Study On The Erosion Mechanism Of Fluid Machinery Based On The Theory Of Pt Boundary Layer

Erosion is one of the main invalidations in the fields of water conservation, electricity, engineering machinery, coal metallurgy, energy transportation, aerospace, and so on. So it has aroused universal interesting to the domestic and foreign researchers. This paper can be completed because of the program (study on the cavitations' mechanism of fluid machinery parts), the main researches are as follows:The dynamic characteristics of sand movement in Pt boundary layer are studied. First, we analyze the force condition of the sand, and the velocity equation of the sand is obtained by the transformation and inverse transformation of Lap-lace. Then the distribution rule of the velocity and shear stress can be studied from this equation.The cause of scratches is analyzed. The bursting phenomenon is coming out because of the different velocity gradient between the sand and water. And this bursting force tries to make surface shape that adapt to sand paths, thus the polished scratches are formed. Then the changing law between the actual impact angle and the velocity is obtained.The influence of the erosion on material,sediment content,velocity,impact angle is discussed. Results show that: the wear resistance of five materials is depended on microstructure and the erosion resistance of Sorbite material is better than Pearlite material. There is a critical value between the sediment content(C) and wear capacity (J). When C is below the critical value, J is increasing with the increasing C, while it gets the critical value; J is not influenced by the changing C which can be described by equation. The relation between the erosive velocity and wear capacity can be expressed by the following formulaby J =m_pu_p~n/qx(?)(sin 2α-6/x sin~2α)-(6π~2ru_p~nμ)/β~3)sinα, from this formula. We know thatwhen u increases, J is increasing; n is influenced by fluid coherency, material and experimental conditions. When erosive angle increases, J also increases.The mechanism of erosion is analyzed. Sands enter the boundary layer with a certain impacting angle and the sweeps plunders caused erosion because of the high speed of these sands based on the bursting phenomenon. The results show that there are two erosion methods in the surface of the water blade including cutting and impact deformation. The main wear of brittle material is fatigue spalling and cutting; while the plastic material is cutting plough ditch.