Investigation Into The Vibration Characteristic Of The Pump And Connected Pipeline In The Aircraft Hydraulic System

The hydraulic systems are wildly used in aircrafts as the power source for flight control and landing gear systems. Pressure compensated pumps are mainly used in aircraft hydraulic systems. The pump flow fluctuation is responsible for decreasing the reliability and lifecycle of the aircraft hydraulic systems. Therefore, it is important to study possibilities to reduce the influence of pressure pulsation on vibration and noise of the aircraft hydraulic systems.In this thesis, the pipeline model with consideration of the bending and friction coupling has been developed by employing the curved stress and friction in the kinetic equations in the traditional model based on the analysis of the one-dimensional long pipeline. In time domain analysis, the differences of the pipewall stress between the calculated and experiment results were within10%compared with73%in the traditional model for the pipe section. In frequency domain analysis, the effect of the pipe curvature on the resonant frequency was ignored in the traditional approach. It was shown from the calculated results using the model developed that the curvature was a determining factor of the pipe frequency response, and it could obviously change both the frequency and peak value. In fact, with the increase of the pipe curvature radius, the corresponding resonant frequency decreased. The interactions of flow rate, pressure and mechanical vibration between the pump and the connected pipeline were very complex, which had not been discussed in previous study. The vibration of the piston pump and connected pipeline in aircraft hydraulic system was also included in the model. The difference of the pipe wall stress between the calculated and experimental results were within0.7%～1.1%, as a comparison to5.4%of the model without connected pipeline. A new pulsation attenuator for aircraft piston pump based upon the RC (fluid resistance and fluid volume) principles was developed and tested. The piston and spring in the attenuator were designed to reduce the noise level with optimal volume and natural frequency. Hence, the mass of the pulsation attenuator was cut down to46g,82%less compared with the mass of the existing buffer bottle. The needed volume of the pulsation attenuator was reduced to31.4cm3, which was85%less than the volume of the buffer bottle. Remarkable reduction on the pressure fluctuation was obtained in the experiments. At the output flow rate of100L/min, the pressure fluctuation without the attenuator was3.9MPa and0.8MPa with the attenuator, reduction was more than79.5%.The main contents of the thesis are as follows:In chapter1, the application of the aircraft hydraulic power system was outlined. The development of the aircraft hydraulic power system vibration control both at home and abroad was summarized. The research background and the main contents of the degree project were introduced.In chapter2, the kinetic model of the aviation piston pump for vibration analysis was developed based on its working condition, principle and structure. The dynamic characteristic of swash plate, pistons, cylinder and the housing was analyzed in detail. The pump model was developed using the software AN SYS. The dynamic performance of the main components of piston pump was discussed.In chapter3, the flow model of the aviation piston pump was proposed, and two main parts of flow fluctuation in piston pump with the kinematic flow fluctuation and the compressible flow fluctuation were analyzed. Flow simulation of the aviation piston pump was carried using the software FLUENT. Pre-compression structure parameter of the aviation piston pump was optimized.In chapter4, the pipeline model composed of curved pipe section and tees was developed. The flow and pressure fluctuations were analyzed both in time and frequency domain. The vibration characteristics of two pipe sections in aircraft were discussed. It was shown in the simulation results that the vibration of the hydraulic power system was affected by the pipe friction coupling and the junction coupling, and the ripple peaks could be reduced by pipeline layout optimization.In chapter5, the oil film model between the slipper shoes, the swash plate and the oil film between the cylinder and the valve plate was developed. The pressure and velocity distributions were obtained. The relationship between the pump vibration and the oil film thickness was analyzed. The interaction between the pump and the pipeline was discussed. Theoretical analysis and experimental test were carried on the vibration characteristics of an aviation piston pump with the connected pipeline. Some suggestions were given on development of the aircraft hydraulic power system with low vibration.In chapter6, the optimizations of pump structure and pipeline arrangement were discussed. A new pulsation attenuator for aircraft piston pump based upon the RC (fluid resistance and fluid volume) principles was developed and tested. Remarkable reduction on the pressure fluctuation was obtained in the experiments.In chapter7, the main results and conclusions were summarized, the progress was concluded, and proposals were given for the future work.