PERIODIC AND QUASIPERIODIC TEMPERATURE OSCILLATIONS IN MIXED CONVECTION

Abstract

We report on temperature oscillations which we observed during experiments in turbulent mixed convection at Ra=2.0x10e8 in a rectangular enclosure with a length of L=2500 mm and aspect ratios of L/H=5 (length over height) and W/H=1 (width over height), heated from below and cooled from above. The measurements were conducted using an arrangement of PT-100 temperature sensors. Depending on the Reynolds number of the flow entering the cell, and thus the Archimedes number, we detected stable flow conditions as well as quasiperiodic and periodic oscillations in the temperature field. Comparison with smoke visualisations allowed us to ascribe the respective temperature distribution to a certain number and arrangement of large scale circulations (LSCs) in the flow. We interpret the temperature oscillations, which reach the highest frequency f=2.0x10e-3 1/s at Ar=1.8, as motions of the LSCs in longitudinal cell direction.