| Erosion refers to a type of gradual wear that occurs when the surface of a material is impacted by solid particles carried by an air or liquid stream.When a transport plane or helicopter flies in sandy environment or encounters a sandy weather,the sand in the air will inevitably be sucked into the engine.Even if the turboshaft engine is equipped with the particle separator,a certain amount of sand could enter the compressor,which will impact the blades at a very high relative speed(250?400 m/s).It causes severe erosion damage to the blades,and the damage mechanism is not clear.Erosion rate refers to the ratio of the removed material mass to the sand mass impacting on the material,which is usually used to evaluate the erosion resistance of materials.However,the existing erosion rate prediction models can not accurately predict it under high-speed erosion conditions.Therefore,the high-speed sand erosion damage mechanism is studied,and the high-precision erosion rate prediction model is developed,to solve the erosion damage prediction problem of compressor blade,which provides theoretical basis and analysis means for compressor blades anti erosion design,protection and field application.Titanium alloy is a common material for compressor rotor blades.In this thesis,the damage mechanism and law of sand erosion and erosion rate prediction model of TC4 titanium alloy and real blades were studied by combining theory and experiment.The main work and achievements of this thesis are as follows.(1)The high-speed impact tests of a single sand particle on titanium alloy flat plate samples were carried out in the range of 250 m/s to 400 m/s,the three-dimensional morphology of the titanium alloy plate damaged parts was measured,and the effects of sand fracture,impact velocity and impact angle on damage were analyzed.The results show that when the impact conditions are similar,the damage caused by fractured sand is significantly lower than that of non fractured sand,and the micro cutting phenomenon is more likely to occur in the case of lower impact speed than that of non fractured sand.the damage area caused by sand fragments is obviously larger than that under high impact angle condition,and the crater volume caused by sand fragment on material surface is relatively small.The sand impact velocity plays a dominant role in the damage factors,and the sand impact angle directly determines the materials damage mode,which is characterized by micro cutting,ploughing and extrusion deformation.(2)By optimizing the design of the existing erosion test equipment to increase the average impact speed of sand,and improving the wear resistance of the sand blast gun in the equipment,the average impact speed of sand reaches 335 m/s,and the blast gun is resistant to The wearability is increased by2 times.On this basis,a high-speed sand and dust erosion test was carried out on a titanium alloy flat specimen and a single real blade.By analyzing the changes of its erosion rate,mass loss rate and microscopic damage characteristics with impact conditions,it revealed that the blade was subjected to sand erosion damage mechanism at high speed.The results show that: for titanium alloy specimens,the material damage type at low impact angles is mainly micro-cutting;when the impact angle is increased to 45°,the material exhibits extrusion and plow damage,as well as deeper cutting damage;The material deposits around the crater are impacted off by subsequent sand,which is the main reason for the material removal under the condition of higher impact angle.The erosion rate is exponentially related to the impact velocity and the average particle size of sand.For a single blade of titanium alloy,under the condition of low sand attack angle,the blade’s leaf pot is mainly damaged by cutting.As the attack angle of sand increases,the damage mode is coexistence of cutting,plowing and extrusion deformation,and extrusion is the main mode of damage at the leading edge of the blade.(3)The probability prediction model of erosion rate based on titanium alloy erosion damage mechanism was studied.Considering the random factors such as impact velocity,particle size,kinetic energy and fracture rate in the erosion process,a mathematical model for erosion rate prediction was proposed,which could meet the probability characteristics of impact conditions.Based on the test data of single sand high-speed impact on titanium alloy plate,the function of sand impact kinetic energy and fracture rate was obtained;through a large number of sand mass and particle size measurement,the probability distribution of sand particle size to mass ratio was obtained;through the sand blasting velocity measurement test of different particle size ranges,the probability distribution of impact velocity in each particle size range was obtained too.By substituting the above probability relationship into the basic formula of erosion rate prediction based on the impact damage mechanism of titanium alloy,the erosion rate prediction model meeting the probability characteristics was obtained.The deviation between the predicted value and the experimental value of erosion rate corresponding to each impact angle is between 1.4% and 9.0%.The results show that the prediction model has high calculation accuracy.(4)The high-speed rotating sand erosion test of real blade was conducted on,and the distribution of sand erosion position on the blade was obtained,and the blade erosion rate was measured.Combined with the sand injection method,impeller rotating speed and impeller aerodynamic parameters in the high-speed rotating erosion test,the sand erosion position coordinate on blade,the sand impact velocity and angle of the blade in the rotating parts were calculated by using the prediction analysis software of the sand erosion position of the blade in the rotating parts.Through further statistical analysis of the results,the probability model of the sand erosion position,velocity and impact angle impact were obtained.Combined with the relationship between particle size and mass probability,the mass distribution was calculated from the known particle size distribution.On this basis,the impact conditions such as impact velocity,angle,kinetic energy,fracture rate were calculated by the above probability model.The sand impact condition was substituted into the erosion rate probability prediction model of titanium alloy,and the blade erosion rate was calculated.Based on this,a blade erosion rate prediction method under high speed rotating condition was proposed.The difference between the predicted erosion rate and the experimental results is 3.9% to 8.6%,which shows that the method has high accuracy and can be used in engineering design and analysis.The mechanism and law of the high-speed sand erosion damage of the titanium alloy blades obtained by the experimental work in this thesis,and the erosion rate prediction method have important guiding for further improving the blade erosion resistance design and the engine field maintenance in our country. |
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