A novel wake flow control method for drag reduction of a high-speed train with vortex generators installing on streamlined tail nose

The head/tail of a high-speed train has been designed in a streamlined way to achieve good aerodynamic performance, which leads to the flow separation point moving close to the tail nose tip. Therefore, the conventional way with some add-ons, i.e., the passive flow control, to suppress the flow separation in advance is not a good choice for this train wake flow improvement. Also, with the increase of the train speed, it is urgent to study new methods for the aerodynamic drag reduction of the train. The wake of the high-speed train is characterized by a pair of counter-rotating vortices, contributing to low surface pressure on the streamlined tail and posing a risk to the train operation. Thus, lowering the intensity of counter-rotating vortices and enhancing the surface pressure become a significantly potential drag reduction method. In the current study, a novel wake flow control method, named the vortex intensity reduction theory (VIRT), for the drag reduction of a high-speed train with vortex generators installing on the streamlined tail nose, was proposed to generate a pair of vortices with opposite rotating directions, expecting to weaken the wake vortices and have a higher-pressure distribution on the tail, as compared to the base case. The results show that with the installation of vortex generators (VGs), the train wake flow intensity is suppressed, and the influence region is reduced, resulting in the better train wake flow structures, as compared to the train without VGs. The VGs have significant impact on the aerodynamic performance of the tail car, while this effect is not evidently observed on the head and middle cars. The VGs contribute to the surface pressure increase on the streamlined tail, resulting into a reduction of pressure difference between the head and tail cars. As a result, a reduction of 5.11% in the aerodynamic drag and a reduction of 14.93% in the aerodynamic lift of the tail car are obtained, while for a three-car grouping train model, the reductions are about 2.23% and 72.66%, respectively. Therefore, the VIRT based on VGs proposed in this paper can effectively reduce the aerodynamic force of the tail car and alleviate the intensity of wake flow of the high-speed train, which will provide a newly potential drag reduction method of the next generation high-speed train.