Investigation On Aerodynaimic Optimization Design And Hot Streak Effects In Counter-Rotating Turbine

Counter-Rotating turbine (CRT) can offer some significant benefits compared with conventional two-stage turbines, such as the elevated efficiency, the reduced weight, the improved performance of aircraft and so on. So, the aviation powers in Europe and America pay great attentions on the study of CRT, and the CRT has been succsfully applied in the military aero-engines and in the civil aero-engines in those countries. However, the recearch level of the CRT in China is very low, especially in the aerodynamic design and optimization. In addition, researchers have found that hot streak can affect the flow field and heat load in conventional turbines, but the study of the hot steak effects on the flow field, aerodynamic performance and heat load in the Vanless Counter-Rotating Turbine (VCRT) is very few. In view of this background, the investigations on the aerodynamic optimization design and hot steak effects in CRT are showed in this paper. The main content in this paper is listed as follows:1. An aerodynamic design of a CRT with low pressure stage stator is performed and the numerical tools are employed to study its flow field and aerodynamic performance. The results show that concave shroud can reduce the reaction in the top and the oppocite C-shape work distribution can increase the difference in the angle radial distribution at the low pressure stage stator outlet.2. The effects of the bowed stator blade on the aerodynamic performance of VCRT are studied. The variations in the flow field and the efficientcy change in the high/low pressure stages due to the different stator bowed angles are showed. The investigations of the influence mechanism of bowed blade on the VCRT aerodynamic performance are carried out. The results indicate that stator with small bowed angle is benifical to the VCRT efficiency.3. Steady/unsteady numerical simulations are performed to reveal the hot streak effections on the radial secondary flow and on the vortex in the VCRT rotor passages. The results show that hot streak can reinforce the radial secondary flow and strength the root passage vortex and wake vortex at high pressure stage rotor passages. The results also show that hot streak can weaken the tip leakage vortex at the high pressure stage rotor passages and weaken the the root passage vortex at low pressure stage rotor passages. 4. The influences of hot streak on the blade surface heat load, the blade tip heat load and the endwall heat load are studied. The study indicates that the heat load is affected by the hot streak, radial secdory flows, leakage vortex and so on. The results show that the heat loat on the aft part of high pressure rotor tip and the heat loat on the aft part of low pressure rotor tip are heavier in hot streak condition due to the passing hot gas. The results also show that the heat load on the aft part of high pressure rotor hub and the heat load on the low pressure stage rotor hub are heavier in the hot streak condition due to the radial secdory flows of hot gas. In addition, the hot gas addrvied to the blade tip remove from shroud due to the leakage vortex, so the heat load on the shroud is lighter in hot streak condition.5. The investigation of hot streak effects on the aerodynamic performance of VCRT is performed. The results indicate that the work of hot gas at the midspan increases and the work of cool gas at the endwall decrease in hot streak condition. The results also show that the efficiency at midspan decrease due to the losing energy of hot gas and the the efficiency at endwall increase due to the getting energy of cool gas in hot streak condition.