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Characteristics of water hammer induced by valve-valve systems are studied numerically. Instead of the conventional reservoir-valve systems, valve-valve systems considered include two valves which close simultaneously and which close respectively with specific time delays. Under these settings, the pressure head and the fluid field of the flow are simulated and observed. The characteristics of wave...
The physics of fluid flow between two parallel rotating disks is the theoretical basis of the analysis and design of rotating machinery such as gas turbine. Rotor-stator system is one of the most pervasive types among rotating disk configurations. In this paper, the flow field in a rotor-stator system with its periphery totally open to atmosphere was numerically studied. The SST k-m model was employed...
In this research, a test rig testing the performance of a hydraulic oil purifier based on HIGEE technology is established. Generally, filler, cone angle, length of vortex finder and flowrate are considered as four kinds of the most important parameters affecting the purification efficiency of the purifier. Thus, each of the parameters with four different levels is investigated during the study. In...
The effects of centrifugal force of oil distribution mechanism in lubrication system at high speed will impact the performance of effective flow area, and change the inflow of lubricating oil. It is needed to study the flow field characteristics inside the oil distribution mechanism. First of all, the theoretical research has been studied on it, and the theoretical flow model of oil distribution mechanism...
High efficient use of axial piston pumps is a key demand for fluid transmission systems today. The efficiency characteristics of piston pumps is mainly studied on the volume losses and the mechanical damage. However, when the pump is working at high speed, small displacement and low pressure conditions, the churning losses due to the rotation of the pump accounts for the main factors of the total...
The pneumatic servo system is used more and more widely in industrial production because of its advantages like low cost, easy maintenance and environmental cleaning. However, due to the compressibility of gases, the nonlinear of the flow rate through valves, and the friction between the piston and the cylinder, the precise control of the pneumatic servo system has many difficulties. Among them, the...
The isolation plugging tool is normally developed for deep water pipeline repairing. It is a mechanical structure of plugging and sealing fluid in high-pressure pipelines to make sure the pipe maintenance operation under normal transmission. In order to design control the plugging tool, the analysis of underlying flow field physics in pipeline is necessary based on the in-situ situation. The flow...
Conventional hydraulic actuator is controlled by mechanically connected orifices valve. The controllability of this method is poor and the energy consumption is huge especially under the over-running condition. So a novel system configuration of the hydraulic excavator is presented to improve the problem mentioned above, in which boom cylinder, stick cylinder and swing motor are controlled with separate...
Aimed at the decline of the rotational speed of rotor in an 11 kW electric motor-pump prototype, the rotational speed characteristic is calculated by means of experiments, theoretical calculations and RMxprt module of Ansoft software. The study shows that viscosity load, which mainly contains air gap and sealing gap, causes the on-load starting, and affects the decline of the rotational speed to some...
Due to their compact and simple design, axial piston pumps are widely used in hydraulic systems. The piston/cylinder lubricating interface is one of the most critical design elements in axial piston pumps, which fulfills the bearing and sealing function simultaneously. Also it is the main source of both friction and volumetric powerloss. In order to realize the optimal design of efficient and reliable...
Single pump flow ripple characteristics associated with its structure had been widely researched. However, dual-pump converging flow ripple characteristics are seldom noticed. This paper aims at investigating the flow ripple properties of dual-pump sources in hydraulic systems. A common algorithm to calculate the sum of two period and piecewise functions with different phase is proposed and the mathematical...
The efficiency of fluid power motors and pumps is a subject to research, which has generated numerous publications during the last three decades. The main incentives for this research are optimization of reliability and efficiency through the study of loss and wear mechanisms, which are very difficult to study experimentally, whereby modeling and simulation are necessary. A common approach to theoretical...
The thermal effect in hydraulic circuits becomes a more significant concern, because of the energy demand and management of the new generation airplane. Although fluid transients in pipelines have been researched for decades, thermal effect is hardly considered. This paper models thermo-fluid characteristics in pipe net analytically as well as other hydraulic components, using the transfer matrix...
A prototype of a fast switching valve for a digital hydraulic machine has been designed and manufactured. The valve is composed of an annular seat plunger connected with a moving coil actuator as the force producing element. The valve prototype is designed for flow rates of 600 l/min with less than 0.5 bar pressure drop, and the models predicts a switching time in the region of a millisecond with...
Journal misalignment often exists in grease lubricated journal bearings. Lubricating grease is a non-Newtonian liquid, and the rheological properties of grease make it difficult to analyze the lubrication performance numerically. In this paper, grease lubrication Reynolds equation is introduced based on the Herschel-Bulkley model which accurately describes the rheological properties of grease. The...
This paper is to investigate the effects of nozzle geometry on reaction thrust characteristics under various nozzle dimensions, inlet and outlet conditions. The reaction thrust formula is deduced based on the elementary momentum theory through the theoretical analysis. CFD simulations are conducted to acquire the pressure and velocity distributions on the outlet cross-section of nozzles. The pressure...
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