| In the trend of reducing carbon dioxide emissions and improving fuel efficiency,turbocharger has become the necessary equipment for most fuel engines.The rotor is the core part of turbocharger,which is widely used.For the high-speed rotating turbocharger rotor,stable operation is necessary and very important.Due to the harsh working environment of the turbocharger,the high-temperature exhaust gas emitted by the engine will transfer a large amount of heat to the turbine impeller and pass it to the compressor impeller through the rotating shaft.However,the compressor impeller is in a normal temperature environment,which causes the rotor to generate a larger temperature gradient.The rotor is composed of a variety of materials,and its material properties will change with the change of temperature.As the speed increases,it will affect the dynamic characteristics of the rotor.If it is operated for a long time,it will cause rotor resonance and the rotor will be destroyed.Therefore,understanding the temperature dynamic characteristics of the rotor under field action is very necessary.According to the actual structure and working conditions of the turbocharger rotor,a three-dimension model of the turbocharger flow field and a rotor model are constructed.For the purpose of studying the dynamic characteristics and structural optimization of the rotor under the action of temperature field,the mathematical model and the finite element model of the rotor under the steady-state flow field are established.In the CFX software,the conjugate heat transfer method is used to calculate the rotor temperature distribution under multiple operating conditions,and the feasibility of the numerical simulation of heat transfer is verified by the turbocharger performance test experiment.The calculated value of the rotor temperature distribution is derived in the form of a node number,which is used for the subsequent rotor finite element simulation calculation.The stiffness and damping coefficient of nonlinear oil film are calculated by dyrobes software,which are used to simulate floating ring bearing.The temperature value of the rotor in the form of node number is inserted into the rotor finite element by using "commands" high-level instruction to calculate the dynamic characteristics of the rotor under the action of normal temperature environment and multi working condition temperature field.The results show that the temperature field has little influence on the first critical speed,and reduces the second,third and fourth critical speeds,resulting in the reduction of the rotor's operating range.The threshold value of the stability limit speed of the rotor is reduced,so that the rotor enters the unstable region ahead of time,and the instability occurs.Through rotor optimization research,the factors that affect the rotor's dynamic characteristics are revealed,and the optimization goals are determined according to the critical speed and the stability limit speed.Three optimization schemes are proposed to increase and shorten the length of the shaft and increase the diameter of the shaft.In order to save calculation time,the rotor dynamic characteristics of the three optimization schemes at room temperature are analyzed,and the final optimization model is determined by comparative analysis.The determined optimization model is imported into CFX software and finite element recalculation and compared with the original model.It is confirmed that the optimized critical rotor speed and stability limit speed are increased by 10.22% and 5.98%. |
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