Single Discretization for Heat Transfer and Thermal Stress Solving: A Water Jacket Study

Abstract

As OEMs look to increase thermal efficiency of their existing engine architectures there is an increased focus on the performance of the cooling system. Water jackets in combination with radiators are the main components to remove excessive heat from the engine block originating from in-cylinder combustion. The temperature reached by the engine block spans from ambient temperature up to 400 K, leading to high thermal gradients and significant failure risks. In this work, the mechanical stresses due to the thermal expansion are evaluated via 3D numerical simulations via an innovative workflow. Typically, solving for the thermal stress, requires two different meshes. In the first mesh, the fluid and solid equations are solved with a finite volume approach. In a second phase, the temperature from the first mesh is mapped onto a second mesh, to allow the thermal stress calculation with a finite element approach, leading to discretization and interpolation errors. In this work, a simplified workflow is proposed, to reduce any numerical error and allow for a more accurate calculation of the thermal stress, deriving from a better representation of the temperature field. The water-filled casing is modelled with a finite volume approach, with the water circulating at a prescribed velocity at the inlet. The solid energy equation and the thermal stress are directly solved on a tetrahedral mesh. The material is modelled as isotropic linear-elastic with the thermal expansion also included to calculate the total displacement. As expected, the highest thermal stresses are observed at the sharpest corners of the engine block in combination with the highest temperature gradients. Such work opens the possibility of improving the understanding of how thermal stresses play a role in water jacket failures, with a more reliable prediction of the mechanical behavior.