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.

Upstream vortex has a significant effect on the secondary flow structure of the downstream turbine in the stage environment. This study investigates the secondary flow structure with non-axisymmetric endwall profiling (NAEW) under the interaction of co-rotating incoming vortex (V_ic). A half-delta wing vortex generator is utilized to model V_ic. The turbine cascade case which exhibited maximum reduction of the cascade loss with NAEW under no incoming vortex is studied. The mechanism of loss reduction with NAEW under the interaction of V_ic is analysed. V_ic could decrease the secondary flow near the endwall region by affecting the horseshoe vortex transport in the cascade. However, its loss reduction was lower than the loss increments of V_ic itself. The arrival of V_ic at the leading edge of the cascade increased the strength of the horseshoe vortex, resulting in a significant increase in loss. Under the interaction of V_ic, NAEW decreased the blade loading near endwall region, which resulted in the reduction of cascade loss.

The active flow control technique of vortex-generator jet (VGJ) was used to control the turbulent separation of a highly loaded compressor cascade at a high incidence. VGJ schemes on suction surface with different jet locations, skewed angles, pitch angles were numerically performed and the control mechanism of VGJ parameters on the flow field of the cascade was revealed. For avoiding the effect of endwall boundary layer, both endwall surfaces of the cascade were set to translational periodicity boundary (TPB). Results show that VGJ significantly eliminates the turbulent separation and improves the performance of cascade. The overall loss coefficient of cascade is reduced by 52.3% at most. The optimal VGJ location in this study is not separation location but 7% axial chord downstream of it, which is probably due to the ultra-high loading of the cascade. The spanwise location and intensity of jet vortices are mainly affected by skewed angle, and will increase with the skewed angle. The VGJ case with a higher pitch angle features better control effect on suction surface but increases the pitchwise scale of the low-velocity region. In addition, as pitch angle increases, the mixing loss between mainstream and jet flow increases, which brings a negative effect on cascade performance. In order to enhance the momentum transporting between mainstream flow and separation flow, counter vortex-generator jet (CVGJ) schemes were designed and studied. Though CVGJ strengthens the jet vortices near the trailing edge and achieves minimum loss near TPB sections at 150% axial chord section, the interaction of jet vortices with opposite rotating direction brings extra loss, which leads to the control effect of CVGJ is weaker than that of VGJ.