A novel approach for the design of axial flow fan by increasing by-pass ratio in a constant-diameter turbofan

Ali Shahsavari, Mahdi Nili-Ahmadabadi ^*

Department of Mechanical Engineering, Isfahan University of Technology, Isfahan, 8415 683111, Iran

Abstract: The present study introduces an innovative aerodynamic redesign of an axial flow fan based on constant diffusion factor and radial equilibrium. All input design parameters such as mass flow rate, hub to tip ratio, aspect ratio, tip diameter and angular velocity are taken from NASA Rotor 67 as a conventional axial flow fan. A computer program is developed to extract the three- dimensional geometry of a fan and to estimate the span-wise distribution of parameters. The new designed fan flow field is investigated in detail by CFD tool at both design and off design conditions. Finally, a turbofan cycle analysis is conducted based on thermodynamic and gas dynamic principles to evaluate the fan performance in a turbofan engine in comparison to NASA Rotor 67. Achieving a higher total pressure ratio, meeting the target pressure ratio in lower rotational speed with higher efficiency, delivering more bypass air in a constant diameter and less fuel consumption for the same specific thrust force are the main advantages for the new design strategy in comparison to the conventional designed fans such as Rotor 67. However, efficiency reduction in fan over speed is the main disadvantage.

Keywords: Axial flow fan; Bypass ratio; Computer simulation; Design methodology; Thermodynamic turbofan cycle analysis