Numerical study on the flow field and air entrainment rate of rectangular gas fires under sidewall and corner restricted conditions

In restricted space, fuel combustion is often constrained by sidewalls and corners, which can alter the air entrainment compared to unrestricted scenarios. To investigate the impact of sidewalls and corners, this paper presents numerical simulations of rectangular propane gas fires under sidewall and corner restricted conditions. The burner had an area of 300 cm², with 5 different aspect ratios (n = 1, 1.5, 2, 3, and 4) and 4 heat release rates of the fire source (12 kW, 18 kW, 24 kW and 30 kW). The results demonstrate variations in the distribution of the flow field under different restricted conditions. For wall fires, when the long side of the burner is against the wall, the velocity in the X direction (u) approaches 0, and the lateral flow velocity on the X–Y plane (V) and the velocity in the Y direction (v) are nearly identical near the short side of the burner. Velocity V near the burner side can be divided into three zones: the high-velocity zone, the low-velocity zone, and the locally high-velocity zone. For corner fires, V increases as it gets closer to the wall. With the increase of n, the streamline where the velocities u and v are equal moves to the long side of the burner. Additionally, the fire entrainment rates of rectangular wall and corner fires at different heights from the burner surface were quantitatively studied. On the basis of the fire entrainment model for square and circular fires in open space, by introducing the equivalent diameter $D_{\text{eff}}^{*}$, a modified entrainment rate model at different heights from the burner surface is proposed, which can well predict the entrainment rate of rectangular wall or corner fires when the aspect ratio of the rectangular burner ranges from 1 to 4 and ${\dot{Q}}_{\text{eff}}^{*}$ ranges from 0.97 to 6.79.