Proposal of Conceptual Shape for Drastic Improvement of Aerodynamic Performance of Heavy-Duty Vehicles

Since air drag is proportional to the square of the speed, it is expected that reducing air drag will significantly improve fuel efficiency for long-distance trucks and buses, which are often driven at high speeds. Therefore, the purpose of this study is to propose a conceptual shape that will dramatically improve the aerodynamic performance of heavy-duty vehicles, assuming that restrictions on overall length will be relaxed in the future. Using NSGA-II, a genetic algorithm, the overall vehicle shape was optimized with the objective functions CD and CL values and design variables as parameters in a total of 13 locations. Among the Pareto solutions, CD = 0.08 was obtained when the CD value was the lowest. Since the CL value remains low with this shape, it can be seen that driving stability does not deteriorate. Among the design variables in optimization, it was confirmed that the corner radius of the vehicle side was particularly effective in reducing the CD value. In addition, when optimizing only the cab shape, the optimal value for the front virtual angle was 30 deg., but in relation to the corner radius, the value for this concept shape was around 40 deg. The CD value of a 1/20 model of the concept shape was measured in a wind tunnel test and compared with the optimization results from the aforementioned numerical analysis. As a result, the CD value reduction effect of the concept shape was confirmed in the wind tunnel test as well, demonstrating the validity of the optimization results described above. A program for calculating fuel consumption rates for heavy-duty vehicles was used to compare fuel efficiency when using the base shape and the concept shape. The weighted average fuel economy in urban driving (JE05) and interurban driving (highway) modes was improved by approximately 21% using the concept shape.