Turbulent incoming flow conditions are closely matched to the crosswinds experienced by trains in windy areas. Therefore, it is important to investigate how the turbulent inflow affects the flow dynamics around a train. The aerodynamic characteristics of a 1:8-scaled high-speed train at a 90{degree sign} yaw angle was studied based on the Improved Delayed Detached Eddy Simulation (IDDES) turbulence model. Four incoming flow conditions were set using a Synthetic Eddy Method (SEM) turbulent generator, including uniform, Lu = 0.5H, Lu = 1H, and Lu = 2H inflow ( Lu is turbulence integral length scale and H is reference height). The aerodynamic loads, surface pressure, mean vorticity, vortex structure, velocity deficit, turbulence characteristics, Reynold stresses, turbulence production term, and anisotropy of turbulence were thoroughly analyzed. Turbulent inflow and increasing inflow Lu increased the standard deviation of the aerodynamic loads on the train. A crisis of inflow Lu appeared around 0.5H, meaning the rolling moment and overturning moment were largest under this crisis condition. Turbulent inflow caused vortices on the train's leeward side to come closer to the train, increasing the vorticity thickness and shortening the back flow region. The Reynolds stresses on the train's leeward side under turbulent inflow conditions were strengthened. The spectrum proper orthogonal decomposition method was used to analyze the dominant mode within the train's leeward region and the corresponding energy distribution in the frequency domain. The aerodynamic admittance function was used to investigate the frequency characteristics of the aerodynamic loads on the train.

The current study attempts to describe associated fluid dynamics of a square finite wall-mounted cylinder (FWMC) immersed within free-stream turbulent flow characterized by different turbulence intensities and integral length scales. Improved Delayed Detached Eddy Simulation (IDDES) method is adopted to numerically reproduce the fully developed turbulent flow fields. Results reveal that, both the turbulence intensities and integral length scales have significant effect on the separated shear layers, base pressure and associated aerodynamic forces of the cylinder. Constrained streamlines along with critical point techniques are employed to further illustrate the influence of parameters of interests on time-averaged flow pattern, including horseshoe vortex, surface flow and wake topology. Distribution of second-order statistics within the wake region shows a shorter longitudinal length of the reversed flow region and enhanced vortex strength when background turbulence intensity increases. The time-dependant interaction between background turbulence and separated flow around the FWMC is illustrated based on the phase difference between pressure of opposing side faces, and the evolution of reverse-flow region. In the end, the spectral proper orthogonal decomposition technique is employed to further investigate the effects of incoming flow turbulence on characteristics of the free-end shear flow and Von Kármán vortex shedding in the wake.

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