Research On The Influence Of Clocking Effects On Unsteady Excitation Of Aircraft Engine Blade

The flow inside the aircraft engine is a typical unsteady flow.Unsteady aerodynamic excitation is the main cause of high-cycle fatigue damage of the blade.Therefore,the study of unsteady aerodynamic excitation has important theoretical and engineering value.Effectively reducing the unsteady excitation of the blades is conductive to improving the structural integrity and reliability of the blades and discs,and has been paid attention by the academic and engineering world.Recent studies have shown that,in addition to affecting the aerodynamic efficiency of aircraft engine,the clocking effect also has a significant effect on the unsteady excitation of the blades,but the law and mechanism of the effect on the clocking effect are not fully understood.In this paper,we use CFD to calculate the numerical simulation of the twodimensional cascade and three-dimensional turbine model.In the calculation of the twodimensional repetitive turbine and compressor cascade model,the relationship between the wake and the unsteady aerodynamic excitation is summarized.Observation of the mutual positions of the wakes between the rotor blade rows shows that the essence of the clocking effect is due to the circumferential phase difference between the adjacent two stator(rotor)blades,resulting in a difference in the effect of the wake and potential flow on the target blade.The spectral decomposition of the unsteady aerodynamic excitation displays that the energy of the downward propagation of the wake is much higher than that of the upward propagation of the potential current,and the propagation distance of the wake generally does not exceed 2 stages.In order to further understand the effect of the clocking effect on the unsteady aerodynamic excitation of the blades in the aircraft engine,this paper takes the twodimensional turbine cascade as an example,by changing the position of the first stage stator blade to obtain 5 clocking positions.The effect of the clocking effect on the unsteady aerodynamic excitation amplitude of the second-stage stator blade reaches51.3%,and the influence on the unsteady aerodynamic excitation amplitude of the firststage rotor blade reaches 34.6%.Then,in the calculation of the three-dimensional two-stage repeated turbine,also by changing the circumferential position of the first-stage stator,10 different clocking positions were obtained,and analysis of the unsteady aerodynamic excitation of the leading and trailing edges of rotor blades,stator blades and different blade heights.Some basic rules are summarized:(1)As the span increases,the effect of the clocking effect on the amplitude of the unsteady aerodynamic excitation of the blade will also increase;(2)The unsteady aerodynamic excitation at the leading edge of the blade is subject to the effect of the clocking effect is greater than that at the trailing edge of the blade;(3)The clocking effect of the stator will affect the unsteady aerodynamic excitation of the rotor blade,but the magnitude of the effect is smaller than that of the stator blade itself.Finally,because the number of blades between each blade row of an aircraft engine is usually relatively prime,it will bring about a modulation effect,which in turn affects the uniformity of unsteady aerodynamic excitation between blades in the same blade row.In this paper,a non-repetitive 2.5-stage turbine planar cascade is introduced to study the effect of clocking-modulation effect on the uniformity of the unsteady excitation of the blades.The effect of modulation on the amplitude of the unsteady aerodynamic excitation of the blade can reach 87.2%,and the modulation effect caused by the potential flow is much higher than that caused by the wake,but the amplitude of the unsteady aerodynamic excitation caused by the wake is much higher than the potential.For the clockingmodulation effect,the calculation shows that for the blade row that is only subjected to the wake or the potential flow,the uniformity of the unsteady aerodynamic excitation of each blade belonging to this type is significantly affected by the clocking-modulation effect compared with other blades.