Investigation Of Performance Based On Flow Control In A Vaneless Counter-Rotating Turbine

Counter-rotating turbine is one of the key technologies of gas turbine engine and it has great potential in elevating thrust-to-weight ratio of aero-engine and improving performance of aircraft. Because the convergent-divergent passage of high-pressure rotor in1+1/2counter-rotating turbine is different from the conventional turbine with convergent passage, the flowfield and the flow control discipline both are different. Meanwhile, the effective flow control methods may be able to further optimize the turbine performance. So the reasonable flow control methods in1+1/2counter-rotating turbine can reduce the shock wave strength and regulate the flow rate, which is significative to strengthen flow stability and improve the aero-engine performance.Based on the flow characteristic of1+1/2counter-rotating turbine, the flow control methods of the suction surface bump in high-pressure rotor, the variable high-pressure guide vane and the coolant injection in high-pressure rotor are adopted respectively, and the validity of flow control is verified by numerical simulations and experiments. The main contents in this paper are listed as follows:1. The bump is fixed on the separation region of high-pressure rotor suction surface, the shape and the area of flow passage has been change with the adjust of the bump position and height. The separation region is suppressed effectively because of the bump. The different conditions of bump position and height are analyzed by numerical simulation and the optimum bump is found finally. When the suction surface bump is fixed in84%～86%axial chord length and the maximum height of the bump is1mm, the bump can inhibit the boundary layer separation effectively.2. Because the throat of the1+1/2counter-rotating turbine locates in the high-pressure rotor and the flow at the outlet of the high-pressure rotor is supersonic, the flow rate of the1+1/2counter-rotating turbine is uniform with the different outlet pressure. So the variable high-pressure guide vane is applied to adjust the turbine flow rate. A detailed numerical simulation has been carried out to investigate the1+1/2counter-rotating turbine performance and flowfield with different openings of high-pressure guide vane, the relationship between the opening and flow rate, efficiency, power and losses is investigated. The results indicate that the variable high-pressure guide vane can effectively control the flow rate of1+1/2counter-rotating turbine, keep the reasonable specific work ratio of high-pressure turbine to that of low-pressure turbine and achieve the good efficiency.3. The coolant protected the high temperature units flows into the cascade passage, which brings some influence on the aerodynamic performance, the high-pressure rotor with convergent-divergent flow passage in the1+1/2counter-rotating turbine is the object of study. A detailed numerical simulation has been carried out to study the influence of the coolant injection on the performance of the convergent-divergent turbine cascade. The cooling-hole position and the massflow ratio between coolant and mainstream are the main influence factors. The numerical results show that the coolant injected from the suction surface where the inner-extending shock impinges can change the shock strength. The main reason is that a large adverse pressure gradient caused by the coolant injection results in the rising pressure before cooling holes and the decreasing the difference of pressure on both side of the shock.4. Some cascade experimental investigations are performed to study the influence of the coolant injection on the cascade performance at off-design conditions in a transonic cascade test facility, meanwhile the schlieren graphs of the shock wave system in the convergent-divergent turbine cascade has been obtained at different expansion pressure ratio. The cascade inlet and outlet parameters, the blade surface static pressure and the endwall static pressure is measured at conditions of different attack angles, different expansion pressure ratios and different coolant flowrate. The results of experiment and numerical simulation are accordant and the flowfield change caused by the inner-extending shock is captured, which indicates that the design, analysis and the experimental system of1+1/2counter-rotating turbine developed by our group is credible.