Research On The Effect Of Active Grille On The Aerodynamic And Cooling Characteristics Of Heavy Trucks

With the increasing number of highways and the adjustment of cargo transportation structure and the booming development of express delivery industry,the market demand for heavy-duty trucks undertaking cargo transportation has increased.In order to meet the demand of high-efficiency transportation,the performance of heavy-duty trucks has been improved and the power has been increased,and the aerodynamic characteristics and cooling characteristics of heavy-duty trucks have also received more attention.Active grille is a new technology that has been developed rapidly in recent years,the technology was first applied to foreign high-end models,and has been gradually used in recent years in China,but in the research of heavy trucks,the active grille technology has not yet been developed,the driving conditions of heavy trucks are more complex,and the aerodynamic resistance,engine cooling and fuel economy are more concerned,so the application of active grille technology on heavy trucks is Therefore,the application of active grille technology on heavy trucks has more practical significance and is of great help to enhance the competitiveness of their products.This paper takes active grille research as the starting point and applies numerical simulation method to study the aerodynamic characteristics and cooling characteristics of heavy trucks.Firstly,the active grille technology and computational fluid dynamics theory are introduced in detail,and a simplified truck model is used as the research object,combined with wind tunnel tests to explore a more accurate numerical simulation strategy.Secondly,in order to study the influence of the intake grille on the aerodynamic characteristics and cooling characteristics of the heavy truck,the basic truck model is processed and the grille is closed to obtain the heavy truck model in the grille closed state,and then the whole vehicle aerodynamic characteristics,cooling characteristics and fuel economy are analyzed under the two states of grille opening and closing,the results show that: after the grille is closed,the aerodynamic drag coefficient decreases obviously,the drag reduction rate is 7.2%,and the fuel saving rate reaches 3.3%.After the grille is closed,the airflow at the front of the cab cannot enter the engine compartment directly,resulting in a higher overall temperature in the engine compartment and a higher reduction of cooling air flow through the intercooler and radiator,which has an impact on the performance of the engine cooling system.Then,on the basis of the original truck model,a simplified model of active grille was established to analyze the influence of active grille opening angle on the aerodynamic and cooling characteristics of the whole vehicle under different grille blade numbers and different vehicle speeds,and the results showed that: except for the grille opening angle of 60°,the overall aerodynamic drag coefficient showed an increasing trend with the increase of grille opening angle.With different grille opening angles,the temperature difference in the engine compartment is more obvious,while the temperature of other parts is less affected,and with the increase of grille opening angle,the temperature in the engine compartment decreases continuously and the high temperature area is reduced.The increase in the number of active grille blades has a greater effect on the aerodynamic drag coefficient and the temperature distribution in the engine compartment in the range where the grille opening angle is small,and produces a smaller effect in the range where the grille opening angle is large.After the vehicle speed is increased,the influence of active grille on the aerodynamic drag coefficient and engine compartment temperature distribution is more obvious,and there is a difference in the change trend of aerodynamic drag coefficient between high speed and low speed,and there is no reduction of aerodynamic drag coefficient when the grille opening angle is 60° under low speed.Finally,combining the aerodynamic drag coefficients and radiator outlet temperatures corresponding to different grille opening angles under different driving speeds,taking into account the drag reduction and heat dissipation effects,the active grille opening angles under different speeds are determined,and the active grille opening control schemes under four operating conditions are formulated,taking into account the hot vehicle and overtaking operating conditions.