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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Mixing of multiple dilution jets with a hot primary airstream for gas turbine combustors

The mixing of multiple air jets with a subsonic heated crossflow in a constant area duct was studied experimentally. The jet-to-mainstream momentum flux ratio was varied from 6 to 60. Temperature and pressure surveys were made at several downstream locations for orifice geometries with parametric variation of orifice size and spacing. A mixing efficiency parameter was defined which characterized the effectiveness of the mixing over the range of conditions examined. It was found that for a given momentum flux ratio, there exists a ratio of orifice spacing to duct height which provides the best mixing.

Holdeman, J. D.↗
NASA NTRS1975

Supersonic Mixing and Combustion in Parallel Injection Flow Fields

Adequate prediction techniques for supersonic, mixing, reacting flows are of great importance in the design and performance analysis of supersonic combustion ramjet (scramjet) engines. Analytical programs for parallel injection flow fields with chemical reaction and turbulent mixing are now available for both single and multiple-jet flows. The application of these analyses to simple flow geometries is discussed, and comparisons also are made with data on the more complex case of multiple-jet, reacting flows. A review is given of Langley investigations of parallel injection flow fields. Among these are single-jet studies of nonreacting, turbulent mixing (H2 in air and H2 in N2), and of reacting turbulent mixing (H2 in air) with both single and multiple jets. Implications of the results of the studies for scramjet fuel injector design are discussed.

Evans, J. S.↗
NASA NTRS1974

Mixing of the lunar regolith

A probabilistic model for mixing and turnover rates for the lunar regolith due to meteoritic impact is presented and evaluated using results from laboratory impact experiments and estimated meteoritic fluxes. The upper millimeter of the lunar surface is shown to be the primary mixing zone in the regolith and an important source for impact melts and vapors. Below this 'mixing layer' the rate of mixing and turnover decreases very rapidly with increasing depth, consistent with well-preserved stratigraphy and resident times deduced from deep drill core tube samples.

Gault, D. E.↗
NASA NTRS1975

A study of reactive turbulent mixing

This paper describes the development of a probe to study turbulent reactive mixing of two hypergolic streams of gas. The streams contain CO and O2 respectively and are mixed at 1400 K. The probe is a water cooled sonic orifice probe followed by a Fanno duct. Tests showed that it rapidly quenched the reaction, and that time-average, ingested gas composition accurately reflected the time-average composition at the sampling point. A new way to measure mixedness to the molecular level in a reactive flow situation is described, based on time-average compositions at the probe. This definition is compared to the definition of intensity of segregation which can be used for unreactive mixing situations. Finally, the probe is used to examine centerline composition in a confined coaxial mixing situation.

Roler, M. A.↗
NASA NTRS1975

Analytical study of mixing and reacting three-dimensional supersonic combustor flow fields

An analytical investigation is presented of mixing and reacting hydrogen jets injected from multiple orifices transverse and parallel to a supersonic airstream. The COMOC computer program, based upon a finite-element solution algorithm, was developed to solve the governing equations for three-dimensional, turbulent, reacting, boundary-region, and confined flow fields. The computational results provide a three-dimensional description of the velocity, temperature, and species-concentration fields downstream of hydrogen injection. Detailed comparisons between cold-flow data and results of the computational analysis have established validity of the turbulent-mixing model based on the elementary mixing-length hypothesis. A method is established to initiate computations for reacting flow fields based upon cold-flow correlations and the appropriate experimental parameters of Mach number, injector spacing, and pressure ratio. Key analytical observations on mixing and combustion efficiency for reacting flows are presented and discussed.

Baker, A. J.↗
NASA NTRS1976

Modeling of three-dimensional mixing and reacting ducted flows

A computer code, based upon a finite element solution algorithm, was developed to solve the governing equations for three-dimensional, reacting boundary region, and constant area ducted flow fields. Effective diffusion coefficients are employed to allow analyses of turbulent, transitional or laminar flows. The code was used to investigate mixing and reacting hydrogen jets injected from multiple orifices, transverse and parallel to a supersonic air stream. Computational results provide a three-dimensional description of velocity, temperature, and species-concentration fields downstream of injection. Experimental data for eight cases covering different injection conditions and geometries were modeled using mixing length theory (MLT). These results were used as a baseline for examining the relative merits of other mixing models. Calculations were made using a two-equation turbulence model (k+d) and comparisons were made between experiment and mixing length theory predictions. The k+d model shows only a slight improvement in predictive capability over MLT. Results of an examination of the effect of tensorial transport coefficients on mass and momentum field distribution are also presented. Solutions demonstrating the ability of the code to model ducted flows and parallel strut injection are presented and discussed.

Zelazny, S. W.↗
NASA NTRS1976

The salinity effect in a mixed layer ocean model

A model of the thermally mixed layer in the upper ocean as developed by Kraus and Turner and extended by Denman is further extended to investigate the effects of salinity. In the tropical and subtropical Atlantic Ocean rapid increases in salinity occur at the bottom of a uniformly mixed surface layer. The most significant effects produced by the inclusion of salinity are the reduction of the deepening rate and the corresponding change in the heating characteristics of the mixed layer. If the net surface heating is positive, but small, salinity effects must be included to determine whether the mixed layer temperature will increase or decrease. Precipitation over tropical oceans leads to the development of a shallow stable layer accompanied by a decrease in the temperature and salinity at the sea surface.

Miller, J. R.↗
NASA NTRS1977

The influence of droplet evaporation on fuel-air mixing rate in a burner

Experiments involving combustion of a variety of hydrocarbon fuels in a simple atmospheric pressure burner were used to evaluate the role of droplet evaporation in the fuel/air mixing process in liquid fuel spray flames. Both air-assist atomization and pressure atomization processes were studied; fuel/air mixing rates were determined on the basis of cross-section average oxygen concentrations for stoichiometric overall operation. In general, it is concluded that droplets act as point sources of fuel vapor until evaporation, when the fuel jet length scale may become important in determining nonuniformities of the fuel vapor concentration. In addition, air-assist atomizers are found to have short droplet evaporation times with respect to the duration of the fuel/air mixing process, while for the pressure jet atomizer the characteristic evaporation and mixing times are similar.

Komiyama, K.↗
NASA NTRS1978

Measurements of mixed-mode crack surface displacements and comparison with theory

A theoretical and an experimental technique is used to determine crack surface displacements under mixed-mode conditions. Crack surface displacements proved to be quite useful in mode 1 fracture analysis in that they are directly related to strain energy release rate and stress intensity factor. It is felt that similar relationships can be developed for the mixed-mode case. A boundary-integral method was developed for application to two-dimensional fracture mechanics problems. This technique was applied to the mixed-mode problem. A laser interferometry technique, for measurement of crack surface displacements under mixed-mode conditions, is presented. The experimental measurements are reported and the results of the two approaches are compared and discussed.

Altiero, N. J., Jr.↗
NASA NTRS1980

A numerical study of the effects of heat diffusion through the base of the mixed layer

In the present paper, a simple numerical model is used to study the warming of the mixed layer during the early summer. It is shown that the springtime temperature increase in the layer below the mixed layer (for example, in the cold pool on a continental shelf) has a maximum value which occurs for a limiting value of the surface heat flux. This is a result of the positive feedback at large Richardson numbers between stability and vertical diffusion of heat. The springtime temperature increase in the mixed layer increases nonlinearly with surface heat flux, because of the same positive feedback. The effects of interseasonal fluctuations of the surface heat flux on the spring and summer mixed layer and deeper temperature increases can be as great as the effect of interseasonal fluctuations of the average heat flux.

Posmentier, E. S.↗
NASA NTRS1981

A three-dimensional simulation of transition and early turbulence in a time-developing mixing layer

The physics of the transition and early turbulence regimes in the time developing mixing layer was investigated. The sensitivity of the mixing layer to the disturbance field of the initial condition is considered. The growth of the momentum thickness, the mean velocity profile, the turbulence kinetic energy, the Reynolds stresses, the anisotropy tensor, and particle track pictures of computations are all examined in an effort to better understand the physics of these regimes. The amplitude, spectrum shape, and random phases of the initial disturbance field were varied. A scheme of generating discrete orthogonal function expansions on some nonuniform grids was developed. All cases address the early or near field of the mixing layer. The most significant result shows that the secondary instability of the mixing layer is produced by spanwise variations in the straining field of the primary vortex structures.

Cain, A. B.↗
NASA NTRS1981

Mixed models and reduced/selective integration displacement models for nonlinear shell analysis

One of the objectives of the present investigation is to identify classes of equivalent mixed models and reduced/selective integration displacement models for curved shell structures. A second objective is concerned with the identification of the spurious modes exhibited by various mixed models and their equivalent reduced integration displacement models. The merits of using mixed models are also evaluated. The mixed elements developed in the current investigation differ from those presented by Noor and Hartley (1977) by the fact that the stress resultants are discontinuous at interelement boundaries and, therefore, are eliminated on the element level. The high accuracy and effectiveness of the elements developed is demonstrated by means of numerical examples, taking into account three geometrically nonlinear problems of shallow shells.

Noor, A. K.↗
NASA NTRS1982

Ordered mixed-layer structures in the Mighei carbonaceous chondrite matrix

High resolution transmission electron microscopy of the Mighei carbonaceous chondrite matrix has revealed the presence of a new mixed layer structure material. This mixed-layer material consists of an ordered arrangement of serpentine-type (S) and brucite-type (B) layers in the sequence SBBSBB. Electron diffraction and imaging techniques show that the basal periodicity is approximately 17 A. Discrete crystals of SBB-type material are typically curved, of small size (less than 1 micron) and show structural variations similar to the serpentine group minerals. Mixed-layer material also occurs in association with planar serpentine. Characteristics of SBB-type material are not consistent with known terrestrial mixed-layer clay minerals. Evidence for formation by a condensation event or by subsequent alteration of pre-existing material is not yet apparent.

Mackinnon, I. D. R.↗
NASA NTRS1983

Ultrasonic mixing of epoxy curing agents

A new technique for mixing solid curing agents into liquid epoxy resins using ultrasonic energy was developed. This procedure allows standard curing agents such as 4,4 prime-diaminodiphenyl sulfone (4,4 prime-DDS) and its 3,3 prime-isomer, (3,3 prime-DDS) to be mixed without prior melting of the curing agent. It also allows curing agents such as 4,4 prime-diaminodiphenyl sulfone (4,4 prime-DDS) and its 3,3 prime-isomer, (3,3 prime-DDS) to be mixed without prior melting of the curing agent. It also allows curing agents with very high melt temperatures such as 4,4 prime-diaminobenzophenone (4,4 prime-DABP) (242 C) to be mixed without premature curing. Four aromatic diamines were ultrasonically blended into MY-720 epoxy resin. These were 4,4 prime-DDS; 3,3 prime-DDA; 4,4 prime-DABP and 3,3 prime-DABP. Unfilled moldings were cast and cured for each system and their physical and mechanical properties compared.

Hodges, W. T.↗
NASA NTRS1983

Simulation of terrain effects using a mesoscale mixed-layer model

The model discussed here is described in the study by Han et al. (1982) and is based on the shallow-water equations. It is noted that the mixed layer is another name for the earth's turbulent boundary layer when the latter is well stirred vertically, as under typical daytime conditions over land. The model abbreviates the vertical resolution by using only one and one-half layers; in this way, the computer power can be concentrated on the horizontal resolution of topographic effects. It is found that a steady flow pattern evolves over terrain when steady forcing occurs in the absence of surface heating or mixed-layer entrainment and that this simplification is removed when surface heating and entrainment do occur. While these findings are regarded as interesting, it is believed that they may be model dependent. The pressure adjustments upon the mixed layer caused by air movements above the mixed layer may be sufficient to preclude the evolution of a steady state on the mesoscale, even under the most ideal conditions.

Deardorff, J. W.↗
NASA NTRS1983

Ultrasonic mixing of epoxy curing agents

A new technique for mixing solid curing agents into liquid epoxy resins using ultrasonic energy was developed. This procedure allows standard curing agents such as 4,4 prime-diaminodiphenyl sulfone (4,4 prime-DDS) and its 3,3 prime-isomer, (3,3 prime-DDS) to be mixed without prior melting of the curing agent. It also allows curing agents with very high melt temperatures such as 4,4 prime-diaminodiphenyl sulfone (4,4 prime-DDS) and its 3,3 prime-isomer, (3,3 prime-DDS) to be mixed without prior melting of the curing agent. It also allows curing agents with very high melt temperatures such as 4,4 prime-diaminobenzophenone (4,4 prime-DABP) (242 C) to be mixed without premature curing. Four aromatic diamines were ultrasonically blended into MY-720 epoxy resin. These were 4, 4 prime-DDS; 3,3 prime-DDA; 4, 4 prime-DABP and 3,3 prime-DABP. Unfilled moldings were cast and cured for each system and their physical and mechanical properties compared. Previously announced in STAR as N83-27018

Hodges, W. T.↗
NASA NTRS1984

Near-field turbulence properties of single- and two-stream plane mixing layers

Detailed mean-flow and turbulence measurements have been made in the near-field of two plane mixing layers in air with a maximum velocity of 21 m/s. The experimental rig enabled mixing layers of velocity ratios 0 and 0.46 to be generated simultaneously. Cases with both tripped and untripped initial boundary layers were studied. In all cases, it was found that the two-stream layer developed to the self-preserving state in a distance much shorter than the single-stream layer which followed accepted criteria for the development distance. The asymptotic levels of the turbulence quantities in the two-stream layer, and the development of the single-stream layer showed agreement with existing data. The results suggest that the two-stream mixing layer should provide a better test case for the development of turbulence models and calculation methods than the single-stream mixing layer.

Mehta, R. D.↗
NASA NTRS1983

Balloon and aircraft measurement of stratospheric sulfate mixing ratio following the El Chichon eruption

Profiles of sulfate mixing ratio versus altitude over the range 15-28 km were obtained from filter samples collected aboard balloons and U-2 aircraft. Observations were made in the summer, fall, and winter following the March-April 1982, El Chichon eruption. Observed sulfate mixing ratios were approximately two orders of magnitude greater than typical background (not volcanically augmented) mixing ratios. The sulfate mixing ratios obtained form the aircraft filter measurements were in good agreement with the results from a wire impactor and a particle counter flown simultaneously. Computations of the amount of sulfate contained in a vertical column of sq m were in agreement with similar calculations from airborne lidar, balloon-borne particle counters, and Solar Mesosphere Explorer satellite radiance retrievals.

Gandrud, B. W.↗