| Cavitation widely exists in hydraulic machinery,the phenomenon may cause cavitation erosion damage to surface materials of flow-passing components,thereby affecting the safety and working efficiency of the entire system.To solve the problem of insufficient research on the cavitation dynamics in the region where cavitation occurs,this paper first analyzes the cavitation behavior under different model coefficients by constructing the cavitation dynamics equation in the restricted region;secondly,the applicability of four sub-grid models in two-dimensional Clark-Y hydrofoil cloud cavitation are compared and analyzed,the optimal sub-grid model is applied to the three-dimensional Delft twist-11 hydrofoil cloud cavitation calculation;finally,based on two cavitation erosion models and Three different reference pressures,the hydrofoil cavitation erosion prediction results induced by typical cavitating flows are obtained.In addition,discrete particles are injected into the flow field,and the pressure along the way of the discrete particles is used to solve the cavitation dynamics equation to define the cavitation dynamics characteristics during the cavitation of the three-dimensional twisted hydrofoil.The main content of this article includes the following parts:(1)Adding the divergent pressure of the pulsating cavitation and the additional pressure in the confined area,the dynamic model of the double cavitation in the restricted area is constructed,and the characteristics of the tiny cavitation under different working conditions are simulated and analyzed.The comparison results show that the modified Gilmore-NASG model can accurately describe the evolution law of cavitation in the compressible liquid in the confined area;in addition,with the increase of the model coefficient δ in the additional pressure,the cavitation pulsation slows down and the peak value decreases.(2)To study the applicability of different sub-grid models in the calculation of cavitation flow around hydrofoils,using numerical simulation,the unsteady dynamic characteristics of cavitation flow around two-dimensional Clark-Y hydrofoil with four sub-grid models are analyzed.The results show that the average lift-drag coefficient predicted by the WALE model has the smallest error with the experimental results;and in a typical cavitation cycle,the instantaneous cavitation shedding characteristics obtained by the WALE model are in good agreement with the experimental results.(3)Considering the influence of three-dimensional lateral flow,the WALE model is continued used to calculate the cavitation flow around the three-dimensional Delft twist-11 hydrofoil,and the eddy current identification technology is used to analyze the relationship between cavitation and vortex.The results show that the simulation successfully predicts the primary shedding and secondary shedding process of the cavitation,and it is found that the occurrence of the two shedding phenomena is the result of the joint action of the re-entrant jet and the side-entrant jet;at the same time,the low-intensity eddy current in the flow field promote the detachment of cavitation.(4)Based on the three pressure conditions,the GLM and EPM cavitation erosion indicators were respectively constructed to numerically predict the cavitation erosion risk of the three-dimensional twisted hydrofoil;at the same time,Discrete particles are injected into the flow field and the pressure along the path is coupled with the bubble dynamics equation as the driving pressure.Compared with experimental results of pitting on the hydrofoil,it is found that the calculation erosion results of the GLM model based on the time-averaged pressure are more consistent with the experimental data;The detachment and collapse of the cavitation will generate a huge cavitation collapse pressure,with an amplitude as high as 48.7MPa. |
PDF Full Text Request