Comparative study of the drag coefficient of NACA airfoil profiles as applied to vehicles using different reference areas

• The total drag coefficient is applied with both actual and assumed reference areas. • Relative changes of friction and total drag coefficients are executed. • Typical height-over-length ratios of commercial vehicles show differences below 10%. • Smaller geometric ratios cause greater discrepancies between two calculating methods. • Offering guidance on choosing the right reference area for aerodynamic calculations. The aerodynamic drag coefficient is a dimensionless parameter essential for evaluating aerodynamic efficiency. This paper investigates the drag coefficient, including pressure and friction coefficients, using two kinds of reference areas: actual and assumed, across four NACA airfoils (0012, 4415, 631412, and 642015) with halved and shortened configurations at velocities from 40 to 160 km/h. The height-over-length ratio of airfoils strongly influences drag components. For ratios ranging from 0.05 to 0.35, the relative change of total drag coefficient between the assumed and actual areas decreases from 81.10% to 5.13% at 100 km/h and from 78.26% to 4.82% at 160 km/h across all airfoils. In commercial vehicles with typical ratios of 0.20 - 0.38, this discrepancy is from 10 to only 5%, while racing cars (Formula 1, Formula 2) and metros with general height-over-length ratios of 0.16 - 0.20 may experience differences up to 18%. These findings emphasize insights into selecting reference areas precisely, a concern often overlooked in the literature, for vehicle aerodynamic drag calculations to achieve reliable solutions within specific height-over-length ratios while balancing computational resources. With advancements in computational technologies and simulation software, the precise determination of reference areas to minimize calculating errors warrants greater attention and serious consideration.