Research On The Mechanism Of The Scale Effect Of Two-dimensional Hydrofoil Cavitation On The Nucleus And Wall Properties

In this work,the mechanism effect of the cavitation scale in two-dimensional hydrofoil is studied in terms of the gas core parameters and the wall surface.Taking the NACA4412 hydrofoil as the research object,the cavitation scale effect resulting from the flow of different hydrofoil size is studied.The heterogeneous nucleation of the liquid argon cavitation process between parallel walls was studied,and then the microcavity theoretical research results were connected to a simplified two-dimensional hydrofoil cavitation process,and the scale of the two-dimensional hydrofoil cavitation was studied.The main research contents are as follows:1.The microscopic molecular simulation is used to study the transient characteristics of liquid argon cavitation nuclei between parallel platinum walls.The cavitation nucleus with a certain size and stably existing between the wall surfaces was subjected to different tensile and different wall wettability studies,and the cavitation nucleus growth,system pressure and total system pressure were analyzed.The results show that the steady state of cavitation nucleus growth in the Pt wall is closely related to the system’s metastable state and wall wettability.There is a critical value for the stretching distance of the wall surface,and the instability degree of the system caused by the stretching above the critical value is greater,thereby facilitating the growth of the cavitation nucleus,and the cavitation is about to be severe.Compared with the shrinkage of the cavitation nucleus between the hydrophobic walls,the nucleation volume between the hydrophilic walls increases significantly,which is more conducive to the growth of the cavitation nucleus,which facilitates the spontaneous growth of the cavitation nucleus,while the hydrophobic wall faces the void.The nuclear nucleus has inhibitory effects and macroscopic cavitation phenomenon.The stronger the hydrophilicity of the wall surface is,the more primary cavitations are generated on the wall surface,which is more beneficial to the occurrence of cavitation.2.Numerical simulation analysis was performed on three NACA4412 hydrofoils with chord lengths of 75,100,and 150 mm,respectivelyto study the unsteady flowprocess of cavitation initiation,development,collapse,and regeneration.The results show that in the initial stage of cavitation,the initial cavitation phenomenon of the150 mm chord-length hydrofoil is the most intense.Combined with the microscopic cavitation study,it is concluded that the larger the size of the hydrofoil leading edge low-pressure region is,the stronger the intensity is,and the degree of system instability increases.Larger is more conducive to cavitation nuclear growth,so when the number of air cores in the same flow,the larger size of the hydrofoil is more conducive to the generation of primary cavitation.The relationship between the cavitation tail shedding and the hydrofoil size on the surface of the hydrofoil was verified.The different cavitation tail high pressure zones had different push strengths for the main cavitation,resulting in different cavitation retraction distances and the smaller the size.The smaller the body’s vacuole retraction distance is.The size of the hydrofoil also determines the unsteady pulsation frequency of the cavitation flow around the hydrofoil.Under the same cavitation number conditions,the unsteady pulsation cycle time of the hydrofoil of different sizes is positively related to the hydrofoil size.The cavitation test in three NACA4412 sizes hydrofoil is studied.The difference of the cavitation scale effect between different sizes of hydrofoil is analyzed under different cavitation numbers.The analysis results show that the size of the initial cavitation number is related to cavitation.The effect of the scale effect lies in the appearance of the cavitation process and the appearance of regeneration cavitation.The difference between the experimental results and the numerical simulation results is caused by different roughness surfaces and different non-condensable gases in the fluid medium.