Study On The Flow Mechanism Of The Flow Field Around The Vehical Under The Condition Of Wheel Rotation

As the number of cars in our country increases year by year,the demand and consumption of energy are also growing rapidly.The automobile industry is facing huge energy challenges.In addition to the existing strategies for developing new energy vehicles,the requirements for energy saving and emission reduction of traditional vehicles are becoming more and more prominent.Using aerodynamics technology to save fuel will effectively alleviate my country’s energy problems.For a mass-produced car,the wheel wind resistance can reach 25%,and the separated flow generated by the rotating wheel of the car has an important influence on the external flow field of the car.Therefore,the feasibility of the method is verified by aerodynamic numerical simulation technology and wind tunnel test.It is of great significance to study the mechanism of the rotating wheel on the flow field around the car.In this paper,the DrivAer model,which is a more realistic general automobile model jointly launched by the Technical University of Munich,BMW and Audi,is used as the research object,and the STAR-CCM+ numerical simulation technology is used to study the flow field around the automobile under the condition of wheel rotation.First,use STAR-CCM+ software to calculate the original working conditions of the DrivAer diagonal model with detailed chassis structure and wheel longitudinal tread used in this paper.The simulation results are compared with the test results and analyzed to confirm the accuracy of the simulation method.After that,the two steadystate simulation methods: rotating wall method and MRF(multiple reference frame)method were compared and studied,and the subsequent wheel area modeling method was determined.To study the flow mechanism of rotating wheels on the vehicle,the first to isolate rotating wheel and the vehicle wheel rotation condition has carried on the comparative study,found that due to wheel cavity block making smaller working condition of vehicle wheel front high range,and keep out of the body side on airflow to the wheel lateral the spokes clearance airflow into the wheel hub cavity,reduce the spokes and air forces,but the existence of wheel cavity,makes the top to flow to the rear wheels forward extrusion wheel cavity and reflux,therefore the working condition of the vehicle wheels the wheel at the back of the shoulder vortex disappeared,partly reduced the rear air drag on the wheels,it is beneficial to improve the aerodynamic performance around the wheel.After the vehicle spinning wheels and vehicle static wheel condition comparison research,found that will make the wheel-the rotation of the wheels to accumulate near the interface of air,partial front high so as to increase resistance coefficient,but will improve the rotation of the wheels at the back of the wheel wake,especially rear wheel wake flow can improve the wake zone structure for vehicle.On the basis of the detailed understanding of the structure of the flow field around the wheel,the two structural components of the wheel and its surroundings,namely the wind block plate and the spokes,are studied and analyzed respectively.It is found that the existence of the baffle can greatly reduce the impact of the front flow on the front wheel,reduce the range of the high pressure area of the front wheel,and help to reduce the complexity of the flow in the front wheel cavity.In addition,the existence of the blocking plate supplements the energy of the airflow flowing to the rear,which makes it difficult to form the horseshoe vortex inside the wheel and reduces the flow complexity behind the wheel.Arc choke plate and flat compared to choke plate is more conducive to flow transition,provides local high range of arc choke choke plate below the plane form,at the same time arc choke plate is more conducive to flow to the wheels of the lateral diffusion,compared to the surface choke plate,the airflow into the body at the bottom of the greatly reduced,which makes the car flow and weakened the effect of the concave part inside at the bottom of the car body,to the great contribution to the aerodynamic performance.For the study of spokes,the influence of different spokes structure on aerodynamic performance was studied by setting spokes of the same shape and different number.It is found that the increase of the number of spokes in the front wheel area reduces the gap between spokes.On the one hand,the interference of airflow on both sides of the wheel is reduced,and more energy of airflow flows to the rear,which is beneficial to compress the wake of the front wheel and improve aerodynamic performance.On the other hand,it will lead to the accumulation of airflow in the hub cavity and increase the pressure,which will increase the resistance coefficient near the front wheel.Therefore,it is necessary to select the appropriate number of front wheel spokes to achieve the best aerodynamic performance.And vehicle rear wheel in the front wheel wake zone,in front of the flow to the impact of the rear wheels were similar,but with the increased number of rear wheel spokes,added to the rear of the flow of air energy,to improve the vehicle wake zone,but the increased number of spokes makes spokes blade and the airflow contact area increases,thus increasing the interaction force between the wheel and airflow,which resulted in increased equivalent wind resistance,therefore also need rear wheel spokes several design combined with actual situation,in order to achieve optimal aerodynamic performance.