"Coupling of liquid transmission line models with 3-dimensional CFD in OpenFOAM"
Coupling of liquid transmission line models with 3-dimensional CFD in OpenFOAM
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Wave propagation effects are of increasing importance in simulation models for fluid power applications due to rising demands for both the accuracy of predicted system responses as well as the range of interesting operating frequencies. Well documented examples can be found in technologies such as fuel injection for internal combustion engines or hydraulically driven punching machines. The distribution system for the pressurized fluid is predominantly made up of pipes and hoses as well as cylindrical bores in the housings of various components. These cylindrical geometries lend themselves conveniently for modeling as a network of elements with a 1 or 2-dimensional spatial representation. This basic modeling approach already hits the wall in case of simple elbow bends or T-junctions, which are very often idealized as lossless Kirchhoff-type nodes, whereas a 3-dimensional modeling approach, namely CFD, could capture flow effects in those more complicated geometries, leading to a more accurate result. The present work deals with the idea of coupling a transmission line model based on the well known frequency-dependent friction theory for transient laminar flow of a weakly compressible viscous fluid for parts with purely cylindrical geometry with a CFD model (the open source code OpenFOAM has been used for the purpose of this work) resolving the local effects occurring at more complex regions, represented by an elbow bend. The investigations in this work are all aiming for highly reduced simulation time simultaneously with increased result accuracy, comparable to 3-dimensional approaches used for the whole system, making a more accurate simulation on commercial computers feasible.