Experimental study on the outlet flow field and cooling performance of vane-shaped pre-swirl nozzles in gas turbine engines

The pre-swirl nozzles are a crucial part of gas turbine's cooling pre-swirl system, because they directly affect the cooling performance of the system and the life of the turbine blades. Vane -shaped pre-swirl nozzles, including cascade vane nozzles (VN) and vane-shaped hole nozzles (VSH) proposed in recent years, are reported to have higher system temperature drop potential. In this paper, the pre-swirl performance as well as the cooling effect of these two types of nozzles were studied and compared experimentally. A five-hole probe was used to measure the flow field at nozzle exits under the outlet conditions of Mach number 0.2 and 0.3, and the comparisons of global deviation angle and pre-swirl effectiveness were carried out. The variations of pre-swirl effectiveness (eta) with aerodynamic parameters, such as pressure ratio and Reynolds number in the range of 3 x 104 to 8 x 105 were also obtained with the help from numerical simulations. The cooling performance of two nozzles were further tested by a system test rig with rotating parts downstream of the two nozzles. Total pressure and outlet flow angle at nozzle exit illustrate that VN have obvious boundary layer separation from the suction surface, and the secondary endwall flow loss is high due to their narrow flow passages. As a result, when Mach number is 0.2, the deviation angle for VN is about 3 degrees and the pre-swirl effectiveness is only 0.77. Well-designed VSH have improved flow passages with appropriate height to pitch ratio and a smaller trailing edge, and they suppress boundary layer separation and secondary flow development. This contributes to a significantly lower deviation angle near 0 degrees, and an increased pre-swirl effectiveness of 0.86. In addition, the pre-swirl effectiveness of these two vane shaped nozzles will first increase with Reynolds number and then tend to a constant at Reynolds number about 4 x 105 and beyond. The maximum effectiveness of VN is 0.85 and that of VSH is about 0.94 and is 10.6% higher. Meanwhile, the measured temperature drop effectiveness of the pre-swirl system with VSH rea-ches 0.49, achieving an 8.9% improvement over the system with VN at 0.45. These results are consistent with the theoretical linear relationship between system temperature drop and nozzle pre-swirl effectiveness. The investigations in this paper also conclude that the pre-swirl effec-tiveness of nozzles is a more accurate parameter in classifying the nozzle performance and system cooling effect than traditionally used discharge coefficient.