Full aerodynamic loss data for efficient squealer tip design in an axial flow turbine

Full aerodynamic data in an axial flow turbine cascade have been measured for squealer tips in the entire ranges of tip gap (h) and squealer height (hst). The results show that as hst/s increases, aerodynamic loss decreases, reaches a minimum, and then increases, regardless of h/s. The minimal loss is always found in the case of hst/s = 1.88% for all test values of h/s. Therefore, this squealer tip is considered as an optimal one in the loss reduction. For h/s = 0.5%, the loss change with hst/s is found to be minute, and hence the squealer tip has only a little benefit compared to the flat tip. When h/s ≥ 1.0%, however, the loss change with hst/s becomes more considerable. Thus, the squealer tip performs better than the flat tip for these wide tip gaps. Near the casing, h/s has a huge impact on flow turning, in contrast to a weak impact of hst/s. The present surface flow visualizations give an explanation of why aerodynamic loss increases with increasing hst/s when hst/s > 1.88%. The full loss data, which are reported for the first time, will serve as a milestone in the efficient blade tip design.