### Contribution of Heiko Schmidt

##### Title

Heterogeneous multiscale concepts in combustion and beyond

##### Topics

"Explosive fate of stars""Planetary atmospheric circulation"

##### Keywords

Multiscale methods, level set, combustion

##### Abstract

A reasonable numerical treatment of multiscale problems is a challenging task due to the complex interaction of the various time and length scales. All these length scales are often not representable on a discrete numerical grid due to restricted computational power. Even if a detailed simulation is feasible, sometimes a quick answer is needed or several problem parameters have to be varied systematically. A modeler's life becomes even more complicated when flows exhibit thin internal boundary layers of large activity, e.g., sharp temperature or concentration gradients, laminar/turbulent interfaces, or stiff chemical source terms. In these cases standard CFD tools normally fail, since they cannot resolve the layer physics due to insufficient grid resolution. Even elaborate physically based subgrid models are than numerically smeared out, so that a distinction between numerical (e.g. discretization errors) and physical effects (e.g. combustion or entrainment) is impossible. The subtile small scale interaction of molecular effects, turbulence, and source terms might only be accessed using direct numerical simulation (DNS) and stochastic turbulence models. In the talk we will sketch the idea of a heterogeneous multiscale ansatz including a possible geometrical representation of thin layers via hybrid level set techniques. Interdisciplinary examples of the concept will be the modeling of thermoacoustic instabilities in combustion devices, radiatively induced buoyancy reversal in a tank, and the modeling of a cloud-topped boundary layer.