Research On Influence Of Notched Foreign Object Damage On Strength And Aerodynamic Performance Of Blade

Foreign Object Damage(FOD)is a problem often occurring during the use of aircraft engines.Hard objects in engine passage are most likely to injure the fan/compressor blades.Notch is the main form of FOD,which will affect its strength and aerodynamic performance.In this paper,the influence of notched FOD on blade strength and aerodynamic performance is studied for TC4 material fan blade.Based on this,suggestions of principle of determining the blade maintenance limit are put forward..This paper analyzes various foreign models of aero engine fan blade maintenance manuals,and results show that: In the actual maintenance,maintenance depth,length,bottom radius of repair area,and radius of arc at the joint between edge of repair area and blade body are taken as required parameters for the maintenance shape.Usually maintenance depth is used as maintenance limit,and the blade is roughly divided into the root,middle,tip and top of the leading and trailing edge,and the division defines the maintenance limit of the blade.The paper calculates fracture speed based on the local strain method.Results show that maintenance shape of notched FOD has little effect on fracture speed of the blade when maintenance depth is constant;When maintenance area is at root,fracture speed decreases with the increase of maintenance depth,and the dangerous point position is shifted to the root of maintenance area.The blade fatigue strength before and after FOD was calculated based on the critical distance method.Comparative analysis shows that: When maintenance area appears in blade root,middle and top of leading edge,fatigue strength decreases with the increase of maintenance depth,and the sharper the maintenance shape,the greater the degree of fatigue strength reduction.Aerodynamic calculations were carried out on blade before and after FOD using commercial software.Results show that: When notched FOD appears at the tip,it has a greater influence on total pressure ratio of inlet and outlet.Based on above research work,combined with analysis results of foreign engine fan blade maintenance manual,the paper finally gives the following suggestions for maintenance limit of FOD blade:(1)Division determines the maintenance limit;(2)Amount of change in parameters such as the breaking speed,fatigue strength and aerodynamic performance of the blade before and after FOD should be used as a limiting condition for determining the maintenance limit.