Numerical Study On The Effect Of Polymer Additives On Hydrofoil Cavitation

Cavitation is the breaking of a liquid medium under excessive stresses,the phenomenon of cavitation widely exists in various liquid flows.While the viscoelastic fluid can be obtained by adding a soluble high molecular polymer to a liquid medium.By CFD commercial software,the cavitation phenomenon in polymer solution is simulated in this paper,and the effect of polymer addition on cavitation is studied.In the numerical simulation,the FENE-P model is used to model the viscoelastic fluid,which provides a constitutive equation taking the polymers’ microstructure into account.And the mixed multiphase flow(Mixture)model was used to characterize fluid cavitation.The Reynolds Average Navier-Stockes equations(RANS)and the Large Eddy Simulation(LES)are used to simulate the cavitation of polymer solutions in two-dimensional and three-dimensional flow fields.The viscoelastic properties of the fluid will change the turbulent structure in the flow field.Due to the interaction between cavitation and turbulence,the incipience and evolution of cavitation in the viscoelastic fluid are expected to be altered.This article aims to simulate the cavitation phenomenon in polymer solutions through calculations,and analyze the effect of its rheological properties on cavitation flow,especially on the morphology,critical cavitation number and bubble shedding mechanism of polymer solutions.In view of these aspects,this paper first adopts the Reynolds Average Navier-Stockes equations(RANS)to numerically simulate the non-cavitation situation of the two-dimensional NACA0015 hydrofoil,and verifies the grid independence by comparing the result with the experimental data.Subsequently,the cavitation phenomenon of two-dimensional hydrofoil in polymer solution was simulated,and the influence of Wi number and airfoil angle of attack on the cavitation phenomenon in polymer solution was discussed.This paper focuses on the analysis of the influence of Wi number changes on the gas volume fraction,cavitation evolution process,and turbulent kinetic energy,viscous force and elastic force distribution in the cavitation flow field around the airfoil.By monitoring the volume fraction of the gas phase in the flow field,the influence of Wi on the critical cavitation number is obtained.The study found that when the Wi number is small,the polymer solution promotes cavitation,and when Wi increases,the promotion effect of the polymer solution on cavitation gradually weakens,and when Wi increases to acertain degree,the polymer solution Cavitation turned into an inhibitory effect.Based on the two-dimensional simulation,this paper applies the Large Eddy Simulation(LES)to perform the unsteady calculation of the cavitation phenomenon of the three-dimensional NACA66 hydrofoil in the polymer solution.In order to study the evolution of cloud-like cavitation in polymer solutions,this paper simulates the process of morphological changes of cavitation under different Wi number conditions to study the relationship between vorticity transport in polymer solutions and cavitation morphology and evolution,and The mechanism of exfoliation of bubbles in polymer solutions with different Wi numbers was analyzed.