Thermal load distributions on the large-scale turbine blade tip with a rounded inlet edge

Abstract

Thermal load and near-wall flow characteristics on the flat tip with a rounded inlet edge are investigated in a large-scale aeroengine turbine cascade with the change of tip gap-to-span ratio (h/s), using the naphthalene sublimation and oil film methods. When h/s <= 1.5%, there exists no distinct flow separation at the tip gap inlet. For h/s = 0.5% and 1.0%, the tip surface near the inlet has high local thermal load, whereas that near the exit has low local thermal load. When h/s >= 1.75%, however, there is a strong flow reattachment after the inlet flow separation, and severe thermal load is found at the reattachment site. Thus, the critical value of h/s, at which the inlet flow separation is triggered, is about 1.75%. The increments of h/s from 0.5% to 1.5%, from 1.5% to 1.75%, and from 1.75% to 2.5% result in a little decrease, a substantial increase, and a relatively small increase in the average tip thermal load, respectively. The rounded flat tip has much lower average thermal load than the simple flat tip especially when 0.5% <= h/s <= 1.5%. In this study, qualitative tip gap flow models over the rounded flat tip are suggested for the wide range of h/s.