# An Automated Framework for Streamlined CFD-Based Design and Optimization of Fixed-Wing UAV Wings
## Appendix A.2.4 Feature Recognition
### Solution Module-Solution Setup  
At the core of CFD lie the Navier-Stokes equations (momentum conservation), the continuity equation (mass conservation), and the energy equation, which govern the behavior of the fluid flow. For the incompressible low-Mach number flows over wings considered in this work, the energy equation is omitted due to the absence of significant compressibility effects and heat transfer [41]. As previously mentioned in Section 3, the k-omega SST is selected as the turbulence model, with its parameters kept to the default values recommended by [PERSON]. Regarding more specific solver settings, the framework incorporates the following key aspects:  
* **Gradient Correction:** According to [PERSON] et al. in [48], the _\"fast-mode warped face gradient correction\"_ option supported by Fluent is enabled due to the unstructured hexahedral type of mesh generated by the mesh module. This option improves the accuracy of gradient calculations on unstructured or highly distorted meshes.
* **Solution Scheme:** The SIMPLE (Semi-Implicit Method for Pressure Linked Equations) solution scheme is utilized within this computational framework. The SIMPLE scheme strikes a balance between computational efficiency and numerical stability, making it well-suited for steady-state external aerodynamic simulations. Compared to other algorithms, the SIMPLE scheme's less stringent requirements on relaxation and computational resources align with the focus on automating simulations within a broad design space.
* **Initialization:** In this work, hybrid initialization is employed as the default approach due to its robustness and efficiency in complex aerodynamic problems. Hybrid initialization combines elements of potential flow solutions and mass-weighted averages to provide a physically realistic starting point for the flow field, minimizing the computational effort required for convergence.
* **Materials:** The state of the material (air) specified for the simulation is determined based on the atmospheric model _\"U.S. Standard Atmosphere 1976\"_[73]. In this model, air properties are defined as functions of altitude. These relationships have been implemented within a Python class called _atmosphere_, enabling direct access to or the calculation of air properties based solely on the specified altitude.
* **Boundary Conditions (BC):** Inlet and outlet BCs are dependent on the angle of attack of the wing. Simulations are performed across a wide range of AoAs to capture the complete drag polar. To account for the changes in the flow field due to varying AoAs, the _\"Upper Far-Field\"_ and _\"Lower Far-Field\"_ PIDs are adjusted accordingly.  
At a _\"Velocity-Inlet\"_ boundary, the freestream parameters must be specified, including the freestream velocity, pressure, and the freestream turbulent characteristics. The freestream velocity is defined component-wise, taking into consideration the angle of attack (\(\alpha\)). According to [PERSON] and [PERSON] in [74], while using the k-omega SST model, the turbulence intensity (\(Tu\)) and turbulence viscosity ratio (\(\beta\)) are calculated from Equation (A4).  
\[Tu=0.0008165\text{ and }\beta=2\times 10^{-7}\;Re\] (A4)  
Similarly, the _\"Pressure-Outlet\"_ BC requires specifying the turbulence characteristics of the outflow, as defined above, along with a gauge pressure set to zero to represent atmospheric conditions at the outlet.