# Assessment of low-altitude atmospheric turbulence models for aircraft aeroelasticity

## TL;DR

This study compares three atmospheric turbulence models to assess their impact on aircraft aeroelastic response predictions, revealing significant differences especially with models that neglect large flow structures at low altitudes.

## Contribution

It introduces a comprehensive comparison of turbulence models of increasing fidelity for aeroelastic load prediction near the ground.

## Key findings

- Large flow structures significantly influence aeroelastic loads.
- Simplified turbulence models underestimate loads on flexible aircraft.
- Full 3D LES models provide more accurate load estimates.

## Abstract

We investigate the dynamic response of flexible aircraft in low-altitude atmospheric turbulence. To this end, three turbulence models of increasing fidelity, namely, the one-dimensional von K{\'a}rm{\'a}n model, the two-dimensional Kaimal model and full three-dimensional wind fields extracted from large-eddy simulations (LES) are used to simulate ambient turbulence near the ground. Load calculations and flight trajectory predictions are conducted for a flexible high-aspect ratio aircraft, using a fully coupled nonlinear flight dynamics/aeroelastic model, when it operates in background atmospheric turbulence generated by the aforementioned models. Comparison of load envelopes and spectral content, on vehicles of varying flexibility, shows strong dependency between the selected turbulence model and aircraft aeroelastic response (e.g. 58\% difference in the predicted magnitude of the wing root bending moment between LES and von K{\'a}rm{\'a}n models). This is mainly due to the presence of large flow structures at low altitudes that have comparable dimensions to the vehicle, and which despite the relatively small wind speeds within the Earth boundary layer, result in overall high load events. Results show that one-dimensional models that do not capture those effects provide fairly non-conservative load estimates and are unsuitable for very flexible airframe design.