Modeling of industrial ventilation systems: design issue of 3D computational mesh

Numerical simulation of gas dynamics flows is the basis of the study of air currents and ventilation devices, aspiration problems. Therefore, an important task is construction of numerical grids for geometrically complex industrial premises using computer-aided design system. The main problem discussed in the article is converting threedimensional models composed of basic shapes (rectangles, cylinders, hemispheres, cones, and pyramids) to regular rectangular grids with the choice of boundary conditions for all facets of each cell. A regular rectangular grid is chosen to use for large industrial facilities due to its access pattern which fits for parallel processing on GPU well. Disadvantages of used grid type appear in representation of rounded and inclined shapes. Graphic user interface of developed software allows constructing threedimensional models composed of basic shapes with definition of boundary conditions for each surface of them. Four types of boundary conditions are supported for separate definition of three variables (velocity, pressure, and temperature) in ghost cells. The algorithm to obtain computational grid consists of three stages. At first there is searching of cells which are inside userdefined shapes. These cells need to have boundary conditions for each facet. To determine whether the cell is inside the shape cell center is brought to coordinate system of this shape. The next step is fulfilling constraints which demand that every cell must have at least one neighbor cell of the same type (either computational or ghost) along each axis. The final step is defining of boundary conditions for each facet of ghost cells. A facet gets boundary conditions from shape surface which is nearer in space and in angle between perpendiculars (facet normal and surface normal). Sample workshop with dimensions $320 \times 90 \times 42$ m is described to examine developed software. Modelled velocity and temperature distributions after $60$ seconds are provided.