Two-phase Flow Simulation of Mist Film Cooling with Different Wall Heating Conditions

Effective cooling of gas turbine combustor liners, combustor transition pieces, turbine vanes (nozzles) and blades (buckets) is a critical task to protect these components from the flue gas at extremely high temperature. Air film cooling has been successfully used to cool these hot sections for the last half century. However, the net benefits from the traditional methods seem to be marginally incremental, but the temperature of working gas is continuously increasing to achieve a high thermal efficiency. Therefore, new cooling techniques need to be developed. One of the promising techniques is to enhance film cooling with mist injection. While the previous study reported the effect of mist on the cooling effectiveness with an adiabatic wall, this paper focuses on the effect of mist injection on heat transfer of film cooling with a non-adiabatic flat wall, using commercial CFD software package Fluent. Both 2-D and 3-D cases are considered with a 2-D slot and diffusive compound angle holes. Modellings of interaction of droplet with uniformly cooled wall as well as conjugate heat conduction inside the solid base are conducted. Different mist droplet sizes and mist concentrations are adopted. Both conditions at a gas turbine operating environment (15 atm and 1561K) and in the laboratory environment (1 atm and 450K) are considered. Results show that injecting 2~10% mist successfully reduces the heat transfer coefficient and the wall temperature. Especially, mist has the prolonged effect of cooling the region downstream of 15 jet hole diameters, where the conventional air film cooling is not effective.