Unsteady numerical simulation of an air-operated piston pump for lubricating greases using dynamic meshes

• Published in: Computers & fluids 2012-03, Vol.57, p.138-150
• Main Authors: Menendez Blanco, A, Fernandez Oro, JM
• Format: Article
• Language: English
• Subjects: Air-operated piston pump; CFD; Computer simulation; Dynamic mesh; Dynamics; Fluidity; Greases; Layering technique; Leakage flow; Lubricating grease; Mathematical analysis; Mathematical models; Non-newtonian pseudoplastic flow; Numerical simulation; Pump aspiration; Pumps; Unsteady; Viscosity
• ISSN: 0045-7930; 1879-0747
• DOI: 10.1016/j.compfluid.2011.12.014

► Modeling of air-operated piston grease pump is performed for the first time. ► Experimental testing and theoretical estimations are used to validate the model. ► Evidences on low fluidity and aspirating limitations are confirmed numerically. ► Unsteady viscosity maps reveal in detail the grease rheological behavior over time. ► The single-phase approach advices for the need of a two-phase scheme in future work. This paper presents the numerical simulation of an air-operated piston pump for lubricating greases. The model, based on the dynamic mesh technique, describes the unsteady displacement of the piston using a layering algorithm. The pump driven velocity has been modified using a parametric user defined function (UDF) that covers the whole range of operating points for the pump, as a function of the discharged outlet pressure. The leakage flow across the feeder plate gap has been analyzed in detail, monitoring its evolution in both forward and backward strokes as a function of the pressure in the adjacent chambers. The comparison between the numerical results and the predictions from the theoretical formulations in the literature for non-newtonian fluids in annular ducts has confirmed the accuracy of the simulation and the correct selection of the discretization for small gaps and inner passages. In addition, the analysis of the flow delivered overtime has provided the numerical distribution and mean values expected from the experimental performance curves supplied by the manufacturer. Finally, the flow conditions in the aspirating region of the pump have been studied in terms of dynamic viscosity and grease fluidity. It has been observed that the fluidity is restricted to those zones presenting large areas of velocity gradients, like the feeder gap and the vicinity of the aspirating inlet, especially close to the solid walls of pump and drum. For the intermediate positions of both advancement and returning stages, when the piston velocity is maximum, the obtained maps reveal that the induced suction reach significant portions of grease within the drum, similar in distance to the pump diameter, and confirms the order of magnitude estimated with an inspectional analysis of the governing equations of grease motion in the aspirating zone.