The mechanism of cavitation cleaning of complex surfaces has received more and more attention. In the present paper, with the help of a high-speed photography experimental system, the dynamic behavior of a cavitation bubble in symmetrical positions near a complex wall with a continuous triangular arrangement is investigated. In terms of the bubble size and the initial wall–bubble distance, the non-uniform shrinkage of the bubble collapse and the movement characteristics of the bubble centroid are revealed. The main conclusions are as follows: (1) The collapse dynamic behavior of the bubble near a complex wall with a continuous triangular arrangement can be divided into three typical cases. (2) According to a large number of experimental results under different parameters, the parameter ranges corresponding to the three cases and the critical values between different cases are given. (3) The larger the bubble size is, or the smaller the initial wall–bubble distance is, the more significant the effect of the complex wall is, and the greater the movement distance towards the complex wall during the collapse stage.
Aerodynamic optimization of the airfoil is of great significance to the shape design for wind turbine blade. However, it is tough to calculate the aerodynamic forces of airfoil with random shape variations. In response to this challenge, a stochastic parameterized model based on uncertainty quantification method is proposed. And the influence of non-deterministic airfoil geometry caused by designed parameters on the aerodynamic characteristics is evaluated through the combination of sparse grid-based polynomial chaos (SGPC) and computational fluid dynamic (CFD) taking two airfoils at different Reynolds numbers as examples. OpenFOAM is employed as CFD solver and connected with the in-house stochastic parametric analysis code in a non-intrusive way. Finally, the aerodynamic responses of lift, drag, as well as the surface pressure coefficients are obtained, and the sensitivity of the lift and drag coefficients to the stochastic designed parameters are evaluated. It can be concluded that for the same type airfoil, the sensitive parameters after stall behavior are effected to some extent by increasing Reynolds number, that is, the impact of the maximum curvature index on pressure surface is weakened. As for two kinds of airfoils, S809 is sensitive to parameters near the maximum curvature of the airfoil and the trailing edge of the suction surface under attached flow, while convert to those near the leading edge and maximum curvature of suction face once stalled. FFA-W3-241 airfoil has no sensitivity factors in attached flow and features the same sensitive indicators after stall. These results will provide a reference for coarse-to-fine strategy in optimizing the sample library which is generally the first step of airfoil design process.
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