This paper describes physics‐based moisture loss models for designing wet‐steam turbines. Steam turbines operating under wet‐steam conditions experience thermodynamic and mechanical losses caused by the presence of moisture. The developed moisture loss models are composed of six categories: supersaturation loss, condensation loss, acceleration loss, braking loss, capturing loss, and pumping loss. These losses are calculated according to the wetness levels in the stationary blade and moving blade rows, and defined by the functions of steam properties and design factors of turbine stages. The supersaturation loss produced by non‐equilibrium expansion of the wet steam is modeled using the pressure ratio and the isentropic exponent of the supersaturated steam. The loss models are compared to full‐size test turbine data for prediction of the overall moisture losses. As a result, the developed loss models are found to be very effective for estimating the moisture losses of turbine stages. © 2013 Wiley Periodicals, Inc. Heat Trans Asian Res, 42(7): 651–664, 2013; Published online in Wiley Online Library (http://wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.20395

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Unsteady aerodynamic and structural interactive analysis method for design and development of highly efficient low pressure last stage blades and results of its main application on very low load conditions are reported in this paper. Main features of this method are the enhanced analysis scope including very low load conditions and validations using measured data of real steam turbines including very low load conditions as well. Our schemes for this project were introducing boundary conditions from measured data in real steam turbines, full annulus all blade unsteady aerodynamic analysis and large scale parallel computing for unsteady structural analysis. The aerodynamic analysis results indicate that one root cause of the relatively large blade vibration at low load conditions seems to be a tip vortex induced by the blade windage. A modified method that introduced accurate structural analysis boundary condition data from aerodynamic analysis results is demonstrated. The structural analysis of a six-blade group with lacing wire dumping structure was performed.

The vibration stress of long steam turbine blades during low load operating conditions is examined in this paper. A series of experiments has been carried out to investigate the vibration stress behavior, and the steady and unsteady pressure fluctuation. It is found that a steady pressure distribution over the blade tip is much to do with the unsteady pressure and fluctuation of the vibration stress. A precise investigation of unsteady wall pressure near blade tip explains the relationship between pressure fluctuation and the vibration stress, and reveals the existence of particular frequency which affects blade axial modes. Blade to blade flow mechanisms and aerodynamic force and properties during low load operating condition were investigated by a steady CFD simulation. FFT of aerodynamic force by another steady full arc CFD simulation provides various pattern of harmonic excitation which account for the behavior of vibration stresses well. The mechanism of the rapid stress increase and a step drop were examined by considering CFD results and measured unsteady pressure data together.

This paper describes physics-based moisture loss models for designing wet-steam turbines. Steam turbines in wet-steam conditions experience thermodynamic and mechanical losses caused by the presence of moisture. The developed moisture loss models are composed of six categories : supersaturation loss, condensation loss, accelerating loss, braking loss, capturing loss and pumping loss. These losses are calculated according to the wetness levels in the nozzle & bucket rows, and defined by the functions of steam properties and design factors of turbine stages. The supersaturation loss produced by the non-equilibrium expansion of the wet steam is modeled using the pressure ratio and the isentropic exponent in the supersaturated steam. The loss models are applied to the full-size test turbine data for the prediction of the overall moisture losses. As a result, the developed loss models are found to be very effective for estimating the moisture losses of turbine stages.