Study On Clearance Leakage Control And Structure Optimization Of Turbine Rotor Blade Tips

With the continuing increase in the thrust-to-weight ratio of aircraft engines and the development in the compact layout of high power gas turbines,the loading of turbine rotor blades is continuously increased.This leads to more intense tip leakage flow and then induces higher aerodynamic loss.Due to this issue,this thesis investigates the characteristic of the tip leakage flow in turbine cascades by means of numerical simulations and wind tunnel experiments.Based on this,the tip configuration is optimized and impacts of optimal tip geometries on the leakage flow and the blade performance are analyzed.These efforts are intended to inhibit the tip leakage flow and improve the efficiency of the blade cascade and the turbine stage.The thesis is divided into four parts as listed below.1.Impacts of the winglet-shroud on the performance of a l inear turbine cascade.Considering the winglet-shroud geometry,effects of the width for a double-side winglet and the location for the partial shroud on the flow structures and the aerodynamic performance of a linear turbine blade are numerically studied.A design criteria for locating the partial shroud is proposed.Two labyrinth seals are then added on the tip surface of the winglet-shroud.Both wind-tunnel experiments and numerical simulations confirm that these seals aid to improve the capacity of the winglet-shroud to control the tip leakage flow.2.Study on the performance of winglet-shrouded turbine stage and the mechanism of the rotor rotation effect.Numerical simulations are conducted for the LISA one-half-stage turbine to assess the effects of the full shroud,double-side winglet and winglet-shroud tips on the turbine aerodynamic performance.Results indicate that the winglet-shroud can improve the turbine efficiency under two values of the rotor blade tip clearance.Then based on the turbine rotor cascade with flat and winglet-shroud tips,influences of the blade rotation and casing rotation on the tip leakage flow and the blade aerodynamic performance are numerically compared and analyzed.It is found that the winglet-shrouded cascade has lower aerodynamic loss than the flat tip case for all rotating conditions.3.A CFD method based on source models(SCFD)and its application in optimization on jet holes of the winglet-shroud.In order to reduce the computational cost,flow and heat transfer governing equations are developed by introducing source models.Typical flow and heat transfer cases in turbines are studied.Effects of uniform meshes and source terms in turbulence model equations on the accuracy of the SCFD method are demonstrated.Then SCFD predictions,CFD simulations using body-fitted meshes(BCFD)and experiments are performed to analyze impacts of the tip injection on the performance of the winglet-shrouded blade cascade.Results prove that the loss under different injection mass flow rates obtained by the SCFD scheme is similar to that by the BCFD and the experiment.Subsequently,an arrangement of tip injection holes that can improve the aerodynamic performance of winglet-shrouded blade cascade is obtained using a SCFD-based optimization.4.Topology optimization on the rotor blade tip structures.A fluid topology optimization system is established via integrating the SCFD approach,a quasi-sensitivity and an adjoint-sensitivity analysis methods.An abrupt expansion pipe and a U-bend channel are first optimized to minimize the total pressure loss between inlet and outlet sections.The potential of the topology optimization to design low-loss and high-performance flow passages are analyzed.Then a topology optimization algorithm is developed for a two-dimensional tip model.Based on this,tip geometries of nine axial planes of the three-dimensional blade cascade are designed.Experiments and BCFD simulations show that the novel tip geometries designed by the topology optimization can reduce the leakage loss in the tip gap and the leakage mass flow rate at the gap exit.The aerodynamic performance of the blade cascade is consequently improved.The above research results provide theoretical basis and technical support for engineering application of the winglet-shroud and for adoption of the topology optimization to the design system of turbines rotor tip geometries.