| The importance of tunnel antifreezing in cold regions have been reached an agreement, a lot of studies on the cold resistance and thermal insulation methods have been done by domestic and foreign scholars. However,there are no researches on the influence of ventilation on frost resistance in tunnels, especially for the study on un-steady state heat transfer.The unsteady heat transfer mechanism of tunnel cross-section in the cold regions has been researched by theoretical deduction and numerical analysis.Changes of heat adjustment circle over time is also included.On the basis of this study.longitudinal unsteady heat transfer mechanism of tunnels in cold regions has been researched in the convection-thermal coupling effect.The temperature distribution of the tunnel surrounding rock has come to a conclusion.In the foundation of the theoretical research and the derivation, this paper uses finite difference program compiled in VC++language to calculate tunnel surrounding rock and air temperature distribution in various ventilation conditions, and then compares with the simulation software of FLUENT to verify its feasibility.Based on Wangdeng railway tunnel in Chenglan Line.through large-scale numerical simulation, this paper compares the temperature longitudinal distribution of tunnel surrounding rock in different natural wind conditions, different ventilation modes, and different operation years.By statistical analysis and consolidation of the simulation results, reasonable frost fortification of tunnel in cold region has been put forward.The conclusions and the results of this paper are as follows:The research of two-dimensional finite difference calculation on heat adjustment circle shows that heat adjustment circle gradually increases with the growth of time, and the value tends to be steady.It is far beyond the range of the heat adjustment circle to select70m surrounding rock range in calculation.Laid between lining and secondary lining,insulating layer has good effect on hindering the heat transfer beacuse of its low thermal conductivity and high specific heat capacity.It could slow down the drop range and speed of surrounding rock temperature. thus slows down the heat adjustment circle growth rate.The calculation by three-dimensional finite difference program compiled in C++in circular tunnel is compared and verificated by using the simulation software of FLUENT in horse-shoe tunnel. The result shows that the temperature changing trends are exactly the same,and the error of calculations is very small.In the condition of extremely low constant wind-warm syndrome and the periodic air temperature which based on the annual mean temperature,the three dimensional finite difference program works out longitudinal temperature distribution of the surrounding rock of tunnel. The results show that natural wind plays an important role on the temperature of the tunnel surrounding rock.The wind flows faster, the rock temperature drops more rapid. The original rock temperature in the tunnel.the speed of the airflow and the direction of the airflow have an important impact on the temperature distribution of the tunnel surrounding rock. The influence of the piston wind on antifreeze depends on the specific operation condition.The antifreezing range is discussed according to the temperature distribution of surrounding rock.The result is calculated by the three-dimensional finite difference program of the cyclical air temperature and the lowest average air temperature. |
PDF Full Text Request