**2. CFD setup**

Generic settings required for setting up any CFD requires the three basic processes:


#### **2.1 Preprocessing**

The object of the study was C-130, and its CAD model was acquired from FlightGear database, which is an open-source platform. Preprocessing involves CAD import, generating and optimizing mesh using various techniques, physics, and environmental settings. The CAD model is imported using inbuilt feature which only supports listed file formats. In this study ".stl" format file is used from CAD software.

Note: It is worth noting here that STAR-CCM+ requires considerable computer hardware resources to work in a faster pace. Loading times, mesh generation, and simulation times are significantly reduced with improvement in hardware. It has been tested by running same simulations at different desktop configuration machines and noticed significant reduction with respect to elapsed time.

After successful importing, the CAD model is visible in current scene. The next step is to generate mesh. "STAR-CCM+ has all-around mesh generating feature that creates unstructured form fitted finite volume meshes of fluid and solid domains. Software is designed such that mesh generation is automatically informed by the surface tessellation and CAD elements defining the geometry, such as local curvature, surface proximity, and retained feature elements, and is further controlled by user-specified meshing parameters. The latter are organized into a hierarchy of global specifications and local refinements that enables precise control to achieve cell quality metrics, such as skewness, connectivity, conformity, near-wall cell

properties, and growth rate with the smallest practical mesh even for exceptionally intricate geometries. STAR-CCM+ also employs a face-based solver technology uniquely designed to recognize arbitrary polyhedral cell topology [9]."

conditions, then the simulations are processed for examination of the applied conditions. Here, the air properties, other physical conditions, result extraction for aerodynamic coefficients, and graphical depiction of iterated data were selected. Physical condition and fluid dynamics models implemented are listed below:

*Development of the Flight Dynamic Model (FDM) Using Computational Fluid Dynamic (CFD)…*

The aerodynamic coefficients generated in the final report were as follows:

*Cl* ¼ roll moment coefficient *Cm* ¼ pitch moment coefficient *Cn* ¼ yaw moment coefficient

*CL* ¼ lift coeffeicient *CD* ¼ drag coefficient

*CY* ¼ side force coeffeceint

These parameters were set up, and each case of simulation had certain control surface deflection and angle of attack. For a four-engine turboprop transporter aircraft, 372 cases were chosen. These cases proved to be sufficient for attaining high-fidelity flight dynamic model for aircraft simulator. The air speed was kept constant at 220 knots and at an altitude of 5000 feet. Air density and viscosity were set up accordingly. After all these steps, the CFD software is ready for analysis. By simply clicking on run button on the top pane, STAR-CCM+ starts running iteration

• All y+ wall treatment

*DOI: http://dx.doi.org/10.5772/intechopen.91895*

• K-Omega turbulence

• Segregated flow

• Steady

• Turbulent

• Wall distance

• Proximity interpolation

• Segregated fluid isothermal

and plots the results simultaneously.

**151**

• SST (Menter) K-omega

• Three-dimensional

• Reynolds-averaged Navier-Stokes

• Constant density

• Gas

• Gradients

For meshing user-specified parameters that were assigned are shown in **Table 2**, these were values adopted for a four-engine turboprop transporter aircraft.

**Tables 2** and **3** values were evaluated after repetitive attempts to achieve a welldefined and fine mesh at zero angle of attack steady flight. After running meshing method, software generated approximately 12 million cells in the mesh. The process of meshing was repeated with mild tweaks in values for every case of angle of attack and control surface deflections. For each case of flight profile, the number of cells in a mesh increases with changes in angle of attack, sideslip, and various configurations of control surfaces.
