The Study About Effect Of Surface Wettability On Cavitating Flow

Chinese hydropower resource reservation and exploitation amount were the highest in the world.The effective use of a lot of water resources needs a lot of hydraulic machinery equipments.However,the cavitation and abrasion have been the main factors restricting the development of hydraulic machinery in China,which has become a key problem to be solved in current hydraulic machinery.Usually,researchers use coatings to improve the mechanical properties of hydraulic machinery material surface,such as hardness and adhesion.However,the cavitation which causes the cavitation abrasion and how to control cavitating flow are ignored.As an important property of the material surface,wettability affects the flow field in the shear layer of the solid surface,thus affecting the formation of cavitation.At present,the research on wettability of materials is mainly focused on drag reduction and cavitation erosion test.However,there is a lack of research on the influence of surface wettability on cavitation flow.Therefore,in view of the surface wettability,the influence of roughness and surface energy on the cavitating flow around hydrofoils is studied by experimental method and LBM numerical simulation method.A set of research methods for the effect of surface wettability on controlling cavitating flow was established.In view of the two sides of effects on surface wettability--surface morphology and surface energy,the hydrofoil model with different surface roughness and surface energy and supporting device are processed,the high speed visualization system with image processing system is used to observe the stages of cavitation.The pressure and velocity distributions on the interaction between hydrofoil and the fluid are simulated by LBM.The mechanism of cavitation flow is elaborated from mesoscale to macroscale.A set of experimental and numerical simulation methods for the effect of surface wettability on cavitation flow was established.The surface roughness of the hydrofoil influences greatly pattern and the development process of the cavitating flow.The influence of roughness on the cavitation around hydrofoils is discussed,and the hydrofoil A and hydrofoil B with the roughness of Ra=0.6?m and Ra=3?m respectively.The result shows that the larger the surface roughness of the hydrofoil is,the more easily cavitation appears;In the sheet cavitation stage,the maximum length of the cavity around the rougher hydrofoil is longer,cavity thickness and dimensionless cavity area near the rougher hydrofoil is larger;In the cloud cavitation stage,The process of cavitation around the different roughness of hydrofoil has obvious periodicity,cavitation growth stage around the rougher hydrofoil for the entire period is shorter,which may appear the twice shedding,and thickness of cloud cavity on the rougher surface is thicker,bubbles groups has larger scale.The surface of the hydrofoil has an obvious influence on the morphology the development process of cavitating flow.The flow patterns of the primary,sheet and cloud cavitating flows around different surface energy hydrofoil are analyzed and compared.It is known that the smaller the surface energy is,the easier the primary cavitation occurs.However,the primary cavity size is small and easy to disperse.In the stage of sheet cavitation,the smaller the surface energy is,the shorter the maximum cavity length is,the more scattered the cavities are.In the stage of cloud cavitation around the hydrofoil with different surface energy appeared two shedding processes,the length of the cavity is smaller,the maximum length of the cavity is shorter,cavity area is smaller,the scales of bubbles groups are smaller,the distance to the surface is farther,which causes less damage.