Long-time wall shear stress patterns in enclosed turbulent Rayleigh-Bernard convection cells EuHIT Funded Project

Team

Ronald du Puits
Technische Universitaet Ilmenau, Ilmenau, Germany
Vladimir Mikulich
TU Bergakademie Freiberg, Freiberg, Germany
Ramis Örlü
Royal Institute of Technology, Stockholm, Sweden

Overview

Research Infrastructure
Barrel of Ilmenau, Germany
Facilities used
Barrel of Ilmenau (BOI)
Project leader
Christoph Bruecker
City University London, London, United Kingdom

Abstract

In this proposal we would like to investigate the long-term structure of the wall shear-stress in turbulent thermal convection. The WSS is a footprint of the larger structures in the buffer layer and correlates with the heat transfer at the wall. Recent measurements revealed the sudden reorganization of the large-scale motion in such cells which happens at time-scales several orders larger than the turnover time of the cell itself. There is evidence that the WSS pattern is a precursor signature to such reorganization. In order to measure the WSS over such long-term periods with sufficient spatial and temporal resolution we recently developed a new sensor based on the principle of the micro-pillar sensor (Brücker et al. 2005, Brücker 2015) which has sufficient resolution power for such low velocities as they appear in the convection cell. Preliminary tests with such a sensor could already reveal physical insight into the reorganization process. However, these test measurements were only possible at a single position due to limits in camera and optical access. The preparation of a 4 x 2 sensor array with larger interspacing allows us to determine the spatial correlation as well as the temporal correlation of the larger-scale motion and to analyze the precursor of such sudden reorganizations by means of the WSS distribution.