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CFD Simulation Methodology for a Rotary Steam Expansion Piston Engine
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on October 30, 2020 by SAE International in United States
In industrial processes, combustion engines and co-generation plants, large amounts of waste heat are generated, which are often lost to the environment. The conversion of this thermal energy into mechanical work and ultimately into electrical power promises a significant improvement in energy utilization, the efficiency of the overall system and, consequently, cost-effectiveness. Therefore, the use of a Rankine Cycle is a well-established technical process. A recent research project investigates a novel expansion machine to be integrated into an RC-process to convert the heat energy into mechanical work. Primarily, the present work deals with the fluid dynamic simulation of this expander, which is based on the principle of a rotary piston engine. The aim is to develop, analyze and optimize the process and the corresponding components. Hence, a CFD model has to be built up, which should correspond as closely as possible to the requirements and geometries of the physical engine. However, the special demands on the simulation model turn out to be very challenging for most commercial CFD tools due to complex rotary kinematics in combination with the port-controlled gas exchange and the unconventional working medium (e.g. occurring phase transition) used. First, the procedure of generating an initial CFD simulation with ANSYS Fluent is examined in detail. Due to the complex processes, which lead to high numerical effort in terms of phase transition and large dynamic mesh changes, this model requires several assumptions and simplifications in order to find an optimal balance between computing time and result quality. Thus, the Fluent model shows some advantages, but also disadvantages, restrictions and occurring difficulties, which motivate the development of alternative simulation models. Consequently, some alternative methods of building up a corresponding simulation model are assessed, which are described and discussed with their associated properties and limitations.