Aerodynamic drag reduction and insulation performance of the roof insulator with dimpled non-smooth surfaces

Aerodynamic drag generated by high-speed train seriously affects the operating economy of trains and restricts a further increase in speed. Currently, the drag reduction method with streamlined bodies has approached the limit. Due to the existence of external insulation equipment, the smoothness of the roof is destroyed, which becomes an important source of aerodynamic drag. However, roof equipment also assumes an essential role of electrical insulation, so both aerodynamic characteristics and insulation performance need to be considered. Therefore, a method of drag reduction based on the non-smooth structure is proposed for the roof insulator, in which the aerodynamic characteristics on and around the insulator are changed by constructing dimpled surfaces on the sheds. In this study, the parameters of the dimple structure with an excellent drag reduction effect were determined, achieving a drag reduction rate of 17.51%. The simulations and experiments were carried out to verify that the dimpled insulator had good electrical insulation performance. Finally, a mechanism analysis of drag reduction with a dimpled structure was provided in terms of the velocity vector, turbulent kinetic energy and turbulent dissipation rate. This study provides guidance for the drag reduction of external insulation equipment and energy savings of high-speed trains.