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Characterisation of Brake Creep Groan Vibrations

Graz University of Technology-Peter Fischer, Manuel Pürscher, Severin Huemer-Kals
University of Ljubljana-Jurij Prezelj
  • Technical Paper
  • 2020-01-1505
To be published on 2020-06-03 by SAE International in United States
Creep Groan is an impulsive brake noise at very low velocities of the vehicle. Generally, stick-slip between brake disc and brake pads is assumed as the most dominating vibration mechanism of creep groan. This contribution will show by sophisticated measurement techniques, that stick-slip and speed dependent friction is an important trigger of this annoying vehicle noise. However, the overall vibration is much more complex than common stick-slip vibration models. It turns out, that in typical brake systems of passenger vehicles creep groan occurs around 15-20 Hz and 70-90 Hz. The mechanism at 15-20 Hz is an impulsive noise. Transitions between stick and slip phases trigger complex nonlinear vibrations of the complete brake and suspension system. At 70-90 Hz, the vibrations show a more harmonic-like behaviour, caused primarily by speed-dependent friction characteristics. Flexibilities in the suspension bushings, elastic deformations of suspension parts, wheel and tyre support the growth of instable self excited vibrations. In practical vehicle operation, the range of 70-90 Hz is the most relevant one. In many cases, the 15-20 Hz vibrations are not…
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A Priori Analysis of Acoustic Source Terms from Large-Eddy Simulation in Turbulent Pipe Flow

Graz University of Technology-Johannes Tieber, Helfried Steiner
  • Technical Paper
  • 2020-01-1518
To be published on 2020-06-03 by SAE International in United States
The absence of combustion engine noise pushes increasingly attention to the sound generation from other, even much weaker, sources in the acoustic design of electric vehicles. The present work focusses on the numerical computation of flow induced noise, typically emerging in components of flow guiding devices in electro-mobile applications. The method of Large-Eddy Simulation (LES) represents a powerful technique for capturing most part of the turbulent fluctuating motion, which qualifies this approach as a highly reliable candidate for providing a sufficiently accurate level of description of the flow induced generation of sound. Considering the generic test configuration of turbulent pipe flow, the present study investigates in particular the scope and the limits of incompressible Large-Eddy Simulation in predicting the evolution of turbulent sound sources to be supplied as source terms into acoustic analogies, which have been proposed for the computation of the acoustic pressure field. To this end, a comprehensive a priori analysis of fully resolved flow fields obtained from Direct Numerical Simulations (DNS) was carried out for different Reynolds numbers. The analysis of the…
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Investigation of the Effect of Tire Deformation on Open-Wheel Aerodynamics

Graz University of Technology-Philipp Eder, Cornelia Lex
U.A.S. Graz-Thomas Gerstorfer, Thomas Amhofer
  • Technical Paper
  • 2020-01-0546
To be published on 2020-04-14 by SAE International in United States
This paper introduces a finite element (FE) approach to determine tire deformation and its effect on open-wheeled racecar aerodynamics. In recent literature the tire deformation was measured optically using cameras during wind tunnel testing. Combined loads like accelerat-ing at corner exit are difficult to reproduce in wind tunnels and would require several camer-as to measure the tire deformation. In contrast, an FE approach is capable of determining the tire deformation in combined load states accurately and additionally provides the possibility to vary further parameters, for example, the coefficient of friction. The FE tire model was validated using stiffness measurements, contact patch measurements and steady-state cornering measurements on a flat belt tire test rig. The deformed shape of the FE model was used in a computational fluid dynamics (CFD) simulation. A sensitivity study was created to determine the effect of the tire deformation on aerodynamics for un-loaded, purely vertically loaded and combined vertical, lateral and longitudinal forces. In addition, the influence of these three tire deformations was investigated in a CFD study using a full vehicle…
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Visualization of Turbulence Anisotropy in the In-cylinder Flow of Internal Combustion Engines

Graz University of Technology-Andreas Wimmer
LEC GmbH-Rajat Soni, Clemens Gößnitzer, Gerhard Pirker
  • Technical Paper
  • 2020-01-1105
To be published on 2020-04-14 by SAE International in United States
Turbulence anisotropy has a great influence on mixture formation and flame propagation in internal combustion engines. However, the visualization of turbulence in simulations is not straightforward; traditional methods lack the ability to display the anisotropic properties in the engine geometry. Instead, they use invariant maps, and important information about the locality of the turbulence anisotropy is lost. This paper overcomes this shortcoming by visualizing the anisotropy directly in the physical domain. Componentality contours are applied to directly visualize the anisotropic properties of turbulence in the three-dimensional engine geometry. Using an RGB (red, green, blue) color map, the three limiting states of turbulence (one-component, axisymmetric two-component and isotropic turbulence) are displayed in the three-dimensional physical domain. Thus, the assessment and interpretation of the results is straightforward and can easily be integrated into a normal post-processing workflow.This paper focuses on unsteady Reynolds-averaged Navier-Stokes equations methods and uses the RNG k-ε model in the simulations. Computational fluid dynamics simulations of the cold flow operation of a single-cylinder research engine demonstrate the strength of this visualization strategy. Different phases…
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Impact of Rim Orientation on Road Vehicles Aerodynamics Simulations

Graz University of Technology-Wolfgang von der Linden, Günter Brenn
Magna Steyr Fahrzeugtechnik AG & Co KG-Gernot Bukovnik
  • Technical Paper
  • 2020-01-0674
To be published on 2020-04-14 by SAE International in United States
Aerodynamic CFD simulations in the automotive industry based on the steady-state RANS (Reynolds-averaged Navier–Stokes) approach typically utilize approximate numerical methods to account for rotating wheels. In these methods, the computational mesh representing the rim geometry remains stationary, and the influence of the wheel rotation on the air flow is modelled. As the rims are considered only in one fixed rotational position (chosen arbitrarily in most cases), the effects of the rim orientation on the aerodynamic simulation results are disregarded and remain unquantified. This paper presents a numerical sensitivity study to examine the impact of the rim orientation position on the aerodynamic parameters of a detailed production vehicle. The simulations are based on the steady-state RANS approach. These investigations are carried out for three rim geometries, and for simulation cases with stationary and rotating wheels for comparison, where the Moving Wall (MW) and the Moving Reference Frame (MRF) methods, as well as combinations of the two approaches are used to model the wheel rotation. For the test vehicle, alterations in the flow field, and subsequently an…
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Experimental Investigation of the Influence of Ignition System Parameters on Combustion in a Rapid Compression-Expansion Machine

Graz University of Technology-Andreas Nickl, Andreas Wimmer
HOERBIGER Wien GmbH-Georg Meyer
  • Technical Paper
  • 2020-01-1122
To be published on 2020-04-14 by SAE International in United States
Lean burn combustion concepts with high mean effective pressures are being pursued for large gas engines in order to meet future stringent emission limits while maintaining high engine efficiencies. Since severe boundary conditions for the ignition process are encountered with these combustion concepts, the processes of spark ignition and flame initiation are important topics of applied research, which aims to avoid misfiring and to keep cycle-to-cycle combustion variability within reasonable limits. This paper focuses on the fundamental investigation of early flame kernel development using different ignition system settings. The investigations are carried out on a rapid compression-expansion machine in which the spark ignition process can be observed under engine-like pressure and excess air ratio conditions while low flow velocities are maintained. The schlieren setup for high-speed optical investigations of the area of the spark plug electrodes is described and a suitable post-processing routine is introduced. The influence of different spark current durations on early flame kernel formation is investigated using a modulated capacitive discharge ignition (MCDI) system. The outcomes reveal that a short spark current…
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Evaluation of Methods for Identification of Driving Styles and Simulation-Based Analysis of their Influence on Energy Consumption on the Example of a Hybrid Drive Train

Gregor Pucher
Graz University of Technology-Marko Domijanic, Mario Hirz
  • Technical Paper
  • 2020-01-0443
To be published on 2020-04-14 by SAE International in United States
Due to current progresses in the field of driver assistance systems and the continuously growing electrification of vehicle drive trains, the evaluation of driver behavior has become an important part in the development process of modern vehicles. Findings from driver analyses are used for the creation of individual profiles, which can be permanently adapted due to ongoing data processing. A benefit of data-based, dynamic control systems lies in the possibility to individually configure the vehicle behavior for a specific driver, which can contribute to increasing customer acceptance and satisfaction. In this way, an optimization of the control behavior between driver and vehicle and the resulting mutual learning and adjustment holds great potential for improvements in driving behavior, safety and energy consumption. The submitted paper deals with the analysis of different methods and measurement systems for the identification and classification of driver profiles as well as with their potential to optimize both vehicle driving behavior and energy consumption on the example of a hybrid drive train. A literature research results in a number of different approaches…
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Analysis of a Prechamber Ignited HPDI Gas Combustion Concept

Graz University of Technology-Andreas Wimmer
Hoerbiger Wien GmbH-Matthias Huschenbett
  • Technical Paper
  • 2020-01-0824
To be published on 2020-04-14 by SAE International in United States
Direct gas injection of natural gas under high pressure (HPDI) into the combustion chamber enables a non-premixed combustion regime known from diesel engines. With this combustion process, knocking combustion cannot occur, enabling an increase in the compression ratio and thus, a possible increase in efficiency. Due to the high injection pressures required, this concept is ideally suited for applications where liquefied natural gas (LNG) is available. In marine applications, the bunkering of and operation with LNG is state of the art. Existing HPDI gas combustion concepts typically use a small amount of diesel fuel for ignition, which is injected late in the compression stroke. The diesel fuel ignites due to the high temperature of the cylinder charge. The subsequently injected gas ignites at the diesel flame. The presented HPDI gas combustion concept is of a monovalent type, meaning that no other fuel than natural gas is used. The high-pressure gas jet is ignited with the aid of flame torches from a gas-scavenged prechamber. Design and layout of the combustion process and the prechamber shape was…
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Uncertainty Quantification of Motorcycle Racing Upstream Flow Conditions

Graz University of Technology-Christoph Simon Feichtinger, Peter Fischer
  • Technical Paper
  • 2020-01-0667
To be published on 2020-04-14 by SAE International in United States
The upstream flow conditions in front of any vehicle are the first barrier a vehicle must overcome beside the acceleration itself. Both together, the vehicle speed and the upstream flow conditions, result in the oncoming wind vector experienced by the moving vehicle. The aim of the present work is to show a new approach to consider the chaotic and random behavior of surrounding flow conditions and their influence on driving performance. Special interest was put on a description of the flow conditions with respect to well know turbulent flow field parameters like the turbulence length scale or the turbulence intensity. Depending on where the flow conditions are measured, stationary in the earth reference frame, or on a moving vehicle, it is quite difficult to get a robust description of the previously mentioned flow field parameters. These parameters are used together with the Reynolds number to predict the aerodynamic behavior by correlation functions or maps. A lot of aerodynamic characteristics for road vehicles are deter-mined in wind tunnels or from numerical flow simulations for specific flow…
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An Integrated View on Automotive SPICE, Functional Safety and Cyber-Security

Graz University of Technology-Georg Macher, Jürgen Dobaj
AVL LIST GmbH-Eric Armengaud
  • Technical Paper
  • 2020-01-0145
To be published on 2020-04-14 by SAE International in United States
Automotive domain has seen safety engineering at the forefront of the industry’s priorities for the last decade. Therefore, additional safety engineering efforts, design approaches and well-established safety processes have been stipulated. Today many connected and automated vehicles are available and connectivity features and information sharing is increasingly used. This increases the attractiveness of an attack on vehicles and thus introduces new risks for vehicle cyber-security. Thus, just as safety became a critical part of the development in the late 20th century, the automotive domain must now consider cyber-security as an integral part of the development of modern vehicles. Aware of this fact, the automotive industry has therefore recently taken multiple efforts in designing and producing safe and secure connected and automated vehicles. As the domain geared up for the cyber-security challenges, they leveraged experiences from many other domains, but nevertheless, must face several unique challenges. For that aim, the domain invested efforts in the development of industry standards to tackle automotive cyber-security issues and protect their assets. The joint working group of the standardization organizations…