Conference Year

2016

Keywords

Fluid-Structure Interaction, Reed valve, Turbulence, Numerical modelling, LES

Abstract

This paper aims at studying numerically the flow of a fluid through reed type valves, which are generally used in some reciprocating compressors and engines. The analysis and design of these valves serve not only to improve the performance of filling or discharging, but also to ensure system reliability. The valve opening-closing process involves fluid dynamics and deformation of a flat plate structure, both physics being completely coupled. To overcome this and other kind of fluid-structure interaction (FSI) problems, an in-house CFD-CSD (Computational Fluid Dynamics-Computational Structural Dynamics) coupled solver has been implemented within TermoFluids code. The CFD solver consists of a three dimensional explicit finite volume fractional step algorithm formulated in a second order, conservative and collocated unstructured grid arrangement. Since this case involves a turbulent flow, the wall adapting local eddy viscosity (WALE) model is employed. In order to save considerable effort in time and cost, the normal mode summation method is used to solve the deformation of the elastic valve. The geometric interaction between both dynamically moving media is managed with a fluid deformable mesh with moving boundaries, which belong to the solid valve. The static bodies, such as the walls, are embedded into the fluid mesh thanks to the immerse boundary method. The ‘CFD - Moving Mesh’ coupling is built by means of the space conservation law. From the point of view CFD-CSD coupling, a partitioned algorithm is used. For each time step, fluid and solid are solved consecutively until fluid pressure on the interface and displacements of the structure converge. In fact, only the Poisson equation for the fluid pressure ought to be coupled with the structure solver. Thus, grid updates and predicted fluid velocity calculation are solved only once at the beginning of the time step. First of all, the simulation platform is validated reproducing a benchmark FSI case from the literature that concerns a transient flat plate deflection analogous to the reed valve's. Then, a sensitivity analysis is carried out in order to compare the transient operation of a generic reed valve under variations in its thickness.

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