Flow Studies in Ducted Twin-Rotor Contra-Rotating Axial Flow Fans

Abstract

The design and testing of a 400 mm diameter contra-rotating fan unit was undertaken to study the flow behavior through the contra-rotating fans, and to find ways and means of improving their design and performance. The performance characteristics of the two-fan unit have shown that large overall stall margins can be achieved. Also, the effect of axial gaps showed that at the design speed combination best performance was observed at an axial gap of 50% of the 1st Fan chord. Studies on the 2nd fan exit flow field, performance characteristics of individual fans and casing boundary layer development have been made. Significant performance enhancement is observed with serration on 2nd fan rotor blade surface. When casing boundary layer suction is employed in between the two blades, the 2nd fan exit flow shows better uniformity and increased total pressure at all radii. However, to obtain a large operating range, careful optimization of the 2nd rotor blade design would be required, taking into account peculiarities shown by the present study in variation of deviation and exit flow angles of the individual fans, and casing boundary layer development with increased axial pressure gradient.