24th International Colloquium Tribology - January 2024 177 Numerical and Experimental Analyses of the Multiscale Effects in the Tribological System Rotary Shaft Seals * Jeremias Grün 1* , Marco Gohs 1 , Simon Feldmeth 1 , Frank Bauer 1 1 University of Stuttgart, Institute of Machine Components, Stuttgart, Germany * Corresponding author: jeremias.gruen@ima.uni-stuttgart.de 1. Introduction In many applications, the tribological system [1] rotary shaft seal [2] is subjected to a variety of dynamic loads on multiple scales. Especially considering the trends in electromobility, rotary shaft seals are exposed to increasingly extreme operating conditions and loads. To address this, it is essential to provide suitable models for numerical computation, as well as conduct appropriate experiments for verification and validation. The following contribution focuses on both numerical and experimental analyses of the function of rotary shaft seals. The numerical methods encompass nonlinear finite element analyses (FEA) of the multiscale structural mechanics [3] and transient multi-phase computational fluid dynamics (CFD) of the flow processes in the sealing gap on the microscale [4]. Test results on endurance test rigs and visual examinations using specialized devices are employed to validate and verify the numerical methods. 2. Numerical simulations and experimental analyses Figure 1 illustrates the general process of multiscale modeling and simulation of rotary shaft seals. The initial step involves utilizing FEA to compute the structural mechanics of the rotary shaft seal. This encompasses evaluating the deformation of the sealing ring during mounting on the macroscale and analyzing the microscopic distortions in the sealing contact between the shaft counter face and the sealing edge [3], [5]. The post-processing of the FEA results establishes the computational domain for the subsequent CFD modeling [4]. The minimum sealing gap height serves as a crucial input parameter for defining the computational domain. Lubricant film thickness equation according to [6], [7] serve to determine the sealing gap height under consideration of surface and material parameters as well as operating conditions. The CFD simulations allow to evaluate the sealing performance on the basis of parameters such as the pumping rate. Moreover, they provide a more in-depth insight into the complex transient flow processes in the lubricant film in the seal gap. Figure 1: Multiscale modeling and simulation of rotary shaft seals 178 24th International Colloquium Tribology - January 2024 Numerical and Experimental Analyses of the Multiscale Effects in the Tribological System Rotary Shaft Seals* Figure-2: Structural mechanical results 3. Results Figure-2 illustrates the results of the structural mechanics analysis, while Figure-3 showcases the findings from the fluid dynamics analysis. Figure-2 shows above the numerical results for the microscopic mechanics in the sealing contact, showcasing the deformed sealing edge surface (Figure-2 ① ) and the contact pressure distribution (Figure-2 ② ). The black dashed line represents the mean displacement of the sealing edge. At the bottom (Figure-2 ③ ), a comparison is made between the numerical results (m = 0.25 … 0.35) and the experimental results (RSS 1 - RSS 4) for the tangential displacement of the sealing edge surface. In Figure-3 the fluid dynamics results are depicted. The upper part illustrates the phase transitions between air and oil (Figure-3 ① ) and the hydrodynamic pressure, along with the formation of cavitation areas (Figure-3 ② ). The bottom section (Figure-3 ③ ) presents a comparison between the pumping rates obtained from endurance tests ṁ exp and those computed numerically ṁ sim . 4. Conclusions The results obtained from both the numerical simulations and experimental analyses demonstrate a substantial level of agreement. This suggests that the employed numerical methods are well-suited for studying the multiscale tribological effects. In summary, the attained numerical and experimental findings offer a comprehensive understanding of the tribological behavior exhibited by rotary shaft seals, serving as a foundation for future advancements and developments in this field. Figure-3: Fluid dynamics results References [1] F. Bauer, Tribologie. Wiesbaden (DE): Springer Fachmedien Wiesbaden, 2021. doi: 10.1007/ 978-3-658- 32920-4. [2] F. Bauer, Federvorgespannte-Elastomer-Radial-Wellendichtungen. Wiesbaden (DE): Springer Fachmedien Wiesbaden, 2021. doi: 10.1007/ 978-3-658-32922-8. [3] J. Grün, M. Gohs, und F. Bauer, „Multiscale Structural Mechanics of Rotary Shaft Seals: Numerical Studies and Visual Experiments“, Lubricants, Bd. 11, Nr. 6, S.-234, Mai 2023, doi: 10.3390/ lubricants11060234. [4] J. Grün, S. Feldmeth, und F. Bauer, „Multiphase Computational Fluid Dynamics of Rotary Shaft Seals“, Lubricants, Bd. 10, Nr. 12, S. 347, Dez. 2022, doi: 10.3390/ lubricants10120347. [5] J. Grün, S. Feldmeth, und F. Bauer, „The sealing mechanism of radial lip seals: A numerical study of the tangential distortion of the sealing edge“, Tribology and Materials, Bd. 1, Nr. 1, S. 1-10, 2022, doi: 10.46793/ tribomat.2022.001. [6] N. Marx, J. Guegan, und H. A. Spikes, „Elastohydrodynamic film thickness of soft EHL contacts using optical interferometry“, Tribology International, Bd. 99, S. 267-277, Juli 2016, doi: 10.1016/ j. triboint.2016.03.020. [7] P. Sperka, I. Krupka, und M. Hartl, „Analytical Formula for the Ratio of Central to Minimum Film Thickness in a Circular EHL Contact“, Lubricants, Bd. 6, Nr. 3, S. 80, Sep. 2018, doi: 10.3390/ lubricants6030080.