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The effects of the tunnel slope on the critical velocity were studied both experimentally and by CFD simulations. A series of experimental tests have been carried out using a small model tunnel with downhill slopes between 0 and 10 deg. A slope correction factor to modify the effect of the downhill slope on the critical velocity has been proposed from the experimental results. Three-dimensional simulations of smoke flow in three tunnels having different cross-sectional geometry have been carried out to examine the effect of the slope on the critical velocity for slope varying from 0 to 45 deg. The critical velocity obtained from the CFD simulation showed that the correction factor proposed from experiments is suitable for all tunnels when the downhill slopes was between 0 and 15 deg. However, this correction factor can not be applied for tunnel with slope greater than 15 deg. When the slope was greater than 15 deg, the effect of the slope on the tunnel critical velocity exhibited two very different trends. For tunnels with modest aspect ratio (tunnel width to height less than 2), the critical velocity stopped varying with the tunnel slope and become constant. In this case, the effect of tunnel slope on the critical velocity is modest. For very wide tunnel, the critical velocity would increase dramatically for the slope between 15 and 20 deg. The critical velocity eventually reached a constant level when the tunnel slope was beyond 30 deg. In this case, the effect of slope on the critical velocity can not be ignored. The phenomenon of the critical velocity becoming insensitive to the tunnel slope and reaching a constant in all tunnels indicated the existence of a super critical velocity.
The effects of the tunnel slope on the critical velocity were studied both experimentally and by CFD simulations. A series of experimental tests have been carried out using a small model tunnel with downhill slopes between 0 and 10 deg. A slope correction factor to modify the effect of the downhill slope on the critical velocity has been proposed from the experimental results. Three-dimensional simulations of smoke flow in three tunnels having different cross-sectional geometry have been carried out to examine the effect of the slope on the critical velocity for slope varying from 0 to 45 deg. The critical velocity obtained from the CFD simulation showed that the correction factor proposed from experiments is suitable for all tunnels when the downhill slopes was between 0 and 15 deg. However, this correction factor can not be applied for tunnel with slope greater than 15 deg. When the slope was greater than 15 deg, the effect of the slope on the tunnel critical velocity exhibited two very different trends. For tunnels with modest aspect ratio (tunnel width to height less than 2), the critical velocity stopped varying with the tunnel slope and become constant. In this case, the effect of tunnel slope on the critical velocity is modest. For very wide tunnel, the critical velocity would increase dramatically for the slope between 15 and 20 deg. The critical velocity eventually reached a constant level when the tunnel slope was beyond 30 deg. In this case, the effect of slope on the critical velocity can not be ignored. The phenomenon of the critical velocity becoming insensitive to the tunnel slope and reaching a constant in all tunnels indicated the existence of a super critical velocity.
Smoke control in tunnels with slope using longitudinal ventilation effect of tunnel slope on critical velocity
Rauchbekämpfung in geneigten Tunneln unter Einsatz des Längs-Lüftungseffektes der Tunnelneigung auf die kritische Geschwindigkeit
Wu, Y. (author)
2003
10 Seiten, 5 Bilder, 8 Quellen
Conference paper
English
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