Experimental Study on the Effect of Boundary Layer on High-Speed Train Aerodynamic Forces Measurement

The influences of boundary layer thickness on the aerodynamic characteristics of a high-speed train head car were investigated with an 1:8 scaled model in an 8 m × 6 m wind tunnel at CARDC. Boundary layer thicknesses at different positions on the ballast surface were measured under the wind velocity range of 40 to 70 m/s and the Reynolds number range of 1.25 × 106 to 2.19 × 106. It was found that the effect of Reynolds number on the head car was small. The boundary layer thickness increased significantly along the ballast and decreased gradually with the increase of the wind velocity. A linearly fitted model was employed to calculate the boundary layer thickness under different wind velocities. The changing patterns of the drag and lift force coefficients with the boundary layer thickness were complex. The drag and lift coefficients increased by 5.57% and 21.97% respectively, when the boundary layer thickness was larger than 118 mm. The effects of boundary layer on lift coefficients were more prominent than on the drag coefficients.