Filip Sadlo
11.07.2008

Title: Numerical Visualization of Physics and Topology in Unsteady Flow

Abstract: 

Numerical flow visualization is gaining more and more
importance because there is a clear trend from experiments towards
computational fluid dynamics. This is especially true for these decades
since computing power and simulation techniques are coming to a level where
experiments are almost dispensable for many applications. This leads to the
situation that reliable numerical data are easily available but often hard
to interpret due to their size and intricacy.

We will present some work resulting from our collaboration with
turbomachinery industry, with focus on optimization of water turbines.
First, we address the development of vortices, which often heavily affect
the operation of turbines. We present a method for visualizing vorticity
transport in unsteady flow, allowing the investigation where vorticity
comes from and which mechanisms it undergoes on its way to a vortex. We
then address vortex rings, and in particular, vortex breakdown bubbles by
methods from vector field topology. These phenomena have the potential of
blocking flows due to their recirculation property, but are beneficial in
the field of e.g. mixing and combustion. Finally we move to the field of
Lagrangian coherent structures, which can be interpreted as a time-
dependent variant of vector field topology. There, we present a technique
for accelerating their computation, based on adaptive mesh refinement.