Validation of a dynamic inflow model based on a flight dynamics model and a Lattice-Boltzmann fluid solver using flight test data

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Bludau, J.
Rauleder, J.
Hajek, M.
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A fully-coupled, real-time-capable fluid dynamics/flight dynamics simulation was developed, that is validated against flight test data measured with a MBB Bo-105 helicopter. The highly-efficient Lattice- Boltzmann based fluid dynamics solver and the blade element based flight dynamics code were coupled through the rotor thrust and inflow. This dynamic inflow model extracted the inflow velocities from the computed flow field and passed them to the flight dynamics code to predict thrust and rotorcraft motion. The local rotor thrust was imposed on the fluid cells comprising the rotor disk. The advantage of this two-way coupled approach is that it enables the real-time calculation of the flow environment and the dynamic inflow into the rotors without prior knowledge of the flow field, and it allows to model the influence of arbitrary moving objects in the vicinity of the rotorcraft on the fluid mechanics and flight dynamics at simulation run-time. Power requirements and controls in trimmed stationary forward flight were predicted well by the new model. The on-axis response of the helicopter to pilot step inputs also correlated well with the flight test data. The off-axis response showed the correct trends, but the amplitudes were mostly underpredicted. This underprediction was similar to results obtained using the Pitt-Peters inflow model instead of the new modeling approach. The results gave confidence in the developed computational model, although areas for improvement were also identified. In the longer term, this new modeling approach may enable more realistic pilot training for challenging operations such as ship deck landings, where rapid changes to the flow field and the environment around the rotorcraft affect its flight dynamics.