A burning incense stick heats up the air surrounding the glow. By thermal expansion the air becomes light and rises rapidly in a hot plume. As the hot air rises heat and momentum diffuse which causes the stream to slow down. Tiny particles from the combustion process are nearly perfectly advected with the flow and act as tracers visualizing the flow pattern by a bundle of streaklines. Due to small disturbances present in the motion of the ambient air, a slight vibration of the incense stick or irregular combustion the stream becomes wavy at first (lower part). The amplitude of the waviness grows further downstream to create large-scale coherent structures (middle part) before the structures decay in a turbulent fashion (upper part).

© 2017 Institute of Fluid Mechanics and Heat Transfer, TU Wien