The flow over two tandem cylinders is investigated with five different spacing ratios L/D = 1.25, 2.0, 3.5, 4.0, and 6.0 and four chamfered-corner ratios ξ = B/D = 0%, 5%, 10%, and 15% at a Reynolds number Re = 5300, where L, B, and D are the distance between cylinders, chamfered corner dimension, and cylinder width, respectively. This work aims to assimilate the effects of ξ and L/D on flow structures, vortex shedding, aerodynamic forces, Strouhal number, and their relationships. We identified three different flow patterns depending on ξ and L/D: overshoot flow (L/D = 1.25, ξ = 0%), reattachment flow (1.25–2.0 ≤ L/D ≤ 2.0–3.5, ξ = 0%–15%), and coshedding flow (L/D ≤ 2.0–3.5, ξ = 0%–15%). The ξ and L/D play a similar role in the qualitative change of the flow structures, albeit with different degrees. As such, when L/D or ξ is increased, an overshoot/reattachment flow may change to a reattachment/coshedding flow. With the same flow pattern, ξ has a greater influence on the aerodynamic facets than L/D. This study establishes a framework for understanding how ξ and L/D influence flow topology and aerodynamic parameters.

The present paper examines the vortex-induced vibration (VIV) of a 5:1 rectangular cylinder with a detached splitter in its near wake. The tested gap ratio between the cylinder and the splitter (g/D, where g is the gap between the cylinder rear and the splitter and D is the depth of the rectangular cylinder) ranges from 0.5 to 2.0, with an increment of 0.5. To serve as a reference case, the rectangular cylinder without the splitter is also tested under the same conditions. The test Reynolds number ranges from 32 320 to 56 507. This study delves into the vibration response, pressure distributions, and power spectral densities (PSD) of the cylinder under varying gap ratios. Based on qualitative and quantitative analyses between the cylinder and the splitter using phase average techniques, smoke-wire visualization, and numerical simulation, the different vortex shedding modes according to different gap ratios were identified. Experimental and numerical results show that the detached splitter and its gap ratio play important roles in determining the cylinder VIV properties. For g/D = 0.5, the detached splitter has a sensible mitigation on the cylinder VIV. However, as the gap ratio increases, the VIV response initially recovers to the reference case at g/D = 1.0 and subsequently enlarges at g/D = 1.5 and 2.0. The pressure distribution results showed that the detached splitter demonstrates its effects primarily through fluctuations in the pressure field rather than the mean field. In addition, at g/D = 0.5, a sensibly decayed PSD is observed, while at g/D = 1.0–2.0, an intensified PSD is detected. The underlying mechanism of the detached splitter on the VIV of the 5:1 rectangular cylinder should be attributed to the von Kármán vortex street compared to the reference case.

This study presents an investigation to quantify the aerodynamics of truss bridge-girders via wind tunnel test and kriging surrogate model. Currently, the conventional methods documented in design specifications only take into consideration the mean drag force at null attack angle. To gain an in-depth understanding on the aerodynamics of truss bridge-girders, experiments on simplified bridge-girder models with various geometric parameters were carried out in uniform flow. A total of 15 truss bridge-girder models with aspect ratio (the ratio of width to height) B/D = 1.0, 1.3, 1.6, 1.9, and 2.2, solidity ratio (the ratio of projected to envelope areas) Φ = 0.20, 0.25, 0.30, 0.35, and 0.40, and two typical truss topologies (Warren and Pratt trusses) were examined in the most concerned range of wind angle of attack α = [–6°, 6°]. These truss bridge-girder models cover most of the high-speed railway bridges widely used in China. Experimental results show that the truss topology has limited effects on the aerodynamics of truss bridge-girders, whereas the effects of α, B/D, and Φ are significant. Based on these wind tunnel results, the ordinary kriging surrogate model was utilized to approximate the aerodynamics of truss bridge-girders. In using this model, aerodynamic force values for test cases can be interpolated with zero variance and uncertainties in unsampled design zones where geometric parameters can be quantified with Gaussian variance.

In this study, wind tunnel experiments were carried out in smooth flow to examine the nexus between flow patterns around a flat-box section and its aerodynamics with the variation of the wind angle of incidence (α). The model cross section closely represents the overall asymmetric geometry and attendant aerodynamics of a class of flat-box decks frequently employed in long-span bridges. To explore the flow around and associated aerodynamic properties of this model that are distinct from a typical symmetric section (e.g., rectangular), detailed wind tunnel tests involving smoke-wire based flow visualizations and synchronous multipoint pressure measurements were carried out. Experimental results were analyzed to identify flow patterns, pressure distributions and associated Strouhal numbers, power spectral densities, aerodynamic force coefficients, proper orthogonal decomposition (POD) analyses, and span-wise correlation. Three typical flow patterns previously observed around symmetric bluff bodies with varying α were also observed in the asymmetric cross section, i.e., the trailing-edge vortex shedding (TEVS), the impinging leading-edge vortices (ILEV), and the alternate-edge vortex shedding (AEVS). However, due to the chordwise asymmetry of the section, the three flow patterns identified are distinct from the classical ones associated with symmetric sections in terms of flow separation points, the static “stall” angle of the section, and characteristics of leading-edge vortices. The roles played by these flow patterns in the aerodynamics of the flat-box section have been identified. It is observed that, if the ILEV or AEVS governs the flow topology, the aerodynamic force coefficients vary nonlinearly with the increase in α, in contrast with the linear variation in the TEVS-dominant case. For cases in which the TEVS dominates, the POD mode participation factors of the fluctuating pressure field display energy in higher modes. In this case, the reconstruction process requires that higher POD modes are retained. Finally, in the TEVS flow pattern, a weaker spanwise correlation of the fluctuating forces is noted as compared to the ILEV and AEVS-type flows. This study is limited to the fundamental examination of asymmetric section aerodynamics in smooth flows, which should be extended in case the influences of turbulence and aeroelastic effect are of interest.

The twin mountains, a common terrain in mountainous areas, tend to induce the acceleration effect under crosswinds, which enhances the wind speed and the turbulence performance of the flow field. To mitigate the impact of the acceleration effect on high-speed trains, structures, and aircraft near the twin mountains, this study investigates the effectiveness of the jet strategies, which are realized on natural mountain slopes by mechanical ventilation, with different jet angles on the flow field and the train. Wind speed tests, flow visualization, wind field prediction, and research on the train's aerodynamic behavior are conducted in this paper using the wind tunnel and the improved delayed detached eddy simulation dynamic models. The results indicate that the wind velocity on the leeward side of the twin mountains increases up to 1.42 folds of the wind velocity of the incoming flow under crosswinds. The jet streams with 0° and 30° angles are the most effective in mitigating the acceleration effect among those tested (0°, 15°, 30°, and 45°), reducing the maximum wind speed by 11.87% and 16%, respectively. Compared with the mitigation effect of the jet stream with the 30° angle, the jet stream with the 0° angle has a better mitigation effect on the aerodynamic loads (4.0%–13.2%) and its fluctuation amplitude (24.4%–42.7%) of the train. These findings are valuable for studying the flow field characteristics of the twin mountains and the designing anti-wind measures for high-speed railways.