Simulation Study On Precision Casting Of Reversible Blades For Marine Gas Turbines

Gas turbines have been widely applied for military and civil ships as main drives,but their inability of direct reversing restricts the flexibility of ships.To this end,researches on marine reversible gas turbines have been conducted with reversible blades of double-layer as the core.This paper conducts simulation studies on solidification process of precision casting of reversible blades,assesses the structural strength of the reversible blades starting from the mathematical models of mold filling and solidification process and the model of microscopic growth during solidification process,and software o CASTPr is used to simulate filling and solidification process of precision casting and analyze its characteristics,which navigates the optimization of practical casting process for reversible blades and lays a theoretical foundation.This paper introduces the structure of reversible blades made of thermal-corrosion resisting nickel-based superalloy.The opposite arrangement of leading and trailing edges of large solid reversible blades and small hollow ones will casue interference during operation which may results in accidents such as blade failures,therefore,FE software is used for 3D modelling and setting of pre-processing parameters including material parameters and loading,strength verification of the reversible blade,and assessment of its structural strength on the basis of criteria.The best pouring combination is designed based on the structural characteristics of the reversible blade,the blade & pouring system is established as well as the solid modeling of the shell,and the meshes are divided.Settings of pre-processing parameters are completed including material parameters,interface heat exchange coefficients and casting parameters.The simulation analysis of mold filling and pouring processes of reversible blades shows the designed combined pouring system can ensure a good filling sequence during pouring.At the same time,the possible positions of filling defects such as pores and cold shuts in the pouring process can be predicted.The simulation analysis of solidfication process indicates that solidification process takes about 5 minutes in the sequence starting from airfoil of hollow small blade-connection between hollow small blades and solid large blades-trailing edge at thin wall of solid large blade-leading edge at thick wall of solid large blade-root of large solid blade.Where,complete solidification of the hollow small blades takes about 1 minute,while it takes about 4 minutes for complete solidification of airfoil of large solid blades.Solidification of the entire system to be poured takes about 23 minutes.Simulation analysis is conducted on the probability and location of possible solidification defects such as porosities and shrinkage during the solidification process of the reversible blades.The results show that porosities mainly concentrate in runner and riser,which proves that the designed pouring system is basically reasonable.Verification by the Niyama function critical criterion shows that porosity or shrinkage tends to form at the bottom of the small blades.