Tip flow and heat transfer prediction of cooling blade with dirt purge holes

Dirty purge holes in the blade tip are used to extract dirt from the coolant flow through centrifugal forces such that these dirt particles do not block small diameter film-cooling holes and injection holes, to ensure safety and reliability of the blade. Whereas, the holes will affect blade tip flow and heat transfer. A numerical study of a turbine blade with dirt purge holes is performed to examine both flow and heat transfer characteristics. Two blade geometry models with and without dirty purge holes are established by a parametric method in CAD software. Coupled aerodynamic and heat transfer numerical simulation is used to predict the blade tip flow and heat transfer, with the integral of the blade solid field, main gas and internal cooling passage flow field. The result shows that, the cool air jet from purge holes can reduce the tip facet average temperature about 25 K, based on the contrast between blades with and without dirty purge holes. Convective heat transfer of internal cooling passage and jet flow of dirty purge holes can reduce the temperature of blade tips 400~600 K. The cooling effect relates to the position of dirt purge holes and the mass flow rate of cooling air. Furthermore, injection of dirt purge holes also reduces blade tip leakage, obviously. It will enhance the total pressure recovery efficient about 0.5%~1.5%, and the effect will be enhanced with the cooling mass flow rate increasing. So the flow and heat transfer influence of jet flow from dirty purge holes can't to be ignored during the cooling turbine blade design.