*2.4. Meshes*

As a full-scale 3D channel section simulation was analyzed, considering many elements installed in the channel, such as vanes and a turbulence flap, which require adequate calculation accuracy, so the implemented mesh is relatively large. The work performed a grid sensitivity analysis, examining grids with the following estimated number of elements: 5.5 × 106, 11 × <sup>10</sup>6, 17.3 × <sup>10</sup>6, 29 × <sup>10</sup>6, 46 × <sup>10</sup>6. The grid element count varies slightly between the analyzed cases, which is a direct result of the different turbulence flap geometries. In investigating the mesh sensitivity, several numerical simulations were performed analyzing parameters such as the final residual sum, mass, energy balance, maximum and minimum temperatures in the domain and pressure drop in the channel. The most reliable results were obtained for grids with 17.3, 29 and 46 million elements. Meshes with approximately 29 million elements were selected for further analysis because the parameters analyzed were highly reliable. The differences between the values obtained in the simulation with the 46 million grid did not exceed 1%. The chosen computational grid is shown in Figure 5.

**Figure 5.** Computational grid of geometry G2 with a zoomed-in view and named selection marked.

As previously mentioned, the analyzed channel section contains many installed irregular-shaped flow control elements that significantly influence the simulation results. Therefore, an unstructured mesh was used in the computational domain, introducing the necessity of using more computing power. The mesh was given appropriately named selections corresponding to the boundary conditions described in the following subsection. The named regions are also shown in Figure 5.
