Abstract: The design parameters of extralong underwater highway tunnels without vertical operating ventilation shaft need to be optimized. In this work, a 3D Fluent simulation model for a new type of operating ventilation scheme of Jiaozhou Bay second underwater highway tunnel without vertical ventilation shaft is established using computational fluid dynamics software. In addition, the influences of integraland separatemode vents, vent area, air valve, and location of top ventilation duct bifurcation on variation law of local resistance coefficient are respectively analyzed. Consequently, the optimal ventilation parameters and the corresponding local resistance coefficients are obtained. The results indicate the following. (1) Under the same conditions, the integralmode vent outperforms the separatemode vent. (2) The local resistance coefficient of vent decreases as vent area increases, and the decreasing rate lowers gradually; the recommended vent area is 45 m2. (3) The local resistance coefficient of vent decreases as the distance between air valve and vent increases, and the amplitude reduction is small; the distance between air valve and vent of 10 m is recommended. (4) The local resistance coefficient of vent decreases at first and then increases as the distance between top ventilation duct bifurcation and vent increases; the recommended distance between top ventilation duct bifurcation and vent is 10~20 m.

Key words: underwater highway tunnel, operating ventilation, Fluent simulation, vent, local resistance coefficient, ventilation duct bifurcation