# Numerical Investigation of Erosion Wear in the Hydraulic Amplifier of the Deflector Jet Servo Valve
###### Abstract  
Although possessing a remarkable anti-contamination capacity, the deflector jet valve is still confronted with erosion wear brought by solid particles in hydraulic oil. To describe the erosion wear mechanism in the hydraulic amplifier of servo valves, a RANS-based CFD simulation is conducted to obtain its internal wear distribution following the Oka erosion model, which shows the erosion wear in servo valves can be divided into four levels and the major wear happens on the shunt wedge, characterized by a regular and fluctuant distribution. Further, there exist multiple relative maximums of erosion rates, whose locations deviate from the jet center. On this basis, the correlation between the contamination level of hydraulic oil and the degree of erosion wear is established. Moreover, according to the working mechanism of the hydraulic amplifier, a new failure criterion of the deflector jet valve is proposed to carry out valve lifespan analyses. Then, a lifespan prediction formula is obtained, and calculations show that hydraulic oil must have a contamination level superior to NAS 5 if a lifespan of over 20,000 h is expected. erosion wear; hydraulic amplifier; numerical simulation; deflector jet servo valve Vol  
considered. These erosion models have provided the foundation of numerical investigation and wear prediction in engineering. Then, we have opportunities to explore the erosion wear in valves efficiently, which has been valued in recent years. As a relatively simple scenario, the erosion wear in choke valves was researched based on experimental data of erosion [10]. The relevant erosion equations built by fitting the data were used to obtain the erosion distribution in a CFD-based simulation. Further, on the basis of Harsha's angle function, a case of the check valve was discussed in detail [11], giving the erosion rates at different flow velocities, particle sizes, valve openings and particle mass rates. However, these valves functioned by fluid throttling rather than jets. While jets in valves mean intense impacts, leading to severe erosion wear. Research on a cylinder blocking the jet has been performed, and the erosion caused by fluid impact was evaluated [12], which unveiled that the central region of the impact was not the most worn location, conforming to the impact angle dependence of erosion wear as already mentioned by [PERSON] [5]. Another investigation of impact erosion came from [PERSON] [13], who conducted CFD-based simulations and experiments to discuss the erosion distribution on the target plate, with the conclusion that the farther away from the jet center, the greater the wear is. In addition, some research on the erosion wear of jet pipe valves has arisen since 2015. Erosion rate distributions were obtained based on the [PERSON] model [14; 15] and the lifespan was estimated [16], reaching up to 95,000 h. Compared with jet pipe valves, although the DJV has a similar working mechanism, the actual size and working conditions are materially different. Still based on the [PERSON] model, a description of DJV erosion rate distribution was given to explore the correlation between erosion and the valve performance [17]. However, the simulation showed that maximum erosion happened in the central region of the jet, not consistent with the conclusions of [PERSON] [12] and [PERSON] [13]. Summarizing, although lots of fundamental theories of erosion wear have been provided, the research on the DJV erosion is quite scarce, which cannot bring us a credible and detailed description of erosion distribution. Moreover, the effect of working conditions, such as the contamination level of oil, on erosion wear of the DJV is still indecisive. And without an effective evaluating criterion, there is a research gap about the durability estimation of DJVs. Aiming at this issue, a three-dimensional CFD model is developed to investigate the erosion wear in the pilot hydraulic amplifier of the DJV.