Using three turbulence simulation methods for modeling the flying of high-speed railway tunnel lining blocks under piston airflow

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The detached tunnel lining concrete blocks poses a serious threat to the safety of moving high-speed train. Understanding the flight characteristics of detached blocks from the tunnel soffit under train piston airflow is essential for devising appropriate measures to mitigate such risks during train operation. Computational Fluid Dynamics (CFD) simulation methods, known for their high efficiency and good repeatability, are effective approaches to study this subject. Large Eddy Simulation (LES), Improved Delayed Detached Eddy Simulation (IDDES), and Unsteady Reynolds-Averaged Navier-Stokes (URANS) are three commonly used turbulence simulation methods in the CFD simulation of train/tunnel aerodynamics. In this study, a three-dimensional CFD simulation model based on the three turbulence simulation methods is established for the airflow-tunnel-train-detached block system, and an experiment is conducted for validating the CFD model. Using the established models, the influence of different turbulence simulation methods on the flight trajectory and aerodynamic coefficients of detached lining blocks under train-induced airflows is compared. By visualizing the macroscopic flow field inside the tunnel and the local flow field near the detached block, the flow mechanisms of detached blocks under different turbulence simulation method conditions are revealed. The results showed that in the 1st stage (BTT stage), the flight of the detached block is influenced by the airflow near the train body, while in the 2nd stage (ATT stage), it is mainly affected by the train wake vortex. Compared with experimental results, the errors of LES and IDDES in simulating the longitudinal direction displacement of the block are only 2.3 % and 5.5 %, respectively, while the error of URANS is 10.6 %. The simulation error of URANS for the longitudinal direction flight speed reached 8.8 % in the ATT stage. In the BTT stage, LES and IDDES predicates more and larger leeward side vortex structures of the detached block, while URANS predicates fewer and smaller vortex structures. Compared with URANS method, the dissipation rate of the vortex structures simulated by LES and IDDES in the ATT stage is slower. These are the main reasons explaining why the flight characteristics of detached lining blocks obtained by URANS method are different from the LES and IDDES methods.