Euler-lagrange Large Eddy Simulation Of Two-phase Flow In Diversion Tunnel Construction Ventilation

During the construction of the diversion tunnel of the hydropower project,the quality of construction ventilation will not only affect the construction schedule and quality,but also influence the health and safety of the construction personnel.Previous researches on construction ventilation in diversion tunnel only obtain the averaged turbulence physical quantity by Reynolds-Averaged Navier-Stokes(RANS)model,which could not reveal the complex instantaneous pulsation of turbulence and the micro movement regularities of particles under the evolution of large eddy structures In addition,among the existing large eddy simulations of construction ventilation in hydropower project,only few efforts have been devoted to grid quality evaluation and analysis.According to these problems,a large eddy simulation(LES)method of Euler-Lagrange two-phase flow was used to study the ventilation process during diversion tunnel construction.In-depth analysis on the problems mentioned above and the achievements were listed as follows:(1)Considering the influence of heat exchange and gas-solid interaction,a large eddy simulation model of the Euler-Lagrange two-phase flow for diversion tunnel ventilation simulation was established.The gas phase was modeled by LES method and the dynamic Smagorinsky subgrid model was applied.The solid phase was modeled by the discrete random walk model which took into account the effect of turbulent random diffusion in a Lagrange way,and the influence of gas-solid coupling on the particle transport was considered.The discretization scheme of the governing equations was discussed and the PISO algorithm was adopted to solve the discrete equation.(2)A high-resolution grid for large-eddy simulation of water diversion tunnel was built using hybrid grid technique and"O"-grid segmentation technique.And grid-sensitivity analysis was carried out.The grid evaluation index LES_IQ_k based on Richardson extrapolation was discussed and the index was used to evaluate the quality of the established grid.The results showed that the ratio of turbulent kinetic energy that can be solved by the established grid is more than 80%,which meets the resolution requirements of large eddy simulation.The reliability of the mathematical model was verified by the comparison with the field measurement data.(3)The aforementioned mathematical model was applied to simulate construction ventilation process of diversion tunnels in a hydropower station,and the wind flow field,wind pressure field,temperature field and dust particle trajectory were analyzed.Then,the simulation results of gas phase simulated by RANS and LES were compared.What's more,the influence of temperature differential flow on the particle migration was discussed.The results show:there are some randomly distributed small-scale vortices in the wind field,and there is irregular fluctuation in the upper and lower edges of the jet flow.But the turbulent small vortex and jet edge fluctuation can not be obtained by RANS method.The average wind speed of breathing zone of the diversion tunnel working face is 0.91m/s,which meets the requirement of construction code.The cooling rate of working area decreases gradually.Under the effect of turbulent large eddy structure,the particles begin to gather in the form of particle clusters,and then disperse by turbulent random diffusion.The particles swarm rise at the front under the influence of temperature differential flow.T=60min time,the maximum concentration of particles in the tunnel decreases to 2mg/m~3,which meets the construction specifications.