A study on aerodynamic noise characteristics of a high-speed maglev train with a speed of 600 km/h

Purpose–This study aims to explore the formation mechanism of aerodynamic noise of a high-speed maglev train and understand the characteristics of dipole and quadrupole sound sources of the maglev train at different speed levels.Design/methodology/approach–Based on large eddy simulation(LES)method and Kirchhoff–Ffowcs Williams and Hawkings(K-FWH)equations,the characteristics of dipole and quadrupole sound sources of maglev trains at different speed levels were simulated and analyzed by constructing reasonable penetrable integral surface.Findings–The spatial disturbance resulting from the separation of the boundary layer in the streamlined area of the tail car is the source of aerodynamic sound of the maglev train.The dipole sources of the train are mainly distributed around the radio terminals of the head and tail cars of the maglev train,the bottom of the arms of the streamlined parts of the head and tail cars and the nose tip area of the streamlined part of the tail car,and the quadrupole sources are mainly distributed in the wake area.When the train runs at three speed levels of 400,500 and 600 km$h1,respectively,the radiated energy of quadrupole source is 62.4%,63.3%and 71.7%,respectively,which exceeds that of dipole sources.Originality/value–This study can help understand the aerodynamic noise characteristics generated by the high-speed maglev train and provide a reference for the optimization design of its aerodynamic shape.

Effect of low operating temperature on the aerodynamic characteristics of a high-speed train

In this study,an improved delayed detached eddy simulation(IDDES)method based on the shear-stress transport(SST)k-ωturbulence model has been used to investigate the underbody flow characteristics of a high-speed train operating at lower temperatures with Reynolds number Re=1.85×10^(6).The accuracy of the numerical method has been validated by wind tunnel tests.The aerodynamic drag of the train,pressure distribution on the surface of the train,the flow around the vehicle,and the wake flow are compared for four temperature values:+15℃,0℃,−15℃,and−30℃.It was found that lower operating t emperatures significantly increased the aerodynamic drag force of the train.The drag overall at low temperatures increased by 5.3%(0℃),11.0%(−15℃),and 17.4%(−30℃),respectively,relative to the drag at+15℃.In addition,the low temperature e nhances the positive and negative pressures around and on the surface of the car body,raising the peak positive and negative pressure values in areas susceptible to impingement flow and to rapid changes in flow velocity.The range of train-induced winds around the car body is significantly reduced,the distribution area of vorticity moves backwards,and the airflow velocity in the bogie cavity is significantly increased.At the same time,the temperature causes a significant velocity reduction in the wake flow.It can be seen that the temperature reduction can seriously disturb the normal operation of the train while increasing the aerodynamic drag and energy consumption,and significantly interfering with the airflow characteristics around the car body.

An IDDES study of the near-wake flow topology of a simplified heavy vehicle

The complex wake flow of a GTS(ground transportation system)model contributes to large percentage of the aerodynamic drag force.Therefore,predicting accurate wake flow will help carry out the drag reduction strategies.In this paper,the near-wake flow topology of the GTS was studied at Re=2.7×104 to assess the capability of a hybrid RANS/LES(Reynolds-averaged Navier–Stokes/large eddy simulation)approach,known as IDDES(improved delayed detached eddy simulation).The current study also aims to understand the effects of different computational parameters,e.g.the spatial resolution,time step,residual level,discretization scheme and turbulence model,on this asymmetrical wake flow configuration.A comparison of IDDES with previous water channel tests,wellresolved LES,partially averaged Navier–Stokes and URANS(unsteady RANS)was included to better understand the benefits of this hybrid RANS/LES approach.The results show that on the medium and fine grids,the IDDES produces an asymmetrical flow topology(known as flow state I)in the near-wake of the vertical midplane,as reported in previous studies.The recommended parameters for the time step(1×10^(–4 )s)and residual level(1×10^(–4))provide sufficient accuracy of wake predictions to show good agreement with experiments.For the convective term of the momentum equation in IDDES,the bounded central difference discretization scheme is proposed to be adopted for discretization.Additionally,URANS cannot accurately capture this asymmetrical flow field.IDDES proves to be capable of predicting thewake flowfield of this simplified heavy vehicle with high accuracy.All obtained conclusions can provide references for the aerodynamic drag reduction of the GTS.