## 2 CFD Analysis
### Analysis of Pressure, Flow, and \(c_{p}\) Distributions  
To estimate the largest aerodynamic load on the profiles, extreme flight conditions were first defined based on the load factor Nz: For cruise profiles with retracted trailing edge, three conditions for Nz = 2.5 (climb) and one for Nz = 1 (level flight), for high-lift profiles with extended trailing edge, three conditions for Nz = 2.0 (climb). These are listed in Table 2.  
In these extreme conditions, 2D CFD analyses were carried out. The simulated pressure and flow (left hand side) and \(c_{p}\) distribution or dimensionless pressure normalized by dynamic pressure (right hand side) around cruise profile S5 are shown in Figure 5. Those around high-lift profiles S5 HL are shown in Figure 6. The maximum suction on the upper side of four profiles S4, S5, S4 HL, and S5 HL represented by \(c_{p}\) and the actual pressure in kPa are listed in Table 3. These data were used for examining required strength, stiffness, and actuation forces for the morphing system being developed, see Section 4.2.  
From these pressure distributions, the following conclusions were drawn. Suction on the upper side near the LE is increased along with AoA. Namely, the largest suction occurs in condition I for the cruise profiles and in condition I\({}^{\prime}\) for the high-lift profiles. The suction peak is located at the leading edge where the highest velocity occurs due to the deflection of the flow direction induced by the aerofoil. At level flight or in condition IV, a large suction peak occurs just under the stagnation point on the lower side. This is especially prominent for profile S5 HL having the fully lowered LE. This is again because of  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Profiles** & **BLHL** & **S4 HL** & **050 HL** & **SSHL** \\ \hline Max Lift Coeff. & 2.80 & 2.69 & 2.91 & 3.06 \\ Stall Angle/\({}^{\circ}\) & 14.2 & 13.2 & 15.0 & 16.4 \\ \hline \hline \end{tabular}
\end{table}
Table 1: List of maximum lift coefficients and stall angles.  
Figure 4: Calculated lift (**a**) and drag (**b**) coefficients for high-lift profiles.  
large acceleration of the flow turning around this point. On the other hand, the positive \(c_{p}\) peak occurs at the stagnation point. The value of this peak, which is nearly 1, implying dynamic pressure, is independent of the AoA.  
Figure 5: Pressure and flow (**left**) and \(c_{p}\) distribution (**right**) for cruise profile S5 in four extreme conditions.  
Figure 6: Pressure and flow (**left**) and \(c_{p}\) distribution (**right**) for high-lift profile S5 HL in three extreme conditions.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Profile** & **Condition** & **Max Pressure Coefficient cp** & **Max Suction (kPa)** \\ \hline \multirow{4}{*}{S4} & I & \(-\)4.53 & \(-\)21.2 \\  & II & \(-\)2.51 & \(-\)16.3 \\  & III & \(-\)1.21 & \(-\)12.3 \\  & IV & \(-\)0.82 & \(-\)7.7 \\ \hline \multirow{4}{*}{S5} & I & \(-\)3.57 & \(-\)16.7 \\  & II & \(-\)2.22 & \(-\)14.4 \\  & III & \(-\)1.25 & \(-\)12.7 \\  & IV & \(-\)2.62 & \(-\)24.5 \\ \hline \multirow{4}{*}{S4 HL} & I\({}^{\prime}\) & \(-\)6.48 & \(-\)20.7 \\  & II\({}^{\prime}\) & \(-\)3.79 & \(-\)15.8 \\  & III\({}^{\prime}\) & \(-\)2.45 & \(-\)12.9 \\ \hline \multirow{4}{*}{S5 HL} & I\({}^{\prime}\) & \(-\)4.82 & \(-\)15.4 \\  & II\({}^{\prime}\) & \(-\)3.14 & \(-\)13.1 \\ \cline{1-1}  & III\({}^{\prime}\) & \(-\)2.24 & \(-\)11.8 \\ \hline \hline \end{tabular}
\end{table}
Table 3: List of suction peak values in extreme conditions.