Tip leakage vortex breakdown (TVB) is an important flow character that affects the performance of axial compressors. In this study, the interaction mechanism between incoming vortex (IV) and TVB is investigated to improve the performance of compressor cascade. First, the pitchwise location effect, swirling direction effect, and intensity effect are investigated under steady condition; then, an unsteady investigation is conducted based on the steady results. Under steady condition, TVB can be completely removed by the incoming vortex near the suction surface with different swirling directions, and the normalized circulation at the edge of incoming vortex is 0.7. The loss coefficient caused by TVB is also reduced; however, a new loss is induced by IV. The flow mechanism is that the interaction between the incoming vortex and tip leakage vortex (TLV) can increase the chordwise momentum at the vortex core and the stability of the TLV. For TLV and IV, the two vortices have a tendency to combine downstream of the compressor cascade if they have the same swirling directions. However, when the swirling directions are different, TLV and IV propagate separately, and the intensity and stability of TLV are much higher. The loss of TLV is higher for the anticlockwise IV scheme because the intensity of the TLV is greater due to the interaction between TLV and IV. By utilizing the incoming vortex under unsteady condition, the TVB can also be reduced. The unsteadiness of the compressor cascade with the incoming vortex is significantly reduced by reducing the TVB.

In highly loaded tandem compressor cascades, corner separations can still exist. In order to eliminate corner separations in highly loaded tandem compressor cascades, incoming vortex–corner separation interaction mechanism was investigated. Different schemes of the vortex generators, which located at different pitchwise locations and could generate vortexes with different rotation directions, were designed and investigated numerically. Results show that, severe corner separation occurred at the front blade passage of the tandem cascade; by utilizing flow control method of incoming vortex–corner separation interaction, the corner separation could be reduced significantly. The optimal control effect of incoming vortex on corner separation was achieved with anticlockwise rotation and the vortex generator is located right ahead of the leading edge of tandem cascade, a maximum loss coefficient reduction of 21.8% being achieved. Different from single blade configuration, the boundary layer of tandem cascade was regenerated at rear blade suction surface due to the injection flow from blade gap between the two blades. Though corner separations could be reduced at both conditions, the loss of tandem cascade with clockwise incoming vortex is higher than that with anticlockwise vortex, and a smaller corner separation region at suction surface was achieved by utilizing clockwise vortex. The mechanism was that anticlockwise incoming vortex reduced the corner separation but increased secondary flow, while clockwise vortex enhanced passage vortex and decreased secondary flow. For clockwise incoming vortex near pressure surface, the vortex would be divided into two parts at the leading edge of rear blade, one would go through the blade gap and deteriorate flow fluid near rear blade suction surface, the other flowed downstream along pressure surface. The rotation direction of different incoming vortexes became the same as the passage vortex at rear blade passage of tandem cascade, which was mainly due to the effect of secondary flow.

The purpose of this paper is to suppress the tip leakage vortex and cavitation of fuel pump by using the casing slot. The flow fields of the blades with different casing slots were studied by numerical simulation under the conditions of no cavitation and cavitation respectively. The results show that the loss with leakage vortex cavitation increases by 37 % compared with the condition without cavitation. Under cavitation conditions, the optimal scheme is c6 scheme, and the loss is reduced by 9.3 %. The tip leakage vortex and vortex cavitation can be effectively reduced by casing slot. Under the condition of no cavitation, the tip leakage flow loss can be effectively reduced by the casing slot in a wide range of axial positions. After the casing slot is applied, the shape of the blade tip leakage vortex is significantly changed, the size of the leakage vortex is significantly reduced, and the loss is reduced. Under cavitation conditions, the casing slot can also effectively improve the tip flow field and inhibit leakage vortex cavitation. In a wide range of axial positions, the casing slot can effectively inhibit leakage vortex cavitation.