Performance estimation of multi-stage cooled axial flow turbines under choked conditions

Abstract

Development of a fast and accurate tool to estimate the performance of axial flow turbines in all range of working conditions including choked region is of great interest in the design steps of turbines. Mean-line (one-dimensional) analysis is one of the solutions that is computationally cost-effective along with producing accurate results. However, the development of a mean-line model that able to solve the flow in a choked turbine (one-row chocking and multi-row choking) is a challenging problem. This study presents a new algorithm for mean-line analysis of axial flow turbines with a set of well-posed boundary conditions, i.e., the inlet total pressure, the inlet total temperature, inlet flow angle, and outlet static pressure and calculates the flow condition through the turbine row-by-row. The proposed algorithm is implemented in an object-oriented C++ code named Axial Turbine Simulator (ATSim). The results of ATSim program is validated and verified under various working conditions, e.g., low and high-pressure ratios (choking condition), for four different turbine configurations including two uncooled single-stage turbines, an uncooled two-stage turbine, and a cooled three-stage turbine. ATSim provide good consistency with previous experimental and numerical studies. Moreover, the results show that ATSim is capable of estimating the performance of the turbine in a very short time over a wide range of working conditions, including choking (one-row choking or multi-row choking) region.