Regensburg 2025 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 4: Focus Session: Nonlinear Dynamics and Stochastic Processes – Advances in Theory and Applications I

DY 4.5: Vortrag

Montag, 17. März 2025, 10:45–11:00, H43

Reduced order stochastic modeling of turbulent passive scalar mixing — Abhishek Joshi, Tommy Starick, •Marten Klein, and Heiko Schmidt — BTU Cottbus-Senftenberg, Cottbus, Germany

Turbulent mixing is composed of chaotic stirring (macromixing) and molecular diffusion (micromixing). The detailed numerical modeling of turbulent mixing has remained a challenge since all relevant flow scales have to be represented in a computationally feasible manner. Map-based stochastic modeling approaches address this challenge by a radical abstraction, which is accomplished by dimensional reduction and utilization of generalized baker’s maps to model turbulent fluid motions. Dimensional reduction introduces limitations, but the modeling approach offers interpretability of the emerging complexity and, hence, further physical insight into turbulent mixing. In this contribution, the Hierarchical Parcel Swapping (HiPS) [Kerstein, J. Stat. Phys. 153, 142–161 (2013)] and the One-Dimensional Turbulence (ODT) [Kerstein, J. Fluid Mech. 392, 277–334 (1999)] models are used to study turbulent mixing of passive scalars. Both models aim to represent the state space of 3-D turbulent mixing by a 1-D computational domain. HiPS is a fully event-based mixing model with prescribed sampling from a turbulent cascade, whereas ODT employs an energy-based rejection sampling only for macromixing such that a turbulent cascade is the result of a prescribed physical forcing mechanism. Capabilities of both models are demonstrated for canonical single and multiple passive scalar mixing cases using standalone model formulations across diffusivities.

Keywords: turbulent mixing; map-based stochastic modeling; scaling cascades; high Reynolds number; variable Schmidt number