为研究水下多匝道互通立交隧道的通风排烟特性，及时有效地排除隧道内烟气，以南昌红谷隧道为工程背景，应用CFD技术和现场试验的方法，对火灾时纵向排烟条件下不同纵坡和火源位置的烟气蔓延特性进行研究,分析坡度、火源与匝道位置等多因素耦合对烟气蔓延特性的影响。主要结论如下： 1)隧道东岸进口匝道排烟临界风速需大于2.5 m/s，各匝道射流风机均应开启，以保证匝道间分岔部位无串烟现象； 2)东岸出口匝道曲度大，隧道阻力较大，排烟临界风速为3.0~3.5 m/s时控烟效果较好，并宜选择流线顺畅、烟气流程较短的匝道进行排烟； 3)根据进出口匝道烟气蔓延特性的差异和相应试验条件下测算的排烟时间，提出对应的排烟策略，调整风机原设计的运行模式，以达到优化排烟气流组织、提高排烟效率的目的。

In order to study the characteristics of ventilation and smoke exhausting of underwater multiramp interchange tunnel and effectively exhaust the smoke, the smoke spread characteristics of different fire source locations under longitudinal ventilation condition and different longitudinal slopes are studied by CFD method and field measurement, by taking Honggu Tunnel in Nanchang for example. And then the influence of coupling factors, such as slope gradient, fire source, ramp location, etc., on smoke spread characteristics is analyzed. Main conclusions are drawn as follows. (1) The critical wind speed of smoke exhausting should be larger than 2.5 m/s at the east import ramps; and all the jet fans at the import ramps should be turned on when fire occurs, so as to avoid the phenomenon of smoke drops in bifurcation of ramps. (2) Due to the large curvature of east exit ramps and high resistance of the tunnel, the smoke control effect will be better when the critical wind speed of smoke exhausting is 3.0-3.5 m/s and adopting the ramp with smooth flow line and short smoke flow. (3) According to the different smoke spread characteristics of import and exit ramps, and the smoke exhausting time calculated from corresponding test conditions, the smoke exhausting strategy, adjusting operation mode of original design of fan, is proposed to optimize the organization of smoke exhausting flow and improve the efficiency of smoke exhausting.