Hydraulic Features of Air-Water Mixture Flow on a Staircase with Rest Platforms

Abstract

To investigate hydraulic features of the flooding flow on a staircase with a rest platform, experiments were conducted on a 1:2-scale physical model of a staircase with a middle rest platform between two stair segments. The transition or skimming flow occurring on the first segment is similar to that on a stepped chute. However, a jet flow forms immediately downstream of the rest platform, followed by a redeveloping transition flow on the second segment. The measured profiles of air concentrations in those flow regions agree well with that in the skimming and transition flow known from stepped spillways. The amount of air entrained into the free-falling jet increases dramatically because of a higher air concentration in the approaching flow. Rapid rises of the air-water mixture depth and the flow velocity in part of the jet and the transition flow downstream were observed. These features could affect human maneuverability on a flooding staircase with rest platform(s) and make it more difficult for people to safely evacuate from underground spaces.