This report addresses the interior design of a 40% scaled wind tunnel model of a generic medium-sized car geometry — the so-called DrivAer body. The model was designed for being investigated inside the wind tunnel facility at the Technische Universität München, which was recently upgraded by a single-belt ground simulation system. The wind tunnel model is very modular: it features several exchangeable parts, such as three exchangeable rear ends, three different underbody configurations, and different wheel rim geometries. In addition to this, the engine compartment is equipped with a model heat exchanger to adjust the mass flow rate through the underhood area. Apart from the model itself, we would also like to introduce some of the measurement equipment that we used during our wind tunnel tests, for example a set of five independent force balances. Furthermore, a method to account for the falsifying rolling resistance of the wheels is shown. Finally, results of experiments to determine the aerodynamic drag generated at the front and the rear axes of the vehicle will be discussed and a small data base of drag values for various vehicle configurations will be provided.
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.
The drag of a car is highly dependent on the topology of its complex wake system. Small changes in the shape of the car, that do not have a big effect when considered separately, can lead to significant changes in the total drag when the vortex systems of the changed part of the car body interact with the wake vortices. To understand these interferences, a method is necessary that decomposes the flow based on dynamic information. In this paper, the feasibility of using the Dynamic Mode Decomposition (DMD) to analyze the dynamic behavior of the wake flow of a car is investigated. The DMD is found to extract useful information from the flow when applied to three dimensional velocity vector fields.
The CFD simulations are validated by yet unpublished experimental results from experiments in two different wind tunnels.
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