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Application of Lobed Mixers to Reduce Drag of Boat-tailed Ground Vehicles
Author(s): Aleksandra Rejniak, Alvin Gatto
Keywords: Drag reduction, Lobed mixers, Boat-tailed vehicles
Minimising the aerodynamic drag of commercial vehicles is important economically and ecologically. This work aims to evaluate lobed mixers as a passive flow control method for base pressure drag reduction. The concept incorporates lobed mixers on a typical boat-tail device to enhance mixing and pressure recovery in the base wake. Comparisons are made against both a baseline and unaltered boat-tail configuration. Experiments were performed on a 1/24th-scale Heavy Goods Vehicle representative model at a Reynolds number of 2.3 x 10e5 with force and hot-wire anemometry measurements used to quantify drag and wake characteristics. Overall, the baseline and unaltered boat-tail showed good correlation to previous results despite the large disparity to full-scale Reynolds numbers. This provided confidence in the methodology adopted. Results using lobed mixers showed up to a 10.2% drag reduction with the added vorticity produced acting to fundamentally shift the nature of the wake. This is manifested principally through the generation of counter-rotating vortical structures which enhance crosswise flow entrainment into the base wake. This action is observed to limit flow entrainment towards the ground leading to a higher wake. Enhanced mixing is also demonstrated. Overall, results suggest the suitability of lobed mixers as an effective means for drag reduction of boat-tailed ground vehicles.