Experimental and Full Scale Investigation of Base Cavity Drag Reduction Devices for Use on Ground Transport Vehicles

Abstract

Comparison studies have been conducted on a 1:16th scale model and a full scale tractor trailer of a variety of sealed aft cavity devices as a means to develop or enhance commercial drag reduction technology for class 8 vehicles. Eight base cavity geometries with pressure taps were created for the scale model. Drag data were acquired on the models using a 6-axis internal force balance for a range of yaw sweeps and at three Reynolds numbers for each base cavity. Pressure surveys for selected base cavities were also completed for the same yaw angles and Reynolds numbers to quantify the change in base pressure. The scale model force data indicated a marked decrease in drag at up to 12 % for two base cavity shapes, however most base cavities reduced drag by 3–10 % and a few did not decrease drag any significant amount. Pressure data indicated the base cavities increased the base pressure over baseline with a $\Delta \mathrm{{C}}_\mathrm{{P}}$ of up to 0.3. Moreover, drag computed from pressure data implied that although the base cavities decreased the base drag due to a pressure increase, the drag may have increased elsewhere on the model. Full-scale tests were also completed using SAE Type II testing procedures. Full-scale tests on the same geometry indicated a fuel savings of over 6.5 %. Overall, the use of these devices shows to be a viable, effective and economical way to reduce fuel consumption on ground transport vehicles.