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Viewing 1 to 25 of 25
2014-04-01
Technical Paper
2014-01-0659
Nikolaos Karras, Timo Kuthada, Jochen Wiedemann
Abstract 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.
2015-04-14
Technical Paper
2015-01-0340
Jan Eller, Thomas Binner, Heinrich Reister, Nils Widdecke, Jochen Wiedemann
Abstract Collective life-cycle data is needed when developing components like elastomer suspension mounts. Life-time prediction is only possible using thermal load frequency distributions. In addition to current extreme load cases, the Idle Load Case is examined at Mercedes-Benz Car Group as a collective load case for Vehicle Thermal Management (VTM) numerical simulations in early development stages. It combines validation opportunities for HVAC, cooling and transmission requirements in hot-country-type ambient conditions. Experiments in climatic wind tunnels and coupled 3D CFD and heat transfer simulations of the Idle Load Case have been performed. Measurements show steady conditions at the end of the load case. Decoupling of the torque converter, changes in ambient temperature and the technical implementation of a wind barrier for still air conditions exhibit influence on component-level results. Solar load, however, does not significantly change the examined component temperatures.
2013-04-08
Technical Paper
2013-01-0873
Mario Disch, Nils Widdecke, Jochen Wiedemann, Heinrich Reister, Ernst Peter Weidmann
In the digital prototype development process of a new Mercedes-Benz, thermal protection is an important task that has to be fulfilled. In the early stages of development, numerical methods are used to detect thermal hotspots in order to protect temperature sensitive parts. These methods involve transient full Vehicle Thermal Management (VTM) simulations to predict dynamic vehicle heat-up during critical load cases. In order to simulate thermal control mechanisms, a coupled 1D to 3D thermal vehicle model is built in which the coolant and oil circuit of the engine, as well as the exhaust flow are captured in detail. When performing a transient 3D VTM analysis, the conduction and radiation phenomena are simulated using a transient structure model while the convective phenomena are co-simulated in a steady state fluid model. Both models are brought to interaction at predetermined points by an automatized coupling method.
1993-03-01
Technical Paper
930300
Jochen Wiedemann, Gerhard Wickern, Bernd Ewald, Christof Mattern
The present paper reveals the design concept as well as results of experimental investigations, which were conducted in the early design stage of the planned AUDI Aero-Acoustic Wind Tunnel. This low-noise open-jet facility, featuring a nozzle exit area of 11 m2 and a top speed of approximately 60 m/s, enables aerodynamic as well as acoustic testing of both, full-scale and model-scale ground vehicles. Ground simulation is provided by means of a moving-belt rig. The surrounding plenum is designed as a semi-anechoic chamber to simulate acoustic free-field conditions around the vehicle. Fan noise will be attenuated below the noise level of the open jet. The work reported herein, comprises 1/8-scale pilot-tunnel experiments of aerodynamic and acoustic configurations which were carried out at the University of Darmstadt.
1996-02-01
Technical Paper
960671
Edzard Mercker, Jochen Wiedemann
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.
1996-02-01
Technical Paper
960672
Jochen Wiedemann
In automobile development, wind tunnel measurements are used to optimize fuel consumption and the vehicle's road behavior. The classic measuring technique is based on a stationary vehicle set up in the wind tunnel with stationary wheels. Relative movement between vehicle and road surface is therefore ignored. In more recent studies, measurements have been taken with improved ground simulation. For example, a belt is used instead of the stationary wind tunnel floor and the car wheels rotate. Ground simulation using a belt and rotating wheels generally leads to a reduction in flow angularity at the front wheels, in the same way as blocking the cooling air flow, whereby, as a matter of fact, the aerodynamic drag is reduced. Analogous air flow angle correlations can be established for the effect of underfloor panels.
2004-03-08
Technical Paper
2004-01-0670
Jochen Wiedemann, Oliver Fischer, Pang Jiabin
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.
2008-04-14
Technical Paper
2008-01-0796
Timo Kuthada, Jochen Wiedemann
This paper presents some recent results concerning the generation and minimization of cooling air drag, achieved in an integrated approach of numerical and experimental investigations. The baseline configuration of a production cars' cooling air flow system is analyzed. The analysis of the created drag shows, that most of the force changes due to the cooling air flow appear in the front region of the vehicle. However, the forces generated by heat exchangers are only a small share of the total changes. Additional drag is generated for example by the front wheels and by the components of the underhood compartment. The investigation of the influence of the vehicle rear end shape on the aerodynamics of the cooling air flow system shows, that two similar cars with different rear end shapes (notchback and squareback) can feature different cooling air drag values.
2008-04-14
Technical Paper
2008-01-0325
Oliver Fischer, Timo Kuthada, Jochen Wiedemann, Patrick Dethioux, Richa Mann, Brad Duncan
Aerodynamic simulations using CFD is now a standard tool in the automotive industry, and is becoming more and more integrated in the aerodynamic design process of new vehicles. This process is distinguished by parallel development with wind tunnel experiments and CFD simulation results, which demands comparable results to be generated by the two development tools. As wind tunnel effects are not simulated in most industrial applications of CFD, the comparison with experimental results normally show differences partly due to wind tunnel effects and ground simulation effects. Therefore a deeper understanding of wind tunnel effects and methods to fully reproduce experimental values with CFD is necessary. In this paper, an extensive validation study with a detailed scale notchback model inside an open jet wind tunnel is presented. This study includes experimental data from the real wind tunnel as well as CFD simulation results with and without wind tunnel effects.
2009-04-20
Journal Article
2009-01-0001
David Schröck, Nils Widdecke, Jochen Wiedemann
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.
2017-03-28
Technical Paper
2017-01-0134
Jan Eller, Heinrich Reister, Thomas Binner, Nils Widdecke, Jochen Wiedemann
Abstract There is a growing need for life-cycle data – so-called collectives – when developing components like elastomer engine mounts. Current standardized extreme load cases are not sufficient for establishing such collectives. Supplementing the use of endurance testing data, a prediction methodology for component temperature collectives utilizing existing 3D CFD simulation models is presented. The method uses support points to approximate the full collective. Each support point is defined by a component temperature and a position on the time axis of the collective. Since it is the only currently available source for component temperature data, endurance testing data is used to develop the new method. The component temperature range in this data set is divided in temperature bands. Groups of driving states are determined which are each representative of an individual band. Each of the resulting four driving state spaces is condensed into a substitute load case.
2004-03-08
Technical Paper
2004-01-0445
Alexander Wäschle, Stephane Cyr, Timo Kuthada, Jochen Wiedemann
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.
2005-05-10
Technical Paper
2005-01-2045
Ernst Peter Weidmann, Jochen Wiedemann, Thomas Binner, Heinrich Reister
This paper describes a method to simulate underhood temperature distributions in passenger cars. A simplified engine compartment simulation test rig is used to perform measurements with well known boundary conditions to validate the simulation strategy. The measurement setup corresponds to idle without working fan. The aim of this setup is to validate cases with strong natural convection, e.g. thermal soaking. A coupled steady-state CFD run and thermal analysis is undertaken to simulate the temperature distribution in the test rig. Convective heat transfer coefficients and air temperatures are calculated in StarCD™. The radiative and conductive heat transfer is considered in a RadTherm™ analysis. The strong coupling of flow field and wall temperature in buoyancy driven flows requires an iterative process. Calculated temperatures are compared to measured results in order to validate the simulation method as far as possible. Some of the results are reported in this paper.
2011-06-09
Journal Article
2011-37-0010
Matthias Horn, Jens Neubeck, Jochen Wiedemann
The combination of enhanced powertrains and adapted vehicle concepts can reduce the energy demand of vehicles significantly, especially when energy conversion efficiency rises and at the same time driving resistances decrease. In addition, new powertrain concepts are able to offer extra functionality due to a growing cross-linking with chassis and vehicle body. The design of highly linked vehicles and powertrain systems requires additional new development methods in order to answer interacting questions of driving dynamics and vehicle energy efficiency at an early stage of development. In the paper a database-based simulation platform is presented which was developed at the IVK of the University of Stuttgart in cooperation with the Research Institute of Automotive Engineering and Vehicle Engines Stuttgart (FKFS). The simulation platform is used as an example to discuss mass reducing developments for various powertrain concepts.
2011-06-09
Journal Article
2011-37-0017
Alexander Hennig, Nils Widdecke, Timo Kuthada, Jochen Wiedemann
The entire automotive industry is moving towards lower CO₂ emissions and higher energy efficiency. Especially for higher driving speeds this can be achieved by minimizing aerodynamic drag. Additionally, aerodynamic downforce is essential to maintain or even improve the handling performance of a vehicle. In order to optimize the vehicle's aerodynamic efficiency in wind tunnel tests, the boundary conditions of a vehicle driving on a road must be simulated properly. Particularly for optimizing the underbody region of a vehicle, ground simulation is an important issue in every wind tunnel. Today rolling road systems featuring one or more moving belts on the wind tunnel floor are a standard tool to simulate the complex boundary condition of a vehicle driving on the road. But generally the technical effort to measure aerodynamic forces accurately increases with improvement of the aerodynamic ground simulation.
2017-03-28
Journal Article
2017-01-1564
Minh-Tri Nguyen, Jürgen Pitz, Werner Krantz, Jens Neubeck, Jochen Wiedemann
Abstract In addition to the analysis of human driving behavior or the development of new advanced driver assistance systems, the high simulation quality of today’s driving simulators enables investigations of selected topics pertaining to driving dynamics. With high reproducibility and fast generation of vehicle variants the subjective evaluation process leads to a better system understanding in the early development stages. The transfer of the original on-road test run to the virtual reality of the driving simulator includes the full flexibility of the vehicle model, the maneuver and the test track, which allows new possibilities of investigation. With the opportunity of a realistic whole-vehicle simulation provided by the Stuttgart Driving Simulator new analysis of the human’s thresholds of perception are carried out.
2015-04-14
Technical Paper
2015-01-1549
Jonathan Jilesen, Adrian Gaylard, Iwo Spruss, Timo Kuthada, Jochen Wiedemann
Abstract Driving when it is raining can be a stressful experience. Having a clear unobstructed view of the vehicles and road around you under these conditions is especially important. Heavy rain conditions can however overwhelm water management devices resulting in water rivulets flowing over the vehicle's side glass. These rivulets can significantly impair the driver's ability to see the door mirror, and laterally onto junctions. Designing water management features for vehicles is a challenging venture as testing is not normally possible until late in the design phase. Additionally traditional water management features such as grooves and channels have both undesirable design and wind noise implications. Having the ability to detect water management issues such as A-pillar overflow earlier in the design cycle is desirable to minimize the negative impact of water management features. Numerical simulation of windscreen water management is desirable for this reason.
2000-03-06
Technical Paper
2000-01-0442
Thomas Klenk, Peter Kappelmann, Jochen Wiedemann, Ulrich Sailer
The manufacturers of passenger cars increasingly assign development and production of complete subsystems to the supplying industry. A brake system supplier has to give predictions about system quality and performance long time before the first prototypical system is built or even before the supplier gets the order for system development. Nowadays, the usage of computer-aided system design and simulation is essential for that task. This article presents a tool designed to support the development process. A special focus will be on how to define quality. A formal definition of quality is provided, illustrated and motivated by two examples.
2000-06-12
Technical Paper
2000-05-0117
Rainer Moser, Jochen Wiedemann, Uwe Honekamp
The development process of electronic control units (ECU) is increasingly supported by different tools. The target-specific code-generation for single micro-controllers becomes a standard technology. Thus a continuous tool support during the whole development cycle is possible. This extends from the specification of the functionality to the implementation of the software on the controller. The next generation of tool support is not only focused on single micro-controllers it also supports the design of systems consisting of different controllers connected via various communication entities. Thus the goal of the tool support is the automatic code-generation for such distributed embedded real-time systems including support of different communication buses (e.g., Controller Area Network CAN, Time Triggered Protocol TTP) and different processor targets.
2003-03-03
Technical Paper
2003-01-0933
Wolfgang Mayer, Jochen Wiedemann
This paper introduces a driving-torque measurement method for the determination of vehicle road load and its components. To increase the accuracy, the torque measurements are combined with rolling resistance measurements performed with a specially developed trailer. This method is a strictly experimental approach and does not use any mathematical models. The experimental techniques are described as well as the proceedings to compare test stand and road measurements. The results that are shown prove that this method is suitable for the investigation of single road load components. Furthermore, the comparison of different rolling resistance measurement devices shows the potential of the measurement trailer and the necessity to perform rolling resistance measurements on real road surfaces and not solely on test stands.
2003-03-03
Technical Paper
2003-01-0429
Jochen Wiedemann, Juergen Potthoff
In 2001 the FKFS (Research Institute of Automotive Engineering and Vehicle Engines, Stuttgart) took into operation state-of-the-art 5-belt systems for road simulation in the 22.45m2-IVK automotive wind tunnel and in the 1.65m2-IVK model wind tunnel. In these systems, a narrow belt running between the vehicles' wheels is fitted with 4 balance-mounted wheel rotation drives and a vehicle restraint system. The FKFS opted for MTS steel belt technology due to its small size, low power requirements and excellent tracking stability. Due to air bearings below the belt, the flat-belt wheel rotation units in the full-scale wind tunnel permit aerodynamic force measurements at full wheel load (8 kN) up to 70 m/s. In combination with the hydrostatic suspension of the units, integrated longitudinal force transducers permit realistic measurements of the wheels' rolling resistance. In the model wind tunnel FKFS wheel rotation units with Poly-V belts are used with small wheel loads up to 80 m/s.
2002-03-04
Technical Paper
2002-01-0969
Werner Krantz, Jens Neubeck, Jochen Wiedemann
Within the scope of a current research project at the Research Institute of Automotive Engineering and Vehicle Engines Stuttgart (FKFS), the potential for an estimation of vehicle side slip angle and yaw rate arising from online measurement of tire forces is evaluated. Investigations focus on how the vehicle state can be determined, if in addition to wheel speeds and steering angle the tire forces currently acting on the vehicle are known. Different estimation procedures based on inverse tire models, direct integration of vehicle accelerations and closed-loop-observer are discussed. The performance is tested with data from vehicle dynamics simulation.
1989-02-01
Technical Paper
890369
Jochen Wiedemann
With the help of theoretical considerations it is shown that the flow between a car and the ground is of boundary layer type, as long as there is no recirculation. Thus, boundary layer theory can be applied to evaluate the order of magnitude of typical effects like displacement and momentum-loss thicknesses of ground-plane boundary layer. If the boundary layer in a wind tunnel with stationary ground is to be controlled, either by distributed suction or by tangential blowing, to simulate on-road conditions, boundary layer theory can provide the orders of magnitude of modifications that have to be applied. Experiments with a ground-effect quarter-scale car with ground simulation by distributed suction and moving belt showed coincidence with theoretical predictions concerning the required suction rate, if integral coefficients (eg CD, CL) of both flow cases are matched.
1990-02-01
Technical Paper
900321
Edzard Mercker, Jochen Wiedemann
*
2002-10-06
Technical Paper
2002-01-2587
Steffen Eppler, Thomas Klenk, Jochen Wiedemann
During the acquisition phase brake system supplier have to make predictions on a system's thermal behavior based on very few reliable parameters. Increasing system knowledge requires the usage of different calculation models along with the progress of the project. Adaptive modeling is used in order to integrate test results from first prototypes or benchmark vehicles. Since changes in the brake force distribution have a great impact on the simulation results fading conditions of the linings have to be integrated as well. The principle of co-simulation is used in order to use the actual brake force distribution of the system.
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