360° The whole cylinder is used for the analysis of the low pressure inner casing with volute inlet steam, and the free grid generation technology is used. In the process of mesh generation, several key positions of strength check are refined to ensure that the number of seeds in the direction of short edge of chamfer is not less than 6. The tetrahedral element c3d10m is used in the software. C3d20 and dc3d20 hexahedral elements are used for bolts.
The low-pressure inner cylinder is cast as a whole and made of nodular cast iron qt400. Its casting performance is good. Under the same casting conditions, chemical composition and pouring temperature, the fluidity of nodular cast iron is higher than that of high grade gray cast iron. Bolt material 35CrMoA is a commonly used bolt material for low pressure inner cylinder.
In many heat transfer modes of steam turbine, the most important one is forced convection. Natural convection mainly exists in the process of shutdown cooling. Only in the absence of convection, the effect of radiation can be investigated, so the radiation can also be ignored. According to experience, it should be assumed that the location of radiation heat transfer is between the high pressure steam inlet pipe and the outer cylinder flange (cavity radiation) and between the steam inlet pipe flange and the surrounding environment (environmental radiation). In other places where there is no steam flow, conductive heat exchange radiation can be simulated, but its effect is very small. For example, there is no convective heat transfer in the area covered by the heat shield, but according to experience and some measurements, there is still leakage steam flow to produce heat exchange. To sum up, this paper only calculates the temperature field of low pressure inner cylinder under forced convection heat transfer coefficient. According to the figure, the heat transfer coefficient of the inlet chamber is larger, and the heat transfer coefficient decreases from the first chamber to the third chamber.