Modeling of collisional transport processes in spray dynamics

  • Modellierung kollisionsinduzierter Transportprozesse in dispersen Sprühstrahlen

Pischke, Philipp; Kneer, Reinhold (Thesis advisor)

Aachen (2014)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2014

Abstract

Liquid sprays are governed by a multitude of fluid- and thermodynamic transport processes between the liquid droplets and the continuous gas phase. At the phase boundary, interfacial transport processes lead to liquid atomization, droplet deformation and breakup, turbulent dispersion and modulation, air entrainment and vaporization into the gas phase. Within the disperse phase, droplet collisions make a major contribution to momentum transport and energy dissipation, and interfere with spray dynamics to great extent. Numerical simulations of disperse multiphase flows are based on sub-models for all significant transport processes. For collisional transport processes within the disperse phase, various collision algorithms and models have been developed, which predict collision incidents and the collision outcomes. However, existing algorithms are restricted to isotropic flows with small velocity gradients, which are not found in typical applications such as high-velocity engine sprays. To describe collisional transport processes under such conditions, a new collision algorithm has been derived in the present work, which accounts for anisotropic droplet dispersions and velocity gradients in the disperse phase, and increases the order of accuracy significantly over benchmark collision algorithms. The new algorithm is validated by synthetic validation cases, and tested with exemplary simulations of turbulent engine sprays. The simulations give an insight into the physics of collisional transport processes and their contribution to spray dynamics.

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