9 research outputs found
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Measurement and simulation of a droplet population in a turbulent flow field
The interaction of a disperse droplet population (spray) in a turbulent
flow field is studied by combining wind tunnel experiments with simulations
based on the model of a population balance system. The behavior of the
droplets is modeled numerically by a population balance equation. Velocities
of the air and of the droplets are determined by non-intrusive measurements.
A direct discretization of the 4D equation for the droplet size distribution
is used in the simulations. Important components of the numerical algorithm
are a variational multiscale method for turbulence modeling, an upwind scheme
for the 4D equation and a pre-processing approach to evaluate the aggretation
integrals. The simulations of this system accurately predict the
modifications of the droplet size distribution from the inlet to the outlet
of the measurement section. Since the employed configuration is simple and
considering that all measurement data are freely available thanks to an
Internet-based repository, the considered experiment is proposed as a
benchmark problem for the simulation of disperse two-phase turbulent flows
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Numerical methods for the simulation of an aggregation-driven droplet size distribution
A droplet size distribution in a turbulent flow field is considered and
modeled by means of a population balance system. This paper studies different
numerical methods for the 4D population balance equation and their impact on
an output of interest, the time-space-averaged droplet size distribution at
the outlet which is known from experiments. These methods include different
interpolations of the experimental data at the inlet, various discretizations
in time and space, and different schemes for computing the aggregation
integrals. It will be shown that notable changes in the output of interest
might occur. In addition, the efficiency of the studied methods is discussed
Numerical simulations and measurements of a droplet size distribution in a turbulent vortex street
A turbulent vortex street in an air flow interacting with a disperse droplet population is investigated in a wind tunnel.
Non-intrusive measurement techniques are
used to obtain data for the air velocity and the droplet velocity. The process is modeled
with a population balance system consisting of the incompressible Navier--Stokes equations
and a population balance equation for the droplet size distribution. Numerical simulations
are performed that rely
on a variational multiscale method for turbulent flows, a direct discretization of the
differential operator of the population balance equation, and a modern technique for the
evaluation of the coalescence integrals. After having calibrated two unknown model parameters,
a very good agreement of the experimental and numerical results can be observed.
Eine turbulente Wirbelstra\ss e in einer Luftstr\"omung mit einer dispergierten Tr\"opfchenpopulation
wird in einem Windkanal untersucht. Nichtintrusive Messtechniken werden verwendet, um Daten bez\"uglich
der Luft-- und Tr\"opfchengeschwindigkeiten zu gewinnen. Der zu Grunde liegende Prozess wird mit
einem Populationsbilanzsystem modelliert, welches aus den inkompressiblen Navier--Stokes--Gleichungen
und einer Populationsbilanzgleichung f\"ur die Tr\"opfchenverteilungsdichte besteht. Numerische Simulationen
werden durchgef\"uhrt, welche ein variationelle Mehrskalenmethode f\"ur turbulente Str\"omungen,
eine direkte Diskretisierung des Differentialoperators der Populationsbilanzgleichung und ein
modernes Verfahren zur Berechnung der Koaleszensintegrale verwenden. Nachdem zwei unbekannte
Modellparameter kalibriert worden sind, kann eine sehr gute Übereinstimmung der experimentellen
und numerischen Ergebnisse beobachtet werden
Numerical methods for the simulation of an aggregation-driven droplet size distribution
A droplet size distribution in a turbulent flow field is considered and modeled by means of a population balance system. This paper studies different numerical methods for the 4D population balance equation and their impact on an output of interest, the time-space-averaged droplet size distribution at the outlet which is known from experiments. These methods include different interpolations of the experimental data at the inlet, various discretizations in time and space, and different schemes for computing the aggregation integrals. It will be shown that notable changes in the output of interest might occur. In addition, the efficiency of the studied methods is discussed
Characterization of a genomic signature of pregnancy identified in the breast.
The objective of this study was to comprehensively compare the genomic profiles in the breast of parous and nulliparous postmenopausal women to identify genes that permanently change their expression following pregnancy. The study was designed as a two-phase approach. In the discovery phase, we compared breast genomic profiles of 37 parous with 18 nulliparous postmenopausal women. In the validation phase, confirmation of the genomic patterns observed in the discovery phase was sought in an independent set of 30 parous and 22 nulliparous postmenopausal women. RNA was hybridized to Affymetrix HG_U133 Plus 2.0 oligonucleotide arrays containing probes to 54,675 transcripts, scanned and the images analyzed using Affymetrix GCOS software. Surrogate variable analysis, logistic regression, and significance analysis of microarrays were used to identify statistically significant differences in expression of genes. The false discovery rate (FDR) approach was used to control for multiple comparisons. We found that 208 genes (305 probe sets) were differentially expressed between parous and nulliparous women in both discovery and validation phases of the study at an FDR of 10% and with at least a 1.25-fold change. These genes are involved in regulation of transcription, centrosome organization, RNA splicing, cell-cycle control, adhesion, and differentiation. The results provide initial evidence that full-term pregnancy induces long-term genomic changes in the breast. The genomic signature of pregnancy could be used as an intermediate marker to assess potential chemopreventive interventions with hormones mimicking the effects of pregnancy for prevention of breast cancer
Characterization of a genomic signature of pregnancy identified in the breast.
The objective of this study was to comprehensively compare the genomic profiles in the breast of parous and nulliparous postmenopausal women to identify genes that permanently change their expression following pregnancy. The study was designed as a two-phase approach. In the discovery phase, we compared breast genomic profiles of 37 parous with 18 nulliparous postmenopausal women. In the validation phase, confirmation of the genomic patterns observed in the discovery phase was sought in an independent set of 30 parous and 22 nulliparous postmenopausal women. RNA was hybridized to Affymetrix HG_U133 Plus 2.0 oligonucleotide arrays containing probes to 54,675 transcripts, scanned and the images analyzed using Affymetrix GCOS software. Surrogate variable analysis, logistic regression, and significance analysis of microarrays were used to identify statistically significant differences in expression of genes. The false discovery rate (FDR) approach was used to control for multiple comparisons. We found that 208 genes (305 probe sets) were differentially expressed between parous and nulliparous women in both discovery and validation phases of the study at an FDR of 10% and with at least a 1.25-fold change. These genes are involved in regulation of transcription, centrosome organization, RNA splicing, cell-cycle control, adhesion, and differentiation. The results provide initial evidence that full-term pregnancy induces long-term genomic changes in the breast. The genomic signature of pregnancy could be used as an intermediate marker to assess potential chemopreventive interventions with hormones mimicking the effects of pregnancy for prevention of breast cancer
Numerical methods for the simulation of a coalescence-driven droplet size distribution
The droplet size distribution in a turbulent flow field is considered and modeled by means of a population balance system. This paper studies different numerical methods for the 4D population balance equation and their impact on an output of interest, the time-space-averaged droplet size distribution at the outlet, which is known from experiments. These methods include different interpolations of the experimental data at the inlet, various discretizations in time and space, and different schemes for computing the coalescence integrals. It will be shown that noticeable changes in the output of interest might occur. In addition, the computational efficiency of the studied methods is discussed