Transition to chaos around an isothermally heated sphere placed in a uniform, downwardly directed flow

摘要

The former experimental research revealed the temporal and spatial heat transfer performance around an isothermally heated sphere placed in a uniform, downwardly directed flow using a micro-foil Heat Flow Sensor. Experiments were carried out using air with a Grashof number of 3.3×10{sup}5 and with several Reynolds numbers up to 3000. Four flow patterns appeared; a steady mixed convection flow, chaotic flow, a steady symmetrical separated flow and an unsteady 3-D separated flow. The aim of this basic study is to reveal the performance of chaotic flow and the transition process from the steady symmetrical separated flow to chaotic flow numerically and experimentally. CFD codes Storm/CFD2000 were used in the numerical simulation. It is shown that the 3-D unsteady flow around the sphere is a spatiotemporal chaos, by calculation of a set of Lyapunov exponents from the calculated time series of a temperature and the flow visualization.