Numerical simulation of flow field and dynamic characteristics of pilot operated directional valve

Abstract:

To obtain the effects of notch type on the flow field and dynamic response characteristic of the pilot operated directional valve, the simulations of steady and transient flow with three kinds of notch based on CFD and Matlab Simulink software are carried out, and the discharge coefficients, the efflux angles into the notch and the axial forces on the spool are obtained. Two-phase Mixture flow model and standard K-epsilon model are used in the flow field simulation. The results show that the smaller the notch opening and the larger the flow rate, the greater the transient axial forces and the possibility of cavitations. When the moving speed of the spool increases, the possibility of cavitations increases during the notch open process, and decreases during the notch close process. There are no cavitations generated with the notch opening 2 mm when the flow rate is within 35 L/min. The direction of flow forces is to open the notch, and the flow forces calculated from Con- ventional Formula do not comply with the real ones. The results from dynamic analysis for the spool show that the spool with K or V notch responds quicker; the working speed of the system mainly depends on the dis- charge coefficient of the notch; and the spool displacement should be limited to avoid oscillation. In conclu- sion, the type of the notch impacts the flow field and dynamic response of a piloted directional valve a lot.