| 1. |
- Liang, Xifeng, et al.
(författare)
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On the aerodynamic loads when a high speed train passes under an overhead bridge
- 2020
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 202
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Tidskriftsartikel (refereegranskat)abstract
- The aerodynamic loads on the overhead bridge bottom surface induced by train passage are reported in this paper. Both moving model test and numerical simulation approaches at the 1:20 scale are used. The numerical work is validated through both mesh independence tests and comparison with experimental data. Typical pressure variation curves are plotted and compared with previous studies. The peak pressure values’ dependence on the Reynolds number is considered through four sets of experiments with different train running speeds. The peak pressure coefficient distribution law for the bridge bottom surface is presented. Differences in the pressure distribution in different bridge bottom areas are explained based on more detailed flow field information. The influence of the bridge height on the aerodynamic load magnitude and time interval is presented. Moreover, the application of the CEN Standard to practical engineering issues is discussed.
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| 2. |
- Dong, Tianyun, et al.
(författare)
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The effect of ground clearance on the aerodynamics of a generic high-speed train
- 2020
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Ingår i: Journal of Fluids and Structures. - : Elsevier BV. - 1095-8622 .- 0889-9746. ; 95
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Tidskriftsartikel (refereegranskat)abstract
- The influence of ground clearance on the flow around a simplified high-speed train is investigated in this paper. Four clearance heights are studied using IDDES. After a grid independence study, the results of the simulations are validated against experimental data present in the literature. It is found that the drag decreases when reducing the clearance gap from the baseline height to a possibly critical height, while drag remains constant when the clearance is lower than this critical height. The negative lift (downforce) increases with the decreasing of the clearance gap. The flow is particularly influenced by the gap height at the underbody and wake regions, where a lower underbody velocity and a higher wake velocity are observed with lower clearance down to case h2. Therefore, the different topologies of the wake are presented and described. Particular attention is paid to the description of the wake flow and to the position and the formation of the flow mixing region. Specifically, with decreasing clearance, the mix of the tail downwash and underbody flows happen earlier, and the core of the counter-rotating vortices in the wake tends to develop with an increasing height trend. Overall, aerodynamic performance and flow structure descriptions show positive and negative effects when decreasing gap clearances, which should be taken into account for new design strategies.
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| 3. |
- Dong, Tianyun, et al.
(författare)
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The effect of reducing the underbody clearance on the aerodynamics of a high-speed train
- 2020
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 204
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Tidskriftsartikel (refereegranskat)abstract
- The effect of lowering the ground clearance, on train aerodynamics is investigated using IDDES. The high speed train geometry with its full underbody complexity is used in the investigation. The clearance is reduced by installing extra panels on the track. The numerical results are verified and validated by a grid independence study and experimental data. This work shows that, when lowered the clearance, the underbody velocity at the head car decreases, while the underbody velocity at the middle and tail car increases. The reduced clearance barely affects the time-averaged slipstream at 3 m away from the center of track. However, at a closer distance to the train body, the difference in velocity is observed to reach up to 50% between the two clearance configurations and the clearance has an opposite effect on the trackside and platform slipstream. Based on the analysis of ensemble-averaged slipstream, lowering the underbody clearance, the characteristic air speed at the trackside and platform height increases by 2.0% and 6.7%, respectively. The total drag is almost unaffected by the clearance, but the changed distribution of the drag indicates a larger drag depends on the bogie structure if longer grouped train is used. The total lift decreases 25.9% after the clearance is reduced. Specifically, 4.1% of the negative lift is increased at the head car, while the positive lift decreases 92.7% and 1.8% for the middle and tail car, respectively. Overall it is shown that reducing the underbody clearance barely affect the slipstream at standard positions, but affects more aerodynamic loads of the train.
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| 4. |
- Wang, Jiabin, et al.
(författare)
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A numerical investigation on the improvement of anti-snow performance of the bogies of a high-speed train
- 2020
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Ingår i: Proceedings of the Institution of Mechanical Engineers, Part F: Journal of Rail and Rapid Transit. - : SAGE Publications. - 0954-4097 .- 2041-3017. ; 234:10, s. 1319-1334
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, numerical simulations combining unsteady Reynolds-averaged Navier-Stokes (URANS) simulation and the discrete phase model are used to study the application of countermeasure for snow accumulation in the regions of bogie cavities of a high-speed train. The influence of the cowcatcher heights and guide structure configurations on the flow features and snow accumulation was studied. The results of the study show that the cowcatcher with a downward elongation of 4% of the distance between the two axles decreases the snow accumulation in the first and the second bogie regions by about 56.6% and 13.6%, respectively. Furthermore, the guide structures have been found to significantly alter the velocity and pressure distribution in the second bogie region, resulting in a relatively large snow-accumulation reduction. The deflector is found to perform better in reducing snow accumulation when compared to the diversion slots. The cowcatcher, elongated in the downward direction, and the deflector proved to be a good countermeasure for snow accumulation around the bogies of high-speed trains operating in snowy weather conditions. © IMechE 2019.
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