Analysis of drag reduction and flow characteristics induced by surface micro-structures on maglev train surfaces

Surface microstructures have shown potential for drag reduction, but their effectiveness on maglev trains remains unclear. This study numerically investigates a 1:20-scale TR08 maglev train with hemispherical dimples arranged on either the streamlined head (HeadConcave) or tail (TailConcave), using large-eddy simulation at 400 km/h to evaluate aerodynamic force, surface pressure behavior, and surrounding wake flow. Results show that TailConcave achieves the best overall performance, reducing the total drag coefficient to 0.1597, about 2.0% lower than the Prototype, mainly through a 2.7% reduction in pressure drag, while HeadConcave increases drag by about 1.5%. Surface-pressure analysis indicates that head dimples intensify local suction and recirculation, promoting earlier separation, whereas tail dimples lower the tail pressure coefficient, smooth pressure recovery, and weaken pressure fluctuations near the tail shoulder, symmetry plane, and guideway-side surface. Wake-flow analysis further shows that TailConcave delays tail separation, extends the dominant vortices downstream, and reduces Reynolds shear stress and turbulent kinetic energy in the near wake. Overall, rear-surface dimples provide a more effective drag-reduction strategy than front-surface dimples.