Investigation on the stability of natural convection in an annular cavity with non-isothermal walls.

• Experimental study of natural convection in non-isothermal annular cavity. • 3D asymmetric oscillatory instability modes observed. • Frequency/amplitude of thermal oscillations mapped. • Routes to chaotic flow reported for different thermal boundary conditions. • Flow bifurcations observed by monitoring temperature data. The onset and nature of unsteady natural convection in a tall, closed annular cavity with non-isothermal walls is investigated experimentally. In the first of a sequence of experiments, thermal boundary conditions imposed on the inner and outer cylinders promote steady bi-cellular natural convection airflow inside the cavity. As the buoyant potential of the upper convection cell is increased, steady flow inside the cavity first bifurcates into mono-periodic flow and then follows a quasi-periodic route to chaotic flow. Similarly, when the buoyant potential of the lower convection cell is increased, steady flow bifurcates into mono-periodic flow and then follows an intermittent route to chaos. All of the observed unsteady airflows inside the annular cavity were three-dimensional, with all of the periodic flows exhibiting a gentle swirling motion in the azimuthal direction. [ABSTRACT FROM AUTHOR]