Modal analysis is a fundamental assessment in the design phase of a nozzle guide vane in a low pressure turbine system. Evaluation is crucial for new concept design but also in case of design modification. The technical requirement is to ensure appropriate durability level (number of flight cycles) and the reliability of the system. An understanding of dynamic behavior is one of the key elements in the high cycle fatigue (HCF) evaluation. Finite element method (FEM) analyses are widely used in new product introduction phases to verify modal characteristics with respect to operating range and engine orders (forcing function, excitation). In the process used 2D representation of the nozzle guide vane approximated by axisymmetric and plane stress with thickness FEM plain elements. The optimization process used geometrical parameters (nozzle outer band and casing shell) and surrogate models to find optimal solutions from a frequency placement perspective. A sensitivity analysis and optimization process revealed casing shell thickness to be a major contribution in the modal response and weight. Excluding casing shell parameters led to a lower frequency shift with respect to the reference configuration. The presented optimization framework is very robust and time effective in completing the optimization task together with a sensitivity analysis for the defined design domain. An FEM model validation of the surrogate model showed consistency in the modal analysis results. A promising solution from the component weight standpoint is the optimization with hook position and leaning only. A future research recommendation is to study an extended parameter range to reduce weight impact for this set.
The aim of the article is to present the approach for modal optimisation of nozzle guide vane in the low-pressure turbine system of aircraft engine. Described analysis assumption related to the finite element model definition, meta-model estimation and optimisation process itself. Goal function has been determined basing on Campbell diagram. Typical approach to solve modal analysis for mentioned structure is full three-dimensional model that is time consuming. For optimisation purposes employed two dimensional one in order to make the process more robust (element types with support of Fourier series). This approach is reducing degree of freedom quantity and is still capable to consider non-axisymmetric structure behaviour. The article provides relationship between geometrical features of nozzle and frequency change.
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