Measurements of Heat Transfer Characteristics of Gap Leakage Around a Misaligned Component Interface

In an attempt to understand the effects of leakage through a component-to-component interface on the turbine end wall heat transfer, this paper describes an experimental efforts on examining the detailed heat transfer characteristics near a leaking gap. Geometric misalignment around the gap is modeled by either a forward-facing step or a backward-facing step. Heat transfer measurement here uses a temperature-sensitive fluorescent imaging of a thermographic phosphor (TGP). The TGP technique reveals detailed distribution of local heat transfer coefficient and adiabatic wall temperature in the vicinity of the leakage. The results suggest that, for a given leakage-to-mainstream mass flow ratio, the adiabatic wall temperature closes to the level of leakage temperature and is relatively insensitive to the nature of misalignment. On the outer hand, however, the value of heat transfer coefficient varies strongly with misalignment and streamwise location relative to the gap. Overall, the leakage thickens the approaching boundary layer and significantly extends the length of reattachment downstream compared to the corresponding cases without leakage. To further qualify the TGP technique, which is relatively new for transient measurement of local heat transfer, an analysis toward its efficacy in resolving complex convective system is developed in this study. One of the main advantages that TGP inherits is its capability of determining both heat transfer coefficient and reference temperature based on a single test. Other methods, such as the transient liquid crystal technique, generally require separate tests each with different thermal conditions.