Determination Of Rotor Permissible Unbalance By Using Dynamic Influence Coefficient

One of the key issues to ensure the competitiveness of gas turbine engines(GTE)is the necessity to increase their specific characteristics,while reducing the size,mass,lifecycle cost,exhaust and noise emission.The consequence of this is the problem of providing the required aggregate resource.Important factor affecting the overall resource is vibration.Therefore,the reduction of vibration activity is a critical task.In turn,one of the main factors that affect the vibration is rotor unbalance,which is formed at the stages of their manufacture,assembly,balancing etc.In the modern literature,there are really few methods for calculating the permissible unbalance,so this paper proposes an innovation method for determining the permissible unbalances using a comprehensive approach,which consists of constructing a mass-inertial model of the rotating machine under study and the use of an analytical dependence linking the permissible vibration level and the permissible rotor unbalance through the dynamic influence coefficient.This method allows to take into account the particularities of an engine design,to determine the most sensitive elements of the rotor,to assess the critical level of permissible unbalance and to verificate existing requirements of permissible unbalance.Also,on the basis of this method,an innovative method of corrective loads distribution for balancing the rotors is proposed,which allows to adjust the operation of the engine at a certain operating mode.This method is demonstrated on a mathematical model of a two-shaft gas turbine engine and the results are compared with the analytical method proposed in ISO.An experimental study that showed the reliability of the results was also made and on their basis.It was revealed that the best scenario of using proposed method of permissible unbalance determining is an addition to existing methods as a verification tool of the results and their correction,because the proposed method allows to estimate only the critical value of permissible unbalance.At the same time,the method of corrective weights distribution on the correction planes meets all expectations and allows to reduce the level of vibration at critical speeds to medium level of vibration.