## 2 Simulation of 3D Ship Airwake by CFD
### Characteristics of the Airflow Along the Ideal Glide Path  
During an ideal landing, the carrier-based aircraft follows a flight trajectory along the angled deck direction, maintaining a 4\({}^{\circ}\) approach angle with the horizontal plane. Upon successful landing, the tailhook captures the second or third arresting wire, located approximately 70-90 m from the stern. In this study, the ideal touchdown point is defined as being 3 m above the flight deck and 70 m from the stern. The ideal glide path is a trajectory extending backward for a distance of 500 m from the ideal touchdown point, at a 4\({}^{\circ}\) elevation angle along the angled deck direction (which is at a 12\({}^{\circ}\) angle to the take-off deck). The glide path corridor is defined as a cylindrical space with a radius of 30 m centered on the ideal glide path.  
Along the ideal glide path, 3D wind velocity data were extracted at intervals of 3 m within 500 m behind the ideal touchdown point. Figures 5-7 illustrate the transient, time-averaged, and steady 3D wind (headwind, crosswind, and vertical wind, respectively) velocity distributions along the ideal glide path (where X means the distance behind the ideal touchdown point), in which the inflow comes from the bow direction to the ship with a heading angle of 0\({}^{\circ}\) and wind speed of 15 m/s, and unsteady DES-SST computations from 900 time-steps (45 s) to 1000 time-steps (50 s).  
Figure 5: Headwind (u) distribution (transient, time-averaged, and steady) along the ideal glide path for inflow with 15 m/s wind speed and 0\({}^{\circ}\) wind direction.  
Figure 6: Crosswind (v) distribution (transient, time-averaged, and steady) along the ideal glide path for inflow with 15 m/s wind speed and 0\({}^{\circ}\) wind direction.  
It can be observed from Figure 8 that the steady-state results from RANS simulations exhibit airflow structures similar to those of the time-averaged results of DES-SST calculations. Along the ideal glide path behind the ideal touchdown point, the airflow field displays significant complexity, particularly within 200 m behind the carrier stern (from X = 70 m to X = 270 m). The headwind maintains a consistent direction from the bow to the stern, though the wind velocity exhibits some fluctuations; however, crosswind velocity and direction exhibit more complex variations, with wind shear present over the rear deck and wake regions, as well as upwash and downwash components in the vertical direction.  
The complexity of the ship airwake in the glide path corridor arises from the geometric configuration of the carrier stern, turbulent fluid dynamics, and multiple couplings with external environmental factors. While the steady RANS model offers faster computational speed, it struggles to capture the transient characteristics of complex turbulence. In contrast, the DES-SST model provides a more precise turbulent structure, revealing the unsteady characteristics of the ship airwake in the glide path corridor. The complex distribution characteristics of the ship airwake along the glide path, such as strong crosswind shear and vertical wind shear, pose significant risks to the take-off and landing control of carrier-based aircraft/UAVs.  
Figure 8: Three-dimensional wind distribution (time-averaged and steady) along the ideal glide path for inflow with 15 m/s wind speed and 0\({}^{\circ}\) wind direction.  
Figure 7: Vertical wind (w) distribution (transient, time-averaged, and steady) along the ideal glide path for inflow with 15 m/s wind speed and 0\({}^{\circ}\) wind direction.