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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Far-infrared Photometry of Low-mass Pre-main-sequence Stars with Broad CO Wings

A sample of 14 low-mass premain-sequence stars were studied in the far-infrared. There is evidence for outflowing material around twelve of these stars; in most cases the evidence includes broad wings on the profiles of the CO J=2 to 1 line. Ten of the objects were detected ( 5 sigma) at 100 micro, and seven were mapped at 50 and 100 micro. The far-infrared emission makes a significant contribution to the total luminosity of the objects. It is found that the force available from radiation pressure is not sufficient to drive the outflows. Any process which taps the same energy source as does the present stellar luminosity must have high efficiency.

Evans, N. J., II↗
NASA NTRS1984

Topics in electrochemical degradation of photovoltaic modules

Electrochemical degradation of photovoltaic modules was examined. It is found that the extent of electrochemical damage is dependent on the integrated leakage current. The PV electrochemical degradation mechanisms in the two polarities are different: (1) degradation rates in the two polarities are of the same order of magnitude; (2) center tapped grounded arrays are a preferred system configuration to minimize electrochemical degradation. The use of thicker pottant layers and polymer substrate films to reduce equilibrium leakage current values is suggested. A metallized substrate layer, if used, should be isolated from the pottant and the frame by polyester layers, and EVA modules appear to be consistent with 30 year life allocation levels for electrochemical damage. Temperature acceleration factors are well behaved and moderately well understood; humidity acceleration factors vary radically with module construction and materials and require additional research.

Mon, G. R.↗
NASA NTRS1984

On the measurement of pilot perceptual workload - A comparison of assessment techniques addressing sensitivity and intrusion issues

A flight simulator-based study was conducted to examine fourteen distinct mental workload estimation measures, including opinion, secondary task, physiological, and primary task measures. Both the relative sensitivity of the measures to changes in mental workload and the differential intrusion of the changes on primary task performance were assessed. The flight task was varied in difficulty by manipulation of the presentation rate and complexity of a hazard-perception task that required each of 48 licensed pilots to rely heavily on their perceptual abilities. Three rating scales (Modified Cooper-Harper, Multi-descriptor, and Workload-Compensation-Interference/Technical Effectiveness), two secondary task measures (time estimation and tapping regularity), one physiological measure (respiration frequency), and one primary task measure (danger-condition response time) were reliable indicants of workload changes. Recommendations for applying the workload measures are presented.

Casali, J. G.↗
NASA NTRS1985

Detailed measurements of the flowfield in the vicinity of an airfoil with glaze ice

An experimental study has been conducted in the OSU subsonic tunnel to measure the characteristics of the separation bubble on an airfoil with glaze ice. A measured glaze ice accretion on a NACA 0012 airfoil was simulated in wood for this dry tunnel test. The 21 inch chord model was pressure belted and the ice shape internally tapped to obtain surface pressures, lift and moment coefficients. A wake survey probe was used to obtain airfoil drag. The separation bubble was explored by measuring the time averaged velocities using a split film probe. The probe was positioned using a computer controlled two-dimensional traversing system. In this paper, airfoil lift, drag, and moment coefficient data are compared for the airfoil with and without glaze ice. Velocity profiles in the separation bubble are presented for several chordwise stations at three angles of attack. The ice shape caused a severe lift and drag penalty. The velocity profiles show clearly the large bubble geometry, regions of reversed flow, and bubble reattachment.

Bragg, M. B.↗
NASA NTRS1985

Experimental study of forward-located jet-interaction nozzles

The effects of forward-mounted sonic jet-interaction nozzles with one, three equal, or one large and two small orifices on the transitional or turbulent boundary-layer flow over a biconic (9-deg-25-arcmin/6-deg) model at angle of attack -10 to the 15 deg and Reynolds number 8.10 x 10 to the 6th/ft are investigated experimentally using pressure taps, force measurements, oil-flow visualization, and schlieren photography in the 20-in. Mach-6 wind tunel at NASA Langley. The injection flow rates are 0.055 and 0.026 lbm/s, with stagnation pressure 500 psia, stagnation temperature 1000 R, and dynamic pressure 8.7 psia. The results are presented in diagrams, graphs, and photographs and characterized. Moment amplification factors of 1.0 or better (maximum 1.8 at angle of attack 15 deg and flow rate 0.055 lbm/s) are observed for all nozzle types, but the configuration with three unequal orifices is found to give improvements of 10 percent over the single-orifice nozzle at a given flow rate.

Cavalleri, R. J.↗
NASA NTRS1985

Aerodynamics of sports balls

Research data on the aerodynamic behavior of baseballs and cricket and golf balls are summarized. Cricket balls and baseballs are roughly the same size and mass but have different stitch patterns. Both are thrown to follow paths that avoid a batter's swing, paths that can curve if aerodynamic forces on the balls' surfaces are asymmetric. Smoke tracer wind tunnel tests and pressure taps have revealed that the unbalanced side forces are induced by tripping the boundary layer on the seam side and producing turbulence. More particularly, the greater pressures are perpendicular to the seam plane and only appear when the balls travel at velocities high enough so that the roughness length matches the seam heigh. The side forces, once tripped, will increase with spin velocity up to a cut-off point. The enhanced lift coefficient is produced by the Magnus effect. The more complex stitching on a baseball permits greater variations in the flight path curve and, in the case of a knuckleball, the unsteady flow effects. For golf balls, the dimples trip the boundary layer and the high spin rate produces a lift coefficient maximum of 0.5, compared to a baseball's maximum of 0.3. Thus, a golf ball travels far enough for gravitational forces to become important.

Mehta, R. D.↗
NASA NTRS1985

A holographic interferometric study of an axisymmetric shock-wave/boundary-layer strong interaction flow

The results of a holographic interferometric and analytical examination of shock wave/turbulent boundary layer interactions occurring in a flow near a cone-cylinder intersection are reported. A Mach 2.85 flow with an Re of 18 million was used, along with cone angles of 12.5, 20 and 30 deg. Negligible, incipient and large scale separations were observed. The subsonic layer of the boundary always remained thin and was usually penetrated by the shock wave. An Abel transform, applied to the interferometric traces, yielded a great deal of data on the density field when combined with data from application of laser velocimeter, pressure tap and oil flow techniques.

Dunagan, S. E.↗
NASA NTRS1986

A survey of the state of the art and focused research in range systems, task 2

Many communication, control, and information processing subsystems are modeled by linear systems incorporating tapped delay lines (TDL). Such optimized subsystems result in full precision multiplications in the TDL. In order to reduce complexity and cost in a microprocessor implementation, these multiplications can be replaced by single-shift instructions which are equivalent to powers of two multiplications. Since, in general, the obvious operation of rounding the infinite precision TDL coefficients to the nearest powers of two usually yield quite poor system performance, the optimum powers of two coefficient solution was considered. Detailed explanations on the use of branch-and-bound algorithms for finding the optimum powers of two solutions are given. Specific demonstration of this methodology to the design of a linear data equalizer and its implementation in assembly language on a 8080 microprocessor with a 12 bit A/D converter are reported. This simple microprocessor implementation with optimized TDL coefficients achieves a system performance comparable to the optimum linear equalization with full precision multiplications for an input data rate of 300 baud. The philosophy demonstrated in this implementation is dully applicable to many other microprocessor controlled information processing systems.

Yao, K.↗
NASA NTRS1985

Radial rift and block tectonics around the Tharsis bulge: Introductional postulation

Although the Vallis Marineris canyon and radial fossae grabens have been extensively studied, their origin and formation mechanism is still the subject of numerous questions. Possible rift formation is only one point of view and does not explain the rifting mechanism and the radial pattern of these structures around the Tharsis bulge. Both active and passive rifting must be taken into account. According to the active mechanism the building of a colcanic complex like the Tharsis bulge is caused by the rising of a huge mantle plume and adjoining extrusions which tap the generated magma. The surrounding fossae and valley structures are caused by more passive crustal rifting due to tensional failure of the surface layers. The main rising mantle plume activated and regenerated failure patterns radial to the centre of activity. These radial zones of weakness are then most easily utilized by the rising mantle plume. Deep zones of weakness regulate the penetration and distribution of hot mantle rock into upper levels while, contrarily, the effective impingement of the hot mantle plume into the lithosphere opens up new weakness zones.

Raitala, J.↗
NASA NTRS1985

An analysis of a separation bubble transition criterion at low Reynolds numbers

Factors which influence the criterion governing the length of the laminar region of a separation bubble on an airfoil at low Re were investigated. The criterion is the onset of separation when a critical Re value is surpassed. Wind tunnel data were gathered for the flow around a NACA 66(3)-018 airfoil at Re from 50,000-200,000. The data were taken with either hot-wire anemometers or pressure taps. The value of the critical Re was influenced by the chord Re, the angle of attack and the level of turbulence in the free stream. However, the turbulence levels examined, up to 0.184 percent, did not greatly affect the critical Re. Further characterizations of the effects of the three factors on the critical Re are necessary before the important features of separation bubbles can be identified with an acceptable level of certainty.

Schmidt, G. S.↗
NASA NTRS1985

Separation bubble behavior for a NACA 23009 airfoil

Results are reported of experiments with smoke-wire flow visualization applied to characterizing the conditions conducive to formation of a separation bubble on an airfoil in low Re flow. An airfoil was used which spanned the test channel of the wind tunnel designed for low turbulence and noise. A wire coated with mineral oil was stretched across the channel upstream of the airfoil and heated. The smoke it gave off was flash-illuminated and photographed with ASA 3000 film. Extending the airfoil over the entire section yielded photographs that gave an essentially two-dimensional perspective. Angles of attack from 0-10 deg were investigated at Re of 33,000, 66,000, 100,000 and 133,000. Sample photographs illustrate the usefulness of the technique and apparatus in the flow regimes examined, particularly when used in conjunction with pressure tap data from the airfoil surface.

Fisher, S. S.↗
NASA NTRS1984

Data analysis and model simulation of the initiation of convection on April 24, 1982

A combined modelling and data analysis is used to examine the initiation and development of a hail-producing mesoscale convective system which developed over the Texas panhandle near Amarillo, Texas, on April 24, 1982, and propagated east into Oklahoma. This event occurred during the NASA AVE-VAS IV experiment, as a dense upper air mesoscale network was collecting data at three-hour intervals. The results show that both synoptic and mesoscale processes separately and in concert help to force the convection. The destabilization of the atmosphere due to cold advection is important in removing any cap to deep convective development. The upper level moistening due to flow from the northwest also helps to increase the convective instability of the atmosphere. The mesoscale convergence due to cloud shading appears dominant over that of topography, but the latter cannot be ignored, especially in its sustained effect. The developing mesoscale circulation also appears to tap a surface supply of moisture feeding the convection.

Mcnider, R. T.↗
NASA NTRS1986

Aerodynamic measurements of an airfoil with simulated glaze ice

An experimental study has been conducted in the OSU subsonic tunnel to measure the detailed aerodynamic characteristics of an airfoil with simulated glaze ice. A special model was built with interchangeable leading edges to be used in this study. One leading edge is that of a NACA 0012, while the other is a simulation of a glaze ice accretion measured in the NACA Lewis Icing Research Tunnel. The model was instrumented with a dense distribution of surface pressure taps to provide excellent detail around the ice shapes and reattachment point. A traversing total pressure probe was used to document the boundary layer characteristics on the NACA 0012 section. The ice shape caused a severe lift and drag penalty, reducing the maximum lift by over 50 percent and causing a 300 percent increase in drag. Surface pressure distributions revealed a large lower surface separation in addition to the expected large upper surface separation.

Bragg, M. B.↗
NASA NTRS1986

LDA measurement of the passage flow field in a 3-D airfoil cascade

Three-dimensional internal flow computational models are currently being developed to predict the flow through turbomachinery blade rows. For these codes to be of quantitative value, they must be verified with data obtained in experiments which model the fundamental flow phenomena. In this paper, the complete three-dimensional flow field through a subsonic annular cascade of cambered airfoils is experimentally quantified. In particular, detailed three-dimensional data are obtained to quantify the inlet velocity profile, the cascade passage velocity field, and the exit region flow field. The primary instrumentation for acquiring these data is a single-channel Laser Doppler Anemometer operating in the backscatter mode, with chordwise distributions of airfoil surface static pressure taps also utilized. Appropriate data are correlated with predictions from the MERIDL/TSONIC codes.

Stauter, R. C.↗
NASA NTRS1986

Application of laser-velocimetry to the study of the flow around a two-dimensional airfoil

The experimental techniques employed by NASA researchers to obtain a high volume throughput of data in a study of high-lift multielement airfoils using a laser velocimeter (LV) are detailed. The two-dimensional LV system recorded mean velocity, turbulence intensities, Re shear stresses, skewness and kurtosis of the flow. A computer-controlled positioning mount for the LV allowed automated surveys of the flows with a 0.001 in. positioning accuracy. The flow was seeded with oil droplets and additional refinement of the wind tunnel controls permitted rapid speedup at selected areas of the flowfield over specific regions of the airfoil. Surface pressure taps furnished data for selecting regions for more detailed investigation. The data processing capabilities processed 30-40 samples every 10 min in an automated mode. Profiles of the data were computed automatically to furnish graphical displays on demand. Numerous samples of the data displays generated are provided.

Braden, J. A.↗
NASA NTRS1985

Evaluation of 16 measures of mental workload using a simulated flight task emphasizing mediational activity

As aircraft and other systems become more automated, a shift is occurring in human operator participation in these systems. This shift is away from manual control and toward activities that tap the higher mental functioning of human operators. Therefore, an experiment was performed in a moving-base flight simulator to assess mediational (cognitive) workload measurement. Specifically, 16 workload estimation techniques were evaluated as to their sensitivity and intrusion in a flight task emphasizing mediational behavior. Task loading, using navigation problems presented on a display, was treated as an independent variable, and workload-measure values were treated as dependent variables. Results indicate that two mediational task measures, two rating scale measures, time estimation, and two eye behavior measures were reliably sensitive to mediational loading. The time estimation measure did, however, intrude on mediational task performance. Several of the remaining measures were completely insensitive to mediational load.

Wierwille, W. W.↗
NASA NTRS1986

Far-infrared photometry of low-mass pre-main-sequence stars with broad CO wings

A sample of 14 low-mass premain-sequence stars were studied in the far-infrared. There is evidence for outflowing material around twelve of these stars; in most cases the evidence includes broad wings on the profiles of the CO J = 2 to 1 line. Ten of the objects were detected (5 sigma) at 100 micros, and seven were mapped at 50 and 100 micros. The far-infrared emission makes a significant contribution to the total luminosity of the objects. It is found that the force available from radiation pressure is not sufficient to drive the outflows. Any process which taps the same energy source as does the present stellar luminosity must have high efficiency.

Evans, N. J., II↗
NASA NTRS1986

An experimental study of the aerodynamics of a NACA 0012 airfoil with a simulated glaze ice accretion

An experimental study was conducted in the Ohio State University subsonic wind tunnel to measure the detailed aerodynamic characteristics of an airfoil with a simulated glaze ice accretion. A NACA 0012 model with interchangeable leading edges and pressure taps every one percent chord was used. Surface pressure and wake data were taken on the airfoil clean, with forced transition and with a simulated glaze ice shape. Lift and drag penalties due to the ice shape were found and the surface pressure clearly showed that large separation bubbles were present. Both total pressure and split-film probes were used to measure velocity profiles, both for the clean model and for the model with a simulated ice accretion. A large region of flow separation was seen in the velocity profiles and was correlated to the pressure measurements. Clean airfoil data were found to compare well to existing airfoil analysis methods.

Bragg, M. B.↗