Multiscale Modeling and Simulation

Anastasia Bukhvostova is a PhD student in the Multiscale Modeling and Simulation group in the Department of Applied Mathematics at the University of Twente. She is working under the supervision of Prof.dr.ir. Bernard J. Geurts and Prof.dr. J.G.M. Kuerten. She got her Master degree at Moscow state University (Russia) in 2011.

Her project focuses on droplets in turbulence; the main aim is to investigate the natural droplet-size distribution that arises from phase transitions, i.e., evaporation and condensation, and from droplet collisions and coalescence along their flight-paths. The central new ingredient of this research is that particles have not only dynamical characteristics but also internal properties such as temperature and mass. These properties are fully coupled to the turbulent flow, and may alter their dynamic response.

The project combines mathematical and physical modeling with large-scale high-performance computing and is part of the FOM program 'Droplets in Turbulence'.

Organization:

Funded by: FOM

PhD: Anastasia Bukhvostova

Supervisor: Bernard Geurts & Hans kuerten

Collaboration:

Multiphase flows in which a large number of small droplets is dispersed in
a gas, play an important role in variety of technological applications- thermal
processing in food manufacturing, air pollution control, energy conversion
industry. Heat conductivity of droplets and phase transition will affect the
heat transfer of the flow, that is widely applied in turbulent spray cooling.

We examine the effect of two-way coupling and phase-transition on Nusselt
number and droplets’ concentration within turbulent channel flow. Nusselt
number shows the influence of droplets on the heat transfer of the whole
mixture, while the concentration of the droplets refers to the effect of
turbophoresis. Turbophoresis is the effect of migration of the particles in the
particle-laden turbulent channel flow to the areas of decreasing turbulence
level.

Mathematical model

The carrier phase is considered to be compressible and Newtonian fluid. The
compressibility assumption becomes very important in case phase transitions are
taken into consideration. In fact, if the carrier phase is assumed to be
strictly incompressible then the inclusion of evaporation and condensation is
subject to the condition that all instantaneous changes in the local
mass-density of air and water vapor cancel each other precisely throughout the
domain. In this project the incompressible model is complemented by a fully
compressible description, which allows to quantify the consequences of
non-constant mass-density of the carrier gas.

The behavior of the carrier phase is described by the continuity equation,
Navier-Stokes equation and energy conservation equation. Particles and droplets
are described by the set of ordinary differential equations. The two-way
coupling is implemented via momentum, energy and mass source terms.