Study On Failure Mechanism And Life Prediction Of Aero-engine Combustor

To improve thrust-weight ratio and thermal efficiency of aero-engine,the working temperature of aero-engine rises rapidly.At the same time,lean-burn combustion mode is adopted to aero-engine due to strict NOx emission regulations,in this case,the portion of air used for combustor cooling system is further reduced,which makes the working environment of combustor getting worse and the fatigue problems of the combustor is increasingly prominent.In this research,the failure mechanism and life prediction were peformed.Fluid-structure interaction model and nonlinear static analysis were carried out to reveal the cracking mechanism of combustor.Based on pure creep and creep-fatigue interaction test,a nonlinear damage accumulation model of Hastelloy X was established to analysis the damage accumulation and fatigue life of sombustor liner.To reduce the thermal load and prolong the service time of combustor,the combustor cooling system structural optimization was carried out.The work can be summarized as follows:(1)Based on the QAR data,the working condition of aero-engine for single flight cycle can be simplified into five typical conditions: idle,take-off,climbing,cruising and descenting.A turbulence combustion fluid-structure interaction model was established to simulation the folw field of combustor numerically.Based on the simulation results,the failure position and failure mode of thermal barrier coating was predicted and compared with the actual failure of thermal barrier coating.Results show that the predicted results from simulation are consistent with the actual failure of thermal barrier coating,and the simulation results are reliable.(2)The micro morphology of the cracks found in the combustor hole detection process is analyzed.Obvious fatigue characteristics can be obsvered.Based on the Fluid-structure interaction simulation results,considering the plastic deformation of combustor liner,nonlinear static analysis is carried out on combustor liner,results show that the maximum plastic strain of the combustor liner under takeoff and climbing state is 0.4476% and 0.4154% respectively,and the maximum strain position is consistent with the crack positions found in the combustor hole detection process.The fatigue damage caused by the cyclic loading of plastic strain during the start and stop of engine and the creep damage caused by the load holding during the steady working condition as well as their interactions would give rise to the damage accumulation and cause the cracks initiation of combustor liner.(3)The low cycle fatigue behavior of Hastelloy X,the matrix material of combustor liner,under asymmetric loads at 25 ℃ and 650 ℃ is studied.The effects of temperature on fatigue life,cyclic stress response behavior,crack initiation and propagation mechanism and deformation mechanism of Hastelloy X were compared and analyzed.The Ostergren model was employed to predict the fatigue life of Hastelloy X under asymmetric load.(4)On the basis of pure fatigue test,60 s tensile load hold was involved to simulate the creep damage during aero-engine steady working condition.The cyclic stress response,crack initiation and propagation mechanism,the deformation behavior of Hastelloy X under creep-fatigue interaction were analyzed.Considering the stress relaxation effect during the holding period,a nonlinear damage accumulation model of Hastelloy X under creep fatigue interaction was established.Damage accumulation and life prediction of combustor dangerous point was carried out.Results show that the life of cracking position found in hole detection is 3424 flight cycles,equals to 5516 flight hours.During the failure process of dangerous point,the contribution of creep damage and fatigue damage to total damage is 0.72 and 0.06 respectively,and the creep damage is the main contribution in the failure process of the dangerous point.(5)To reduce the working temperature and thermal load of combustor liner and prolong the service life of combustor,the cylindrical hole,conical hole,fan-shaped hole and console hole are introduced into the combustor cooling system,and the effect of cooling hole configurations on heat transfer,combustion,and structural strength of the combustor are studied numerically.Results show that the maximum temperature of thermal barrier coating is reduced by 149.01 ℃、208.12 ℃、248.64 ℃、257.78 ℃and the maximum plastic strain changes to 0.4091%、0.3925%、0.3417%、0.6889%respectively under take-off stage.After optimizing the combustor cooling system with fan-shaped holes,the minimum life of combustor increases to 4405 flight cycles,equals to 7096 flight hours.