The importance of a full 3D fluid dynamic analysis to evaluate the flow forces in a hydraulic directional proportional valve Riccardo Amirante, Luciano Andrea Catalano and Paolo Tamburrano Department of Mechanics, Mathematics and Management (DMMM) – Polytechnic University of Bari, Bari, Italy Abstract Purpose – The purpose of this paper is to present a full 3D Computational Fluid Dynamics (CFD) analysis of the flow field through hydraulic directional proportional valves, in order to accurately predict the flow forces acting on the spool and to overcome the limitations of two-dimensional (2D) and simplified three-dimensional (3D) models. Design/methodology/approach – A full 3D CAD representation is proposed as a general approach to reproduce the geometry of an existing valve in full detail; then, unstructured computational grids, which identify peculiar positions of the spool travel, are generated by means of the mesh generation tool Gambit. The computational grids are imported into the commercial CFD code Fluent, where the flow equations are solved assuming that the flow is steady and incompressible. To validate the proposed computational procedure, the predicted flow rates and flow forces are compared with the corresponding experimental data. Findings – The superposition between numerical and experimental curves demonstrates that the proposed full 3D numerical analysis is more effective than the simplified 3D flow model that was previously proposed by the same authors. Practical implications – The presented full 3D fluid dynamic analysis can be employed for the fluid-dynamic design optimization of the sliding spool and, more generally, of the internal profiles of the valve, with the objective of reducing the flow forces and thus the required control force. Originality/value – The paper proposes a new computational strategy that is capable of recognizing all 3D geometrical details of a hydraulic directional proportional valve and that provides a significant improvement with respect to 2D and partially 3D approaches. Keywords CFD, Flow forces, Hydraulic proportional directional valve Paper type Research paper The current issue and full text archive of this journal is available at www.emeraldinsight.com/0264-4401.htm Received 27 September 2012 Revised 28 May 2013 Accepted 30 May 2013 Engineering Computations: International Journal for Computer-Aided Engineering and Software Vol. 31 No. 5, 2014 pp. 898-922 r Emerald Group Publishing Limited 0264-4401 DOI 10.1108/EC-09-2012-0221 This work is in memory of dear Luciano Andrea Catalano. Luciano prematurely departed during the revision process of this paper. At the time of his death he was 47 years old and he was a devoted father-of-three, beloved husband and son. He was a Full Professor in the Department of Mechanical Engineering of the Polytechnic of Bari, Italy, and his genius will remain unchanged in the minds forever. This work has been supported by Miur under contract PRIN 2007, and by the “Distretto Pugliese della Meccatronica” – MEDIS (PNR 2005-2007). The authors thank Angelo Innone, Antonio Ferrara, Giuseppe Tammone, Francesco Giordano, Vito Mele, Michele Mizzi for their technical assistance in the numerical and experimental tests. 898 EC 31,5