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Influence of a Diffuser to the Wake Flow of a Passenger Car

Jesper Marklund (Institutionen för tillämpad mekanik, Fordonsteknik och autonoma system) ; Lennart Löfdahl (Institutionen för tillämpad mekanik, Fordonsteknik och autonoma system)
FEDSM2012 ASME 2012 Fluids Engineering Summer Meeting, July 8-12, 2012, Rio Grande, Puerto Rico, USA (1093-4928). p. 53-62. (2012)
[Konferensbidrag, refereegranskat]

To achieve more energy efficient transportation we have to reduce losses and resistance forces all over the vehicle. Aerodynamic drag is one of the primary resistance forces a passenger vehicle has to overcome and the force increases exponentially with increased speed. The under-body and rear-end geometry of a passenger car is a significant contributor to the overall aerodynamic drag and the shape of it is normally a compromise between styling, cost and other properties. To reduce the aerodynamic drag it is very important to have a good pressure recovery at the rear-end; to end up with a base pressure as high as possible. It is not necessarily the case that an optimized lower part of the rear-end for a square-back car has the same performance as a notch-back or fast-back car. This work investigates the rear-end flow and aerodynamic performance of a sedan and wagon car with varying rear-end under-body design parameters. The study is a numerical analysis using a standard CFD approach commonly used in the automotive industry. A parameter study of under-body covers with varying rear angles, making the rear floor act like a diffuser. The function of the rear floor working as a diffuser is similar regardless of the upper geometry, but its function as a drag reduction device can be very different. Results from this study show a potential to reduce aerodynamic drag of the sedan car approximately 10%, with the best diffuser angle and cover plates over the floor. The best drag reduction for the wagon car was 2-3 % and the optimum was at a smaller diffuser angle. Flow analysis of the wake shows how important it is the wake is balanced.

Nyckelord: Aerodynamics, Passenger cars, Fluid mechanics



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Denna post skapades 2013-01-18. Senast ändrad 2015-07-03.
CPL Pubid: 171582

 

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