Full Coverage Effusion Cooling with a Narrow Duct Backside Coolant Supply

摘要

Full coverage effusion cooling was studied for a square array of 90° effusion cooling holes with backside cooling using a 5 mm duct air supply to the coolant holes. Active cooling was used with metal walls and 300K effusion cooling into a 27 m/s mean velocity duct flow at 770K crossflow temperature. The 152 mm square test section had 15 rows of holes and the hole diameter, D, was varied for constant hole pitch, X. The X/D values studied were 11.0, 7.0 and 4.6. At a constant coolant mass flow rate the wall pressure loss was reduced as X/D was reduced and there was an associated reduction in the film blowing ratio, M. The duct air feed to the holes enhanced the backside cooling of the wall. These results were compared with previous work using a plenum chamber air feed. The increased duct air feed velocity relative to the plenum low velocity air feed resulted in an increase in the overall cooling effectiveness due to the additional heat transfer by the duct crossflow velocity, However, the trailing edge cooling effectiveness improvement was small as there was no residual cross flow here and the greatest effect was at the leading edge of the test wall. The decrease in X/D was the most effective way of increasing the overall cooling effectiveness as this reduced the blowing rate without decreasing the coolant mass flow rate. This was more effective than using 30° inclined holes with an X/D of 11, as the hole exit velocity was much lower for the same coolant mass flow rate with 90° holes at an X/D of 4.8 than with 30° holes at an X/D of 11.0.