Cavitation suppression in the nozzle-flapper valves of the aircraft hydraulic system using triangular nozzle exits

Hydraulic control system is one of the fundamental subsystems of the various aircraft systems, e.g., flight control system, brake system and fuel regulation system. As a pivotal actuator of the hydraulic control system, the nozzle-flapper servo valve converts the control signals to the hydraulic output. The flow cavitation in the valves could lead to some intractable problems, e.g., vibration, noise and erosion, which could produce detrimental effects on the performance and reliability of the hydraulic system, even damage the aircraft. This work provides a numerical investigation on the cavitation attenuation in the nozzle-flapper valve using triangular nozzle exit. The flow imaging and mass flow rate measurement are conducted to qualitatively and quantitatively verify the numerical model, respectively. It is observed that the presence of the vapour phase is remarkably suppressed under the effect of the triangular nozzle exit. For both circular and triangular nozzle exits, the occurrence of the vapour phase is highly affected by the nozzle-to-flapper distance, inlet pressure and chamber diameter while the flapper diameter exerts an insignificant impact on the formation of the vapour phase. Compared with the circular nozzle exit, the triangular nozzle exit could effectively reduce the flow cavitation at the same geometry and inlet pressure. The physical mechanism behind the cavitation suppression may be ascribed to the generation of the inclined impinging jet upon the chamber wall and the wall jet without impingement.