Film Cooling Measurements for Cratered Cylindrical Inclined Holes

Abstract

Film cooling performance is studied for cylindrical holes embedded in craters. Different crater geometries are considered for a typical crater depth. Cratered holes may occur when blades are coated with thermal barrier coating layers by masking the hole area during TBC spraying resulting in hole surrounded by TBC layer. The film performance and behavior is expected to be different for the cratered holes compared to standard cylindrical holes. Detailed heat transfer coefficient and film effectiveness measurements are obtained simultaneously using a single test transient IR thermography technique. The study is performed at a single mainstream Reynolds number based on free-stream velocity and film hole diameter of 11000 at four different coolant-to-mainstream blowing ratios of 0.5, 1.0, 1.5 and 2.0. The results show that film cooling effectiveness is slightly enhanced by cratering of holes but a substantial increase in heat transfer enhancement negates the benefits of higher film effectiveness. Three different crater geometries are studied and compared to a baseline flush cylindrical hole, a trenched hole, and a typical diffuser shaped hole. CFD simulation using Fluent was also performed to determine the jet-mainstream interactions associated with the experimental surface measurements.

Surrogate-based optimization of a cratered cylindrical hole to enhance film-cooling effectiveness

“…5, the optimum number of grids was determined to be 3.5 million. Validation of the numerical results was performed for three different film-cooling holes, i.e., cylindrical, trenched and cratered holes, by comparison with experimental data measured by Lu et al (2009b) as shown in Fig. 6, which shows the distributions of laterally-averaged film-cooling effectiveness at a blowing ratio of 0.5.…”

“…Table 3 shows results of the optimization in comparison with a reference design using three surrogate models, i.e., RSA, RBNN, and Kriging models. The geometry reported by Lu et al (2009b) was selected as the reference design. The predicted optimum values obtained by the RSA and RBNN models, represent relatively large deviations from the values calculated by RANS analysis with relative errors of 7.4% and 9.8%, respectively.…”

“…Fric and Campbell (2002) first introduced the cratered film-cooling hole, which has an elliptical exit in a shallow elliptical surface cup or depression. Lu et al (2009b) performed experimental and numerical analyses to evaluate the film-cooling effectiveness and heat transfer coefficients for three different cratered hole shapes; cylindrical, trenched, and shaped diffuser holes. In this study, the cratered holes did not perform well compared to the shaped holes and trenched holes, but yielded higher film-cooling effectiveness at a lower blowing ratio compared to the cylindrical holes.…”

A Review of Hole Geometry and Coolant Density Effect on Film Cooling

“…Shaped diffuser hole reduced the jet momentum at hole exit and outperformed the trench cases. Lu et al (2007b) also presented results for cylindrical holes embedded in craters. Different crater geometries were considered for a typical crater depth which was identified by Lu et al (2007a) as 0.75D.…”

On the effect of geometry of w-wave trenches on film cooling performance of gas turbine blades

“…14 and Lu et al. 15 investigated various trench downstream edge configurations, and found edge shaping for trenches to exert a remarkable impact on film cooling performance.…”