Research On The Characteristics Of Microscopic Cavitation Interface Based On Different Metal Wall Surfaces

Cavitation is a complex phenomenon that is common in nature,and the harmfulness and application value of cavitation have a significant impact on many fields such as hydraulic machinery and ship engineering.In order to minimize the damage caused by cavitation and make full use of the beneficial application of cavitation,it is absolutely necessary to carry out an all-round and deepgoing research on the mechanism and nature of cavitation inception,so as to provide theoretical support for further improving the level of active cavitation technology.In this paper,based on the molecular dynamics simulation method,the nucleation process of the cavitation bubbles is connected with solid-liquid interface dynamics,the cavitation inception phenomenon of liquid water on the surface of different metals(Cu,Pt,Fe)is studied,and the interface characteristics are analyzed.The main research contents and achievements of this article are as follows:1.Based on the Coulomb and 12-6 Lennard-Jones force field potential energy,the SPC/E water molecule model is selected to study the cavitation inception phenomenon of liquid water on the copper and platinum wall surfaces,and comparatively analyze the inception process of cavitation nucleus in water,the development and volume changes of cavitation bubble,the interfacial energy of metal wall and bubble surface,water molecules diffusion law and its radial distribution function.The results show that:(1)The cavitation inception of the water molecular system of copper and platinum wall is the heterogeneous nucleation behavior of the metal surface,that is,the corresponding critical cavitation nuclei are generated.The rising density of gas phase water in the critical cavitation nucleus promotes its further development into cavitation bubble,which is accompanied by the vapor-liquid phase change process caused by the negative pressure tensile stress on the liquid water.In addition,liquid water is not prone to cavitation inception in the low temperature or high temperature state.(2)During the development of cavitation bubbles,the force field constraint of the copper wall system is more stable than that of the platinum wall system,and no other cavities appear in the liquid water.In the temperature range of 273 K to 318 K,as the negative pressure tensile stress on the metal wall surface of the water molecular system increases,the volume of the cavitation bubble expands to varying degrees.However,the growth process of the cavitation bubble of the copper wall system at 308 K and the platinum wall system at 318 K is not always showing the trend of expansion.Instead,it shrinks or even disappears after a period of time.(3)The sorption of water molecules on the platinum surface is stronger than that of copper surface,while its internal diffusion rate is relatively slow.And the interfacial energy stability of the platinum wall surface system is better than that of the copper wall system.In addition,the cavitation bubble also has a certain bubble wall interfacial energy to stabilize the internal and external pressure balance of the bubble.(4)Temperature affects the diffusion rate of water molecules at the interface.In a system with a higher temperature,water molecules have a faster diffusion rate due to the intensification of vapor-liquid phase change.The degree of water molecule distribution and aggregation in the platinum surface system is relatively obvious.2.Based on the potential energy of the ReaxFF reaction force field between Fe_O_H atoms,the cavitation inception phenomenon of bulk water system on the metallic iron wall surface is studied,and the development and change process of cavitation bubble in water,the interfacial energy of Fe atoms wall and cavitation bubble surface,the dynamic diffusion characteristics of bulk water and Fe atoms,the arrangement law of interfacial water are analyzed.The results show that:(1)During the development and change of the cavitation bubble,the potential energy of the reaction force field at 308 K temperature is relatively stable.In the force field adaptation stage,the cavitation bubble volume expansion trend is more obvious.In the force field reaction stage,the continuous and stable dynamic energy balance of force field causes the cavitation bubble to expand gently.(2)At the temperature of 273 K system,the adsorption energy of water at the interface of Fe atomic wall is relatively weak.At the same time,when the system is in the stage of force field reaction,the covalent interaction between the oxygen element in the liquid water and the iron element at the temperature is not obvious.(3)In the force field adaptation stage,the increase rate of the water molecule diffusion rate is more obvious,and its diffusion barrier is larger.In the force field reaction stage,the water molecule diffusion coefficient is relatively stable,and the diffusion coefficient increment of Fe atoms in the wall is surface is more obvious.In addition,in the system with higher temperature,the internal diffusion of bulk water and Fe-Fe is relatively fast.(4)The radial distribution function of oxygen atoms in bulk water conforms to the law of short-range(2.45~5.65?)ordered and long-range disordered,and the temperature change has a certain influence on the peak intensity of short-range ordered distribution around the water molecules.The interfacial water is relatively densely arranged in the 4000 fs moment,and at the same time,its stable distribution structure can be better quantitatively reflected at the system temperature of 308 K.