Air flow distribution study in the mainframe of TBM by using computational fluid dynamics - Case study TBM in Chamshir tunnel

The numerical study of airflow has mainly concentrated on underground mines and road tunnels. Ventilation during the construction of long tunnels, especially the ventilation of TBMs, has received less attention. This paper aims to study airflow pattern in TBMs with regard to safety and as such reduce dead zones area. The results show that the airflow pattern of a TBM ventilation system, which can help to design an effective ventilation system for the TBMs.

The Tunnel Boring Machines (TBMs) has revolutionized the tunneling industry to create underground space safer, healthier and more economical. Ventilation is one of the main components of mechanized tunneling. The airflow quality and the related mass flow rate in the ventilation system should be sufficient to dilute gases and remove the dust inside the tunnel. Since most of TBM crews stay and work in the mainframe area, ventilation of this zone is very important.

In this study, we modeled the TBM ventilation system using CFD method to understand airflow behavior in TBM. Numerical solution of the governing equations and boundary conditions are performed by utilizing the commercial CFD code Ansys CFX 18.1. Tests of mesh-independence were conducted based on four different meshing creations. To define the boundary conditions, airflow velocity sampling was performed using multi-point sampling method in the ductwork outlet. To complete the discretization of the advection term, the high-resolution scheme was computed. Root Means Square (RMS) < was considered as the convergence criterion of mass and momentum equations.

The results show that there is not enough air flow in 89.2% of TBM space in its current state. There are many dead zones from control cabin to the end of mainframe. The main direction of the back airflow moves along the segment feeder and increasing air mass flow has no effect in decreasing dead zones area. The results from the study present show that by increasing the air mass flow rate by 60% the volume of the dead zones in TBM is decreased by 13.42% and has no effective decrease dead zone in the personnel breathing zone. The results from the present study clearly indicate that maximum mass flow capacity of jet fans is not possible to reduce dead zones that will only increase energy costs