Calculation method of Moisture Flow Discharge Coefficient in Steam Turbines

Hiroyuki Kawagishi (Toshiba Corporation), Tomohiro Tejima, Akihiro Onoda, Naoki Shibukawa, Yoshiki Niizeki (Japan Society of Mechnical Engineers)

This paper describes a calculation method of moisture flow discharge coefficient for designing wet-steam turbines. The flow discharge coefficient in wet-steam conditions is different from that in dry-steam conditions, because the former is affected by supersaturation phenomenon and wetness fraction. An accurate prediction of the flow discharge coefficient is required for flow-pattern design in turbine stages. The developed calculation method is divided into four models according to the wetness level in the nozzle & bucket rows, and defined by the functions of wet-steam properties, such as saturated & supersaturated isentropic exponents, wetness fraction and pressure ratio in the nozzle & bucket rows. 

The calculation method was verified by comparison of measured and calculated results. modeFRONTIER was used to set up a workflow for the optimization calculation. The output variables in the workflow define the target value of each of the 12 rotor blades for pressure measurement, outlet pressure and nozzle flow coefficient. The algorithm selected for the multi-objective optimization wasMOGA II. The calculation method is applied to a full-size model test turbine data for the prediction of the moisture flow discharge coefficient. As a result, the developed calculation method is found to be very effective for estimating the moisture flow discharge coefficient in a wide range of wetness fractions.