Fluid flow and mixing characteristics in a partially filled horizontal rotating cylinder

• Applicants: Professor Dr.-Ing. Carsten Schilde; Professor Dr.-Ing. Stephan Scholl
• Subject Area: Technical Thermodynamics
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 576320648

A locally restricted power input to mix a volume promotes high inhomogeneities of local flow velocities and the occurrence of high local shear forces. Due to the resulting stress, these can lead to undesired process behavior of shear-sensitive disperse phases, such as microorganisms or fragile crystal systems. A horizontally rotating cylinder geometry is intended to address this issue by offering a large wetted surface to provide a high uniformity of power input with low local stress peaks. Of particular interest are cylinders with short lengths and an expected high influence of the moving axial walls. For this geometry, there is currently insufficient knowledge about the flow and the related mixing behavior. The aim of this project is a systematic investigation of the fundamental flow and the dominant flow structures in very flat cylinders. In particular, the distribution of local energy dissipation rates, the maximum occurring energy dissipation or stress, the overall power input and the influence of a variable axial wall distance on the core flow will be investigated to examine the hypothesis of a uniform and gentle flow pattern. The interaction of the flow with the mixing process is also essential for the use as a reactor and will be investigated with local resolution. Together with the fluid dynamics, the derived quantities are to be converted into empirical models of dimensionless numbers. These will allow a description of the fluid dynamics and mixing conditions in a general manner and a process engineering design and evaluation of the flat cylinder. After characterizing the basic cylinder geometry, the question of how the installation of mixing elements can influence the mixing behavior and support the goal of a gentle mixing effect will be addressed. Based on the experimental and simulation results obtained, target functions are derived to assess the mixing performance of varying mixing elements. By coupling CFD simulation and an evolutionary genetic algorithm, an AI-supported optimization of the element geometry according to the identified target functions and an experimental realization and verification of the determined mixing elements follows. These steps represent the 1st phase of the project and will be extended in the 2nd phase by the use of heterogeneous systems. These will address the superordinate goal of using the cylinder geometry for shear sensitive disperse phases. The aim is to study the suspension of solids of different particle phases, their local particle concentration distributions, the influence on flow and power input as well as the resulting stress level by taking into account collisions of the discrete particles.

• DFG Programme: Research Grants