The flow over a road vehicle is much more complex than the one around an airfoil: we have to deal with ground effect, rotation of the wheels and complex geometries leading to fully 3-dimensional flows. If we want to control the flow we need more insight into the flow structure and dynamics. One major difference with aeronautic aerodynamics, apart from the take-off and landing situations, is that the we are not dealing with skin friction problems but with pressure drag and lift. We emphasize that lift reduction is also important as it provides stability and braking improvement. In consequence we are not concerned with the control of wall turbulence but with the control of separation and large coherent structures. We present an experimental study on flow control over a classic 3D bluff-body used in automotive aerodynamics. Flow control is achieved through moving flaps fixed on every edge around the two rear flat surfaces of the model. Different pairs of flaps, with variable angle compared to the walls, are tested. Parametric studies show that the most efficient configuration for the flaps is along the side edges of the rear slant, i.e. in the region where longitudinal vortices are created, and also at the junction between the roof and the rear slant, where the flow separates. We also explore the combinations of different flap configurations. We find interesting results showing cumulative effects between some configurations leading to 25 % drag reduction and 105 % lift reduction. Finally, particle image velocimetry measurements show that one of the key effects is the control of the longitudinal vortices created at the side edges of the rear slant.
Drag and lift reduction of a 3D bluff body using flaps
Widerstands- und Auftriebsreduzierung an einem stumpfen 3D Körper mittels Klappen
Experiments in Fluids ; 44 , 4 ; 491-501
2008
11 Seiten, 13 Bilder, 3 Tabellen, 20 Quellen
Aufsatz (Zeitschrift)
Englisch
Strömungsmechanik , Strömungsmessung , Aerodynamik , Klappe , Rezirkulation , Wirbel (Strömung) , experimentelle Untersuchung , Versuchsaufbau , Strömungsgeschwindigkeit , Reynolds-Zahl , Turbulenzgrad , Grenzschichtdicke , Teilchenabbildgeschwindigkeitsmessung , CCD-Kamera , Strömungsabriss , berührungsloses Messverfahren
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