NUMERICAL ASSESSMENT OF AN OPEN ROTOR 1P LOADS AT TAKE-OFF AND CRUISE

Unsteady in-plane forces, also referred to as 1P loads, are
a critical aspect in open rotor propulsion systems due to their
influence on vibration, aeroelastic stability, and structural fatigue.
Their accurate quantification is therefore fundamental
for both aerodynamic performance evaluation and structural design.
This study presents a methodology for assessing 1P loads
and their structural implications using an open-rotor geometry
representative of modern open-fan concepts. High-fidelity
full-annulus CFD simulations were performed for take-off and
cruise conditions, using dedicated meshing strategies to resolve
unsteady flow features at angles of attack of up to 30° and 6°, respectively.
The global loads are decomposed into thrust and inplane
components, with a focus on the 1P harmonic. Unsteady
pressures are then projected onto the first bending mode of the
blade to obtain modal forces, which are coupled with a singledegree-
of-freedom oscillator to predict vibration amplitudes and
alternating stresses. Results show that the projection step is critical,
as global force harmonics alone fail to estimate the effective
dynamic excitation. The approach enables a direct evaluation of
vibration amplitudes, indicating that oscillation amplitudes remain
below 1% of the blade span. This approach provides a
reliable method for the detailed design and fatigue assessment of
open-fan blades.