Film Cooling With a Thermal Barrier Coating: Round Holes, Craters, and Trenches

Abstract

Little work has been done to understand the interconnected nature of film cooling and thermal barrier coatings (TBCs) on protecting high temperature turbine components. With increasing demands for improved engine performance it is vital that a greater understanding of the thermal behavior of turbine components is achieved. The purpose of this study was to investigate how various film cooling geometries affect the cooling performance of a thermally conducting turbine vane with a TBC. The vane model used in this study was designed to match the thermal behavior of real engine components by properly scaling the convective heat transfer coefficients along with the thermal conductivity of the vane wall. This allowed for the measurement of temperatures at the interface of the TBC and vane wall which, when nondimensionalized, are representative of the temperatures present for actual engine vanes. This study found that the addition of a TBC on the surface of an internally cooled vane produced a near constant cooling performance despite significant changes in the blowing ratio. The craters, trench, and modified trench of this study were found to provide much better film cooling coverage than round holes; however, the improved film cooling coverage led to only slight improvements in temperature at the interface of the TBC and vane wall. These results suggest that there is minimal advantage in using more complicated cooling configurations, particularly since they may be more susceptible to TBC spallation. However, the improved film coverage from the trench and crater designs may increase the life of the TBC, which would be greatly beneficial to the long-term thermal protection of the vane.

Conjugate Heat Transfer Measurements and Predictions of a Blade Endwall With a Thermal Barrier Coating

“…The values in the table show that the improvement due to the addition of TBC is about three times greater than the improvement from increasing blowing ratio. Changing blowing ratio is less effective than TBC at reducing endwall temperatures, which is consistent with the findings on the vane surface [10].…”

“…The TBC case had cooler leading edge wall temperatures but hotter external TBC temperatures due to the insulating effect of the TBC. Davidson et al [10] investigated the improvement in wall temperature when TBC was added to a matched Bi vane with Bi of 0.3-1.1. The cooling performance increased significantly with TBC to the point that increasing blowing ratio did not provide a further reduction in the vane wall temperature.…”

Conjugate heat transfer modeling of a turbine vane endwall with thermal barrier coatings

“…However, the improvement due to the addition of the TBCs is considerably greater than the improvement from increasing coolant mass flow rate. It is concluded that the use of TBCs is more effective than increasing coolant mass flow rate in reducing endwall metal temperatures, which is in accordance with the findings on the vane surfaces by Davidson et al (13) . In comparison with the round hole film cooling configuration, in spite of better adiabatic film cooling from the crater holes, craters cause a little more endwall surfaces to be exposed to the hot gas, resulting in slightly higher endwall metal temperature, that is, lower overall effectiveness improvement (see Table 3).…”

“…The leading edge metal was cooler but hotter temperatures were found on the TBC external surfaces due to insulating effect of the TBCs. Davidson et al (12,13) investigated the reduction in metal temperatures in presence of TBCs and compared the thermal protection from various film cooling configurations in a scaled-up vane. The presence of the TBCs alleviated the variations in overall cooling effectiveness due to changes in blowing ratio.…”

Numerical Study of the Effects of Thermal Barrier Coating and Turbulence Intensity on Cooling Performances of a Nozzle Guide Vane

“…To prolong and give good service to the turbine airfoils, TBC has been widely utilized in gas turbine designs as a thermal insulator between hot mainstream and metal surfaces. The insulating thermal capabilities of TBC are affected by many factors, such as porosity, thickness, thermal conductivity, and phase stability of the TBC material as well as the TIT and Tu of hot gas as reported by researches [9][10][11][12][13][14]. Figure 1 illustrates the definitions of thermal parameters in Equations (1)- (6).…”