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The aerodynamic performance and wake dynamics of wind turbines are known to be affected by platform surge motion. This study utilized an improved delayed detached eddy simulation combined with the overset grid method to investigate the effect of surge motion amplitudes and periods (frequencies) on the aerodynamics and wake instabilities of wind turbines. The effect of the Reynolds number and azimuthal increment sensitivity analysis (time step) on the wind turbine loads and flow fields were investigated in detail. A comparison of the mean loads of the power coefficient and thrust coefficient between the numerical simulation and experiment with a consistent Reynolds number shows that the grid and simulation parameters used in this study can accurately capture the flow field and aerodynamic performance of the wind turbine. A detailed analysis of the flow fields, wake vortex structure, and mean Reynolds stress distribution was utilized to explore the effect of surge motion amplitudes and periods on the wind turbine performance, as well as the mechanism of the wake instability. Our results indicate that the surge motion can improve the efficiency of power generation and promote wake instabilities and vortex interactions. Meanwhile, surge motion amplitudes and frequencies have a positive effect on the wake recovery. • IDDES is employed to model aerodynamics performance and wake dynamics of OFHAWT under surge motion. • The flow field near the blade and wake region is analyzed in detail. • Surge motion promotes the wake instabilities and vortex interaction. • Surge motion amplitudes and frequencies have a positive effect on the wake recovery process. [ABSTRACT FROM AUTHOR]

The aerodynamic loads on the overhead bridge bottom surface induced by train passage are reported in this paper. Both moving model test and numerical simulation approaches at the 1:20 scale are used. The numerical work is validated through both mesh independence tests and comparison with experimental data. Typical pressure variation curves are plotted and compared with previous studies. The peak pressure values' dependence on the Reynolds number is considered through four sets of experiments with different train running speeds. The peak pressure coefficient distribution law for the bridge bottom surface is presented. Differences in the pressure distribution in different bridge bottom areas are explained based on more detailed flow field information. The influence of the bridge height on the aerodynamic load magnitude and time interval is presented. Moreover, the application of the CEN Standard to practical engineering issues is discussed. [ABSTRACT FROM AUTHOR]

With an increase in train speed, the aerodynamic effects caused by the train could escalate, especially for a train running in a tunnel. A number of large transient pressure waves are generated owing to the confined spaces within the tunnel, resulting in possible damage to the vehicle structure and the facilities in the tunnel. Therefore, it is necessary to study the aerodynamic performance of a train running in a tunnel. A scaled moving model test system was constructed to facilitate the simulation of the aerodynamic effects caused by a train running in a tunnel. In this study, the influence of grid density, calculation time step, and turbulence model on the pressure caused by the train entering the tunnel was analyzed, which is helpful for choosing suitable values of the aforementioned parameters to simulate the aerodynamic performance of the train in the tunnel. The impacts of Reynolds number effect on the distribution of the surface pressure and peak of pressure wave along the train, and the pressure waveform were also studied through numerical simulation on three scaled model trains (full scale, 1/8, 1/20, and 1/32 scaled). The findings aid in understanding the relationship between the Reynolds and pressure amplitude, and the results of the scaled test can be applied to a full-scale train. [ABSTRACT FROM AUTHOR]

Abstract The improved delayed detached eddy simulation (IDDES) was used to study the influence of the train's nose length on its aerodynamic performance. Both the time-averaged and instantaneous near-wake structures and the associated distribution of slipstream velocity are compared for three nose lengths. As the nose length increases, the mean and Std values of the drag and lift force are decreased. The shorter nose-length case results in a higher slipstream velocity. In particular, at the TSI track-side position, the TSI value U 2δ for the 5-m nose length case is 30% and 32% higher than the corresponding values for the 7.5-m and 10-m nose length cases, respectively. The dynamical flow topology in the wake reveals that the flow structures of the 5-m nose length are different from those of the other two cases in the tail streamline surface. As nose length increases, the longitudinal vortices are weaker, and the angle and distance between the longitudinal vortices are smaller. The shear production from the P x y caused by the separation of the boundary layer at the lateral wall of the tail train is greater than that of the P x z caused by the separation of the boundary layer at the top and bottom of the tail train. [ABSTRACT FROM AUTHOR]