CFD Analyses of HPT Blade Air Delivery System With and Without Impellers

Abstract

In the design of a HPT blade cooling air delivery system, sufficient supply pressure is required to guarantee HPT blades are working properly in the high temperature environment. A design goal is to set a pressure level at the blade inlet that will prevent the ingestion of gaspath air into the blades which is caused by pressure fluctuations under various operating conditions and other uncertainties. Traditional 1-D design tools are not sophisticated enough for detailed system analysis. Therefore, CFD (Computational Fluid Dynamics) analysis was utilized for designing HPT blade cooling air delivery system to guarantee meeting the supply pressure requirement. Two HPT blade air delivery systems were explored. The baseline is a cooling air delivery system without radial impellers. It provides a simplistic design at low manufacturing cost, however CFD analysis shows that the system has a larger pressure loss at the broach slot entrance and delivers low supply pressure. The alternative is a cooling air delivery system with radial impellers. CFD analysis shows that the system with impellers results in much better aerodynamic performance at the broach slots and provides high supply pressure, but comes with the price of high manufacturing cost and lower TSFC due to the parasitic drag induced by impellers. For the alternative approach, three high solidity impeller designs were analyzed. The alternative approaches analyzed had inlet angles of 0°, 30°, 90° and exit angles of 0°, respectively. Comparisons of detailed aerodynamic performance are presented in the paper. CFD simulation reveals that the source of pressure loss without impellers is caused by mismatch of the swirl ratio at broach slot entrance. CFD results show that a system with radial impellers produces a better matched swirl ratio at broach slot entrance. Radial impellers enhance aerodynamic performance and improve pressure distribution within broach slots.