Reduction of Secondary Flow Effects in a Linear Cascade by Use of an Air Suction From the Endwall

The objective of this study is to reduce secondary flow effects in a linear cascade by sucking the working fluid from the endwall. It is widely known that the secondary flow developed in a cascade has a significant impact on the cascade loss or blade erosion in steam turbines. Therefore, a number of studies have been made on the physics of the secondary flow and several devices to control the secondary flow, such as a fence, have been examined. In this study, considering the application to nozzles in gas turbines or steam turbines, the air suction approach is investigated for reducing the secondary flow effects. A suction slit is provided on the lower endwall of the cascade and a flow rate of the sucked air is controlled by adjusting the exit pressure of the slit. The effects of the suction upon the flow nearby the endwall and the secondary flow are observed through several flow visualizing techniques, for example an oil flow method or a tuft method. Furthermore, velocity and stagnation pressure measurement are conducted by a five-hole pressure tube. This clearly demonstrates the vorticity and loss profiles downstream of the cascade with and without the endwall suction.