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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Near-earth thermal environmental criteria study

A study was made to determine improved values and definitions to be used for thermal environmental design parameters for a spacecraft in near-earth orbit. An algorithm was used to derive a total earth thermal radiation based on a mathematical relationship. Several albedo and earth thermal radiation grid maps were produced on seven track digital magnetic tape. Each map contained the values obtained during a 24 hour period over the entire earth. The output statistics are summarized, and the data processing program is described.

Dash, J. M.↗
NASA NTRS1975

An improved numerical procedure for the parametric optimization of three dimensional scramjet nozzles

A parametric numerical procedure permitting the rapid determination of the performance of a class of scramjet nozzle configurations is presented. The geometric complexity of these configurations ruled out attempts to employ conventional nozzle design procedures. The numerical program developed permitted the parametric variation of cowl length, turning angles on the cowl and vehicle undersurface and lateral expansion, and was subject to fixed constraints such as the vehicle length and nozzle exit height. The program required uniform initial conditions at the burner exit station and yielded the location of all predominant wave zones, accounting for lateral expansion effects. In addition, the program yielded the detailed pressure distribution on the cowl, vehicle undersurface and fences, if any, and calculated the nozzle thrust, lift and pitching moments.

Dash, S.↗
NASA NTRS1975

An improved source flow characteristic technique for the analysis of scramjet exhaust flow fields

The process is discussed of designing a nozzle for a hypersonic airbreathing vehicle which involves a complex study of the inter-relationship among many parameters: internal-external expansion, vehicle lift, drag, pitching moments, and structural and weight limitations. The source flow characteristic approach to the design process was extended and improved, and streamline interpolation procedure was incorporated. All characteristic and boundary calculations were made compatible with frozen, equilibrium and ideal gas thermodynamic options, while slip surface calculations (cowl interaction) were extended to underexpanded flow conditions. Since viscous forces can significantly influence vehicle forces, pitching moments and structural/weight considerations, a local integration via flat plate boundary layer skin friction and heat transfer coefficients was included. These effects are calculated using the Spalding and Chi method, and all force and moment calculations are performed via integration of the local forces acting on the specified vehicle wetted areas.

Delguidice, P. D.↗
NASA NTRS1975

Numerical methods for the calculation of three-dimensional nozzle exhaust flow fields

Numerical codes developed for the calculation of three-dimensional nozzle exhaust flow fields associated with hypersonic airbreathing aircraft are described. Both codes employ reference plane grid networks with respect to three coordinate systems. Program CHAR3D is a characteristic code utilizing a new wave preserving network within the reference planes, while program BIGMAC is a finite difference code utilizing conservation variables and a one-sided difference algorithm. Secondary waves are numerically captured by both codes, while the underexpansion shock and plume boundary are treated discretely. The exhaust gas properties consist of hydrogen-air combustion product mixtures in local chemical equilibrium. Nozzle contours are treated by a newly developed geometry package based on dual cubic splines. Results are presented for simple configurations demonstrating two- and three-dimensional multiple wave interactions.

Dash, S. M.↗
NASA NTRS1978

Shock capturing finite-difference and characteristic reference plane techniques for the prediction of three-dimensional nozzle-exhaust flowfields

This report summarizes work accomplished under Contract No. NAS1-12726 towards the development of computational procedures and associated numerical. The flow fields considered were those associated with airbreathing hypersonic aircraft which require a high degree of engine/airframe integration in order to achieve optimized performance. The exhaust flow, due to physical area limitations, was generally underexpanded at the nozzle exit; the vehicle afterbody undersurface was used to provide additional expansion to obtain maximum propulsive efficiency. This resulted in a three dimensional nozzle flow, initialized at the combustor exit, whose boundaries are internally defined by the undersurface, cowling and walls separating individual modules, and externally, by the undersurface and slipstream separating the exhaust flow and external stream.

Dash, S.↗
NASA NTRS1977

Reflection and radiation due to a quadrupole near a fluid interface

The reflection of sound at an interface between two fluid half-space in relative motion (one in motion and the other at rest), but with different density and different sound speed, is considered. The reflection coefficient is found in an explicitly closed form. A brief discussion of the effect of mean velocity, i.e., corresponding Mach number on different noise generating quadrupole directivities concludes the presentation of the paper. The graphs provided illustrate this aspect in a rather more convincing way.

Dash, R.↗
NASA NTRS1977

Computational models for the analysis of three-dimensional internal and exhaust plume flowfields

This paper describes computational procedures developed for the analysis of three-dimensional supersonic ducted flows and multinozzle exhaust plume flowfields. The models/codes embodying these procedures cater to a broad spectrum of geometric situations via the use of multiple reference plane grid networks in several coordinate systems. Shock capturing techniques are employed to trace the propagation and interaction of multiple shock surfaces while the plume interface, separating the exhaust and external flows, and the plume external shock are discretely analyzed. The computational grid within the reference planes follows the trace of streamlines to facilitate the incorporation of finite-rate chemistry and viscous computational capabilities. Exhaust gas properties consist of combustion products in chemical equilibrium. The computational accuracy of the models/codes is assessed via comparisons with exact solutions, results of other codes and experimental data. Results are presented for the flows in two-dimensional convergent and divergent ducts, expansive and compressive corner flows, flow in a rectangular nozzle and the plume flowfields for exhausts issuing out of single and multiple rectangular nozzles.

Dash, S. M.↗
NASA NTRS1978

Analysis of flight effects on noise radiation from jet flow using a convecting quadrupole model

The effects of flight on noise radiation from convecting quadrupoles in a jet flow are examined. The analysis shows that as flight velocity increases there is a steadily increasing amplification of the sound that is radiated into the forward arc and a large reduction of the sound that is radiated into the rearward arc. The analysis also shows the same trend when there is a reduction in the exhaust velocity with, however, a further rise in amplification in the forward quadrant and a drop in attenuation in the aft quadrant. Finally, it is concluded that there is a transmission effect tending to enhance the sound radiation by a density ratio pf/pj which increases with increasing jet temperature.

Dash, R.↗
NASA NTRS1978

Prediction of nearfield jet entrainment by an interactive mixing/afterburning model

The development of a computational model (BOAT) for calculating nearfield jet entrainment, and its application to the prediction of nozzle boattail pressures, is discussed. BOAT accounts for the detailed turbulence and thermochemical processes occurring in the nearfield shear layers of jet engine (and rocket) exhaust plumes while interfacing with the inviscid exhaust and external flowfield regions in an overlaid, interactive manner. The ability of the model to analyze simple free shear flows is assessed by detailed comparisons with fundamental laboratory data. The overlaid methodology and the entrainment correction employed to yield the effective plume boundary conditions are assessed via application of BOAT in conjunction with the codes comprising the NASA/LRC patched viscous/inviscid model for determining nozzle boattail drag for subsonic/transonic external flows. Comparisons between the predictions and data on underexpanded laboratory cold air jets are presented.

Dash, S. M.↗
NASA NTRS1978

Analysis of three-dimensional ducted and exhaust plume flowfields

Computational procedures are described for analyzing three-dimensional supersonic internal flows and multinozzle exhaust plume flowfields. The computer codes (BIGMAC and CHAR3D) embodying these procedures cater to a broad spectrum of geometric situations via the use of multiple reference plane grid networks in several coordinate systems. Shock capturing techniques are employed to trace the propagation and interaction of multiple shock surfaces. Gas properties consist of combustion products in chemical equilibrium. The computational accuracy of the codes is assessed via comparisons with the results of other codes and experimental data. Results are presented for the flows in two-dimensional ducts, corner flows, flow in a rectangular nozzle, and the plume flowfields for exhausts issuing out of single and multiple rectangular nozzles.

Dash, S. M.↗
NASA NTRS1978

Uniform magnesium oxide adsorbents

Kr adsorption on MgO is used to characterize the surface uniformity of MgO smoke and thermally decomposed Mg(OH)2. It is found that initially heterogeneous samples develop progressively sharper stepwise isotherms with increasingly-high-temperature heat treatment, apparently due to the removal of imperfections and high-energy facets, leaving surfaces of highly uniform (100) planes.

Dash, J. G.↗
NASA NTRS1978

A computational model for the prediction of jet entrainment in the vicinity of nozzle boattails (the BOAT code)

The development of a computational model (BOAT) for calculating nearfield jet entrainment, and its incorporation in an existing methodology for the prediction of nozzle boattail pressures, is discussed. The model accounts for the detailed turbulence and thermochemical processes occurring in the mixing layer formed between a jet exhaust and surrounding external stream while interfacing with the inviscid exhaust and external flowfield regions in an overlaid, interactive manner. The ability of the BOAT model to analyze simple free shear flows is assessed by comparisons with fundamental laboratory data. The overlaid procedure for incorporating variable pressures into BOAT and the entrainment correction employed to yield an effective plume boundary for the inviscid external flow are demonstrated. This is accomplished via application of BOAT in conjunction with the codes comprising the NASA/LRC patched viscous/inviscid methodology for determining nozzle boattail drag for subsonic/transonic external flows.

Dash, S. M.↗
NASA NTRS1979

A numerical study of jet entrainment effects on the subsonic flow over nozzle afterbodies

A viscous-inviscid interaction model has been developed which accounts for jet entrainment effects in the prediction of the subsonic flow over nozzle afterbodies. The jet entrainment model is based on the concept of a weakly interacting shear layer in which the local streamline deflections due to entrainment are accounted for by a displacement-thickness type correction to the inviscid plume boundary. The entire flowfield is solved in an iterative manner to account for the effects on the inviscid external flow of the turbulent boundary layer, turbulent mixing and chemical reactions in the shear layer, and the inviscid jet exhaust flow. The individual components of the computational model are described and numerical results are presented which illustrate the interactive effects of entrainment on the overall flow structure. The validity of the interactive model is assessed by comparisons with data obtained from flowfield measurements on cold-air jet exhausts. Numerical results and experimental data are also given which show the entrainment effects on nozzle boattail drag under various jet exhaust and freestream flow conditions.

Wilmoth, R. G.↗
NASA NTRS1979

Analysis of flight effects on noise radiation from dual-flow coaxial jets

A theoretical study has been made of the effects of flight on noise from dual-flow coaxial jets. The theory is based on an instability free, vortex sheet flow model. It is shown that the flight effects are more favorable (and hence produce less forward-arc amplification) for coaxial jets than for single-stream jets. Further, the theory predicts that, like the single-stream jet case, flight effects induce noise amplification in the forward quadrant and attenuation in the aft quadrant and have virtually no effect at theta = 90 deg to the jet axis, where theta is the angle between the directions of convection and emission at the retarded time. Amplification in the forward quadrant diminishes as the inner flow velocity increases and becomes optimum when the outer-to-inner velocity ratio is about 0.5. The theory also shows that the higher the outer-to-inner area ratio, the lower the forward-arc amplification due to flight.

Dash, R.↗
NASA NTRS1979

Effects of forward velocity on sound radiation from convecting monopole and dipole sources in jet flow

A theoretical model is presented of the effects of forward velocity of an aircraft at arbitrary subsonic speed on sound radiated from convecting monopole and dipole sources embedded in the jet flow. It is found that with increasing forward velocity there is a steadily increasing amplification (over the static case) of the sound radiated into the forward arc and a large reduction of the sound which is radiated into the rearward arc. The same trend is also shown to result when there is a reduction in the exhaust velocity, with, however, a further rise in amplification in the forward quadrant and a drop in attenuation in the aft quadrant.

Dash, R.↗
NASA NTRS1980

Computational models for the viscous/inviscid analysis of jet aircraft exhaust plumes

Computational models which analyze viscous/inviscid flow processes in jet aircraft exhaust plumes are discussed. These models are component parts of an NASA-LaRC method for the prediction of nozzle afterbody drag. Inviscid/shock processes are analyzed by the SCIPAC code which is a compact version of a generalized shock capturing, inviscid plume code (SCIPPY). The SCIPAC code analyzes underexpanded jet exhaust gas mixtures with a self-contained thermodynamic package for hydrocarbon exhaust products and air. A detailed and automated treatment of the embedded subsonic zones behind Mach discs is provided in this analysis. Mixing processes along the plume interface are analyzed by two upgraded versions of an overlaid, turbulent mixing code (BOAT) developed previously for calculating nearfield jet entrainment. The BOATAC program is a frozen chemistry version of BOAT containing the aircraft thermodynamic package as SCIPAC; BOATAB is an afterburning version with a self-contained aircraft (hydrocarbon/air) finite-rate chemistry package. The coupling of viscous and inviscid flow processes is achieved by an overlaid procedure with interactive effects accounted for by a displacement thickness type correction to the inviscid plume interface.

Dash, S. M.↗
NASA NTRS1980

Strouhal number influence on flight effects on jet noise radiated from convecting quadrupoles

The paper reports a complementary extension of previous work to include the high-frequency features reflected in the discussion of the higher Strouhal number influence on flight effects. It is found that, in addition to the usual features of flight effects on noise from ordinary flows, the high Strouhal number flows exhibit some more interesting features which are uniquely characteristic to them. The additional features are as follows: (1) Flight effects are more favorable to hot jets than to cold jets; (2) the higher the Strouhal number of the jet flow, the lesser the forward arc amplification due to flight; (3) as the Strouhal number increases, the peak amplification angle in the forward quadrant and the peak suppression angle in the aft quadrant move toward 90 deg and get closer, thus reducing the amplification exposure to a constricted angular region; (4) the silence zone is disturbed and displaced from its normal position parallel to the jet flow to give rise to multiple crossings of flight curves with the static line; and (5) the occurrence of multiple crossings is a strange phenomenon solely characteristic of high Strouhal number with high subcritical jet flows in flight.

Dash, R.↗
NASA NTRS1981

A viscous-inviscid interaction model of jet entrainment

A viscous-inviscid interaction model for predicting jet entrainment effects on axisymmetric, nozzle afterbodies at subsonic speeds is presented. The model is based on a displacement thickness correction to the inviscid jet boundary that accounts for mixing-induced streamline deflections in the inviscid region. The displacement correction is shown to be related to the local mass entrainment rate and, for thin mixing layers, the model is shown to be analogous to displacement models used in conventional boundary-layer interaction theory. A method is presented for computing the entrainment rate by an overlaid mixing layer model that accounts for the nonsimilar behavior and pressure gradients occurring in the near field region. An iterative scheme for coupling the model to analyses for the external inviscid flow, the external boundary layer, and the inviscid jet exhaust is also given. Results are presented that illustrate the qualitative behavior of the entrainment interaction under various flow conditions and that demonstrate the validity of the model by comparisons with experiment.

Wilmoth, R. G.↗