Computational analysis of recess vane geometry modification in the casing treatment approach to enhance stall margin in axial flow fans

Stall margin improvement, though finite, has great influence on performance of a compressor and fan. Modification to the geometry of the recess and the recess vane used in the recess vane casing treatment approach would increase the operating range of an axial flow fan by removing the whirl component of circulatory flow near the blade tip. The present paper investigates the combined effect of variation of recess height and amount of blade chord exposure on flow characteristics and stall margin in low speed axial flow fan. Numerical simulations and modeling was performed using CFX 13.0 and ICEMCFD. The simulated pressure rise, work input and efficiency characteristics agreed well with the experimental data of a low sped fan obtained from the literature. The range of the flow rates which correspond to the stall free operating range of the untreated fan is compared with the same for the different modifications carried out to the geometry. The sensitivity of the operating range to the modifications is analyzed and the effect of recess vane geometry parameters on stall margin improvement is evaluated. Simulations suggest that within the ranges of parameters investigated stall margin improvement increases with both blade chord exposure and height. Copyright © 2013 by ASME.