Mechanism Investigation Of The Tip Leakage Flow In Turbine Cascade Controlled By The Honeycomb Tip

To meet the design requirements of high performance and high thrust-to-weight ratio aero-engines,aerodynamic load of turbine component is constantly increased,which further highlights the influence of rotor tip leakage flow.Tip leakage flow is an important source of internal loss in turbine,which restricts the improvement of turbine performance.On the basis of the existing research,it is one of the breakthrough contents and cutting-edge research topics of key technologies of aero-engine to carry out in-depth research on turbine tip leakage flow mechanism and develop efficient leakage flow control technology.The excellent sealing characteristics of the honeycomb and the turbulent drag increasing effect of the spherical vortex sag provide a research idea for the honeycomb tip control technology,and the purpose of controlling turbine tip leakage flow can be achieved through efficient clearance flow organization.In this study,the control mechanism of honeycomb tip control technology on turbine tip leakage flow and its leakage flow characteristics are systematically studied by experimental and numerical methods on a high-load turbine plane cascade.On this basis,the improved structure of honeycomb tip is proposed to enhance the effect of honeycomb tip on turbine tip leakage flow control.Firstly,a parameter identification study of the SST k-w turbulence model based on the Kriging surrogate model method is carried out.Combined with the results of cascade wind tunnel experiments,ten closed constants in the turbulence model are optimized.Combined with the analysis of closed constant range,the four factors that have great influence on the prediction accuracy of leakage flow loss in the model are finally determined and modified,they are ?*,?₁,?_?,1 and ?_i,1.The modified SST k-w turbulence model is used to improve the prediction accuracy of turbine tip leakage loss.Secondly,experiments and numerical studies on the mechanism of honeycomb tip to inhibit turbine tip leakage flow are carried out.The cascade experiment mainly compares the static pressure of the upper end wall and the oil flow display of the flow field,the loss of the cascade outlet and the secondary streamline,and the static pressure coefficient of the blade surface of the cascades with flat tip and honeycomb tip.The flow field in the clearance,the vortex interaction in the channel and the heat transfer at the top of the blade are analyzed in detail.The results show that under the action of non-uniform pressure field in the gap,airflow vortices will form in the honeycomb tip unit.The energy dissipation and efflux effect of a series of vortex structures are the action mechanism to restrain the clearance leakage flow.Apply the honeycomb tip to the 1.5-stages real turbine rotor,which reduced the relative leakage flow rate by 8.2% and improved the efficiency of turbine stage by 0.5%,which reflected the application value of honeycomb tip control technology in real turbines.On the basis of the above research,the influences of honeycomb geometry size,tip clearance height,inlet impact angle and periodic unsteady inlet conditions on the sealing performance of honeycomb tip and the aerodynamic performance of cascade are studied,and the influences of these factors on the total parameters of tip leakage flow and the development of major vortex structures in the flow field are mainly discussed.The results show that the honeycomb height is the main geometric parameter that affects the development of the vortex and the characteristics of the leakage flow field in the honeycomb cell.The clearance height is an important factor affecting the leakage flow.The honeycomb tip control technology can not only reduce the sensitivity of turbine cascades to the change of clearance height,but also allow the turbine to have a smaller clearance value under operating conditions to enhance its sealing effect.Under the condition of the change of the inlet attack angle,the honeycomb tip with hexagonal structure characteristics can suppress the local enhancement of leakage flow caused by the change of the inlet attack angle to a certain extent,which makes the turbine cascade have better impact adaptation characteristics.Under the condition of periodic unsteady inlet flow,the honeycomb tip can effectively reduce the average leakage flow at irregular intervals and reduce the fluctuation amplitude of the leakage flow with time,which reflects the leakage flow control effect of honeycomb tip under the condition of non-uniform inlet flow.Finally,based on the mechanism of honeycomb tip inhibiting tip leakage flow,the structure of honeycomb tip is optimized and combined by changing the internal wall constraints of the honeycomb units.Three kinds of improved structures,including inclined honeycomb tip,honeycomb-prismoid composite tip and honeycomb-spherical bottom composite tip,are studied to reveal the mechanisms to strengthen the control effect of honeycomb tip control technology on tip leakage flow.The influences of geometric characteristic parameters on the sealing performance and turbine aerodynamic performance are discussed to obtain the optimal improved structural design schemes of honeycomb tip.