THERMAL INSTABILITIES IN A MIXED CONVECTION PHENOMENON - NONLINEAR DYNAMICS

The influence of mixed convection due to buoyancy for a flow in a unif ormly heated horizontal duct is a well-known phenomenon. Experimentall y the overall effect of the heating is characterized by a temperature difference between the top and bottom of a cross section. An increase in the average velocity of the fluid or the heating power leads to an instability phenomenon which manifests itself through the appearance o f large-amplitude temporal fluctuations in temperature. The amplitude of these fluctuations depends on their position in the test section, t he heat flux supplied to the wall and the fluid velocity. The aim of t his paper is to describe these thermal instabilities, and to simulate them utilizing a low-dimension model which shows the nonlinear dynamic of the system.