Effects of vortex generator jet on flow separations in bowed compressor cascades

A combined flow control was performed by using a vortex generator jet (VGJ) in bowed compressor cascades. Loss calculations were done over a wide range of parameters including jet mass flow, jet direction and jet location, to determine their effectiveness in controlling flow separation. The topology theory is introduced in this paper to analyze the changes of separation structures in bowed cascades caused by VGJ. The results in this paper indicate that not all kinds of VGJs made up of jet parameters in any arrangement can improve the flow conditions of bowed cascades, but that there are optimal combinations of jet parameters attaining the largest total pressure loss reduction of up to 2.7% and 9.1% for positively and negatively bowed blades, respectively. The VGJ comprised of optimal jet parameters make the flow separation on the suction side of the positively bowed blade basically disappear. The VGJ in the optimal case renders flow separation on the suction side of the negatively bowed blade be relieved so that a separation line on it disappears accordingly. In addition, the mechanisms of VGJs in cases which increase the loss in bowed cascades were chosen to be analyzed in detail. The consequences show that VGJ, in that case, causes that two passage vortices are produced in the positively bowed blade, so the flow field is deteriorated. For the negatively bowed blade, the VGJ leads to the result that the flow separation on the suction side is severer and the separation nodal point corresponding to the corner vortex is transformed from a degenerately nodal point to a spiral point which means that the loss caused by the corner vortex increases.