Optimization Design Of Root And Groove Profiles For Turbine Structure

Fir-tree root and groove are widely used in industrial steam turbine structures.Due to its small size and the large centrifugal load during high-speed operation,the fir-tree root is highly stressed,yielding the earlier failure of turbine structures.Performing the structural design of the fir-tree root and groove is an effective and economic way to solve this problem.To characterize the root and groove configuration,the arc-line method used in literature is incapable of representing the complex irregular curves,such as ellipse,which restricts the optimization domain.In this paper,we propose the characterization approaches by using superellipse-line,Fourier series-line and B-spline curve to describe the fir-tree root and groove.Compared with the arc-line method,these approaches have high fidelity,completeness and are effective to describe more root configurations and helpful to widen the optimization domain to find the novel design of fir-tree root and groove.For the design optimization,the conventional objective function,minimizing peak stress,has a highly nonlinear feature,which leads to severe iterative oscillation and convergence difficulty.In this paper,the KS function and the P-Norm function are adopted to aggregate stresses and defined as objective function,this reduces the nonlinearity and ensures the fast convergence of the optimization.One should note that,the characterization approach and design optimization method proposed in this paper have a high versatility and promising industrial applications,and can be easily extended to configuration optimization for other industrial structures.We perform the design optimization with three-tooth fir-tree root and groove as sample.The results show that,compared with the arc-line method and the minimum peak stress optimization strategy,the superellipse-line,Fourier series-line,B-spline curve method and P-norm,KS aggregation function are effective to reduce the stress level of the turbine root and groove.The three-dimension elastoplastic analysis validates the rationality and effectiveness of our optimized results.Most of the design optimization studies of turbine root and groove structure are based on commercial finite element software and optimization package,and few self-developed design optimization platforms exist.In this paper,we use the open-source platform QT and C++ programming language to develop the design optimization platform of fir-tree root and groove,including the automatically environment definition,process monitor,automatically generation of report,which is helpful to find the feasible solution of the fir-tree root and groove.For the configuration characterization,the platform provides methods with feature and spline to perform the optimization of global and local configurations.For the design optimization,the platform provides a variety of optimization algorithms and weighted peak stress minimization optimization strategies to find the optimal configuration.The comparison between optimized results for several configurations proves the certain optimization performance of our design optimization platform.