Luo Xiaohui

Study on the Effect of Inlet Fluctuation on Cavitation in a Cone Flow Channel

A mathematical method was conducted to investigate the mechanism of formation of cavitation cloud, while the inlet stream contains a fluctuating flow. Based on the Rayleigh-Plesset equation and the static pressure distribution in a cone flow channel, parameters related to cavitation cloud are estimated, and the collapse pressure of the cavitation cloud is obtained by solving the equation of Mørchs model. Moreover, the effect of the amplitude and frequency of inlet fluctuation on cavitation is studied. Results revealed that the smaller the amplitude, the smaller the cloud and the lower the collapse pressure. And frequency of fluctuating stream was found to have a relative great effect on frequency of peak pressure but not so significant on peak collapse pressure and size of cloud. It is concluded that limiting the inlet fluctuation reduces the erosion and noise generated by cavitation collapse.

Research of a water hydraulic piston pump applied for water mist fire suppression system

Fire is one of the fatal threats in manned spacecraft, water mist fire suppression technology has become one of the most important methods to preventing fires. As the main motive components, high pressure water hydraulic piston pump is very important for the development of water mist fire suppression technology. A novel crankshaft piston pump was studied through simulations and experiments in this paper. Furthermore, an attenuator was designed and utilized to reduce the pressure pulsation for the improvement of the performance of the piston pump. Analysis results show that the pump has many essential advantages, such as little lateral force, low PV value, good friction and wear conditions, as well as high volumetric efficiency. In addition, the performances of the pump were obtained through simulations using AMESim. Simulation results indicated that the piston pump has a good flow rate property. The flow rate is well in agreement with the theoretic design and it reaches to 235L/min. However, the flow pulsation unavoidably occurs, and it further causes pressure pulsation. Generally, the pressure pulsation frequency is the product of the shaft rotation frequency and the piston number. Fortunately, the utilization of attenuator could effectively reduce the pressure pulsation, so that the performance of the piston pump is well improved. The pressure pulsation ratio could be reduced to 1%. The new type crankshaft piston pump with low pressure pulsation is helpful to the development of water hydraulic technology and the water mist fire suppression system.

Research on the modeling and simulation of reaction thrust characteristics of water jet

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 and velocity distributions are substituted into the reaction thrust formula and therefore the computational results of reaction thrust are calculated. The results indicate that the water jets issuing from the streamline nozzle produce considerably lager reaction thrust compared to the other two geometries. The reaction thrust reaches the maximum when the aspect ratio (length to diameter ratio) l/d=1. Under the same flowrate and aspect ratio, the bigger the diameter, the smaller the reaction thrust. The reaction thrust shows linear and quadratic growth with increasing inlet pressure and flowrate, respectively. The outlet pressure has little effect on reaction thrust.

New approach of suppressing cavitation in water hydraulic components

Cavitation frequently appears in high pressure water hydraulic components and leads to serious hydraulic erosions and horrible hydrodynamic noises. In this paper, a novel approach of suppressing cavitation was proposed, inducing the outlet pressure back to the orifice to improve the pressure distribution of throttle valves. In order to realize this approach, an optimized throttle valve chamber structure was designed. After that, the anticavitation performance of the valve was investigated. A theoretical cavitation cloud model was built based on bubble dynamics. In order to solve the mathematic cavitation model, the velocity field and pressure distribution of the novel throttle valve were simulated through Computational Fluid Dynamics(CFD). Combining the simulation results, the mathematic cavitation cloud model was solved through numerical calculations. Moreover, new indexes estimating cavitation intensity were proposed scientifically to investigate cavitation phenomenon. Then, the comparison of the novel throttle valve (with an innovative valve chamber) and traditional throttle valve in anticavitation performance was conducted under different conditions. Finally, the experiment about anticavitation performance was completed on the test rig. The calculation and experiment results indicated that the approach, inducing the outlet pressure back to the orifice, was effective in suppressing cavitation.

Simulation research of grease-releasing mechanism for oil-retaining bearing

Focusing on oil-retaining bearing worked in water environment, simulation analysis of the whole oil-retaining bearing is carried out to investigate the grease-releasing mechanism of sintered metal-powder bearing, and the overflow process is simulated by way of water displacing oil. The result shows that threshold pressure gradient exists while oil flows, and the value of gradient has a complicated relationship with extent of porosity, but it is well correlated with permeability of bearing. The overflow speed of grease is dependent on porosity, the temperature of flow field, pressure, and the overflow speed rises while one of above-mentioned factors increases.

Optimization and simulation on a cartridge valve with silencing grooves

The use of cartridge valves with high pressure and large flow rates in a hydraulic system usually causes serious vibration and noise issues. In this paper, a type of cartridge valve with silencing grooves was presented and its mathematic model was built up. Four types of silencing grooves were selected for the cartridge valve, and they were optimized separately based on the actual application system for testing the safety valve in hydraulic support. Through simulation, their silencing effects were analyzed. The U-shaped groove has been found to be dominant among all the investigated groove types and it can significantly reduce the peak pressure gradient of the tested valve compared with no grooves. This research not only provides a new solution for reducing the vibration and noise of a hydraulic system, but also presents an effective method for the design of silencing grooves on a cartridge valve.

The Interval Estimation of Set-Valued Model for the Chance Constraint Programming

The optimal value of un-linear objective function of chance constrain programming worked out interval estimation from mathematical statistic angle, discussed the improvement estimate precision method and analyzed the size relation of two random variables according to the threshold value tenable concept. Based on the analysis of chance constraint, constraint condition of chance constrained programming would be changed as set-valued constraint. The optimum value of objective function could be obtained by genetic algorithm and interpolation method.

Region-wise variational principles and generalized variational principles on large strain for consolidation theory

The difference of constitutive character and large deformation as to soil mass are basic questions to analyze deformational feature. According to the description method of limited deformation, the large deformation consolidation equations of soil mass were created and its variational principles were rigorously testified. The regionwise variational principles of consolidation theory were deduced using sub-structure continuous condition of region-wise. Quoting the method of Lagrangian multiplier operator, generalized variational principles of region-wise of large deformation consolidation in the nonconstrained condition were created and approved.