An inverse design of a double-pitch passage for an infinite cascade model experiment

Abstract

In this study, sidewalls of a turbine cascade experimental apparatus are designed to satisfy periodic flow conditions with two blades without any flow control or tailboards. Generally, the turbine cascade experimental apparatus needs removing fluid from the cascade walls or adjusting tailboards located downstream of the cascade to establish periodic flow conditions through the cascade blades. If a linear turbine cascade often consists of only a few blades within a passage, advantages to this experimental arrangement are increased from using larger turbine cascades, a lower mass flowrate and corresponding decrease in required power, and easier optical access within the cascade passage. However, fewer blades in the cascade make it difficult to establish periodic flow conditions between blades compared to infinite cascade flow conditions. In order to test a turbine cascade with a few blades without flow control devices, only two turbine blades are installed within a double-pitch passage. Sidewall shape is designed with 12 geometric design variables using a gradient-based optimization method, and surface isentropic Mach number distribution on the blades is chosen for the existence of periodic flow conditions. The computed result shows periodic flow conditions obtained by modifying only the sidewalls of the double-pitch passage as a cascade experimental apparatus.