Non-equilibrium throughflow analyses of low pressure, wet steam turbines

A throughflow computational method is described which combines wet steam theory with an axisymmetric streamline curvature technique in order to predict nonequilibrium effects in low pressure steam turbines. The computer program developed is able to deal with both subsonic and fully choked supersonic flows and steam properties are represented by a truncated virial equation of state. A number of theoretical test cases were investigated, including the nonequilibrium flow in the primary nucleating stage of a low pressure turbine, the effect of droplet size on last stage performance, and the complete analysis of a six stage 320 MW operational turbine. The calculations are able to provide information on the spanwise variation of the Wilson point, the average droplet size nucleated, the degree of supercooling throughout the flowfield, the thermodynamic wetness loss and the nonequilibrium choking mass flowrate, in addition to the aerodynamic parameters which are of interest to the designer.