Thermoelastic Analysis of Compressor Spool in Turbojet Engine and Redesign it Using Functionally Graded Materials with Opti-mal Coefficients

In this article, an exact analysis of compressors spool in a turbojet engine has been investigated. The spool is modeled as a rotating thick-walled hollow circular cylinder with free-clamp ends. It is subjected to centrifugal load due to its constant rotational speed, uniform internal and external radial loads and arbitrary thermal gradients. The analysis is initially investigated for the homogeneous state. Then FGM state is investigated to improve the safety factor of the spool. In order to calculate the safety factor, Von-Mises criterion has been used. In FGM state, thermoelastic properties of material would vary in radial direction. The function of these properties changes is assumed exponential. To obtain the highest safety factor, the numerical optimization method has been used and the optimal results have been compared with the homogeneous state. To drive the relations for free-clamp ends boundary condition, at first spool is considered clamp-clamp ends. Then, the effect of releasing one of the ends has been calculated and finally, using the principle of superposition, the results for clamp-free ends state has been investigated. In addition, the effect of changing the non-homogeneous coefficients, spool rotating speed, radial loads and thickness on the safety factor are investigated. Increasing the thickness and radial loads would lead to a change in the optimal coefficient and would result in reducing the safety factor of optimum state. The results showed that utilization of FGM state with optimal coefficient could significantly increase the safety factor and reduce displacements. Furthermore, increasing the rotation speed and radial loads would result in a change in the optimal non-homogeneous coefficient and reduce its equivalent safety factor.