and 50% of the totalforebody area, respectively. The Y3 configuration issimilar to the P3 configuration, except that porosit)extends further back to 50% chord, and is applied to the

left wing only. Finally, the Y4 and Y5 configurationsare combinations of the Y 1, Y2, and Y3 designs.

A single plenum was used to connect upper and lowersurface porosity in the P1, P2, Y l, Y2, and Y3configurations. Two separate plenums were used forthe P3 case, one for each wing-body junction region.

Three separate plenums were used in the P4 and P5cases, one for the forebody region, and one for each

wing-body junction region. Similarly, two separateplenums were used in the asymmetric Y4 and Y5 cases.one for the forebody, and one for the left wing.


AIAA 2001-0249

Longitudinal Control

Results for the PI configuration are shown in Figures13-16. Comparing the (,p contours in Figure 13 withthose of the baseline configuration (Figure 9), it isobvious that the application of passive porosity resulted

in a large overall increase in local pressure on theforward upper surface of the forebody, but pressure onthe lower surface was _irtually unchanged (as

expected). Figure 14 gives a plot of surface Cp versuspolar angle around the forebody at FS = 100, for thebaseline and PI configurations. At this location, theupper surface pressure in the PI configuration is nearlyconstant at Cp ,- -0.65, leveling out the suction peaks ofthe baseline configuration.

l)ownstream of the porous region, the upper surface

pressure distribution is very similar to the baseline case.Looking at the particle traces depicted in Figure 15, it

appears that passive porosity delayed onset of theforebody vortices: instead of rolling up at the nose, thevortices formed downstream of the porous region, as

indicated by the red particle traces. Crossflowstreamlines at FS = 100 are shown in Figure 16(a) and16(b), for the baseline and Pl configurations,

respectively. Based on the information shown here, itwould seem that passive porosity prevented windward

flow from rolling into vortices as it separated across thechine. This is likely a direct result of mass transfer outof the upper porous surface, which blunted the effect ofthe chine, filled in the wake on the leeward side of the

forebody, and deterred the formation of secondaryflows.

Results for the P2 configuration are shown in Figures17-20. In this case, the application of passive porosityprovided a notable increase in upper surface pressure onthe entire forebods, and also increased pressure in theleading-edge wing-body junction region. As a result,formation of the forebody and wing body junctionvortices was greatly inhibited. Instead of the distinctvortex families seen in the baseline and Pl cases,

particle traces for the P2 configuration roll up into alarger, less organized vortex system on each side of theaircraft (see Figure 18).

An upper surface Cp plot for the P3 configuration, withpassive porosit 3 applied to the leading-edge wingregion forward of the CG, is given in Figure 21. Theseresults show that the application of passive porosityincreased pressure and smoothed out pressure gradientsin the leading-edge wing-body junction region. This isconfirmed by the Cp plot in Figure 22 (taken at thespanwise location BL =-100), which shows that thewing's suction peak was leveled off to a near constantvalue over much of the upper surface, while the lowersurface pressure was largely unaffected. Based on thevortical flow field depicted in Figure 23, it appears that

passive porosity completely eliminated the wing-body

.junction vortices seen in the previous configurations.Here. blue particle traces originating from the wing-bod3 ,junction region roll into the forebod5 vortices,which are better defined and more coherent than thebaseline case.

Results for the P4 and P5 configurations are shown in

Figures 24-27. As expected, these configurationsincorporate flow features and characteristics from thebasic PI-P3 porosit_ layouts. The P5 configurationshows the most striking results: by combining full

forebody porosity from P2 with wing porosity from P3,major pressure gradients on the upper surface of the P5configuration appear to be complete 5 blended out.Accordingly, particle traces for the P5 configuration inFigure 27 show a lack of the strong vortical flowspresent in earlier cases, with only minor rollup over theaft portion of the aircraft.

Pitch Increments

Nose-down pitch control effectiveness for the five

passive porosity configurations is summarized in Figure28, along with data for selected ACWFF pitch controleffectors [24I. The passive porosity control effectors

provided nose-down pitch increments ranging fromAC_ = -0.089 for the P1 configuration to AC,,, = -0.3 Ifor the P5 configuration, comparing favorabb to therange of ACWFI" devices and conventional controls.Both the P2 and P5 configurations provided enough

nose-down pitch increment to reach "'absolute" nose-down control, countering the configuration's inherentnose-up pitching moment at the M = 0.14, _ = 28 °condition. With increments of A('n, =-0.243 and

AC,,, = -0.3 I, respectively, the I'2 and P5 configurationsroughb equaled or exceeded the AC,, = -0.25 providedby the con_ entional ACWFF elevons deflected to 60 °.

Associated Lift Increments

Lift increments for the PI-P5 configurations are shownin Figure 29, along with estimates made from theACWFT data 124]. Like the ACWFI" forebody devices,the porous configurations generate nose down pitch b)reducing local lift on the aircraft forebods, whichreduces overall lift in each case. This is in contrast to

conventional aft-mounted pitch effectors, whichincrease overall lift. Relative to the baseline

configuration's CL= 1.748, the PI, P3, and P4configurations reduced lift by 6-13c_. These levelscompare favorably to the ACWFT forebody devices,which reduced lift by 4-17c_ for similar nose-downpitch levels. The P2 and P5 configurations reduced liftby larger amounts - 17% and 26%, respectivel 5 - butthese reductions are commensurate with the larger pitch

increments provided by these configurations.

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AIAA 2001-0249

Pitch Control Trends

Using the baseline and porous results obtained here asguidance, one can construct the trends given inFigure 30, which show that the passive porosity pitchsystem provides control effect that varies linearly withporous forebody area. These results indicate that asimple means of controlling the open porous area on theforebody (such as the sliding plates or louvers shown in

Figure 3) would yield a passive porosity effector systemwith linear, variable pitch control.

Lateral-Directional Control

Results for the Y I and Y2 yaw control configurationsare presented in Figures 31-36. As asymmetriccounterparts of the P1 and P2 configurations, thepressure and flow field results seen here are consistentwith earlier discussion. The partial porosity of the Y 1configuration is seen to raise pressure on thefor_vard-left upper surface region of the forebody anddelay the onset of the vortex on that side, while the fullporosity of the Y2 configuration raised pressure on theentire left side of the forebody upper surface and nearlyeliminated the vortex on that side. Cp plots for the Y2configuration at FS = 100 and 220 (Figures 35 and 36)more clearly show the asymmetric effect of passiveporosity. While pressure on the left upper surfaceregion of the forebody (180-270 ° ) changedconsiderabl} from the baseline case, the remainder ofthe foreN_ly surface pressure was unaffected to a largeextent. This demonstrates the capability of passive

porosity to act as a localized control effector.

Results for the Y3 configuration are shown in Figures37 and 38, and are in line with previous results seen forthe similar P3 configuration. The application of passiveporosit5 to the forward half of the left wing is seen tohave a notable effect on thc upper surface pressuredistribution shown in Figure 37. Porosity smoothed outpressure gradients in the wing-body junction area,eliminated the wing-body junction vortex, and raisedthe overall wing upper surface pressure. As shown inFigure 39, the wing suction peak was reduced andupper surface pressure was leveled off to a nearconstant value of Cp - -0.9 at the BL = -100 location.

Upper surface Cp plots and particle traces for thecomposite Y4 and Y5 configurations are given inFigures 40-43. These results are amalgamations ofearlier results seen for the Y1-Y3 configurations,

combining the various elements from each case. Notsurprisingly, the Y5 configuration appears to give thebest results, by combining full forebody porosity (Y2)

with wing porosity (Y3) on the left side of the aircraft.Particle traces in Figure 43 show only weak signs ofvortical flow along the left side of the aircraft, withslow roilup aft of the wing.

Yaw Increments

Yaw control effectiveness for the Y I-Y5 configurationsis summarized in Figure 44, along with ACWFI"control effector and historical data 124]. The passiveporosity control effectors provided yaw incrementsranging from ACn = 0,012 to 0,051, compared with thelevels of 0.018 to 0.020 for conventional ruddercontrols on the F-15 and F/A-18, and 0.011 to 0.025 forthe various ACWFT devices. While the Y I and Y3

configurations provided yaw increments in line with theACWFT devices and conventional rudders, the Y2, Y4,

and Y5 configurations performed significantly better,generating 2-5 times more yaw than the other effectors.

Associated Forces and Moments

Adverse roll increments are presented in Figure 45,which shows that roll levels generated by the Y I-Y5porous yaw control effectors are in line with otherACWFT devices [24[, and well within the ACk = 0.06

level of corrective roll authority available from theACWFI" aileron system. The porous yaw controleffectors also induced nose-down pitch and liftincrements, summarized in the table below.

Table I : Assoc. PRch & Lift hwrements. YI- Y5 Configs.

YI Y2 Y3 Y4 I Y-0"I80_ACm -0.035 -0. t21-0.060 -0.098

ACL -0.030 -0=11_. ! -0.149 -0.179 /-0.226_

Ideally, the generation of yaw should be accomplishedwith as little net sideforce as possible. Figure 46 showssideforce increments generated by the Y i-Y5 porousconfigurations compared to estimates from ACWFIdata and typical historical levels 1241. Increments ofACv = 0.029-0.039 for the Y 1, Y3, and Y4 cases fallbelow the sideforce levels of the ACWFT devices and

conventional rudders for equal or greater ya_increments, indicating that the porous configurationsare more effective at producing yaw. The Y2 and Y5

configurations produced larger sideforce increments, of0.076 and 0.105 respectively, but these levels areconsistent with the larger amounts of yaw produced bxthese control effectors. In reality, the Y2 and Y5configurations produce about the same amount ofsideforce for a given yaw as the other porous cases.

Yaw Control Trends

As in the previous discussion of pitch control effectors,the baseline and Y I-Y5 data were used to construct

control trends, shown in Figure 47. Like the pitch case,the passive porosity system is seen to provide ya_control increments that vary linearly with porousforebody area.

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AIAA 2001-0249

Concluding Remarks

Advanced aerodynamic design and analysis of passive

porosity control effectors has been conducted in thisinvestigation. Using a generic tailless fighter aircraftconcept, Navier-Stokes CFD and aerodynamic designtools were applied to develop control effectors capable

of generating longitudinal and lateral-directionalcontrol for low-speed high angle of attack conditions.

Specific conclusions and comments are as follows:

I. For longitudinal (pitch) control, the P1-P5 passiveporosity effectors provided nose-down pitch incrementsthat were competitive _ith ACWFI' devices andconventional controls. Two of the porousconfigurations actually produced large enough pitchincrements to effect absolute nose-down control at the

high-alpha condition, equaling or exceeding the controlauthority provided b5 conventional elevons. The pitchcontrol came with reductions in overall lift rangingfrom 6 to 26c_. Passive porosity pitch control effectorswere seen to provide control increments that were alinear function of porous forebod3 area.

Acknowledgements

The authors would like to thank Neal Frink, Paresh

Parikh, and Shahyar Pirzadeh for their help and supportwith USM3D, VGRID, and ViGPIot, all part of theTetrahedral Unstructured Software System "'TetrUSS'"

developed at NASA l_angle 5.

I.

2.

References

.

Wood, R.M. and Bauer, S.X.S. "'Advanced

Aerodynamic Control Effectors". SAE Paper,1999-01-5619, October 1999.

.

Scott, M., Montgomery', R., and Weston, R."'Subsonic Maneuvering Efectiveness of HighPerformance Aircraft which Emplo 3 Quasi-Static

Shape Change Devices". SPIE 3326-24, 1998.

2. In terms of lateral-directional control, the Y 1 and Y2

porous control effector configurations generated yawincrements in the range of conventional rudder controlsand ACWFI" devices. The remaining three porous

configurations had yaw increments that were 2-5 times

greater than the other effectors. All of the porous 5.configurations generated acceptable levels of adverseroll, and provided less sideforce for a given yaw thanconventional rudders and ACWFI" devices. Yawcontrol increments were also seen to form a linear trend

with porous forebody area.

3. This work demonstrates the tremendous potential of 6.

passive porosity to yield simple control effectorsystems that have no external moving parts and willpreserve an aircraft's fixed outer moldline. Based onthe linear behavior observed in this study for low-speed 7.

high-alpha conditions, a full5 implemented variablegeometr3 _passive porosity system (using simple slidingplates or louvers to control porous area) would be ableto provide continuous increments in nose-down pitch 8.

control ranging from ACm = 0 to -0.3, and yaw controlincrements ranging from AC0 = -0.05 to 0.05.

l)orsett, K.M. and Mehl, D.R. "'Innovative Control

Effectors (ICE)". Wright Laborato_ ReportWI,-TR-96-3043, January 1996.

4. Though the current study focused on low-speedhigh-alpha conditions, the passivc porosit 5 controleffector concept applies equally well to other flight

regimes, including low-lift conditions or other caseswhere pressure differentials on an aircraft surface aresmall. In these instances, planform layout and surface

contouring ma_ be used to modify local pressuregradients, and become a ke5 part of control effectordesign. As such, development of full-envelope passive

porosity control effectors may require new planformsand surface shapes.

McGowan. A.R., Horta, L.G., Harrison, J.S., and

Raney, I).L. "Research Activities Within NASA'sMorphing Program" NATO-RTO Workshop onStructural Aspects of Flexible Aircraft Control,Ottawa, Canada, October 18-21, 1999.

Kudva, J.N., Martin, C.A., Scherer, L.B., Jardine,

A.P., McGowan, A.R., Lake, R.C.. Sendeck3j,G.P., and Sanders, B.P. "'Overview of theDARPA/AFRL/NASA Smart Wing Program".

SPIE Paper 3674-26, March 1999.

Pack. L.G., and Joslin, R.D. "'()_erview of Active

Flow Control at NASA Langle_ Research ('enter".

SPIE Paper 3326-24, 1998.

Donovan, J.F., Kral, I,.D., and Cary, A.W. "'ActiveFlow Control Applied to an Airfoil".AIAA 98-0210, January 1998.

Seifert, A. and Pack, L.G. "'Oscillatory Control of

Seperation at High Reynolds Numbers".A IAA 98-0214, Januar 3 1998.

9. Nae, C. "'Synthetic Jet Influence on a NACA 0012Airfoil at High Angles of Attack". A1AA 98-4523.

10. Lachowicz. J.T., Yao, C., and Wlezien, R.W.

"'Scaling of an Oscillator':' Flow-Control Device".AIAA 98-0330, Januar)' 1998.

II. Ho, C.M. and Tai, Y.C. "'Review: MEMS and its

Applications for FIo_ Control". Journal of Fluids

Engineering 118(3), 1996.

7


AIAA2001-0249

12. Joslin, R., Horta, L., and Chen, F. "TransitioningActive Flow Control to Applications".AIAA 99-3575, June 1999.

13. Kml, L., Donovan, J., Cain, B., and Cary, A.Numerical Simulation of Synthetic Jet Actuators".AIAA 97-1824, 1997.

14. Raghunathan, S. "Passive Control of Shock -Boundary Layer Interaction". Progress in

Aerospace Sciences, Volume 25, t988.

15. Nagamatsu, H.T., Trilling, T.W., and Bossard, J.A."Passive Drag Reduction on a Complete NACA0012 Airfoil at Transonic Mach Numbers".

AIAA 87-1263, June 1987.

16. McCormick, D.C. "Shock - Boundary LayerInteraction Control with Low-Profile Vortex

Generators and Passive Cavity". AIAA 92-0064,January 1992.

17. Bauer, S.X.S., and Hernandez, G. "Reduction of

Cross-Flow Shock-Induced Separation with aPorous Cavity at Supersonic Speeds".AIAA 88-2567, June 1988.

18. Raghunathan, S. "Passive Shockwave BoundaryLayer Control Experiments on a Circular ArcModel". AIAA 86-0285, January 1986.

19. Nagamatsu, H.T., Brower, W.B., Bahi, L., andMarble, S.K. "Investigation of Passive ShockWave / Boundary Layer Control for TransonicAirfoil Drag Reduction". First Annual report forNASA Grant NSG 1624, 10/1/79 to 9/30/80.

20. Wood, R. M.; Banks, D. W.; and Bauer, S, X. S.:

Assessment of Passive Porosit3 with Free andFixed Separation on a Tangent Ogive Forebody.AIAA 92-4494, 1992.

21. Wilcox, F. J. "Experimental Investigation of theEffects of a Porous Floor on Cavity Flow Fields atSupersonic Speeds". NASA TP 3032, 1990.

22. Bauer, S. X. S. and Hemsch, M.J. "Alleviation of

Sideforce on Tangent-Ogive Forebodies UsingPassive Porosity". Jo0rnal of Aircraft, Vol 31, No2, p354-361. March-April 1994.

23. NASA Langley Research Center, Office ofExternal Affairs. "NASA Contributions to F/A-

18E/F: Centerpiece of US Navy's Carrier-BasedFighter/Attack Fleet Updated with NASAAeronautics Technology". FS- 1999-08-46-LaRC,August 1999.

24.

25.

26.

27.

28.

29.

30.

31.

O'Neil, P.J., Krekeler, G.C., Billman, G.M., and

Creasman, F. "'Aero Configuration / WeaponsFighter Technology (ACWFI') - SummaryTechnical Report". Wright Labs WL-TR-95-3002,December 1994.

Frink N. "Tetmhedral Unstructured Navier-StokesMethod for Turbulent Flows". AIAA Journal, Vol.

36, No. 11, pp 1975-1982. November 1998.

Spalart, P.R., and Allmaras, S.R. "A One-EquationTurbulence Model for Aerodynamic Flows".

AIAA 92-0439, January 1992.

Pirzadeh, S. "Progress Toward a User-OrientedUnstructured Viscous Grid Generator".

AIAA 96-003 !, January 1996.

Samareh, J. "'GridTool: A Surface Modeling andGrid Generation Tool". Proceedings of theWorkshop on Surface Modeling, Grid Generation,and Related Issues in CFD Solutions.

NASA CP-329 I, May 1995.

N. Frink, D. Bonhaus, V. Vatsa, S. Bauer,E. Nielsen, and A. Tinetti. "A Boundary Conditionfor Simulation of Flow over Porous Surfaces".

Extended abstract for the 19th AIAA AppliedAerodynamics Conference to be held in Anaheim,California, June 1 I-14, 2001.

Bush, R. H. "Engine Face and Screen Loss Modelsfor CFD Applications". AIAA 97-2076, June 1997.

B. McGrath, D. Neuhan, G. Gatlin, and P. O'Neil.

"Low-speed Longitudinal AerodynamicCharacteristics of a Flat-Plate Planform Model of

an Advanced Fighter Configuration".NASA TM-109045, March 1994.

8


External Flow

gp,'

r O _D /p,o o qD

liT" o -Region _ J

Plenum

PorousOuterSurface

S(_idInnerSurface

Fi,_ure 1."Passive P_rosity Concept

Tail/Afterbody: Pitch/Yaw ControlWings: Roll/Pitch/Yaw Control

Forebody: Pitch/Yaw Control

Figure 2: Passive Porosity Aerodynamic Control Effector Concept

Sliding Cover Plates

necting Plenum

Control ValveLouvers

Figure 3: Passive PorosiO, Control Effector Schematic

9


Figure 4: ACWFT 1204 Configuration

$1204

Overall Details

Length: 690 IN

Wing Span: 396 INCG: FS = 365 IN (30% MAC)

Chine Angle: 12 °

BL 198 ............

WL 125 ...................... '_WL 93WL 58 ...........................

Wing Details4% t/c Bi-Convex Airfoil

Area: 425 sq ft

LE/TE Sweep: 30 °MAC: 182 IN

PS0

FS FS FS298 365 493

FS690

Figure 5: Simplified Sl204 Configuration

10

American Institute of Aeronautics and Astronautacs

Figure 6: Semi-span S1204 Computational Grid

. /

Figure 7." Full-span S1204 Surface Mesh

II

American Institute of Aeronautics and A stronautics

0.5

0.0

-0.5

Ao

-1.0

-1.5.2o

-2.0

-2.5

-3.0

I ! ] r ] I

J I I i

0 1000 2O00 3OOO 40OO 50O0 6OOO 7000

Iteration

8(a) Residual

2.0 ! I I I [ I

1.5

1.0

0.5

',_°, ,4,," ...... " ...........................

0.0 I! -- CL

-- -- -CD-0.5 ......... Cm

-1.0 i J ,0 1000 2000 3000 4000 5000 6000 7000

Iteration

8(b) Forces and Moments

Cp

0310.2

0.1

0.0

-0.1

-0.2

-0.3 ,i

0

I ] ] I [

......... Ayg SurfacePlenum

; _ I I I I

1O0O20OO30OO4O005OO06OOO7OO0

Iteration

m

0.04

0.03

0.02

0.01

0.00

-0.01

-0.02

-0.03

-0.040

I I I ] I

I I I I I

1000200030004000500060007000

Iteration

8(c) Porous BC Pressures 8(d) Porous Surface Net Mass Flow

Figure 8: Typical Convergence History

12


Upper Surface

Lower Surface

1.0

0.0

-4.0

Figure 9: Upper and l_z_werSurface Pressure Coefficient- Baseline Configuration (M = 0.14, _z= 28 °)

Figure 10: Upper Surface Vortex Flow - Baseline Configuration (M = O. 14. ct = 28 °)

13


&C m per unit area x 105

1 l(a) Nose-down Pitching Moment

-7.0

-6.0-5.0

-4.0

-3.0

-2.0

-1.0

0.0

AC n per unit area x 105

1 l(b) Yawing Moment

1.50

1.251.00

0.75

0.50

0.25

0.00

Figure I 1: Target Areas for Passive Porosi_ - Baseline S1204 Upper Surface

Figure 12: Passive Porosi_ Control Effector Configurations.PI-P5 for Nose-down Pitch Control, Y I-Y5 for Yaw Control.

Shaded regions indicate upper and lower surface porosity.

14


Upper Surface

1.0

0.0

-1.0

Lower Surface

-2.0

-3.0

-4.0

Figure 13: Upper and Lower Surface Pressure Coefficient - P I Pitch Control Configuration

Dashed lines indicate porous regions.

Cp

Cp

-2.0

-1.5

-1 0

-05

0.0

0.5

POROUS REGION >

, ! i i _1 i i i

i----4--

- m i

0 45 90 135 180 225 270 315 360

-- Baseline......... P1 Porous

FS 100 /_k

Z

} ° i_ °o°°°°

Figure 14: Comparison of Forebody Surface Pressure Coefficient at FS = 100Baseline and PI Pitch Control Configuration

15


Figure 15: Upper Surface Vortex Flow- P1 Pitch Control Configuration

Dashed lines indicate porous regions.

16(a) Baseline Configuration

16(b) P 1 Pitch Control Configuration

Figure 16." Cros_flow Streamlines at FS = 100

16


I 1.00.0

-1.0

_ -4.0

Figure 17: Upper Surface Pressure Coefficient - P2 Pitch Control Con[iguration

I -2.0-3.0

Cp

Figure 18: Upper Surt_'e Vortex Flow - P2 Pitch Control Configuration

17

American [nstitute of Aeronautics and Astronautics

Cp

POROUS REGION-2 0

• i _ i I _ t I I I t i 1

-1.5

-1.0

-0.5

0.0

0.5

0 45 90

i i i i

135 180 225 270 315 360

Baseline

......... P2 Porous

FS 100

Z

Figure 19: Comparison of Forebody Sur[ace Pressure Coefficient at FS = 100

Baseline and P2 Pitch Control Configuration

Cp

-2.0

-1.5

-1,0

-0.5

0.0

0.5

-----POROUSREGIONII II I! II 11 11 II I1

II II tl II II II

0 45 90 135 180 225 270 315 360

Baseline

......... P2 Porous

FS 220

Z

. I _D

y =

_ ss SS

Figure 20: Comparison of Forebody Surface Pressure Coefficient at FS = 220


18


U 1.00.0

-1,0

i -2.0-3.0

-4.0

Figure 21: Upper Surface Pressure Coefficient - P3 Pitch Control Configuration

Cp

Cp

-30

-2 5

-2 0

-1 5

-1 0

-0 5

0.0

POROUSREGION

0 5 ._

10"1 , , , i

0.0 0.25 0.50 0.75

xlc

.0

-- Baseline

......... P3 Porous

Figure 22: Comparison qf Wing Surface Pressure Coefficient at BL = -I00


Figure 23: Upper Surface Vortex Flow- P3 Pitch Control Configuration

19


iii

i II 1

1.00.0

-1.0

i -2.0-3.0

-4.0


Cp

Figure 25: Upper Surf.ce Vortex Flow - P4 Pitch Control Configuration

1.00.0

-1.0

I -2.0-3.0

-4.0


Cp

2O


Figure 27: Upper Surface Vortex Flow - P5 Pitch Control Configuration

-0.35

AC,.

-O. 30

-0.25

-0 20

-0.15

-0.10

-0.05

0.00

Level Required for Absolute Nose-down Control-0.310

F//////_

_//////_

-0.250 -0.243 _'_'._

z//////_¢itttzt,

:_%_:.z%% -o.17sg/./././__fillJi,'//.t.t.41.

-0.120 _-

"-/-/-///-_ -0.102

-0.089 ....... _

"/////_

.......-o.o6o _#_._:

N .......r//////.

-0.025 :_."_/.:

,.//////_n i a i i ¢//./-..¢..,-.o-, , |

ACWFT ACWFT ACWFT ACWFT Passive Passive Passive Passive PassiveElevons Forel:_ Fomb_:h/ TE Flaps Porosity Porosity Porosity Porosity Porosity

@ 60° Flaps Fences @ 30° P 1 P 2 P 3 P 4 P 5

Figure 28: Nose-down Pitch Control Summary

21


0.60

ACL

0.40

0.20

0.00

-0.20

-0.40

-0.60

0.198

-0.289

-0.064

0.057

-0.104

-0.305

-0.185-0.234

-0.450

ACWFT ACWFT ACWFT ACWFT Passive Passive Passive Passive PassiveElevons For•body Forebody TE Flaps Porosity Porosity Porosity Porosity Porosity@60 ° Flaps Fences @30 = P1 P2 P3 P4 P5

Figure 29: Associated Lift h_crements

-0.4

ACm

-0.3

-0.2 P4

P5•

P2 e

-o.1• P3P1

o.oe0 20 40 60 80 1oo

Percent Porous Region of Forebody

Figure 30: Nose-down Pitch Control Trend

Note: Porous region starts from nose. The baseline and P3 configurations have 0% porous forebody area, the PI and P4configurations have 33_, porous forebody area, and the P2 and P5 configurations have 100% porous forebody area.

22


I 1.00.0

-I .0

I Cp

-2.0

-3.0

-4.0

Figure 31."Upper Surface Pressure Coefficient - YI Yaw Control Ccmfigurat#m

Figure 32: Upper Surface Vortex Flow - YI Yaw Control Configuration

I 1.00.0

-1.0

i -2.0-3.0

-4.0

Cp

Figure 33: Upper Surface Pressure Coefficient - 1/2 Yaw Control Configuration

23

American Institute of Acronautics and Astronautics

Figure 34: Upper Surface Vortex Flow - Y2 Yaw Control Configuration

Cp

-2.0

-1.5

-1.0

-0.5

0.0

0.5

POROUS REGION

iii!II. II II

0 45 90 135 180 225 270 315 360

Baseline

......... Y2 Porous

FS 100

J N.

Z

Figure 35." Comparison of Forebody Surface Pressure Coefficient at FS = 100

Baseline and Y2 Yaw Control Configuration

24


Cp

-2.0

-1.5

-1.0

-05

0.0

05

0 45 90 135

!

mar t • ! :

t i

POROUS REGION' [ ' ' 1 ....

P

I [ I

180 225 270 315 360

-- Baseline I......... Y2 Porous

FS 220 /'_

Figure 36: Comparison of Forebody Surface Pressure Coefficient at FS = 220

Baseline and Y2 Yaw Control Configuration

I 1.00,0

• • ' n -20i -3.0

_' I

• I

• - -4.0

Figure 37: Upper Surface Pressure Coefficient - Y3 Yaw Control Configuration

Cp

Figure 38." Upper Surface Vortex Flow - Y3 Yaw Control Configurat#m

25


Cp

-3.0

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

POROUS REGION

0,5

1.00.0

1

i

F I I I i I I I

0.25 0.50 0.75 1.0

xlc

-- Baseline

......... Y3 Porous

Figure 39: Comparison of Wing Surface Pressure Coefficient at BL = -100Baseline and Y3 Yaw Control Configuration

1.00.0

, -1.0

i -2.0-3.0

-4.0

Figure 40: Upper Surface Pressure Coefficient - I/4 Yaw Control Configuration

Cp

Figure 41 : Upper Surface Vortex Flow - Y4 Yaw Control Configuration

26


Figure 42: Upper Surface Pressure Coefficient - Y5 Yaw Control Configuration

1.00.0

I -20-3.0

-4.0

Cp

Figure 43: Upper Surface Vortex Flow - Y5 Yaw Control Configuration

27


0.06

0.05

0.04

&Cn 0.03

0.02

0.01

0.00

0.051

0.038 rf::

...... 0.033 ....

v J J//, ......

0.025 "//"/" 0.025

0.020 _ _:'g::: 3;:0.018 -- 0.017 ...... ;:: _

0.011 0.012 ,-...,"-"_f_ rfl __ Jffff_ # #"

I f f,/ f/i....... _ _////_ ---

F-15 F/A-18 ACWFT ACWFT ACWFT Passive Passive Passive Passive Passive

Rudder Rudder Canted Afferbody Asymm Porosity Porosity Porosity Porosity PorosityVertical Popup Forebody Y 1 Y 2 Y 3 Y 4 Y 5

Tail Effector Flap

Figure 44: Yaw Control Summary

-0.06 _####################_-

ACWFT Aileron Roll Control Available &C: = 0.06

-0.05

-0.04

&Co -0.03

-0.02

-0.01

0.00

-0.009

-0.003 _ -0.005

-0.028

-0.014

-0.006

-0.035

f//

-0.025 _-_-"

_///2

¢J.._//. jf_

VI/I/, ;; 2#z _,//_ ===

Historica_ ACWFT ACWFT ACWFT Passive Pas_ve Passive Passive Pas,_ve

Rudder Canted Afterbody Asymm Porosity Porosity Porosity Porosity PorosityVertical Popup Forebody Y 1 Y 2 Y 3 Y 4 Y 5

Tail Effector Flap

Figure 45: Adverse Roll due to Yaw

28


0.12

ACv

0.10

0.08

0.06

0.04

0.02

0.00

0.040

• ,

Historical

Rudder

0.041

iii i iiiii

ACWFT

Canted

Vertical

Tail

0.059

! i

ACWFT

Affert_ly

P_upEffector

0.058

7

0.029

ACWFT Passive

Asymm Porosity

Forebody Y1

Flap

0.076P.P.P.PTq

ss/Fs

_////;/////;

il!_-"//

r j/fie

_///h 0.039

_/./.4v////

.///(.Z: ..... :

Passive Passive

Porosity Porosity

Y2 Y3

Figure 46: Comparison of Sideforce Increments

0.033

,,

Passive

PorosityY4

0.105

Ff_f//

..'/..'//j

///I/_;

/'/JJ/j

I1.1/.t'._

9"////;

iiii1_

f ..*'///_

,....-....-..

_///_"////..'I,,

Passive

Porosity

¥5

0.06

0.05

Y5

ACn

0.04

0.03

Y30.02

0.01

Y4

Y1

Y2

0.00•0 10 20 30 40 50

Percent Porous Region of Forebody

Figure 47: Yaw Control Trend

Note: Porous region starts from nose. The baseline and Y3 configurations have 0_ porous forebod_ area, the Y I/Y4

configurations have 17% porous forebody area, and the Y2/Y5 configurations have 50% porous foreb(xty area.

29


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