Sliding Vane Expander, CFD, OpenFOAM, SCORG, Rotor Grid Generation
Recent studies on the use of 3D Computational Fluid Dynamics (CFD) for the analysis and design of sliding vane machines has proved beneficial for the detailed evaluation and optimisation of the vane expanders for a given working fluid and operating condition. The authors have earlier developed a customised rotor grid generator for integration with commercial CFD solvers and validated it for use in typical small-scale ORC expanders for waste heat recovery. In this paper, this customised grid generation is extended to an open source CFD solver OpenFOAM, by using a connectivity methodology originally developed for roots blower and twin-screw machines. The control of the rotor grid deformation is through a user code integrated within the flow solver. A case study of the reference ORC expander operating with R245fa was used for validation. The available experimental data for three operating conditions are compared with the results calculated with ANSYS CFX and OpenFOAM-v1912 solvers. During the filling and expansion process, the internal pressure traces are accurately captured by both the solvers and the difference is within 0.05 bar with measurements. However, between the outlet port closure and inlet port opening process the pressure and temperature prediction with OpenFOAM solver is considerably different from the ANSYS CFX solver. It was observed that the OpenFOAM solver is resulting into a non-physical low temperature zone upstream to the tangency region of the rotor and the stator that goes below 80℃. Overall, CFD solution obtained with the commercial solver ANSYS CFX is much more stable and robust than the open source OpenFOAM solver. The generic nature of the deforming grid generation used with an open source CFD solver presented in the paper allows broadening of the utilisation of CFD modelling tools for the design of vane machines.