DESIGN AND INTERNAL FLOW ANALYSIS OF A DUCTED CONTRA-ROTATING AXIAL FLOW FAN Ali Mohammadi Amirkabir University of Technology Tehran, Iran Masoud Boroomand Amirkabir University of Technology Tehran, Iran ABSTRACT This paper presents the design procedure of a ducted contra- rotating axial flow fan and investigates the flow behavior inside it using ANSYS CFX-15 flow solver. This study investigates parameters such as pressure ratio, inlet mass flow rate and efficiency in different operating points. This system consists of two rotors with an outer diameter of 434 mm and an inner diameter of 260 mm which rotate contrary to each other with independent nominal rotational speeds of 1300 rpm. Blades’ maximum thickness and rotational speeds of each rotor will be altered as well as the axial distance between the two rotors to investigate their effect on the overall performance of the system. Designed to deliver a total pressure ratio of 1.005 and a mass flow rate of 1.8 kg/s at nominal rotational speeds, this system proves to be much more efficient compared to the conventional rotor-stator fans. NACA-65 airfoils are used in this analysis with the necessary adjustments at each section. Inverse design method is used for the first rotor and geometrical constraints are employed for the second one to have an axial inlet and outlet flow without using any inlet or outlet guide vanes. Using free vortex swirl distribution method, characteristic parameters and the necessary data for 3D generation of this model are obtained. The appropriate grid is generated using ATM method in ANSYS TurboGrid and the model is simulated in CFX-15 flow solver by employing k-ε turbulence model in the steady state condition. Both design algorithm and simulation analysis confirm the high anticipated efficiency for this system. The accuracy of the design algorithm will be explored and the most optimum operating points in different rotational speed ratios and axial distances will be identified. By altering the outlet static pressure of the system, the characteristic map is obtained. INTRODUCTION There is currently a growing tendency toward developing contra-rotating fans and compressor stages due to their compactness in length and reduction in weight which is the result of omitting stators from the conventional models. Many researchers working in this area have reported higher quantities in efficiency and pressure ratio for contra-rotating fans, propellers and compressor stages in comparison to rotor-stator assembly. Started in 1930s, Lesley [2] showed that an addition of fixed counter-propeller blades increases the efficiency of a four-blade fixed counter-propeller in combination with a two-blade rotating propeller by two percent. In 1980s, Sharma et al. [3] examined the effect of altering rotational speed ratios of two rotors and also different axial spacing between them in one stage of a compressor which had blades with 0.66 hub-tip ratio. It was concluded that alteration of these factors has strong influence on the stalling behavior of the stage. Also it was mentioned that if the second rotor contra-rotates 50% faster than the first one, rotating stall phenomenon would be suppressed and in case of large axial distances, contra-rotation would lose its benefits. In 2009, an increase in efficiency and a decrease in fuel consumption rate were reported by Min et al. [4] in a contra rotating propeller system. They claimed that by using the rotational flow energy behind the first rotor, the propulsive efficiency of the system would be improved. Later, Nouri et al. [5] further analyzed the effect of the rotational speeds ratios of the rotors and the axial distance between them in a low number of blade contra-rotating axial flow fan. They reported optimum quantities for these parameters and validated the results experimentally. Finally, Mistry et al. [6] conducted a similar experiment on high aspect ratio contra-rotating axial fan stage. They reported high quantities of efficiency in design and off design operating points. In this research, after choosing an optimum blade thickness, operation of a high number of blades axial flow fan in different axial distances and also with different rotational speed ratios would be investigated to indicate its characteristic map. In near future, an actual model will be built based on the design procedure introduced in this article. Proceedings of the ASME 2014 International Mechanical Engineering Congress and Exposition IMECE2014 November 14-20, 2014, Montreal, Quebec, Canada IMECE2014-39883 1 Copyright © 2014 by ASME