Simulations of Smoke Flow Fields in a Wind Tunnel Under the Effect of an Air Curtain for Smoke Confinement

Abstract

Computational Fluid Dynamics (CFD) simulation results, obtained with Fire Dynamics Simulator (FDS 6.0.1), are presented in order to analyze the performance of an air curtain in blocking fire-induced smoke in a tunnel configuration. The flow and temperature fields are discussed for different air curtain jet velocities and for a range of smoke inlet temperatures. The key objective is the determination of the effectiveness of a vertical air curtain in blocking the fire-induced smoke spreading downstream of the air curtain, as function of the momentum of the air curtain. The results are presented in non-dimensional form, in terms of a ‘momentum ratio’ R, defined as $R = \frac{{\rho_{j} A_{j} V_{j}^{2} }}{{\rho_{s} A_{s} V_{s}^{2} }}$. This is the ratio of the vertically downward air curtain momentum to the horizontal smoke layer momentum at the position of the air curtain. This allows interpretation of the results, obtained at reduced-scale, in full-scale configurations. The smoke blocking is quantified by means of sealing effectiveness E, defined as one minus the ratio of the average temperature increase in the region downstream of the air curtain to the average temperature increase in the same region without activated air curtain. For small values of R, the sealing effectiveness E increases as the momentum ratio R increases. A maximum sealing effectiveness, E ≈ 60%, is attained for R = 8–10. Higher values of R lead to less effective sealing because the downward impinging air flow pushes smoke into the downward region. For very high values of R the effectiveness increases again, due to dilution of the smoke pushed in the downward region.