A semi-empirical procedure for the evaluation of multi-stage turbine performances

Abstract

The available tools for the analysis of fluiddynamic processes inside turbomachines are nowadays extremely powerful and versatile. Despite this, the use of simplified procedures, such as the 2D meridional approach, is still relevant, due to its great running simplicity and good accuracy. The full three-dimensional analysis, in fact, even if it could model thoroughly details the fluid-dynamic phenomena occurring in turbomachines, requires huge computational resources and longer computational times with respect to two-dimensional approaches, and this is justified only after a simplified preliminary study of the machine. Also management simplicity, consistence of the required data and usability of results are aspects that should not be ignored, above all for the possibility of creating tools easily available for turbomachines designers. A through flow method, formulated in terms of pressure rather than velocity, for the analysis of multistage axial turbines is presented. It is designed to provide reliable radial distributions of circumferentially averaged values for the fundamental unknowns. The proposed form of the radial equilibrium equation can represent also sharp velocity gradients in radial direction and deal with very realistic situations as discussed in the applications presented. The code has been used for the analysis of both an experimental multistage gas turbine and an industrial steam turbine. The results obtained have been compared with the circumferentially averaged results of a viscous fully 3D commercial code.