| 1. |
- Dong, Tianyun, 1990, et al.
(author)
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Numerical investigation of a high-speed train underbody flows: Studying flow structures through large-eddy simulation and assessment of steady and unsteady Reynolds-averaged Navier-Stokes and improved delayed detached eddy simulation performance
- 2022
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In: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 34:1
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Journal article (peer-reviewed)abstract
- The underbody flow of a truncated, 1:10 scaled, CRH380A model is investigated at Re = 2.78 × 105 in this paper. The large-eddy simulation (LES) is used to study the main features of the development of the underbody flow under the snowplow, in the bogie/cavity region and after the cavity (equip-cabin region). A grid independence study and a validation against experimental data have been done prior to the investigation. The snowplow region is dominated by a pair of separated counter-rotating vortices, which further affects the downstream flow. A strong shear layer is observed in the cavity region, and the turbulent flow is intensively triggered by the shear instability and the complex bogie components within the cavity region. The equip-cabin region allows the turbulent flow to develop without any disturbance, decreasing the turbulence intensity. Moreover, the steady and unsteady Reynolds-averaged Navier-Stokes (RANS, URANS) model and the improved delayed detached eddy simulation (IDDES) are used to compute the same flow, and to compare the results to LES. The solution differences, in terms of aerodynamic forces and the underbody flow state, are analyzed. Specifically, the minimum velocity discrepancy, at line2, between RANS (URANS) and LES is 14.4%, while IDDES is 3.6%. The solution accuracy vs the computational cost is also reported.
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| 2. |
- He, Kan, et al.
(author)
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Numerical investigation of the wake bi-stability behind a notchback Ahmed body
- 2021
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In: Journal of Fluid Mechanics. - : Cambridge University Press (CUP). - 0022-1120 .- 1469-7645. ; 926, s. A36-1-A36-29
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Journal article (peer-reviewed)abstract
- Large-eddy simulations are used to investigate the origin of the wake asymmetry and symmetry behind notchback Ahmed bodies. Two different effective backlight angles, beta(1) = 17.8 degrees and beta(2) = 21.0 degrees, are simulated resulting in wake asymmetry and symmetry in flows without external perturbations, in agreement with previous experimental observations. In particular, the asymmetric case presents a bi-stable nature showing, in a random fashion, two stable mirrored states characterized by a left or right asymmetry for long periods. A random switch and several attempts to switch between the bi-stability are observed. The asymmetry of the flow is ascribed to the asymmetric separations and reattachments in the wake. The deflection of the near-wall flow structures behind the slant counteracting the asymmetry drives the wake to be temporarily symmetric, triggering the switching process of the bi-stable wake. The consequence of deflection that forces the flow structure to form on the opposite side of the slant is the decisive factor for a successful switch. Modal analysis applying proper orthogonal decomposition is used for the exploration of the wake dynamics of the bi-stable nature observed.
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| 3. |
- Minelli, Guglielmo, 1988, et al.
(author)
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Bluff Body Flow Control Using a Genetic Algorithm Optimization
- 2019
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Conference paper (other academic/artistic)abstract
- This first preliminary study highlights few important points: • ML techniques applied to flow control show impressive and sometimes surprising results concerning actuation strategies • A very weak actuation applied at the front rounded cor- ner of the body is able to strongly influence the body wake and sets the starting point for the following future steps: • The backtracking of the evolution results finding pat- terns to explain the flow physics brought by the actuation • The application of the GA to a 3D geometry • The application of a linear genetic programming (LGP) to generate a higher degree of freedom actuation signal
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| 4. |
- Wang, Jiabin, 1993, et al.
(author)
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The effect of bogie fairings on the slipstream and wake flow of a high-speed train. An IDDES study.
- 2019
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In: Journal of Wind Engineering and Industrial Aerodynamics. - : Elsevier BV. - 0167-6105. ; 191, s. 183-202
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Journal article (peer-reviewed)abstract
- In this study, an improved delayed detached eddy simulation (IDDES) method based on shear-stress transport k-ω turbulence model has been used to investigate the slipstream and wake flow around a high-speed train with different bogie fairings at Re = 1.85 × 10^6. The accuracy of the numerical method has been validated by wind tunnel experiments and full-scale field tests. Further, the train slipstream, underbody flow and wake structures are compared for three cases. The results show that the bogies covered by full size bogie fairings significantly decrease the train slipstream velocity and weaken the pressure fluctuation around the high-speed train, especially near the bogie regions. Compared to the maximum slipstream velocity at trackside position in Case 2 (half size fairings), it increases by 15.2% in Case 1 (no fairing) and decreases by 16.1% in Case 3 (full size fairings), respectively. The larger size fairings are found to reduce the scale of longitudinal vortices and decrease the streamwise vorticity level in the wake region, thereby lowering the slipstream velocity distribution in the wake. Finally, the larger bogie fairings are recommended to improve the train aerodynamic performance as well as to improve the safety of trackside workers and passengers standing on the platform.
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