Study On Flow Characteristics Of Wet Steam In Turbine Cascade With Non-Axisymmetric Endwall

With the continuous progress of technology, researchers have paid more attention to the energy conversion efficiency in turbines. A steam turbine, known as the most important equipment in the Thermal Power Plant Industry and Driving device in a warship, it always takes remarkable position in scientific research work to improve the operating efficiency of a steam turbine. Since the working medium is water vapor, there will not only be an inevitable secondary flow, but also be a complex steam condensation process in the steam turbine cascade. So it is necessary for the design of high performance steam turbine in the future to reduce the loss of the secondary flow and steam condensation process in the steam turbine.Since the non-axisymmetric endwall could change the pressure distribution in the turbine cascade, the secondary flow can be reduced. Pressure changes can also affect the steam condensation process. In order to study how to control the loss of the secondary flow and steam condensation at the same time, in this paper, we try to transform the hub of the White cascade to the non-axisymmetric end wall. We select the end wall profiling method based on trigonometric function, this method of end wall modeling could generate different heights of non-axisymmetric endwall modeling at different axial positions. The grid number is about 0.8 million. The SST turbulence model is adopted. Numerical result and experimental result are compared to prove that the SST turbulence model is appropriate and the numerical result in this paper is right.In chapter 3,we have built up 9 different numerical models,and the numerical results shows that the secondary flow loss and humidity are both decreased when the nonaxisymmetric end wall modeling is in the middle of the cascade. Among them, with the 5% blade height amplitude in the middle of the axial chord, the secondary loss of the cascade under 22% blade height decreases 2.1%,the humidity under 30% blade height decreases 1.2%. And with the 10% blade height amplitude in the middle of the axial chord, the secondary loss of the cascade under 26% blade height decreases 3.5%,the humidity under 30% blade height decreases 5.3%.In this paper, we also analyzed the aerodynamic performance and the control of steam condensation when angle of attack is changed in 2 modeling schemes which is proved to be better in controlling the secondary flow and humidity. The results of numerical simulation shows that the application of the non-axisymmetric end wall modeling of White cascade has good adaptability in angle of attack. Under the condition of positive attack angle, the secondary flow loss below 20% height of blade increased slightly, but the average aerodynamic parameters at the exit section of the blade were not changed. Under the condition of negative attack angle, the secondary flow loss is reduced and the high pressure area at the suction side near the hub gradually increased with the increasing of attack angle as well as moving toward the middle of the axial location. So the condensation phenomenon in the middle of the suction surface of the blade is suppressed.