LAUSR

Abstract A 3D modeling of the fluid dynamics and heat transfer in an advanced free-piston Stirling engine was conducted. The transient and conjugate fluid dynamics and thermodynamics of the coupling fluid-solid domain over the working cycle were comprehensively investigated. The comparisons among different turbulent CFD models and Sage result of the engine were performed. Results indicate that the k-epsilon turbulence model with improved wall treatment yields reasonable accuracy and stable convergence. The CFD results of the pressure drop in the regenerator are nearly the same as engine Sage design code results, while the pressure drop inside cold heat exchanger has about 10.43% deviation compared to the Sage result. The flow diffuser guide flow more evenly distributed inside the regenerator, but it was found that it causes a vast turbulent dissipation rate. The instantaneous transport variables such as temperature, density and viscosity cannot be treated as uniform distribution due to the complicated interaction and coupling between the fluid-fluid and fluid-solid during the operation. The ejecting and injecting flows result in non-uniformly distributed temperature, pressure and density in the regenerator. The flow friction coefficient in the regenerator over one cycle cannot be simply correlated by typical empirical equations. The linearly distributed temperature profile in the regenerator solid matrix in the Stirling engine is confirmed by this CFD modeling. The optimization results of the diffuser and regenerator are also discussed.