Investigation On The Control Strategy Of Variable Guide Vane(VGV) Endwall Leakage Loss And Its Flow Characteristic

Gas turbine has the advantages of high power density, fast startup etc..It has beenwidely utilized in the fields of aviation, ships, vehicles, power generation.The turbine is one of the core components of gas turbine. The variable geometry turbine has been widely used in terms of that this kind of technology could improve the gas turbine characteristics of startup, acceleration, braking and varying duty conditons. Adjusting turbine guide vane angle is an effective way to achieve the variable geometry requirement. In order to ensure the turbine guide vane can be rotated, there are gaps at the both ends of guide vane between the hub and casing, which causes leakage loss. To solve this problem, the control strategy of variable guide vane(VGV) endwall leakage loss and its flow characteristics are investigated. The main contents are as follows:(1) The simulation work was carried out regarding the power turbine VGV aerodynamic performance of a three-stage axial turbine. It was analyzed the effect of the VGV angle change to the turbine performance of a three-stage gas turbine. And the optimal angle of the power turbine VGV to be fit to varying partial load conditions was investigated. The results showed that the mass flow, efficiency, expansion ratio allocation and power allocation of the turbine can be adjusted by changing the angle of the power turbine VGV. The inlet flow angle and energy loss of each stage were also affected obviously by the angle of the power turbine guide vane, and the effect became smaller if the distance got longer. Furthermore, under different working conditions, gas turbine can work at high efficiency by adjusting guide vane angle.(2) The control strategy of VGV endwall leakage loss were investigated. In order to reduce the leakage loss of the VGV endwall, a disk at each end of the VGV was added, and they were embedded in hub and casing, respectively. The shapes of hub and casing around the VGV were designed to be concentric spheres, and the surface of the disk on the flow passage side are also at same sphere of hub and casing, respectively. The rotation axis of VGV pass through the center of sphere to keep flow path unchanged and VGV endwall gap minimum when VGV rotated. This strategy could reduce VGV endwall leakage loss. Increasing the diameter of disk and decreasing radial clearance(t) could reduce the leakage loss and improve turbine performance.(3) The flow characteristics of different VGV endwall structures were investigated. The results showed that when VGV having no endwall gaps with large inlet flow angle, there are complex separation at leading edge of VGV hub which formed two saddle points, two separated lines and one reattached line. When VGV endwalls having partial gap, there are four leakage flows at VGV endwalls, forming one saddle point and one separation line. When VGV endwalls having full gap, there were two strong leakage flows at VGV endwalls. The saddle point and separation line disappeared, and the leakage flow dominated the secondary flow. The disk diameter, radial clearance(t) and VGV angle had significant impacts on secondary flow.(4) The power turbine VGV aerodynamic performance coupled with heat transfer were investigated. The results showed that different VGV endwall structures have less impact on VGV temperature distribution. When VGV endwalls having partial gap, the leakage flow intensity at both endwalls was small, and the temperature distribution of rotor blade had little change compared to VGV endwalls without gap. However, the surface temperature of rotor blade was significantly improved when VGV endwalls having full gap. That was because of the strong endwalls leakage flow of the VGV. The rotor blade temperature would increase when reducing the diameter of VGV endwall disk. The radial clearance(t) had less impact on the rotor blade temperature which VGV endwalls with partial gap compared with full gap. Of the three endwall structures, when increasing VGV angle, the rotor blade temperature could be increased, and it had the biggest increase when the VGV having no endwall gaps, followed by the partial gaps, and then the full gaps.