Numerical Investigation of Performance and Flow Characteristics of a Tunnel Ventilation Axial Fan with Thickness Profile Treatments of NACA Airfoil

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.

Suppression of Stall-Induced Instability and Positive Slope at Low Flow Rates of an Axial Fan With Two-Dimensional Anti-Stall Fin

“…In the stalling flow rates (0.4, 0.5, 0.6, and 0.7U d ), it was 60.43, 0.24, 0.24 and 0.20%, respectively. Here, the evaluation of extended uncertainty was performed in a previous study [33].…”

“…where x, Q, P, q, and subscript 2 denote the angular velocity, volume flowrate, total pressure, air density, and blade outlet, respectively and u 2 was assigned for the blade tip. Meanwhile, the axial fan showed a peak point at 0.8U d on the Q-P (or U-W) curve and contained a positive slope in the lower flow rates than 0.8U d [33].…”

Effect of the Radial Velocity Distribution on the Loss Generation of a Contra-Rotating Fan in a Ventilation System

“…They found that optimized velocity distribution could improve the separation distribution and enhance flow stability, which reduced flow losses at the hub and shroud areas. Kim et al [ 10 ] examined the effect of an airfoil’s maximum thickness position on an axial fan’s aerodynamic performance. They summarized that the highest performance could be expected due to narrowed loss region near the hub when the maximum thickness position was at 30% of the chord length.…”

Turbulence Structure and Dynamics Investigation of Turbulent Swirl Flow in Pipe Using High-Speed Stereo PIV Data

“…Numerical models are developed on the basis of these experimental results, but only for specific cases. Researchers have made significant efforts regarding the complex research of the axial fans and their applications in various systems [1][2][3][4].…”