Control of aerosol migration with temperature gradients
Funded by: STW
PhD: Briti Sundar Deb
Supervisor: Bernard Geurts & Herman Clercx
The main aim in this project is the mathematical modelling of the dynamics of small aerosol particles in homogeneous isotropic turbulent flow and in turbulent boundary layer flow, under the influence of externally imposed temperature gradients. For this study we design high-order pseudo-spectral methods to simulate these processes. We are particularly interested in understanding the dynamics of aerosol droplets under the influence of evaporation and condensation. These have a direct influence on the particles responsiveness to turbulent motion and the externally imposed temperature field. We develop phenomenological models to understand these complex interactions.
Fig. 1: The trajectory of an inertial particle in a turbulent flow.
Control of aerosol migration by temperature gradients has a wide variety of applications from pollution control to atmospheric processes. A typical example is the prediction of rain where one has to know the size-distribution of the water droplets that develops as a result of the phase changes in the turbulently moving atmospheric cloud. This also has direct relevance in the field of process engineering.
In order to simulate the flow field we use the Direct Numerical Simulation (DNS) strategy. We solve the incompressible Navier-Stokes equations using a pseudo spectral method. We adopt a sufficiently high spatial resolution in order to capture all scales of the turbulent flow. For homogeneous turbulence simulations, we investigate both decaying and forced turbulence. For the discrete dispersed droplet phase we use a Lagrangian approach and track the trajectory of individual particles. Each particle experiences various types of forces while moving in the flow field. The dominant contribution for small spherical droplets is Stokes drag, which is characterized by the Stokes number of the particle. The Stokes number ultimately depends on the size of the particle. This size is a dynamic parameter that can change along the flight path of individual droplets due to different evaporation and condensation that occurs in the course of time. Currently, research is conducted for turbulent flow in a domain with periodic boundary conditions. This basic problem setting will be used to develop the heat- and mass-transfer model. Subsequently, this study will be extended to flow near a solid wall, concentrating on particle deposition on such a wall under the presence of a temperature gradient.
Fig. 2: PDF of the size distribution of the particles due to evaporation and condensation.
Briti S. Deb, Lilya Ghazaryan, Bernard J. Geurts, Herman J.H. Clercx, Hans G.M. Kuerten and Cees W.M. van der Geld. “The effect of phase transitions on the droplet size distribution in homogeneous isotropic turbulence.pdf”, ECCOMAS CFD 2010. LISBON. PORTUGAL
Briti S. Deb,, Bernard J. Geurts, Herman J.H. Clercx, “Dynamics of Droplets in Turbulence.pdf”, ECCOMAS CFD 2010. LISBON. PORTUGAL-