Hybrid LES/RANS Two Phase Flow Simulation Of Costruction Ventilation In Diversion Tunnel

Ventilation is the key link that affects the construction degree of progress and safety in the construction process of the diversion tunnel for hydropower engineering,Traditional ventilation design mostly determined only by engineering experience,which leads to poor ventilation effect and resource waste.The proposal and development of Computational Fluid Dynamics(CFD)technology provides an effective way to solve these problems.However,the current CFD simulation of the diversion tunnel construction ventilation mainly adopts Reynolds time-averaged equations to obtain the average characteristics of the construction ventilation turbulent flow field.Although calculation time is effectively reduced,the time-averaged method of the flow field causes the simulation cannot obtain accurate turbulence temporal information.A few studies used LES method to obtain turbulent instantaneous pulsation information,but its high dependence on mesh accuracy led to high computational costs and inadequate model applicability.Aiming at these problems,this paper proposes a hybrid LES/RANS Two-Phase Flow simulation method based on the Realizable k-ε Two Equation Turbulence model for diversion tunnel construction,which not only considers the efficiency and precision,but also makes up insufficiency of the current research of the hybrid LES/RANS Two-Phase Flow simulation model on diversion tunnel construction ventilation.The principal results are as follows:(1)A hybrid LES/RANS two-phase flow model for diversion tunnel construction was established in this study based on the Realizable k-ε two-equation turbulence model.Among them,the hybrid LES/RANS model is used for solving gas phase.The LES method is adopted for the main area of large-scale vortex-dominated ventilation,and the RANS method is used for the near-wall area where small-scale vorticity dominates,taking into account the calculation accuracy and computational efficiency.The stochastic particle trajectory model is used to simulate the particle phase.The effects of turbulent stochastic diffusion and gas solid coupling on dust particle transport are considered.Finally,the discretization scheme of the governing equations is discussed and the SIMPLEC algorithm is used to solve the discrete equations.(2)The independence of the grid is analyzed by the percent change of the variable,and a reasonable calculation grid division scheme is selected;the hybrid LES/RANS model established is verified based on field experimental data,proving the reliability of the mathematical model;The simulation results of the hybrid RANS/RANS model are compared with those of the RANS model and the LES model to verify the superiority of the hybrid LES/RANS method for the construction of the ventilation tunnel.(3)The proposed method is applied to verifying the feasibility of mixed LES/RANS in the construction ventilation of diversion tunnel for a hydropower station in southwest of China.Firstly,the distribution characteristics of air-flowing field and the pressure field are analyzed,secondary,the law of aeration-cooling near the working face is discussed,then,the changes of dust particle concentration and the particle trajectory is revealed,finally,the dust emission rate of construction ventilation is abstained,the research results can provide the theoretical guidance and technical support for engineering practice.