Flame height and oscillation frequency of rectangular-source fires at different separation distances from a facade wall

This manuscript presents an experimental investigation on the effect of varying separation distances from a facade wall on the flame height and oscillation frequency of a rectangular-source fire. Four sets of burners, each with the same area but different aspect ratios, were utilized. The burner aspect ratio, separation distance from the facade wall, and fire heat release rate were considered as test conditions. The flame oscillation frequency, determined based on flame height, was recorded and analyzed using Fast Fourier Transform (FFT). The results demonstrate that the flame oscillation frequency of the rectangular-source fire increases as the separation distance from the facade wall increases, while remaining unaffected by the heat release rate of the fire source. The factors influencing the flame oscillation frequency under different separation distances from the facade wall are analyzed. It is revealed that the air entrainment from the facade side is constrained, which affects the length scales used to determine the flame scale and flame oscillation frequency. The controlling correlation length scale for flame height is found to be related to the perimeter of the rectangular-source fires, whereas for oscillation frequency, it is related to the hydraulic diameter of the rectangular-source fires. These length scales are adjusted as the distance from the facade wall changes. Furthermore, the effective heat release rate in the flame height modeling is modified to account for changes in the distance from the wall. Based on these new developments, similarity correlations for flame height and oscillation frequency well reproduce the experimental results.