# A Power Based Analysis for a Transonic Transport Aircraft Configuration through 3D RANS Simulations
## 3 Results and Discussion
### Power Conversion of Wing Body Configuration  
This section aims to illustrate the mechanical power conversion process of the wing body configuration. All power terms listed in Table 1 in the flow field were assessed. For the wing body configuration, the wake energy inflow (rate), \(\hat{\mathrm{E}}_{\mathrm{w,in}}\), for the entire computational domain was zero due to the free stream flow inflow. Shaft power, \(\mathrm{P}_{\mathrm{s}}\), was not involved in this case. The only mechanical power input was the drag power, \(\mathrm{DV}_{\infty}\), and it was used as the reference power for the normalization of power terms in this case. The output power terms of the wing body configuration include the wake energy flow (rate), \(\hat{\mathrm{E}}_{\mathrm{w}}\), and viscous dissipation, \(\Phi\). \(\hat{\mathrm{E}}_{\mathrm{w}}\) was assessed at the survey planes and the outlet plane. The integrand of the wake power, \(\hat{\mathrm{E}}_{\mathrm{w}}\), was visualized at the survey planes, as shown in Figure 12. This figure visualizes the wake power passing through the aircraft and in the downstream flow. Crossing the aircraft, the high-intensity wake power over the body surface is highlighted. This region was thicker than the boundary layer of the body, and it was associated with the wake of the wing root. The original design of the DLR-F6 geometry suffers flow separation issues at the body-wing junction [29], as shown on the bottom right of Figure 12. High-intensity \(\hat{\mathrm{E}}_{\mathrm{w}}\) was also observed in the vicinity of the wing tip, denoting the high wake power of the wing tip vortices. In the downstream region, the intensity of the wake power gradually reduced, and the area of high wake power separated into two parts: the one corresponding to the body wake and the one for wing tip vortices. Figure 12: Contours of the \(\hat{\mathrm{E}}_{\mathrm{w}}\) integrand around the wing body configuration. Viscous dissipation, \(\Phi\), is the sink term of power. As elaborated in Section 2.1, it exists in the viscous region (boundary layer and wake) where the velocity gradient exists. The top plot in Figure 13 illustrates the integrand of the viscous dissipation in the flow field. A high intensity of \(\Phi\) was observed in the region over the airframe surface and in the downstream wake. In the downstream wake, the intensity of \(\Phi\) in the body wake was higher than that of the wing wake. Compared with the wing wake, the body wake might be less stable, and its mechanical energy dissipated at a faster pace. This study visualized the change in power terms by placing their values at the corresponding X coordinates, as shown at the bottom of Figure 13. This plot illustrates how the power conversion process occurred in the flow field: drag power, DV\({}_{\infty}\), was transferred into wake power, E\({}_{\rm w}\), as well as viscous dissipation, \(\Phi\). The wake power, E\({}_{\rm w}\), increased quickly after the nose, reaching the peak value (37% of the total power input) after the wing. After that, it dropped quickly after the tail and decreased slowly downstream. The abrupt increase in E\({}_{\rm w}\) was the result of mechanical power accumulation due to the boundary layer, the separated flow in the body-wing junction, and the wing tip vortices. The mild decrease in E\({}_{\rm w}\) downstream of the fuselage corresponded to the dissipation of the aircraft wake. At the outlet plane, E\({}_{\rm w}\) remained 35% of the total power input, indicating a substantial amount of mechanical power in the aircraft wake, as shown in Figure 12.  
Figure 13: The intensity of viscous dissipation and the power conversion process of the wing body configuration. Viscous dissipation, \(\Phi\), remained almost zero before the aircraft nose, mildly increased along the frontal fuselage, and quickly increased through the wing region. In general, it kept increasing from the nose to the tail.