Effect of Tandem Blading in Contra-Rotating Axial Flow Fans

Abstract

With the ever-increasing demand for improved fuel efficiency and lower emissions, there is a significant emphasis on finding innovative design solutions that can replace or significantly improve the present-day turbomachinery designs. The concepts of contra-rotation and tandem blade configuration are two different methods of achieving better performance. Though several independent studies have been carried out on the concepts of contrarotation and tandem blade configuration, a combination of both these techniques to achieve better performance is a thought unexplored. Therefore, the present work explores the applicability of tandem blading in a low-speed contra-rotating fan. The idea is to replace the front rotor of the contra-rotating fan stage with tandem blades. Several combinations of percent pitch for the tandem arrangement are analyzed to obtain the best configuration suitable for the case. The performance of the baseline contra-rotating fan is established numerically. A detailed numerical investigation of the flow physics associated with the contrarotating stage reveals some interesting phenomena affecting its performance. A comparison of the performance of tandem configuration with that of the baseline is carried out. The interaction of gap flow and the wake of the front blade with the tip-leakage flow of the rear blade of the tandem configuration is analyzed in detail. The performance of the stage is evaluated through stage loading or pressure rise and the stability margin.