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  • FLUID MECHANICS AND HEAT TRANSFER  (94)
  • 1990-1994  (94)
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  • 1991  (94)
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  • 1
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    Some effects of swirl on turbulent mixing layer development (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Effects of swirl on the development of an axisymmetric turbulent mixing layer have been studied. The development of the zero swirl case is found to be consistent with that of a single-stream mixing layer developing from a tripped boundary layer. In particular, the consistency of the measured stress levels shows the accuracy of the measurement system. Swirl increases all the Reynolds stress levels with the increased scaling with swirl number. The shear stresses are found to be affected significantly more than the normal stresses. The stress increases are partly explained by considering extra production terms in the transport equations that are activated by the presense of the swirl. The thickness and growth rate for the lower swirl rate are found to be comparable to the zero swirl case, while those for the higher swirl rate are increased significantly, in line with the increased Reynolds stresses.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 3; 2716-272
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    NASA TECHNICAL REPORTS
  • 2
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    Experimental study of cross-stream mixing in a cylindrical duct (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: An experimental investigation of cross stream injection and mixing has been conducted with application to a low NO(x) combustor for the HSCT. Mixing in a cylindrical chamber has been studied for transverse injection from slanted slot and round orifice injectors. Momentum ratio, density ratio, and injector geometry were the primary variables. Slanted slots of various size, aspect ratio, and number were studied. Quantitative measurement of injectant concentration distributions were obtained by planar digital imaging of the Mie-scattered light from an aerosol seed uniformly mixed with the injectant. The unmixedness, defined as the ratio of the rms concentration fluctuation to mean concentration in a plane perpendicular to the main flow direction, was found to be primarily a function of momentum ratio and injector spacing. An optimum spacing is indicated. Unmixedness is also a function of orifice size, or mass flow ratio, but the mass flow dependence can be accounted for by normalizing the unmixedness with its maximum theoretical value. The data indicate that density ratio greater than unity retards mixing. It was found that above a certain momentum flux ratio, mixing with slanted slot injectors was better than with round hole injectors.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 91-2459
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    NASA TECHNICAL REPORTS
  • 3
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    Numerical analysis of rarefied slit flows. II - Navier-Stokes simulations (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The model problem of pressure-driven flow of a rarefied monatomic gas through a two-dimensional slit is analyzed via full Navier-Stokes numerical simulation. Parametric solutions are generated for slit-height based Knudsen number ranging from continuum to transitional flow and for reservoir pressure ratios leading to subsonic and supersonic flow. The change in the structure of the flowfield near the slit as a function of pressure ratio and Knudsen number are quantified from a purely continuum standpoint. The choice of numerical domain size, boundary conditions and treatment of the slit are also discussed. As expected, comparison with a Direct Simulation Monte Carlo solution for a highly rarefied case shows large differences in the predicted mass flow. The cause of these differences can be quantified through detailed comparison of the local flowfield properties. For the larger pressure ratio cases qualitative trends with increasing rarefaction are discussed, including the change in the sonic line shape in the slit and the in total mass flow.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 91-1748
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    NASA TECHNICAL REPORTS
  • 4
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    Computational methodology for radiation heat transfer in the flowfield of an AOTV (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A computational methodology is developed for the calculation of radiation heat transfer in a non-scattering medium where nonequilibrium conditions exist and give rise to complex spectra. The specific problem of radiation in an aeroassisted orbital transfer vehicle (AOTV) flowfield is addressed. Nonequilibrium radiation from the gases around a hypersonic vehicle is evaluated using the NASA-Ames NEQAIR program together with a three-dimensional geometrical flowfield model. Nonequilibrium compositions and temperatures are taken from NASA-Langley 3-D hypersonic flowfield calculations that include real-gas effects and finite-rate chemical kinetics. It is shown that the concept of a transmission path adjustment, together with precomputations of curves of growth based upon local properties at flowfield locations, facilitates radiation calculations. Sample calculations of directional and spectral distributions of gas radiation received upon a hypersonic vehicle are presented.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 91-1407
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    NASA TECHNICAL REPORTS
  • 5
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    The design/analysis of flows through turbomachinery - A viscous/inviscid approach (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A new design/analysis system for the flows through turbomachinery is currently being developed for studying turbomachinery problems with an axisymmetric viscous/inviscid 'average-passage' throughflow code. The advantage of this approach, compared to streamline curvature codes, is that the solutions obtained simulate some of the unsteadiness, compressibility and viscous effects of a multistage turbomachine. The design/analysis system consists of three elemental parts, the axisymmetric block grid generator, the blade surface element code, and the axisymmetric flow code. Each element of the system will be discussed and the flow solutions for three axisymmetric geometries will be shown compared to experimental data where available. The computations are shown to be in very good agreement with test data for SR7 spinner body and transonic boattail geometry obtained in the wind tunnels at NASA Lewis Research Center. The VIADAC Rotor 67 Fan results were compared to PARC2D calculated results and shown to be in very good agreement.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 91-2010
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    NASA TECHNICAL REPORTS
  • 6
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    Effects of turbulence and number density on the drag coefficient of droplets (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Droplet drag coefficients for polydispersed drops are determined via the behavior of drops decelerating on the stagnation streamline of a cylinder with an afterbody mounted in a wind tunnel test section. A variety of velocity, turbulence levels, and droplet number densities were studied. A force balance equation technique was used to determine drag coefficient. For the levels of number density, up to 700/cc, and turbulence, up to about 7 percent, no definite effects were seen. However, the smallest drops in the high turbulence case showed some evidence of drop-turbulence and/or drop-drop interactions. The drag results that were developed for this set of measurements agreed well with other empirical relations previously determined.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 91-0074
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  • 7
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    No-vent fill pressurization tests using a cryogen simulant (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The results are described of an experimental program which studied the performance of various no-vent fill techniques for tank-to-tank liquid transfer. The tests were performed using a cryogen simulant (Freon-114) and a test bed consisting of a multiple tank/plumbing network that enabled studies of a variety of different inlet flow and active mixing regimes. Several results and conclusions were drawn from the 26 transfer experiments comprising the program. Most notable was the significant improvement in fill performance (i.e., minimized fill time and maximized fill fraction) with increased agitation of the liquid surface. Another was the close correlation between measured condensation rates and those predicted by recent theories which express condensation as a function of turbulent eddy effects on the liquid surface. In most cases, test data exhibited strong agreement with an analytical model which accounts for tank heat transfer and thermodynamics in a 1 g environment.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-103561 , NAS 1.15:103561
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    NASA TECHNICAL REPORTS
  • 8
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    Observations of the freeze/thaw performance of lithium fluoride by motion picture photography (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: To gain direct observation of the molten salt phase change, a novel containerless technique was developed where the high surface tension of lithium fluoride was used to suspend a bead of the molten salt inside a specially designed wire cage. By varying the current passing through the wire, the cage also served as a variable heat source. In this way, the freeze/thaw performance of the lithium fluoride could be photographed by motion picture photography without the influence of container walls. The motion picture photography of the lithium fluoride sample revealed several zones during the phase change, a solid zone and a liquid zone, as expected, and a slush zone that was predicted by thermal analysis modeling.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: IECEC ''91: Intersociety Energy Conversion Engineering Conference; Aug 04, 1991 - Aug 09, 1991; Boston, MA; United States
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    NASA TECHNICAL REPORTS
  • 9
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    Frequency effects on the stability of a journal bearing for periodic loading (1991)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The stability of a journal bearing is numerically predicted when a unidirectional periodic external load is applied. The analysis is performed using a cavitation algorithm, which mimics the Jakobsson-Floberg and Olsson (JFO) theory by accounting for the mass balance through the complete bearing. Hence, the history of the film is taken into consideration. The loading pattern is taken to be sinusoidal and the frequency of the load cycle is varied. The results are compared with the predictions using Reynolds boundary conditions for both film rupture and reformation. With such comparisons, the need for accurately predicting the cavitation regions for complex loading patterns is clearly demonstrated. For a particular frequency of loading, the effects of mass, amplitude of load variation and frequency of journal speed are also investigated. The journal trajectories, transient variations in fluid film forces, net surface velocity and minimum film thickness, and pressure profiles are also presented.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-TM-105226 , E-6242 , NAS 1.15:105226 , AVSCOM-TR-91-C-040 , AD-A247566 , STLE-ASME Joint Tribology Conference; Oct 13, 1991 - Oct 16, 1991; St. Louis, MO; United States
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    NASA TECHNICAL REPORTS
  • 10
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    Local lattice-gas model for immiscible fluids (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A lattice-gas model is presented for two-dimensional immiscible fluid flows with surface tension that uses strictly local collision rules. Instead of using a local total color flux as Somers and Rem (1991), local colored holes are used to be the memory of particles of the same color. Interactions between walls and fluids are included that produce arbitrary contact angles.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physical Review A (ISSN 1050-2947); 43; 7053-705
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