Smoke flow bifurcation due to opposing buoyancy in two horizontally connected compartments

• Experimental investigation is used to show the existence of multiple solutions of smoke flow.
• Density variation of smoke induced by high temperature is considered.
• Bifurcation analysis of smoke flow is performed.
• The implications of smoke flow bifurcation on smoke control in an atrium or building with a stairwell are discussed.

We consider two horizontally connected compartments with four openings and one compartment on fire; the height of one compartment is fixed, while that of the other varies. A simple small-scale experimental study using air was performed to demonstrate the existence of two stable flow solutions at the same height ratio. Moreover, a macroscopic zonal model is used to theoretically analyze smoke flow direction and smoke mass flow rate. Under different ranges of height ratio, four patterns of smoke flow are identified and studied. One of the solutions is unstable, while the other three solutions are stable, as shown by nonlinear dynamic analysis. Therefore, two stable solutions of smoke flow exist at the same height ratio and ambient conditions when the height ratio is larger than a critical value, and the critical value is shown to be a transcritical bifurcation point. The implications of smoke flow bifurcation on smoke control in an atrium or building with a stairwell are also discussed.