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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

The effects of trace impurities in coal-derived liquid fuels on deposition and accelerated high temperature corrosion of cast superalloys

The effects of trace metal impurities in coal-derived liquids on deposition, high temperature corrosion and fouling were examined. Alloys were burner rig tested from 800 to 1100 C and corrosion was evaluated as a function of potential impurities. Actual and doped fuel test were used to define an empirical life prediction equation. An evaluation of inhibitors to reduce or eliminate accelerated corrosion was made. Barium and strontium were found to limit attack. Intermittent application of the inhibitors or silicon additions were found to be effective techniques for controlling deposition without losing the inhibitor benefits. A computer program was used to predict the dew points and compositions of deposits. These predictions were confirmed in deposition test. The potential for such deposits to plug cooling holes of turbine airfoils was evaluated. Tests indicated that, while a potential problem exists, it strongly depended on minor impurity variations.

Lowell, C. E.↗
NASA NTRS1980

Structure of the low latitude boundary layer

Observations at high temporal resolution of the frontside magnetopause and plasma boundary layer, made with the LASL/MPE fast plasma analyzer onboard the ISEE 1 and 2 spacecraft, revealed a complex quasiperiodic structure of some of the observed boundary layers. A cool tailward streaming boundary layer plasma was seen intermittently, with intervening periods of hot tenuous plasma which has properties similar to the magnetospheric population. While individual encounters with the boundary layer plasma last only a few minutes, the total observation time may extend over one hour or more.

Sckopke, N.↗
NASA NTRS1981

Li/SO2 cell performance

The development of a Li/SO2 cell exhibiting intermittent storage capability at 98 C and instantaneous voltage response is discussed. Results of short circuit, cell puncture, and forced discharge testing are presented along with elevated temperature storage and temperature cycling responses.

Cloyd, J. S.↗
NASA NTRS1981

High temperature cyclic oxidation furnace testing at NASA Lewis Research Center

A standardized method of testing the cyclic oxidation resistance of various alloys in static air to 1200 C was developed and is routinely used at NASA Lewis Research Center. Test samples are automatically raised and lowered into a resistance wound furnace for a series of fixed interval heating and cooling cycles. Spall catchers collect the accumulated spall from each sample. The samples are weighed intermittently to generate specific weight change/time data. At various test times the samples and the accumulated spall are analyzed by X-ray diffraction. A computer program uses this gravimetric and X-ray data as input to print out the oxidation curves and specific weight change/time and X-ray results in a published format, organizes, and indexes the data. So far, several hundred Fe, Ni, and Co base alloys were tested using this same basic procedure and results form the basis of a series of cyclic oxidation handbooks to be published by NASA. Such specific weight change/time data were used to estimate the oxidative metal consumption by several computer modeling techniques to rank alloys and for use in life testing estimates.

Barrett, C. A.↗
NASA NTRS1981

The influence of a local wall deformation on the development of natural instabilities in a laminar boundary layer

The natural instabilities which propagate in the laminar boundary layer of a flat plate composed of intermittent wave trains are described. A spectral analysis determines the frequency range and gives a frequency and the harmonic 2 only if there is a wall deformation. This analysis provides the amplitude modulation spectrum of the instabilities. Plots of the evolution of power spectral density are compared with the numerical results obtained from the resolve of the Orr-Sommerfeld equation, while the harmonic is related to a micro-recirculating flow near the wall deformation.

Burnel, S.↗
NASA NTRS1981

Study of the development of natural instabilities in a laminar boundary layer in incompressible flow

Natural instabilities which are created in a laminar boundary layer and which consist of intermittent wave trains were studied. The spectral analysis of these fluctuations makes it possible to localize them in terms of frequency and to isolate their spectrum of amplitude modulation. The variation in terms of abscissa value and ordinate value of these instabilities is compared with the results derived from the solution of the Orr-Sommerfeld equation.

Burnel, S.↗
NASA NTRS1981

Modification in drag of turbulent boundary layers resulting from manipulation of large-scale structures

The effects of placing a parallel-plate turbulence manipulator in a boundary layer are documented through flow visualization and hot wire measurements. The boundary layer manipulator was designed to manage the large scale structures of turbulence leading to a reduction in surface drag. The differences in the turbulent structure of the boundary layer are summarized to demonstrate differences in various flow properties. The manipulator inhibited the intermittent large scale structure of the turbulent boundary layer for at least 70 boundary layer thicknesses downstream. With the removal of the large scale, the streamwise turbulence intensity levels near the wall were reduced. The downstream distribution of the skin friction was also altered by the introduction of the manipulator.

Corke, T. C.↗
NASA NTRS1981

Concepts for design of an energy management system incorporating dispersed storage and generation

New forms of generation based on renewable resources must be managed as part of existing power systems in order to be utilized with maximum effectiveness. Many of these generators are by their very nature dispersed or small, so that they will be connected to the distribution part of the power system. This situation poses new questions of control and protection, and the intermittent nature of some of the energy sources poses problems of scheduling and dispatch. Under the assumption that the general objectives of energy management will remain unchanged, the impact of dispersed storage and generation on some of the specific functions of power system control and its hardware are discussed.

Kirkham, H.↗
NASA NTRS1980

Modification in drag of turbulent boundary layers resulting from manipulation of large-scale structures

The effects of placing a parallel-plate turbulence manipulator in a boundary layer are investigated by means of flow visualization and hot-wire measurements. The manipulator was found to be effective in inhibiting the intermittent large scale structure of the boundary layer, and the effect persists for at least 70 boundary-layer thicknesses downstream of the manipulator. With the removal of the large scale, there was an observed reduction in the streamwise turbulence intensity levels near the wall. The downstream distribution of the skin friction coefficient, determined from the stream wise change in fluid momentum, was also altered by the introduction of the manipulator. The data from both the visualization and hot wire studies are provided.

Corke, T. C.↗
NASA NTRS1981

Spatial and temporal variations of EUV coronal bright points

This paper reports results of an analysis of Skylab observations of coronal bright points made in EUV spectral lines formed in the chromosphere, chromospheric-coronal transition region and corona. The most important result is that the observed bright points exhibited large variations in EUV emission over time scales as short as 5.5 min, the temporal resolution of the data. In most cases strong enhancements in the coronal line were accompanied by strong enhancements in the chromospheric and transition region lines. The intensity variations appear to take place within substructures of the bright points, which most likely consist of miniature loops evolving on time scales of a few minutes. Coronal cooling times derived from the data are consistent with an intermittent, impulsive coronal heating mechanism for bright points.

Habbal, S. R.↗
NASA NTRS1981

SERT II 1980 extended flight thruster experiments

The SERT II spacecraft, launched in 1970, has been maintained in an operational, but intermittent status since 1971. This paper presents the flight results obtained from mid 1979 through December 1980. Near continuous solar power in 1979 and 1980 has enabled long periods of thruster endurance testing. Three of four propellant tanks have been exhausted with no significant change in thruster system operation before being empty. A new plasma mode thrust has been characterized and direct thrust measurements obtained. Other tests, including beam neutralization by various neutralizer sources, give insight to electron conduction across plasmas in space and provide a basis to model neutralization of thruster arrays.

Kerslake, W. R.↗
NASA NTRS1981

Circumnutation augmented in clinostatted plants by a tactile stimulus

Dark-grown, 4-day old, Helianthus annuus seedlings were rotated for 20 hr on horizontal clinostats to minimize the amplitude of circumnutation. Then a Plexiglas sheet was placed gently against the tip of the cotyledons. By time-lapse video imaging (using intermittent IR illumination to which the plants were insensitive) movements of the clinostatted plants were observed before, during, and after the period of mechanical contact. Immediately after the Plexiglas sheet was removed residual nutation increased in amplitude almost three-fold, then declined over the next 7 hr to the prestimulation level. This demonstration of enhancement of circumnutation by mechanical contact is consistent with the model of an endogeneous oscillator that can be stimulated by factors other than gravity.

Chapman, D. K.↗
NASA NTRS1981

High temperature cyclic oxidation furnace testing at NASA Lewis Research Center

A standardized method of testing the cyclic oxidation resistance of various alloys in static air up to 1200 C has been developed and routinely used at the NASA Lewis Research Center. Test samples are automatically raised and lowered into a resistance wound furnace for a series of fixed-interval heating and cooling cycles. Spall catchers collect the accumulated spall from each sample. The samples are weighed intermittently to generate specific weight change with time data. At various test times the samples and the accumulated spall are analyzed by X-ray diffraction. A computer program is used to print out the specific weight change versus time data and the X-ray data in tabular form and to plot the specific weight change versus time data in a publishable format. The data are also organized and indexed. So far several hundred Fe-, Ni-, and Co-base alloys have been tested using this basic procedure and will form the basis of a series of cyclic oxidation handbooks to be published by NASA. Such specific weight change/time data have been used to estimate the oxidative metal consumption by several computer modeling techniques both to rank alloys and to estimate life.

Barrett, C. A.↗
NASA NTRS1951

Effectiveness of Thermal-Pneumatic Airfoil-Ice-Protection System

Icing and drag investigations were conducted in the NACA Lewis icing research tunnel employing a combination thermal-pneumatic de-icer mounted on a 42-inch-chord NACA 0018 airfoil. The de-icer consisted of a 3-inch-wide electrically heated strip symmetrically located about the leading edge with inflatable tubes on the upper and lower airfoil surfaces aft of the heated area. The entire de-icer extended to approximately 25 percent of chord. A maximum power density of 9.25 watts per square inch was required for marginal ice protection on the airfoil leading edge at an air temperature of 00 F and an airspeed of 300 miles per hour. Drag measurements indicated, that without icing, the de-icer installation increased the section drag to approximately 140 percent of that of the bare airfoil; with the tubes inflated, this value increased to a maximum of approximately 620 percent. A 2-minute tube-inflation cycle prevented excessive ice formation on the inflatable area although small scattered residual Ice formations remained after inflation and were removed intermittently during later cycles. Effects of the time lag of heater temperatures after initial application of power and the insulating effect of ice formations on heater temperatures were also determined.

Gowan, William H., Jr.↗
NASA NTRS1952

Preliminary Results of Cyclical De-Icing of a Gas-Heated Airfoil

An NACA 65(sub 1)-212 airfoil of 8-foot chord was provided with a gas-heated leading edge for investigations of cyclical de-icing. De-icing was accomplished with intermittent heating of airfoil segments that supplied hot gas to chordwise passages in a double-skin construction. Ice removal was facilitated by a spanwise leading-edge parting strip which was continuously heated from the gas-supply duct. Preliminary results demonstrate that satisfactory cyclical ice removal occurs with ratios of cycle time to heat-on period (cycle ratio) from 10 to 26. For minimum runback, efficient ice removal, and minimum total heat input, short heat-on periods of about 15 seconds with heat-off periods of 260 seconds gave the best results. In the range of conditions investigated, the prime variables in the determination of the required heat input for cyclical ice removal were the air temperature and the cycle ratio; heat-off period, liquid water content, airspeed, and angle of attack had only secondary effects on heat input rate.

Gray, V. H.↗
NASA NTRS1981

A prospectus for a theory of variable variability

It is proposed that the kind of stellar variability exhibited by the Sun in its magnetic activity cycle should be considered as a prototype of a class of stellar variability. The signature includes long 'periods' (compared to that of the radial fundamental model), erratic behavior, and intermittency. As other phenomena in the same variability class we nominate the liminosity fluctuations of ZZ Ceti stars and the solar 160 m oscillation. We discuss the possibility that analogous physical mechanisms are at work in all these cases, namely instabilities driven in a thin layer. These instabilities should be favorable to grave modes (in angle) and should arise in conditions that may allow more than one kind of instability to occur at once. The interaction of these competing instabilities produces complicated temporal variations. Given suitable idealizations, it is shown how to begin to compute solutions of small, but finite, amplitude.

Childress, S.↗
NASA NTRS1981

Autonomous attitude determination from star data for a dual-spin planetary spacecraft

A batch mode process which identifies three reference stars within a rotor-mounted star scanner's field-of-view based on the criteria of intensity and geometry was established. The sequential mode which continuously tracks the reference stars provides star transit times and estimates of rotor's spin rate. A least-square estimator was formulated which sequentially determines the spacecraft attitude from sucessive star crossings by minimizing the error in the star and scanner slit normal orthogonality. This spacecraft attitude also provides intermittent updates for the gyro propagated inertial attitude of the despun science platform. Simulation results are presented, showing successful star identification and attitude convergence in the presence of nutation and star transit time uncertainty.

Wong, E. C.↗
NASA NTRS1982

The P-POD Project

The programmable pilot oriented display (P-POD), a multiprocessor based flight information processing and display unit, is discussed. Communication protocols between the three Z-80 processors inside P-POD are reviewed. The interface between the video processor, P2, and the main processor, P1, was tested. Hardware and software were revised. Data flow between P1 and P2 is illustrated. While running diagnostic routines to exercise the P1/P2 interface at maximum speed an intermittent failure was observed. A check of possible noise sources or race conditions in the hardware did not reveal the source of this failure. Possible software timing problems were also fully investigated. To eliminate the effects of this type of failure a performance monitor routine was used to detect these occasional failures and correct them. The data transmission cycle between P1/P2 is either allowed to continue normal operation or is re-initialized and restarted when an error is detected.

Littlefield, J. A.↗