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  • FLUID MECHANICS AND HEAT TRANSFER  (15)
  • PHYSICS, ATOMIC, MOLECULAR, AND NUCLEAR  (4)
  • 1990-1994  (15)
  • 1970-1974  (4)
  • 1950-1954
  • 1
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    The present state and future direction of second order closure models for compressible flows (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: The topics are presented in viewgraph form and include: (1) Reynolds stress closure models; (2) Favre averages and governing equations; (3) the model for the deviatoric part of the pressure-strain rate correlation; (4) the SSG pressure-strain correlation model; (5) a compressible turbulent dissipation rate model; (6) variable viscosity effects; (7) near-wall stiffness problems; (8) models of the Reynolds mass and heat flux; and (9) a numerical solution of the compressible turbulent transport equation.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA. Lewis Research Center, Workshop on Engineering Turbulence Modeling; p 249-275
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  • 2
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    Studies in turbulence (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: Various papers on turbulence are presented. Individual topics addressed include: modeling the dissipation rate in rotating turbulent flows, mapping closures for turbulent mixing and reaction, understanding turbulence in vortex dynamics, models for the structure and dynamics of near-wall turbulence, complexity of turbulence near a wall, proper orthogonal decomposition, propagating structures in wall-bounded turbulence flows. Also discussed are: constitutive relation in compressible turbulence, compressible turbulence and shock waves, direct simulation of compressible turbulence in a shear flow, structural genesis in wall-bounded turbulence flows, vortex lattice structure of turbulent shear slows, etiology of shear layer vortices, trilinear coordinates in fluid mechanics.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: ; 615 p.
    Format: text
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  • 3
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    Modeling the dissipation rate in rotating turbulent flows (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A variety of modifications to the modeled dissipation rate transport equation that have been proposed during the past two decades to account for rotational strains are examined. The models are subjected to two crucial test cases: the decay of isotropic turbulence in a rotating frame and homogeneous shear flow in a rotating frame. It is demonstrated that these modifications do not yield substantially improved predictions for these two test cases and in many instances give rise to unphysical behavior. An alternative proposal, based on the use of the tensor dissipation rate, is made for the development of improved models.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-187485 , ICASE-90-88 , NAS 1.26:187485 , AD-A232079
    Format: application/pdf
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  • 4
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    An analysis of RNG based turbulence models for homogeneous shear flow (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: In a recent paper, the authors compared the performance of a variety of turbulence models including the k-epsilon model and the second-order closure model based on Renormalization Group (RNG) Methods. The performance of these RNG models in homogeneous turbulent shear flow was found to be quite poor, apparently due to the value of the constant C(sub epsilon1) in the modeled dissipation rate equation which was substantially lower than its traditional value. However, recently a correction has been made in the RNG based calculation of C(sub epsilon1). It is shown that with the new value of C(sub epsilon1), the performance of the RNG k-epsilon model is substantially improved. On the other hand, while the predictions of the revised RNG second-order closure model are better, some lingering problems still remain which can be easily remedied by the addition of higher order terms.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-187552 , NAS 1.26:187552 , ICASE-91-37 , AD-A236667
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  • 5
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    Modeling the pressure-strain correlation of turbulence: An invariant dynamical systems approach (1990)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The modeling of the pressure-strain correlation of turbulence is examined from a basic theoretical standpoint with a view toward developing improved second-order closure models. Invariance considerations along with elementary dynamical systems theory are used in the analysis of the standard hierarchy of closure models. In these commonly used models, the pressure-strain correlation is assumed to be a linear function of the mean velocity gradients with coefficients that depend algebraically on the anisotropy tensor. It is proven that for plane homogeneous turbulent flows the equilibrium structure of this hierarchy of models is encapsulated by a relatively simple model which is only quadratically nonlinear in the anisotropy tensor. This new quadratic model - the SSG model - is shown to outperform the Launder, Reece, and Rodi model (as well as more recent models that have a considerably more complex nonlinear structure) in a variety of homogeneous turbulent flows. Some deficiencies still remain for the description of rotating turbulent shear flows that are intrinsic to this general hierarchy of models and, hence, cannot be overcome by the mere introduction of more complex nonlinearities. It is thus argued that the recent trend of adding substantially more complex nonlinear terms containing the anisotropy tensor may be of questionable value in the modeling of the pressure-strain correlation. Possible alternative approaches are discussed briefly.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-181979 , NAS 1.26:181979 , ICASE-90-5 , AD-A227187
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  • 6
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    On the prediction of free turbulent jets with swirl using a quadratic pressure-strain model (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Data from free turbulent jets both with and without swirl are used to assess the performance of the pressure-strain model of Speziale, Sarkar and Gatski which is quadratic in the Reynolds stresses. Comparative predictions are also obtained with the two versions of the Launder, Reece and Rodi model which are linear in the same terms. All models are used as part of a complete second-order closure based on the solution of differential transport equations for each non-zero component of the Reynolds stress tensor together with an equation for the scalar energy dissipation rate. For non-swirling jets, the quadratic model underestimates the measured spreading rate of the plane jet but yields a better prediction for the axisymmetric case without resolving the plane jet/round jet anomaly. For the swirling axisymmetric jet, the same model accurately reproduces the effects of swirl on both the mean flow and the turbulence structure in sharp contrast with the linear models which yield results that are in serious error. The reasons for these differences are discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: NASA-CR-194964 , NAS 1.26:194964 , ICASE-94-70
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  • 7
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    Modeling the dissipation rate in rotating turbulent flows (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A variety of modifications to the modeled dissipation rate transport equation that have been proposed during the past two decades to account for rotational strains are examined. The models are subjected to two crucial test cases: the decay of isotropic turbulence in a rotating frame and homogeneous shear flow in a rotating frame. It is demonstrated that these modifications do not yield substantially improved predictions for these two test cases and in many instances give rise to unphysical behavior. An alternative proposal, based on the use of the tensor dissipation rate, is made for the development of improved models.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: In: Studies in turbulence (A94-12376 02-34); p. 129-151.
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  • 8
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    An alternative assessment of second-order closure models in turbulent shear flows (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The performance of three recently proposed second-order closure models is tested in benchmark turbulent shear flows. Both homogeneous shear flow and the log-layer of an equilibrium turbulent boundary layer are considered for this purpose. An objective analysis of the results leads to an assessment of these models that stands in contrast to that recently published by other authors. A variety of pitfalls in the formulation and testing of second-order closure models are uncovered by this analysis.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AD-A279072 , NASA-CR-194881 , ICASE-94-10 , NAS 1.26:194881
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  • 9
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    Glauber calculations of polarization of Lyman-alpha resulting from e/-/-H/1s/ collisions. (1972)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: We have calculated the polarization fraction of the Lyman-alpha radiation emitted in e/-/-H/1s/ collisions using the Glauber, Born, and various Vainshtein approximations, and have compared these predictions with observation. We find that the Born, Glauber and all forms of the Vainshtein yield results which are very close to each other and to the data in the energy range from 30 to 700 eV. The comparatively small differences between the various approximations are detailed in the text; also, the reason for the close agreement of the predicted polarization fractions - although the computed 1s-2p total and differential cross sections are not so close - is explained. With respect to the Glauber approximation, the importance of computing the phase integral along a direction perpendicular to the momentum transfer q at each value of q, is stressed.
    Keywords: PHYSICS, ATOMIC, MOLECULAR, AND NUCLEAR
    Type: Journal of Physics; vol. 5
    Format: text
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  • 10
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    Glauber amplitudes in charged particle hydrogen atom collisions (1971)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Glauber scattering amplitudes for atomic hydrogen excitation by electrons or protons, presenting closed form expressions requiring no numerical integration
    Keywords: PHYSICS, ATOMIC, MOLECULAR, AND NUCLEAR
    Type: ; - ASTRONOMY 1969- TE
    Format: text
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