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The equipment cabins of high‐speed trains encountered alternating pressure loads during operation. A fatigue evaluation methodology based on sub‐zone aerodynamic loading was proposed. Theoretical model was given between pressure load at each zone and the accompanying six structural stress components. Stress recovery matrix was formulated by finite element analysis (FEA) in sub‐zone loading cases to relate the stress to the measured pressure loads. Vehicle test gathered the pressure time‐history data of cabin sub‐zones at the head car in different ambient conditions, from which the two‐dimensional stress spectrum was derived by rain‐flow counting. The fatigue damage of welds was then assessed utilizing the Miner's and Corten Dolan's rules, yielding maximum equivalent damages of 0.72 and 0.23, respectively. The structural fatigue damage under high environmental wind conditions was 1–3 times greater than in calm weather. Nonetheless, the fatigue damage incurred by the metal matrix was significantly lower, demonstrating a substantial safety margin. Highlights: Proposed a sub‐zone aerodynamic load‐stress conversion model.Welds exhibit higher aerodynamic fatigue damage than metal matrix.Strong winds heighten fatigue damage in the equipment cabin of high‐speed trains. [ABSTRACT FROM AUTHOR]

This paper investigates the flow dynamics around a square finite wall-mounted square cylinder of two different aspect ratios (A R = H / D = 6 and 10, H and D are the height and width, respectively) under six boundary layer thickness ( δ / D = 0.5 – 4.0 , δ is the boundary layer thickness) using the improved delayed detached eddy simulation turbulence model. The Reynolds number based on the square cylinder width and incoming velocity is Re = 1.4 × 10 4 . The aerodynamic force, surface mean and fluctuating pressure, wake closure length, Reynolds stresses, turbulence production, and the anisotropy of turbulence are analyzed in detail to investigate the effect of A R and δ / D combinations. The Q-criterion vortex identification method is adopted to identify and classify the vortex structures of different A R and δ / D combinations. The parametric diagram based on A R and δ / D to predict the dipole/quadrupole wake structure proposed in Yauwenas et al. ["The effect of aspect ratio on the wake structure of finite wall-mounted square cylinders," J. Fluid Mech. 875, 929–960 (2019)] is refined based on results of the present study (quadrupole wake for A R = 6 with δ / D ≥ 1.5 and A R = 10 with δ / D ≥ 1.0). The instantaneous space–time pressure distribution along the whole span proves the existence of cellular shedding (A R = 10 for δ / D = 0.5 – 2.0), and the spectral proper orthogonal decomposition technique is adopted to investigate the cellular shedding phenomenon and its distribution. With the increase in δ / D from 2.0 to 4.0, the cellular shedding process is absent, implying the inhibitory effect of increasing boundary layer thickness on the cellular shedding. [ABSTRACT FROM AUTHOR]

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 current research attempts to describe the association between the aerodynamic drag and flow structures induced by train running in time-averaged and time-dependant views. A ICE2 train model is used as the research object, with the flow field solved by Large Eddy Simulation (LES). The validation is carried out through comparison with existing research data, and grid independence study in terms of time-averaged and second-order statistics. Numerical results are firstly presented by description of the time-averaged near wake flow topology based on surface flow visualization. Then, the wake integration method is used both time-averaged and instantaneously to link the aerodynamic force with integrated flow quantities on different wake planes: from the time-averaged perspective, the contribution of different flow terms to total drag is presented and compared; from the instantaneous perspective, the overall wake variation tendency is linked to the fluctuating component of aerodynamic force, based on the wake convection velocity and downstream distance of wake planes. The dynamic features of flow quantities in different locations are presented, with cross-correlation method used to describe the correlation between fluctuating aerodynamic drag and wake motion. Approaches and findings presented in the current study could serve as fundamentals which support future study. • Large eddy simulation employed to solve flow field around a generic ICE2 high-speed train model. • Surface flow visualization techniques utilized to illustrate the time-averaged near wake flow topology. • Wake integration method applied to link the aerodynamic force with integrated flow quantities on different wake planes. • Dynamic features of flow quantities presented, with cross-correlation method used to describe correlation between aerodynamic drag and wake motion. [ABSTRACT FROM AUTHOR]

The improved delayed detached eddy simulation (IDDES) was used to study the influence of the platoon configuration of trains on its aerodynamic performance. CFD simulations were validated against the wind tunnel test and different mesh refinement to further verify the flow field around the high-speed train. The platoon configuration mainly affects the aerodynamic forces of the tail car of the front train (car3) and the head car of the rear train (car4) through flow interference. The surface pressure distribution of the train and the time domain and frequency domain characteristics of the aerodynamic force under different spacing are analyzed, and the changing law of the aerodynamic force and the lateral stability of the trains are summarized. The boundary layer and slipstream of trains in platoon are also compared with those of single trains. Meanwhile, both the time-averaged and instantaneous near-wake structures are compared for different cases. • IDDES k-w turbulence model is used to model the wake interaction and detailed flow field structure. • The aerodynamic force, slipstream, and boundary layer under different spacing are evaluated. • The dominant equivalent full-scale frequency (Hz) at 300 ​km/h lies between 1.87 and 3.33 ​Hz (0.09 ≤ S t ≤ 0.16). • The largest oscillating side forces for the car4 in platoon is 157.62 ​N. [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 the increasing need for passenger transportation, the double-unit formation of high-speed trains (HSTs) has been widely employed. However, the dynamic characteristics of the flow around double-unit HSTs have rarely been studied. In this study, the Improved Delayed Detached Eddy Simulation (IDDES) method is employed to analyse the differences in flow fields around single- and double-unit trains. The numerical case is validated through wind tunnel experiments, mesh independence tests and IDDES assessments. The results show that the existence of the double region concentrates the Strouhal number of the aerodynamic force of the wake at 0.15. For the flow downstream of the double region, the slipstream velocity detected until the far-wake region is higher than that in the single-unit case. The standard deviation of the velocity, which reflects the intensity of the turbulence, is also higher for the double-unit case. For the near wake, the vortex dominate region is dominated by flow structure shedding from the snow plough thus similar for two cases; for the downwash dominate region, the double-unit wake exhibits more turbulent flow structures and lower dominant frequency for velocity. The proper orthogonal decomposition results also indicate more turbulent wakes within the downwash dominate region in the double-unit case. [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]