Effect of Differential Tip Clearance on the Performance of a Tandem Rotor

Abstract

Tandem blade is an interesting concept that promises a higher total pressure rise per stage. Owing to two separate tip leakage vortices and their interaction, losses are likely to increase particularly near the tip region. Although, rotors are designed with optimum tip clearance, the clearance changes during engine operation as well as during its service life. In the case of tandem rotors, the forward and the aft rotors can have different tip clearances. This will also impact the performance of the stage. Six different tip clearances have been investigated. ANSYS CFX is used for steady RANS computational analysis. The results suggest that the performance of the tandem rotor is highly sensitive to the forward rotor tip clearance. Higher tip clearance adversely affects the total pressure rise and operation stability of the tandem rotor. At design mass flow rate, the performance degradation for tandem configuration with the higher tip clearance (Case2, Case 3, Case 5, and Case 6), is attributed to the vortex breakdown of TLV1, which leads to the sudden expansion of the blockage region near the rotor tip. Vortex breakdown primarily depends upon the swirling strength of TLV1 and TLV2 as well as on the adverse pressure gradient. Near the stall point, the role of the adverse pressure gradient becomes more dominant in the vortex breakdown.