EFFECTS OF MAINSTREAM INCIDENCE ANGLE ON THE COOLING PERFORMANCE OF THE ROTATIONAL TURBINE BLADE TIP

The rotation fluctuation or the mainstream unsteadiness could cause the variation of the incoming incidence angle, affecting the cooling performance of the turbine blade. Most literature concentrates on the effects of incidence angle in the mid-pitch region, leaving the tip region less concerned. Considering that the complicated flow field in the tip region could sometimes worsen cooling effectiveness, this paper investigates the effects of mainstream incidence angle on the cooling performance of the rotational blade tip. The first stage of GE-E3 high pressure turbine blade with full composite cooling structure is used in this study and conjugate heat transfer numerical simulations are conducted on ANSYS CFX 2019R3 to calculate both the flow field and the solid temperature field. SST k-w turbulence model is adopted to enclose the RANS methods after multiple validations. Three rotational speeds, namely, 90%, 100% and 110% of the design point (13287 rpm), are simulated in three coolant mass flow rates (1.65%, 3.3% and 4.95% of the main flow rate) and three tip clearance ratios (0.5%, 1% and 1.5% of the total blade pitch). According to the results, the pressure side rim consistently gets cooler as the incidence angle changes from positive to negative because less leakage gets over the pressure rim. But in comparison, the trends of the suction side are complex. At the positive incidence angle, the large pressure difference forces nearly all coolant to exhaust over the suction rim, facilitating the coolant coverage there. At zero incidence angle, the leakage over the suction rim could raise the temperature in the thickest area. But as the incidence angle turns negative, the larger mainstream leakage over the suction rim could form an anti-rotating vortex. With large coolant flow rate or small tip clearance, the mainstream invasion would increase the temperature whereas with small coolant flow rate or large tip clearance, the vortex entrainment could decrease the temperature.