A New Approach to Simulate Stirling Engine Regenerators as Porous Media under Low Reynolds Conditions

The regenerator of a Stirling engine is widely studied both numerically and experimentally because it greatly influences the global performance of such an engine. In this work, a new numerical approach is developed to analyse the regenerator performance. As in conventional porous media models, this approach consists of defining the wires of the regenerator as regions with a high value of inverse permeability. On the other hand, a lower porosity value is used in the boundary layers and additional terms are introduced in the governing equations to correctly reproduce the flow structure and the overall regenerator performance. This approach leads to a very interesting reduction of the computational cost of the simulations w.r.t. standard CFD analyses. OpenFOAM libraries are used and low Reynolds number conditions (Re lower than 200) are considered. At first, it is shown that at low Re the incompressible flow hypothesis is accurate enough to predict fluid-dynamic and thermal performances of the regenerator. Hence, the proposed porous media model has been implemented by considering the fluid as incompressible. The model is applied to a test case under several flow conditions and the results are compared with those obtained by the standard CFD incompressible model, showing a good agreement for both the friction coefficient and the thermal efficiency.