Determination of a Local Bulk Temperature Based Heat Transfer Coefficient for the Wetted Surfaces in a Single Inline Row Impingement Channel

High performance turbine airfoils are typically cooled with a combination of internal cooling channels and impingement. In such applications, the jets impinge against a target surface, and then exit along the channel formed by the jet plate, target plate, and side walls. Local convection coefficients are the result of both the jet impact, as well as the channel flow produced from the exiting jets. Numerous studies have explored the effects of jet array and channel configurations on both target and jet plate heat transfer coefficients. However, most current studies use the plenum temperature as the reference temperature in heat transfer calculations. This presents some difficulty to designers who need to determine heat transfer rates based on the local bulk temperatures. This paper examines three different methods to determining the local bulk temperature in a steady state impingement channel heat transfer experiment. The various methods will be compared based on their ease of application as well as their accuracy in describing the results. One method proves to be the most accurate, while another proves to be more easily implemented. The methods are compared for a single case previously studied, on a 15 hole, single row impingement channel, with dimensions of $X/D=5$⁠, $Y/D=4$⁠, $Z/D=1$ and 3, and an average jet based Reynolds number of 17,000 and 45,000. Effects due to the choice of the reference temperature in heat transfer calculations are shown to cause significant variations in the calculated heat transfer coefficients. These results point to a transition between different flow regimes in the post-impingement flow.