| The engineering geological condition of the large-scale deep water diversiontunnels is complex. The long-distance construction ventilation is of great difficulty, sodoes the organization and management tasks. The traditional ventilation designusually just focused on the equipment allocation research under the peak constructionstrength conditions. As it did not consider the influences of the time-variable anddynamic air demand and the thermal storage effect of the long deep tunnels on theventilation effect, it may lead to resource waste, poor ventilation effect etc. Therefore,the study on the construction ventilation of the large-scale deep long-distance waterdiversion tunnel is vital to the theoretical research and the engineering application.Many key issues exist in the construction ventilation for the large-scale deepwater diversion tunnel, such as smoke extraction difficulties caused by the thermalstorage effects of the deep tunnel, the complexity issues of the construction ventilationof two phase flow simulation and the air leakage issues along the pipe system. Aimingat these challenging key scientific issues to be solved, the study was made based onthe mechanical properties of the gas-solid two-phase, the thermal characteristics andthe diffusion transport characteristics in the construction ventilation. Considering thegas-solid heat exchange, the intercoupling between the dust particles, and the airleakage effects on the airflow, a gas-solid two-phase Euler-Lagrange turbulence flowmodel was established for the construction ventilation of the large deep waterdiversion tunnel. PISO algorithm was used to solve the mathematical model.With the comparison of the simulation values and the on-site ventilation test dataof the4#tunnel in the Jinping Second-cascade Hydropower Station, it verified thatthe construction ventilation mathematical model is reliable. A grid dependency studywas performed to obtain a reasonable mesh scheme. The project of the deep longdiversion tunnel in the water conservancy and Hydropower engineering was taken asa case. The construction ventilation mathematical model was applied to simulate theconstruction ventilation dynamically. The simulation results are as follows:(1) Space-confined turbulent jet flow is formed in the pipe outlet. There are fourzones in heading face, i.e. jet zone, wall-attached jet zone, recirculation zone and eddyzone. The jet velocity along the moving path decreases slowly. The jet radius firstly increases and then decreases. The longitudinal airflow velocity in the heading faceregion increases with the Z values. With the increasing distance from the exit oftunnel, the air leakage rate and the volumetric air quantity are both reduced graduallyalong the duct.(2) The convection heat exchange between the air in the tunnel and the tunnel`swall is extremely strong. With the ventilation time increasing, the temperature of theheading face gradually decreases. When the ventilation time is30min, theconstruction ventilation cooling basically meets the requirements of construction.(3) With the increase of the ventilation time, the surface heat transfer coefficientsof the tunnel firstly increase and then become stable values. The maximum valuesappear in the heading face. A decreasing tendency exists from the section center to thewall of the heading face. But a contrary tendency exists in the remaining sections.With the contrast analysis of the experience formula values and the simulation values,the application of the temperature wall function method to solve heat transfercoefficients is feasible(4) Under the interaction of the airflow`s drag effect, the thermal density floweffect and the density current effect, most dusts migrate along the bottom of the tunnel,While part of the dusts float in the upper tunnel. It appears that some dusts move back,and the resuspension phenomenon turns up. The particle collision will result in theextension of the dust exhausting time and is harmful to the construction ventilation. |
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