Effects Of Different Loads On Combined Compressor Rotors’ Strength

Axial-centrifugal combined compressors are widely used in small aero engines.Predicting the strength of the rotors accurately is important for improving the reliability of the compressor design.The rotors suffer the combination function of centrifugal load,thermal load and aerodynamic load when the compressor is working.Investagating the influence of different loads on the strength of combined compressor rotors and find its principle and mechanism can offer a basis for computing the strength of compressor rotors accurately in different design phase.In this paper,a conjugate heat transfer analysis is used to calculate the flow field of the compressor and the temperature field of the rotors to obtain the aerodynamic load and thermal load of the compressor.Then a flow-solid coupling method is used to calculate the strength of the rotors under different loads.After comparision and analysis,the mechanism and principle of the influences of different loads on the stress and modal of the combined compressor rotors are obtained.Investigating the influences of different loads on the multistage axial compressor rotors of the combined compressor shows that centrifugal load is decisive to the total stress,and the proportion of centrifugal stress to total stresses is always above 80%.Centrifugal load also has a big influence on the modal,and will increase the harmonic frequency of the rotors.Thermal load mainly influence the stress of the front stage rotors,and the propotion of thermal stress to total stress can be 20%.Thermal load influence the modal of the rotors by temperature and thermal stress.Both of which decrease the harmonic frequency of the rotors,as the temperature increase,the influence of the temperature is much larger than that of the thermal stress.The propotion of aerodynamic stress to total stress is usually under 4%,but can be much bigger where the blade is thin.The influence of aerodynamic load on the rotor’s modal is very small and can be ignored.Investigating the influences of different loads on the strength of the centrifugal impeller of the combined compressor shows that,for a same working condition,the stress caused by centrifugal load varies with the inlet conditions,and is only 40% of the total stresses when the inlet temperature is low but can be above 90% when the inlet temperature is high.The centrifugal load has a big influence on the modal,and it increase harmonic frequency the impeller except for the first order.The influence of thermal load on the stress also veries with the inlet conditions,and when the inlet temperature is low,the propotion of thermal stress to total stress can be 60% and is less than 10% when the inlet temperature is high.The influence of the temperature on the modal of the impeller is big and is in the same order with that of the thermal stress.Aerodynamic load has little influence on the stress of the impeller;the influence of aerodynamic load on the impeller’s modal is very small and can be ignored.Thus,in the conceptional design phase,for axial compressor rotors,the calculation of the stress can only consider the centrifugal load,but for centrifugal impeller,thermal load should also be considered.The calculation of the modal for both for axial and centrifugal rotors can only consider the centrigual load.In the preliminary three-dimensional design phase,centrifugal and thermal load should be considered in the calculation of stress for both axial and centrifugal rotors.In the calculation of madal,for axial rotors,the influence of centrigual stress and temperature should be considered,for centrifugal impeller,the influence of thermal stress should also be considered.In the optimized three-dimensional design phase,all the three loads should be considered in the calculation of the strength of the combined compressor rotors.