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11.
Klaus Hoyer Markus Holzner Beat Lüthi Michele Guala Alexander Liberzon Wolfgang Kinzelbach 《Experiments in fluids》2005,39(5):923-934
In this article, we present an experimental setup and data processing schemes for 3D scanning particle tracking velocimetry
(SPTV), which expands on the classical 3D particle tracking velocimetry (PTV) through changes in the illumination, image acquisition
and analysis. 3D PTV is a flexible flow measurement technique based on the processing of stereoscopic images of flow tracer
particles. The technique allows obtaining Lagrangian flow information directly from measured 3D trajectories of individual
particles. While for a classical PTV the entire region of interest is simultaneously illuminated and recorded, in SPTV the
flow field is recorded by sequential tomographic high-speed imaging of the region of interest. The advantage of the presented
method is a considerable increase in maximum feasible seeding density. Results are shown for an experiment in homogenous turbulence
and compared with PTV. SPTV yielded an average 3,500 tracked particles per time step, which implies a significant enhancement
of the spatial resolution for Lagrangian flow measurements. 相似文献
12.
We derive a large scale mixing parameter for a displacement process of one fluid by another immiscible one in a two-dimensional heterogeneous porous medium. The mixing of the displacing fluid saturation due to the heterogeneities of the permeabilities is captured by a dispersive flux term in the large scale homogeneous flow equation. By making use of the stochastic approach we develop a definition of the dispersion coefficient and apply a Eulerian perturbation theory to determine explicit results to second order in the fluctuations of the total velocity. We apply this method to a uniform flow configuration as well as to a radial one. The dispersion coefficient is found to depend on the mean total velocity and can therefore be time varying. The results are compared to numerical multi-realization calculations. We found that the use of single phase flow stochastics cannot capture all phenomena observed in the numerical simulations. 相似文献
13.
From laboratory experiments it is known that bacterial biomass is able to influence the hydraulic properties of saturated porous media, an effect called bioclogging. To interpret the observations of these experiments and to predict possible bioclogging effects on the field scale it is necessary to use transport models, which are able to include bioclogging. For these models it is necessary to know the relation between the amount of biomass and the hydraulic conductivity of the porous medium. Usually these relations were determined using bundles of parallel pore channels and do not account for interconnections between the pores in more than one dimension. The present study uses two-dimensional pore network models to study the effects of bioclogging on the pore scale. Numerical simulations were done for two different scenarios of the growth of biomass in the pores. Scenario 1 assumes microbial growth in discrete colonies clogging particular pores completely. Scenario 2 assumes microbial growth as a biofilm growing on the wall of each pore. In both scenarios the hydraulic conductivity was reduced by at least two orders of magnitude, but for the colony scenario much less biomass was needed to get a maximal clogging effect and a better agreement with previously published experimental data could be found. For both scenarios it was shown that heterogeneous pore networks could be clogged with less biomass than more homogeneous ones. 相似文献
14.
H. Horner D. Bormann M. Frick H. Kinzelbach A. Schmidt 《Zeitschrift für Physik B Condensed Matter》1989,76(3):381-398
Approximate dynamic mean field equations for a generalized Hopfield model are derived, which allow to calculate transient properties of this model. These equations are exact for short times and yield the replica symmetric solution as a stationary solution. They allow reliable computation of retrieval trajectories and basins of attraction of retrieval states, as demonstrated by comparison with simulations. The equations are derived for networks with arbitrary mean activity and results are given for the standard model and for low activities. 相似文献
15.
An optical method is presented to measure simultaneously and separately the velocity field of both phases in particle-laden
flows. The fluid is seeded with flow markers which are fluorescent at a specific wavelength and thus can be distinguished
from the sediment particles by applying an optical filter. The motion of each phase is recorded by two CCD cameras, which
are triggered such that a high correlation between subsequent images is guaranteed. The velocity fields are determined by
means of least-square matching of a group of particles. The whole set-up was applied to study the sedimentation of particles
through a rapidly evolving mixing layer.
Received: 14 June 1999/Accepted: 15 January 2000 相似文献
16.
Matthias Kinzel Markus Holzner Beat Lüthi Cameron Tropea Wolfgang Kinzelbach Martin Oberlack 《Experiments in fluids》2009,47(4-5):801-809
From Lie-group (symmetry) analysis of the multi-point correlation equation Oberlack and Günther (Fluid Dyn Res 33:453–476, 2003) found three different solutions for the behavior of shear-free turbulence: (i) a diffusion like solution, in which turbulence diffuses freely into the adjacent calm fluid, (ii) a deceleration wave like solution when there is an upper bound for the integral length scale and (iii) a finite domain solution for the case when rotation is applied to the system. This paper deals with the experimental validation of the theory. We use an oscillating grid to generate turbulence in a water tank and Particle Image Velocimetry (PIV) to determine the two-dimensional velocity and out-of-plane vorticity components. The whole setup is placed on a rotating table. After the forcing is initiated, a turbulent layer develops which is separated from the initially irrotational fluid by a sharp interface, the so-called turbulent/non-turbulent interface (TNTI). The turbulent region grows in time through entrainment of surrounding fluid. We measure the propagation of the TNTI and find quantitative agreement with the predicted spreading laws for case one and two. For case three (system rotation), we observe that there is a sharp transition between a 3D turbulent flow close to the source of energy and a more 2D-like wavy flow further away. We measure that the separation depth becomes constant and in this sense, we confirm the theoretical finite domain solution. 相似文献