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  • FLUID MECHANICS AND HEAT TRANSFER  (17)
  • Mechanical Engineering  (1)
  • 1
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    Comparison of generalized Reynolds and Navier Stokes equations for flow of a power law fluid (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: This paper compares a finite element solution of a modified Reynolds equation with a finite difference solution of the Navier-Stokes equation for a power law fluid. Both the finite element and finite difference formulation are reviewed. Solutions to spiral flow in parallel and conical geometries are compared. Comparison with experimental results are also given. The effects of the assumptions used in the Reynolds equation are discussed.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
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  • 2
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    Finite difference solution for a generalized Reynolds equation with homogeneous two-phase flow (1987)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: An attempt is made to relate elements of two-phase flow and kinetic theory to the modified generalized Reynolds equation and to the energy equation, in order to arrive at a unified model simulating the pressure and flows in journal bearings, hydrostatic journal bearings, or squeeze film dampers when a two-phase situation occurs due to sudden fluid depressurization and heat generation. The numerical examples presented furnish a test of the algorithm for constant properties, and give insight into the effect of the shaft fluid heat transfer coefficient on the temperature profiles. The different level of pressures achievable for a given angular velocity depends on whether the bearing is thermal or nonisothermal; upwind differencing is noted to be essential for the derivation of a realistic profile.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
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  • 3
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    Two-phase flows and heat transfer within systems with ambient pressure above the thermodynamic critical pressure (1986)
    In:  Other Sources
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    Publikationsdatum: 2011-08-19
    Beschreibung: In systems where the design inlet and outlet pressure P sub amb are maintained above the thermodynamic critical pressure P sub c, it is often assumed that heat and mass transfer are governed by single-phase relations and that two-phase flows cannot occur. This simple rule of thumb is adequate in many low-power designs but is inadequate for high-performance turbomachines, boilers, and other systems where two-phase regions can exist even though P sub amb P sub c. Heat and mass transfer and rotordynamic-fluid-mechanic restoring forces depend on momentum differences, and those for a two-phase zone can differ significantly from those for a single-phase zone. By using a laminar, variable-property bearing code and a rotating boiler code, pressure and temperature surfaces were determined that illustrate nesting of a two-phase region within a supercritical pressure region. The method of corresponding states is applied to bearings with reasonable rapport.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
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  • 4
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    Refrigerated dynamic seal to 6.9 MPa (1000 psi) (1985)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The self sealing, high shear flow passage approach which was extended to large pressure differences was studied. In a refrigerated seal the fluid to be sealed flows through a refrigerated housing or constriction. The fluid can be frozen to the housing during the transient phase. Under steady state conditions the refrigerated seal proves to be a dynamic low leakage seal. The concept is extended to pressure differences of 6.9 MPa.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-TM-87108 , E-2708 , NAS 1.15:87108
    Format: application/pdf
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  • 5
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    Numerical and analytical study of fluid dynamic forces in seals and bearings (1987)
    In:  CASI
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    Publikationsdatum: 2019-06-28
    Beschreibung: A numerical model based on a transformed, conservative form of the three dimensional Navier-Stokes equation and an analytical model based on lumped fluid parameters are presented and compared with studies of modeled rotor bearing seal systems. The rotor destabilizing factors are related to the rotative character of the flow field. It is shown that these destabilizing factors can be reduced through a decrease in the fluid average circumferential velocity. However, the rotative character of the flow field is a complex three dimensional system with bifurcated secondary flow patterns that significantly alter the fluid circumferential velocity. By transforming the Navier-Stokes equations to those for a rotating observer and using the numerical code PHOENICS-84 with a nonorthogonal body fitted grid, several numerical experiments were carried out to demonstrate the character of this complex flow field. In general, fluid injection and/or preswirl of the flow field opposing the shaft rotation significantly intensified these secondary recirculation zones and thus reduced the average circumferential velocity; injection or preswirl in the direction of rotation significantly weakened these zones.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-TM-100268 , E-3903 , NAS 1.15:100268
    Format: application/pdf
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  • 6
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    Numerical modeling of multidimensional flow in seals and bearings used in rotating machinery (1988)
    In:  CASI
    Details
    Publikationsdatum: 2019-06-28
    Beschreibung: The rotordynamic behavior of turbomachinery is critically dependent on fluid dynamic rotor forces developed by various types of seals and bearings. The occurrence of self-excited vibrations often depends on the rotor speed and load. Misalignment and rotor wobbling motion associated with differential clearance were often attributed to stability problems. In general, the rotative character of the flowfield is a complex three dimensional system with secondary flow patterns that significantly alter the average fluid circumferential velocity. A multidimensional, nonorthogonal, body-fitted-grid fluid flow model is presented that describes the fluid dynamic forces and the secondary flow pattern development in seals and bearings. Several numerical experiments were carried out to demonstrate the characteristics of this complex flowfield. Analyses were performed by solving a conservation form of the three dimensional Navier-Stokes equations transformed to those for a rotating observer and using the general-purpose computer code PHOENICS with the assumptions that the rotor orbit is circular and that static eccentricity is zero. These assumptions have enabled a precise steady-state analysis to be used. Fluid injection from ports near the seal or bearing center increased fluid-film direct dynamic stiffness and, in some cases, significantly increased quadrature dynamic stiffness. Injection angle and velocity could be used for active rotordynamic control; for example, injection, when compared with no injection, increased direct dynamic stiffness, which is an important factor for hydrostatic bearings.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-TM-100779 , E-3909 , NAS 1.15:100779
    Format: application/pdf
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  • 7
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    Analogy between fluid cavitation and fracture mechanics (1983)
    In:  CASI
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    Publikationsdatum: 2019-07-13
    Beschreibung: When the stresses imposed on a fluid are sufficiently large, rupture or cavitation can occur. Such conditions can exist in many two-phase flow applications, such as the choked flows, which can occur in seals and bearings. Nonspherical bubbles with large aspect ratios have been observed in fluids under rapid acceleration and high shear fields. These bubbles are geometrically similar to fracture surface patterns (Griffith crack model) existing in solids. Analogies between crack growth in solid and fluid cavitation are proposed and supported by analysis and observation (photographs). Healing phenomena (void condensation), well accepted in fluid mechanics, have been observed in some polymers and hypothesized in solid mechanics. By drawing on the strengths of the theories of solid mechanics and cavitation, a more complete unified theory can be developed.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-TM-83071 , E-1519 , NAS 1.15:83071 , Thermal Eng. Joint Conf.; Mar 20, 1983 - Mar 24, 1983; Honolulu, HI; United States
    Format: application/pdf
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  • 8
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    Thermomechanical loading of multilayered cylindrical geometries in thermal cycling from 300 to 1300 K (1983)
    In:  CASI
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: The principal of multiple material layering is well known as an effective method of reducing heat transfer; however, thermal gradients can impose significant loads and lead to delamination and subsequent component failure. An analysis is developed and experimental data are discussed for the thermomechanical effects of multilayered materials on a heat sink substrate of cylindrical geometry subject to thermal cycling. The geometry is heated in cross-flow by a high-velocity flame and cooled in crossflow by ambient-temperature air from a critical flow orifice. Each layer of material possesses a threshold beyond which small changes in temperature or mechanical loading greatly influence the life in thermal cycling of the layered materials. Comparisons are made between the thermomechanical loads predicted by various numerical codes for the linear case and by a simplified analytic model.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-TM-83312 , E-1518 , NAS 1.15:83312 , Thermal Eng. Joint Conf.; Mar 20, 1983 - Mar 24, 1983; Honolulu, HI; United States
    Format: application/pdf
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  • 9
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    Torque Transmission Device at Zero Leakage (2005)
    In:  CASI
    Details
    Publikationsdatum: 2019-07-13
    Beschreibung: In a few critical applications, mechanical transmission of power by rotation at low speed is required without leakage at an interface. Herein we examine a device that enables torque to be transmitted across a sealed environmental barrier. The barrier represents the restraint membrane through which the torque is transmitted. The power is transferred through elastic deformation of a circular tube into an elliptical cross-section. Rotation of the principle axis of the ellipse at one end results in a commensurate rotation of an elliptical cross section at the other end of the tube. This transfer requires no rigid body rotation of the tube allowing a membrane to seal one end from the other. Both computational and experimental models of the device are presented.
    Schlagwort(e): Mechanical Engineering
    Materialart: NASA/TM?2005-212693 , ISROMAC10?2004?038 , E?14195 , 10th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery; Mar 07, 2004 - Mar 11, 2004; Honolulu, HI; United States
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  • 10
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    Thermomechanical design criteria for ceramic-coated surfaces (1986)
    In:  CASI
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    Publikationsdatum: 2019-07-13
    Beschreibung: Some early history of ceramic applications is presented. Finite element modeling of components to determine service and fabrication loads found inelastic behavior and residual stresses to be significant to component life. Inelastic behavior mitigates peak strains but enhances residual strains. Results of furnace, Mach 0.3 burner, and engine tests are discussed and categorized into design criteria (loading, geometry, fabrication, materials, analysis, and testing). These design rules and finite element analyses are brought to bear on two test cases: turboshaft engine seals, and rocket thrust chambers.
    Schlagwort(e): FLUID MECHANICS AND HEAT TRANSFER
    Materialart: NASA-TM-87328 , E-3002 , NAS 1.15:87328 , CIMTEC World Congress on High Tech Ceramics; Jun 23, 1986 - Jun 28, 1986; Milan; Italy
    Format: application/pdf
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