Abstract
An axial flow fan, which is applied for ventilation in underground spaces such as tunnels, features a medium–large size, and most of the blades go through the casting process in consideration of mass production and cost. In the casting process, post-work related to roughness treatment is essential, and this is a final operation to determine the thickness profile of an airfoil which is designed from the empirical equation. In this study, the effect of the thickness profile of an airfoil on the performance and aerodynamic characteristics of the axial fan was examined through numerical analysis with the commercial code, ANSYS CFX. In order to conduct the sensitivity analysis on the effect of the maximum thickness position for each span on the performance at the design flow rate, the design of experiments (DOE) method was applied with a full factorial design as an additional attempt. The energy loss near the shroud span was confirmed with a quantified value for the tip leakage flow (TLF) rate through the tip clearance, and the trajectory of the TLF was observed on the two-dimensional (2D) coordinates system. The trajectory of the TLF matched well with the tendency of the calculated angle and correlated with the intensity of the turbulence kinetic energy (TKE) distribution. However, a correlation between the TLF rate and TKE could not be established. Meanwhile, the Q-criterion method was applied to specifically initiate the distribution of flow separation and inlet recirculation. The location accompanying the energy loss was mutually confirmed with the axial coordinates. Additionally, the nonuniform blade loading distribution, which was more severe as the maximum thickness position moved toward the leading edge (LE), could be improved significantly as the thickness near the trailing edge (TE) became thinner. The validation for the numerical analysis results was performed through a model-sized experimental test.
Highlights
An axial flow fan is one of the most important pieces of fluid machinery helping the circulation and ventilation of air in various industrial sites
The equations are based on the conservation laws for mass, momentum, and energy; this study focused on the isothermal condition, allowing the equation for the such as large pipes, fans, wind tunnels, or ventilation flows [34]
The whole process and the facilities for the experimental test were fully implemented in accordance with the international standard, ANSI/AMCA 210-07 [35]
Summary
An axial flow fan is one of the most important pieces of fluid machinery helping the circulation and ventilation of air in various industrial sites. The direction for the suction and discharge of the working fluid (air) is parallel to the shaft, and the blades and guide vanes are paired to form a stage. Energies 2020, 13, 5831 raises the total pressure with respect to the working fluid inside an axial fan, and the guide vane is attached as the rear part of the blade to recover the dynamic pressure to static pressure. The pressure acts as a generated energy to transport the working fluid. In cases that require high pressure, additional stages would be added in series as a pair (blade and guide vane). Understanding the aerodynamic mechanism of each part is a basic requirement to predict energy consumption, and the rotating part (blade), which is the main focus of this study, is the most important aspect when designing an axial fan
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