Influence of wind-blown sand movement induced by downburst wind on aerodynamic characteristics of a train running on viaduct

As a strong sinking airflow, thunderstorm downbursts are prone to cause convective sandstorms, seriously affecting the safety of high-speed trains (HST) running on bridges. Firstly, an impinging jet flow model was used to simulate the downburst wind field, and nonlinear least-squares fitting was applied to obtain vertical wind velocity profiles from the simulation results. Then, these profiles were combined with inlet conditions to induce sand movement, creating a sandstorm environment. Finally, the discrete phase model (DPM) was applied to analyze the effects of radial distance and sand particle diameter on the HST aerodynamic characteristics. The results indicated that sand concentrations initially increased and then decreased with radial distance, while they consistently increased with larger particle diameters. Since the effect of crosswinds played a dominant role, variations in the pressure coefficient were more sensitive to radial distance than to sand diameter. Furthermore, under different conditions with and without sand, the drag force coefficient (C_X), lateral force coefficient (C_Z), and overturning moment coefficient (C_MX) exhibited the most significant differences at radial distance r = 1.0 D_jet, with 6.63 %, 5.02 %, and 3.47 %, respectively. For the lift force coefficient (C_Y), the maximum difference of 6.10 % occurred at a radial distance of r = 0.5 D_jet. Additionally, as the sand diameter increased from 0.05 mm to 0.5 mm at r = 1.0 D_jet, C_X, C_Y, C_Z, and C_MX of the entire train increased by 87.09 %, 5.16 %, 3.95 %, and 6.01 %, respectively, under radial distance r = 1.0 D_jet.