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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 1,477 records · Page 82
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

A zonal method for modeling powered-lift aircraft flow fields

A zonal method for modeling powered-lift aircraft flow fields is based on the coupling of a three-dimensional Navier-Stokes code to a potential flow code. By minimizing the extent of the viscous Navier-Stokes zones the zonal method can be a cost effective flow analysis tool. The successful coupling of the zonal solutions provides the viscous/inviscid interations that are necessary to achieve convergent and unique overall solutions. The feasibility of coupling the two vastly different codes is demonstrated. The interzone boundaries were overlapped to facilitate the passing of boundary condition information between the codes. Routines were developed to extract the normal velocity boundary conditions for the potential flow zone from the viscous zone solution. Similarly, the velocity vector direction along with the total conditions were obtained from the potential flow solution to provide boundary conditions for the Navier-Stokes solution. Studies were conducted to determine the influence of the overlap of the interzone boundaries and the convergence of the zonal solutions on the convergence of the overall solution. The zonal method was applied to a jet impingement problem to model the suckdown effect that results from the entrainment of the inviscid zone flow by the viscous zone jet. The resultant potential flow solution created a lower pressure on the base of the vehicle which produces the suckdown load. The feasibility of the zonal method was demonstrated. By enhancing the Navier-Stokes code for powered-lift flow fields and optimizing the convergence of the coupled analysis a practical flow analysis tool will result.

Roberts, D. W.↗
NASA NTRS1989

Far field expansion for anisotropic wave equations

A necessary ingredient for the numerical simulation of many time dependent phenomena in acoustics and aerodynamics is the imposition of accurate radiation conditions at artificial boundaries. The asymptotic analysis of propagating waves provides a rational approach to the development of such conditions. A far field asymptotic expansion of solutions of anisotropic wave equations is derived. This generalizes the well known Friedlander expansion for the standard wave operator. The expansion is used to derive a hierarchy of radiation conditions of increasing accuracy. Two numerical experiments are given to illustrate the utility of this approach. The first application is the study of unsteady vortical disturbances impinging on a flat plate; the second is the simulation of inviscid flow past an impulsively started cylinder.

Hariharan, S. I.↗
NASA NTRS1989

Growth of a mat-forming photograph in the presence of UV radiation

Knowledge of the survival and growth of microorganisms in the presence of ultraviolet radiation is important for understanding the potential for life to exist in environments exposed to high fluxes of UV radiation. The growth of a mat-forming phototrophic prokaryote, Chloroflexus aurantiacus, was examined in the presence of continuous high UV irradiation under otherwise optimal growth conditions. Evidence was sought for an intrinsic ability to grow in the presence of UV radiation in a carefully chosen organism known to be unusually resistant to UV radiation, of ancient lineage among the phototrophs, to resemble ancient microfossils from the Precambrian, and to be a mat-former. It was assumed that even a high intrinsic UV resistance would be inadequate for survival and growth in the presence of very high UV fluxes, and iron (Fe3+) was selected as a common, abundant UV-absorbing substance that might protest microorganisms growing in or under iron-bearing sediments. The effectiveness of Fe(3+) was tested as a UV protective agent at low concentrations in thin layers. It was concluded that intrinsic UV resistance in some organisms may account for growth, not just survival, of these organisms when exposed to high UV fluxes under otherwise optimal growth conditions in an anoxic environment. It was also concluded that Fe(3+) bearing sediments of 1 mm or less in thickness may provide an adequate shield against high UV fluxes permitting the growth of microorganisms just below their surface. As long as growth conditions were met, then the evolution and development of microorganisms would not be hampered by high UV fluxes impinging upon the surface of iron-bearing sediments.

Pierson, Beverly K.↗
NASA NTRS1989

Static internal performance of a nonaxisymmetric vaned thrust reverser with flow splay capability

An investigation was conducted in the Static Test Facility of the Langley 16-Foot Transonic Tunnel on a dual-port, nonaxisymmetric, block-and-turn type thrust reverser model with vane cascades in the reverser ports which turned the flow in the splay direction and aided in turning the flow in the reverse direction. Splaying reverser flow is a method of delaying to lower landing ground roll speeds the reingestion of hot exhaust flow into the inlets. Exhaust flow splay can also help prevent the impingement of hot exhaust gases on the empennage surfaces when the reverser is integrated into an actual airframe. The vane cascades consisted of two sets of perpendicular vanes with a variable number of turning and splay vanes. A skewed vane box was also tested which had only one set of vanes angled to provide both turning and splay. Vane cascades were designed to provide different amounts of flow splay in the top and bottom ports. Inner doors, trim tabs, and an orifice plate all provided means of varying the port area for reverser flow modulation. The outer door position was varied as a means of influencing the flow reverse angle. Nozzle pressure ratio was varied from 1.75 to approximately 6.00.

Bangert, Linda S.↗
NASA NTRS1988

Acoustical scattering from finite compliant surfaces bounding a duct

Acoustic radiation effects of a finite compliant surface covering a transverse slot in a two-dimensional parallel walled rigid duct are investigated. Radiation from a harmonic source external to the duct is shown to impinge on the slot, reradiating to the half plane and propagating through the duct. Integral equation techniques are employed to study the cases of an open slot, a membrane cover, and a flexible plate cover. The total power radiated to the half plane external to the duct and to the region internal to the duct is determined, taking into account slot-width and fluid-loading variations and the effect of the surface on the power radiated.

Smith, M. E.↗
NASA NTRS1988

Laminar flow control leading edge systems in simulated airline service

The feasibility of two candidate leading-edge flow laminarization systems applicable to airline service was tested using representative airline operational conditions with respect to air traffic, weather, and airport insect infestation. One of the systems involved a perforated Ti alloy suction surface with about 1 million 0.0025-in. diameter holes drilled by electron beam, as well as a Krueger-type flap that offered protective shielding against insect impingement; the other supplied surface suction through a slotted Ti alloy skin with 27 spanwise slots on the upper and lower surface.

Wagner, R. D.↗
NASA NTRS1989

Shock-wave-induced mixing enhancement in scramjet combustors

An experimental study of the interaction between a weak shock wave and a supersonic shear layer was carried out to determine the possibility of shock-induced mixing enhancement. A supersonic (Mach 2.5) stream of nitrogen was mixed with a sonic helium jet downstream of a rearward-facing step to simulate the mixing region in the vicinity of a SCRAMJET flameholder. A small wedge was used to generate an oblique shock wave that impinges on the mixing layer. Schlieren flow visualization and Rayleigh scattering concentration measurements were carried out. The results indicate that significant spreading of the shear layer may occur downstream of the shock/shear layer interaction region. Further study is required to determine the mechanism of the observed spreading and the extent of the increase in mixing efficiency. Since there are shock-induced losses, an optimum mixing enhancement configuration will have to be determined before the method can be validated and successfully implemented in a SCRAMJET combustor.

Menon, S.↗
NASA NTRS1989

A three-dimensional upwind finite element point implicit unstructured grid Euler solver

A three-dimensional upwind finite element technique that uses cell-centered quantities and implicit and/or explicit time marching was developed for computing hypersonic inviscid flows using adaptive unstructured grids. This technique was used to predict shock interference on a swept cylinder. An attempt was made to determine the flowfield and, in particular, the pressure augmentation caused by an impinging shock on the swept leading edge of a cowl lip of an engine inlet.

Thareja, Rajiv R.↗
NASA NTRS1989

A numerical investigation of the influence of surface roughness on heat transfer in ice accretion

The flowfield and resulting heat transfer rate over a series of ice accretion shapes is obtained by solving the Navier-Stokes equations. The influence of surface roughness on surface heat transfer is examined by including blockage, form drag, and stagnation heating effects as source terms in the governing equations. The results indicate increases of a factor of three in cooling rates due to distributed roughness compared to smotth surfaces. In addition, droplet impingement efficiencies are studied for the same series of ice accretion shapes using a time-dependent solution procedure.

Scott, J. N.↗
NASA NTRS1989

Thermal analysis of engine inlet anti-icing systems

A hot air anti-icing system of a gas turbine engine inlet is analyzed numerically. A three-dimensional potential flow code, which accounts for compressibility effects, is used to determine the flowfield in and around the inlet. A particle trajectory code is developed using a local linearization technique. The trajectory code is used to calculate local water impingement rates. Energy balances are performed on both the surface runback water and the metallic skin to determine their temperature distributions. A variety of test cases are considered in order to validate the various numerical components of the process as well as to demonstrate the procedure.

Keith, Theo G., Jr.↗
NASA NTRS1988

An automated ozone photometer

A photometer capable of automatically measuring ozone concentration data to very high resolution during scientific research flights in the earth's atmosphere was developed at the NASA Ames Research Center. This instrument was recently deployed to study the ozone hole over Antarctica. Ozone is detected by absorbing 253.7-nm radiation from an ultraviolet lamp which shines through the sample of air and impinges on a vacuum phototube. A lower output from the phototube indicates more ozone present in the air sample. The photometer employs a CMOS 280 control, data collection, and storage.

Lavelle, Joseph R.↗
NASA NTRS1988

Chemical nonequilibrium and viscous flow computation for conic aerobrake bodies

Three-dimensional analyses are presented for the viscous, reactive flow over a complete entry-body configuration with a wide-angle conic surface. The predictive method uses a split approach that solves iteratively the Navier-Stokes and the continuity equations of chemical species. The finite-difference formulation and the computational grid are adapted to the bow shock and the conformally mapped body such that the velocity components are in the computational spherical-polar space. Combinations of several conic forebody and afterbody configurations have been studied using wind-tunnel, Space Shuttle, and aerobraking orbital transfer vehicle (AOTV) entry conditions. The effects of the borebody bluntness and of finite-rate chemical reactions on the shock layer, the wall catalycity on the boundary layer, the shear-layer impingement on the afterbody, and the base-flow environment are discussed.

Li, C. P.↗
NASA NTRS1989

Dynamic loading on impact surfaces of a high subsonic elliptic jet

The feedback resonance in a high subsonic velocity range was investigated for the case where a small aspect ratio (2:1) elliptic jet impinged perpendicularly on a flat plate. This resonance was observed for Mach numbers greater than 0.7 for plate locations between 4 and 9 major radii downstream of the exhaust plane. At the predominant resonant conditions, the loading region and sound source terms were found to be concentrated along the major axis direction on the impact surface.

Wat, J. K.↗
NASA NTRS1989

Calculation of winged-body-like flow fields using an implicit upwind space-marching code

The Mach-8 flow past a 60-deg swept fin mounted on a 12-degree ramp has been simulated using a parabolized Navier-Stokes solver employing an upwind algorithm in order to investigate the interference patterns that develop when a bow shock impinges on a wing shock. Good agreement with experimental data is found downstream of the interaction for each of three meshes of varying grid point density and computed surface pressure and heat transfer. In the wedge flow region, some disagreement with experimental data is noted for both pressure and heat transfer.

Lawrence, Scott L.↗
NASA NTRS1989

Measured and predicted aerodynamic heating on a cylinder in wake of AFE configuration at incidence

Thin-film resistance gages were used to measure cylinder surface heat-transfer rates in the near wake of the Aeroassist Flight Experiment vehicle configuration, while surface-streamline directions were ascertained by the oil-flow techniques under the same configuration and test conditions. Both heat transfer distributions and flow over the entire cylinder surface were influenced by impingement of that portion of the free shear layer originating at the forebody shoulder in the upper symmetry plane. Heating rate distributions predicted with a Navier-Stokes solver computer code were in general agreement with measurements.

Wells, William L.↗
NASA NTRS1989

Hypersonic blunt body computations including real gas effects

Various second-order explicit and implicit TVD shock-capturing methods, a generalization of Roe's approximate Riemann solver, and a generalized flux-vector splitting scheme are used to study two-dimensional hypersonic real-gas flows. Special attention is given to the identification of some of the elements and parameters which can affect the convergence rate for high Mach numbers or real gases, but have negligible effect for low Mach numbers, for cases involving steady-state inviscid blunt flows. Blunt body calculations at Mach numbers of greater than 15 are performed to treat real-gas effects, and impinging shock results are obtained to test the treatment of slip surfaces and complex structures. Even with the addition of improvements, the convergence rate of algorithms in the hypersonic flow regime is found to be generally slower for a real gas than for a perfect gas.

Montagne, J.-L.↗
NASA NTRS1990

Insulation For Cryogenic-Liquid Tanks

Rigid foam and radiation shields prevent excessive heating in variety of environments. Report discusses design, development, and test of thermal-protection system for liquid-oxygen and liquid-hydrogen tanks of now discontinued Shuttle/Centaur G' project. System protects tank from excessive heat before and during launches, while in orbit around Earth, and during premature landings from aborted launches. Designed to withstand stresses of launch and emergency landing, acoustical loads, rapid changes in pressure, and impingement of rapidly flowing gas near vents of cargo bay in Space Shuttle. Primary requirements in design, system presents no hazard to Space Shuttle or its crew.

Knoll, Richard H.↗
NASA NTRS1990

Exact Chord-Length Distribution For SEU Calculations

Computed rates of SEU's more accurate. Exact integral chord-length distribution derived for use in calculations of rates of single-event upsets (SEU's) (changes in logic states) caused by impingement of cosmic rays or other ionizing radiation on electronic logic circuits.

Buehler, Martin G.↗