유동제어 장치를 이용한 화물차의 항력 저감 기술에 대한 실험적 연구

Abstract

The reduction of aerodynamic drag of heavy vehicles is one of the main challenges for improving fuel saving and decreasing environmental pollution. For a tractor-trailer driving on a highway, approximately 45% of the total aerodynamic drag is resulted from the forebody of the vehicle. The other contributions are trailer base (25%) and underbody flow (30%). Numerous flow control devices have been introduced to reduce the aerodynamic drag exerting on heavy vehicles, including cab-roof fairing (CRF), gap fairing (GF), side skirts (SS), boat tails (BT), and vortex generators. For forebody drag reduction, cab-roof fairing (CRF) and gap fairing have been developed to reduce the drag exerted on the forebody. Conventional CRFs with a 2D streamlined curvature have limitations in enhancing the driving stability and in additional reduction of drag on the forebody. To overcome the existing limitations, new CRFs including modified and advanced bio-inspired CRF were proposed with adopting multi-curvature and flow-guiding structures inspired by the external forehead shape of sea lions. The modified CRF and the advanced bio-inspired CRF considerably reduced drag coefficient of the 15-ton model by 18.6% and 20.1%, respectively. The side force related with driving stability was also reduced by up to 8% for the 15-ton model attached with the advanced bio-inspired CRF at a yaw angle of ϕ = 3°. The drag reduction of GF was investigated with varying gap length and deflecting angle. The GF devised in this these exhibits 16.4% drag reduction at maximum. Furthermore, we newly developed the aero cab fairing (ACF) and the extended aero cab fairing (EACF) which considerably reduce drag coefficient by approximately 11.1% and 17.5%, respectively. To control the underbody flow, the side skirt which consists of straight panels curtaining the space between the front and rear wheels is one of the most effective underbody drag-reduction devices. Flap-type side skirt (FSS) that has flapped surface behind the rear wheels was proposed and the drag coefficient is reduced by 6.1 %. Aero full package (AFP) of a tractor–trailer, which integrated GF, FSS and, lower inclined air deflector (LIAD) BT was tested for examining fuel saving through real-scale proving ground test. On the basis of the drag measurement result, AFP was found to significantly modify the flow structure around the vehicle, thereby leading to a 26.5% reduction in drag coefficient (CD). Flow characteristics including spatial distributions of mean velocity, vorticity, and turbulent kinetic energy around the scaled-down 15-ton and tractor-trailer model with and without additive devices were experimentally investigated by using a particle image velocimetry (PIV) technique to analyze the drag-reduction mechanism of the proposed flow control devices. The proposed devices delays large-scale flow separation and reduce turbulent kinetic energy around the heavy vehicles. Based on the experimental results of drag and flow measurements, the PG test for real tractor–trailers attached with the proposed flow control devices officially verified that the integrated AFP provides 13.4% fuel saving. The installation of AFP may result in an average of 3300 US$ saving per year in fuel cost for each tractor–trailer vehicle in Korea. The present results will provide practical and useful information for improving the aerodynamic performance and fuel efficiency of heavy vehicles with enhancing driving stability.