Timo Kuthada

Design and First Test of the New Synchronous 200 Hz System for Unsteady Pressure Field Measurement

This paper introduces an innovative pressure measurement system for unsteady flow measurement. Unsteady flow is currently one of the hot topics of road vehicles aerodynamics and an inexpensive, simple-to-use tool for its investigation has long been missing. Conventional pressure measurement systems with centralized pressure scanners and long tubings do not satisfy the needs of unsteady phenomena. An approach of miniature MEMS pressure sensors is used instead, whereby the sensors are installed directly on the surface of the body under investigation. This concept not only enables the possibility of unsteady flow measurement but also offers a fast and reliable method of pressure field investigation. Finally, the measurement system was aimed at the specific needs of road vehicle productive testing and provides an effective tool capable of rapid experiment preparation, reliable measurement and simple post-processing.

Classification of aerodynamic tyre characteristics

The geometric shape of the tyres can have a large influence on the aerodynamic drag of a passenger car as it has been shown already in different publications. However, so far it is not possible to quantify the aerodynamic characteristics of a tyre without measuring it mounted on a vehicle in a wind tunnel and comparing it to other tyres. For this reason a research project at the Institute for Internal Combustion Engines and Automotive Engineering at the University of Stuttgart (IVK) was launched with the intention of categorising the aerodynamic characteristics of passenger car tyres.

The influence of wheel and tire aerodynamics in WLTP

The geometric shape of passenger car wheels can have a large influence on the aerodynamic drag of a vehicle as it has been shown already in different publications. In combination, tire and rim cause approximately 25% of the overall drag. Until now, the challenge for aerodynamicists is to find the rim / tire combination with the best aerodynamic characteristics, which then is used for the official cD-value of the vehicle and for the determination of fuel consumption according to NEFZ regulations.

Aerodynamics as troubleshooting of wet fading

The prevention of soiling of glass panes and brakes is an important safety issue. Studies conducted in the thermal wind tunnel of FKFS have shown that brake discs and brake pads at aerodynamically optimized vehicles have greater traction in wet an dirty conditions.

Investigation of refraction properties of light at wetted vehicle glass planes

At night, an unobstructed view onto the surrounding traffic is particularly important for safety. The eyes adapted to the dark are sensitive to light stimulus. When driving on a wetted road, water and dirt can be swirled up and wet the vehicle glass. Thus water accumulations of varying sizes and shapes arise and soil the window. The light can be refracted in these water accumulations and cause brightening. These brightening can lead to distraction and even glare. Therefore, a new evaluation method is presented which assesses the brightening of droplets on a horizontal glass plane depending on the light source and the water accumulation. It provides information about the brightening behaviour of droplets and the impact factors of the light source and the soiled window.

Investigation of visibility properties through wetted glass planes on vehicles

When driving a car, the view onto the surrounding traffic must be ensured at all times. Especially the view through the side window onto the rear view mirror and other traffic participants is very important. When driving on a wetted road, water and dirt can impair driving comfort and safety. Surface bound water droplets and rivulets on the windshield and the side glass reduce the visibility. Therefore, a new evaluation method is presented which assesses the view through pools of water on a horizontal glass plane depending on wettability of the glass and the volume of single droplets or the height of water films. It provides information about the transparency behavior of water droplets and the impact factors of a soiled side window on the view through it.

Increase in range of a battery electric vehicle by means of predictive thermal management

Battery electric vehicles (BEV) allow local emission free travelling and are also capable of reducing the anthropogenic emission of CO2. Since the waste heat of a BEV is much smaller than in any combustion engine driven car the energy for the heating of the cabin has to be taken from another source. If the energy is drawn from the traction battery the driving range is affected severely. Hence, offering more comfort and extending the driving range become counteracting development strategies. To predict how the driving range is influenced by the need for comfort a predictive simulation tool was developed. The paper will show how the range of the battery electric vehicle can be increased by thermal management strategies. The objective of the presented investigations is to quantify the potential of optimizations of the thermal management system. Therefore, the thermal management system is configured in a modular way. Thus, it is possible to attribute savings achieved via single alterations in the system, such as the addition of a cabin heat exchanger or a heat pump. For the use in a BEV the capability of the thermal management system has been increased to be able to include predictive strategies and adapt to the driver’s demands. Furthermore, the effect of preconditioning on the total energy balance and range is analyzed and depicted. This shows the importance of including preconditioning in thermal management to increase the range of a BEV. The paper is a summary of the results of the FVV project “Warmemanagement an batteriebetriebenen Elektrofahrzeugen (WBEF)”.

New horizons of vehicle aerodynamics

Vehicle aerodynamics and wind tunnel technology are progressing towards more realistic simulations of the real-world on-road environment. This paper presents an overview of the new systems which were implemented during the recent wind tunnel upgrade at Forschungsinstitut für Kraftfahrwesenund Fahrzeugmotoren Stuttgart as well as comparable computational fluid dynamics simulations. The fully interchangeable road simulation system features an interchangeable five-belt system and three-belt system in the same full-scale automotive wind tunnel. This system offers the efficiency of a five-belt system combined with the more sophisticated ground simulation technique of a wide belt system, which is necessary to assess the aerodynamic properties of sports cars and racing cars. In order to simulate on-road wind conditions, a side-wind generator can be installed to generate a turbulent flow field in the wind tunnel test section. It could be shown that the commonly determined drag coefficient at 0° yaw angle in the smooth flow environment of today’s wind tunnels is not representative of the drag found in real on-road wind conditions. Additionally, the investigations in unsteady side-wind conditions indicate that the commonly used approach to determine the side-wind sensitivity of a vehicle underestimates the forces occurring in turbulent flow conditions. A validated simulation model is presented. The simulation results are in good agreement with the experimental results and can be used as a complementary tool when assessing the unsteady aerodynamic behaviour of a vehicle; this behaviour can be coupled to a vehicle dynamics model for virtual road testing in the Stuttgart full-motion driving simulator. The unsteady-behaviour effects can be evaluated comprehensively, and the results allow a subjective assessment of the unsteady response of the vehicle. Furthermore, the aeroacoustic wind noise in on-road wind conditions is investigated during the development of the vehicle. The side-wind generator reproduces the natural stochastic cross-wind and allows the effect of these wind conditions to be investigated in the aeroacoustic wind tunnel. The results show similar ratings to those in on-road tests when compared with subjective listening tests. In summary, the techniques introduced open up new horizons in the field of vehicle aerodynamics and aeroacoustics, which are a step closer towards real-world conditions in automotive engineering.

Methodical Investigation of Vehicle Side Glass Soiling Phenomena

Bad weather conditions such as rain and snow affect driving comfort and safety. An unobstructed view onto the surrounding traffic is indispensable. Water whirled up by preceding vehicles can soil the vehicle windows. Depending on the resulting soiling pattern, this can impair the visibility. Therefore, the origin of the vehicle side glass soiling and its influencing factors were investigated in a wind tunnel, resulting in the identification of different soiling phenomena. A crucial parameter is the surface condition as a function of the velocity. Additionally, a new evaluation method is presented which detects and classifies the different types of water accumulations and illustrates the local soiling frequency. It provides information about the composition of soiling patterns and thus can support to during the development process for side glass soiling.

Investigation of Time-Resolved Nozzle Interference Effects

Automotive wind tunnels still see an increasing significance in the vehicle development process. Nevertheless, the flow topology in the test sections of open jet wind tunnels is not yet understood completely. A large source for transient structures is the shear layer developing between the high velocity nozzle flow and the calmly air in the plenum.