Heat Transfer Lab Thermal Measurements in Film Cooling Flows

The most common parameter for rating the effectiveness of a film cooling flow is in terms of adiabatic effectiveness. Adiabatic effectiveness is a parameter that rates the cooling potential that remains along a surface downstream of film cooling holes. In an actual engine, coolant is introduced at temperatures of 1000-1300K whereas the freestream may be at 1700-2000K. Downstream of a coolant injection location, the surface will be at some temperature in between the two. The closer the surface temperature is the coolant temperature, the more effective the cooling is in that region. In a low-temperature, experimental environment, this same assessment can be performed by imposing a temperature difference between the freestream and coolant. The local wall temperature is then measured to determine the effectiveness. The surface downstream of the holes is adiabatic. To measure these temperatures in the present research thermocouple techniques were employed. Thermocouples were immersed in the freestream and coolant-supply flows to measure those temperatures. A traversing thermocouple was used to collect near-wall data from which the local adiabatic wall temperature was extrapolated. In general, effectiveness is highest nearest the hole exit (0 - Twall=Tfs; 1.0 - Twall=Tc). The effectiveness decreases in moving in the streamwise direction due to dissipation of the coolant. Spreading of the coolant, though, provides a gradual increase in effectiveness between holes in moving downstream. Below, effectiveness dsitributions for streamwise injection with L/D=2.3 at two blowing rates are provided. Due to the trajectory of the VR=1.0, it tends to have lower effectiveness in the near-hole region.

Adiabatic Effectiveness x-z Profiles for Two Blowing Rates:

Adiabatic Effectiveness for M=0.5 Adiabatic Effectiveness for M=1.0
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