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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 415 records · Page 23

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NASA NTRS1979

Siple station experiments on wave-particle interactions in the magnetosphere

Natural and controlled whistler-mode signals have been used to study nonlinear mechanisms of wave growth and wave-wave interactions (WWI) in the magnetosphere; three general classes of WWI (triggering, suppression, and entrainment) are identified and interpreted in terms of a model based on cyclotron resonance interaction. This model is also used to estimate the wave field intensity associated with different types of WWI. A new type of triggered emission, the band-limited impulse (BLI) is interpreted in terms of the switching of phase-bunched currents. In addition, an experiment to find a threshold for the excitation of the coherent wave instability is discussed, and observed VLF wave-induced transient bursts of X-rays, light and E-region ionization enhancements are considered with regard to a step function wave interacting with all resonant electrons in a given energy range.

Helliwell, R. A.↗

NASA NTRS1980

Conditional instability of the first kind upside-down

It is shown that entrainment leads to the generation of turbulence kinetic energy in a stratocumulus layer when the virtual temperature jump at the cloud top is weaker than a critical value. The critical value increases as the relative humidity of the air above the cloud top decreases. This result is interpreted as a criterion for the instability of the layer cloud to penetrative downdrafts. The role of the instability in determining the subtropical and tropical distributions of boundary-layer cloudiness is assessed.

Randall, D. A.↗

NASA NTRS1980

Some observations on supersonic wing design

The paper presents a brief review on the development of supersonic wing design. Attention is given to linearized aerodynamic theory, emphasizing equations for drag and ratios of slopes and Mach lines. Diagrams that depict conditions for minimum drag as well as the effects of fore-and-aft dimension of wings and Mach numbers on areas of lateral entrainment are presented.

Jones, R. T.↗

NASA NTRS1980

Reduced bleed air extraction for DC-10 cabin air conditioning

It is noted that a significant fuel savings can be achieved by reducing bleed air used for cabin air conditioning. Air in the cabin can be recirculated to maintain comfortable ventilation rates but the quality of the air tends to decrease due to entrainment of smoke and odors. Attention is given to a development system designed and fabricated under the NASA Engine Component Improvement Program to define the recirculation limit for the DC-10. It is shown that with the system, a wide range of bleed air reductions and recirculation rates is possible. A goal of 0.8% fuel savings has been achieved which results from a 50% reduction in bleed extraction from the engine.

Newman, W. H.↗

NASA NTRS1980

A visual investigation of turbulence in stagnation flow about a circular cylinder

A diagnostic visualization study of turbulence in stagnation flow around a circular cylinder was carried out to gain physical insight into the coherent structure of turbulence in flow around a bluff body advanced by the vorticity-amplification theory. The visualization was conducted at a cylinder-diameter Reynolds number of 8000 utilizing titanium dioxide white smoke for an approaching flow containing turbulence at scales larger than the neutral wavelength of the stagnation flow. Analyses of the flow events focused on tracing out the temporal and spatial evolution of a cross-vortex tube outlined by the entrained smoke filaments from its emergence near the stagnation zone through its penetration into the cylinder boundary layer.

Sadeh, W. Z.↗

NASA NTRS1980

Jet decay rate effects on hover jet-induced loads

The paper explains the mechanisms for observed jet decay rate effects on jet-induced loads on a flat plate for cross-flow and hover configurations. Examples are presented for the influence of the decay rate on integrated loads on a flat plate induced by the jet issuing at a right angle from the plate into still air; knowledge of these jet-induced loadings is of particular importance for VTOL aircraft design because they produce an effective loss in the lift force available in hover. The apparent inconsistency between existing lift loss vs jet decay rate trends is explained in light of the different mechanism which determine the jet mixing and trajectory, i.e., entrainment, blockage, and the vortex pair associated with a jet in crossflow.

Kuhlman, J. M.↗

NASA NTRS1979

Experimental studies of combustion in a two dimensional free shear layer

The effect of combustion on the turbulent free shear layer formed at a rearward facing step has been studied. Schlieren movies confirm the importance of large scale vortices in determining entrainment and mixing behavior. The movies, long exposure schlieren photographs, and laser anemometry velocity profiles are used to observe the spreading rate of the layer and to study the vortex formation process. It is concluded that to first order, the primary effect of combustion is felt through the change in density ratio across the layer and acceleration of the flow due to volumetric expansion of the fluid in a confined duct.

Pitz, R. W.↗

NASA NTRS1982

High-Speed Laser Anemometer

New high-speed laser anemometer system rapidly and efficiently maps gas-flow velocities within rotating blade rows of turbomachinery. Small seed particles entrained in gas flow fluoresce when they pass through probe volume, which is the fringe pattern formed by intersecting laser beams. Transit time of particles is obtained by use of suitable optics, photomultiplier tube and electronic signal processor. Data are then sent to a minicomputer.

Powell, J. A.↗

NASA NTRS1980

Photogeological constraints on lunar and planetary vulcanism, part 2

The use of several simple theoretical modelling approaches in simulating lava erosion were evaluated. Both one dimensional and two dimensional models were used with the two dimensional model being superior. The two dimensional model accounts, in a purely phenomenological way, for the effects of turbulence and mechanical erosion in a flow. Criteria for mechanical erosion was related to the basal stress and the effect of entrained eroded material on fluid properties was parameterized.

Source record↗

NASA NTRS1979

Theoretical analysis of an augmentor wing for a VTOL fighter

A method based on potential flow theory was developed for predicting forces and moments acting on augmentor wings for prescribed ejector jet characteristics. A three dimensional nonplanar vortex lattice is laid out on the chordal planes of the augmentor wing components. Jet induced effects are included in the boundary condition from which the horseshoe vortex strengths are obtained. The jet within the diffusor is made to expand from the primary nozzles to the diffusor exit and is represented by a distribution of vorticity on the jet boundary to provide proper entrainment. The jet downstream of the diffusor exit is modeled by a vorticity distribution and blockage panels and its centerline location and spreading rate are taken from experimental data. The vortex lattice and jet models are used in an iterative manner until the predicted diffusor exit velocity matches the specified one. Some comparisons with available data show good agreement at lower power settings.

Dillenius, M. F. E.↗

NASA NTRS1980

Flow visualization study of spanwise blowing applied to the F-4 fighter aircraft configuration

Water tunnel studies were performed to define the changes that occur in vortex flow fields above the wing due to spanwise blowing over the inboard and outboard wing panels and over the trailing-edge flaps. Flow visualization photographs were obtained for angles of attack up to 30 deg and sideslip angles up to 10 deg. The sensitivity of the vortex flows to changes in flap deflection angle, nozzle position, and jet momentum coefficient was determined. Deflection of the leading edge flap delayed flow separation and the formation of the wing vortex to higher angles of attack. Spanwise blowing delayed the breakdown of the wing vortex to farther outboard and to higher angles of attack. Spanwise blowing over the trailing edge flap entrained flow downward, producing a lift increase over a wide range of angles of attack. The sweep angle of the windward wing was effectively reduced in sideslip. This decreased the stability of the wing vortex, and it burst farther inboard. Reduced wing sweep required a higher blowing rate to maintain a stable vortex. A vortex could be stabilized on the outboard wing panel when an outboard blowing nozzle was used. Blowing from both an inboard and an outboard nozzle was found to have a favorable interaction.

Lorincz, D. J.↗

NASA NTRS1978

A correlation method to predict the surface pressure distribution on an infinite plate from which a jet is issuing

A correlation method to predict pressures induced on an infinite plate by a jet issuing from the plate into a subsonic free stream was developed. The complete method consists of an analytical method which models the blockage and entrainment properties of the jet and a correlation which accounts for the effects of separation. The method was developed for jet velocity ratios up to ten and for radial distances up to five diameters from the jet. Correlation curves and data comparisons are presented for jets issuing normally from a flat plate with velocity ratios one to twelve. Also, a list of references which deal with jets in a crossflow is presented.

Perkins, S. C., Jr.↗

NASA NTRS1981

A diagnostic model for studying daytime urban air quality trends

A single cell Eulerian photochemical air quality simulation model was developed and validated for selected days of the 1976 St. Louis Regional Air Pollution Study (RAPS) data sets; parameterizations of variables in the model and validation studies using the model are discussed. Good agreement was obtained between measured and modeled concentrations of NO, CO, and NO2 for all days simulated. The maximum concentration of O3 was also predicted well. Predicted species concentrations were relatively insensitive to small variations in CO and NOx emissions and to the concentrations of species which are entrained as the mixed layer rises.

Brewer, D. A.↗

NASA NTRS1981

The Lewis Chemical Equilibrium Program with parametric study capability

The program was developed to determine chemical equilibrium in complex systems. Using a free energy minimization technique, the program permits calculations such as: chemical equilibrium for assigned thermodynamic states; theoretical rocket performance for both equilibrium and frozen compositions during expansion; incident and reflected shock properties; and Chapman-Jouget detonation properties. It is shown that the same program can handle solid coal in an entrained flow coal gasification problem.

Sevigny, R.↗

NASA NTRS1980

Addition to the Lewis Chemical Equilibrium Program to allow computation from coal composition data

Changes made to the Coal Gasification Project are reported. The program was developed by equilibrium combustion in rocket engines. It can be applied directly to the entrained flow coal gasification process. The particular problem addressed is the reduction of the coal data into a form suitable to the program, since the manual process is involved and error prone. A similar problem in relating the normal output of the program to parameters meaningful to the coal gasification process is also addressed.

Sevigny, R.↗

NASA NTRS1981

Report of the panel on theoretical aerodynamics

Interactions between theoretical aerodynamics and the NTF are discussed. The development and validation of computational fluid dynamics computer codes, the determination of Reynolds number scaling laws, and extension of the data bases of entrainment type turbulence models to include high Reynolds number data are recommended areas of study. The major benefit theoretical aerodynamics could have on the NTF is in the quantitative description of wind tunnel wall interference effects.

South, J. C., Jr.↗

NASA NTRS1980

A numerical determination of the evolution of cloud drop spectra due to condensation on natural aerosol particles

The time variation in size of aerosol particles growing by condensation is studied numerically by means of an air parcel model which allows entrainment of air and aerosol particles. Particles of four types of aerosols typically occurring in atmospheric air masses were considered. The present model circumvents any assumption about the size distribution and chemical composition of the aerosol particles by basing the aerosol particle growth on actually observed size distributions and on observed amounts of water taken up under equilibrium by a deposit of the aerosol particles. Characteristic differences in the drop size distribution, liquid water content and supersaturation were found for the clouds which evolved from the four aerosol types considered.

Lee, I. Y.↗

NASA NTRS1981

Turbulent jet patterns in accelerating flows

Results of flow visualization experiments, and a semi-empirical model of a single turbulent jet injected perpendicularly to a different density cross flow are presented. The model is based on integral conservation equations, including the pressure terms appropriate to accelerating flow. It uses an entrainment correlation obtained from previous experiments of a jet in a cross stream. The results show trajectories and spreading rates, and are typified by a set of three parameters: momentum ratio, Froude number and density ratio. Agreement between test and calculated results is encouraging, but tend to be poorer with increasing momentum ratio.

Lipshitz, A.↗