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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 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

The influence of stripe width on the threshold current of double-heterojunction lasers

Experimental measurements of the threshold current of oxide-isolated stripe laser as a function of stripe width and p-layer resistivity are presented. A calculation of the influence of carrier outdiffusion has been made, including the effect of current leakage beyond the stripe edges. The calculated threshold increase is in substantial agreement with experiment for stripe widths down to about 10 microns. The data also yield an effective diffusion length of about 7 microns for the lasers studied. Deviations between experimental and calculated thresholds occurring at stripe widths of 4-6 microns are represented by an empirical curve which is compared with previously published calculations of threshold gain.

Ladany, I.↗
NASA NTRS2002

The Opposition Effect: A Very Unusual Case

The reflection of electromagnetic radiation from a planetary regolith involves a combination of geometric and physical optics processes which contribute to the signal returned to the remote observer. The geometric optics effects are the product of singly and multiply scattered radiation from the surfaces of the regolith particles, combined with radiation which has undergone various combinations of transmission through one or more regolith grains followed by one or more scatterings from other particles. The physical optics effects include diffraction of radiation around the edges of large irregular particles and cooperative coherent scattering between particles which are small when compared to the wavelength of the incident radiation. These effects produce measurable changes in the intensity and polarization of reflected light as a function of illumination and viewing geometry. In particular, as phase angle becomes small, the reflectance of a particulate material will increase non-linearly and exhibit the 'opposition effect'. In the planetary science context, the phase curve, and in particular the size of the opposition surge and the width of the phase curve near zero degrees, have been attributed to two processes commonly called 'shadow hiding' (SHOE) and 'coherent backscattering' (CBOE).

Nelson, R. M.↗
NASA NTRS1932

The aerodynamic characteristics of a model wing having a split flap deflected downward and moved to the rear

Tests were made on a model wing with three different sized split trailing-edged flaps, in the NACA 7 by 10 foot wind tunnel. The flaps were formed of the lower rear portion of the wing and were rotated downward about axes at their front edges. The lift, drag, and center of pressure were measured with the axis in its original position and also with it moved back in even steps to the trailing edge of the main wing, giving in effect an increase in area. The split flaps when deflected about their original axis locations gave slightly higher maximum lift coefficients than conventional trailing-edge flaps, and the lift coefficients were increased still further by moving the axes toward the rear. The highest value of C(sub L max), which was obtained with the largest flap hinged at 90 per cent of the chord from the leading edge, was 2.52 as compared with 1.27 for the basic wing.

Weick, Fred E↗
NASA NTRS1974

Effect of upper-surface blowing on static longitudinal stability of a swept wing

A low-speed wind-tunnel investigation was conducted on a sharp-edged 75 deg delta wing, to determine the effect of upper-surface blowing on static longitudinal stability characteristics. The model incorporated nozzles, located at 0.50 mean aerodynamic chord length, supplied by compressed air to provide blowing on the upper surface. A full span trailing-edge flap was also tested as an additional high-lift device. The angle of attack was varied from 0 to 24 deg for a range of thrust coefficients from 0 to 0.45. The results of the static force tests showed that favorable increments in static longitudinal stability and lift were obtained using upper-surface blowing.

Coe, P. L., Jr.↗
NASA NTRS1993

An Experimental Parametric Study of Geometric, Reynolds Number, and Ratio of Specific Heats Effects in Three-Dimensional Sidewall Compression Scramjet Inlets at Mach 6

Since mission profiles for airbreathing hypersonic vehicles such as the National Aero-Space Plane include single-stage-to-orbit requirements, real gas effects may become important with respect to engine performance. The effects of the decrease in the ratio of specific heats have been investigated in generic three-dimensional sidewall compression scramjet inlets with leading-edge sweep angles of 30 and 70 degrees. The effects of a decrease in ratio of specific heats were seen by comparing data from two facilities in two test gases: in the Langley Mach 6 CF4 Tunnel in tetrafluoromethane (where gamma=1.22) and in the Langley 15-Inch Mach 6 Air Tunnel in perfect gas air (where gamma=1.4). In addition to the simulated real gas effects, the parametric effects of cowl position, contraction ratio, leading-edge sweep, and Reynolds number were investigated in the 15-Inch Mach 6 Air Tunnel. The models were instrumented with a total of 45 static pressure orifices distributed on the sidewalls and baseplate. Surface streamline patterns were examined via oil flow, and schlieren videos were made of the external flow field. The results of these tests have significant implications to ground based testing of inlets in facilities which do not operate at flight enthalpies.

Holland, Scott D.↗
NASA NTRS2005

The Influence of Projectile Trajectory Angle on the Simulated Impact Response of a Shuttle Leading Edge Wing Panel

In support of recommendations by the Columbia Accident Investigation Board, a team has been studying the effect of debris impacting the reinforced carbon-carbon panels of the shuttle leading edge. The objective of this study was to examine the effect of varying parameters of the debris trajectory on the damage tolerance. Impacts at the upper and lower surface and the apex of the leading edge were examined. For each location, trajectory variances included both the alpha and beta directions. The results of the analysis indicated in all cases the beta sweep decreased the amount of damage to the panel. The increases in alpha resulted in a significant increase in damage to the RCC panel. In particular, for the lower surface, where the alpha can increase by 10 degrees, there was a nearly 40% increase in the impulse. As a result, it is recommended that for future analyses, a 10 degree offset in alpha from the nominal trajectory is included for impacts on the lower surface. It is also recommended to assume a straight aft, or zero beta, trajectory for a more conservative analysis.

Spellman, Regina L.↗
NASA NTRS2015

A 3-D Computational Study of a Variable Camber Continuous Trailing Edge Flap (VCCTEF) Spanwise Segment

Results of a computational study carried out to explore the effects of various elastomer configurations joining spanwise contiguous Variable Camber Continuous Trailing Edge Flap (VCCTEF) segments are reported here. This research is carried out as a proof-of-concept study that will seek to push the flight envelope in cruise with drag optimization as the objective. The cruise conditions can be well off design such as caused by environmental conditions, maneuvering, etc. To handle these off-design conditions, flap deflection is used so when the flap is deflected in a given direction, the aircraft angle of attack changes accordingly to maintain a given lift. The angle of attack is also a design parameter along with the flap deflection. In a previous 2D study,1 the effect of camber was investigated and the results revealed some insight into the relative merit of various camber settings of the VCCTEF. The present state of the art has not advanced sufficiently to do a full 3-D viscous analysis of the whole NASA Generic Transport Model (GTM) wing with VCCTEF deployed with elastomers. Therefore, this study seeks to explore the local effects of three contiguous flap segments on lift and drag of a model devised here to determine possible trades among various flap deflections to achieve desired lift and drag results. Although this approach is an approximation, it provides new insights into the "local" effects of the relative deflections of the contiguous spanwise flap systems and various elastomer segment configurations. The present study is a natural extension of the 2-D study to assess these local 3-D effects. Design cruise condition at 36,000 feet at free stream Mach number of 0.797 and a mean aerodynamic chord (MAC) based Reynolds number of 30.734x10(exp 6) is simulated for an angle of attack (AoA) range of 0 to 6 deg. In the previous 2-D study, the calculations revealed that the parabolic arc camber (1x2x3) and circular arc camber (VCCTEF222) offered the best L/D characteristics and minimum drag in cruise. In the present 3-D study, calculations show that for the same C(sub t), the 3-D circular arc camber wing segment produces the largest drag for a given lift, larger than either of the two 2-D configurations, as was also conjectured in the previous study. This study indicates a wing stall around 4.5 deg angle of attack.

Camber↗
NASA NTRS1992

Silver Teflon blanket: LDEF tray C-08

A study of the Teflon blanket surface at the edge of tray C-08 illustrates the complexity of the microenvironments on the Long Duration Exposure Facility (LDEF). The distribution of particulate contaminants varied dramatically over a distance of half a centimeter (quarter of an inch) near the edge of the blanket. The geometry and optical effects of the atomic oxygen erosion varied significantly over the few centimeters where the blanket folded over the edge of the tray resulting in a variety of orientations to the atomic oxygen flux. A very complex region of combined mechanical and atomic oxygen damage occurred where the blanket contacted the edge of the tray. A brown film deposit apparently fixed by ultraviolet light traveling by reflection through the Teflon film was conspicuous beyond the tray contract zone. Chemical and structural analysis of the surface of the brown film and beyond toward the protected edge of the blanket indicated some penetration of energetic atomic oxygen at least five millimeters past the blanket-tray contact interface.

Crutcher, E. Russ↗
NASA NTRS1988

Residual thermal and moisture influences on the free-edge delamination of laminated composites

A simple delamination analysis method is developed. It is based on a shear-type deformation theory and includes hygrothermal effects. The method is applied to mixed-mode edge delamination specimens made of T300/5208 graphite/epoxy. It is found that residual thermal influences were alleviated when moisture stresses were included. Thermal effects on the interlaminar shear stress and total energy release rate were totally alleviated for the same specific moisture content. Moreover, this value of moisture content was not significantly affected by the stacking sequence for the laminates considered.

Armanios, Erian A.↗
NASA NTRS1989

Influence of shock-shock interactions on the blunt body flow field at hypersonic flight speeds

The effect of shock impingement on the blunt leading edge of the inlet cowl of a scramjet engine is investigated numerically. The impinging shock is caused by the vehicle forebody. The interaction of this forebody shock with the cowl leading edge shock results in a very complex flowfield containing local regions of high pressure and intense heating. In the present investigation, this complex flowfield is calculated by solving the full Navier-Stokes equations using a finite-volume flux splitting technique due to Van Leer. Results are also obtained for the downstream effects into the inlet of the leading edge shock-shock interactions. Results of the present numerical investigation are compared with available experimental results.

Singh, D. J.↗
NASA NTRS1962

The Effect on the Buckling of Perfect Cylinders of Prebuckling Deformations and Stresses Induced by Edge Support

Large deflection theory is used to compute buckling loads of simply supported initially perfect cylinders under axial compression, external hydrostatic pressure, and combinations of axial compression and internal or external pressure. Important results are obtained by taking into account prebuckling deformations and stresses induced by edge support. For example, the presence of these deformations and stresses can decrease the axial-compression buckling load of an unpressurized perfect cylinder by 50 percent or more.

CYLINDER↗
NASA NTRS1974

Cold-air study of the effect on turbine stator blade aerodynamic performance of coolant ejection from various trailing-edge slot geometries. 1: Experimental results

Trailing-edge slot configurations were investigated in a two-dimensional cascade of turbine stator blades. The trailing-edge slots were incorporated into blades with round trailing edges. The five blade configurations investigated included blades with two different trailing-edge thicknesses and four different slot widths. The results of the investigation showed that there was, in general, a significant increase in primary-air efficiency due to the coolant flow, the increase varying with slot configuration. For the five configurations tested, the average percent change in primary-air efficiency per percent coolant flow varied almost linearly from zero to about 1.4 percent over a range of coolant- to primary-air exit-velocity ratios between 0 and 1.2. However, for different configurations there was considerable deviation from the average values in the lower range of exit velocity ratios.

Prust, H. W., Jr.↗
NASA NTRS1984

Navier-Stokes solutions for two-dimensional subsonic base flow

Methods for determining the effects of mass injection from the trailing edge of a bluff body at low speeds and in transonic flow were numerically studied along with an unmodified blunt-based body to gain insight into the effects of vortex shedding on the base drag. The methodology used to obtain finite-difference solutions to the Navier-Stokes equations for subsonic compressible two-dimensional near-wake flows is presented. The effectiveness of an introduced outflow boundary condition which minimizes reflections back into the computational domain was demonstrated with the solution of a model vortex problem. Calculations of the near-wake flow past a circular cylinder were in excellent agreement with experimental data. Laminar-flow solutions for a blunt-based model with and without a base cavity and with mass injection into the wake agreed qualitatively with experimental observations. The drag reduction capability provided by such base modifications was demonstrated.

Rudy, D. H.↗
NASA NTRS1973

Application of an electronic image analyzer to dimensional measurements from neutron radiographs

Means of obtaining improved dimensional measurements from neutron radiographs of nuclear fuel elements are discussed. The use of video-electronic image analysis relative to edge definition in radiographic images is described. Based on this study, an edge definition criterion is proposed for overcoming image unsharpness effects in taking accurate diametral measurements from radiographs. An electronic density slicing method for automatic edge definition is described. Results of measurements made with video micrometry are compared with scanning microdensitometer and micrometric physical measurements. An image quality indicator for estimating photographic and geometric unsharpness is described.

Vary, A.↗
NASA NTRS1989

An experimental study of forced streamwise vortical structures in a plane mixing layer

Streamwise structures have been shown to ride among the primary spanwise vortices in past flow visualization investigations of plane mixing layers. More recently, quantitative measurements were obtained which showed the origin and evolution of streamwise vortices within a mixing layer. In the present study, the effects of perturbing the mixing layer using two different mechanisms are investigated. A serration on the splitter plate trailing edge was found to have a relatively small effect, confined to the near-field development of the streamwise structures. The installation of cylindrical pegs in the high-speed side boundary layer, however, not only generated a regular array of vortex pairs, but also affected the mean development of the mixing layer far downstream. In both cases, the mean streamwise vorticity was found to decay rapidly with increasing downstream distance.

Mehta, Rabindra D.↗