This paper investigated the effects of longitudinal ventilation on exhausting efficiency of the shafts with different heights,and determined the optimal ventilation velocity by scaled experiments and FDS numerical simulations.The critical conditions of plug-holing were discussed through analyzing the effects of ventilation velocity and shaft height on plug-holing and boundary layer separation.Five ventilation velocities (0.096,0.226,0.356,0.485,0.629 m/s)and 4 heights of the shaft (0.133,0.2,0.333,0.533 m),were considered in the scaled experimental tests.The experimental results showed that when the ventilation velocities were 0.096,0.226,0.356 m/s (corresponding to the actual wind speed of 0.37,0.87,1.38 m/s), plug-holing could be restrained,but the boundary layer separation of the smoke would be aggravated with increase of the ventilation velocity.The critical criterion of plug-holing,i.e.,Fcritical＝ 1.5,was not applicable under the tested longitudinal ventilation conditions,while Ri′critical＝ 1.4 was still applicable.The simulated results indicated that the smoke exhaust rate decreased with increase of the longitudinal ventilation velocity when shaft heights were 1 ,1.5 and 2 m.For shaft height over 3 m,however,the smoke exhaust rate increased first and then decreased with increase of the longitudinal ventilation velocity when shaft heights were 3,4 and 5 m,and the maximum value occurred at 1.5 m/s.%通过开展小尺寸实验以及 FDS数值模拟实验,研究纵向通风对不同高度竖井的排烟影响并确定最佳通风风速.通过分析纵向通风风速、竖井高度对吸穿现象、边界层分离的影响规律,讨论了吸穿现象的临界条件.小尺寸实验中纵向通风风速考虑了0.096 m/s、0.226 m/s、0.356 m/s、0.485 m/s、0.629 m/s 五种工况,竖井高度考虑了0.133 m、0.2 m、0.333 m、0.533 m四种工况.实验结果表明:当纵向通风风速为 0.096 m/s、0.226 m/s、0.356 m/s (对应实际风速0.37 m/s、0.87 m/s、1.38 m/s)时,可抑制吸穿现象,但烟气边界层分离现象随着风速的增加而加剧.吸穿现象临界判据F critical＝ 1.5 在本文所测试的纵向通风条件下不再适用,但Ri′critical＝ 1.5 依然适用.数值模拟结果表明:当竖井高度为 1m、1.5m、2m时,排烟量随纵向通风的增加而降低,而当其为 3m、4m、5m 时,排烟量先上升后降低,在测试风速为 1.5 m/s时达到最高值.
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