Flow visualization of buoyant instability in a cross-flow: An implication for flame spread over forest fuel beds

The paper presents finding from visualization of the flow of smoke over a heated flat surface inside of a low-speed wind tunnel. Time-series images of illuminated smoke flow patterns show four flow structures: organized horizontal vortex flows; weak vortex flow interactions; strong vortex flow interactions; and turbulent flows. Results show that this non-reactive flow experiments can be used to study the fluid dynamics aspect of fire behavior. It allows detailed imaging of the flow field within and around fire zone. This types of experiments can be used to simulate the area behind (upstream) a fire zone where burnt products are still hot enough to generate enough buoyancy which then interacts with horizontal air flow (driven by inertia) and creates vortex flow. Thus, the fire zone may experience upcoming well-organized vortex flow rather than chaotic turbulent (wildfire case) or laminar (wind tunnel burns) one. The present experimental approach can be a useful tool in the investigation of time-dependent (flickering, pulsing and vortex shedding) behavior of propagating fire zone.