Thomas Schütz

WLTP – On the increased importance of aerodynamics and impact on development procedures

For some years a new test procedure has been developed among the UN for the determination of pollutant and CO2 emissions and fuel consumption, which should represent the average customer behaviour. Beside the EU various other countries are involved (e.g., India, Japan). The test procedure WLTP and the underlying driving cycle WLTC was developed with the help of worldwide accumulated driving data and covers driving situations from city up to highway traffic.

Rear-End Shape Influence on the Aerodynamic Properties of a Realistic Car Model: A RANS and Hybrid LES/RANS Study

The present work is concerned with the computational investigation of aerodynamic properties of the so-called ‘DrivAer’ car model representing a ‘generic realistic car configuration’ created by ‘merging’ the original geometries of two medium sized cars from the Audi A4 and the BMW 3 series, Heft et al. [7]. Three down-scaled (1:2.5) configurations differing in the rear-end shape—fastback, notchback and estate back geometries—investigated experimentally at the Institute of Aerodynamics and Fluid Mechanics Technical University in Munich are presently considered. The present numerical study focuses on the application of the ERM-capable (Elliptic-Relaxation Method) eddy-viscosity-based \(\zeta -f\) RANS model [6] describing turbulence within the Unsteady RANS (Reynolds-Averaged Navier-Stokes) and the so-called PANS (Partially-Averaged Navier-Stokes) computational frameworks. The latter approach representing a variable-resolution Hybrid RANS/LES (Large-Eddy Simulation) method is formulated and implemented into the CFD software package AVL-FIRE by Basara et al. [3]. The main objective of the present work is to check the models’ feasibility in computing the unsteady flow past the ‘DrivAer’ car configuration. The focus is on the varying structural properties of the flow arising from differently-shaped rear-ends and their impact on the surface pressure distribution and subsequently on the drag and lift force coefficients.

Luftkräfte und deren Beeinflussung an Personenkraftwagen

Kapitel 3 hat gezeigt: Die Fahrleistungen eines Personenwagens werden masgeblich von dessen Luftwiderstand bestimmt. Das macht es unverzichtbar, dass bei einer Neuentwicklung der im Lastenheft festgeschriebene c W-Wert auch tatsachlich erreicht wird. Hies es fruher beim c W-Wert haufig nur „so niedrig wie moglich – und vom Design gerade noch hinnehmbar“, so geht es langst um die Erfullung einer definitiven Vorgabe. Der Auftrieb des Fahrzeugs entlastet die Achsen und beeinflusst damit die Kraftubertragung zwischen Reifen und Fahrbahn. Hier gilt selbiges: Das Erreichen der Zielvorgaben fur die Auftriebe, bezogen auf die Achsen, ist unerlasslich. Um an das Phanomen Luftwiderstand heranzufuhren, sollen zunachst anhand Abb. 4.1 einige Korper gleicher Volligkeit verglichen werden, also Korper mit gleichem Verhaltnis von Hohe h bzw. Durchmesser d des Korpers zu seiner Lange l. Fur Pkw gilt h / l ≈ 0,3. Mit 0,5 > c W > 0,15 kann der Pkw zwischen dem Rotationskorper, fur den c W ≈ 0,05 gilt, und dem langs angestromten scharfkantigen Quader mit c W ≈ 0,9 eingeordnet werden.

Active flow control analysis at the rear of an SUV

This paper aims to present an experimental investigation of an active flow control solution mounted at rear of a sport utility vehicle (SUV) with the objective of drag reduction, thanks to a selection of flow control parameters leading to a pressure increase on the tailgate.,A flow control design of experiments was conducted with a pulsed jet system mounted on the top and sides of the rear window of the vehicle. The wall pressure, instantaneous velocity and drag were measured with this prototype in a wind tunnel. A dynamic modal decomposition (DMD) analysis of the pressure enables to describe the pressure fluctuations. Fluid dynamic computations show relation between pressure and velocity fields.,Measurements with this prototype in the wind tunnel revealed small improvements in drag for the best flow control configurations. This small benefit is because of the core of the upper span wise vortex further away from the rear window than the lower span wise vortex. These small improvements in drag were confirmed with pressure measurements on the rear window and tailgate. The DMD analysis of the surface pressure showed a low frequency pendulum oscillation on the lower area of the tailgate, linked with low velocity frequencies in the shear layers near the tailgate.,Experimental and numerical results show interest to increase pressure at bottom of the rear end of this SUV prototype. The dynamic description of the wall pressure shows importance of flow control solutions reducing pressure fluctuations at low frequencies in the lower area of the tailgate.