CMFF18

This volume of Technische Mechanik contains selected papers presented at CMFF18, the 17th event of the international conference series on fluid flow technologies now called Conference on Modelling Fluid Flow. This conference took place in Budapest between Sept. 4th and Sept. 7th, 2018, with more than 120 participants from over 25 countries. The next conference is scheduled for September 2021. Please bookmark http://www.cmff.hu if you want to be kept informed. As reflected in its title, this conference covers many fields of fluid mechanics. Key results from theoretical, numerical, as well as experimental studies have been presented in Budapest, with some of the most significant papers being invited to special issues. Articles dealing with turbomachines are being published separately in the International Journal of Turbomachinery, Propulsion and Power. The present special issue covers the following topics: Complex fluids Turbulence Multiphase flows Flows with heat transfer Reacting flows We hope that you enjoy reading the content! Dominique Thévenin, János Vad, Csaba Horváth, and Gábor Janig

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

Impact of Flow Conditions and Geometrical Parameters on the Separation of Two Immiscible Liquids in Helical Pipes

The separation of two immiscible liquids was studied in helical pipes with different flow and geometrical conditions. The main objective is to investigate the impact of the geometrical dimensions on the phase separation in helical pipes. The Volume Of Fluid (VOF) method was used to model the two-phase flow. The separation performance was quantified and compared using the average mixing coefficient of the two liquids. A perfect mixture of two liquids (water and amine) was always assumed at the inlet. Comparing different flow orientations, proper separation could only be obtained when the helical pipe is oriented horizontally. A laminar flow at the optimal range of Reynolds number for separation was considered (approximately Re = 225-563), where Re = 225 leads to a slightly better separation. The three key geometrical dimensions of helical pipes; the coil pitch, the pipe diameter, and the coil diameter were studied within the ranges of 16-60 mm, 5-15 mm, and 70-150 mm, respectively. The results show that changing the coil pitch has no significant effect on the separation behavior, while high enough pipe and coil diameters are needed to preserve an efficient separation of immiscible liquids and easier extraction of the lighter phase

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