Investigation On Unsteady Flow Structures Around A Simplified Car Under The Crosswind

With the deeply improvement of auto industry,all the aspects have been being excelsior.Under the circumstances,automobile aerodynamics attract more and more attentions.It makes perfect sense not only in energy conservation and emission reduction,but also in vehicle drives.In especial,the crosswind brings overwhelming numbers hidden dangers when the car is moving on the road,which is in aspects of operational stability and running safety.What is worse,disastrous traffic accident happens.Thus,it the first choice that exploring the flow structures around the car under the crosswind.With the knowledge of flow structures and the formation mechanism,the aerodynamic characteristics under the crosswind will be improved in furthermore.This work choices the Ahmed mode which is an classical mode in auto aerodynamics with 25 slanting angle.The unsteady flow structures is been researched under three different yawing angles with 0°?10 °and 20°.Numerical simulation is the main method and Particle Image Velocimetry(PIV)is verified.Both speeds of wind are 27.78m/s.Firstly,Star-ccm+ calculate flow around the mode.Secondly,vortex value and pressure value are exported which includes three directions.By Tecplot both steady and unsteady flow information can be obtained.From then,the formation mechanism of flow and the difference between different yaw angles can be analyzed.Thirdly,an experimental in wind tunnel has been gone,which produces flow information of three directions and data of vorticity?velocity and speed streamlines.Experiment data is used for verifying the facticity of numerical simulation.Lastly,in a sum,the whole flow under three yawing angles can be conclude in schematic diagrams.Firstly,without yaw same vortexes has been formed,including a pair of C-pillar?a pair of induced vortex?a pair of I vortex?a pair of H vortex?A vortex and B vortex and G vortex under the gap.The symmetry and the equal vortex value are the strongest features.Secondly,with 10°yawing angle,there are huge changes comparing with no yaw.The most feature is the flow separation of head.Distribution of all vortexes are not symmetrical any more.H vortex and G vortex have changed so much.A pair of top edge vortex appear with the side top edges.The right half of I vortex is separated by right top edge vortex.The half of H vortex disappears,however,the left half of H vortex still exists.The air flow deviates from the longitudinal direction of the body,forming an irregular G vortex.Thirdly,with 20°yawing angle,the vortex is quite complicated than it is 10°.Air separation of head is even more significant and asymmetry is more serious.Top edge vortex?H vortex?and G vortex last the variation trend under 10°yawing angles.The almost right C-pillar situates at the longitudinal symmetry plate.The mainly vortex is extremely changeful.Characters of the vortexes are obviously different.The article studied the whole flow structures around Ahmed mode under different kinds of crosswind,including flow separation?the formation and the development of vortex?the influence within each other?the location and shape.The analysis of crosswind flow structures has theoretical guidance meaning for aerodynamics characteristics variation by crosswind.