# Assessment of a Mid-Fidelity Numerical Approach for the Investigation of Tiltrotor Aerodynamics
## 3 Numerical Models
### Full Vehicle Numerical Model
Thus, the DUST simulations for the full vehicle were advanced in time using the same time discretisation selected for the single proprotor test case--i.e., 40 time steps for rotor revolution for a total simulation length of ten rotor revolutions. The wake of all the lifting bodies, i.e., the wing, the vertical, and horizontal tailplanes was modelled by vortex particles. The developed wake for the full-vehicle simulations ranges from around 140 thousands vortex particles in hover flight condition to around 80 thousands vortex particles in cruise. The computational time for a single flight condition of the full vehicle was about 80 min. over a workstation that was equipped with a Intel(r) CoreTM i9-9980 XE processor running on a base frequency of 3.00 GHz, with 18 physical cores and 2 threads for each core. In the present work, the DUST simulations analysed the different flight conditions that characterise the tiltrotor mission--i.e., hover, conversion, and cruise. In particular, the flight parameters that were investigated in the CFD works by [PERSON] et al. (2017) and by [PERSON] and [PERSON] (2016) were reproduced in DUST simulations, as shown in Table 4. The main parameters of the aircraft are illustrated in the sketch of Figure 5. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Flight Condition** & \(V_{\infty}\) & \begin{tabular}{c} **Vehicle Pitch** \\ **Attitude (\(\alpha_{V}\))** \\ \end{tabular} & \begin{tabular}{c} **Nacelle** \\ **Angle (\(\theta_{N}\))** \\ \end{tabular} & \begin{tabular}{c} **Rotor Speed** \\ **\(\Omega\)** \\ \end{tabular} & \
\begin{tabular}{c} **Flap** \\ **Angle** \\ \end{tabular} &
\begin{tabular}{c} **Flaperon** \\ **Angle** \\ \end{tabular} \\ \hline Hover & 0 knots & \(0^{\circ}\) & \(90^{\circ}\) & 589 RPM & \(40^{\circ}\) & \(25^{\circ}\) \\ \hline Conversion & 40 knots & \(8.569^{\circ}\) & \(75^{\circ}\) & 589 RPM & \(40^{\circ}\) & \(25^{\circ}\) \\ Conversion & 100 knots & \(2.851^{\circ}\) & \(60^{\circ}\) & 589 RPM & \(40^{\circ}\) & \(25^{\circ}\) \\ Conversion & 140 knots & \(-0.773^{\circ}\) & \(30^{\circ}\) & 589 RPM & \(40^{\circ}\) & \(25^{\circ}\) \\ \hline Cruise & 160 knots & \(4.332^{\circ}\) & \(0^{\circ}\) & 517 RPM & \(0^{\circ}\) & \(0^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Parameters of the full XV-15 vehicle configurations considered for the numerical simulations. Figure 4: Layout of the numerical model of the full XV-15 tiltrotor. The test conditions were considered from the Generic Tiltrotor (GTR) flight simulation data that were provided by [PERSON] [46]. Following the same procedure that was suggested by the CFD works [16; 17] for DUST simulations, the thrust (\(T\)) and H-force (\(H\)) on the wing-mounted proprotors were trimmed to the simulator data [46] by adjusting the rotor collective and longitudinal cyclic pitch angles. The lateral cyclic pitch angle was set to zero for all the simulated configurations, since the lateral cyclic control was not installed on the XV-15. The trim targets for the thrust and H-force of the single proprotor obtained by the DUST simulations are compared to the GTR data [46] in Figure 6 for all the flight conditions tested, as presented in the CFD work by [PERSON] et al. [17]. Moreover, Figure 7 compares the average proprotor torque computed by DUST in these trimmed conditions to the GTR data [46] for all of the flight conditions considered and the flight test data available for the only cruise condition [48]. The quite good agreement of the torque behaviour provides confidence in the accuracy of the numerical models built for the DUST simulations. Figure 5: Definition of the main parameters of the full XV-15 tiltrotor configuration. Figure 6: Trim targets for the proprotor thrust and H-force provided by Generic Tiltrotor (GTR) [46] compared with the results from the trimmed DUST simulations for all the flight conditions considered.