Flow Control Investigations of Steady and Pulsed Jets in Bowed Compressor Cascades

Abstract

Based on the previous research about the combined flow control method which was carried out by applying the endwall steady VGJ to the bowed compressor cascades to reduce the secondary flow loss, for the consideration that the pulsed jets may save the mass flow required for control, therefore the unsteady VGJs over the different actuation frequencies and blowing ratios were investigated in detail. Under the conditions of same jet geometry parameters, the improvements to the fluid fields in the bowed compressor cascades caused by the pulsed jets are less than that induced by the steady cases. With the pulsed VGJ, for the positively bowed blade, the enhancement of the time-averaged aerodynamic performance can be achieved when the blowing ratio is greater than 0.6, but all of the unsteady conditions in this research can improve the flow field in the negatively bowed blade. The time-averaged total losses decrease by 1.6% and 7.0% at most for the positively and negatively bowed blades, respectively. The mechanisms by which the endwall pulsed vortex generator jets delay flow separation and reduce loss were explored. The results show that, being different from the single vortex produced in steady VGJ, the pulsed case generates a pair of streamwise vortices with the opposite sense of rotation. One vortex suppresses the development of the secondary flow, but the other one increases the size of the passage vortex. Furthermore, for the endwall pulsed VGJ, the changes of the blowing ratio plays a more important role in improving the flow fields in the bowed cascades than that of the actuation frequency.