Modeling approaches for numerical simulations that consider the influence of motor oil on the engine acoustics Fabian Duvigneau / Sebastian Koch / Elmar Woschke / Ulrich Gabbert Otto-von-Guericke-University Magdeburg Universitätsplatz 2, Magdeburg, D-39106 Germany The acoustic behavior of the combustion engine is primarily dominated by the sound radiation of the oil pan. Therefore, the vibration behavior of the oil pan as prominent noise emission source is investigated in this paper with the help of numerical simulations on the one hand and measurements on the other hand. In a previous study the acoustic behavior of a running combustion engine was analyzed via numerical simulations using the finite element method (FEM) and experiments [1]. In these simulations the numerical model of a combustion engine consists of the most important components like the cylinder crankcase and the oil pan, because these components define the main characteristics of the resulting engine sound [2]. All other influences and interactions as the combustion process and the crank drive motion have been taken into account by applying suitable excitations and boundary conditions to the numerical simulation model [3]. The comparison of the results raised the question, how the motor oil in the oil pan influences the vibration behavior of the combustion engine as well as the sound radiation [1]. A first study has shown that a fluid filling of an oil pan shifts the eigenmodes to lower frequencies and reduces the vibration amplitudes as well. In contrast, the shape of the eigenmodes show only slightly changes with regards to different filling levels. In the present paper different modeling approaches for taken into account the oil are evaluated and compared with experimental results. It was the object of this approach to identify the simplest but reliable option to consider the influence of motor oil in the numerical vibration analysis. The experimental investigations have been performed with the help of a three-dimensional scanning laser vibrometer. In the numerical analysis the following three different approaches have been applied: (i) only the fluid has been taken into consideration with the help of additional mass elements without stiffness; (ii) the fluid has been modeled as elastic continuum with adapted material parameters; and (iii) the fluid has been modeled with the help of the smoothed particle hydrodynamics method (SPH). It should be noted that a combination of FEM and SPH cannot be used within commercial software tools, such as Ansys or Abaqus. As a first step, the vibration analysis and the fluid dynamics are solved in a not fully coupled approach in this paper. The results of the three different modeling approaches are discussed and compared with the measurements. Finally, a recommendation how to consider the oil in the simplest but reliable manner is given, avoiding time consuming approaches such as a fully coupled computational fluid dynamic simulation.

Keywords: FEM, vibration analysis, influence of oil, SPH, laser vibrometer References [1] F. Duvigneau, T. Luft, J. Hots, J. L. Verhey, H. Rottengruber and U. Gabbert, Thermo-acoustic performance of full engine encapsulations - A numerical, experimental and psychoacoustic study, Applied Acoustics, Volume 102, 2016, pp. 79-87. DOI: 10.1016/j.apacoust.2015.09.012. [2] F. Duvigneau, S. Liefold, M. Höchstetter, J. L. Verhey and U. Gabbert, Analysis of simulated engine sounds using a psychoacoustic model, Journal of Sound and Vibration, Volume 366, 2016, pp. 544-555. DOI: 10.1016/j.jsv.2015.11.034. [3] F. Duvigneau, S. Nitzschke, J. Strackeljan and U. Gabbert, Virtual engineering approach for the analysis of the acoustic behavior of an engine, 22nd International Congress on Sound and Vibration – ICSV 22, 2015, ISBN 978-88-88942-48-3.