Hood-nose and windshield geometry effects on the aerodynamic drag of agricultural tractor trailer couple

Three different agricultural tractor geometries that incorporate a driver cabin/compartment are investigated regarding aerodynamic drag while a trailer is attached. The tractor trailer couple was modelled and scaled down in an open wind tunnel. The main geometrical variables are nose (in front of the hood) form and the windshield angle. The main operational variable is the Reynolds number. Aerodynamic drag force, drag coefficient, and static pressure distribution on the symmetry plane of the tractor trailer couple parameters are found. Reynolds independency was sought to extrapolate results to real world scale. Aerodynamic resistance or drag force was measured in a single axis as well as static pressure from 29 different points. It is found that agricultural tractor trailer couple has an aerodynamic drag coefficient about unity. So, dynamic pressure of the relative flow can be directly multiplied with projected area of the tractor trailer couple that is perpendicular to the relative motion. However, the results also suggests that the drag coefficient can be up to 20 % high based on geometrical variables. Although the drag coefficient does not change marginally, tractor form influences the drag force regarding precise estimations. Obtained findings can be used for complex models or digital twins of transportation.