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  • Articles  (10)
  • turbulence  (10)
  • 2020-2024
  • 2000-2004  (10)
  • Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics  (10)
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  • Articles  (10)
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  • 1
    Electronic Resource
    Electronic Resource
    Transportation of passive scalar in inhomogeneous turbulence (2000)
    Springer
    Acta mechanica Sinica 16 (2000), S. 21-28 
    Details
    ISSN: 1614-3116
    Keywords: turbulence ; passive scalar ; Large Eddy Simulation
    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 paper studies the transportation of passive scalar in the inhomogeneous turbulence by means of large eddy simulation. The prediction accuracy is verified by the well-known Comte-Bellot spectrum of the homogeneous turbulence. The mean transportation properties are predicted with satisfaction and the underestimation of the thermal flux by the phenomenological models has been disclosed. The high intermittence of the temperature fluctuations has been found in the inhomogeneous turbulence and it is the reason for the underestimation of turbulent thermal flux by the phenomenological model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02487938
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  • 2
    Electronic Resource
    Electronic Resource
    Approximate Wall Boundary Conditions in the Large-Eddy Simulation of High Reynolds Number Flow (2000)
    Springer
    Flow, turbulence and combustion 63 (2000), S. 269-291 
    Details
    ISSN: 1573-1987
    Keywords: turbulence ; large-eddy simulation ; wall models ; channel flow ; separation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The near-wall regions of high Reynolds numbers turbulent flows must be modelled to treat many practical engineering and aeronautical applications. In this review we examine results from simulations of both attached and separated flows on coarse grids in which the near-wall regions are not resolved and are instead represented by approximate wall boundary conditions. The simulations use the dynamic Smagorinsky subgrid-scale model and a second-order finite-difference method. Typical results are found to be mixed, with acceptable results found in many cases in the core of the flow far from the walls, provided there is adequate numerical resolution, but with poorer results generally found near the wall. Deficiencies in this approach are caused in part by both inaccuracies in subgrid-scale modelling and numerical errors in the low-order finite-difference method on coarse near-wall grids, which should be taken into account when constructing models and performing large-eddy simulation on coarse grids. A promising new method for developing wall models from optimal control theory is also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009958917113
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  • 3
    Electronic Resource
    Electronic Resource
    Detached-Eddy Simulations Past a Circular Cylinder (2000)
    Springer
    Flow, turbulence and combustion 63 (2000), S. 293-313 
    Details
    ISSN: 1573-1987
    Keywords: separation ; simulation ; cylinder ; turbulence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The flow is calculated with laminar separation (LS) at Reynolds numbers 50,000 and 140,000, and with turbulent separation (TS) at140,000 and 3 × 106. The TS cases are effectively tripped, but compared with untripped experiments at very high Reynolds numbers. The finest grid has about 18,000 points in each of 56 grid planes spanwise; the resolution is far removed from Direct Numerical Simulations, and the turbulence model controls the separation if turbulent. The agreement is quite good for drag, shedding frequency, pressure, and skin friction. However the comparison is obscured by large modulations of the vortex shedding and drag which are very similar to those seen in experiments but also, curiously, durably different between cases especially of the LS type. The longest simulations reach only about 50 shedding cycles. Disagreement with experimental Reynolds stresses reaches about 30%, and the length of the recirculation bubble is about double that measured. The discrepancies are discussed, as are the effects of grid refinement, Reynolds number, and a turbulence-model curvature correction. The finest grid does not give the very best agreement with experiment. The results add to the validation base of the Detached-Eddy Simulation (DES) technique for smooth-surface separation. Unsteady Reynolds-averaged simulations are much less accurate than DES for LS cases, but very close for TS cases. Cases with a more intricate relationship between transition and separation are left for future study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009901401183
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  • 4
    Electronic Resource
    Electronic Resource
    A Length-Scale Equation (2000)
    Springer
    Flow, turbulence and combustion 63 (2000), S. 1-21 
    Details
    ISSN: 1573-1987
    Keywords: turbulence ; RANS ; modeling ; length-scale
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We derive an equation for the average length-scale in a turbulent flow from a simple physical model. This is a tensorial length-scale. We use as a model the evolution of a blob of turbulent kinetic energy under the influence of production, dissipation, and transport, as well as distortion by the mean motion. A single length-scale is defined which is biased toward the smallest of the scales in the various directions. Constants are estimated by consideration of homogeneous decay. Preliminary computations are carried out in a mixing layer and a two-dimensional jet, using the new length-scale equation and the equation for the turbulent kinetic energy. The results are compared with data and with the predictions of the classical k-epsilon equations; the new results are quite satisfactory. In particular, the plane jet/round jet anomaly is approximately resolved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009957503000
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  • 5
    Electronic Resource
    Electronic Resource
    A Probability Density Function Method for Modelling Liquid Fuel Sprays (2000)
    Springer
    Flow, turbulence and combustion 63 (2000), S. 379-394 
    Details
    ISSN: 1573-1987
    Keywords: droplets ; fuel sprays ; combustion ; turbulence ; dispersion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A stochastic model is proposed for modelling the turbulent dispersion of liquid fuel sprays. The approach adopted is based on the evolution equation for the joint probability density function (PDF) of the droplet properties. Turbulent dispersion is described by Langevin's equation in which a Weiner process is used to represent the stochastic force term. The method leads to plausible results when applied to a kerosene spray flame and provides a rational framework for the incorporation of liquid film break up and droplet formation processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009984220148
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  • 6
    Electronic Resource
    Electronic Resource
    Reynolds Number Dependence of Velocity Structure Functions in a Turbulent Pipe Flow (2000)
    Springer
    Flow, turbulence and combustion 64 (2000), S. 95-117 
    Details
    ISSN: 1573-1987
    Keywords: turbulence ; Reynolds number ; pipe flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Low-order moments of the increments δu andδv where u and v are the axial and radial velocity fluctuations respectively, have been obtained using single and X-hot wires mainly on the axis of a fully developed pipe flow for different values of the Taylor microscale Reynolds numberR λ. The mean energy dissipation rate〉ε〈 was inferred from the uspectrum after the latter was corrected for the spatial resolution of the hot-wire probes. The corrected Kolmogorov-normalized second-order structure functions show a continuous evolution withR λ. In particular, the scaling exponentζ v , corresponding to the v structure function, continues to increase with R λ in contrast to the nearly unchanged value of ζ u . The Kolmogorov constant for δu shows a smaller rate of increase with R λ than that forδv. The level of agreement with local isotropy is examined in the context of the competing influences ofR λ and the mean shear. There is close but not perfect agreement between the present results on the pipe axis and those on the centreline of a fully developed channel flow.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009900120828
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  • 7
    Electronic Resource
    Electronic Resource
    Measurements of Vortex Shedding and Wake Decay Downstream of a Turbine Inlet Guide Vane (2000)
    Springer
    Flow, turbulence and combustion 64 (2000), S. 253-278 
    Details
    ISSN: 1573-1987
    Keywords: pneumatic probes ; hot wires ; secondary flows ; vortex shedding ; turbulence ; nozzle stage
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The flow in the second stage stator of a gas turbine with contoured end-wall is measured in a low speed wind tunnel. The investigation is focused on the flow in proximity to the blade trailing edge and in the wake. The measurements include mean velocity, total and static pressure at the cascade exit together with the analysis of intensity and spectral characteristic of turbulence. Measurements have been carried out using a miniaturized five-hole pneumatic probe developed in-house and a single hot wire anemometer on a measurement grid covering different distances from the blade trailing edge. The very fine measurement grids allow a detailed description of secondary flows and the possibility to trace the development of the vortex structures in the trailing edge region. The combined use of the pneumatic probe and of the hot-wire measurements allow to get a wide set of information on mean and turbulent characteristics of the three-dimensional flow at the exit of the cascade and identify the changes in the flow at different blade spans.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1026535810140
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  • 8
    Electronic Resource
    Electronic Resource
    Modeling Turbulent Droplet Motion in Vaporizing Sprays (2000)
    Springer
    Flow, turbulence and combustion 65 (2000), S. 1-29 
    Details
    ISSN: 1573-1987
    Keywords: turbulence ; spray ; model ; vaporization ; dispersion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The present article is concerned with the influence of turbulent gas-velocity fluctuations on both droplet dispersion and droplet-gas slip velocity in the context of spray simulation. The role of turbulence in generating slip and thus enhancing interphase heat and mass transfer has so far received little attention and is investigated in this work. A model for turbulent gas-velocity fluctuations along droplet trajectories is presented and is first tuned to reproduce elementary dispersion phenomena. It is then shown to give good results for more general dispersion problems as well as for slip velocities. As a fundamental source of information and for the purpose of model validation and comparison, direct numerical simulation (DNS) of droplet motion in homogeneous isotropic steady turbulence (HIST) is used. Dispersion of “injected” droplets (i.e. droplets under the influence of drift due to high injection velocity) as well as slip velocities for linear and nonlinear droplet drag are studied, and reasonable agreement is found with the model. The distributions of the slip velocity are found to be very similar for linear and highly nonlinear drag law. The present model is also used to investigate the influence of turbulence on droplet penetration. Comparison is made with an eddy-interaction model (the KIVA-2 model), which reveals various weaknesses of this model, in particular the underprediction of average slip velocity. The influence of slip due to turbulence on vaporization is shown for a fuel spray injected into a premix gas-turbine combustor. The classical eddy-interaction model is seen to underestimate the rate of vaporization due to the underprediction of slip.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009903802812
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  • 9
    Electronic Resource
    Electronic Resource
    Large-Eddy Simulation of a Turbulent Hydrogen Diffusion Flame (2000)
    Springer
    Flow, turbulence and combustion 65 (2000), S. 163-175 
    Details
    ISSN: 1573-1987
    Keywords: LES ; turbulence ; reacting flow ; diffusion flame ; time-stepping scheme
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In this work a large-eddy simulation (LES) of a turbulent hydrogen jet diffusion flame is presented. The numerical method handles fluctuations of density in space and in time, but assumes density to be independent of pressure (incompressibility). The chemical composition of the fluid is described by solving the filtered transport equation for mixture fraction f. Density, viscosity and temperature are evaluated assuming chemical equilibrium. To account for sub-grid fluctuations of f, its sub-grid distribution is presumed to have the shape of a β-function. The results of the simulation are discussed extensively. The influence of inlet boundary conditions is addressed and radial profiles at different axial positions are shown for a complete set of one-point statistical data. Agreement of numerical results and experimental data is very good. Furthermore, a comparison of Reynolds- and Favre-averages is done and energy spectra at different locations in the flame are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011497715385
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  • 10
    Electronic Resource
    Electronic Resource
    Mixing in Isotropic Turbulence with Scalar Injection and Applications to Subgrid Modeling (2000)
    Springer
    Flow, turbulence and combustion 65 (2000), S. 113-131 
    Details
    ISSN: 1573-1987
    Keywords: mixing ; turbulence ; probability density function ; subgrid-scale model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A new technique for injecting scalar fluctuations in a DNS of isotropic turbulence is presented. It is used to study statistically steady states associated with different levels of mixing. The results are analysed in terms of spectra and PDF, and they are used as a database to investigate the effect of the filtering operation that is performed in LES. It is shown that the PDF of the scalar is substantially affected by the filtering operation. It is also shown that the Cook and Riley [1] subgrid model allows reconstruction of a PDF which is in fairly good agreement with the unfiltered DNS results. The consequences of estimating the scalar subgrid variance by scale similarity assumptions are investigated. It is found that the results are improved by a local determination of the model constant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1011454026194
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