HEAT (MASS) TRANSFER AND FILM-COOLING EFFECTIVENESS WITH INJECTION THROUGH DISCRETE HOLES .1. WITHIN HOLES AND ON THE BACK SURFACE

A jet stream entering a crossflow is investigated for injection throug h a single hole and an array of holes for blowing rates of 0.2 to 2.2. The naphthalene sublimation technique has been employed to study the local mass (heat) transfer in the injection hole and in the vicinity o f the hole entrance. The Sherwood number is fairly uniform along the c ircumference of the inside hole surface even at the low blowing rate c onsidered. This is quite different from the case without injection (ze ro blowing rate), when the Sherwood number is highly nonuniform. The t ransfer rare in the hole is weakly influenced by the crossflow and the zone, which is directly affected is confined close to the hole exit ( about 0.15 hole diameter in depth). The average Sherwood number is sim ilar to that in the absence of crossflow except at low blowing rates. The Sherwood numbers on the hole entrance surface (backside) are the s ame as when there is no crossflow. Thus, the Sherwood numbers inside t he hole and on the back surface can be closely approximated from exper iments without crossflow.