The scale effect of the wind tunnel test on the drag force of a stationary train under crosswinds

The experimental errors of the buffeting force caused by the scale effect become more significant when the reproduced turbulence scale is not very large in comparison with the characteristic dimension of the test model. From a fluid mechanics perspective, the scale effect can be divided into the three-dimensional (3D) effect in the spanwise direction and the distortion effect in the streamwise direction. A theoretical model of the 3D drag admittance is proposed to study the influence mechanism of the scale effect. Wind tunnel tests were conducted to clarify the effects of turbulence intensities (Iu) and scales (Lu/D) on the spatial distribution characteristics of drag force on a stationary train under crosswinds. The results indicate that the Iu mainly influences the drag coeffi- cient. In comparison, the Lu/D is the key parameter in determining the scale effect on the drag force, which becomes more significant when the turbulence scale decreases. Based on the wind tunnel tests, an improved and double-exponential coherence model of drag force is proposed, resulting in a generalized 3D AAF model to rapidly modify the scale effect on the drag force of a stationary train.

Automated summary

The experimental errors caused by the scale effect become more significant when the reproduced turbulence scale is not very large compared to the test model's characteristic dimension. The scale effect can be divided into the 3D effect in the spanwise direction and the distortion effect in the streamwise direction. A theoretical model of the 3D drag admittance is proposed to study the influence mechanism of the scale effect.