Study On Diffusing Shape And Channeling Problem Of Exhaust Gas For Highway Tunnel Portal

Along with the rapid development of highway engineering, tunnels have increasingly appeared in highway engineering field. Moreover, the problems of tunnel portal exhaust gas diffusing shape and channeling are attracting more and more attentions due to their close relations with tunnel ventilation and environment. Based on the related subjects such as the western transportation construction scientific and technological project of Transportation Department’Highway tunnel intelligent linkage control technology research", the National Science Found for Distinguished Young Scholars of China’key scientific problem of construction and operation for extra-long traffic tunnel’and so on, adopted many methods such as extensive study, field test, theoretical analysis, comprehensive analysis, and systematic numerical analysis, supported by specific projects such as Beibei tunnel and Zhongliangshan Tunnel, some research on highway tunnel portal exhaust gas diffusion shape and channeling problems are carried out in this paper. All the main works and results can be summarized as follows:1. According to the characteristics of concentration distribution of exhaust gas from highway tunnel portal under the comprehensive effect of unsteady multi-factors, the programme and analysis of the concentration distribution testing based on the extremum is put forward. Supported by Beibei Tunnel and Zhongliangshan Tunnel, the research of the whole field test about concentration distribution of exhaust gas from highway tunnel portal is carried out, and the automatic flue gas analyzer is the first applied to the synchronous measurement of the different points of Zhongliangshan Tunnel. A series of curves families of the maximum concentration distribution of the actual operation exhaust gas around of highway tunnel portal are the first obtained for the various operation conditions or terrains, and a series of various ingredients synchronous concentration-time curves families are also obtained firstly. Based on these series of curves families, the diffusion rules of the highway tunnel portal exhaust gas are analyzed, which conform to the ones of fluid flow diffusion transmission. And the concordant results of two kinds of testing plan have mutually proved that it is a reasonable and feasible method of the concentration field test and analysis which based on the extreme.2. According to the flow characteristics of the highway tunnel portal exhaust gas diffusing into the environment atmosphere, combined the analysis of study of the relative field, jet theory is the first introduced, and according to the relevant research on the self-hold state for the gas free jet and combined with the grid generation technique of effective simulation of complex terrain, a suitable regional model of numerical analysis of the turbulent jet spreading is established. And then, the three dimensional differential mathematical model groups and the appropriate solution are deduced or choosed for the corresponding multicomponent gas diffusion transmission.3. Combined the field test of concentration distribution programme and analysis based on the extremum with the simulation theory of turbulent jet together, a comprehensive analysis method adapted to the unsteady diffusion characteristics of tunnel portal exhaust gas is discussed, in which a simulation scheme of a series of working conditions under the functions of multi-factors of the test is put forward, thus resulting in a appropriate comparative analysis between the testing and the simulation data, and in allusion to the different influencing factors in test mode such as natural wind velocity, air flowing temperature difference between outside and inside of tunnel, and the operating wind velocity of both tunnels, the influence rules of the exhaust gas diffusing and channeling around highway tunnel portal are discussed systematically under the corresponding working conditions groups, moreover, on the basis of field test data, under the forward different operation conditions.the maximum concentration range of the corresponding tunnel portal actual exhaust gas is also deduced out,and finally, the corresponding exhaust gas channeling status and the improvement status of the gas channeling under the wind block wall set up on the side of export tunnel are simulated.4. A systematic numerical analysis of the tunnel portal structure factors influencing on the exhaust gas channeling is carried out. Firstly, for the parallel tunnel portal with open terrain, from three angles such as the different transverse spacing of the both tunnel portals, the different natural wind speed, the wind block wall with different size set up in the middle and so on, the impact study of exhaust gas channeling around the portal is carried out. secondly, the correlational study of the influence factors on the parallel tunnel portal exhaust gas channeling is explored, and specially for the tunnel portals with the specific transverse clear distance, consideration of these structure factors such as whether or not the parallel tunnel both portals are longitudinal stagger, whether or not the block wall set up on the side of the exit tunnel, the entrance tunnel and in the middle, different length and height of the block wall and so on, adopting the six factors and different levels orthogonal experiment scheme, the impact researches on the exhause gas channeling around the parallel portal are carried out systematically. Finally, some suggestion on tunnel portal civil structures which are helpful or against to weaken the effect of the parallel portal exhause gas channeling are proposed.The curve families related to the measured data accumulate the most direct and reliable information for the research of the highway tunnel portal exhaust gas diffusing, and the analysis method and means for this testing provides a feasible new idea or a new approach for the testing and evaluation of some physical quantity which is under the action of unsteady multifactor. The suitable analysis regional model and the solving method for the exhaust gas turbulent jet diffuseness of highway tunnel portal provides an effective platform and means for systematic discuss. The integrated analyses method combining the measured data with the simulation theory of the turbulent jet diffusion provide a degree of reliability proof for numerical analysis. The forward prediction based on the measured data of the portal exhaust gas concentration and the favorable or unfavorable civil structure type of highway tunnel portal for the weakening of the exhaust gas channeling are proposed as some engineering suggestions for reference.