A tool for preliminary design and selection of industrial fans

Industrial fans are used as ancillaries inside complex ventilation systems. Even if fans are energy-consuming, the knowledge gathered in recent decades in the aerodynamic design and optimization of axial-flow compressors was not successfully transferred to the field of axial fans because of lack of interest by manufacturers and not-straightforward applicability of compressors design methods: fans are designed to cover a large operating range with different duty points. The aim of this work is the development of a tool for preliminary design and selection of industrial fans. The design code, named AxDGen, is written in Python and is based on an axisymmetric solution of the indirect problem in which the tangential velocity is specified (by assigning the vortex distribution along the blade) and the axial velocity is computed accordingly by the application of radial equilibrium equation. In addition to the traditional free-vortex assumption, the code can use a series of controlled vortex distributions, in which the prescribed circulation, Euler work and the isentropic total pressure rise increase along the blade. These assumptions offer same potential benefit as a better utilization of blade section at higher radii or a reduction of hub losses by unloading the blade root. The rotor blade design is based on several methods, exploiting a combination of empirical rules, geometrical correlations and design constraints in order to complete the system of equations needed to define the blade geometry. In particular, two new design methods are presented here: they are based on the connection between the prescribed flow distribution resulting from the vortex selection, and the aerodynamic performance of the airfoil. The iterative procedure involving the aerodynamic performance of the profile is based on the Kutta-Joukoski theorem that relates the lift generated by an airfoil to the speed of the airfoil through the fluid, the fluid density and the circulation. Successively the code generates the blade, built by a NACA 4-digit or NACA 65- series. This profile is generated in order to analyze the aerodynamic performance of new blade and to compute the blade polar curves