ISBN 978-3-8439-5821-9

978-3-8439-5821-9, Reihe Ingenieurwissenschaften

Oskar Wengrzyn
Loose and Tight Coupling for Helicopter Airframe Vibration Prediction using High-Fidelity CFD and CSD

153 Seiten, Dissertation Universität Stuttgart (2026), Hardcover, A5

Zusammenfassung / Abstract

This dissertation investigates numerical methods for predicting helicopter airframe vibrations, focusing on the interaction between high-fidelity Computational Fluid Dynamics (CFD) and Computational Structural Dynamics (CSD). It extends a tight-coupling framework with advanced structural dynamics models and develops a novel, computationally efficient loose-coupling approach for cabin vibration prediction.

The tight-coupling framework is first used to assess how structural modeling fidelity affects vibration prediction. A Detailed Finite Element Model (DFEM) of the main gearbox is integrated into the CSD model and compared with a simplified lumped-mass model, showing how gearbox modeling affects vibration transmission to the cabin. Aerodynamic excitation is examined by analyzing the fuselage pressure distribution in the frequency domain.

The second part develops the Loose Structural Coupling (LSC) method, which introduces elastic airframe effects into the CFD domain using comprehensive analysis (CA) codes. By exploiting the periodicity of helicopter aeromechanics, LSC drastically reduces computational cost. Key contributions are a novel load transfer method that represents unsteady aerodynamic loads accurately in the CA code, and a robust methodology for transferring airframe deformations and rigid-body motions back to the CFD domain. The FLOWer CFD solver is coupled with CAMRAD II.

Both strategies are applied to an H145-D3 helicopter in high-speed forward flight and compared. LSC predicts vibrations successfully in parts of the structure, but where the structural response or aerodynamic excitation is non-harmonic or transient, tight-coupling is required. LSC is therefore suited to early design phases, tight-coupling to detailed analysis in the final design stages. The work provides a validated, multi-fidelity toolchain for rotorcraft aeromechanics, allowing engineers to balance computational efficiency against physical accuracy.