Features of flows numerical modelling in Z-shaped elbows of ventilation and air conditioning systems of buildings and structures
Problem statement. When developing ventilation systems, the main difficulty lies in determining the resistance of shaped parts connected in a combination of two or more elements. If two consecutive 90° elbows are located close, a Z-shaped configuration of the unit is possible. The hydraulic resistance of such a node is not equal to the sum of the resistances of the individual components and largely depends on the distance between them. To conduct their modelling in a previously unexplored three-dimensional setting is of interest. The purpose of the research is to conduct numerical studies using the computational fluid dynamics complex AnsysFluent to select the most optimal structure of the computational grid, parameters of the numerical scheme, configure the turbulence model options, control the convergence process of the solution for the problems of airflow in a rectangular duct with a shaped element in the form of a «sharp» Z-shaped elbow. Results. As a result of checking the non-stationary formulation of the problem, it is showed that the difference from the known experimental values of the local resistance coefficient is about 5-20 %, for the stationary formulation - 1-5 %. As a model of turbulence, the «standard» k-s model of turbulence with «enhanced wall treatment» is proved to be suitable. For boundary conditions, the choice of a uniform and developed velocity profile at the input boundary, as well as setting the turbulence intensity and relative turbulent viscosity instead of kinetic energy and dissipation, leads to the same result - the difference between the local resistance coefficient and the reference data is no more than 5-10 %. Conclusions. The significance of the results for the construction industry is in the development of a «numerical scheme» of the solution for studies of flows in channels with complex units of shaped elements, which allows to determine the shape of the vortex zones and to develop aerodynamically improved designs of such shaped elements of ventilation systems.