Aerodynamic Optimization Design Of Aspirated High Pressure Ratio Fan Stage

The design of a high total pressure ratio and high efficiency aspirated compressor/fan is the key technology for an aircraft engines with high thrust–weight ratio and low fuel consumption.The pressure gradient in blade passage is high for a high loaded aspirated compressor/fan.Thus the boundary layers on blade surface and endwalls are thick and easy to separate.The boundary layer bleed technology can effectively control the development of boundary layers and improve the stage load and efficiency.This paper study the optimization design method of aspirated fan,and design an aspirated fan with high pressure ratio.The main reaseach work and contents are as follows:1.The study of aerodynamic optimization design method of aspirated fanThe complete design platform for high load aspirated platform is established through the study of the aerodynamic optimization design method study of aspirated fan.The platform includes S2 stream surfac design platform,two-dimensional(2D)blade profile design platform(plane blade profile and S1 stream surfac rotary surface blade profile)and three-dimensional(3D)blade optimization design platform.In S2 through-flow design,the loss feedback is used to solve the inapplicability of the conventional loss model,that is,the actual loss/efficiency of the aspirated fan rotor/stator is radially extracted as the loss model of S2 through-flow design,which ensures accuracy of the loss model.In S1 profile design,an optimization design method is constructed in which the profile and suction flow parameters are simultaneously set as design parameters.The three-dimensional optimization design set the geometric parameters of the blade profile along the span,stacking line aweep and bend,suction parameters,and meridian geometry parameters as design variables to consider the mutual influence of the blade geometry parameters and suction parameters.And an optimization design test of an aspirated stator profile was carried out to verify that the coupling optimization is better than the uncoupling optimization.In addition,it is also verified that coupling the profile and suction flow parameters results in a design that outperforms the uncoupled design;therefore,designing an aspirated compressor blade by arranging suction flow on a conventional blade without considering suction flow is not a good method.2.The improvement of numerical optimization methodThe numerical optimization method adopts genetic algorithm(GA).Because the GA randomly approximates the global optimal individual according to the probability,the search efficiency is low and the local search ability is poor,the optimization effect is affected.In order to improve the optimization effect of GA,two improved methods are proposed.The local optimization ability of the original GA is improved by using the simplex method with strong local optimization ability.In the evolution of GA,the individuals generated by GA constitute simplex,and a one-dimensional search is carried out inside the simplex,and the individuals generated by simplex replace the inferior individuals generated by GA.The simplex method is coupled with GA,and the local optimization ability of optimization method is improved.Typical test functions show that the IGA can effectively improve the optimization effect over that of the original GA.To further verify the IGA's practicability,an aspirated compressor profile is optimised with profile,suction flow rate and suction flow location as coupled design parameters.The results again show that the IGA has a better optimising effect than the GA.The second improved method uses Bezier curve to parameterize the blade surface,and uses its equivalent recurrence characteristics to realize the variant space optimization of GA evolutionary process to improve the search efficiency and global search ability.The parameters related to this method are investigated by an optimization test of the simple curve approximation,which is then used for optimization designs of a supersonic and transonic profiles.The results show the GA can be improved if the variant space search method is added.3.The aerodynamic design of high load aspirated fan stageAn asparitaed fan stage(load coefficients 0.69)was designed by using the aspirated fan stage design method and software plateform.Firstly,S1/S2 flow surface 2D design method were used to design the rotor and stator blade,and the S1 flow surface profiles and suction parameters were idytified by coupling optimization design method;the flow loss model of S2 flow surface design was idytified by iterative design method.The blades design by S1/S2 flow surface 2D design method were set as initial blades to carry out the 3D optimization design.The aspirated fan stator was optimized in the stage environment to consider the interaction between rotor and stator.The computation results show that,the aerodynamic performance parameters of aspirated fan stage at design point is as follows: mass flow rate is 34.00kg/s,total pressure ratio is 3.445,isentropic efficiency is 0.9213,and static total pressure coefficient is 0.9641.And it achives the design goal of massflow rate with high efficiency,which verifies the feasibility of design method based on S1/S2 flow surface 2D design method and 3D optimization design method.4.Influence law study of the of key parameters on the aerodynamic performance of aspirated fanFor the above designed aspirated fan,the influence of parameters such as stacking line sweep,suction parameters,and the effect of suction itself on the efficiency was studied.Research shows that: 1)For the aspirated fan rotor,the main effect of the shock wave position and shape control is the asprated technology,and the effect of the stacking line sweep is weak.Thus,for the aspirated fan rotor,the stacking line sweep can not increase efficiency,pressure ratio,and stability margin of the aspirated rotor;2)There is an optimal suction position for on the blade surface.This optimal suction position is located after the shock wave,and before the boundary layer develops;and on the optimal suction position,there is a best suction volume,so that the boundary layer is just bleed out and the shock wave intensity is not too strong,thus the losses of the shock waves and boundary layer are minimized and the efficiency is higher;3)Considering the effect of the energy taken by the suction itself on the efficiency of the aspirated compressor/fan rotor and stage,under the same suction position,when the suction volume increases,the efficiency decreases;under the same suction volume,when the suction position moves backward,the efficiency is reduced.The influence degree of suction on the efficiency of stator is much higher than that of the rotor,thus,the effect of the energy taken by the suction on efficiency cannot be ignored,especially for the stators.