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  • SOLID-STATE PHYSICS  (5)
  • RESEARCH AND SUPPORT FACILITIES (AIR)  (3)
  • 2020-2024
  • 2020-2022
  • 1995-1999
  • 1985-1989  (8)
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Year
  • 1
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    Directional solidification in an imperfect furnace (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The upward directional solidification of a binary alloy in which the rejected solute is more dense than the solvent is considered. The system is stably stratified both thermally and solutally. If heat is lost through the sidewalls, horizontal thermal gradients drive a steady double-diffusive convection. Solidification cells with small aspect ratios (width/length) A are considered, and asymptotic solutions to the steady double-diffusive system are obtained as A tends to 0 under the assumption heat losses are also small. When the thermal Grashof number is large, buoyancy boundary layers are at the sidewalls. The shape of the crystal-melt interface is determined by the coupled effects of local thermodynamic equilibrium, diffusion and convection.
    Keywords: SOLID-STATE PHYSICS
    Type: PCH/PhysicoChemical Hydrodynamics (ISSN 0191-9059); 9; 1-2,; 9-14
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Applications of adaptive-wall wind tunnels (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A novel processing technique for the flowfield data generated by an adaptive wall wind tunnel is presented whose basic premise is the possible undesirability of forcing such a wind tunnel to simulate free-air conditions. The concept of a 'phantom' wind tunnel is introduced for both two- and three-dimensional wind tunnels, yielding a continuous spectrum of flow fields, ranging from the original passive and ventilated configuration to a fully adaptive one. In order to implement these procedures, active control is limited to floor and ceiling surfaces.
    Keywords: RESEARCH AND SUPPORT FACILITIES (AIR)
    Type: Journal of Aircraft (ISSN 0021-8669); 23; 158-160
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Shallow cells in directional solidification (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The existing theory on two-dimensional transitions (appropriate to thin parallel-plate geometries) is presented in such a way that it is possible to identify easily conditions for the onset of shallow cells. Conditions are given under which succinonitrile-acetone mixtures should undergo supercritical bifurcation in experimentally accessible ranges. These results suggest a means for the quantitative test of the Mullins and Sekerka (1964) model and its weakly nonlinear extensions.
    Keywords: SOLID-STATE PHYSICS
    Type: Physical Review Letters (ISSN 0031-9007); 63; 573-575
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Directional solidification with heat losses (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The upward directional solidification of a dilute binary alloy in a tall, thin, two-dimensional slot is considered. Heat losses from the sidewalls produce curved isotherms, interface deformations, and melt convection. An asymptotic approach is used which relates the small heat loss to the thinness of the solidification cell, and solutions are obtained for the resulting melt convection, interface deflection, and the distribution of heat and solute. The model is compared to the numerical results of Chang and Brown (1983) which exclude the effects of solute buoyancy and thermodynamic equilibrium at the interface. The radial segregation at the interface (consistent with both interface shapes and temperature fields) is computed, and it is found that the radial segregation is independent of interfacial shapes; the radial segregation cannot be calculated from only a knowledge of the interface shape.
    Keywords: SOLID-STATE PHYSICS
    Type: Journal of Crystal Growth (ISSN 0022-0248); 91; 4, Se; 538-556
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Similarity solutions for phase-change problems (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A modification of Ivantsov's (1947) similarity solutions is proposed which can describe phase-change processes which are limited by diffusion. The method has application to systems that have n-components and possess cross-diffusion and Soret and Dufour effects, along with convection driven by density discontinuities at the two-phase interface. Local thermal equilibrium is assumed at the interface. It is shown that analytic solutions are possible when the material properties are constant.
    Keywords: SOLID-STATE PHYSICS
    Type: Metallurgical Transactions A - Physical Metallurgy and Materials Science (ISSN 0360-2133); 20A; 225-235
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    The evolution of adaptive-wall wind tunnels (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Since its inception, adaptive wall wind tunnel design has developed three major configurational possibilities: streamlined walls, variable porosity walls, and segmented plenum arrangements. All of these methods have demonstrated their feasibility for transonic flow research; development programs are noted to be underway for three-dimensional adaptive wall tunnels. With the availability of advanced computational procedures, routine angle-of-incidence or Mach sweeps may be treated numerically, while adaptive wall wind tunnels are employed for complementary point-design and for testing at flow conditions that are beyond the capabilities of current numerical modeling.
    Keywords: RESEARCH AND SUPPORT FACILITIES (AIR)
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    NASA TECHNICAL REPORTS
  • 7
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    Generalized adaptive-wall wind tunnels (1985)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Adaptive-wall technology is being seriously considered for many aeronautical wind tunnel applications. A new degree of freedom is introduced into adaptive-wall wind tunnels. It is shown that the adaptive control system used to adjust wall boundary conditions may be used to select a wide variety of flow fields. These flow fields, in turn, maybe directly related to many useful unconfined or semiconfined flows. The generalized adaptive-wall concept is demonstrated for both two- and three-dimensional flows using simple analytical techniques.
    Keywords: RESEARCH AND SUPPORT FACILITIES (AIR)
    Type: AIAA PAPER 85-0225
    Format: text
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    NASA TECHNICAL REPORTS
  • 8
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    Crystal growing from the melt (1987)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The mechanical and electrical properties of crystals produced by a unidirectional process depend strongly on the temperature and flow fields since these control the concentration of solute at the melt-crystal interface. The solute gradient there drives morphological instabilities that lead to cellular or dendritic interfaces. In the presentation several features of flow-solidification interactions will be discussed. These will include the effects of convection driven by density changes and buoyancy and the imposition of forced flow.
    Keywords: SOLID-STATE PHYSICS
    Type: Interdisciplinary issues in materials processing and manufacturing; Dec 13, 1987 - Dec 18, 1987; Boston, MA; United States
    Format: text
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    NASA TECHNICAL REPORTS
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