# Assessment of a Mid-Fidelity Numerical Approach for the Investigation of Tiltrotor Aerodynamics
## 4 Results and Discussion
### Wing-Prorotor Simulations
#### 4.1.1 Wing Effect on Prorotor  
Firstly, the effect of the wing on the global loads acting on the proprotor is investigated. Table 5 presents the comparison of the average thrust and power variations acting on the proprotor when the wing is installed, where the DUST values are evaluated by averaging the loads that are computed over the last two rotor revolutions. Figure 7: Comparison of the proprotor torque computed by DUST with GTR [46] and flight test data. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**CFD**} & \multicolumn{2}{c}{**DUST**} \\ \hline  & \(\Delta\) & \(\Delta\) \% & \(\Delta\) & \(\Delta\) \% \\ \hline Thrust [lbs] & 104 & 12.7 & 64.5 & 7.9 \\ Power [hp] & 64 & 8.1 & 41.7 & 5.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Comparison of the average proprotor global thrust and power variations due to the wing installation, \(\alpha=5^{\circ}\), \(V_{\infty}=220\) kts, \(\Omega=517\) RPM. The comparison of the average loads shows that DUST correctly captures the increase in both the proprotor thrust and torque due to the wing installation, coherent with the physics of the aerodynamic interaction. Only a slight underestimation of the load variation is observed with respect to CFD. This issue could be related to the relatively lower spatial discretisation used to model the blades and to the lower accuracy of the numerical model with respect to CFD. Moreover, Figure 8 shows the comparison of the variations in the rotor thrust and power calculated with the wing installed with respect to the single proprotor test case over the last rotor revolution. The behaviour of the time histories of the delta load curves that were provided by DUST clearly underlines the interference effect provided by the wing, as shown by the three peaks related to the passage of the three blades in front of the wing. These trends reproduce the results of CFD quite well, with small discrepancies concerning the amplitude of the delta values of both rotor thrust and power. Figure 9a,b show a comparison of the contours of the blade non-dimensional normal force (\(M^{2}c_{n}\)) computed over the last rotor revolution when the wing is installed in order to provide a detailed insight into the rotor/wing aerodynamic interaction effect on the local blade airloads. The DUST simulation results clearly show the doublet of the blade  
Figure 8: Comparison of the time history of the proprotor global thrust and power variations due to the wing installation, \(\alpha=5^{\circ}\), \(V_{\infty}=220\) kts, \(\Omega=517\) RPM. normal force occurring in the region of azimuth around \(\psi=270^{\circ}\) due to the passage of the blade in front of the wing. The global behaviour of the normal force contour plot is quite similar to the one computed by CFD, thus showing that lifting line modelling that is based on the use of tabulated aerodynamic sectional data considering viscosity effects is able to capture the variations in propropt blade performance due to interactional flow phenomena. A more quantitative comparison is provided by Figure 9c,d, showing, respectively, the time histories of the blade \(M^{2}c_{n}\) computed for different radial stations in the outer region of the blade span and the radial distributions of the blade \(M^{2}c_{n}\) computed for different azimuthal angles of the blade along the last rotor revolution. In particular, the comparison of the normal force time histories evaluated for all the three considered blade radial positions shows that DUST captures well both the amplitude and phase of the force doublet due to the blade passage computed by high-fidelity CFD.