Thermal convection on a rough or structured surface is a physical process that reflects reality much better in many problems, e.g. in technical systems for heat transfer, in the cooling of electronic components or in research into the urban climate, than the models usually used with smooth surfaces are able to do. Although there have been a large number of publications on this problem in the past, the local transport processes in the immediate vicinity of such a structured wall in particular are still largely misunderstood. This lack is due to the fact that there are only very few convection experiments in which the transport quantities near the wall can be measured with an adequate spatial and temporal resolution and that the computational effort for direct numerical simulations is currently still disproportionately high.
In the planned research project, the local velocity and temperature field during convective heat transfer on a rough surface is to be measured in the "Ilmenau Barrel" convection experiment. Due to the large dimensions of the convection cell, with a diameter of 7.1 m and a total height of 8.0 m, these measurements can be carried out at very high Rayleigh numbers up to Ra = 10^{12}. At the same time, the spatial resolution of these measurements is so high that the functional relationships sought in the fluid layer near the wall can be validated with sufficient certainty. In the course of the research project, different types of roughness patterns are to be investigated, including both uniform and staggered structural elements.
As a result of these investigations, the scientists want to assess in particular the relevance of various flow phenomena, such as the increase in the rate of emitted plumes, the "thinning" of the thermal boundary layer at the surface of the structural elements or the local transition of the convective boundary layer to turbulence, to the changes in convective heat transport on a structured surface observed in the past. A further aim of the planned project is to compare the measurement data on different types of roughness patterns and to search for fundamental similarities with regard to their influence on the flow field and thus on heat transport. Ideally, this search will result in a surface model that is as universally applicable as the hydraulic roughness model for pipe and shear flows.
Funded by: DFG
Period 01.05.2022 - 31.01.2025
Researcher:
