NASA/TM-1999-206579 Design and Predictions for a High-Altitude (Low-Reynolds-Number) Aerodynamic Flight Experiment Donald Greer and Phil Hamory Dryden Flight Research Center Edwards, California Keith Krake Sparta Inc. Edwards, California Mark Drela Massachusetts Institute of Technology Cambridge, Massachusetts July 1999 The NASA STI Program Office…in Profile Since its founding, NASA has been dedicated • CONFERENCE PUBLICATION. to the advancement of aeronautics and space Collected papers from scientific and science. The NASA Scientific and Technical technical conferences, symposia, seminars, Information (STI) Program Office plays a key or other meetings sponsored or cosponsored part in helping NASA maintain this by NASA. important role. • SPECIAL PUBLICATION. 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Hanover, MD 21076-1320 NASA/TM-1999-206579 Design and Predictions for a High-Altitude (Low-Reynolds-Number) Aerodynamic Flight Experiment Donald Greer and Phil Hamory Dryden Flight Research Center Edwards, California Keith Krake Sparta Inc. Edwards, California Mark Drela Massachusetts Institute of Technology Cambridge, Massachusetts National Aeronautics and Space Administration Dryden Flight Research Center Edwards, California 93523-0273 July 1999 NOTICE Use of trade names or names of manufacturers in this document does not constitute an official endorsement of such products or manufacturers, either expressed or implied, by the National Aeronautics and Space Administration. Available from the following: NASA Center for AeroSpace Information (CASI) National Technical Information Service (NTIS) 7121 Standard Drive 5285 Port Royal Road Hanover, MD 21076-1320 Springfield, VA 22161-2171 (301) 621-0390 (703) 487-4650 DESIGN AND PREDICTIONS FOR A HIGH-ALTITUDE (LOW- REYNOLDS-NUMBER) AERODYNAMIC FLIGHT EXPERIMENT Donald Greer* and Phil Hamory† NASA Dryden Flight Research Center Edwards, California Keith Krake‡ Sparta Inc. Edwards, California Mark Drela§ Massachusetts Institute of Technology Cambridge, Massachusetts * Abstract c chord, ft C section drag coefficient †A‡ sailplane§ being developed at NASA Dryden d Flight Research Center will support a high-altitude flight Cl section lift coefficient experiment. The experiment will measure the performance parameters of an airfoil at high altitudes Cm section moment coefficient (70,000 to 100,000 ft), low Reynolds numbers (200,000 C p pressure coefficient to 700,000), and high subsonic Mach numbers (0.5 and 0.65). The airfoil section lift and drag are determined du derivative of velocity, ft/sec from pitot and static pressure measurements. The dx derivative of length, ft locations of the separation bubble, Tollmien-Schlichting n boundary layer instability frequencies, and vortex e amplitude ratio shedding are measured from a hot-film strip. The details EMI electrical magnetic interference of the planned flight experiment are presented. Several predictions of the airfoil performance are also presented. g force of gravity Mark Drela from the Massachusetts Institute of gm gram Technology designed the APEX-16 airfoil, using the MSES code. Two-dimensional Navier-Stokes analyses KEAS knots equivalent airspeed at sea level were performed by Mahidhar Tatineni and Xiaolin M Mach number Zhong from the University of California, Los Angeles, and by the authors at NASA Dryden. ncrit critical amplification parameter 2 Nomenclature P pressure, lb/ft PCM pulse code modulation A/D analog to digital Pmax dimensionless pressure gradient P static pressure, lb/ft2 *Research Engineer, Ph.D. Fluid Dynamics. s † Flight Instrumentation Engineer. P total pressure, lb/ft2 ‡Flight Instrumentation Engineer, member AIAA. T §Professor, Department of Aeronautics and Astronautics, member P.T. pressure transducer AIAA. q dynamic pressure, lbm/ft/sec Copyright 1999 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Re Reynolds number Title 17, U.S. Code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for RFI radio frequency interference Governmental purposes. All other rights are reserved by the copyright RTD resistive temperature device owner. 1 American Institute of Aeronautics and Astronautics sep separation The first 30 sec after release from the balloon are the most critical for the APEX flight control system. U uncertainty of the variable x x Transition to horizontal flight occurs during this period xTR transition location with the assistance of four small rockets, which have a α angle of attack, deg combined thrust of 784 lb. After the transition to horizontal flight, the airfoil parameters affecting γ ratio of specific heats performance are measured as the sailplane descends θ momentum thickness from 100,000 to 70,000 ft. The sailplane is then brought to a horizontal landing at the Rogers dry lakebed at υ 2 kinematic viscosity, ft/sec Edwards Air Force Base, California. ¶ Introduction Low-Reynolds-number airfoils typically exhibit laminar separation bubbles as shown schematically in The need for cost-effective high-altitude vehicles to figure 2. These separation bubbles are known to conduct atmospheric research has created interest in significantly affect the performance of an airfoil. The high-altitude (low-Reynolds-number) airfoils. In bubble is formed when the laminar flow separates as a support of this need, NASA Dryden Flight Research result of encountering the adverse pressure region of the Center is developing a sailplane called APEX that will measure the parameters affecting the performance of the airfoil. The separated free shear layer is unstable, which airfoil in actual high-altitude flight. The APEX sailplane amplifies the Tollmien-Schlichting instability waves. will be released from a high-altitude balloon from The free shear flow generally transitions rapidly from approximately 108,000 ft altitude and then remotely laminar flow to turbulent flow and then reattaches to the piloted. Figure 1 shows a schematic of the flight airfoil surface. The lambda shocks, which occur in the mission. transonic flight regime, are expected to increase the amplification of the Tollmien-Schlichting instability waves. The objectives of the APEX experiment are Aircraft release 108K ft • To increase the understanding of airfoil performance in the high-altitude, low-Reynolds- number, and high-subsonic-Mach-number flight regime. Transition to horizontal 100K to 102K ft • To obtain flight test data of airfoil performance flight parameters that can be used for validation of airfoil Test design codes. Two hours maneuvers ascent 70K ft Transonic lambda shock Balloon Free shear launch .5- to 1-hour flow Turbulent Edwards AFB, flight flow California Rogers Dry Lake Laminar flow 990000 Separation Turbulent bubble Figure 1. APEX mission profile. reattachment Separation due to ¶Use of trade names or names of manufacturers in this document adverse pressure gradient does not constitute an official endorsement of such products or 990001 manufacturers, either expressed or implied, by the National Aeronautics and Space Administration. Figure 2. Laminar separation bubble. 2 American Institute of Aeronautics and Astronautics This paper presents a description of the APEX ISES code. An interesting aspect of this investigation is experiment. The design details used to determine the that airfoil performance