“During film cooling, cool air is bled from the compressor stage, ducted to the internal chambers of the blades and vanes, and discharged through small holes in the blade and vane walls. This air provides a thin, cool insulating layer along the surface of the blades and vanes,” explained Jens Dickhoff, technical manager at B&B Agema.
Tests were carried out at Kawaskai’s L30A gas turbine. Hereby, Nekomimi technology combines the two cylindrical holes of the DJFC within a single hole design to overcome the inefficiency of the air supply situation. This was achieved by shifting the holes of the DJFC configuration to the same streamwise position, uniting both holes, and replacing the two supply holes with a central one.
The computational domain used to virtually test the cooling effectiveness of different shaped holes: The result has been profound cooling improvements of 200% to 300% in the nekomimi designs over reference shaped holes – technology that has been co-patented by KHI and B&B Agema
Recently B&B Agema and KHI decided to automate their design search through the use of HEEDS, the design exploration software from Siemens PLM’s Red Cedar Technology subsidiary, and the HEEDS-based Optimate+TM add-on module for STAR-CCM+. “This change makes it possible for them to evaluate hundreds of designs in the time previously required to assess just a handful, methodically comparing large numbers of traditional fan-shaped hole designs to nekomimi-shaped holes,” researchers explained.
During the design search procedure, Optimate+ was used for the automated design exploration process, STAR-CCM+ for fluid flow and heat transfer simulation as well as geometry modeling of the fan-shaped holes, Siemens NX for parametric geometry modeling of the nekomimi-shaped holes, and HEEDS Post for visualizing and interpreting results.
This novel approach makes it possible to build a database of the best nekomimi cooling-hole designs for a variety of pressure ratios and coolant mass flow rates. From this database, cooling-design engineers can select the best design to achieve higher cooling effectiveness and lower cooling air consumption.
“For all kinds of film cooling holes, this study strongly enhances basic understanding of secondary flow phenomena and their impact on cooling effectiveness. Further, it proves the value of automated design space exploration for solving a broad range of standard engineering problems,” Dickhoff concluded.