Numerical investigation on effect of rotor blade lean angle variation on single stage fan stability

Modern day research is striving towards the improvement of stability margin of Fans and Compressors. Flow control techniques are implemented to enhance the performance and increase the stability margin however the control mechanism complexity can be reduced if performance enhancement is built into design of turbomachinery with minimum possible design variables. In this paper numerical investigation on single stage low speed fan has been presented with effect of blade lean angle variation to be the design variable. The said fan has been designed for test rig to be installed at School of Power and Energy, Northwestern Polytechnic University (NWPU). Recent numerical investigations on stall mechanism have revealed that the single stage low speed fan stalls due stator hub-corner stall. The details of flow mechanism (specifically at hub corner region of stator) with the variation of rotor blade lean angle at near stall conditions are presented in this paper. Commercial CFD code NUMECA FINE/TURBO has been used to carry out all simulations. Two approaches have been adopted for blade lean angle modification: one is to modify the blade lean angle with linear stacking line secondly with simple Bezier Curve. The maximum variation of ±10° has been kept for lean angle variation for both approaches. Steady state simulations are run for shorter number of iterations to get the best lean angle including the base line angle. Harmonic method has been used to compute the unsteady near stall and just stall operating points. Positive lean angle (in the direction of rotation) has been found to slightly suppress the hub corner stall for both approaches. Linear stacking line has proven to be more effective than simple Bezier curve for both near and just stall operating conditions.