Numerical Simulation Of Volute-seat Ring Welding Based On Similarity Theory

Turbine is the key equipment of hydropower generation.Spiral case and stay ring are the components of turbine.As a water diversion component,the water flow is led to the runner with less loss to drive the blade to rotate.The spiral case and stay ring of hydraulic turbine are connected by welding.The spiral case structure is huge and the plate is thick,so the welding process is complex.The rapid change of temperature will lead to the change of stress,strain and microstructure.During the operation of the turbine,the flow impact is large,which will lead to component failure.In order to ensure the safe operation of the equipment,it is necessary to study and analyze the welding process.In this paper,the welding numerical simulation is studied and applied to the welding process of spiral case stay ring based on the similarity theory.The main contents of this paper are as follows:(1)The welding numerical simulation analysis of flat butt joint and T-joint is carried out based on the welding similarity theory.The similarity theory model with the size of 1:2 was established,and the simulation analysis was carried out on the similarity model under different welding processes: the plate welding adopts 4 layers of 7 passes,5 layers of 11 passes,6 layers of 12 passes,7 layers of 16 passes.The numerical simulation of T-type welding adopts 3 layers of 4 passes,4 layers of 7 passes,5 layers of 8 passes,6 layers of 12 passes.By analyzing the simulation results and combining with the actual welding process,the plate joint adopts 5 layers of 11 passes,and the Tjoint adopts 4 layers of 7 passes,which is the appropriate welding process.(2)The original model of plate joint and T-joint was numerically simulated by using the welding process parameters obtained from the numerical simulation of the similarity theory.By comparing the results of temperature,stress,and deformation,it shows that welding simulation based on similar theories is feasible.It can effectively reduce the welding numerical simulation time and improve the calculation efficiency.(3)The flat joint with the same size as the similar model and suitable welding process parameters were used to verify the flat joint.The temperature of 8 feature points was collected during the welding process,and the feature 8 points at the same position were selected in the numerical simulation.According to the specific heat cycle curve,the temperature variation trend is basically the same in the welding process.After cooling the workpiece,the residual stress at 5 points perpendicular to the weld direction was measured,and compared with the stress curve of numerical simulation in this direction.Residual stresses measured by simulation and experiment are in good agreement.(4)The similarity model was established for the volute and seat ring based on the similarity theory.The welding numerical simulation was carried out between the volute and seat ring and between two volutes respectively.In the welding between the volute and the volute,the backwelding was adopted.The highest temperature of welding upper,middle and lower part of two volute is compared,and the highest temperature is in the lower part of volute.We collected and analyzed the residual stress of the weld.The residual stress of the weld presented double hump shape,and the maximum position of the stress was on both sides of the weld center.The stress in the center of the weld is relatively small,the maximum stress of the weld is about 400 MPa,and the stress in the heat-affected zone near the weld is about 300 MPa.After welding,the deformation analysis showed that the deformation of the upper part of the volute was larger than that of the bottom,and the maximum deformation was 11.58 mm.