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  • 1
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    Flow in out-of-plane double S-bonds (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Developing flows in two out-of-plane double S-bend configurations have been measured by laser-Doppler anemometry. The first duct had a rectangular cross-section 40mmx40mm at the inlet and consisted of a uniform area 22.5 deg. - 22.5 deg. S-duct upstream with a 22.5 deg.- 22.5 deg. S- diffuser downstream. The second duct had a circular cross-section and consisted of a 45 deg. - 45 deg. uniform area S-duct upstream with a 22.5 deg. -22.5 deg. S-diffuser downstream. In both configurations the ratio of the mean radius of curvature to the inlet hydraulic diameter was 7.0, the exit-to-inlet area ratio of the diffusers was 1.5 and the ducts were connected so that the centerline of the S-duct lay in a plane normal to that of the S-diffuser. Streamwise and cross-stream velocity components were measured in laminar flow for the rectangular duct and in turbulent flow for both configurations; measurements of the turbulence levels, cross-correlations and wall static pressures were also made in the turbulent flow cases. Secondary flows of the first kind are present in the first S-duct and they are complemented or counteracted by the secondary flows generated by the area expansion and by the curvature of the S-diffusers downstream. Cross-stream velocities with magnitudes up to 0.19 and 0.11 of the bulk velocity were measured in the laminar and turbulent flows respectively in the rectangular duct and six cross-flow vortices were evident at the exit of the duct in both flow cases. The turbulent flow in the circular duct was qualitatively similar to that in the rectangular configuration, but the cross-stream velocities measured at the exit plane were smaller in the circular geometry. The results are presented in sufficient detail and accuracy for the assessment of numerical calculation methods and are listed in tabular form for this purpose.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-176981 , NAS 1.26:176981 , FS/86/30
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  • 2
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    A low-Reynolds-number two-equation turbulence model for predicting heat transfer on turbine blades (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A modified form of the Lam-Bremhorst low-Reynolds number kappa-epsilon turbulence model was developed for predicting transitional boundary layer flows under conditions characteristic of gas turbine blades. The application of the model to flows with pressure gradients is described. Tests against a number of turbine blade cascade data sets are included. Some additional refinements of the model that were made in recent months are explained.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA, Lewis Research Center, Turbine Engine Hot Section Technology, 1987; p 155-167
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  • 3
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    Prediction of transition on a flat plate under the influence of free-stream turbulence using low-Reynolds-number two-equation turbulence models (1987)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The prediction characteristics and capabilities of two popular two-equation low-Reynolds-number turbulence models (Jones, Launder 1972; Lam, Bremhorst 1981) have been evaluated with respect to the prediction of transition of a flat plate under the influence of free-stream turbulence. The sensitivity of the predictions to free-stream turbulence intensity, initial starting location of the calculation, and the assumed initial starting profiles for k and epsilon has been determined and presented. Although both models predict the correct qualitative characteristics of transition, they also exhibit significant quantitative deficiencies with regard to both the predicted location and the length of transition. A modification to the production term in the turbulent kinetic energy equation is proposed which is based on a simple stability criterion and correlated to the free-stream turbulence level. The modification becomes inactive in the fully turbulent regime, but is shown to improve both the qualitative and quantitative characteristics of the transition predictions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: ASME PAPER 87-HT-32
    Format: text
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  • 4
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    The liquid-vapor interface of a binary liquid mixture near the consolute point (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The present investigation is concerned with measurements of the reflectance of polarized light by the liquid-vapor interface above liquid mixtures of a fluorocarbon and an alcohol in the vicinity of the consolute point of the liquid mixture. The denser fluorocarbon is preferentially adsorbed at the interface. The denser fluorocarbon is preferentially adsorbed at the interface. The data are consistent with a simple model of the dielectric constant vs height profile in the interface region. Liquid mixtures of isopropanol (i-C3H7OH) and perfluoromethylcyclohexane (C7F14) near their consolute point (Tc = 363 K) are utilized in the conducted experiments. The primary quantity measured is the ellipticity as a function of temperature and liquid composition. Attention is given to details regarding the experimental techniques, model dielectric constant profiles, and the calculation of the ellipticity.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Chemical Physics (ISSN 0021-9606); 83; 1829-183
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  • 5
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    Multigrid techniques for the solution of the passive scalar advection-diffusion equation (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The solution of elliptic passive scalar advection-diffusion equations is required in the analysis of many turbulent flow and convective heat transfer problems. The accuracy of the solution may be affected by the presence of regions containing large gradients of the dependent variables. The multigrid concept of local grid refinement is a method for improving the accuracy of the calculations in these problems. In combination with the multilevel acceleration techniques, an accurate and efficient computational procedure is developed. In addition, a robust implementation of the QUICK finite-difference scheme is described. Calculations of a test problem are presented to quantitatively demonstrate the advantages of the multilevel-multigrid method.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Numerical Heat Transfer (ISSN 0149-5720); 8; 1 19
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  • 6
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    Wetting layers and dispersion forces for a fluid in contact with a vertical wall (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Ellipsometric measurements of the thickness of the wetting layer of sulfur hexafluoride that forms on a fused-silica surface partially immersed in the liquid are presented. The components of the experiment included a He-Ne laser (0.6328 micron), polarizer, and quarter-wave plate with 45-deg azimuth. An optical-grade fused-silica prism was polished to wavelength/20, and strain-induced birefringence was accounted for. It was found that the layer thickness decreases from 40 to 20 nm with a height increase from 0.7 to 3 mm above the liquid-vapor interface. The thickness is independent of the temperature between 10 and 0.1 K below the critical temperature (319 K). The results are compared in detail to the theory of Dzyaloshinskii et al. (1961), and are noted to coincide closely.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physical Review Letters (ISSN 0031-9007); 54; 707-710
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  • 7
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    Two-Equation Low-Reynolds-Number Turbulence Modeling of Transitional Boundary Layer Flows Characteristic of Gas Turbine Blades (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The use of low Reynolds number (LRN) forms of the k-epsilon turbulence model in predicting transitional boundary layer flow characteristic of gas turbine blades is developed. The research presented consists of: (1) an evaluation of two existing models; (2) the development of a modification to current LRN models; and (3) the extensive testing of the proposed model against experimental data. The prediction characteristics and capabilities of the Jones-Launder (1972) and Lam-Bremhorst (1981) LRN k-epsilon models are evaluated with respect to the prediction of transition on flat plates. Next, the mechanism by which the models simulate transition is considered and the need for additional constraints is discussed. Finally, the transition predictions of a new model are compared with a wide range of different experiments, including transitional flows with free-stream turbulence under conditions of flat plate constant velocity, flat plate constant acceleration, flat plate but strongly variable acceleration, and flow around turbine blade test cascades. In general, calculational procedure yields good agreement with most of the experiments.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-4145 , E-3960 , NAS 1.26:4145
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  • 8
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    Development of low Reynolds number two equation turbulence models for predicting external heat transfer on turbine blades (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A research effort was underway to study the use of two equation low Reynolds number turbulence models in predicting gas side heat transfer on turbine blades. The major objectives of this work are basicly threefold: study the predictive capabilities of two equation low Reynolds number turbulence models under the conditions characteristic of modern gas turbine blades; explore potential improvements to the models themselves as well as to the specification of initial conditions; and provide a comparison of the predictions of these models with the experimental data from a broad range of recently available turbine cascade experiments. The problems associated with predicting the boundary layer transition from laminar to turbulent flow are emphasized, as this may be the most serious deficiency of current modeling techniques. The results and conclusions of the first two phases are briefly described.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA, Lewis Research Center, Turbine Engine Hot Section Technology 1986; p 219-232
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  • 9
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    A multilevel-multigrid technique for recirculating flows (1985)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: A solution algorithm has been developed for the prediction of recirculating flows. Brandt's multilevel acceleration technique is used with Leonard's QUICK differencing scheme and a modified pressure implicit operator splitting scheme. Intermediate calculations enable a tau error distribution to be used for the identification of regions for local grid refinement, i.e., multigrid. The algorithm was tested for the prediction of laminar flow in a shear-driven and a buoyancy-driven cavity.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Numerical Heat Transfer (ISSN 0149-5720); 8; 5 19
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