ISBN 9783843917223

978-3-8439-1722-3, Reihe Thermodynamik

Chengxiang Zhu
Numerical Investigation on the Instability and the Primary Breakup of Inelastic Non-Newtonian Liquid Jets

129 Seiten, Dissertation Universität Stuttgart (2014), Softcover, A5

Zusammenfassung / Abstract

The present numerical work gives a first deep insight into the primary breakup of non-Newtonian shear thinning liquid jets to address the need for a more complete understanding of jet flows. Direct numerical simulations on the primary breakup of non-Newtonian fluids are carried out. The flow structure and the surface behavior of the jet are studied in detail. Vortex structures in the jet caused by the inflow turbulence can be observed clearly, indicating complex flow patterns of the jet. The shear thinning behavior of the viscosity and correspondingly the local Ohnesorge number are analyzed in particular. Additionally, a specific shear thinning breakup mechanism, the cavity breakup, is detected which gives a novel perspective for the analysis of jet disintegration.

The range of the investigated nondimensional quantities covers: Reynolds number: 492~1312, Weber number: 5867~41719 and Ohnesorge number: 0.1557. Three different destabilizing factors are considered, to see their influence on the breakup of non-Newtonian liquid jets. The first destabilizing factor studied in this work is the velocity profile. Three different nozzle configurations are applied to generate various inlet velocity profiles. The corresponding jet structure and non-Newtonian characteristics are compared and analyzed. In particular, the breakup regime of liquid jets is discussed based on local nondimensional quantities.

The second destabilizing factor considered is the inlet Reynolds number. Emphasis is put on the shear behavior and the non-Newtonian characteristics. Shear rates and the liquid viscosity for selected cross sections are analyzed. With increasing Reynolds number, the arithmetic mean value of the viscosity decreases. And within the range of the Reynolds number in the present work, the mean viscosity of the liquid varies over 17%.

The influence of the inflow turbulence is studied from two aspects: the turbulence intensity and the turbulent length scale. In the intensity part, development of the gas shear layer and the jet tip head are discussed. The temporal evolution of the maximum gas Weber number, the spatial and temporal development of surface waves are studied as well. In the section about the turbulent length scale, the 3D jet structure, the surface behavior and the surface area are compared. Analysis on the distribution of the shear thinning viscosity and correspondingly on the non-Newtonian characteristics are also provided.