考虑离心项的螺旋槽液膜密封空化特性数值分析

针对液膜密封中空化问题,建立基于质量守恒JFO边界条件的螺旋槽液膜密封数学模型,采用流线迎风有限元法求解考虑液膜离心项的Reynolds控制方程,获得端面膜压分布,进而分析了操作参数对空化特性的影响。结果表明:不同操作参数下,空化发生时的液膜破裂位置均位于螺旋槽边界线上;转速的增大、膜厚及介质压力的减小促进空化的生成,反之,抑制空化发生。计算结果为液膜密封在不同操作条件下的设计和应用提供理论指导。     

计入空化效应的表面微织构滑动轴承特性分析

基于N-S流体计算方程,利用CFD软件建立表面微织构滑动轴承三维有限元模型,在计入和未计入空化效应条件下对比分析微织构分布特征对滑动轴承静特性的影响规律。研究表明:计入空化效应时滑动轴承的油膜最大压力和承载力大于未计入空化效应时油膜的最大压力和承载力;表面微织构的合理分布能有效提高润滑油膜的承载力,降低摩擦因数,分布在收敛间隙出口位置的微织构效果最为明显;在未计入空化效应时表面微织构作用效果更加明显,计入空化效应时微织构能抑制空穴区域的产生。     

涡流空化-机械研磨协同强化大豆粕蛋白溶解的研究

在涡流空化-机械研磨协同作用下,强化大豆粕蛋白溶解。利用单因素实验研究了水力空化压力、水力空化时间、水力空化温度、料液比、机械研磨转速、机械研磨时间对大豆粕蛋白溶解度的影响。利用响应面实验法优化了涡流空化-机械研磨协同强化大豆粕蛋白溶解工艺条件,测定了涡流空化-机械研磨协同强化大豆粕蛋白水溶液的表面活性。结果表明:涡流空化-机械研磨协同强化大豆粕蛋白溶解最优工艺条件为水力空化压力0. 36 MPa,水力空化时间65 min,水力空化温度43℃,料液比1. 8∶100,机械研磨转速2 000 r/min,机械研磨时间30 min;在最优条件下进行处理,大豆粕蛋白溶解度由原料的0. 780 mg/mL提高到1. 624 mg/mL;涡流空化-机械研磨协同强化大豆粕蛋白水溶液具有一定表面活性。     

基于GoogLeNet和ResNet的深度融合神经网络在脉搏波识别中的应用

为了提高脉搏波识别的准确率,提出改进的深度融合神经网络MIRNet2.首先,经过主波提取、划分周期和制作hdf5数据集等,获得Caffe可处理的数据集.其次,提出由Inception模块和残差模块构成的融合网络Inception-ResNet （IRNet）,包含IRNet1、IRNet2和IRNet3.在此基础上,改进Inception模块、残差模块和池化模块,构造Modified Inception-ResNet （MIRNet）,包含MIRNet1和MIRNet2.与本文其它神经网络相比,MIRNet2的分类性能最好,特异性、灵敏度和准确率分别达到87.85%、88.05%和87.84%,参数量和运算量也少于IRNet3.     

An experimental study on the impact behavior of cavitation inside tip clearance of a hydrofoil

Tip clearance cavitation is one of the most common cavitation phenomena exist on duct propellers,pumps and some hydraulic turbines,which may lead to erosion of the components.Due to the influence of the nearby wall,cavitation inside the tip clearance is more complicated than other cases without interaction.So far,the understanding about the impact mechanism of tip clearance cavitation is still limited.In this paper,to obtain the impact behavior of tip clearance cavitation,a high-speed camera was used to capture the cavitation behavior inside the tip clearance of a hydrofoil,and surface paint coating peeling method was applied to show the impact region.Results indicated that cavitation around the tip of the hydrofoil was composed of a tip separation cavity and a tip leakage vortex cavity,and the one with contribution to impact was the tip separation cavity.Through the comprehensive analysis of the paint peeling region and dynamic behavior of tip separation cavity,the impact was found to be related to the local collapse and rebound of the cloud cavitation shed from the attached part.In addition,the influence of tip clearance size on the behavior of tip clearance cavitation was also investigated.As the tip clearance size increased,the tip separation cavity tended to transfer from sheet cavitation to vortex cavitation.These findings can provide a sound basis for evaluating the erosion risk arising from the tip clearance cavitation.     

LES investigation of the tip vortex cavitating flow with special emphasis on the interaction between cavitation and vorticity by a modified cavitation model

Cavitation within the tip vortex(TV)flow remains a challenging issue in the design of high-speed and low-noise hydraulic machinery.In this paper,the TV cavitating flow around an elliptical hydrofoil is calculated by using large eddy simulation(LES)combined with a modified Schnerr-Sauer(S-S)cavitation model.The original S-S cavitation model is modified by taking into account the typical effect of vortex flow.The partial pressure term which can describe the vortex quantitatively and qualitatively is confirmed asρmω2xr2c and is considered into the R-P equation of the modified S-S cavitation model.Comparison between the numerical and experimental results shows good agreement in the form and evolution of cavities,including attached cavities(AC)and tip vortex cavities(TVC).The vorticity transport equation is utilized to investigate the dynamic mechanisms of the vortex development around the TVC.Further analyses indicate that cavitation in the TV flow influences the pressure in the core of the cavity and the local flow patterns.Typical vortex structures in the TV cavitating flow include TV,secondary vortex(SV)and wake vortex(WV).The direction and magnitude of the rotation effect can be described by axial vorticity which is drawn on the iso-surface of Q=1×105s-2.The development of the TV cavitating flow can be divided into two stages:Stage I,the development and fusion of TV,SV,stage Ⅱ,the dissipation of SV.The stretching term dominates the evolution of TV,and the dilatation term is the main reason in the mergence process of SV.     

Investigation on strong nonlinear interactions between underwater explosion and water surface based on compressible multiphase flow with phase transition

The strong nonlinear interactions between underwater explosion and water surface were numerically investigated using a phase transition model based on a four-equation system,which can deal with the complex deformable interface among different phases,including water,air,explosion bubble,and cavitation.The numerical method is verified by comparing the numerical results with experimental results,and good agreements are found.This study considers an ideal sine wave for simulating the shape of water surface.Two examples of different detonation depths of charge are investigated.In each example,the first case is the basic simulation without surface wave,and the other three cases are the simulations with sine waves of different wavelengths.Unique characteristics of the interactions,such as shock wave propagation,explosion bubble expansion,and the generation,development,and collapse of cavitation,are observed in the numerical simulations.By capturing the detailed density and pressure contours during the interaction process,we can better understand the underlying mechanisms of the explosion bubble,cavitation,and surface waves.These numerical results demonstrate that geometric nonlinearity impacts cavitation evolution and the explosion bubble movement mechanism.Additionally,the secondary cavitation phenomenon has been found in the cases without surface wave,and its fundamental physical mechanism is presented in detail.The present results can expand the existing database of multiphase flow in the underwater explosion and provide an insight into the strong nonlinear interaction between the underwater explosion and water surface.     

Effect of liquid viscoelasticity on the interactions between cavitation bubbles and free surfaces

The influence of liquid viscoelasticity on the interaction between cavitation bubbles and free surfaces is of great practical significance in understanding bubble dynamics in biological systems.A series of millimeter cavitation bubbles were induced by laser near the free surfaces of the water and viscoelastic polyacrylamide(PAM)solutions with different concentrations.The effects of liquid viscoelasticity on the interactions of cavitation bubbles with free surfaces are analyzed from the perspectives of the evolution of free surface and bubble dynamics.The experimental results show that as the dimensionless standoff distance increases,the evolutions of free surface behaviors in all experimental fluids can be divided into six types of water mounds,i.e.,breaking wrinkles,spraying water film,crown,swallowed water spike,hillock,and slight bulge.All the critical values of the dimensionless distance dividing different types decrease with increasing concentration.The evolutions of first four types of water mounds in PAM solutions differ from those in the water.Water droplets splashing in different directions are produced around the breaking wrinkles in the water.Meanwhile,the breaking wrinkles in PAM solution move with the\"liquid filaments\"towards the central axis.The water spike in the pattern of spraying water film in PAM solution is more stable than that in the water.As the solution concentration increases,the water skirt in the pattern of crown contracts earlier and faster,and the rate of increase in the height of the water skirt decreases.For swallowed water spike in PAM solution,the upper part of the newly formed water spike is not significantly thicker than the middle part,and thus the water waist structure does not form.Liquid viscoelasticity inhibits the bubble growth and collapse,and the bubble migration as well,especially in the second period.Shorter and thicker cavities are formed in PAM solutions with higher concentration,while slender and stable cavities formed in the water at the same dimensionless distance.The velocity and displacement of the tip of bullet jet both decrease as the solution concentration increases.     

Laser-induced cavitation bubble near boundaries

Laser-induced cavitation bubble has been widely used to investigate the mechanisms of hydraulic machinery cavitation erosion and to explore applications in atomization,alloy strengthening,ultrasonic chemistry,biomedicine,surface cleaning and materials processing.This paper consolidates existing research findings on the cavitation bubble dynamics near different boundaries and provides insights for future research work.Firstly,the dynamics of a single cavitation bubble in an infinite field is presented.Subsequently,the focus shifts to the dynamics of cavitation bubble near a rigid wall,angular walls,particles and hydrofoil.Lastly,the paper delves into the dynamics of cavitation bubble within a droplet,revealing the microscopic mechanism of droplet breakup induced by cavitation bubble.     

长期运行老化导线表面状态及电晕特性变化研究

目的研究某地区长期运行的导线的表面状态、表面成分以及电晕特性,分析老化导线的表面特性变化规律。方法采用场发射扫描电子显微镜分析导线表面物质成分及分布状态,采用紫外成像仪对施加不同电压等级下电晕放电光子数进行计数,表征其放电的强弱程度。结果导线表面物质成分中非金属元素主要是氧、碳、硫、硅和少量的磷,金属元素主要是铁、铝、钙、钠、镁、钾,且表面状态与所处环境有关;长期运行导线表面在相同放电电压下放电光子数比新导线多。结论污秽颗粒、不规则的表面结构是长期运行的导线在正常运行电压下发生电晕放电的根源,导线表面的污秽成分与所处地区有关,导线表面凹凸不平会导致其起晕电压比新导线要小。导线的运行年限对表面状态和电晕放电特性有影响。