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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Predicted Variations in Flow Patterns in a Horizontal CVD Reactor

Expressions in terms of common reactor operating parameters were derived for the ratio of the Grashof number to the Reynolds number, Gr/Re, the ratio of the Grashof to the square of 2 the Reynolds number, Gr/Re(exp 2), and the Rayleigh number, Ra. Values for these numbers were computed for an example horizontal CVD reactor and compared to numerical simulations to gauge their effectiveness as predictors of the presence or absence of transverse and longitudinal rolls in the reactor. Comparisons were made for both argon and hydrogen carrier gases over the pressure range 2- 101 kPa. Reasonable agreement was achieved in most cases when using Gr/Re to predict the presence of transverse rolls and Ra to predict the presence of longitudinal rolls. The ratio Gr/Re(exp 2) did not yield useful predictions regarding the presence of transverse rolls. This comparison showed that the ratio of the Grashof number to the Reynolds number, as well as the Rayleigh number, can be used to predict the presence or absence of transverse and longitudinal rolls in a horizontal CVD reactor for a given set of reactor conditions. These predictions are approximate, and care must be exercised when making predictions near transition regions.

Kuczmarski, Maria A.↗
NASA NTRS1947

Comparison of Wind-Tunnel Predictions with Flight Measurements of the Longitudinal-Stability and -Control Characteristics of a Douglas BTD-1 Airplane

Low Mach number longitudinal-stability and control characteristics as predicted by use of wind tunnel data from a powered 3/16-scale model are compared with flight test measurements of a Navy BTD-1 airplane. The accuracy of the wind tunnel data and the discrepancies involved in attempting to correlate with flight data are discussed and analyzed. The comparison showed that wind tunnel predictions were, in general, in good agreement with flight test data. The predicted values were for the most part sufficiently accurate to show the satisfactory and unsatisfactory characteristics in the preliminary design stage and to indicate possible methods of improvement. The discrepancies which did occur were attributed principally to physical dissimilarities between model and airplane and the instability to determine accurately the flight power conditions. The effect of Mach number was considered negligible since the maximum flight test value was about 0.5. In order to simulate more closely the flight conditions and hence obtain more accurate data for predictions, it appears desirable to perform large-scale tests of unorthodox control surfaces such as the sealed vaned elevators with which the airplane was equipped.

Bunnell, Mort V.↗
NASA NTRS2022

Unique Observational Constraints on the Seasonal and Longitudinal Variability of the Earth’s Planetary Albedo and Cloud Distribution Inferred From EPIC Measurements

Thorough comparison to observations is key to developing a credible climate model forecasting capability. Deep Space Climate Observatory (DSCOVR) measurements of Earth’s reflected solar and emitted thermal radiation provide a unique observational perspective that permits a more reliable model/data comparison than is possible with the otherwise available satellite data. The uniqueness is in the DSCOVR satellite’s viewing geometry, which enables continuous viewing of the Earth’s sunlit hemisphere from its Lissajous orbit around the Lagrangian L1 point. The key instrument is the Earth Polychromatic Imaging Camera (EPIC), which views the Earth’s sunlit hemisphere with 1024-by-1024-pixel imagery in 10 narrow spectral bands from 317 to 780 nm, acquiring up to 22 high spatial resolution images per day. The additional feature is that the frequency of EPIC image acquisition is nearly identical to that of the climate GCM data generation scheme where climate data for the entire globe are ‘instantaneously’ calculated at 1-h radiation time-step intervals. Implementation of the SHS (Sunlit Hemisphere Sampling) EPIC-view geometry for the in-line GCM output data sampling establishes a precise self-consistency in the space-time data sampling between EPIC observational and GCM output data generation and sampling. The remaining problem is that the GCM generated data are radiative fluxes, while the EPIC measurements are backscatter-dependent radiances. Radiance to flux conversion is a complex problem with no simple way to convert GCM radiative fluxes into spectral radiances. The more expedient approach is to convert the EPIC spectral radiances into broadband radiances by MODIS/CERES-based regression relationships and then into solar radiative fluxes using the CERES angular distribution models. Averaging over the sunlit hemisphere suppresses the meteorological weather noise, but preserves the intra-seasonal larger scale variability. Longitudinal slicing by the Earth’s rotation permits a self-consistent model/data comparison of the longitudinal model/data differences in the variability of the reflected solar radiation. Ancillary EPIC Composite data provide additional cloud property information for climate model diagnostics. Comparison of EPIC-derived seasonal and longitudinal variability of the Earth’s planetary albedo with the GISS ModelE2 results shows systematic overestimate of cloud reflectivity over the Pacific Ocean with corresponding underestimates over continental land areas.

DSCOVR↗
NASA NTRS1977

Stability of higher-order Bragg interactions in active periodic media

The stability of waves in unbounded, longitudinally periodic media is studied for index and gain coupling. Time-independent periodic media are found to support both stable and absolutely unstable waves. The wave characteristics depend upon average gain or loss, coupling type, and Bragg order. The extended coupled waves equations provide explicit values of threshold, frequency, and temporal growth rate for instabilities at all Bragg resonances through the dispersion relation. Applications to multiharmonic periodicities and complex couplings are briefly discussed with particular note taken of possible reductions of the stability thresholds and removal of threshold degeneracies. Comparisons are made to the longitudinally bounded case of distributed feedback lasers.

Jaggard, D. L.↗
NASA NTRS1984

Comparison of ozone data derived from SBUV and SAGE with emphasis on longitudinal variations

Stratospheric ozone observations performed by the SBAV and SAGE satellite instruments in March and April 1979 are analyzed and compared to other data, where available; in the absence of ground-truth data the experimental uncertainties are modeled by intercomparison of the measurements. The signal-to-noise ratios for the detectability of longitudinal variation in ozone are estimated for both SBUV and SAGE instruments. The analysis of longitudinal variation data reveals significant differences in amplitudes obtained in individual events in which rapid amplitude changes with height were present. Finally, a systematic overestimation of ozone by 20 percent by the SAGE instrument and underestimation by SBUV by about 15 percent at 50-70 latitudes at 10 mb is noted.

Cunnold, D.↗
NASA NTRS1961

Effects of Gyroscopic Cross Coupling Between Pitch and Yaw on the Handling Qualities of VTOL Aircraft

Gyroscopic cross coupling between pitch and yaw was simulated with a variable-stability helicopter while hovering in a yawing maneuver to ascertain the effect of cross coupling on handling qualities. Pilot ratings of the controllability of cross coupling were obtained for various combinations of longitudinal control power, angular velocity about the yaw axis, and simulated engine angular momentum. A theoretical investigation, supplemented by simulator data, was undertaken to determine the effect of longitudinal damping on the coupling controllability. Also, a comparison was made between flight and simulator data. The results indicated that for an aircraft with otherwise satisfactory longitudinal handling qualities, the level of cross coupling is satisfactory when less than 30 percent of the available longitudinal control will trim out the largest gyroscopic coupling moment which might be encountered. Increased longitudinal damping resulted in a significant increase in the controllability of pitch-yaw gyroscopic cross coupling.

Garren, John F., Jr.↗
NASA NTRS1993

Satellite Radar Interferometry for Monitoring Ice-Sheet Motion: Application to an Antarctic Ice Stream

As a new means of monitoring the flow velocities and grounding-line positions of ice streams, which are indicators of response of the Antarctic and Greenland ice sheets to climatic change or internal instability, the method of satellite radar interferometry (SRI) is here proposed and applied to the Rutford Ice Stream, Antarctica. The method uses phase comparison of the radar signal obtained for a pair of SAR images taken a few days apart to plot an interferogram which directly displays relative ground motions that have occurred in the time interval between images. The detection limit is about 1.5 mm for vertical motions and about 4 mm for horizontal motions in the radar beam direction. In the Rutford Ice Stream, SRI velocities agree fairly well with earlier ground-truth data over a longitudinal interval of 29 km; the comparison suggests a secular decrease in velocity of about 2 percent from 1978-80 to 1992...

Goldstein, R. M.↗
NASA NTRS1993

Satellite Radar Interferometry for Monitoring Ice-Sheet Motion: Application to an Antarctic Ice Stream

As a new means of monitoring the flow velocities and grounding-line positions of ice streams, which are indicators of response of the Antarctic and Greenland ice sheets to climatic change or internal instability, the method of satellite radar interferometry (SRI) is here proposed and applied to the Rutford Ice Stream, Antarctica. The method uses phase comparison of the radar signal obtained for a pair of SAR images taken a few days apart to plot an interferogram which directly displays relative ground motions that have occurred in the time interval between images. The detection limit is about 1.5 mm for vertical motions and about 4 mm for horizontal motions in the radar beam direction. In the Rutford Ice Stream, SRI velocities agree fairly well with earlier ground-truth data over a longitudinal interval of 29 km; the comparison suggests a secular decrease in velocity of about 2 percent from 1978-80 to 1992...

Goldstein, R. M.↗
NASA NTRS2013

Longitudinally Jointed Edge-wise Compression Honeycomb Composite Sandwich Coupon Testing and FE Analysis: Three Methods of Strain Measurement, and Comparison

Three means (i.e., typical foil strain gages, fiber optic sensors, and a digital image correlation (DIC) system) were implemented to measure strains on the back and front surfaces of a longitudinally jointed curved test article subjected to edge-wise compression testing, at NASA Goddard Space Flight Center, according to ASTM C364. The Pre-test finite element analysis (FEA) was conducted to assess ultimate failure load and predict strain distribution pattern throughout the test coupon. The predicted strain pattern contours were then utilized as guidelines for installing the strain measurement instrumentations. The strain gages and fiber optic sensors were bonded on the specimen at locations with nearly the same strain values, as close as possible to each other, so that, comparisons between the measured strains by strain gages and fiber optic sensors, as well as the DIC system are justified. The test article was loaded to failure (at approximately 38 kips), at the strain value of approximately 10,000mu epsilon As a part of this study, the validity of the measured strains by fiber optic sensors is examined against the strain gage and DIC data, and also will be compared with FEA predictions.

Farrokh, Babak↗
NASA NTRS2022

Unique NISTAR-Based Climate GCM Diagnostics of the Earth’s Planetary Albedo and Spectral Absorption Through Longitudinal Data Slicing

Deep Space Climate Observatory (DSCOVR) measurements of Earth’s reflected solar and emitted thermal radiation permit a unique model/data comparison perspective that is not readily available from other satellite data. The key factor is the unique Lissajous orbital viewing geometry from the Lagrangian L1 point, which enables a continuous view of Earth’s sunlit hemisphere. The National Institute of Standards and Technology Advanced Radiometer (NISTAR) is the DSCOVR Mission energy budget instrument, which views the reflected and emitted radiation of the Earth’s sunlit hemisphere by means of single pixel active cavity full-spectrum (Band-A, 0.2–100 μm) and filtered solar wavelength (Band-B, 0.2–4.0 μm; and Band-C, 0.7–4.0 μm) radiometer measurements. An additional solar wavelength photodiode channel (0.3–1.1 μm) provides a calibration reference. The objective of this study is the assessment of climate GCM performance via direct model/data comparisons. Such comparisons are difficult due to quasi-chaotic natural variability present in real-world observational data and in climate GCM simulations. This is where the unique DSCOVR viewing geometry makes possible the longitudinal data slicing methodology for more direct model/data comparison. The key point of the longitudinal slicing approach is that data integration over the entire sunlit hemisphere eliminates the quasi-chaotic meteorological weather-scale noise, while preserving intra-seasonal and planetary-scale variability. The rotation of the Earth that retrieves this climate-style, large-scale longitudinal and seasonal variability. The hemispheric averaging is accomplished automatically in NISTAR measurements with its single-pixel view of the Earth. For climate GCMs, this requires implementing the Sunlit Hemisphere Sampling (SHS) scheme to operate on the GCM run-time output data, utilizing the DSCOVR Satellite Ephemeris data to assure precise viewing geometry between NISTAR measurements and GCM output data, while averaging out the meteorological weather noise. However, GCM generated data are radiative fluxes, while NISTAR (and EPIC) measurements are near-backscattered radiances. Conversing NISTSR measurements into radiative fluxes cannot be accomplished using NISTAR data alone, even with detailed support from conventional satellite data. But the identical viewing geometry of Earth’s sunlit hemisphere, and synergistic analyses of EPIC data make it feasible for this conversion of NISTAR near-backscatter radiances into radiative fluxes.

deep space climate observatory↗
NASA NTRS1981

Space Shuttle entry aerodynamic comparisons of flight 1 with preflight predictions

Results of comparisons of predictions of aerodynamic performance, longitudinal trim, and reaction control jet interaction with data from the initial Shuttle flight are presented. The Shuttle's control surfaces are described, and it is noted that the flight plan contained no provisions for maneuvering capability tests. Wind tunnel testing totaling 35,000 hr were used to replace graduated flight testing, and calculations were made to allow for nonsimulated structural deformation, flowfield parameters, and profile drag. The goal was to desensitize the flight control system with respect to the aerodynamics by adding variations to the predictions. Lift/drag agreed well above Mach 1, while lower drag was encountered below Mach 1. Trim characteristics were predicted accurately between Mach 2-10, and less than satisfactorily outside that range. Discrepancies were also observed for jet interaction effects for the aft yaw jets at Mach numbers greater than 10.

Young, J. C.↗
NASA NTRS1985

Hypersonic characteristics of an advanced aerospace plane

A series of hypersonic wind-tunnel tests have been conducted in the NASA Langley Hypersonic Facilities Complex to obtain the static longitudinal and lateral-directional aerodynamic characteristics of an advanced aerospace plane. Data were obtained at 0 to 20 deg angles of attack and -3 to 3 deg angles of sideslip at Mach numbers of 6 and 10 in air and 20 in helium. Results show that stable trim capability exists at angles of attack near maximum lift-drag ratio (L/D). Both performance and stability exhibited some Mach number dependency. The vehicle was longitudinally unstable at low angles of attack but stable at angles of attack near and above maximum L/D. It was directionally unstable with positive dihedral effect. The rudder showed an inability to provide lateral-directional control, and removing the vertical tail resulted in increased directional instability. Analytical predictions of the static longitudinal aerodynamic coefficients gave relatively good comparisons with the experimental data.

Mccandless, R. S.↗
NASA NTRS1988

A study of helicopter stability and control including blade dynamics

A linearized model of rotorcraft dynamics has been developed through the use of symbolic automatic equation generating techniques. The dynamic model has been formulated in a unique way such that it can be used to analyze a variety of rotor/body coupling problems including a rotor mounted on a flexible shaft with a number of modes as well as free-flight stability and control characteristics. Direct comparison of the time response to longitudinal, lateral and directional control inputs at various trim conditions shows that the linear model yields good to very good correlation with flight test. In particular it is shown that a dynamic inflow model is essential to obtain good time response correlation, especially for the hover trim condition. It also is shown that the main rotor wake interaction with the tail rotor and fixed tail surfaces is a significant contributor to the response at translational flight trim conditions. A relatively simple model for the downwash and sidewash at the tail surfaces based on flat vortex wake theory is shown to produce good agreement. Then, the influence of rotor flap and lag dynamics on automatic control systems feedback gain limitations is investigated with the model. It is shown that the blade dynamics, especially lagging dynamics, can severly limit the useable values of the feedback gain for simple feedback control and that multivariable optimal control theory is a powerful tool to design high gain augmentation control system. The frequency-shaped optimal control design can offer much better flight dynamic characteristics and a stable margin for the feedback system without need to model the lagging dynamics.

Zhao, Xin↗
NASA NTRS2006

Free Body Dynamics of a Spinning Cylinder With Planar Restraint (a.k.a. Barrel of Fun)

The dynamic motion of a cylinder on a floor or hard surface is both entertaining and instructive. With maintenance torques, motion can be sustained and controlled as illustrated in a video clip that can be viewed in the PDF file of this document. The analysis of such a cylinder with and without end caps is burned on rotation about its center of mass and restrained by a plane normal to the axis passing through its center of mass at an angle alpha. For small values of alpha, the governing equations are simplified, and for symmetric bodies, stability requires rotation greater than [2 square root of(JWL*)]/J(sub X), where J is the transverse mass moment of inertia, W is the weight of the cylinder, L* is the cylinder length from the base to the center of mass, and JX is the mass moment of inertia about the longitudinal axis OX of the barrel. Comparisons to data are made and some applications are discussed.

Moraru, Laurentiu↗
NASA NTRS2011

ARES I Aerodynamic Testing at the NASA Langley Unitary Plan Wind Tunnel

Small-scale force and moment and pressure models based on the outer mold lines of the Ares I design analysis cycle crew launch vehicle were tested in the NASA Langley Research Center Unitary Plan Wind Tunnel from May 2006 to September 2009. The test objectives were to establish supersonic ascent aerodynamic databases and to obtain force and moment, surface pressure, and longitudinal line-load distributions for comparison to computational predictions. Test data were obtained at low through high supersonic Mach numbers for ranges of the Reynolds number, angle of attack, and roll angle. This paper focuses on (1) the sensitivity of the supersonic aerodynamic characteristics to selected protuberances, outer mold line changes, and wind tunnel boundary layer transition techniques, (2) comparisons of experimental data to computational predictions, and (3) data reproducibility. The experimental data obtained in the Unitary Plan Wind Tunnel captured the effects of evolutionary changes to the Ares I crew launch vehicle, exhibited good agreement with predictions, and displayed satisfactory within-test and tunnel-to-tunnel data reproducibility.

Erickson, Gary E.↗