Effects of coolant flow rates on cooling performance of the intermediate pressure stages for an ultra-supercritical steam turbine

The effects of the coolant flow rates on the thermal and flow fields of the first two intermediate pressure (IP) stages of an ultra-supercritical steam turbine was numerically investigated using the Conjugate Heat Transfer (CHT) method, and the un-cooled case was also simulated for comparison. The three-dimensional Reynolds-Averaged Navier-Stokes (RANS) solution was utilized to analyze the flow field and temperature distributions of the first two IP stages. The numerical results show that the steam cooling system has proved its ability to cool down the high temperature components, even in the case with the low coolant flow rate. The cooling performance can be improved with increased coolant flow rate, however, great flow losses would be induced and make the stage efficiency reduce by 1.23%. The different coolant flow rates also lead to great differences in the flow field in the front cavity of the first stage: ingress dominated flow condition with the low coolant flow rate and egress dominated flow condition with the high coolant flow rate. The negative influence of the ingested hot main steam on the cooling effect was also described.