Deflected turbulent buoyant jet flame: Flow field measurement and flame geometry prediction

This paper investigates the geometrical characteristics and flow structure of deflected turbulent flames in still air. Flame tests were conducted at various initial Froude numbers (Fr 0 ) and flame angles (θ 0 , relative to horizontal orientation). Flow fields within the flames were measured utilizing PIV techniques. Results show that for a fixed Fr 0 , decreasing θ 0 reduces flame length due to enhanced air entrainment. Buoyancy-induced flame deflection creates an asymmetric flow field within the flame. In the upper region, buoyancy and streamline curvature effects promote turbulence generation and transport, triggering a detrainment phenomenon that disrupts velocity distribution self-similarity. Conversely, in the lower region, buoyancy inhibits turbulence generation while preserving this self-similarity. Second-order turbulence quantities increase with rising Fr 0 , indicating higher turbulence levels from momentum and buoyancy effects. Under low Fr 0 conditions, momentum-driven and buoyancy-induced fluctuations jointly induce bifurcation in radial distributions of turbulent normal stresses, which progressively diminishes as Fr 0 increases. Turbulence intensity normalized by peak velocity decreases with increasing Fr 0 , indicating reduced influence from buoyancy. A predictive model for flame geometry is established that accurately reproduces geometrical parameters across varying Fr 0 , θ 0 , and flame scale conditions. Additionally, model predictions elucidate significant effects of buoyancy and streamline curvature on flame turbulence. Predicted trends in turbulence intensity align with experimental observations.