Experimental and Numerical Investigation of Automotive Aerodynamics Using DrivAer Model

Abstract

The use of experimental and numerical investigation to predict the aerodynamic characteristics of road vehicles is a standard practice in automotive design and development. Fundamental research has been often conducted on generic models with limited applicability to realistic cars. The DrivAer model developed in TU München possesses more representative car features. To encourage the use of the DrivAer model in independent research work, the experimental results and some numerical results were published. In this paper, a new developed wind tunnel setup of the DrivAer model was introduced. A new suspension system was designed in such a way that drag and lift force could be measured whilst the wheels are rolling on the moving ground without wheel struts (In this paper we call it wheels-on setup). The more close-truth experimental results of different rear end configurations were obtained. The lift force of the total model was firstly obtained. Additionally, the influences of the wheel struts and top sting were studied. Numerical investigation for performing finite-volume-based Reynolds-averaged Navier-Stokes (RANS) for the prediction of aerodynamic forces of passenger vehicles developed was presented, using the open-source CFD toolbox OpenFOAM®. Validation of the predictions was done on the basis of detailed comparisons to experimental wind tunnel data, both of the basic body (wheelhouse covered and without wheels) and the new wheels-on model. Results of drag coefficient were found to compare favourably to the experiments.

Upstream wind tunnel model mounting: The forgotten method for road vehicle aerodynamics

“…From this perspective, these results suggest the front-mounted sting design adopted does not markedly affect the performance near the moving ground, similar to the top and side supports typically used for these applications. 3,4,9,11 Impact on mean turbulence production within the wake. The contours of mean turbulent kinetic energy (K) presented in Figure 8 provide differences in turbulence production within T2.…”

“…This technique also facilitates moving ground use and wheel rotation, and has been shown to be less detrimental to drag measurements. 3,8 Miao et al 4 reported drag coefficient increases limited to 2% on a notchback passenger car model with both fixed and moving ground use. For the hatchback configuration on a stationary ground, drag increased by 1.4%, with results using a moving ground found only marginally more significant (1.7%).…”

“…Further work 10 highlights the magnitude of these effects on a hatchback model with up to 7.5% and 28.2% increases in drag and lift coefficients, respectively. Notchback, fastback and motorsport configurations were shown less susceptible, with changes limited to between 1% and 3% 3,4 and 5% 10 for drag and lift, respectively. The primary source of such changes was shown by Hetherington and Sims-Williams 10 to vary between model configurations, with the increase in drag for notchback vehicles originating largely from the junction flow, and for hatchbacks, the support wake and consequent interactions with downstream flow being the main contributor.…”

“…2,[9][10][11] Furthermore, Hetherington 3 shows the total force on a mounted ground vehicle model to be larger than the sum of the individual components (model and supports). Separate measurements using dummy supports (not connected) are normally used to correct such inconsistencies, [3][4][5] but a combination of both experimental and computational methodologies to obtain similar estimates can also be used, as outlined by Zhang et al 6 Many different road vehicle mounting techniques have been developed over the years, with each tending to be most suitable for specific test conditions and goals. One of the most common concepts is to support the model from above.…”

“…While the main aim of these structures is to hold the model, their presence often acts to increase measurement uncertainty in ways that remain difficult to quantify and challenging to predict. 2–6 Among the most common effects are changes to the surrounding flow-field, such as those occurring at the support-model junction. 3 Simpson 7 studied such junction flows between planar surfaces and streamlined obstructions, and showed the stagnation at the obstruction’s leading edge to provoke the upstream surface boundary layer to separate, resulting in the generation of horseshoe vortices, which propagate downstream.…”