Numerical study of steam flow on the low-pressure turbine under off-design conditions: a case study of the Neka steam power plant

In the repowering of conventional steam power plants, we face off-design conditions. In this paper, a numerical study of the steam flow in the blades of the last stage of the low-pressure turbine of the Neka thermal power plant was carried out. To analyze the steam flow in the turbine, one design mode and two off-design modes including part-load and over-load were considered. In this research, three-dimensional Reynolds-averaged Navier-Stokes equations were simulated by using Ansys CFX software. Also, the SST k-omega method was used to model the turbulent flow. According to the obtained results, the effect of steam mass flow rate changes on the low-pressure turbine performance, such as velocity triangles, pressure, Mach number, and temperature distribution on blade surfaces, flow angles, degree of reaction, back pressure, steam quality, and efficiency, was investigated. For example, the loss of isentropic efficiency of the last stage in the off-design mode was less than 0.37% compared to the design conditions. Furthermore, the changes in the degree of reaction of the blades due to the changes in the mass flow rate of the fluid were less than 3%. Validation of the numerical solution was done in two-dimensional and three-dimensional models, and the results showed that there was a good agreement between numerical simulation and experimental data.