Feasibility of particle image velocimetry in vegetative fire spread experiments

Abstract

This study is part of an ongoing effort to improve the understanding of mechanisms that control the spread of fires with a focus on the turbulent flow modified by the flame front. A large-scale PIV system was used to measure the flow field inside and in the vicinity of a flame front spreading across a bed of fuel in an open environment. The vegetative fuel consisted of a 10-m-long and 5-m-wide bed of excelsior (1 kg/m² fuel load) leading to a nearly 1.5-m-high flame front. The velocity field was investigated in a measurement region about 1.5 m high and 2 m long. In such a configuration, a 450-mJ laser source was used to generate the light sheet, and the flow was seeded using zirconium oxide particles (ZrO₂). The PIV measurements in the presence of flame were improved by the use of a liquid crystal shutter in front of the PIV camera, allowing very short exposure times and eliminating the flame trace in the tomographic pictures. Despite the variability of the external conditions, leading to a difficult seeding over the whole PIV area, the present study shows the feasibility of the optical method of fluid visualization in the field. The measurements of the velocity fields show some features of the dynamics of fire plumes. This preliminary study demonstrates the feasibility of the method in the open, but some strong efforts to improve the seeding of the flow must be made.