Abstract
Over the last decade, Computational Fluid Dynamics (CFD) has been increasingly applied for the design and analysis of positive displacement machines employed in vapor compression and power generation applications. Particularly, single-screw and twin-screw machines have received attention from the researchers, leading to the development and application of increasingly efficient techniques for their numerical simulation. Modeling the operation of such machines including the dynamics of the compression (or expansion) process and the deforming working chambers is particularly challenging. The relative motion of the rotors and the variation of the gaps during machine operation are a few of the major numerical challenges towards the implementation of reliable CFD models. Moreover, evaluating the thermophysical properties of real gases represents an additional challenge to be addressed. Special care must be given to defining equation of states or generating tables and computing the thermodynamic properties. Among several CFD suite available, the open-source OpenFOAM tool OpenFOAM, is regarded as a reliable and accurate software for carrying out CFD analyses. In this paper, the dynamic meshing techniques available within the software as well as new libraries implemented for expanding the functionalities of the software are presented. The simulation of both a single-screw and a twin-screw machine is described and results are discussed. Specifically, for the single-screw expander case, the geometry will be released as open-access for the entire community. Besides, the real gas modeling possibilities implemented in the software will be described and the CoolProp thermophysical library integration will be presented.
Highlights
Positive Displacement machines (PDMs) play a crucial role in a huge number of applications.Air compression, vapor compression, and Organic Rankine Cycles (ORCs) are just few examples in which PDMs are widely employed
The workflow for the Computational Fluid Dynamics (CFD) analysis of a single screw expander (SSE) starts with the definition of a proper mesh generator able to provide meshes that are suitable for the motion technique that will be employed
Mesh Adaption—Dynamic Remeshing and Key Frame Remeshing rely on the deformation of the grid: the operation of the machine is intrinsically evaluated by updating the cells close to the wall
Summary
Positive Displacement machines (PDMs) play a crucial role in a huge number of applications. Vapor compression, and Organic Rankine Cycles (ORCs) are just few examples in which PDMs are widely employed These machines are typically preferred to dynamic machinery for a number of reasons including high pressure ratio preserving compactness, unsteadiness of the working conditions, and low enthalpy jump can cause dramatic efficiency losses [1,2]. Within this framework, the performances of PDMs are receiving growing attention by the researchers. These include typical cubic equations of state ( Peng-Robinson [18], Redlich-Kwong [19], Aungier-Redlich-Kwong [20], Soave-Redlich-Kwong [21]) and a new functionality of the software that implements a CoolProp wrapper for OpenFOAM is presented [22]
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