The Orifice-type Impinging Cooling Jet Applied Internally At Gas Turbine Blade Leading Edge

The impinging jet for cooling is treated in previous studies as discharged from a long nozzle with a large length-to-diameter ratio to ensure the inside flow is fully developed and fully turbulent.However,for the real internal cooling structure at the leading edge of gas turbine blade,because of the narrow space,the coolant has to flow through orifices drilled at the thin wall of internal serpentine cooling passage to form jets.The separated flow at the inlet of orifice cannot reattach at the inner wall,having its cross section first decreased to the minimum value and then increase.The jet structure is completely different from that for a long nozzle.In addition,because the cooling air at blade leading edge first gathered at one side of the cooling passage and then forced to turn sharply to exit through the orifices.Therefore,each orifice-type jet becomes asymmetric,skewed with respect to the axis of its hole and this leads to a non-symmetric heat transfer distribution on the target surface.Although it is practical,there is no relative study on neither the fluidic features nor the heat transfer properties of such asymmetric orifice-type jet.In view of this,this study conducts experiments on asymmetric orifice-type jet impingement on a flat plate to address its detailed jet structure and resultant heat transfer characteristics.The jet Reynolds number R_e=20,000,orifice wall thickness-to-diameter ratio t/D_j=0.5,and the jet exit-to-target plate distance H/D_jranges from 0.5 to4.0.Results newly demonstrate that:(1).The velocity profiles measured in two orthogonal planes(x-z plane and y-z plane)proved the jet is asymmetric.The velocity profiles in y-z plane are wider than that measured in x-z plane,showing the wider spread of jet in y-z plane.Besides,the peaks of profiles in x-z plane deflect towards the positive x-direction,showing the jet in skewed towards the positive x-direction with an angle ofα=5°.In addition,the jet in this study has a short potential core(L_p=2D_j).(2).The asymmetric jet caused the non-symmetric heat transfer distribution on the target plate.Because of the jet’s wider spread in y-z plane,the local Nusselt number distribution on the target plate is wider.The skewed jet in x-z plane caused the peak of local Nusselt number distribution to shift towards the uphill side,i.e.,the direction where jet comes from.In addition,the maximum of stagnation heat transfer varying with different impingement distance(H/D_j)happened at small distance due to a short potential core.