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Development and Validation of Thermo-mechanical CFD Simulation Methodology for a Commercial Vehicle Exhaust Manifold
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on September 22, 2021 by SAE International in United States
The performance of exhaust manifold is governed by the flow and thermal parameters. Flow resistance and back pressure affect the engine performance and emissions; temperature profile on the manifold causes the development of thermo-mechanical stresses in the manifold, eventually leading to structural failure. In this paper, an iterative process has been followed to optimize the CFD thermo-mechanical simulation methodology and an engine-level correlation has been established for its validation. In this paper, conjugate heat transfer concept is utilized in order to model the heat transfer from the high temperature fluid zone i.e. exhaust gas to the outer surface of the solid zone i.e. manifold through the thickness of the manifold. The thermal properties of the solid material and the heat transfer parameters defined for the mechanism are the two important parameters which govern the formation of the temperature profile and subsequently the thermo-mechanical stresses. Multiple iterations of the simulation are performed at different flow rates from no load to full load condition. Correspondingly, the inlet temperatures of the exhaust gases are also changed towards the maximum value. Along with these conditions, the surface heat transfer coefficients and the free stream temperature for convection are also modified. A similar setup at the engine level is tested at the same operating conditions as the CFD simulation. Observation locations are defined on both the physical component and the CFD model. Correlation between test rig and simulation is carried out at these locations, in order to obtain the optimum value of heat transfer coefficient and free stream temperature. The validation is successful, with more than 90% correlation being observed between Test and CFD at all operating conditions. The methodology is modified with the obtained vales and the resultant temperature profile is found to be in correlation with that obtained on the engine test rig.