| With the acceleration of economic development and urban construction, urban construction land drop sharply and traffic accidents increase densely, urban underground road has become an important means to solve such problems as land resource constraints and traffic congestion, however, urban regional planning and the surrounding ambient air quality standard restrictions on urban tunnel ventilation and sewage control put forward higher requirements.The longitudinal jet fan ventilation mode is widely used in urban tunnel ventilation sewage. There are a lot of research on this ventilation mode at home and abroad, as to the defects and deficiencies which develop from the longitudinal jet fan’s widely use in urban tunnel ventilation sewage,the paper is developed based on this line of research as follows:firstly, based on the urban tunnel field measurement results,we find that there exists delay effect of longitudinal jet fan ventilation,mechanism of this phenomenon is studied;Combining with aerodynamic equations, mathematical derivation of the flow field variation caused by the fan acceleration and deceleration in the simple longitudinal ventilation tunnel is provided, this theoretical equation is verified by the Qianjiang Road city tunnel’s field measurement results, and relevant parameter analysis has been conducted;Then describe in detail the mathematical model of the tunnel longitudinal jet flow ventilation, after meshing and correctly setting the boundary conditions, verify the applicability of the CFD model by contrast to norms and the scaled-model test results, and then study the relationship between exit velocity of the jet fan, jet fan mounting angle and comprehensive effect coefficient of jet fan,the relationship is found, and also the best mounting angle of the jet fan;Finally, introduce the fan variable frequency technology, study different speed combinations of the ventilation system in the tunnel according to the previously deduced equations of the dynamic effects, discover the best way of ventilation in the tunnel.Through research,this paper gives the simple expression of the longitudinal jet ventilation tunnel’s delayed effect and its parametric analysis,concludes that the comprehensive effect coefficient of jet fan is generally a location parameter,finds the best installation angle by a lot of CFD numerical simulation,discusses the best ventilation way of tunnel combining with variable frequency technology, finally the paper applies research results to practical engineering summary and relative research development are provided. |
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