Multiple Solutions of Smoke Flow in a Building with an Opposing Wind

In a simple single-zone building with two openings under an opposing wind, a macroscopic theoretical analysis of smoke flow direction and smoke mass flow rate is carried out. Three solutions of smoke flow are identified under the same building geometry, the same heat release rate and the same ambient conditions at the steady state. Two of the solutions are shown to be stable and one is unstable. In the two stable solutions, one is an upward smoke flow with an upper smoke layer and a lower air layer, which may be considered relatively safe in terms of smoke control and human evacuation. The other is a relatively unsafe downward smoke flow with the entire building space fully mixed with smoke. The effect of the initial conditions and perturbations of the smoke flow system are also discussed. Additionally, computational fluid dynamics (CFD) simulations are used to simulate the existence of multiple solutions of smoke flow, and a hysteresis phenomenon is found. The existence of solution multiplicity of smoke flow in a simple building shows that a further study of more complex and realistic situations is necessary.