Session: 10-01 Fan Aerodynamic Design

Paper Number: 154241

Effects of Blade Solidity and Aspect Ratio on a 0.5 Hub-to-Tip Ratio Tube-Axial Fan 

Blade solidity and aspect ratio are the two geometrical parameters that bridge the fan preliminary design – which defines the basic size and rotational speed of the rotor as well as the shape of the fan meridional geometry – with the aerodynamic design of the blade – which defines the shape of the rotor blade channels. In spite of the well-acknowledge fact that the selection of solidity and aspect ratio values strongly affects the maximum efficiency achievable by a fan design, there are very few contributions in the recent literature dealing with this fundamental aspect of the preliminary design. Few years ago, the present authors started investigating the topic with a rather comprehensive experimental campaign focused on 0.2 hub-to-tip ratio propeller fans with rotor blades implementing a controlled-vortex design that induces an approximately uniform distribution of the swirl velocity downstream of the rotor exit section. As further research step, this paper reports the extension of the experimental data set to tube-axial fan rotors with 0.5 hub-to -tip ratio. Aim of the work is twofold: first, widen the experimental data set of industrial fans with high degree of design parameter similarity except for those directly related to the solidity and aspect ratio values; second to propose a preliminary comparison between the effect of the two design parameters when the hub-to-tip ratio moves from values very close to the minimum one technically feasible for propeller-fans to values close to the maximum one reasonable in terms of acceptable efficiency for tube-axial fans. To this end the performance measured in accordance with the ISO-5801 standard for 22 prototypes of a 315 mm-diameter tube-axial fan were compared. As for the previous experimental campaign performed on the 0.2 hub-to-tip ratio propeller fan, all fan prototypes were derived from four baseline designs conceived to ideally achieve the same best efficiency operation with different values of the aspect ratio and permit operation with different blade counts (i.e., with different rotor solidities at a fixed blade aspect ratio). The sensitivity and trends of the fan pressure and efficiency with respect to the blade aspect ratio and solidity were identified for a tip clearance value equal to the one fixed for the 0.2 hub-to-tip ratio fan tests and reasonable for practical applications of small industrial fans with adjustable-pitch blades. The results show that some trends of aspect ratio and solidity effects hold regardless of the hub-to-tip ratio value (i.e. are reasonably general for any ducted axial-flow fan design belonging to the propeller and tube-axial types), whereas some other trends are noticeably dependent on the fan hub-to-tip ratio.

Presenting Author: Piero Danieli University of Padova

Presenting Author Biography: -

Authors:

Massimo Masi University of Padova
Piero Danieli University of Padova