Discussion On Evolution Mechanism Of The Tip Leakage Vortex With Unsteady Plasma Actuation

Design schemes of high-load and small-aspect-ratio turbine blade have been widely used.And it can aggravate the pressure gradient on both sides of the gap,which exacerbates the blade tip leakage flow and generates more complex vortex in the flow fluid,so that the aerodynamic loss is increased.In recent years,DBD plasma flow control technology has developed rapidly,in which the unsteady actuation especially has attracted much attention for its low energy consumption and its ability to be coupled with the flow field frequency.It has broad prospects for improving the flow field structure and the aerodynamic efficiency of the turbine,providing new methods for controlling the gap flow.Based on the advanced model of Shyy,the flow characteristics of the turbine blade cascade with or without unsteady actuation was compared and analyzed.Another,the interaction between the vortex structure induced by the unsteady plasma actuation and the vortex structures in the cascade flow fluid was explored.In addition,this study discussed the changes of pressure,velocity,swirling strength,energy loss coefficient and other parameters with the actuation period.the interaction between the flow structure induced by the unsteady plasma actuation and the vortex structures in the cascade flow fluid was explored.As the calculation results showing,the induced vortex 1 was formed on the pressure side with the unsteady actuation,which accelerated the breaking process of the separation bubble and reduced the generation of low-energy fluid.Furthermore,the induced vortex 2 was formed on the suction side,occupying a certain height of the gap in the longitudinal direction,which hindered the leakage flow.So that the leakage flow rate was decreased accordingly,which reached the minimum at 2/4T.Under the unsteady actuation,the gap leakage flow deflects toward the trailing edge,delaying the formation of the leakage vortex,the strength as well as the size of it were reduced,and the location of it was moved up and close to the suction side.Additionally,the capacity of maintaining a stable vortex core of the leakage vortex was weakened and the distance to the downstream development of it was shortened,so that it broken ahead of that time.Moreover,the swirling strength of the leakage vortex reached the minimum at 2 / 4T,and the corresponding energy loss was the lowest.On the basis of the above study,the influence of the unsteady actuation parameters,such as actuation strength,actuation frequency and duty factor on controlling the gap flow was discussed in this paper,and the response of parameters,such as the leakage flow rate,swirling strength,etc,was analyzed.After that,the vortex structures and the distribution of the streamlines in the blade cascade flow field were discussed.As the actuation intensity and duty factor increased,the leakage flow rate was decreased,leading to a decrease of the size and the strength of the leakage vortex,as well as the angle between the axial chord and it.At the same time,the stability of the leakage vortex was weakened,which caused that the distance to the downstream development of it with its stable vortex structure was shortened.Besides,the actuation frequency only affected the leakage flow rate near the trailing edge of the blade tip gap,leading to that the development of the leakage vortex differed only in this area.