Impact of Different Nose Lengths on Flow-Field Structure around a High-Speed Train

Abstract

In this study, the time-averaged and instantaneous slipstream velocity, time-averaged pressure, wake flows, and aerodynamic force of a high-speed train (HST) with different nose lengths are compared and analyzed using an improved delayed detached-eddy simulation (IDDES) method. Four train models were selected, with nose lengths of 4, 7, 9, and 12 m. To verify the accuracy of the numerical simulation results, they were compared with wind tunnel test results. The comparison results show that the selection of the numerical simulation method is reasonable. The research results show that with increasing nose length, the peak values of the time-averaged slipstream velocity of the trackside position (3 m from the center of track and 0.2 m from the top of rail) and the platform position (3 m from the center of track and 0.2 m from the top of rail) decrease continuously, and show a trend of rapid reduction at first, and then a slow decrease. As the nose length increased from 4 to 12 m, the time-averaged slipstream velocity at the trackside position and platform position are decreased by 57% and 19.5%, respectively. At a height of 1.6 m from the top of the rail, ΔCP max (maximum pressure coefficient), |ΔCP min| (the absolute value of minimum pressure coefficient), and ΔCP (pressure change coefficient) decrease with increasing nose length, which is similar to the peak value of time-averaged slipstream velocity, decreasing rapidly at first and then slowly. As the nose length increased from 4 to 12 m, decreases of ΔCP max, |ΔCP min|, and ΔCP by 26.5%, 58.5%, and 44.8% were shown, respectively. Different nose lengths also have a significant impact on wake flow.

Aerodynamic Characteristics When Trains Pass Each Other in High-Speed Railway Shield Tunnel

“…At present, with the rapid development of computer technology, numerical simulations are not only convenient to perform but also yield accurate results. Thus, numerical simulations have been widely used [15][16][17][18][19][20][21][22][23][24][25][26][27][28]. They can also greatly reduce the costs of actual vehicle tests and dynamic model tests.…”

Numerical Study of the Unsteady Aerodynamic Performance of Two Maglev Trains Passing Each Other in Open Air Using Different Turbulence Models

“…Furthermore, this method can effectively solve the existing problems of classical detached eddy simulations or delayed detached eddy simulation models that contain model stress dissipation, gridinduced separation, and logarithmic layer mismatch [28,30]. Consequently, IDDES has been widely used to simulate external flows around a train, particularly small-scale vortex structures [12,18,19,22,23]. To combine the delayed detached eddy simulation and wall modelling LES, the IDDES length scale is redefined as follows:…”

“…The vertical planes were coloured by the dimensionless longitudinal velocity (U x = u/u tr ). The wake vortex of a single train travelling without crosswind is symmetrically distributed [17,18,22]. However, Figure 17 shows that the interaction between vortices V c1 and V c1 on the intersection side causes vortices V c1 and V c2 (or V c1 and V c2 ) to be asymmetric.…”

“…of the airflow around the train, especially the unsteady wake flows. Wake flows when a single train runs in open air have also been investigated [17][18][19]. The surrounding flow of two trains passing each other in open air is different from that of a single train moving in open air.…”

“…In this study, we adopted a hybrid RANS/large eddy simulation (LES) approach to capture the small-scale vortex structures around the trains. This approach has been widely employed to capture wake vortex structures and is highly effective [12,18,19,22,23]. We selected the improved delayed detached eddy simulation (IDDES) model based on Spalart-Allmaras (SA), denoted as SA−IDDES, and shear stress transport (SST) k-ω, denoted as SST−IDDES.…”