Search

Experiments on the aerodynamics of a two-dimensional bluff body simplified from a China high-speed train in crosswinds were carried out in a wind tunnel. Effects of wind angle of attack α varying in [−20°, 20°] were investigated at a moderate Reynolds number Re = 9.35 × 104 (based on the height of the model). Four typical behaviors of aerodynamics were identified. These behaviors are attributed to the flow structure around the upper and lower halves of the model changing from full to intermittent reattachment, and to full separation with a variation in α. An alternate transition phenomenon, characterized by an alteration between large- and small-amplitude aerodynamic fluctuations, was detected. The frequency of this alteration is about 1/10 of the predominant vortex shedding. In the intervals of the large-amplitude behavior, aerodynamic forces fluctuate periodically with a strong span-wise coherence, which are caused by the anti-symmetric vortex shedding along the stream-wise direction. On the contrary, the aerodynamic forces fluctuating at small amplitudes correspond to a weak span-wise coherence, which are ascribed to the symmetric vortex shedding from the upper and lower halves of the model. Generally, the mean amplitude of the large-amplitude mode is 3 times larger than that of the small one. Finally, the effects of Reynolds number were examined within Re = [9.35 × 104, 2.49 × 105]. Strong Reynolds number dependence was observed on the model with two rounded upper corners. [ABSTRACT FROM AUTHOR]

A wind tunnel test of synchronized pressure measurement on a spring-suspended sectional model of a flat closed box deck at a large scale of 1/20 was carried out by taking Xiangshan Harbour Bridge in China as background. The chordwise correlation of the fluctuating aerodynamic pressures (FAP) on the surface of the box deck was then investigated at both stationary state and vortex-induced resonance (VIR) states of the deck model. Afterwards, an approximate approach was developed for estimating the spanwise correlation coefficients of pure vertical vortex-shedding force (VSF) on the deck under VIR state. On this basis, the spanwise correlation coefficients of both the integrated total vertical fluctuating aerodynamic force (FAF) and the pure vertical VSF on the flat box deck were then studied and compared to each other quantitatively at the stationary state as well as the VIR states at various wind speeds. Finally, the spanwise correlation coefficients of the surface FAP at some typical positions on the deck cross section were calculated and compared with that of the total vertical FAF and the vertical VSF. The results show that the chordwise correlation of the FAP on stationary deck is not strong at most part of the deck surface, however, can be enhanced with the increase of incident wind speed. The chordwise correlation of FAP can also be enhanced quite significantly by the deck oscillation under VIR states, but is still imperfect. Furthermore, the spanwise correlations of FAP at different positions on the deck cross section are clearly different from each other, and much weaker than that of the total vertical FAF, for both the stationary state and the VIR states of the deck. However, they are generally much stronger than that of the pure VSF in cases of notable VIR, and much weaker in the cases of slight VIR, such as near the onset of VIR. The spanwise correlation characteristics of both the pure vertical VSF and the total vertical FAF are hence very different from those of the surface pressures. Moreover, the spanwise correlation of the total vertical FAF on cross sections can be greatly intensified by the VIR because of the existence of a large portion of vortex-induced self-excited force (VISEF). On the other hand, the spanwise correlation of the vertical VSF under the VIR states is much weaker than that of total vertical FAF as well as that of the pure vertical VSF under the stationary state at same wind speeds. Finally, the variations of the spanwise correlation of both the total vertical FAF and the pure vertical VSF with the response displacement of VIR is quite complicated. The most violent VIR, the most correlated total FAF and the most correlated VSF occur generally at different wind speeds. [ABSTRACT FROM AUTHOR]

Double-unit trains composed of the same type of high-speed trains (HSTs) are relatively common. The connection of different types of trains, however, has been rarely studied. Therefore, we adopted an improved delayed detached-eddy simulation (IDDES) method to investigate the aerodynamic characteristics on double-unit trains formed by different types of HSTs. Two standardized HSTs—Train A and Train B at present in China—are used to form four different cases (A-A, A-B, B-A, and B-B). We conducted algorithm validation and grid independence to ensure the reliability of numerical results. The results showed the drag of case B-B was smaller when the same HST units were connected, whereas the drag of case A-B was smaller when the different HST units were connected. Downstream the coupling region, the structures of vortex shedding presented obvious differences for each case, which further led to different fluctuation intensities in wake vortices. The order of the height of the wake vortices was as follows: h 1(A-A) > h 3(B-A) > h 2(A-B) > h 4(B-B). The tail of the upstream vehicle had a dominant influence on the slipstream peak in the coupling region. • The minimum drag of double-unit train formations with different combinations is obtained. • The discontinuous coupling region has an obvious influence on the downstream vortices. • The tail of the upstream vehicle has a dominant influence on the slipstream peak in the coupling region. [ABSTRACT FROM AUTHOR]

Two vortex-induced vibration (VIV) events of the main girder of long-span bridges successively happened on the Yingwuzhou suspension bridge and Humen suspension bridge in China, 2020, and drew public attention. Especially for the Humen suspension bridge, the amplitude of VIV was so notable that the traffic was closed for 10 days. Generally, VIV is sensitive to the structural and ambient issues and large-amplitude VIV is unacceptable for engineering structures as it could result in potential fatigue failure of some key joint components. Therefore, it is of great significance to explore the excitation mechanism of VIV and develop effective methods to mitigate excessive vibration of main-girders. From the perspective of vortex dynamics, we present a selective review of recent progress on the mechanism of VIV occurred in long-span bridges and aerodynamic countermeasures to attenuate the VIV amplitude. Notwithstanding the VIV mechanism of girders has not been thoroughly clarified, it is generally accepted that VIV rises from the unsteady vortex shedding from the main girder. Besides, the flow control methods, which are proposed to manipulate the surrounding flow patterns around the girder, are also focused in this review. Some perspectives are finally presented for future studies in fluid–structure interaction and aerodynamic vibration mitigation of long-span bridges. [ABSTRACT FROM AUTHOR]

A submerged floating tunnel (SFT) is a promising alternative to conventional bridges and tunnels, and can be potentially built in the Qiongzhou Strait in China. However, this area is under the threat of disasters including mega tsunamis and severe storm surges. To evaluate the hydrodynamic loads of the SFT in this hazardous zone subject to severe tsunami and typhoon impacts, the Delft3D-FLOW hydrodynamic model and SWAN wave model are coupled, and a Computational Fluid Dynamics (CFD) method is adopted. The maximum probable tsunami and typhoon Rammasun (July 2014) are selected as hazard assessment conditions in the Qiongzhou Strait. Whether the tsunami and hindcast storm surge cause extreme forcing and bring challenges to the SFT engineering design, operation, and maintenance in the Qiongzhou Strait are discussed in this study. We reveal that the typhoon impacts are more devastating than tsunami for an SFT in the Qiongzhou Strait. In order to determine the optimal SFT cross-section under extreme events, we use a parametric Bezier curve profile compared with two simpler shapes including circular and elliptical cross sections. In-line force and lift are respectively applied to evaluate the SFT's hydrodynamic behaviour. Our results reveal that the gross horizontal force on the parametric Bezier curve shape is more sensitive to flow acceleration, while the circular cross-section is dominated by current speed. The parametric Bezier curve cross-section shape has the preferable property of reducing the in-line force and postponing serious vortex shedding compared with the two simpler shapes. • Extreme disasters including mega tsunamis and severe storm surges accessed in the Qiongzhou Strait. • An integrated atmosphere-ocean modelling combined with CFD framework established for tunnel forcing evaluation. • Preferable property of a parametric submerged floating tunnel cross-section than the simpler shapes. • The typhoon impacts are more devastating than tsunami for the submerged floating tunnel in the Qiongzhou Strait. [ABSTRACT FROM AUTHOR]