A numerical study of flow field in a flapper-nozzle pilot valve under working condition

It is well known that the flapper-nozzle pilot stage plays a vital role in converting the electric signals into hydraulic outputs between the torque motor and main spool in the electro-hydraulic servo-valve. The characteristics of the flow field greatly influence the working performance of the flapper-nozzle pilot valve. This paper has presented the flow field characteristics in the pilot valve with the flapper under working conditions, which means that the flapper is moving. The velocity of the flapper is imposed based on the dynamic response of the torque motor and spool valve approximately. Meanwhile, the displacement of the flapper is determined using the general design criterion of the servo-valve. During the simulation, the dynamic mesh strategy is utilized to update the moving mesh. Then the simulation results are firstly validated in terms of the mass flow rates of the two nozzles comparing with the theoretical evaluations. The results show that the numerical method is able to predict the flow field of the flapper-nozzle pilot valve under working condition. Finally, the transient velocity field, pressure field and vorticity field are presented. The results prove that the movement of the flapper can result in asymmetric flow field distribution and increase the static pressure and vorticity in the smaller clearance between the flapper and nozzle.