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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 325 records · Page 18

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NASA NTRS1980

Generation and injection of e.m. waves in space plasma by means of a long orbiting tether

The generation and injection of electromagnetic waves in space plasma by means of a long orbiting tether are considered. The objectives include an estimation of the portions of the primary electrodynamic power developed by the tether that goes to excite each of various wave generation and injection mechanisms expected to be present during a tether's orbital flight, an evaluation of the signal levels associated with each one of the mechanisms above, and verification of their detectability with state-of-the-art instrumentation on the Earth surface or elsewhere. The generation and injection of Alfven waves and electron whistler waves were identified as the most relevant mechanisms activited by the electrodynamic tether. The physical mechanisms that govern these two families of phenomena were investigated and the ratio between the power that goes in Alfven waves and in whistlers was derived. The analysis of the possible production of accelerated electrons by the electrodynamic tether was initiated.

Source record↗

NASA NTRS1980

Solar wind ion injections in the morning auroral oval

Energy versus time dispersion of precipitating ion bursts was observed during two rocket flights in the morning auroral oval. Individual bursts lasted about 20 seconds and repeated on a time scale of 100 seconds. The dispersion is interpreted as energy-dependent time-of-flight delay which provides identification of ion charge-to-mass ratio as well as injection source distance. The data are consistent with injections of magnetosheath ions with injection distances ranging from 7 to 19 earth radii. Individual events extended over a regin of at least several degrees of magnetic longitude and 0.3 degrees of invariant latitude. It is suggested that these events are associated with turbulent plasma entry into the magnetospheric entry layer.

Carlson, C. W.↗

NASA NTRS1981

Space shuttle launch era spacecraft injection errors and DSN initial acquisition

The initial acquisition of a spacecraft by the Deep Space Network (DSN) is a critical mission event. This results from the importance of rapidly evaluating the health and trajectory of a spacecraft in the event that immediate corrective action might be required. Further, the DSN initial acquisition is always complicated by the most extreme tracking rates of the mission. The DSN initial acquisition characteristics will change considerably in the upcoming space shuttle launch era. How given injection errors at spacecraft separation from the upper stage launch vehicle (carried into orbit by the space shuttle) impact the DSN initial acquisition, and how this information can be factored into injection accuracy requirements to be levied on the Space Transportation System (STS) is addressed. The approach developed begins with the DSN initial acquisition parameters, generates a covariance matrix, and maps this covariance matrix backward to the spacecraft injection, thereby greatly simplifying the task of levying accuracy requirements on the STS, by providing such requirements in a format both familiar and convenient to STS.

Khatib, A. R.↗

NASA NTRS1982

Radiometer Noise-Injection Control

New technique for controlling noise injection in Dicke feedback noise-injection microwave radiometer utilizes digital counter in which noise injection is kept on during countdown interval. Digital portion of loop replaces analog filters used in previous systems.

Stanley, W. D.↗

NASA NTRS1982

Fabrication of sinterable silicon nitride by injection molding

Transformation of structural ceramics from the laboratory to production requires development of near net shape fabrication techniques which minimize finish grinding. One potential technique for producing large quantities of complex-shaped parts at a low cost, and microstructure of sintered silicon nitride fabricated by injection molding is discussed and compared to data generated from isostatically dry-pressed material. Binder selection methodology, compounding of ceramic and binder components, injection molding techniques, and problems in binder removal are discussed. Strength, oxidation resistance, and microstructure of sintered silicon nitride fabricated by injection molding is discussed and compared to data generated from isostatically dry-pressed material.

Quackenbush, C. L.↗

NASA NTRS1982

Catalytic combustion with steam injection

The effects of steam injection on (1) catalytic combustion performance, and (2) the tendency of residual fuel to burn in the premixing duct upstream of the catalytic reactor were determined. A petroleum residual, no. 2 diesel, and a blend of middle and heavy distillate coal derived fuels were tested. Fuel and steam were injected together into the preheated airflow entering a 12 cm diameter catalytic combustion test section. The inlet air velocity and pressure were constant at 10 m/s and 600 kPa, respectively. Steam flow rates were varied from 24 percent to 52 percent of the air flow rate. The resulting steam air mixture temperatures varied from 630 to 740 K. Combustion temperatures were in the range of 1200 to 1400 K. The steam had little effect on combustion efficiency or emissions. It was concluded that the steam acts as a diluent which has no adverse effect on catalytic combustion performance for no. 2 diesel and coal derived liquid fuels. Tests with the residual fuel showed that upstream burning could be eliminated with steam injection rates greater than 30 percent of the air flow rate, but inlet mixture temperatures were too low to permit stable catalytic combustion of this fuel.

Anderson, D. N.↗

NASA NTRS1983

Comparative evaluation of gas-turbine engine combustion chamber starting and stalling characteristics for mechanical and air-injection

The effectiveness of propellant atomization with and without air injection in the combustion chamber nozzle of a gas turbine engine is studied. Test show that the startup and burning performance of these combustion chambers can be improved by using an injection during the mechanical propellant atomization process. It is shown that the operational range of combustion chambers can be extended to poorer propellant mixtures by combined air injection mechanical atomization of the propellant.

Dyatlov, I. N.↗

NASA NTRS1981

Investigations of stability and dynamic performances of switching regulators employing current-injected control

The stability and dynamic performances of a buck/boost regulator employing a current-injected control are examined. Small-signal models for the power state, the multi-loop error processor and the duty-cycle pulse-modulator are developed. The error-processor model which incorporates the current-injected loop, the dc loop and the compensation network permits evaluation of the effects of each individual control loop and their combined efforts toward shaping the performance characteristics of the closed-loop system. Comparisons are made between this modeling approach and earlier approaches. Some important yet subtle dissimilarities are discussed. This model predicts the constant-frequency 50 percent duty-cycle instability which is inherent to the current-injected control.

Lee, F. C.↗

NASA NTRS1982

Laboratory simulation of injection particle beams in the ionosphere

A series of experiments were carried out in large vacuum chambers in an attempt to understand the physics of the beam injection experiments. In the experiments, the electron beam was injected into an initially neutral gas. A plasma then accumulated as a result of ionization of the gas by the electron beam. The long interaction length and the longitudinal magnetic field resulted in the accumulation plasma densities considerably greater than the beam density. The most significant experimental result is that electron beams in the low keV energy range can ignite the beam plasma discharge (BPD) when their perveance is greater than 5 x 10 to the -7th AV exp -3/2, for pressures typical of the ionosphere. Ignition of the BPD may provide an explanation for many of the puzzling results observed in flight injection experiments.

Kellogg, P. J.↗

NASA NTRS1984

An investigation into the injection molding of PMR-15 polyimide

The chemorheological behavior of the PRM-15 molding compounds were characterized, the range of suitable processing parameters for injection molding in a reciprocating screw injection molding machine was determined, and the effects of the injection molding processing parameters on the mechanical properties of molded PMR-15 parts were studied. The apparatus and procedures for measuring viscosity and for determining the physical response of the material during heating are described. Results show that capillary rheometry can be effectively used with thermosets if the equipment is designed to overcome some of the inherent problems of these materials. A uniform temperature was provided in the barrel by using a circulating hot oil system. Standard capillary rheometry methods can provide the dependence of thermoset apparent viscosity on shear rate, temperature, and time. Process conditions resulting in complete imidization should be carefully defined. Specification of controlled oven temperature is inadequate and can result in incomplete imidization. For completely imidized PMR-15 heat at 15 C/min melt flow without gas evolution occurs in the temperature range of 325 C to 400 C.

Colaluca, M. A.↗

NASA NTRS1983

Dynamical injections as the source of near geostationary quiet time particle spatial boundaries

The question whether the noon-dusk feature is a manifestation of the spatial structures that should arise from quasi-stationary convection is examined. The key consideration here is whether the energy dispersion of the feature can be explained. It is shown that the observed energy dispersion cannot be attributed to the standard stationary convection configurations, either perturbed or unperturbed. It is also demonstrated, using a detailed computer simulation, that the nighttime, double-spiral-shaped injection boundary (used previously to reproduce the fast changing nighttime features) is successful at reproducing the noon-dusk feature by allowing the particles to evolve for periods of 12 to 36 hours after the injection. It is stressed that the portion of the injection boundary responsible for the feature looks very different from the standard convection boundaries configuration. Conclusions are offered concerning the importance of quasi-stationary convection as the mechanism by which the near geostationary regions are populated.

Mauk, B. H.↗

NASA NTRS1985

Flow visualization study of the effect of injection hole geometry on an inclined jet in crossflow

A flow visualization was studied by using neutrally buoyant, helium-filled soap bubbles, to determine the effect of injection hole geometry on the trajectory of an air jet in a crossflow and to investigate the mechanisms involved in jet deflection. Experimental variables were the blowing rate, and the injection hole geometry cusp facing upstream (CUS), cusp facing downstream (CDS), round, swirl passage, and oblong. It is indicated that jet deflection is governed by both the pressure drag forces and the entrainment of free-stream fluid into the jet flow. For injection hole geometries with similar cross-sectional areas and similar mass flow rates, the jet configuration with the larger aspect ratio experienced a greater deflection. Entrainment arises from lateral shearing forces on the sides of the jet, which set up a dual vortex motion within the jet and thereby cause some of the main-stream fluid momentum to be swept into the jet flow. This additional momentum forces the jet nearer the surface. Of the jet configurations, the oblong, CDS, and CUS configutations exhibited the largest deflections. The results correlate well with film cooling effectiveness data, which suggests a need to determine the jet exit configuration of optimum aspect ratio to provide maximum film cooling effectiveness.

Simon, F. F.↗

NASA NTRS1985

Characteristics of heat exchange in the region of injection into a supersonic high-temperature flow

An experimental investigation of the local heat transfer coefficient distribution during gas injection into the supersonic-flow portion of a Laval nozzle is discussed. The controlling dimensionless parameters of the investigated process are presented in terms of a generalized relation for the maximum value of the heat transfer coefficient in the nozzle cross section behind the injection hole. Data on the heat transfer coefficient variation along the nozzle length as a function of gas injection rate are also presented, along with the heat transfer coefficient distribution over a cross section of the nozzle.

Bakirov, F. G.↗

NASA NTRS1984

Tunable mode and line selection by injection in a TEA CO2 laser

Tunable mode selection by injection in pulsed CO2 lasers is examined, and both analytical and numerical models are used to compute the required injection power for a variety of experimental cases. These are treated in two categories: mode selection at a desired frequency displacement from the center frequency of a transition line in a dispersive cavity and mode (and line) selection at the center frequency of a selected transition line in a nondispersive cavity. The results point out the potential flexibility of pulsed injection in providing wavelength tunable high-energy single-frequency pulses.

Menzies, R. T.↗

NASA NTRS1985

Mixing layer control for tangential slot injection in turbulent flows

Tangential injection into turbulent flows is one of the most promising methods of minimizing skin friction and providing thermal protection. The technique also has application to laser hardening. The effectiveness of the injected material can be increased if the spreading rate of the resulting mixing region can be reduced. Various techniques which have been shown to be effective in manipulating the rate of growth of mixing layers under certain conditions have been applied to a slot configuration having a thick external turbulent boundary layer. These include geometry modifications to the slot lip trailing edge and acoustic excitation of the slot exit plane over a wide range of frequencies. Neither of these approaches produced any noticeable effect on the downstream evolution of the mixing layer. This lack of effectiveness is attributed to the dominating influence of the well-developed incoming turbulent boundary layer. The placement of large-eddy breakup devices in this boundary layer upstream of the injection point did produce significantly lower velocities in the near-wall region of the flow downstream of the slot exit.

Mcinville, R. M.↗

NASA NTRS1986

Measurements of a single lateral jet injected into swirling crossflow

Experiments have been conducted to document the time-mean and turbulent flowfield of a deflected turbulent jet in a confined swirling crossflow. The jet-to-crossflow velocity ratio of 4 was investigated with swirler vane angles of 45 and 70 degrees. A six-orientation single hot-wire technique was used to measure the velocities and turbulence properties of the flow. In addition, a five-hole pitot probe technique was used to measure the time-mean velocities or verification purposes. The results are presented in the form of r-x plots to aid visualization of the fully three-dimensional flowfield. The swirl in the crossflow intensified the local velocity at the location of the injected jet, which effectively reduced the jet-to-crossflow velocity ratio. This caused the trajectory of the injected jet to follow the path of the local flow direction of the crossflow, and reduce its penetration into the crossflow. The time-mean velocity measurements using the hot-wire corresponded to pitot-probe data obtained in identical flow conditions. Turbulence stress data show the same trends as previous swirl flow data without lateral injection. The lateral jet was found to deflect the axis of the precessing vortex core.

Ong, L. H.↗

NASA NTRS1985

Competing atomic processes in Ba and Sr injection critical velocity experiments

The critical ionization velocity effect requires a superthermal electron population to ionize through collisional impact. Such superthermal electrons can however lose energy to competing atomic processes, as well as to ionization, thus limiting the efficiency of the effect. Considering Ba and Sr magnetospheric injection experiments designed to test the CIV theory, it is found that in both cases roughly 60 percent of the superthermal electron energy is lost on exciting line radiation. Moreover, energy loss to background neutral oxygen places a strict limit on the injected cloud densities for which critical velocity effects are possible; a finding which explains the consistently negative results in radial injection experiments.

Newell, P. T.↗

NASA NTRS1985

Processing study of injection molding of silicon nitride for engine applications

The high hardness of silicon nitride, which is currently under consideration as a structural material for such hot engine components as turbine blades, renders machining of the material prohibitively costly; the near net shape forming technique of injection molding is accordingly favored as a means for component fabrication. Attention is presently given to the relationships between injection molding processing parameters and the resulting microstructural and mechanical properties of the resulting engine parts. An experimental program has been conducted under NASA sponsorship which tests the quality of injection molded bars of silicon nitride at various stages of processing.

Rorabaugh, M. E.↗