Improving vehicle fuel consumption,performance and aerodynamic efficiency by drag reduction especially in heavy vehicles is one of the indispensable issues of automotive industry.In this work,the effects of adding append devices like deflector and cab vane corner on heavy commercial vehicle drag reduction were investigated.For this purpose,the vehicle body structure was modeled with various supplementary parts at the first stage.Then,computational fluid dynamic(CFD) analysis was utilized for each case to enhance the optimal aerodynamic structure at different longitudinal speeds for heavy commercial vehicles.The results show that the most effective supplementary part is deflector,and by adding this part,the drag coefficient is decreased considerably at an optimum angle.By adding two cab vane corners at both frontal edges of cab,a significant drag reduction is noticed.Back vanes and base flaps are simple plates which can be added at the top and side end of container and at the bottom with specific angle respectively to direct the flow and prevent the turbulence.Through the analysis of airflow and pressure distribution,the results reveal that the cab vane reduces fuel consumption and drag coefficient by up to 20 % receptively using proper deflector angle.Finally,by adding all supplementary parts at their optimized positions,41% drag reduction is obtained compared to the simple model. Improving vehicle fuel consumption, performance and aerodynamic efficiency by drag Reduction especially heavy vehicles is one of the indispensable issues of automotive industry. In this work, the effects of adding append devices like deflector and cab vane corner on heavy commercial vehicle drag reduction were investigated .For this purpose, the vehicle body structure was modeled with various supplementary parts at the first stage. Chen, computational fluid dynamic (CFD) analysis was utilized for each case to enhance the optimal aerodynamic structure at different longitudinal speeds for heavy commercial vehicles. results show that the most effective supplementary part is deflector, and by adding this part, the drag coefficient is decreased considerably at an optimum angle.By adding two cab vane corners at both frontal edges of cab, a significant drag reduction is not be.Back vanes and base flaps are simple plates which can be added at the top and side end of container and at the bottom wit h specific angle respectively to direct the flow and prevent the turbulence. Through the analysis of airflow and pressure distribution, the results reveal that the cab vane reduces fuel consumption and drag coefficient by up to 20% receptively using proper deflector angle. Finally, by adding all supplementary parts at their optimized positions, 41% drag reduction is obtained compared to the simple model.