AlAA 2004-2623 Active Flow Control Activities at NASA Langley Scott G. Anders, William L. Sellers 111, Anthon- E. Washb rn NASA Langley Research Center Hampton, VA 2nd AlAA Flow Control Conference 28 June - 1 July 2004 Portland, OR For permission to copy or to republish, contact the copyright owner named on the first page. For AIAA-held copyright, write to AIAA Permissions Department, 1801 Alexander Bell Drive, Suite 500, Reston, \'A, 20191-4344. AIAA-2004-2623 2"d A I MF low Control Conference, June 28 - July I, 2004, Portland, OR Active Flow Control Activities at NASA Langley Scott G. Anders', William L. Sellers Illt, and Anthony E. Washburn NASA Langley Research Center, Hampton, VA 23681-2 199 NASA Langley continues to aggressively investigate the potential advantages of active flow control over more traditional aerodynamic techniques. This paper provides an update to a previous paper and describes both the progress in the various research areas and the significant changes in the NASA research programs. The goals of the topics presented are focused on advancing the state of knowledge and understanding of controllable fundamental mechanisms in fluids as well as to address engineering challenges. An organizational view of current research activities at NASA Langley in active flow control as supported by several projects is presented. On-center research as well as NASA Langley funded contracts and grants are discussed at a relatively high level. The products of this research are to be demonstrated either in bench-top experiments, wind-tunnel investigations, or in flight as part of the fundamental NASA R&D program and then transferred to more applied research programs within NASA, DOD, and U.S. industry. Nomenclature a Angle of Attack (degrees) b Span (inches) C Chord <CP> Oscillatory excitation momentum coefficient, <J'>/cq CL 3-D Wing lift Coefficient C1 Sectional lift Coefficient Cd Sectional drag Coefficient U C, Mass flux coefficient, kg/s, Q - S C, Rolling moment coefficient 6 flap deflection angle D Drag Force f Frequency, Hz Modulating frequency fm i F- Reduced frequency, -h P L', h Height of contour bump or slot height or width J' Oscillatory momentum at slot exit, phu;? L Lift force m Mass flow rate, kg/s M Mach number Q Volumetric flow rate Re Reynolds number S Surface area T Thrust u, u9 Mean and fluctuating velocity component W Weight x Distance from baseline separation to reattachment SP ' Research Engineer, Flow Physics and Control Branch, MIS 170. ' Branch Head, Flow Physics and Control Branch, MIS 170, Associate Fellow. Research Engineer, Flow Physics and Control Branch, M/S 170, Senior Member. This material is declared a work of the U.S. Government and is not subject to copyright protection in the United States 1 r = Thrust-vectoring efficiency, deglpercent injection P = density Abbreviations AFC = Active Flow Control AIP = Aerodynamic interface plane BART = Basic Aerodynamics Research Tunnel BLI = Boundary Layer Ingestion BWB = Blended Wing Body CFD = Computational Fluid Dynamics DNS = Direct numerical simulation DoD = Department of Defense EET = Energy Efficient Transport EPNdB = Effective perceived noise in dB FLINT = Fluidic Injection Nozzle Technology JETF = Jet Exit Test Facility LES = Large eddy simulation LV = Laser Velocimetry MVGs = Micro Vortex Generators OVERFLOW = Navier-Stokes flow solver for structured grids PIV -- Particle image Velocimetry PJ -- Zero-mass jets on port wing PSL -- Polystyrene Latex QSP = Quiet Supersonic Platform RANS = Reynolds averaged Navier-Stokes SAE = Society of Automotive Engineers SJ -- Zero-mass jets on starboard wing SOA = State-of-the-A rt SFC -- Specific fuel consumption TCT = Transonic Cryogenic Tunnel TSFC = Thrust specific fuel consumption URANS = Unsteady Reynolds average Navier-Stokes Superscripts 9 -- Fluctuating component max -- max value Subscripts AM -- Amplitude modulation j -- conditions at excitation slot 00 -- Freestream conditions I. Introduction There have been numerous studies and reviews’,’ conducted by NASA over the last two years that look at possible visions for aeronautics and aerodynamics in the future. Included in these reviews were discussions of the future impact of increased growth in air traffic and environmental and airspace restrictions that may limit the projected growth of air travel. These impacts will result in economic loss and increased delays on airlines and increased cost and restrictions on personal air travel. In each of these reviews a bold view of the future is provided if one opens up the design space of current vehicle technology and incorporates it into a new airspace management system. Aerodynamic research has been particularly hard hit due to the perception that it is a mature science and that only incremental gains are possible. Reference 2 discussed the aerodynamic opportunities and challenges that could provide the foundation for a revolutionary change in air vehicle technology. These included dramatic increases in computational power, artificial intelligence, active flow and noise control, computational fluid dynamics, and radical 2 American Institute of Aeronautics and Astronautics new air vehicles that combine these technologies in a new and synergistic manner. These new technologies provide their greatest impact when included early in the design process and a need was identified for improving our conceptual design capability. Active flow control is the main focus of this paper, and the definition of active flow control in this paper will follow the delineation proposed by Gad el Hak3, which defines active flow control as requiring energy to be expended for control to take place. It has been stated that the greatest impact for either the airframe' or the engine4, from active flow control (AFC) technology is to remove some prior barrier to a vehicle or engine concept. This paper will provide a discussion of the technologies that are being pursued at NASA Langley Research Center (LaRC) that provides some of the enabling technology for the future NASA vision. The paper updates the projects and results from Washburn’ that summarized the prior work at Langley. 11. Goals and Organizational Structure Any discussion of flow control at Langley should be taken in the context of the programs setting the goals and supporting the research. In this section, a description of the goals and structure of the Vehicle Systems Program (VSP) and the objectives and technology focus areas will be described. The NASA Vehicle Systems Program has undergone major revisions in the last two years. As a result of continued pressure from Congress and the Office and Management and Budget, NASA has sought to restructure the research effort to clearly identify the return on investment through greater efficiency, accountability. and partnerships with industry and academia. The VSP has also striven to cooperate more effectively with the DoD and other government agencies, and to stress innovation through competition. The restructuring effort is being accomplished with significant input from our industrial partners and includes external review panels. A. Aeronautics Themes for the Public Good The key to the restructuring was to align the VSP in a simple and straightforward manner with the agency’s mission, goals, themes, and objectives that are described in the NASA Strategic Plan‘. A main thrust of the VSP is to address the agency goal to enable a safer, more secure, Aeronautics Theme Objectives efficient, and environmentally friendly air transportation A system. The VSP adopted four theme objectives for the lm&a public good that included, protecting the environment, increasing mobility, exploring new aerospace missions, and partnerships for national security. The mu) environmentally friendly air transportation theme would 2 include a major effort to protect the local and global a environment by reducing aircraft noise and emissions. A u) 3 brief summary of some of the environmental impacts of air 0 0 transportation was provided in Ref 2. The mobility theme LL would include a thrust to enable more people and goods to travel faster and farther with fewer delays. The new aerospace missions theme would look to pioneer revolutionary new vehicle concepts that support science missions and terrestrial and space applications. To support and manage this research effort the VSP has put together a matrix of technology focus areas that will enable six vehicle capability sets that in turn support the aeronautics theme objectives as shown in Figure 1. Vehicle Capability Sets The vehicle capability sets were developed iteratively over several workshops, where various vehicle concepts Figure 1 Matrix of objectives, capability sets, and and mission profiles were considered. Thirty-one vehicle technology focus areas concepts were originally considered at a meeting in Reno in 2003. A later meeting down selected 12 concepts andI mission profiles to support the theme objectives. In discussions with various review panels that number was still considered too large and another down select reduced it to six. The vehicle capability sets that were selected for focus over the next five years included the following concepts or classes of vehicles: Quiet, Efficient Subsonic Transport (QUEST); 3 American Institute of Aeronautics and Astronautics Extreme Short Takeoff & Landing Transport (ESTOL); Silent Small Supersonic Transport (S4T); Easy-to-use, Quiet, Personal Transportation (EquiPT); High Altitude, Long-Endurance, Remotely Operated Aircraft (HALE ROA); Heavy-Lift Vertical/Short Takeoff & Landing (HeVSTOL). In the following section the vehicle capabilities that are required to enable the QuEST, ESTOL, and S4T missions and concepts are discussed because they will be a major focus for active flow control technology. This is not to imply that AFC will not be utilized in other areas such as EquiPT. It just means that in the prioritization process the QuEST, ESTOL, and S4T have identified immediate areas for AFC. B. Vehicle Capability Sets In the down select process a set of capabilities and performance goals were identified that began with an assessment of the current state of the art and projected the required performance/vehicle improvements over a 15 year period. The Goals, Objectives, Technical Challenges, and Approaches (GOTChA) process pioneered by the DoD was used to focus research in high payoff areas to meet the overall goals of each vehicle class. 1. QuEST The Quiet, Efficient Subsonic Transport concept has as it main goal a low-noise, low-emission, highly efficient transport aircraft. Using a Boeing 777 with GE90 engines representing the current state-of-the-art (SOA), the QuEST vehicle concept adopted the following 1 target goals: a 50% reduction in CO2, a 90% iw/o M reduction in NOX emissions, and reducing the 65 dB noise contour to within a 55 mi2 area 4 69 representing a typical airport boundary. To meet E 'If these targets, performance goals were set to ~ _ _ _ improve L/D to 25, reduce the empty weight %+, LL ' fraction to 0.37, improve TSFC (installed @ f Trip Fuel oer Distance cruise) to 0.51, and increase to 5.75 the installed TripFurl SFC I$' engine T/W. 0% LIhrlml 1 ' Several recent papers'" have described the Typically (long range Uc): primary technologies required to reduce WE0 .3'StNCt + 0.2'sySt + O.CFuel+ O.1'Payload emissions such as COz, NOX, and HzO. Reductions in '02 emissions are tied to Figure 2 Potential for fuel consumption reduction over the reductions in fuel bum. The potential for a 50% next 2o years (from Ref. ), reduction in fuel bum in the next 15 years can be attained using a combination of aerodynamic, engine, and structural improvements as shown in Figure 2. The GOTChA process formalized which technologies are important and directly related to reaching the target goals. Active flow control can play an important role in several areas ranging from improving L/D over a wider operational range to reducing various forms of drag. Active flow control can also provide exciting new benefits when applied to an integrated airframe propulsion system. For example, ingesting the large turbulent boundary layer on a blended wing body type vehicle can provide large drag benefits. The goal is to accomplish this without presenting a highly distorted flow to the engine, which can increase high cycle fatigue and engine performance losses. 2. ESTOL The Extreme Short Takeoff and Landing (ESTOL) concept presents a unique challenge to vehicle technology and operation. What sets this vehicle apart from previous ESTOL military-type concepts', are the additional requirements necessary for a successful commercial vehicle. The goal is to move from today's SOA and within the next 15 years provide the technology for a vehicle that can operate with a balanced field length of 2,000 ft, cruise at Mach 0.80, carry 90 passengers, and have a range of 1,400 nm. To accomplish this task and simultaneously open up new airports for commercial travel, the vehicle will require a takeoff and landing speed of 50 kts and a 1/4 nm turn radius in the terminal area. An ESTOL vehicle must be a good neighbor at community airports and that means that noise and efficiency will be critical considerations. By incorporating new airspace procedures with the vehicle's capabilities the goal will be to keep the objectionable noise within the airport boundary. This vehicle sector has identified specific technology targets that include a CL,,,~o f 10, an L/D of 16, a 20 EPNdB reduction in noise from today's SOA, and reduce the empty weight fraction to 0.43. The propulsion system will need improvements in 4 American Institute of Aeronautics and Astronautics engine TIW of 120% and a 10% reduction in TSFC. lmproving CL,,,~f rom the current SOA of 7 will most likely require flow control and innovative new powered lift concepts. Flow control is not new to ESTOL. Wimpress’ described the innovative leading-edge blowing and pop-up vortex generators that were coupled with the upper surface blowing on the YC-14 powered-lift system. The challenge for today is to integrate these and other technologies more efficiently using smart materials and pulsed or unsteady active flow control in an effort to avoid separation, reduce drag, and to minimize the bleed requirements from the engine. 3. S‘T The recently retired Concorde Super Sonic Transport (SST) was a marvel of engineering for its time and provides the benchmark for the current SOA. The Mach 2.0, 3,400 nm range vehicle was restricted to supersonic travel over water due to issues regarding the sonic boom. In the hture an SST will still have to deal not only with the boom issues, but also the environmental restrictions regarding emissions and takeoff and landing noise. The S4T sector seeks to revitalize the investment in supersonic technologies and focus efforts on an efficient multi-Mach aircraft in 15-years. The concept vehicle will have a range of 5,500 nm and be able to cruise efficiently within a range of Mach numbers from 0.95 to 2.0. The 150 to 200 passenger vehicle will operate out of fields less than 8,500 ft and will generate a sonic boom signature that is acceptable for overland operations. An extremely tough set of technology goals have been set for this sector that includes an L/D of 10.5 at Mach 2.2 cruise and a takeoff LID of 8.5. The emissions and noise requirements are equally stringent and include reducing the Stage 4 requirements by 4 EPNdB. The operating empty weight fraction has been set at 0.38 with propulsion T/W of 6. The technology areas that are receiving immediate focus include sonic boom and drag reduction. Shaping a vehicle for a tailored boom signature has been demonstrated on the highly successful DARPA Quiet Supersonic Platform (QSP) Programg using a modified F-5 aircraft. The S4T sector hopes to extend that technology for the larger commercial concepts that are being considered. Drag reduchon can take many forms and in the supersonic arena, laminar flow control can play a big role. NASA demonstrated”,” the use of hybrid laminar flow control during the F16-XL flight experiment. Using the improved understanding, new techniques, and the predictive tools available today, the hope is to develop and optimize a system that is simpler and can integrate into a low-boom configuration. Simpler and lighter high-lift systems and innovative control surfaces can provide additional weight and drag reduction benefits for this concept vehicle. C. Strategic Technology Focus Areas The VSP has identified six strategic technology focus areas that are mamxed into the vehicle capability sets as shown in Fig. 1 based on preliminary systems analysis and input from our industrial partners. They represent the key long-term investment areas and the primary places where technology advances will occur. A description” of the focus areas is provided below: 1. Environmentally Friendl’7, Clean Burning Engines: Developing innovative technologies to enable intelligent turbine engines that significantly reduce harmful emissions while maintaining high performance and increasing capability. 2. New Aircraft Energy Sources and Management: Developing new energy sources and intelligent management techniques directed towards zero emissions and enable new vehicle concepts for public mobility and new science missions. 3. Quiet Aircraft for Community Friendly Service: Developing and integrating noise reduction technology to enable unrestricted air transportation service to all communities. 4. Aerodynamic Performance for Fuel Efficiency: Improving aerodynamic efficiency, structures and materials technologies, and design tools and methodologies, to reduce fuel bum and minimize environmental impact and enable new vehicle concepts and capabilities for public mobility and new science missions 5. Aircruft Weight Reduction and Community Access: Developing ultra light smart materials and structures, aerodynamic concepts, and lightweight subsystems to increase vehicle efficiency, leading to high altitude long endurance vehicles, planetary aircraft, advanced vertical and short takeoff and landing vehicles and beyond. 6. Smart AircraJt and Autonomous Control: Enabling aircraft to fly with reduced or no human intervention, to optimize flight over multiple regimes, and to provide maintenance on demand towards the goal of a feeling, seeing, sensing, sentient air vehicle. tt Richard Wlezien: “Capability Based Research: New Horizons for Aeronautics”, Invited presentation at the 42”d AlAA Aerosciences Meeting, Reno, NV, January 5‘h,2 004. 5 American Institute of Aeronautics and Astronautics The technological improvements to meet the vehicle capability goals were broken into 5-year segments with clearly defined intermediate goals at the end of each 5-year segment. In the first 5-year segment, seven projects have been identified to manage and address the technology improvements for the various vehicle sector goals. These multidisciplinary projects include: Quiet Aircraft Technology (QAT), Ultra-Efficient Engine Technology (UEET), Efficient Aerodynamics Shapes and Integration (EASI), Integrated Tailored AeroStructures (ITAS), Autonomous Robust Avionics (AURA), Low-Emission Alternative Power (LEAP), and Flight and Systems Demonstration (F&SD). The flow control activities at Langley will be discussed within the range of the projects that are supporting them. 111. Flow Control Research Topics Flow control provides the enabling technology for many of the contour Bump advanced vehicles being considered. Both passive and active Boundary Layer Injestion hagR eduction technologies can play an important role. When changing flow conditions are not the critical issue, passive technologies offer the Anwe Jet promise of simplicity. Active flow control enables optimization at off- design conditions or when it becomes necessary to react to rapidly Clrculatlo" Control changing flow conditions. Both active and passive flow control technologies have many potential uses on future transonic and High-LiftO rciilatory supersonic vehicles as shown by the examples in Figure 3. Flow Separatlo" Control control provides the technology to enable improved vehicle performance, safety, and environment impact of future aircraft in both Laminar Flow Control the commercial and military arena. D. Lift Enhancement The design of a modern high-lift system is a challenging and complex balancing act between many variables. Small changes to the high-lift system can result in large increases in performance or cost benefits. Wimpress" describes the balancing required for the landing, Figure 3 Potential uses for flow control takeoff, and climb out portions of the flight vehicle and the leverage that the high-lift system provides. The landing approach speed is a 16 function of wing loading and the maximum CL available. To illustrate Landlng Distance is Total Dlstnnm From 50 fl Height the benefits of high lift systems, Wimpress uses an example of a 14 . No reverse thrust vehicle that is weight limited by the available field length. For takeoff, . Sa levev*. Standard day a 5% increase in CLmar esults in a 20% increase in allowable payload. 12 . 70 I& Wing Loading During climb out, L/D becomes important because sufficient thrust is required to overcome drag and climb at the required climb angle. 10 * AR I 7.0 Wimpress estimates that a 5% decrease in drag (increased L/D) results CLmax Possible Limb of in a 40% increase in payload. In terms of landing performance, 8 Circulation Lit( Wimpress assumes again that the vehicle is limited by landing weight. Approach speed is the most important parameter during this phase, and can be reduced by increasing CLmaxA. 5% increase in results in a 65% increase in the payload carried into the field. Wimpress cautions that his estimates are simplified, but claims that the results are representative of the benefits from small improvements in high lift system performance. For a short takeoff and landing or Landing Distance, R ESTOL vehicle, aerodynamic lift is not enough to provide short field Figure 4 Effect of aerodynamic lift on lengths; some form of powered lift is required. Wimpress shows in landing distance (from Ref 12) Figure 4 an estimate of the lift coefficients required versus field length for a typical airplane. Circulation control or powered lift is critical to achieving field lengths less than 2,000 ft. Simplified high lift systems can provide substantial improvements in both vehicle weight and reduced drag. System studies by Boeing13 have shown that a high lift system consisting of a simple hinged flap with a drooped leading edge can result in a 3.3% reduction in drag and a 3.3% reduction in weight. Separation control is critical on both the leading edge and trailing edge flaps on a simplified high lift system. NASA Langley is pursuing both areas (e.g. powered lift and separation control) to support the high lift objectives of the various vehicle sectors. 6 American Institute of Aeronautics and Astronautics 4. Separation Control Separation control is an important area of flow control research because it is so pervasive in nature, and can cause Slat Actuator Trailing Edge significant losses in performance. Langley has been pursuing Actuator Flap / Actuator active separation control in partnership with Tel Aviv University (TAU) for more than 5 years. The partnership builds on the pioneering experience developed at TAU on the use of oscillatory blowing for separation control. During this partnership, NASA / I Langley and TAU researchers took the low Reynolds number Flap hinge data obtained at TAU and demonstrated the technology at high Slat hinge Reynolds numbers on a 0015 airfoil equipped with both leading edge blowing slots and a simple trailing edge flap. As a result of Figure 5 Modular EET model used for that successful effort, the systems study by Boeing, described experiment, c=406.4mm (from Ref. 14) earlier, was initiated. The systems study identified the benefits. but also identified research areas that needed addressing. These areas included data using a modem supercritical wing, higher flap deflections, and the impact of any interactions when using both pulsed leading edge and flap blowing. The team conducted a series of investigation^'^,'^ and Washburn16 provides a summary of their separation control research. Their research was based on the NASA Energy Efficient Transport (EET) supercritical shown in Figure 5. The model was equipped wlth a drooped leading edge slat and a simple hinged trailing edge flap. The model was modular so that it could change blowing locations with actuators on different parts of the airfoil. The test was conducted in the NASA Langley Basic Aerodynamics Research Figure 6 Simplified high lift version of EET Tunnel” (BART) at a freestream speed of 60 mis (Re/m = airfoil model installed in the BART 0.345~10~F)i.g ure 6 shows a picture of the model installed in the tunnel with the leading and trailing edge flaps deflected. 2.5 Pack demonstrated in Reference 14, that controlling separation on the drooped leading edge slat increased lifting capability by - 12%. Amplitude modulation (FTA~ 1). of the high frequency sine wave driving the zero-net-mass actuators reduced the <cp> requirements by 50 percent. Controlling separation on the trailing edge flap required larger <c,,> compared to the leading edge flap as described in Reference 15. There were important differences in cI performance gains when comparing combinations of pure sine and amplitude modulation of actuation on the slat and trailing edge 1.5 -- flaps, and additional research was needed. The most recent studylg included a series of experiments to Baseline, no control Leading edge, Trailing edge, & Flap determine if improvements in airfoil performance could be obtained 4%Lea-din g edge 8 Flap by combining multiple actuators. The effects of phase angle 1. o between actuators, duty cycle of the excitation waveform, and 0.0 5.0 10.0 15.0 20.0 combining leading edge slat, trailing edge, and flap actuation (see a, deg Figure 5) were investigated. Particle image Velocimetry (PIV) data Figure 7 CI versus a for various actuation was obtained to study the large-scale structures in the flow and their locations (from Ref. 19) interactions. The phase angles between actuation waveforms had a complex, but significant effect on both lift and drag. The results showed that the maximum lift increment occurred when the phase angle was *30”. Figure 7 shows that combining leading edge, trailing edge and flap actuation augmented the lift over the baseline (no control) case by approximately 25% at approach angles of attack, and increased Clmaxb y 6%. The interaction of all three actuators near Clmaxis very complex and requires additional study. 7 American Institute of Aeronautics and Astronautics 5. Circulation Control Circulation control has a proven history of successm in generating high lift. Because of this, circulation control is a strong candidate for integration into an ESTOL vehicle high- lift system. Past circulation control investigations have relied - on steady blowing concepts to achieve significantly higher lift compared to conventional systems. However, the mass- - flow requirement for steady blowing is an important concern. -- -- Steady (Dual-Radius flap) Therefore pulsed blowing has been investigated to see if -E- Pulsed (10 Hz, NPR sweep) __ Steady (Elliptical trailing edge) there is potential to generate equal or greater lift with less net __-e- Pulsed (35 Hz, Duty Cycle sweep: mass flow. Jones" performed pioneering research in the area of pulsed circulation control, and found that pulsed blowing reduced the mass flow requirements for ACI (lift increment due to blowing) less than one. The maximum mass flow reduction" was 48% for a CI = 1.0 (ACI = 0.4). Jones and Engla? investigated pulsed circulation control for traditional rounded Coanda surfaces (circular and elliptical) and for a 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 dual-radius simply hinged Coanda flap. A sample of their CP results is shown in Figure 8. Both configurations show Figure 8 Comparison of pulsed and steady mass-flow reductions of about 50% for ACI of 0.3 to 0.4. blowing for GTRI and LaRC CC Their results also demonstrate that the pulsed authority, investigations through frequency and duty cycle, can have a significant impact on the required mass flow to achieve a given performance. However, their results are limited to the boundary layer control (BLC) region shown in Figure 9. It is unknown if there is a benefit to pulsing in the super- circulation range. This is significant because the need for higher ACI implies a much higher C, range. Unfortunately the pulsed systems did not have the authority to generate C, in the higher super-circulation range. Future tests at LaRC plan to address the higher pulsed C, range. Jones and Engla?3 also propose solutions to the cruise drag issue for a circulation control high-lift system. The solution for the elliptical Coanda surface is to use dual-slot blowing to close the wake. For the dual-radius Coanda flap, the solution is to rotate it to zero degrees for cruise and thus close out the airfoil with a sharp trailing edge. However, all of the experimental data for these configurations are for 0.00 0.05 0.10 0.1 5 0.20 Mach < 0.2 and Re < 500,000. CP NASA Langley and the Office of Naval Research Figure 9 Area of super-circulation needed to sponsored a circulation control workshopz4, in March 2004. obtain additional lift increment due to The last circulation control workshopz was held in 1986 at blowing NASA Ames. The 2004 workshop topics included applications, experiments, and computational fluid dynamics. Applications covered the terrestrial, airborne, and marine environments. The experimental results focused on aerodynamic and hydrodynamic performance and flow physics. Computation fluid dynamics focused on circulation control airfoils for marine and airborne applications. Among these was a common airfoil geometry, with experimental results, that was provided before the conference as a test caseB. There was a very large amount of disparity in the success of matching the experimental data, even for different codes running the same turbulence models. Therefore the level of confidence in predicting circulation control performance still remains low. Efforts at NASA LaRC are concentrating on the turbulence modeling deficiencies. Plans include using a very detailed 1986 experimental dataset generated by N0vak2'~~th at includes LDV measurements. The dataset was generated specifically for supporting the development of computational tools for prediction of circulation control performance. 8 American Institute of Aeronautics and Astronautics E. Drag Reduction A major emphasis of the EASl project described above is the reduction of fuel bum and therefore COz emissions. The drag buildup on a modem transonic aircraft is typically divided into major categories such as skin friction, induced drag, interference, and wave drag as shown in Figure 10. Skin friction and induced drag represent the bulk of the drag of a modem optimized transonic aircraft. Wave drag varies from one vehicle type to another. The EASl project is presently supporting flow control targeting skin friction and wave drag. Reduction of wave drag involves the flow physics of the interactions of shock waves and boundary layers. Skin friction reduction technology depends on whether one is working with laminar or turbulent boundary m - m Ok layers. Langley has a long history of laminar flow control SkinFrict'on Busrnass Jct technology that includes pioneering research and flight demonstrations of hybrid laminar flow control in both the Figure 10 Breakdown of drag components transonic and supersonic flow regimes. In the early 80's Langley (from Ref 2) also had an extensive effort in turbulent drag reduction that resulted in the development and flight demonstrations of passive flow control techniques such as riblets. The focus of the current turbulent drag reduction efforts is in the area of active drag reduction technologies. 6. ShocWBoundaty Layer Interaction NASA Langley has put together a multi-disciplinary team to investigate the use of contour bumps for transonic drag reduction. The Europeans have put together an extensive investigation of the devices" as part of Euroihock i and 11. Stanewskym summarized the results and possible applications in which he discusses adaptive wing and flow control technology. The prime advantage of the contour bump technology is the reduction of wave drag at off-design conditions. These conditions become important in that a long-haul aircraft can only fly near its design point for a limited time due to the change of altitudes and weight during the flight profile. The use of localized contour bumps to actively control shockhoundary layer interactions enables the optimization of L/D over a wider range of lift coefficients and the possible increase in the buffet boundaries as described in reference 30. The Langley effort has focused on the use of the MSES and CDISC design and optimization codes to study a family of contour bumps. To provide an accurate benchmark, a new SOA 2D transonic airfoil was designed and designated NASA TMA-0712. The airfoil has a design lift coefficient of 0.7 and a thickness to chord ratio of 12 percent. Multi-point optimization was accomplished using the MSES flow solver and the LINDOP' optimizer. The airfoil was also evaluated using the FUN2D viscous unstructured Navier-Stokes flow solver. The drag divergence 0.040 h O'O0 0.035 - +Undop bump (xlc = 0.61.00) -Z-CDlSC bump (dd.7- 0.9) 0.030 - N1y,iUAQ712 -4.00 0.025 - F c* 0.020 -10.00 - -12.00 - 5 -14.00 - OO..OOOO05 0 .7 0.72 0.74 0.76 0.78 0.8 - ~ . . " ~ . ~ " . . . " . ~ . " . . . " . . . " . . ~ " . -16.00 Freestream Mach number 0 0.002 0.004 0.006 Maximum bump height, Wc Figure 11 Drag divergence of the NASA TMA-0712 airfoil (C, = 0.70, & = 30 x lo6) Figure 12 Drag reduction from contour bumps 9 American Institute of Aeronautics and Astronautics