Two-phase flow simulation of mist film cooling on turbine blades with conjugate internal cooling

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 past half century. However, the net benefits from the traditional methods seem to be incremental, but the temperature of working gas is continuously increasing to achieve 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 oil the cooling effectiveness with an adiabatic wall, this paper focuses on the effect of mist injection on heat transfer of film cooling with a nonadiabatic flat wall, using the commercial computational fluid dynamics software package FLUENT. Both 2D and 3D cases are considered with a 2D slot and diffusive compound-angle holes. Modeling of the interaction of a droplet with a unformly cooled wall as well as conjugate heat conduction inside, the solid base are conducted. Different mist droplet sizes and mist concentrations are adopted. Conditions both in a gas turbine operating environment (15 atm and 1561 K) and in a laboratory environment (1 atm and 450 K) are considered. Results show that injecting 2-10% mist reduces the heat transfer coefficient and the wall temperature. Especially, mist has the prolonged effect of cooling the region downstream for 15 jet hole diameter, where conventional air film cooling is not effective.