Institute Seminar
On Monday, March 6th, from 12:15-1:15 PM (room 3, building 34), mgr Ahmad Ababaei will give a lecture on the topic of “A novel hybrid numerical approach for modeling cloud microphysical processes”.
Abstract
In recent decades, massively parallel direct numerical simulations (DNS) have emerged as an effective tool to study microphysical processes in atmospheric clouds. Accurate description of these phenomena is an important step towards improving the verifiability of weather and climate forecasts. Mechanisms that govern the droplet–droplet and droplet–air interactions determine the collision rate and thus the precipitation formation. These processes cannot be resolved in the numerical weather prediction (NWP) systems since the horizontal grid spacing of these models is of the order of one kilometer. DNS simulations feature full representation of turbulent scales in the dissipative range of the energy spectra, but the challenge is to model aerodynamic interactions in the systems with many droplets. Due to the high complexity these mutual interactions are usually represented by employing simplified approaches. An example is the superposition method in which the net drag force acting on a given droplet is evaluated by superimposing perturbations generated by all other droplets in its proximity. A key shortcoming of this method is its inability to represent short-range lubrication forces.
To overcome this problem, a new computational approach has been proposed that incorporates the effect of long-range many-body aerodynamic interactions along with the short-range lubrication forces. The implementation couples hybrid DNS with the analytical solutions of two rigid spheres moving in an unbounded fluid. Moreover, the model takes into account internal circulation of water inside droplets, and noncontinuum molecular effects.
The present talk discusses methods and algorithms for organization of computations in the model along with most recent simulation results. These include dynamic and kinematic collision statistics of droplets under conditions representative for moderate to strong convection.