ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    Scale-Invariance and Turbulence Models for Large-Eddy Simulation (2000)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Fluid Mechanics 32 (2000), S. 1-32 
    Details
    ISSN: 0066-4189
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Relationships between small and large scales of motion in turbulent flows are of much interest in large-eddy simulation of turbulence, in which small scales are not explicitly resolved and must be modeled. This paper reviews models that are based on scale-invariance properties of high-Reynolds-number turbulence in the inertial range. The review starts with the Smagorinsky model, but the focus is on dynamic and similarity subgrid models and on evaluating how well these models reproduce the true impact of the small scales on large-scale physics and how they perform in numerical simulations. Various criteria to evaluate the model performance are discussed, including the so-called a posteriori and a priori studies based on direct numerical simulation and experimental data. Issues are addressed mainly in the context of canonical, incompressible flows, but extensions to scalar-transport, compressible, and reacting flows are also mentioned. Other recent modeling approaches are briefly introduced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.fluid.32.1.1
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Generalized Smagorinsky model for anisotropic grids (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2306-2308 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Smagorinsky subgrid model is revised to properly account for grid anisotropy, using energy equilibrium considerations in isotropic turbulence. For moderate resolution anisotropies, Deardorff's estimate involving an equivalent grid scale Δeq=(Δ1Δ2Δ3)1/3 is given a rigorous basis. For more general grid anisotropies, the Smagorinsky eddy viscosity is recast as νT=[csΔeqf(a1, a2)]2||S˜||, where f(a1,a2) is a function of the grid aspect ratios a1 and a2, and ||S˜|| is the resolved strain rate magnitude. The asymptotic behavior of νT at several limits of the aspect ratios are examined. Approximation formulas are developed so that f(a1,a2) can easily be evaluated in practice, for arbitrary values of a1 and a2. It is argued that these results should be used in conjunction with the dynamic model of Germano et al. whenever the anisotropy of the test-filter differs significantly from that of the basic grid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858537
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Effects of small-scale turbulent motions on the filtered velocity gradient tensor as deduced from holographic particle image velocimetry measurements (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 14 (2002), S. 2456-2474 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of small-scale motions on the inertial range structure of turbulence are investigated by considering the dynamics of the velocity gradient tensor (A˜ij) filtered at scale Δ. In addition to self-interactions and the filtered pressure Hessian, the evolution of A˜ij is determined by the subgrid-scale stress tensor. As in the so-called restricted Euler dynamics, the evolution equations can be simplified by considering the invariants RΔ and QΔ of A˜ij. The effects of the subgrid-scale stress tensor on RΔ and QΔ can be quantified unambiguously by evaluating conditional averages that appear in the evolution equation for the joint probability distribution function of these invariants. The required conditional averages are computed from three-dimensional measurements of fully developed turbulence in a square duct, at Reτ(approximate)2360. The measurements are performed using holographic particle image velocimetry [Tao et al., Phys. Fluids 12, 941 (2000); Tao et al., J. Fluid Mech. 457, 35 (2002)]. The velocity distributions are spatially filtered in the inertial range using a box filter at about 30 Kolmogorov scales to separate large from small scales. The results show that the subgrid scale (SGS) stresses have significant effect on the evolution of filtered velocity gradients. In particular, along the so-called Vieillefosse tail at RΔ〉0 and QΔ〈0, they oppose the formation of a finite-time singularity that occurs in restricted Euler dynamics. Various other trends are quantified in different parts of the (RΔ,QΔ) plane. Included are the SGS dissipation rate of kinetic energy, and the effect of the SGS stress in modifying the so-called "discriminant," which is a conserved quantity in restricted Euler dynamics. A priori tests of the Smagorinsky, nonlinear, and mixed models show that all reproduce the real SGS stress effect along the Vieillefosse tail, but that they fail in several other regions. An attempt is made to optimize the mixed model by letting the two coefficients be functions of RΔ and QΔ. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1472506
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    Spatial correlations in turbulence: Predictions from the multifractal formalism and comparison with experiments (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 158-172 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Questions about applicability of multiplicative cascade models for turbulent small-scale intermittency (such as lognormal, random curdling, β, α, p models, etc.) are addressed by using the multifractal formalism to predict new properties of two-point moments. These predictions are compared with experimental data. Measurements are performed in the wake of a cylinder and grid turbulence. Data at high Reynolds number in the atmospheric surface layer are also considered. The autocorrelation function of the local singularity strength α(x), as well as mixed moments of the form 〈εr(x)qεr(x+s)−q(approximately-greater-than) are computed from the kinetic energy dissipation obtained from single-component, single-probe measurements using Taylor's hypothesis. For flows at high-enough Reynolds number, the α(x) autocorrelation function exhibits logarithmic decay with distance, as predicted from a random multiplicative cascade process. Some discrepancies exist in the quantitative details, implying enhanced randomization. The mixed moments are found to exhibit a scaling transition, also in agreement with the multiplicative models. The results illustrate the usefulness of the two-point multifractal formalism in characterizing intermittency and, as far as two-point statistics is concerned, lend further (qualified) support to the multiplicative cascade models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858801
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Statistics of filtered velocity in grid and wake turbulence (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 12 (2000), S. 1143-1165 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Data on spatially filtered turbulence are commonly needed for a priori sub-grid model studies and for a posteriori testing of large eddy simulation (LES) codes. In this paper, hot-wire anemometry is used to record very long records of such data, required for good convergence of high-order statistics. An array consisting of four X-wire probes placed transversal to the flow direction is built. Unlike previous single-probe hot-wire measurements, which only allowed stream-wise filtering using Taylor's hypothesis, the array permits cross-stream filtering as well. Measurements which are spatially filtered at a length-scale Δ pertaining to the inertial-range of turbulence are performed in grid and wake turbulence. The data can be used directly to compare with results from LES. From the data, fundamental differences between filtered and unfiltered velocity fields are examined through probability density functions and the scaling behavior of high-order structure functions. A comparative study of probability density functions of filtered and unfiltered velocity increments shows that the tails of the distributions are affected by the filtering even at scales much larger than the filter scale. Significant differences are also observed in regard to the scaling of structure functions. It is shown that extended self-similarity, a recent technique for measuring inertial range scaling exponents, yields questionable results when applied to structure functions of filtered velocity. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870368
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    Conditional subgrid force and dissipation in locally isotropic and rapidly strained turbulence (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 2317-2329 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Modeling of the small scales of turbulence for large eddy simulation (LES) requires a sound understanding of the relationships between large and small scales of motion. Conditional averaging allows us to isolate the effects of specific large-scale flow features in a statistically meaningful fashion. We study how regions of large-scale straining, rotation, and energy cascade rate affect SGS quantities of direct dynamical relevance for LES, namely the subgrid-scale (SGS) force (the divergence of the SGS stress tensor), and the SGS dissipation rate. Conditional averages are measured from experimental data in two flows: (i) the far field of a turbulent jet, and (ii) initially near-isotropic turbulence undergoing rapid axisymmetric expansion. These data are representative of near-equilibrium, locally isotropic turbulence, and of a nonisotropic, nonequilibrium turbulent flow, respectively. The separation between large and small scales is performed with a spatially compact box filter. Results for the locally isotropic data show that the SGS force surrounding points of large strain-rate magnitude is nearly radial. Due to the divergence-free condition of the velocity field, such SGS force can only affect the resolved pressure field. Being directed outwards, the SGS force decreases the resolved pressure in regions of high strain-rate magnitude. Similar results are obtained in regions of large resolved dissipation, defined as the energy flux into the smallest resolved band of scales. No effect of the resolved vorticity is found. In the rapidly distorted flow, the SGS force in regions of large positive resolved dissipation is found to affect both the resolved pressure (again decreasing it) and the resolved velocity (the SGS motions oppose the mean deformation). Regions of large negative resolved dissipation (backscatter) exhibit the opposite effect, acting in such a way as to favor the mean deformation. The mixed model is shown to provide better predictions of conditional SGS dissipation than the Smagorinksy or the similarity models alone. However, observed discrepancies in the conditional SGS force imply the need for further model improvements. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870094
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    Comment on "Is intermittent motion of outer flow in the turbulent boundary layer deterministic chaos?'' [Phys. Fluids A 3, 1941 (1991)] (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 1587-1588 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recently, Tsuji et al. [Phys. Fluids A 3, 1941 (1991)] presented measurements of the probability density of sizes of laminar regions in the upper portion of a turbulent boundary layer. This size distribution was shown to have a power-law decay exponent close to −4/3, and it was shown that certain one-dimensional chaotic maps have the same property. Here, it is argued that the experimental observations can also be explained by two different paradigms for the interface separating turbulent from irrotational fluid. The first is that of a globally self-similar fractal surface of Hausdorff dimension DH=7/3. The second is that of a power-law spiral sheet with a box dimension of the same value. Both are consistent with other experimental evidence to date, as well as with the Kolmogorov scaling of turbulent velocity fluctuations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858432
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    On the Lagrangian nature of the turbulence energy cascade (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 2820-2825 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spatial and temporal evolution of turbulence kinetic energy at different scales is studied using direct numerical simulations of isotropic turbulence. To explicitly follow the energy during the cascade process in physical space, a Lagrangian correlation coefficient between local kinetic energy at different scales is computed. This correlation is found to peak only after a Lagrangian time delay that is an increasing function of the scale separation. It is shown that a characteristic length reduction of a factor of 2 is achieved approximately after the local eddy-turnover time scale. The results show that the view of spatially localized eddy structures transferring their kinetic energy to smaller scales appears to be, on average, quite realistic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868170
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Geometry and scale relationships in high Reynolds number turbulence determined from three-dimensional holographic velocimetry (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 12 (2000), S. 941-944 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Holographic particle image velocimetry measurements of a fully developed turbulent flow in a square duct (ReH=v¯cH/ν=1.2×105, η=100 μm, Reλ=310) are used for examining the relative alignment between filtered vorticity, strain-rate and subgrid-scale stress tensors. Similar to DNS and previous measurements, the filtered vorticity has a preferred alignment with the intermediate strain-rate eigendirection. Contrary to typical eddy viscosity models, the most compressive strain-rate and most extensive subgrid-scale stress eigendirections have a strongly preferred relative orientation of 34°. The orientations of the other eigendirections are less deterministic and more complex. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870348
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    Intermittency and relative scaling of subgrid-scale energy dissipation in isotropic turbulence (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 928-937 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The rate at which large-scale kinetic energy in turbulent flows is transferred to, or from, unresolved scales (smaller than a filter scale Δ) is given by Π(x,t)=−τijS˜ij, where τij is the subgrid stress, and S˜ij is the resolved strain-rate tensor. The spatial distribution of Π(x,t) is computed from DNS of isotropic turbulence, and is found to be highly intermittent with increasing levels of intermittency as the filter size decreases. Relative scaling exponents of high-order moments of Π are measured using extended self-similarity, and are compared to those of longitudinal velocity structure functions. Reasonably good agreement is found, both sets of exponents clearly departing from the Kolmogorov (1941) theory. Relative scaling exponents of the SGS dissipation as predicted by several models are measured a priori from the DNS, and are compared to those of the true dissipation. We find the constant and spectral eddy viscosity models to be significantly less intermittent, and the local dynamic model to be much more intermittent than the true SGS dissipation field. The traditional and volume-averaged dynamic Smagorinsky models, together with the similarity model, yield more realistic levels of intermittency. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869615
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...