Validation of structural integrity in assembled rotor modules with bolted flange connections using multiple surrogate models

Bolted flange connection structures play a critical role in the assembly of aircraft engines. These structures bring together the fixed and moving parts of the engine, ensuring its safe and effective operation. In the initial stages of the design process, various design parameters such as the dimensions of the flanges, the number and size of the bolts, and their arrangement are considered. The selection of these parameters is made to ensure the structural integrity of the engine. To guarantee structural integrity and identify the most suitable design, comprehensive simulations are conducted using finite element analysis. During operation, the assembled rotor group is subjected to various thermal and mechanical loads. Each of these loads can affect the structural integrity of the rotor group. Therefore, it is essential to ensure that the rotor group meets these integrity criteria under every loading condition. These criteria include stresses, the preloading forces of the bolts, and the condition of contact points. The design process can be complex and time-consuming due to the large number of variables that must be considered. Therefore, various methods are applied to enhance the efficiency of the design process and develop new design approaches. In this study, as described in NASA's E3 High Pressure Turbine Test Hardware Detailed Design Report, a surrogate modeling method for the optimization of bolted flange connection design has been used. This method aims to accelerate the design process and achieve more accurate and effective results. The work was carried out on a rotor group similar to the E3 turbine module, and separate finite element models were developed for each flange. Design parameters were used as inputs for the surrogate models, which were created using Latin Hypercube Sampling (LHS) and Genetic Assembly Response Surface (GARS) methods. Multi-Objective Genetic Algorithm (MOGA) was employed for optimization to achieve optimum designs. The resulting designs were fed into the rotor module, and a comprehensive finite element model of the rotor module as a whole was established. The stress and reaction force values obtained for the flange areas of the rotor module are in agreement with the results from the optimization of the surrogate models, with a difference of only 0.1%. Although there was a mass increase of 3.27% in the optimized first flange area compared to the initial condition, the desired minimum flange reaction force for complete torque transfer could not be achieved in the fifth loading step of the initial flange area configuration. Improvements were observed in the stress levels of three holes in the first flange, with reductions of 5.10%, 3.03%, and 1.75%, respectively, compared to the initial condition. For the second flange area, there was a mass increase of 2.97% and a worsening of stresses by 1.94% in the middle hole area of the second flange. Similarly, the initial configuration of the second flange area could not provide the necessary flange reaction force. For the third flange area, due to the more flexible criteria defined in the design report, the optimization efforts resulted in a mass reduction of 13.66% and improvements in the stresses of the flange holes by 15.60%, 5.12%, and 4.89%, respectively. The results demonstrate that the use of multiple surrogate models in the design of flanged connections for assembled rotor groups enables precision analyses to be conducted in short periods without losing accuracy, and achieving optimum designs that meet structural integrity criteria is possible.