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  • 1
    Publication Date: 2018-03-21
    Description: Tregidgo et al. (1) show that size-selective overfishing has drastically depleted and downsized populations of tambaqui (Colossoma macropomum) along the Purus River, Amazonia. Because fishers have historically targeted the largest individuals, tambaqui ∼1,000 km upriver are twofold larger than those near the Manaus rainforest metropolis (1). Here, we demonstrate that...
    Keywords: Letters, Sustainability Science
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 2
    Publication Date: 2013-08-31
    Description: The viewgraphs and discussion of the status of the F-16XL SSLFC numerical design validation are provided. The F-16XL Supersonic Laminar Flow Control Program (SSLFC) is a joint effort involving Rockwell's North American Aircraft Division, NASA Ames-Dryden Flight Research Facility, and NASA Langley Research Center. The objectives of the program are to demonstrate that laminar flow can be obtained on a highly swept wing at supersonic speeds, validate the capabilities of a numerical methodology designed to predict boundary layer transition, and validate the capabilities of the methodology in the design of active and passive laminar flow control (LFC) concepts. The F-16XL SSLFC Program consists of the design, fabrication, installation, and flight test of an active laminar flow control glove for the F-16XL. The glove design emphasized the active (suction) control of attachment line and crossflow boundary condition instabilities. The glove design envelop was constrained by the existing geometry, safety of flight considerations, and space requirements for the suction mechanism. The leading edge extension of the glove was limited to 10 inches for consideration of asymmetric flying qualities and the glove height above the existing surface restricted to two inches. The active (suction) portion of the wing extends to nominally 25 percent chord. The glove was constructed of a micro-perforated titanium sheet (hole diameter = 0.025 inches, spacing ratio = 1/8, and sheet thickness = 0.0025 inches). The glove design includes 22 separate chambers to allow suction variation in the chordwise direction. The F-16XL SSLFC program is currently in the flight test phase.
    Keywords: AERODYNAMICS
    Type: NASA. Langley Research Center, First Annual High-Speed Research Workshop, Part 4; p 1843-1889
    Format: application/pdf
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  • 3
    Publication Date: 2011-08-19
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Journal of Aircraft (ISSN 0021-8669); 28; 622-629
    Format: text
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  • 4
    Publication Date: 2019-06-28
    Description: A flight experiment to test and evaluate the skin friction drag characteristics of a riblet surface in turbulent flow at supersonic speeds was conducted at NASA Dryden. Riblets of groove sizes 0.0030 and 0.0013 in. were mounted on the F-104G flight test fixture. The test surfaces were surveyed with boundary layer rakes and pressure orifices to examine the boundary layer profiles and pressure distributions of the flow. Skin friction reductions caused by the riblet surface were reported based on measured differences of momentum thickness between the smooth and riblet surfaces obtained from the boundary layer data. Flight test results for the 0.0030 in. riblet show skin friction reductions of 4 to 8 % for Mach numbers ranging from 1.2 to 1.6 and Reynolds numbers ranging from 2 to 3.4 million per unit foot. The results from the 0.0013 in. riblets show skin friction reductions of 4 to 15 % for Mach 1.2 to 1.4 and Reynolds numbers ranging from 3.6 to 6 million per unit foot.
    Keywords: AERODYNAMICS
    Type: NASA-TM-4387 , H-1774 , NAS 1.15:4387
    Format: application/pdf
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  • 5
    Publication Date: 2019-06-28
    Description: A three-dimensional Navier-Stokes code is used to computationally simulate the flow about a modified F-16XL. Transition mechanisms (e.g. attachment line location and crossflow instability) near the swept wing leading edge are analyzed in detail. Flow visualization is used to study the influence of angle-of-attack on the aforementioned transition mechanisms. Validation of the code is accomplished by comparison of numerically generated surface pressures with that obtained by in-flight experiments.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 91-1621
    Format: text
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  • 6
    Publication Date: 2019-06-28
    Description: The results are discussed of the variable sweep transition flight experiment (VSTFE). The VSTFE was a natural laminar flow experiment flown on the swing wing F-14A aircraft. The main objective of the VSTFE was to determine the effects of wing sweep on boundary layer transition at conditions representative of transport aircraft. The experiment included the flight testing of two laminar flow wing gloves. Glove 1 was a cleanup of the existing F-14A wing. Glove 2, not discussed herein, was designed to provide favorable pressure distributions for natural laminar flow at Mach number (M) 0.700. The transition locations presented for glove 1 were determined primarily by using hot film sensors. Boundary layer rake data was provided as a supplement. Transition data were obtained for leading edge wing sweeps of 15, 20, 25, 30, and 35 degs, with Mach numbers ranging from 0.700 to 0.825, and altitudes ranging from 10,000 to 35,000 ft. Results show that a substantial amount of laminar flow was maintained at all the wing sweeps evaluated. The maximum transition Reynolds number of 13.7 x 10(exp 6) was obtained for the condition of 15 deg of sweep, M = 0.800, and an altitude of 20,000 ft.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-101712 , H-1531 , NAS 1.15:101712
    Format: application/pdf
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  • 7
    Publication Date: 2019-06-28
    Description: For the supersonic laminar flow control research program, tests are being conducted to measure the attachment-line flow characteristics and its location on a highly swept aircraft wing. Subsonic wind tunnel experiments were conducted on 2D models to develop sensors and techniques for the flight application. Representative attachment-line data are discussed and results from the wind tunnel investigation are presented.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA PAPER 92-4089 , In: AIAA Biennial Flight Test Conference, 6th, Hilton Head Island, SC, Aug. 24-26, 1992, Technical Papers (A93-11251 01-05); p. 404-414.
    Format: text
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  • 8
    Publication Date: 2019-06-28
    Description: This paper discusses and evaluates the test measurement techniques used to determine the laminar-to-turbulent boundary layer transition location in the F-14 variable-sweep transition flight experiment (VSTFE). The main objective of the VSTFE was to determine the effects of wing sweep on the laminar-to-turbulent transition location at conditions representative of transport aircraft. Four methods were used to determine the transition location: (1) a hot-film anemometer system; (2) two boundary-layer rakes; (3) surface pitot tubes; and (4) liquid crystals for flow visualization. Of the four methods, the hot-film anemometer system was the most reliable indicator of transition.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-100444 , H-1461 , NAS 1.15:100444 , AIAA PAPER 88-2110
    Format: application/pdf
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  • 9
    Publication Date: 2019-06-28
    Description: The variable sweep transition flight experiment (VSTFE) was conducted on an F-14A variable sweep wing fighter to examine the effect of wing sweep on natural boundary layer transition. Nearly full span upper surface gloves, extending to 60 percent chord, were attached to the F-14 aircraft's wings. The results are presented of the glove 2 flight tests. Glove 2 had an airfoil shape designed for natural laminar flow at a wing sweep of 20 deg. Sample pressure distributions and transition locations are presented with the complete results tabulated in a database. Data were obtained at wing sweeps of 15, 20, 25, 30, and 35 deg, at Mach numbers ranging from 0.60 to 0.79, and at altitudes ranging from 10,000 to 35,000 ft. Results show that a substantial amount of laminar flow was maintained at all the wing sweeps evaluated. The maximum transition Reynolds number obtained was 18.6 x 10(exp 6) at 15 deg of wing sweep, Mach 0.75, and at an altitude of 10,000 ft.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-101701 , H-1565 , NAS 1.15:101701
    Format: application/pdf
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  • 10
    Publication Date: 2019-08-28
    Description: NASA is directing research to develop technology for a high-speed civil transport. Supersonic laminar flow control has been identified as a program element, since it offers significant drag-reduction benefits and is one of the more promising technologies for producing an economically viable aircraft design. NASA is using two prototype F-16XL aircraft to research supersonic laminar flow control. The F-16XL planform is similar to design planforms of high-speed civil transports. The planform makes the aircraft ideally suited for developing technology pertinent to high-speed transports. The supersonic laminar flow control research programs for both aircraft are described. Some general results of the ship-1 program demonstrate that significant laminar flow was obtained using laminar flow control on a highly swept wing at supersonic speeds.
    Keywords: AERODYNAMICS
    Type: SAE PAPER 921994 , ; 14 p.|SAE, Aerotech ''92 Conference; Oct 05, 1992 - Oct 08, 1992; Anaheim, CA; United States
    Format: text
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