Abstract
The structural design of the streamlined shape is the basis for high-speed train aerodynamic design. With use of the delayed detached-eddy simulation (DDES) method, the influence of four different structural types of the streamlined shape on aerodynamic performance and flow mechanism was investigated. These four designs were chosen elaborately, including a double-arch ellipsoid shape, a single-arch ellipsoid shape, a spindle shape with a front cowcatcher and a double-arch wide-flat shape. Two different running scenes, trains running in the open air or in crosswind conditions, were considered. Results reveal that when dealing with drag reduction of the whole train running in the open air, it needs to take into account how air resistance is distributed on both noses and then deal with them both rather than adjust only the head or the tail. An asymmetrical design is feasible with the head being a single-arch ellipsoid and the tail being a spindle with a front cowcatcher to achieve the minimum drag reduction. The single-arch ellipsoid design on both noses could aid in moderating the transverse amplitude of the side force on the tail resulting from the asymmetrical vortex structures in the flow field behind the tail. When crosswind is considered, the pressure distribution on the train surface becomes more disturbed, resulting in the increase of the side force and lift. The current study reveals that the double-arch wide-flat streamlined design helps to alleviate the side force and lift on both noses. The magnitude of side force on the head is 10 times as large as that on the tail while the lift on the head is slightly above that on the tail. Change of positions where flow separation takes place on the streamlined part is the main cause that leads to the opposite behaviors of pressure distribution on the head and on the tail. Under the influence of the ambient wind, flow separation occurs about distinct positions on the train surface and intricate vortices are generated at the leeward side, which add to the aerodynamic loads on the train in crosswind conditions. These results could help gain insight on choosing a most suitable streamlined shape under specific running conditions and acquiring a universal optimum nose shape as well.
Highlights
Aiming at four typical streamlined structures of high-speed trains’ noses, the current study numerically studies ambient flow field and analyzes these four structures’ influence upon aerodynamic loads and slipstream, in order to gain theoretical insight on acquiring a universal optimum nose shape
This study validated the precision of the detached-eddy simulation (DDES) method and the viability of the mesh configuration referring to the wind tunnel experimental data
Targeted at the eight-grouped high-speed train model, streamlined structures such as double-arch ellipsoid, single-arch ellipsoid, a spindle with a front-mounted cowcatcher, double-arch wide-flat shape, and their impacts on the train aerodynamic performance under static and crosswind environmental circumstances were analyzed by means of DDES
Summary
Ku YC et al [17] proposed a vehicle modeling function (VMF) parametric method to parameterize the high-speed train’s head and tail, and analyzed the influence of key design variables of the streamlined shape on the train aerodynamic performance. These studies have mainly described the relationships between the geometric shapes and aerodynamic performance but not yet pointed out how the streamlined structures of the noses affect the flow field around a train. Aiming at four typical streamlined structures of high-speed trains’ noses, the current study numerically studies ambient flow field and analyzes these four structures’ influence upon aerodynamic loads and slipstream, in order to gain theoretical insight on acquiring a universal optimum nose shape.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
