Design Of The Variable Guide Vane Of The Variable Nozzle Radial Turbine And Study On Flow Characteristics

Turbocharging is one of key technology to realize the engine's energy-saving and environmental protection, especially for the turbocharger with the variable guide vanes, which can be matched with the engine in the full operating conditions, has become a basic technical approach to improve the engine's dynamic performance and fuel economy. When the engine works in the low speed range, corresponding opening angle of the variable guide vane is small. The investigations on the efficiency and internal flow of turbine stage in the small opening of the variable guide vane have been paid widely attentions. Additionally, in the brake condition of engine, the opening of the guide vane is small and the expansion ratio is large, and the shock wave will be formed near the guide vanes' trailing edge. The shock wave will induce the high cycle fatigue fracture of downstream turbine blades. At present, the researches on the flow mechanism of the guide vanes mainly focus on the tip leakage flow of the guide vanes and its influence on the turbine performance. Few attentions have been paid on the design of the guide vanes and the weakening of the shock waves at the trailing edge. The purpose of this research is to improve the efficiency of the whole turbine stage and weakening the shock wave intensity near the guide vanes' trailing edge by designing a superior guide vane.Considering the shock wave and clearance leakage flow caused the excessive acceleration airflow in the guide vane passage, a kind of aft-loaded guide vane was designed, and the aerodynamic performance of the whole turbine stage was studied. Firstly, the numerical calculation results of the the original turbine stage model in small openings were validated by the the experimental values, this showed the numerical calculation is reliable. Then, the steady and unsteady calculations of the original model and new design model were conducted respectively and the internal flow field of the two models were analyzed.A type of aft-loaded vane was designed in the paper. The results show that compared with fore-loaded original vane, the aft-loaded vane can reduce the total pressure loss of guide vane section and improve the efficiency of turbine stage by decreasing the tip leakage vortex intensity of the guide vane. Because airflow velocity in aft-loaded guide vane is relatively uniform, this weakens the throat shock wave and trailing edge shock wave in the guide vane passage. The weakening of guide blade clearance leakage flow and the elimination of the trailing edge shock wave make the static pressure fluctuation strength on rotor blade surface decrease significantly, thus increases the reliability of the rotor blade.A type of aft-loaded vane was designed in the paper. The results show that compared with fore-loaded original vane, the aft-loaded vane can reduce the total pressure loss of guide vane section and improve the efficiency of turbine stage by decreasing the tip leakage vortex intensity of the guide vane. Because airflow velocity in aft-loaded guide vane is relatively uniform, this weakens the throat shock wave and trailing edge shock wave in the guide vane passage. The weakening of guide blade clearance leakage flow and the elimination of the trailing edge shock wave make the static pressure fluctuation strength on rotor blade surface decrease significantly, thus increases the reliability of the rotor blade.