Impinging jet simulations using a multi-field approach with free surface detection


Impinging jet simulations using a multi-field approach with free surface detection

Hänsch, S.; Lucas, D.; Krepper, E.; Höhne, T.; Danciu, D.-V.

The calculation of impinging liquid jets and the associated bubble entrainment is a challenging problem in two-fluid model applications. The various mechanisms behind these phenomena are not well understood and a better appreciation of them is vitally important for industrial and scientific issues. The difficulty of simulation arises from the fact that impinging jets show a mixture of both segregated and dispersed flow regimes. Therefore they demand a multi-fluid simulation to capture larger gas structures with resolved interfaces as well as many small bubbles of different sizes that require an averaged treatment. In order to deal with the complexity of these mechanisms a new CMFD-strategy of a generalized two-phase flow (GENTOP) is presented.
Currently, the GENTOP-concept combines a three-field simulation with the recently developed inhomogeneous Multiple Size Group (MUSIG)-approach. The flow is represented by a liquid phase, a polydispersed gas phase, containing different bubble size groups, and a continuous gas phase. Within the MUSIG-framework, transfers between the different bubble size groups due to bubble coalescence and -breakup are described. By modelling an additional mass transfer between the continuous and the polydispersed gas phase, transitions between different gas morphologies can be considered. The continuous gas phase summarizes all gas structures larger than a certain bubble diameter so that for these structures the gas-liquid interfaces are resolved. In order to blend the gaseous morphology basic ideas of the Algebraic Interfacial Area Density (AIAD)-model are used. Generalized formulations for interfacial area density and drag are introduced considering free surfaces within a multi-fluid simulation. This new concept can provide more detailed information about complex flow situations with higher gas fractions such as the impinging jet being just one particular application.
First results computed by the CFD-code CFX 13.0 are compared to experiments carried out at the HZDR and empirical correlations from literature. The flow field is adapted to the experiments considering inlet velocity of the jet v0=1.7m/s, jet length Lj=10mm and jet diameter d0=16mm as well as the dimensions of the water tank. The computational results show good qualitative agreement with the experiments regarding typical continuous and polydispersed gas structures. The values of air entrainment rate and bubble plume length are determined as quantitative values characterizing the results. Further developments consist of new generalized closure models for bubble coalescence and –breakup processes between continuous and dispersed gas phases.

Keywords: turbulent impinging jet; air entrainment; CMFD; gas-liquid interface; MUSIG-model; AIAD-model

  • Contribution to proceedings
    International Symposium on Multiphase Flow and Transport Phenomena, 22.-25.04.2012, Agadir, Marokko
  • Lecture (Conference)
    International Symposium on Multiphase Flow and Transport Phenomena, 22.-25.04.2012, Agadir, Marokko

Permalink: https://www.hzdr.de/publications/Publ-16805
Publ.-Id: 16805