Session: 36-01 Preliminary Design and Structural Optimisation

Paper Number: 151707

Enhancing Blade Durability to Foreign Object Damage Through Multidisciplinary Design Optimization 

Foreign Object Damage (FOD), caused by ingesting hard particles such as small stones or debris during flight, remains a persistent and critical challenge for aero engines due to its inevitability and severe consequences. Despite ongoing efforts to understand and mitigate FOD, there is still a significant gap in research focused on designing airfoils with improved resistance. This work aims to address that gap by developing new design guidance to enhance the FOD robustness of aero-engine airfoils while preserving their aerodynamic performance. However, design modifications intended to improve structural robustness often negatively affect the aerodynamic behavior of individual airfoils and their interaction with neighboring stages. To balance these competing requirements, this work employs a multidisciplinary optimization approach.

The study uses the 1.5-front stage of an 8-stage axial compressor as a test case. The goal is to enhance the FOD robustness of the rotor blisk while restricting the aerodynamic investment and keeping the airfoils of the upstream IGV (Inlet Guide Vane) and downstream stator unchanged. The first step in performing the aero-structural optimization is developing a multidisciplinary process chain to assess both structural mechanics and aerodynamics. This involves parallel numerical simulations: FEM for structural evaluation and CFD for aerodynamic performance. These simulations provide the metrics that define the constraints and objective function of the optimization problem. In the structural mechanics workflow, static and modal stresses are evaluated and combined to determine the allowable stress concentration factor (Kt), representing the allowable stress increase due to localized damage, such as FOD impact. Therefore, the overall objective of improving airfoil robustness is reflected in the optimization goal to maximize Kt in regions of the airfoil with a high probability of FOD occurrence. Simultaneously, the flow behavior across the 1.5-stage compressor is modeled using the Reynolds-Averaged Navier- Stokes equations. Key aerodynamic performance parameters, such as stage efficiency and pressure ratio, are constrained to ensure that the optimized design maintains its aerodynamic performance. The optimizer adjusts the airfoil geometric parameters derived from an initial parameterization of the 2D airfoil section and the radial stacking line. These free design variables are fine-tuned to improve structural robustness without reducing the aerodynamic performance beyond the set boundaries. The optimization is carried out using AutoOpti, a multiobjective evolutionary algorithm developed at the DLR's Institute of Propulsion Technology. To accelerate and improve the optimization process, the high-fidelity Kriging surrogate model is employed. This model enables faster evaluations by approximating the objective function, thereby reducing the computational cost of the high-fidelity simulations.

The primary outcome of this work is to provide design guidance for enhancing the FOD robustness of rotor airfoil. This is accomplished by analyzing two optimized designs generated by the optimizer. The investigation focuses on identifying the key design variables that improve structural robustness while minimizing the impact on aerodynamic performance and the matching with neighboring rows.  Additionally, off-design assessments are conducted to evaluate the surge margin, ensuring the optimized designs maintain stable operation under various conditions.

This work aims to contribute to a deeper understanding of how design modifications affect airfoil robustness and overall aero-engine performance, offering valuable considerations for future airfoil design.

Presenting Author: Simona Rocchi Technical University of Munich

Presenting Author Biography: Simona Rocchi is a PhD student at the Chair of Turbomachinery and Flight Propulsion at the Technical University of Munich. Her interest in this field began during her studies in Aerospace Engineering at the Polytechnic University of Turin, where she obtained her master’s degree in 2020. Specializing in turbomachinery and flight propulsion, she deepened her expertise through her master’s thesis at the Technical University of Munich. She is now pursuing her PhD in collaboration with MTU Aero Engines, focusing on multidisciplinary optimization to enhance FOD robustness of compressor airfoil.

Authors:

Simona Rocchi Technical University of Munich
Adam Koscso MTU Aero Engines AG
Volker Gümmer Technical University of Munich