Aerodynamic effects of the gap spacing between adjacent vehicles on wind tunnel train models

Abstract

A certain gap spacing between adjacent vehicles is usually inevitable in wind tunnel force tests of high-speed trains under no crosswind, which may affect the wind tunnel test results. Thus, to understand the influence of gap spacings on the train aerodynamics, the aerodynamic drag, pressure distributions and airflow structures of 1/8th-scale high-speed train models with gap spacings of 0, 5, 8, 10, 20, and 30 mm were studied using RANS based on SST k-ω turbulence model. The simulation method was verified by the wind tunnel experiment data. The results show that the gap spacing significantly affects the airflow structure around inter-car gap and aerodynamic resistances of train models. For the high-speed train model scaled at 1/8th at zero yaw, compared with gap spacing of 0 mm, the gap spacings lead to a significant reduction in the aerodynamic drag of the head car and an increase in that of the tail car, whereas which of the middle car is not significant. The maximum difference of the drag coefficient of the entire train model is smaller than 2.0%. When the gap spacing does not exceed 8 mm, the discrepancies of the drag coefficients of three cars are within 6.15%.

Structure clearance design in wind tunnel tests with implications for aerodynamic drag of high-speed trains

“…This bullish-bearish change phenomenon might happen because the air ow easily passed through the inter-car gap and changed the ow eld between the head and middle cars when VDG was large. This bullish-bearish change of C x−head and C x−middle is different from previous numerical simulation results of Li et al (2019) and Xia et al (2020), in which there were not sudden changes for the C x−head and C x−middle . Except for the spacing of 22 mm, the in uence of VDG on C x−head was much smaller than those of C x−middle and C x−tail .…”

“…Numerical calculations were conducted to demonstrate that the total drag coe cient of a 1/8th-scale HST model with a vestibule diaphragm gap less than 10 mm was equal to that of a model without a gap (Li et al, 2019). However, it was previously reported through numerical calculations that the drag coe cient discrepancy of a 1/8th-scale HST model test reached up to 6.15% (Xia et al, 2020). Very few experimental discussions on structure clearance value setting in HST train tests are available, and a limited number of experimental investigations have addressed the in uences of different types of structure clearance on the aerodynamic drag of the head, middle, and tail cars of a HST train model.…”

Numerical investigation on the aerodynamic resistances of double-unit trains with different gap lengths

“…Therefore, it is very important to research the aerodynamics of DUT. The research methods for the aerodynamic characteristic of high-speed trains include mainly numerical simulations (Medina et al, 2012;Xia et al, 2020), as well as wind tunnel experiments. Considering the cost and computational time, the numerical simulations mainly focus on the study of simple train models (Hemida & Krajnovic, 2009;Li et al, 2019), and the train models used in the numerical simulations are almost all made up of three cars (Han & Yao, 2017).…”

Influence of height of earth embankment type windbreak wall on flow field characteristics and catenary wind-induced displacement

“…A segregated incompressible finite-volume solver was adopted for the simulations presented in this paper, and the SIMPLE pressure-velocity coupling method was employed. To discretize the convective term, a hybrid scheme that switched between a bounded central-differencing scheme (BCDS) and a second-order upwind scheme (Travin et al, 2002;Xia et al, 2020) was employed. Additionally, a second-order upwind scheme was used for the turbulence equations, and the BCDS was applied in the LES region.…”