Start
Feb 16, 2012 - 17:00
End
Feb 16, 2012 - 18:00
Venue
Room 118 (Creativity Hall) Ground Floor Chemical Engineering Department
Event Type
Speaker
Dr. Partha Sarathi Goswami CSIR-Centre for Mathematical Modeling and Computer Simulation Bangalore.
Title
Particle dynamics in a turbulent particle-gas suspension at high Stokes number
Abstract: Particle laden turbulent flows find applications in many industrial processes. There are strong interactions between the turbulent fluctuations in the fluid velocity fields and the velocity fluctuations of the particles. In order to understand the different physical properties such as stresses heat and mass transfer in turbulent suspensions it is necessary to have a good understanding of not just the mean flow of the gas and particles but also of the fluctuations in the two phases. In the seminar the detail of a new modeling approach for turbulent particle laden flows `fluctuating force' model will be discussed. Such a model has been used to capture the effect of turbulent fluid velocity fluctuations on the particle phase in a turbulent gas-solid suspension in the limit of high Stokes number which is the ratio of particle relaxation time to the fluid time scale. In the fluctuating force model forces exerted by the turbulent fluid velocity fluctuations are incorporated in the equation of motion of the particles as anisotropic Gaussian white noise. The noise amplitude is determined from the time correlations of the spatially varying and non-isotropic turbulent fluid velocity fluctuations obtained from Direct Numerical Simulations (DNS). A quantitative comparison of the results obtained from fluctuating force model and DNS for a shear flow (Couette flow where there is a homogeneous centre region) will be discussed first. Then the applicability of `fluctuating force' model for gravity driven inhomogeneous flow in a vertical channel will be addressed highlighting the concept of `moving Eulerian' reference frame. Comparisons are also made with experimental measurements of the particle velocity distributions using PIV and Particle Tracking Velocimetry using polydisperse particle in the fluctuating force simulations (FFS). Experimental results for both the low and high solid mass loading will be discussed. From the experiments it is observed that there is no significant modification of the fluid phase turbulent intensity at low particle mass loading but at a higher particle mass loading there is a significant increase in the turbulent velocity fluctuations due to the presence of particles. Therefore it becomes necessary to incorporate the modified fluid turbulence intensity in the fluctuating force modeling to capture the particle statistics.