| 1. |
- Su, Xinchao, 1991, et al.
(författare)
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Comparison of flow characteristics behind squareback bluff-bodies with and without wheels
- 2023
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Ingår i: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 35:3
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Tidskriftsartikel (refereegranskat)abstract
- The wake dynamics of two referenced variations of the squareback Windsor model with and without wheels is numerically studied by performing improved delayed detached eddy simulation. Numerical assessments are validated against publicly available experimental data. The focus of this study is on the wake states influenced by the wheels and the thick oncoming floor boundary layer. Results show that the addition of the wheels significantly changes the aerodynamic forces, the underbody flow, and the wake topology. The wake bi-stability is also enhanced with wheels in place due to the increased curvature of lateral shear layers in the near wake. However, the bi-stable behavior is largely suppressed when immersed in a thick boundary layer. These alterations depend on the degree of interaction between the wake recirculation and the bottom flow, and such degree is strongly affected by the underbody flow momentum. The evolution of low-order flow organizations and complementary spectral analysis highlight the differences in the coherent dynamics of the wake. The finding of this present work suggests that the wake bi-stability behind the squareback body can exist not only for a simplified geometry but also for a more realistic car with wheels in real-world upstream conditions.
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| 2. |
- Wu, Yitong, et al.
(författare)
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Numerical and experiment study on ventilation performance of the equipment compartment of Alpine high-speed train
- 2023
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Ingår i: Engineering Applications of Computational Fluid Mechanics. - 1994-2060 .- 1997-003X. ; 17:1
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Tidskriftsartikel (refereegranskat)abstract
- Alpine High-Speed Train serves on the Lanzhou-Urumqi Line in northwest China, where the terrain is mainly the Gobi Desert. To adapt to this complex environment, the independent-air duct is mainly used for the electrical facilities inside the equipment compartment to prevent the spread of sand particles. This isolated air duct makes ventilation characteristics of the equipment susceptible to the external environment. For this reason, this work aims to clarify and investigate the ventilation characteristic of electrical facilities. A two-step simulation method using IDDES (Improved Delayed Detached Eddy Simulation) and a real-vehicle tracking test using the T-typed pitot tubes were conducted. In the simulation, it is found that the ventilation performance can be influenced by the location of the equipment compartment, facilities and the fan mounted inside. By comparing the results of the test and simulation, they share the same characteristic that the air outlet volume of the converter near the head car is being promoted while it near the tail car is being inhibited. The maximum deviation ratio between the test and simulation is 9%. Therefore, the measurement method in this study is relatively reliable.
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| 3. |
- Xia, Yutao, 1995, et al.
(författare)
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Investigation of the dynamic airtightness coefficient of high-speed trains traveling through a tunnel: A field study
- 2023
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Ingår i: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 236
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Tidskriftsartikel (refereegranskat)abstract
- Determining the dynamic airtightness coefficient (τdyn) of train carriages using a high-accuracy and high-efficiency method is essential regarding the study of the dynamic airtightness performance of high-speed trains (HSTs) traveling through tunnels. This study set out to provide a systematic elaboration and investigation of the whole process of establishing the calculation methodology of τdyn of HST carriages. Moreover, the applicability of three different typical optimization algorithms in the calculation of τdyn was explored and compared. These were the traversal algorithm (TRAA), the trichotomy algorithm (TRIA), and the genetic algorithm (GA). Using the established calculation method, the values of τdyn of different HST carriages for tunnels with different lengths were calculated based on field test data of pressure outside and inside HST carriages. Results revealed that the selection of optimization algorithms had significant effects on the calculation process of τdyn because of their different optimization mechanisms. These three optimization algorithms were proven to be feasible for establishing the calculation method of τdyn and gave the same calculation result of τdyn for the calculation example within the expected accuracy. The elapsed time of the TRAA and GA were approximately 100 and 80 times that of the TRIA regarding the calculation example. The TRIA was the preferable choice for the calculation of τdyn among the three algorithms because of its uncomplicated implementation logic and high efficiency. Within the tunnel-length range involved, the tunnel length itself had no significant effect on τdyn of HST carriages. A significant increasing trend in τdyn of HST carriages was found along the train length. Compared to the head car, the increasing ratio of τdyn of the second car was varying from 0.2 to 0.5, while the increasing ratio of the seventh car was ranging from 0.8 to 1.7 considering different tunnel lengths. These findings provide a reference basis for the design of the calculation method of τdyn of HST carriages and also enhance understanding of τdyn of HST carriages under different operating circumstances.
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| 4. |
- Xu, Kewei, 1992, et al.
(författare)
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Active flow control of the airflow of a ship at yaw
- 2023
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018. ; 273
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Tidskriftsartikel (refereegranskat)abstract
- This paper implements the steady Coanda effect active flow control (AFC) on the Chalmers ship model (CSM) to study its influence on the ship's side force and airwake under the yaw effect. The study is conducted numerically using Large Eddy Simulation (LES) with Wall-Adapting Local-Eddy Viscosity (WALE) model. Numerical methods are validated by the experimental data acquired from the baseline CSM under 10∘ port-side wind. The model with AFC is created by modifying the square-shaped hanger base to the Coanda surface and added with injection slots along the base's roof edge and two side edges. The results show that the base-shape modification significantly alters the vortex structure on deck from z-direction vortex (ZV) to streamwise vortex (SV), and the steady Coanda effect with a momentum coefficient (Cμ) of 0.02 further enhances the SV with the removal of port-side vortex (PV). The side force and yaw moment are reduced by 5.27% and 7.97%, respectively in the AFC case due to the reduction of port-side (windward) ship-surface pressure. Furthermore, the current AFC can suppress the low-speed region and alleviate the velocity gradient in the lateral direction, which mitigates the regions of high TKE (turbulent kinetic energy) and high shear stress along the port-side deck.
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| 5. |
- Xu, Kewei, 1992, et al.
(författare)
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Large eddy simulation of ship airflow control with steady Coanda effect
- 2023
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Ingår i: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 35:1
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Tidskriftsartikel (refereegranskat)abstract
- This paper numerically studies the steady Coanda effect for drag reduction and airwake manipulations on the Chalmers ship model (CSM) using large eddy simulation with wall-adapting local-eddy viscosity model. Numerical methods are validated by experimental data acquired from the baseline CSM. In creating the flow control model, the hanger base of the baseline CSM is modified with Coanda surfaces and injection slots along its roof edge and two side edges. Four representative cases are studied: a no-jet case and three cases with the same momentum coefficient of the jet flow activated at different locations (roof, sides, and combined). The results show that the four cases have various performances in drag reduction and vortex structures on the deck. They are also different in mean and turbulent quantities as well as POD (proper orthogonal decomposition) modes in their airwake. It is found that the roof-jet has a stronger Coanda effect and is more vectored toward the low-speed area (LSA) on the deck than the side-jets that detach earlier from the Coanda surface. The energization process is, therefore, different where the roof-jet is more effective that directly brings high momentum to LSA and side-jets manipulate shear layers for mixing enhancement. The cases with roof-jet achieve better mitigation of flow re-circulation and higher recovery of streamwise velocity with lower turbulent fluctuation in the airwake. POD analysis suggests that the roof-jet can stabilize the wake.
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