Numerical and Analytical Investigation of Heat Transfer Mechanisms and Flow Phenomena in an IP Steam Turbine Blading During Startup
Abstract As a result of an ever-increasing share of volatile renewable energies on the world wide power generation, conventional power plants face high technical challenges in terms of operational flexibility. Consequently, the number of startups and shutdowns grows, causing high thermal stresses in the thick-walled components and thus reduces lifetime and increases product costs. To fulfill the lifetime requirements, an accurate prediction of the metal temperature distribution inside these components is crucial. The objective of this paper is to understand the predominant basic heat transfer mechanisms during an IP steam turbine startup. Convective heat transport is described by means of HTC's as a function of dimensionless parameters, considering predominant flow structures. Based on steady-state and transient CHT- simulations the HTC's are derived during startup and compared to correlations from the literature. The simulations outline that the local HTC generally increases with increasing axial and circumferential Reynolds' number and is mostly influenced by vortex systems such as passage and horseshoe vortices. The HTC's at the turbine stage surfaces can be modeled with a high accuracy using a linear relation with respect to the total Reynolds' number. The comparison illustrates that the correlations underestimate the convective heat transfer by approx. 40% on average. Results show that special correlation-based approaches from the literature are a particularly efficient procedure to predict the heat transfer within steam turbines. in the design process. Overall, the computational effort can be significantly reduced by applying analytical correlations while maintaining a satisfactory accuracy.