Investigation On Aerodynamic Design Of Variable Geometry Turbine For Variable Cycle Aero Engine

The variable cycle aero-engine can maintain low fuel consumption under wide flight envelope and increase sufficient thrust for fighter.Its excellent off design performance has been paid attention to by various countries.As one of the important components of variable cycle engine,variable geometry low-pressure turbine needs to maintain high efficiency under all operating conditions.Its aerodynamic parameters can not simply refer to the rules of traditional fixed geometry turbine,and its large meridian expansion form and adjustable guide vane clearance bring obvious end area loss,which seriously affects the performance of variable geometry turbine.Therefore,it is very important for the development of variable cycle engine to carry out the research on high efficiency aerodynamic design of variable geometry turbine.Firstly,based on the existing clearance leakage loss model,combined with the geometric characteristics of variable geometry turbine guide vane large meridian expansion and adjustable guide vane partial clearance,the maximum prediction error of the loss model is 3%;based on the one-dimensional total stator blade exhaust function method,the one-dimensional performance prediction method for variable geometry turbine is developed The results show that the maximum error of the method is 3.69% in the range of 20% flow change,and can accurately predict the influence of guide vane rotation on relative inlet angle and one-dimensional aerodynamic parameters.Secondly,combined with the above methods,the one-dimensional mean pitch diameter method was used to evaluate the turbine characteristics under different flow rate changes,revealing the rules of variable geometry turbine aerodynamic parameters selection,and summarizing the Simth diagram of variable geometry turbine.The research results show that the guide vane angle of variable geometry turbine is flat compared with the traditional turbine under the same conditions in the flow rate variation range of ± 20% The results show that the optimal reaction,axial speed ratio and flow coefficient of the average efficiency are slightly smaller than those of the conventional turbine.The specific reason is that when the load factor is 1,the optimal reaction degree of the variable geometry turbine decreases by about 10%,while the optimal flow coefficient decreases by 8.57% when the reaction degree is 0.4.Finally,the end loss control method of variable geometry turbine(VGT)is studied.The influence of 40%,50%,60% axial position and "concave first and convex" end wall profile on the selection of variable geometry turbine adjustable guide vane clearance and turbine performance is discussed.The results show that the "concave first and then convex" end wall can greatly reduce the trailing edge clearance of the adjustable guide vane,reduce the upper leakage loss by 20% and the upper channel vortex loss by 20% Compared with the straight end wall,the "concave first and convex" end wall with amplitude of one twelfth of the maximum thickness improves the variable geometry turbine efficiency at full angle,and the average efficiency at three angles increases by 0.497% compared with the straight end wall.