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The increasing importance of electric mobility results into the need for optimizing all power train components to further reduce the energy consumption of the vehicle. The aim of this study is to predict the thermal behavior and the pressure losses in water jackets of electric machines by use of CFD. The heat loss of electric machines in passenger cars is sufficient to let its components reach critical temperatures. For this reason, the optimization of heat dissipation plays an important role. The goal of efficient heat dissipation is a high heat transfer coefficient. At the same time, the pressure loss should be low in order to reduce the required power of the pump. Flow simulations can help to evaluate different water jacket concepts in an early stage of development. In this work, the validation of flow simulations in water jackets is based on measurements of a simplified geometry with constant boundary conditions.

Previous work by the authors showed the development of an aerodynamic CFD model using the Lattice Boltzmann Method for simulating vehicles inside the IVK Model-Scale Wind-Tunnel test-section. In both experiment and simulation, alternate configurations of the wind-tunnel geometry were studied to change the pressure distribution in the wind-tunnel test section, inducing a reduction in aerodynamic drag due to interference between the wind-tunnel geometry and the pressure on the surface of the vehicle. The wind-tunnel pressure distribution was modified by adding so-called “stagnation bodies” inside the collector to create blockage and to increase the pressure in the rear portion of the test section. The primary purpose of previous work was to provide a validated CFD approach for modeling wind-tunnel interference effects, so that these effects can be understood and accounted for when designing vehicles.

Automotive vehicles operate in complex, transient aerodynamic conditions that can potentially influence their operational efficiency, performance and safety. A moving-model facility combined with a wind-tunnel is an experimental methodology that can be utilized to model some of these transient aerodynamic conditions. This experimental methodology is an alternative to wind-tunnel experiments with additional crosswind generators or actively yawing models, and has the added benefit of modelling the correct relative motion between the vehicle and the ground/infrastructure. Experiments using a VW Golf 7 were performed with a 1:10 scale model at the moving-model facility at DLR, Göttingen and a full-scale, operational vehicle at the BMW Ascheim side-wind facility.

This paper presents velocity and pressure measurements obtained around an isolated wheel in a rotating and stationary configuration. The flow field was investigated using LDA and a total pressure probe in the model scale wind tunnel at IVK/FKFS. Drag and lift were determined for both configurations as well as for the wheel support only. These results were used as a reference for comparing numerical results obtained from two different CFD codes used in the automotive industry, namely STAR-CD™ and PowerFLOW™. The comparison gives a good overall agreement between the experimental and the simulated data. Both CFD codes show good correlation of the integral forces. The influence of the wheel rotation on drag and lift coefficients is predicted well. All mean flow structures which can be found in the planes measured with LDA can be recognized in the numerical results of both codes. Only small local differences remain, which can be attributed to the different CFD codes.

In automotive wind tunnels with modern road simulation installations boundary layer pre-suction is a widely-used technique for boundary layer control. The consequence of boundary layer pre-suction is an additional pressure gradient in front of the model. In order to investigate the effects of the additional pressure gradient on drag, experiments were conducted with two different models (scale 1:5) in the IVK Model Wind Tunnel. In these experiments the suction velocity of the boundary layer pre-suction served as a parameter to change the static pressure gradient along the test section and was for this purpose adjusted higher and lower than the standard suction velocity. It is shown that the total drag increment due to boundary layer pre-suction consists of at least two parts: the ground simulation increment and the static pressure gradient increment. The ground simulation increment is due to a decrease in the boundary layer thickness and the resulting modified flow beneath the model.

The wind tunnel is the standard tool in the development and improvement of vehicle aerodynamics. Usually, automotive wind tunnels contain an open test section, which results in a shear layer developing on the edge of the jet. This shear layer brings instabilities that can lead to resonance effects in the wind tunnel influencing the pressure distribution in the test section. To investigate the resonance effects, the classic wind tunnel corrections were applied to averaged drag measurements recorded in a resonance and nonresonance configuration of the model scale wind tunnel of the University of Stuttgart. The Mercker-Wiedemann-Method shows good compensation for the differing pressure gradients. Pressure measurements on the surface of the DrivAer Notchback model show different separation points on the rear window for measurements in resonance and nonresonance configuration. This means that the resonance effects can influence the separation significantly.

This paper presents an integrated numerical and experimental approach to take best possible advantage of the common development tools at hand (1D, CFD and wind tunnel) to determine the cooling air mass flow at the different vehicle development stages. 1D tools can be used early in development when neither 3D data nor wind tunnel models with detailed underhood flow are available. A problem that has to be resolved is the dependency on input data. In particular, the pressure coefficients on the outer surface (i.e. at the air inlet and outlet region) and the pressure loss data of single components are of great importance since the amount of cooling air flow is directly linked to these variables. The pressure coefficients at the air inlet and outlet are not only a function of vehicle configuration but also of driving velocity and fan operation. Both, static and total pressure coefficient, yield different advantages and disadvantages and can therefore both be used as boundary conditions.

This paper deals with the correction for interference effects on the flow about bluff bodies in open-jet wind tunnels. Altogether, five different interference effects in open-jet tunnels are identified and described by physical models. Besides the classical jet-expansion correction which has been treated repeatedly by various authors throughout the last 60 years, the new correction method also includes the effect of jet deflection due to the proximity of a vehicle to the nozzle. Furthermore, far-field interference effects originating from the nozzle and the collector are described. For this purpose nozzle and collector effects are treated as solid- wall blockage phenomena, and with the aid of Biot-Savart principles the induced velocity at the model position is calculated. Finally, the static- pressure gradient in an empty test section generates a horizontal buoyancy force when a model is placed in a wind tunnel stream.

The unsteady environment road vehicles are exposed to is subject of many investigations that are currently made. Yet, the approaching flow is only one aspect of unsteady forces acting on the vehicle. Unsteady wake structures also lead to time-varying surface pressures and consequently fluctuating forces even in steady and low turbulent flows. However, little is known about the influence of realistic flow conditions, i.e. as found on road, on the unsteady surface pressures and wake structures of a vehicle. Therefore, to derive a deeper understanding of the unsteady aerodynamic properties of a vehicle this paper presents results of measurements conducted on a vehicle body both in smooth and turbulent flow conditions in the IVK model scale wind tunnel. Unsteady surface pressure measurements in the area where separation occurs and the base of the vehicle were made together with time accurate total pressure measurements in the wake.