Search

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 improved delayed detached-eddy simulation (IDDES) method based on the shear-stress transport (SST) κ-ω turbulence model was employed to investigate the ballast height influence on aerodynamic performance at Re ​= ​9.12 ​× ​106. Both time-averaged and instantaneous slipstreams and near-wake flow structures and associated slipstream velocity distributions are compared for four cases. Results reveal that the mean lift force coefficient decreases with increasing ballast height. At the Technical Specifications for Interoperability (TSI) trackside position, the maximum slipstream velocity with a ballast height of 1.825 ​m (Case 3) is 97.4%, 15.6% and 11.7% lower than with a ballast height of 0 ​m (Case 1), 0.825 ​m (Case 2) and 2.825 ​m (Case 4), respectively. The TSI values in Case 3 ​at both the trackside and platform positions are the lowest. In the wake region, increasing the ballast height greatly constrains the outward and downward movements of vortices. The slipstream velocity in the wake region in Case 3 is the lowest among all cases. In this study, we found that Case 3 greatly decreases the slipstream velocity around the train and improves the flow structure in the wake region, which reduces the risk to workers and equipment along the railway. • The CFD results were validated with wind tunnel experiment and found good agreement. • IDDES k-w turbulence model is used to model the detailed flow field structure. • The effect of height of ballast on the slipstream and wake dynamics of train is investigated. [ABSTRACT FROM AUTHOR]

In this study, an experimental and computational study of the pressure transients of a high-speed train passing through a station is presented. The experiments were performed using 1/20th scale train models with a head car and an end car on a moving model rig with a speed of 300 km/h. The pressure transients were measured using kulite pressure sensors on the car body surface and the platform screen roof and doors. Computationally, an overset grid and an IDDES k-w turbulence model were adopted to simulate the pressure transients inside a railway station. A numerical simulation with different platform screen doors heights was conducted. The obtained results showed that the CFD simulation results were consistent with the reduced-scale test results. The peak pressure coefficient distribution for the station roof bottom surface, platform screen door surface, and details of the flow field structure is also presented in this article. Moreover, the application of the CEN Standard to practical engineering issues concerning the pressure load and time interval is discussed. • A 1/20 moving model experiment is established to model movement of the high-speed train relative to the ground. • IDDES k-w turbulence model combined with overset grid is used to model the moving of train and detailed flow field. • The CFD results were validated with moving model experiment. • The application of the CEN Standard to practical engineering issues is discussed. [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]

The pressure variations induced by a CRH380A EMU on a 2.15 m high bridge noise barrier are investigated in a field measurement. The familiar fluctuating pressure time history curves and the peak-to-peak pressure ( ΔP ) distributions attributing to the train head on the barrier surfaces are presented. A comparison of the positive head pulse pressure is made between the measurement results and the data calculated by empirical equations in EN 14067-4. Furthermore, the influences of train speed, train running lines, locations of measurement points, train marshalling length and environmental wind speed on ΔP are analysed. The results indicate as the train speed increases, the corresponding time intervals of ΔP decrease gradually, whereas their slopes become increasingly steep. For a CRH380A EMU, the aerodynamic length of the train head is between 7.63 and 7.64 m, which differs from the physical length of a realistic train with 12.00 m. Along the noise barrier from bottom to top, the ΔP values on the inner surface decrease with the increase of height, while these values on the outer surface increase. Taking the wind direction into account, the ΔP values are a little higher when the high-speed trains run against the wind direction. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the effects of oblique tunnel portals on train and tunnel aerodynamics using a 1:20 scale moving model device. Transient pressure and micro-pressure waves were measured using pressure sensors as the train model travelled through various tunnel models at a speed of 350 km/h. The mitigation physical mechanism of oblique tunnel portal on the initial compression wave was explained. Experimental results showed that oblique tunnel portals had obvious mitigation effect on- the pressure gradient and micro-pressure wave induced by the train model passing through the tunnel model. A hat oblique tunnel portal combined with a buffer structure with top holes was particularly effective. [ABSTRACT FROM AUTHOR]

The aerodynamic characteristics of a high-speed train in an atmospheric boundary layer are investigated in a wind tunnel. In addition, different atmospheric boundary layer simulations are performed by changing the turbulence intensity generated by a collection of spires in a wind tunnel. Turbulent flow information, measured with the Cobra probe, is used to describe the atmospheric boundary layer. Furthermore, the effect of velocity on the atmospheric boundary layer is also studied. Both the train’s unsteady aerodynamic force and surface pressure are measured at a Reynolds number of 7.5 × 10 5 , and their mean and standard deviation are used to describe and explain the effect of turbulence and observed trends with varying turbulence intensity. [ABSTRACT FROM AUTHOR]