A novel approach for predicting inlet pressure of aircraft hydraulic pumps under transient conditions

Cavitation caused by insufficient suction is a major factor that influences the life of aircraft pumps. Currently, pressurizing the tank can solve the cavitation problem under steady largeflow conditions. However, this method is not always effective under transient conditions(from zero flow to full flow in a very short time). Moreover, to apply and design other measures, such as a boost impeller, the suction dynamics during the transient period must be investigated. In this paper,a novel approach based on the pressure wave propagation theory is proposed for predicting the inlet pressure of an aircraft pump under transient conditions. First, a dynamic model of a typical aircraft pump is established in the form of differential equations. Then, the transient flow model of the inlet line is described using momentum and continuity equations, and the governing equations are discretized by the method of characteristics and the finite difference method. The simulated results are in good agreement with the results from verification tests. Further simulation analysis indicates that the wave velocity and transient time may influence the inlet and reservoir pressure as well as the size of the inlet line. Finally, solutions for upgrading the inlet pressure are discussed. These solutions provide guidelines for designing inlet installations.

Numerical investigation of effect of a centrifugal boost impeller on suction performance of an aircraft hydraulic pump

An integrated boost impeller can effectively improve the suction performance of an aircraft hydraulic pump(AHP).It must be designed very carefully;however,few studies thus far have investigated boost impellers.To explore the effect of the boost impeller,this study developed a three-dimensional computational fluid dynamics(CFD)model for an AHP based on the k-εturbulence model and full cavitation model.The results of verification tests demonstrated that the model is reliable for simulating the delivery characteristics of piston pumps and the boost capacity of the inlet impeller.Steady-state simulations reveal that the boost impeller can remarkably improve the suction performance and mitigate the cavitation damage due to insufficient fluid filling while only consuming a small proportion of the total input power.Transient-state simulations show that the pump with an impeller is more capable of catching up with a sudden increase in flow demand,and it has a lower suction flow ripple and impact.However,such a boost impeller also has some limitations such as magnifying the suction pressure fluctuation and having little effect on mitigating the cavitation caused by the back-flow jet.

A comparative investigation on wear behaviors of physical and chemical vapor deposited bronze coatings for hydraulic piston pump

The cylinder block/valve plate interface is one of the most critical frictional interfaces of the swashplate-type axial piston pump.However,the poor lubrication interface caused rapid wear and high friction loss in an elastohydrodynamic lubrication system,decreasing the pump lifetime.Wear resistant bronze coatings were fabricated on 38CrMoAl substrate by Physical Vapor Deposition(PVD)and Chemical Vapor Deposition(CVD),respectively.Ball-on-disc wear tests were performed to comparatively investigate the wear behaviors of the coatings and bulk ductile iron samples.It can be found that the PVD-bronze coating exhibited better wear resistance than the other two samples.This enhanced wear resistance was attributed to the unique composite microstructure and desired mechanical strength,which could resist to mechanical shear and spallation,decreasing friction loss.The appropriate hardness of(1.33±0.07)GPa could be beneficial for enhancing its wear resistance.The PVD-bronze coating possessed a much lower and stable coefficient of friction(about 0.1)and wear rate(about 6000μm3.N-1.m-1)under the loading forces of about 100 N after 20 min.The wear mechanism was the abrasive wear.