Rigorous, Transient 3D CFD Models of Unusually Complicated Fluid Networks/Circuits

Rigorous, Transient 3D CFD Models of Unusually Complicated Fluid Networks/Circuits
27
Jun

The role of fluid dynamics simulation in the design and development of various products has recently undergone what is arguably a paradigm shift due to the ability to simulate unusually complicated, multi-component, hydraulics flow circuits using three dimensional (3D) computational fluid dynamics (CFD) models.  The example shows a lubrication system model (developed using the Simerics-Sys / PumpLinx CFD software) for a 16 cylinder reciprocating internal combustion engine.  This represents an advance in system-level modeling of hydraulic fluid networks over the current state of the art which is a blend of zero and one-dimensional models.  This also represents continued progress in the role of CFD from the traditional component level modeling to system level modeling.  System level modeling provides insight into interactions between components.  Finally, it is equally important that model setup and run times are reasonable relative to development time scales.

The computational domain in the example shown includes the positive displacement gear pump, the pressure regulation valve, 49 journal bearings, 32 lifters, piston pins, piston cooling jets, the oil cooler, the oil filter etc.  The motion of the regulation valve was predicted by strongly coupling a rigorous force balance on the valve to the flow.  The orbital motion of every journal within bearings as well as deformation of all the bearings was modeled.  A moving, deforming mesh containing 8 million predominantly hexahedral cells was used.

The model validation is shown in the Table below which gives the percent difference in the oil pressures between model predictions and experimental measurements.

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The pressure fluctuations in the main bearings (Figure A) and con rod bearings (Figure B) are largely caused by the orbital motion of the journals within the bearings.

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The time-averaged results show that the majority of the system pressure drop and flow rates occur in bearings, lifters and piston cooling jets, confirming the importance of a three-dimensional treatment for these components versus a relatively empirical zero or one-dimensional treatment.

The present advance in CFD capability can also drive the development of system-level models in adjacent areas of topical interest such as engine oil warm up, interaction between lube oil and coolant temperatures, engine oil temperatures and oil life, uncovering of the oil pick up tube, priming of the oil pump, cavitation and dry spots in bearings, oil aeration, piston cooling jets, variable displacement vane pump and other related topics.  The present CFD capability will not supplant the traditional role of zero/1-D analysis but instead will supplement and augment it.  CFD can now be a new analysis tool in the efforts to meet the performance and durability requirements in the above design areas.

Questions? Email rr@simerics.com

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