Structural Dynamics Optimization of Rotor Systems for a Small-Size Turboprop Engine

This paper presents the results of the rotordynamic analysis and design optimization performed for a turboprop engine-rotor system consisting of a free-power turbine and a gas generator. Predictions of static stresses, natural frequencies, and amplitudes are obtained by the in-house finite-element code. A detailed analysis of the finite-element method model (various beam formulations, three-dimensional axisymmetric model, point masses, and one-dimensional rigid disk elements) is provided. A sizing optimization problem of total shaft mass minimization is considered. Design variables are inner radii and wall thicknesses of shaft sections. Constraints are imposed on static stresses, natural frequencies, and amplitudes of the unbalance response. Changes in design variables are constrained to avoid contacts between the shafts of the twin-spool configuration. An in-house implementation of the sequential quadratic programming method is coupled with hybrid, analytical and numerical, sensitivity analysis. Results of the optimization show that a significant mass reduction in comparison with the baseline configuration can be achieved with all constraints being simultaneously satisfied. The optimal designs, however, must be finalized to meet other requirements not considered during the optimization. The Campbell diagram of the free-power turbine rotor system is significantly affected by the optimization.