Comparative study on the unsteady slipstream induced by a single train and two trains passing each other in a tunnel

The train-induced airflow in a tunnel has great significance for tunnel ventilation, fire rescue, and equipment installations. In particular, the aerodynamic effects induced by two trains passing each other in a tunnel are fiercer and complicated than those of a single train. In this research, a comparative CFD study of the three-dimensional slipstreams induced by a single train and two trains passing by in a tunnel was conducted using the unsteady Reynolds-Averaged Navier–Stokes (URANS) method. Three-dimensional computational models of a high-speed train and a tunnel are developed based on the sliding mesh technique and validated through experiments. The characteristics of the components of the slipstream were fully reported in three directions at different spatial positions. The results demonstrated that the impact of the tunnel pressure waves on the local airflow was independent of the spatial locations for the same cross-section. The variations of the longitudinal component (u) and the resultant slipstream (U_R) were generally consistent with each other, demonstrating that the slipstreams inside the tunnel were mainly longitudinal flow. In addition, the piston effect was more pronounced when the space was constrained by another train for the crossing-trains case. The largest discrepancy of the maximum peak value at different positions for the crossing-trains case was 34% larger than that of the single-train case.