Heat (mass) transfer and film cooling effectiveness with injection through discrete holes. Part I: Within holes and on the back surface

A jet stream entering a cross-flow is investigated for injection through 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 of the hole entrance. The Sherwood number is fairly uniform along the circumference of the inside hole surface even at the low blowing rate considered. This is quite different from the case without injection (zero blowing rate), when the Sherwood number is highly nonuniform. The transfer rate in the hole is weakly influenced by the cross-flow 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 similar to that in the absence of cross-flow except at low blowing rates. The Sherwood numbers on the hole entrance surface (backside) are the same as when there is no cross-flow. Thus, the Sherwood numbers inside the hole and on the back surface can be closely approximated from experiments without cross-flow.