Advanced Aerodynamic Design of Passive Porosity Control Effectors

AIAA 2001-0249ADVANCED AERODYNAMIC DESIGN OF PASSIVE POROSITY CONTROL EFFECTORSCraig A. Hunter', Sally A. Viken _, Richard M. W_×)d, and Steven X.S. BaueF tNASA Langley Research CenterHampton, VirginiaAbstractThis paper describes aerodynamic design work aimed atdeveloping a passive porosit3 control effector systemfor a generic tailless fighter aircraft. As part of thiswork, 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.IntroductionSince 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 thatis 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 flowphysics 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 interactioncontrol 114-191. Based on the initial control cffectorresearch 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 masstransfer 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 thepressure 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 controlforce 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 beensuccessful, 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