Aerodynamic drag reduction on a realistic vehicle using continuous blowing

Abstract

The aerodynamic drag reduction of a realistic vehicle model through continuous blowing was numerically analyzed based on the open-source computational fluid dynamics (CFD) program, OpenFOAM. Simulations were performed on a realistic passenger vehicle model with available wind tunnel test data, DrivAer, at four different Reynolds numbers (Re). The aerodynamic drag coefficient decreased with increasing Re. The CFD technique was validated by comparing the aerodynamic drag coefficients at Re = 4.87 × 106. Predicted drag coefficients of the DrivAer estate model show less than 3% difference from wind tunnel test data, whereas those of fastback and notchback vehicles showed less than 1% difference. Sectional pressure distributions agreed well with wind tunnel test data. The effect of continuous blowing was investigated using the DrivAer estate model with a blowing position at the end of the roof for vertical blowing and at the C-pillar for lateral blowing. Simulations were performed at Re = 4.87 × 106 and 9.75 × 106 and blowing speeds of 20%, 40%, 60%, and 100% of the vehicle driving speed. The effect of continuous blowing increased with Re. The drag reduction was more than 6% for roof blowing due to increasing rear pressure when the blowing speed equaled the vehicle driving speed. The maximum drag reduction was approximately 7.5% for simultaneous roof and lateral blowing. The results indicate that continuous blowing can efficiently reduce vehicle aerodynamic drag and consequently greenhouse gas emissions.