Reduction Method for the Secondary Flow Loss in Turbine Cascade

Abstract

The aerodynamic loss accounted to the secondary flow, or secondary loss, is one of the most prominent cause of the internal losses in turbine cascades. Secondary losses are mostly due to the interaction of Horse-Shoe Vortex and endwall crossflow. Authors have developed a so called endwall fence to reduce the secondary loss in gas turbine cascade by mitigating this interaction. However, the improvements resulting by the application of this method to a steam turbine cascade proved to be not so remarkable as for the gas turbine cascade. By conducting total pressure measurements at the endwall, previous results showed that the stream wise evolution of the losses presents two peaks; Horse-Shoe Vortex peak and crossflow peak. The abovementioned endwall fence is blocks the Horse-Shoe Vortex, but its screening effect on the crossflow is not sufficient. So in this research the use of two kinds of fences is proposed to reduce the secondary loss: one is to block the pressure side leg of the Horse-Shoe Vortex, the second is to block and guide the crossflow, which starts from the middle of the blade passage, toward the outlet. Therefore, they are called respectively Horse-Shoe Vortex fence and crossflow fence. The tests are carried out using the wind tunnel cascade and the test fences are made by 3D printer. The total loss is estimated by means of an automatically moving pitot tube located downstream the cascade. Many kinds of fences are tested and the optimum fence shape and position to minimize the secondary loss is obtained.