advanced simulation technologies F O C U S 2 1 MULTI-DISCIPLINARY THERMO-MECHANICAL SIMULATION Powertrain components must satisfy increasingly stringent demands in view of performance and durability while maintaining optimal cost efficiency. Coupling AVL EXCITE™ and AVL FIRE™ has now made thermal load calculation more accurate than ever. > Thermo-mechanical loads in an internal combustion engine. Downsizing and downspeeding are current trends in engine development. Combined with increased power and torque, they lead to higher mechanical and thermal loads up to the point of component failure. Components at particular risk are the piston assembly, the cylinder head and the cylinder block. Numerical simulation allows detecting thermally critical areas at different operating loads at early development stages and defining countermeasures in the form of design adaptations. For a reliable prediction of component temperatures it is necessary to analyze the heat release inside the combustion chamber, the heat transfer through the structure to the coolant and possibly the cooling of the piston. Consideration must also be given to the thermal flows between piston, piston rings and the cylinder liner, along with the additionally generated heat input from friction between the piston, rings and liner. One of the more established thermal analysis methods used for cylinder head/block compound analysis is the so-called fluid-structure-interaction (FSI) analysis. This technique uses CFD software to calculate the incylinder flow, as well as the flow in the cooling water jacket and the related heat transfers to neighboring structures. These results serve as boundary conditions for calculating heat transfer and temperature distribution in the engine components. For the heat flow between the piston, piston rings and the cylinder liner usually assumptions are made based on empirical models. Consequently, there is a high risk of not achieving the level of result accuracy needed for damage prediction. For this reason, AVL has made some significant improvements to the traditional calculation methodology. Instead of adopting an empirical approach to determine the heat flows between the piston assembly and the cylinder liner, the structural dynamics analysis software AVL EXCITE™ is used, which relies upon detailed physical models to calculate piston and piston ring contacts. This approach also implicitly takes into account the dependency of the heat flow on gap widths, the amount of oil in the gap, relative motions as well as friction heat and temperature differences between the component surfaces. In combination with the CFD software AVL FIRE™, this results in consistent numerical modeling with improved reliability and accuracy. Furthermore, AVL FIRE™ facilitates the simultaneous calculation of coolant flow and the temperature field within the engine components. Since an additional finite element analysis is no longer needed, this represents a major simplification of the calculation process. <
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