Characteristics of flow and heat transfer in first stage nozzle of a gas turbine with various flow rates of cooling gas

The operation of gas turbines under off-design conditions is becoming more frequent to absorb the power supply fluctuations from renewable power. By operating gas turbines at the off-design point, the flow rates of cooling air through the nozzle guide vanes (NGVs) and blades can be varied. It is necessary to understand the influence of the flow rate change of cooling air on the deterioration of aerodynamic components in gas turbines to realize suitable maintenance work. We conducted conjugated heat transfer simulations of the 1st stage nozzle with flow simulation of the following stages. The numerical method was validated by comparison with the operation data from a working power plant. It was found that the deteriorated NGV was damaged around the leading edge near the hub-side end wall due to corrosion. The numerical results showed that the entire wall cooling efficiency of the NGV increased as the flow rate of cooling air increased, excepting for the leading edge near the hub-side end wall. This was because the pressure upstream the NGV is too high to increase the cooling air flow rate. The results also showed that the gas turbine performance was maintained regardless the flow rate change of the cooling air.