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  • 1
    Monograph available for loan
    Monograph available for loan
    Turbulence in fluids (1997)
    Dordrecht [u.a.] : Kluwer Academic Publishers
    Associated volumes
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    Call number: M 98.0158
    In: Fluid mechanics and its applications
    Type of Medium: Monograph available for loan
    Pages: xvi, 515 S.
    Edition: 3., rev. and enl. ed.
    ISBN: 0792344162
    Series Statement: Fluid mechanics and its applications vol. 40
    Classification:
    C.3.7.
    Language: English
    Location: Upper compact magazine
    Branch Library: GFZ Library
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  • 2
    Electronic Resource
    Electronic Resource
    Large- and small-scale stirring of vorticity and passive scalar in a 3-D temporal mixing layer (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 1451-1451 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigate, with the aid of a three-dimensional direct-numerical simulation at high resolution, the origin and topology of the longitudinal vortex filaments which appear in the temporally growing mixing layer. The basic velocity field is a hyperbolic-tangent profile U tanh(2y/δi), with a Reynolds number of Uδi/ν =100. The calculation uses pseudospectral methods, and is carried out at a resolution of 1283 grid points in a cubic box of size L containing four fundamental most-amplified wavelengths (L=4λa). The initial velocity field is the basic velocity, upon which is superposed a three-dimensional Gaussian perturbation of wide spectrum, peaking at ka=1/2πλa, with kinetic energy equal to 10−4U2, modulated by a Gaussian exp[−(y/δi)2] in the transverse direction. A passive-scalar transport equation is solved as well, with the same initial profile as the basic velocity profile. Isosurfaces of the passive scalar and three vorticity components are visualized, permitting the 3-D vortex structure of the flows to be revealed.Because of the initial spanwise decorrelation of the perturbation phase, the fundamental spanwise vortices that appear have strong spanwise oscillations which are not in phase, and hence cannot be interpreted in terms of the translative instability investigated by Pierrehumbert and Widnall.1 Pairings between the primary vortices exhibit the same spanwise decorrelation, and reconnections of the billows occur. Visualizations also show the generation of thin longitudinal vortices from the regions of reconnection. The vortex lines at the same moment indicate that the thin longitudinal vortices result from an intense longitudinal stretching of the spanwise vortex line when it is severely twisted in the reconnection region. Reconnected Kelvin–Helmholtz billows give rise to a three-dimensional Λ-shaped structure of the passive scalar. This behavior is in agreement with the theory developed by Lesieur et al., where it was proposed that the large-scale three-dimensionality of the temporal mixing layer perturbed randomly was governed by two-dimensional turbulence unpredictability mechanisms. It might explain the experimental findings of Breidenthal2 and Bernal and Roshko3 concerning a spatially-growing, unforced mixing layer. Notice also that the thin longitudinal filaments forming in our calculation do not seem to be explained by the mechanism proposed by Lasheras and Choi,4 where they originate from the straining by the big rollers of a spanwise vortex filament perturbed about the stagnation line.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858038
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  • 3
    Electronic Resource
    Electronic Resource
    Stabilizing and destabilizing effects of a solid-body rotation on quasi-two-dimensional shear layers (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 403-407 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of a solid-body rotation, characterized by an angular velocity Ω, on a two-dimensional mixing layer (in a plane perpendicular to Ω) of relative vorticity ω2D, upon which is superposed a small three-dimensional turbulent perturbation, is considered. Using the Kelvin theorem in the frame rotating with Ω, and with the aid of arguments based on the straining of absolute vortex filaments by the basic velocity, it is shown that the rotation is always stabilizing (with respect to the nonrotating case) in the cyclonic case. In the anticyclonic case, a slight rotation is destabilizing. At a local Rossby number R0=||ω2D||/2||Ω|| of the order of 1, the anticyclonic rotation disrupts catastrophically the coherent structures of the mixing layer. Anticyclonic rotation becomes stabilizing again for R0〈0.5. Also presented are three-dimensional numerical simulations which support the theory, and agree qualitatively with experimental results. The consequences for oceanic and atmospheric vortices are briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858149
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  • 4
    Electronic Resource
    Electronic Resource
    The decay of kinetic energy and temperature variance in three-dimensional isotropic turbulence (1987)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 30 (1987), S. 1278-1286 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: With the aid of the eddy-damped quasinormal Markovian statistical theory (EDQNM) developed by Orszag [J. Fluid Mech. 41, 363 (1970)], the dynamics of a passive scalar (such as the temperature in a slightly heated flow) in three-dimensional isotropic turbulence is studied. Starting initially with kinetic energy and temperature spectra exponentially decreasing above a wavenumber ki, it is shown that in the limit of zero viscosity (ν→0) and conductivity (κ→0) the temperature gradient variance diverges at a finite critical time tc, together with the enstrophy. After tc, the kinetic energy and temperature variance are dissipated at finite rates that are independent of ν and κ if both are small. Afterward, the decay laws of the temperature variance and the wavenumber kθ characteristic of the temperature spectrum maximum are determined analytically when the temperature is initially injected at kθ(very-much-greater-than)ki. First, a Richardson law for the temperature integral scale is demonstrated without any assumption on the low k behavior of the temperature spectrum. Second, it is shown that kθ(t) rapidly catches up with ki(t), which explains some "anomalous'' temperature decay behavior, as observed experimentally by Warhaft and Lumley [J. Fluid Mech. 88, 659 (1978)]. The analytical analysis of the latter phenomenon generalizes, for an arbitrary infrared temperature spectrum, an earlier study of Nelkin and Kerr [Phys. Fluids 24, 1754 (1981)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866295
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  • 5
    Electronic Resource
    Electronic Resource
    Large-eddy simulation of passive scalar diffusion in isotropic turbulence (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 718-722 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A spectral large-eddy simulation of the velocity and passive temperature fields in three-dimensional isotropic turbulence is developed at high Reynolds numbers and a Prandtl number of the order of 1. The temperature spectrum in the large scales is shown to develop a range of the form ET(k)(approximate)0.1η[〈u2〉/ε]k−1, where ε and η are the kinetic energy and temperature variance dissipation rates, respectively. This range, which is a result of shearing by large scale velocity gradients, is followed by a k−5/3 inertial-convective range at higher wavenumbers. The temperature variance decays much faster in time than the kinetic energy. Finally, the spectral eddy conductivity rises logarithmically with k toward small wavenumbers, contrary to the eddy viscosity that displays a plateau.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.857365
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  • 6
    Electronic Resource
    Electronic Resource
    Large- and small-scale stirring of vorticity and a passive scalar in a 3-D temporal mixing layer (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2761-2778 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: With the aid of a three-dimensional direct-numerical simulation (using pseudospectral methods) at high resolution (1283 grid points in a cubic box containing four fundamental longitudinal wavelengths), the origin and topology of the longitudinal vortex filaments which appear in the temporally growing mixing layer are investigated. The basic velocity field is a hyperbolic-tangent profile U tanh 2y/δi, with a Reynolds number Uδi/ν=100. The basic flow is forced initially by two small Gaussian random perturbations: a three-dimensional one, of kinetic energy ε3D U2, and a two-dimensional one, of kinetic energy ε2D U2. For ε2D=10−4 and ε3D=10−5, quasi-two-dimensional large coherent Kelvin–Helmholtz rolls form and merge. Because of unstable oblique modes, they oscillate slightly as in the translative instability proposed by Pierrehumbert and Widnall [J. Fluid Mech. 114, 59 (1982)], but not exactly in phase. Between these big rollers, weak vortex lines are stretched. For ε2D=0 and ε3D=10−4 the oblique modes observed in the previous case yield local roll-ups and pairings occurring in certains regions of the span only, giving rise to a large-scale vortex lattice similar to that observed by Nygaard and Glezer in forced experiments [Phys. Fluids A 2, 461 (1990)]. This is numerical evidence of Pierrehumbert and Widnall's helical-pairing instability. Furthermore, a thin and intense streamwise hairpin vortex appears, stretched in between the large vortices of the lattice. A low Reynolds number counterpart of the mixing transition occurs during the second pairing, characterized by short k−5/3 subranges in the spectra, intense vorticity extrema, and intermittent distributions of local helicity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858334
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  • 7
    Electronic Resource
    Electronic Resource
    Infrared pressure spectra in two- and three-dimensional isotropic incompressible turbulence (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 1535-1543 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We show, using a quasinormal or Eddy Damped Quasinormal Markovianised (EDQNM) approximation to evaluate fourth-order velocity correlations in Fourier space, that the pressure spectrum in three-dimensional isotropic incompressible turbulence is proportional to k2 in the limit k→0. This result is independent of both the infrared kinetic-energy spectrum and Reynolds number. Afterwards, direct numerical simulations and large-eddy simulations (LES) of decaying isotropic turbulence are performed: they agree with this prediction, and show a fast pressure-spectrum decay in this range. LES predict an asymptotic collapse of the infrared pressure spectrum as Epp(k,t)(approximate)0.3∫0kC[E2(q,t)/q2]dqk2, where E(k,t) is the kinetic-energy spectrum. This permits us to predict theoretically that the pressure variance is exactly proportional to the squared kinetic energy, which we check numerically. The same QN/EDQNM analysis carried out in two dimensions predicts pressure spectra slopes of k, k−7/3, and k−5 in the infrared, inverse energy-cascade (in case of forcing), and enstrophy-cascade ranges, respectively. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870016
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  • 8
    Electronic Resource
    Electronic Resource
    Satellite-sensed turbulent ocean structure (1981)
    [s.l.] : Nature Publishing Group
    Nature 294 (1981), S. 673-673 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] RECENTLY Gower et al1 have reported interesting results concerning the concentration of phytoplankton as measured by the Landsat multispectral scanner on 19 June 1976 in a region south of Iceland. The observed concentration fluctuation spectra is found to follow approximately a k-2.92 law, close to ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/294673a0
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  • 9
    Electronic Resource
    Electronic Resource
    Understanding coherent vortices through computational fluid dynamics (1993)
    Springer
    Theoretical and computational fluid dynamics 5 (1993), S. 177-193 
    Details
    ISSN: 1432-2250
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A new definition of coherent vortices in turbulence is proposed, where the vorticity equation reduces to a cyclostrophic balance. Afterward, we describe five fundamental vortex interactions, the sheet, the spiral, the pairing, the even longitudinal, and the odd longitudinal modes. Numerous examples of these interactions are provided from direct numerical or large-eddy simulations. The resulting vortices are responsible for the internal intermittent character of turbulence, with highly nongaussian tails for the probability density functions of vorticity, passive scalar, and low pressure. In a mixing layer, the combination of the odd longitudinal and the pairing modes (helical pairing) is inhibited by compressibility, above a convective Mach number of ≈0.7. When turbulence is submitted to a solid-body rotation, anticyclonic vortices of local Rossby number of the order of 1 transform into intense perpendicular Görtler-type alternate longitudinal vortices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00271657
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  • 10
    Electronic Resource
    Electronic Resource
    Direct and large-eddy simulations of transition in the compressible boundary layer (1992)
    Springer
    Theoretical and computational fluid dynamics 3 (1992), S. 231-252 
    Details
    ISSN: 1432-2250
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The transition to turbulence in the three-dimensional compressible boundary layer over a semi-infinite insulated flat plate is studied by means of direct and large-eddy simulations. Results are presented in the quasi-incompressible (Mach number equal to 0.5) and high supersonic (Mach number equal to 5) cases, both in temporal and spatial configurations. Simulations of controlled transition, in which a two-dimensional wave corresponding to the primary instability is introduced at the initial stage, allows us to study the secondary instability of the flow. The latter is triggered with the aid of a three-dimensional white-noise perturbation of small amplitude superposed upon the wave. At a low Mach number, a direct-numerical simulation shows that the fundamental mode is selected, leading to the peak-valley structure found by Klebanoff et al. (1962). The complete transition process is then studied, with emphasis on vortex-filament dynamics. It is shown that the development to turbulence is well simulated, at least for the prediction of average quantities of the flow. In the high Mach number case, no direct-numerical simulation is possible, and we use a subgrid-scale model, the structure-function model, in order to perform a large-eddy simulation of the transition. In this case, the subharmonic mode appears, giving rise to a staggered pattern of ∧ vortices. These vortices, which affect the whole thickness of the boundary layer, are more elongated than in the incompressible case.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00417915
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