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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Boundary-layer transition effects on airplane stability and control

Surface contamination of laminar-flow airfoils can significantly modify the location of transition from laminar-to-turbulent boundary-layer flow. The contamination can be the result of insect debris, environmental effects such as ice crystals and moisture due to mist or rain, surface damage, or other contamination adhering to the surface. Location and mode of transition have a dominant effect on the lift-and-drag characteristics of a lifting surface. The influences of laminar boundary-layer flow behavior on airplane stability and control are examined through theoretical results and experimental (wind-tunnel and free-flight) data. For certain airfoils with a relatively steep pressure recovery it is shown that loss of laminar flow near the leading edge can result in premature separation of the turbulent boundary layer and, consequently, in loss of lift and control effectiveness. Aerodynamic modifications which minimize boundary-layer transition effects on airplane stability and control are also discussed.

Van Dam, C. P.↗
NASA NTRS1993

CFD code calibration and inlet-fairing effects on a 3D hypersonic powered-simulation model

A three-dimensional (3D) computational study has been performed addressing issues related to the wind tunnel testing of a hypersonic powered-simulation model. The study consisted of three objectives. The first objective was to calibrate a state-of-the-art computational fluid dynamics (CFD) code in its ability to predict hypersonic powered-simulation flows by comparing CFD solutions with experimental surface pressure dam. Aftbody lower surface pressures were well predicted, but lower surface wing pressures were less accurately predicted. The second objective was to determine the 3D effects on the aftbody created by fairing over the inlet; this was accomplished by comparing the CFD solutions of two closed-inlet powered configurations with a flowing-inlet powered configuration. Although results at four freestream Mach numbers indicate that the exhaust plume tends to isolate the aftbody surface from most forebody flowfield differences, a smooth inlet fairing provides the least aftbody force and moment variation compared to a flowing inlet. The final objective was to predict and understand the 3D characteristics of exhaust plume development at selected points on a representative flight path. Results showed a dramatic effect of plume expansion onto the wings as the freestream Mach number and corresponding nozzle pressure ratio are increased.

Huebner, Lawrence D.↗
NASA NTRS1990

Stress field rotation or block rotation: An example from the Lake Mead fault system

The Coulomb criterion, as applied by Anderson (1951), has been widely used as the basis for inferring paleostresses from in situ fault slip data, assuming that faults are optimally oriented relative to the tectonic stress direction. Consequently if stress direction is fixed during deformation so must be the faults. Freund (1974) has shown that faults, when arranged in sets, must generally rotate as they slip. Nur et al., (1986) showed how sufficiently large rotations require the development of new sets of faults which are more favorably oriented to the principal direction of stress. This leads to the appearance of multiple fault sets in which older faults are offset by younger ones, both having the same sense of slip. Consequently correct paleostress analysis must include the possible effect of fault and material rotation, in addition to stress field rotation. The combined effects of stress field rotation and material rotation were investigated in the Lake Meade Fault System (LMFS) especially in the Hoover Dam area. Fault inversion results imply an apparent 60 degrees clockwise (CW) rotation of the stress field since mid-Miocene time. In contrast structural data from the rest of the Great Basin suggest only a 30 degrees CW stress field rotation. By incorporating paleomagnetic and seismic evidence, the 30 degrees discrepancy can be neatly resolved. Based on paleomagnetic declination anomalies, it is inferred that slip on NW trending right lateral faults caused a local 30 degrees counter-clockwise (CCW) rotation of blocks and faults in the Lake Mead area. Consequently the inferred 60 degrees CW rotation of the stress field in the LMFS consists of an actual 30 degrees CW rotation of the stress field (as for the entire Great Basin) plus a local 30 degrees CCW material rotation of the LMFS fault blocks.

Ron, Hagai↗
NASA NTRS1993

Shape optimization for aerodynamic efficiency and low observability

Field methods based on the finite-difference approximations of the time-domain Maxwell's equations and the potential-flow equation have been developed to solve the multidisciplinary problem of airfoil shaping for aerodynamic efficiency and low radar cross section (RCS). A parametric study and an optimization study employing the two analysis methods are presented to illustrate their combined capabilities. The parametric study shows that for frontal radar illumination, the RCS of an airfoil is independent of the chordwise location of maximum thickness but depends strongly on the maximum thickness, leading-edge radius, and leadingedge shape. In addition, this study shows that the RCS of an airfoil can be reduced without significant effects on its transonic aerodynamic efficiency by reducing the leading-edge radius and/or modifying the shape of the leading edge. The optimization study involves the minimization of wave drag for a non-lifting, symmetrical airfoil with constraints on the airfoil maximum thickness and monostatic RCS. This optimization study shows that the two analysis methods can be used effectively to design aerodynamically efficient airfoils with certain desired RCS characteristics.

Vinh, Hoang↗
NASA NTRSDate not supplied

Scoping of an Air Supply Configuration for AFC on a Commercial Transport Airplane High Lift System

A scoping study is being conducted on the air supply for a microjet-based active flow control (AFC) system on a twin-turbofan commercial transport airplane. Microjets provide circulation control using small surface-normal pneumatic jets located near the trailing edge of a lifting surface such as a wing or flap. When located on the pressure side of the lifting surface they increase the lift, and when located on the suction side they decrease lift. In this study, microjets are considered for installation in the flaps of the high-lift version of the Common Research Model (CRM-HL). An air supply system involving bleed air from the airplane’s auxiliary power unit (APU) plus ram air provides the air to the microjets. A model based on the 1D compressible flow equations is applied to analyze the air supply system configuration and predict the microjet flow rate with the resulting airplane performance changes based on Reynolds-averaged Navier-Stokes modeling of microjets on the CRM-HL. The results of this scoping study are encouraging in that APU air can be used to entrain ram air and thereby increase the AFC mass flow rate to achieve effective lift control and airplane performance enhancement during takeoff and landing.

AATT↗
NASA NTRSDate not supplied

Scoping of an Air Supply Configuration for AFC on a Commercial Transport Airplane High Lift System

A scoping study is being conducted on the air supply fora microjet-based active flow control (AFC) system on a twin-turbofan commercial transport airplane. Microjets provide circulation control using small surface-normal pneumatic jets located near the trailing edge of a lifting surface such as a wing or flap. When located on the pressure side of the lifting surface they increase the lift, and when located on the suction side they decrease lift. In this study, microjets are considered for installation in the flaps of the high-lift version of the Common ResearchModel (CRM-HL). Two different architectures to supply the air for the microjets are considered: (1) bleed air from the airplane’s auxiliary power unit (APU) plus ram air, and (2) engine fan bleed air plus ram air. A model based on the 1D compressible flow equations is applied to analyze the air supply system architectures and predict the microjet flow rate with the resulting airplane performance changes based on Reynolds-averaged Navier-Stokes modeling of microjets on the CRM-HL. The results of this scoping study are encouraging in that pressurized air from the APU or the engine fan can be used to entrain ram air and thereby increase the AFC mass flow rate to achieve effective lift control and airplane performance enhancement during takeoff and landing.

AATT↗
NASA NTRS1993

Physiological Anatomical Rodent Experiment (PARE) .04 Feasibility Test 1

The objective of this feasibility study was to investigate the environmental/treatment stresses in the proposed PARE.04 experiments in a ground based study to determine if these stresses were of sufficient magnitude to compromise the planned shuttle experiments. Eighty pregnant Sprague-Dawley rats were received on day 2 (day l equals day of vaginal plug) of gestation (G2) and on G7 60 were laparotomized to determine the condition of pregnancy and allow assignment to test groups. The five test groups (N equals 10 each group) were as follows: Group 1, nominal flight; Group 2, laparotomy control; Group 3, hysterectomy control; Group 4, vivarium control; Group 5, caesarean delivery. On G17, groups 1, 2, and 5 were subjected to unilateral hysterectomy to obtain fetuses for evaluation. There was no difference in fetal crown-rump length, fetal weight, or placental weight in any of the test groups subjected to unilateral hysterectomy at G17. Animals were allowed to go to term and animals in each group delivered between the morning of G22 and the afternoon of G23. Rats assigned to Group 5 began delivering vaginally prior to the designated time for caesarean section, thus only 2 animals in this group were delivered by caesarean section. After delivery, a blood sample was taken from the dam, and they were euthanized and the thymus and adrenal glands weighed. Pups from experimental dams were tattooed for identification, the anogenital distance of male pups was photographed for later measurement, and all pups placed with foster dams and litter sizes were standardized to 10. On day 7, all pups were euthanized, and pup adrenal glands and thymus weighed. Laparotomy at G7 with or without unilateral hysterectomy at G17, had no effect on pregnancy maintenance or vaginal delivery. There was no difference in maternal adrenal or thymus weights or plasma levels of catecholamines, estradiol, progesterone, or corticosterone. Likewise, there was no difference in the anogenital distance (index of fetal stress) of neonatal male pups, between any of the experimental groups. From days 0-7, weight gain from dams in all experimental groups was similar. Lastly, there was no difference in weights of thymus and adrenal glands in pups euthanized at day 7. Collectively, these data indicate that treatment stresses inherent in the proposed PARE.04 experimental design should not compromise the planned shuttle experiments.

Burden, Hubert W.↗
NASA NTRS2002

Hypergravity Effects on Rodent Pregnancy and Parturition

No mammal has yet undergone birth, or parturition, in the microgravity of space. Previous studies (Ronco & Alberts, 2000) have shown that mid-pregnant rat dams exposed to spaceflight (0-g) and landed 48-72 hrs before term successfully delivered robust, healthy offspring Microgravity-exposed dams exhibited twice the expected numbers of labor contractions whereas length of pregnancy, duration of labor, fetal wastage, number of neonates born and litter gender ratios were identical to controls. In the present study, we report the results of rodent pregnancy and parturition at the opposite end of the gravity spectrum, in hypergravity. Dams exposed to either: 1.0-g, 1.5-g, 1.75-g or 2.0-g from Gestational day (G) 11 and throughout the births of their litters had comparable pregnancy and labor durations, fetal wastage, numbers of neonates born and litter Tender ratios. During parturition, hypergravity-exposed dams exhibited significantly fewer labor contractions as compared to 1.0-g controls. Dams that underwent birth in hypergravity had significantly fewer offspring surviving the immediate postpartum period (P1: 1.0-g, 11.92 +/- 2.84; 1.5-g, 10.88 +/- 2.17; 1.75-g, 9.22 +/-1.99; 2.0-g, 8.83 +/- 3.31). Within 24 hrs postpartum, neonatal survival was further diminished in hypergravity [P2: 100% (1.0-g); 96% (1.5-g); 96% (1.75-g); 73% (2.0-g)] and continued to decline (P10: 100%(1.0-g.); 90%(1.5-g); 87%(1.75-g), 40%(2.0-g)]. Neonatal losses stabilized by P5 for the 1.5-g andl.75-g conditions but continued until P9 for the 2.0-g condition. Together, these findings show that postnatal, but not prenatal, survival is compromised following birth in hypergravity, Maternal and neonatal factors that contribute to peri-parturitional vulnerability to altered gravity environments will be discussed.

Ronca, A. E.↗
NASA NTRS1993

Photovoltaic Power Without Batteries for Continuous Cathodic Protection

The objective of this project was to successfully demonstrate that renewable energy can efficiently and economically replace dedicated non-renewable power sources. The COASTSYSTA designed, installed, and started up on 20 Jan. 1990, a state-of-the-art photovoltaic powered impressed current cathodic protection system (PVCPSYS) for steel and iron submerged structures. This system does not require any auxiliary/battery backup power. The PVCPSYS installed on 775 ft. of steel sheet piling of a Navy bulkhead is continuing to provide complete, continuous corrosion protection. This installation is well documented by COASTSYSTA and was verified on-site by the U.S. Army Corps of Engineers. The PVCPSYS uses only renewable energy and is environmentally clean. A patent is pending on the new technology. Other possible PVCPSYS applications are mothballed ships, docks, dams, locks, bridges, marinas, and pipelines. The Department of Defense Photovoltaic Review Committee and Sandia National Laboratories consider this successful and cost effective system a major advance in the application of photovoltaics.

Muehl, W. W., Sr.↗
NASA NTRS1992

Subsonic High-Lift Flight Research on the NASA Transport System Research Vehicle (TSRV)

Flight tests are being conducted on the Transport Systems Research Vehicle (B737-100 aircraft) at the NASA Langley Research Center as part of a multi-phased research program to obtain detailed flow characteristics on a multi-element, high-lift flap system. Recent test results obtained for a full-chord wing section including the slat, main-wing, and flap elements are presented. In addition, program status and future plans are discussed. Pressure distributions were obtained using pressure belts over the slat, main-wing, and flap elements at one spanwise station. Test conditions included a range of flap deflections, chord Reynolds numbers (10 to 21 million), and Mach numbers (0.16 to 0.40). In addition to the pressure distributions, Preston-tube measurements on the slat upper surface indicated relaminarization of turbulent flows which were introduced by the pressure belt on the slat leading-edge surface. Comparisons of the in-flight pressure measurements with predictions from a two-dimensional, viscous multi-element method modified by simple-sweep theory showed reasonable agreement; however, the overprediction of pressures on the flap elements shows a need for better modeling of confluent boundary layers and inclusion of three-dimensional effects.

Flight Testing↗
NASA NTRS1974

Satellite geological and geophysical remote sensing of Iceland

The author has identified the following significant results. The seasonal change in size of sediment plumes from the many glacial rivers which discharge into the sea along the south coast gives an indication of seasonal changes in melting rates of glaciers. Changes in area of lakes, particularly glacier-margin lakes can be mapped of most of the area covered by glacial ice in Iceland. Recently deglaciated terrain can be distinguished on MSS color composites. The increase in surface area of the ice-dammed lake, Graenalon, was monitored until the occurrence of a jokulhlaup, after which the surface area of the lake was considerably reduced. The effect of two subglacial jokulhlaups on the overlying ice cover can be seen in the form of collapse features in the surface of Vatnajokull. MSS color composites permit the mapping of five distinct vegetation types; forests, cultivated areas, grasslands, reclaimed areas, and lichen-covered bedrock. Features as small as 100 m can be discerned. The ability to map landforms, vegetation distribution, occurrence of snowcover, glaciers, and geologic structure stereoscopically permits a much greater accurate analysis of these features.

Williams, R. S., Jr.↗
NASA NTRS1999

Update on the Effects of Space Flight on Development of Immune Responses

This study has been completed, and the following is an update of the results as published. Pregnant rats were flown on the Space Shuttle in the NIH.R I mission for 11 days, and pregnant control rats were maintained in animal enclosure modules in a ground-based chamber under conditions approximating those in flight. Additional controls were in standard housing. The effects of the flight on immunological parameters (including blastogenesis, interferon-gamma production, response to colony stimulating factor and total immunoglobulin levels) of dams, fetuses, and pups was determined.

Sonnenfeld, G.↗
NASA NTRS2011

Risk Management of Jettisoned Objects in LEO

The construction and maintenance of the International Space Station (ISS) has led to the release of many objects into its orbital plane, usually during the course of an extra-vehicular activity (EVA). Such releases are often unintentional, but in a growing number of cases, the jettison has been intentional, conducted after a careful assessment of the net risk to the partnership and to other objects in space. Since its launch in 1998 the ISS has contributed on average at least one additional debris object that is simultaneously in orbit with the station, although the number varies widely from zero to eight at any one moment. All of these objects present potential risks to other objects in orbit. Whether it comes from known and tracked orbiting objects or from unknown or untrackable objects, collision with orbital debris can have disastrous consequences. Objects greater than 10cm are generally well documented and tracked, allowing orbiting spacecraft or satellites opportunities to perform evasive maneuvers (commonly known as Debris Avoidance Maneuvers, or DAMs) in the event that imminent collision is predicted. The issue with smaller debris; however, is that it is too numerous to be tracked effectively and yet still poses disastrous consequences if it intercepts a larger object. Due to the immense kinetic energy of any item in orbit, collision with debris as small as 1cm can have catastrophic consequences for many orbiting satellites or spacecraft. Faced with the growing orbital debris threat and the potentially catastrophic consequences of a collision-generated debris shower originating in an orbit crossing the ISS altitude band, in 2007 the ISS program manger asked program specialists to coordinate a multilateral jettison policy amongst the ISS partners. This policy would define the acceptable risk trade rationale for intentional release of a debris object, and other mandatory constraints on such jettisons to minimize the residual risks whenever a jettison was accepted. Although ISS-related debris often presents untenable risks to the EVA crew, IVA crew, or to a departing cargo vehicle for a controlled disposal, such released objects also present a ballistic nuisance to the visiting vehicle traffic, and a potential fragmentation threat to the hundreds of other functional and debris objects whose perigees lie below the ISS orbital altitude. Thus, every such jettison decision is a conscious risk trade.

Bacon, John B.↗
NASA NTRS1978

Comparison of reusable insulation systems for cryogenically-tanked earth-based space vehicles

Three reusable insulation systems concepts have been developed for use with cryogenic tanks of earth-based space vehicles. Two concepts utilized double-goldized Kapton (DGK) or double-aluminized Mylar (DAM) multilayer insulation (MLI), while the third utilized a hollow-glass-microsphere, load-bearing insulation (LBI). All three insulation systems have recently undergone experimental testing and evaluation under NASA-sponsored programs. Thermal performance measurements were made under space-hold (vacuum) conditions for insulation warm boundary temperatures of approximately 291 K. The resulting effective thermal conductivity was approximately .00008 W/m-K for the MLI systems (liquid hydrogen test results) and .00054 W/m-K for the LBI system (liquid nitrogen test results corrected to liquid hydrogen temperature). The DGK MLI system experienced a maximum thermal degradation of 38 percent, the DAM MLI system 14 percent, and the LBI system 6.7 percent due to repeated thermal cycling representing typical space flight conditions. Repeated exposure of the DAM MLI system to a high humidity environment for periods as long as 8 weeks provided a maximum degradation of only 24 percent.

Sumner, I. E.↗
NASA NTRS1988

Effects of compressibility on design of subsonic fuselages for natural laminar flow

Compressible linear boundary-layer stability analyses of two representative axisymmetric fuselage geometries indicate that a favorable effect will be exerted on the characteristics of a fuselage's axisymmetric boundary layer by compressibility. A freestream Mach number increase from 0.6 to 0.8 significantly reduces TS wave growth rates in the laminar boundary layer of the fuselages analyzed. The generally destabilizing effect of increasing length Re number on boundary layer stability can be overpowered by the favorable effects of compressibility on the fluid.

Vijgen, P. M. H. W.↗
NASA NTRS1998

Postnatal development under conditions of simulated weightlessness and space flight

The adaptability of the developing nervous system to environmental influences and the mechanisms underlying this plasticity has recently become a subject of interest in space neuroscience. Ground studies on neonatal rats using the tail suspension model of weightlessness have shown that the force of gravity clearly influences the events underlying the postnatal development of motor function. These effects depend on the age of the animal, duration of the perturbation and the motor function studied. A nine-day flight study has shown that a dam and neonates can develop under conditions of space flight. The motor function of the flight animals after landing was consistent with that seen in the tail suspension studies, being marked by limb joint extension. However, there were expected differences due to: (1) the unloading of the vestibular system in flight, which did not occur in the ground-based experiments; (2) differences between flight and suspension durations; and (3) the inability to evaluate motor function during the flight. The next step is to conduct experiments in space with the flexibility and rigor that is now limited to ground studies: an opportunity offered by the International Space Station. Copyright 1998 Published by Elsevier Science B.V.

Non-NASA Center↗
NASA NTRS2020

Combustion Dynamics Characteristics and Fuel Pressure Modulation Responses of a Three-Cup Third-Generation Swirl-Venturi Lean Direct Injection Combustion Concept

This paper presents the combustion dynamic data and fuel modulation response of a three-cup Lean Direct Injection combustor developed by Woodward, FST. The test was conducted at the NASA Glenn Research Center CE-5 flame tube test facility. The facility provided inlet air up to 922 K and pressure up to 19.0 bar. At the low-power configuration, the combustion noise was quiet. Large combustion pressure oscillations were observed with the High-power configuration at an off design condition, with low inlet air temperature and pressure conditions and a high equivalence ratio (about T3=600 K, P3 = 800 kPa, and ER =0.46). The noise amplitude was as high as 1.5 psi at around 220 Hz. As inlet air pressure and temperature increased, this combustion instability decreased. Fuel modulated signals were produced with the WASK fuel modulator located in the fuel line upstream of the center cup pilot fuel-air mixer. The amplitudes of the modulated signals detected in the combustor were low. Only less than 0.13% (0.06 psi) of the input energy was detected, and the signal amplitudes decreased as the modulated frequencies increased. Interaction between the modulated signals and the combustion noise varied with operating conditions. At a condition with low combustion noise around 150 hz, modulating a signal at around the same frequency would increase the combustion noise from 0.2 psi to as high as 0.6 psi, whereas at a condition with a high combustion instability around 250 hz, the modulated signal did not seem to have much effect on the combustion noise.

Fuel flexible combustor↗