New experimental data are provided for full-coverage effusion cooling and impingement array cooling, as applied simultaneously onto the respective external and internal surfaces of a single instrumented test plate. For the effusion cooled surface, presented are spatially resolved distributions of surface adiabatic film cooling effectiveness, and surface heat transfer coefficients. For the impingement cooled surface, presented are spatially resolved distributions of surface Nusselt numbers. Impingement jet arrays at different jet Reynolds numbers, from 7930 to 18,000, are employed. Experimental data are given for spanwise and streamwise impingement hole spacing such that coolant jet hole centerlines are located midway between individual effusion hole entrances. For the effusion cooling, streamwise hole spacing and spanwise hole spacing (normalized by effusion hole diameter) are 15 and 4, respectively. Effusion hole angle is 25 deg, and effusion plate thickness is 3.0 effusion hole diameters. In regard to the impingement cooled cold-side surface of the effusion plate, associated surface Nusselt number variations provide evidence that impingement jets are turned and redirected as they cross the impingement passage, just prior to the entrance of coolant into individual effusion holes. In regard to the effusion cooled hot-side surface of the effusion plate, when compared at particular values of injectant and mainstream Reynolds numbers, streamwise location x/de and blowing ratio BR, significantly increased thermal protection is provided when the effusion coolant is provided by an array of impingement cooling jets (compared to a cross flow channel supply arrangement).
The present study provides new effusion cooling data for both the surfaces of the full-coverage effusion cooling plate. For the effusion-cooled surface, presented are spatially resolved distributions of surface adiabatic film cooling effectiveness and surface heat transfer coefficients (measured using transient techniques and infrared thermography). For the impingement-cooled surface, presented are spatially resolved distributions of surface Nusselt numbers (measured using steady-state liquid crystal thermography). To produce this cool-side augmentation, impingement jet arrays at different jet Reynolds numbers, from 2720 to 11,100, are employed. Experimental data are given for a sparse effusion hole array, with spanwise and streamwise impingement hole spacing such that coolant jet hole centerlines are located midway between individual effusion hole entrances. Considered are the initial effusion blowing ratios from 3.3 to 7.5, with subsonic, incompressible flow. The velocity of the freestream flow which is adjacent to the effusion-cooled boundary layer is increasing with streamwise distance, due to a favorable streamwise pressure gradient. Such variations are provided by a main flow passage contraction ratio CR of 4. Of particular interest are effects of impingement jet Reynolds number, effusion blowing ratio, and streamwise development. Also, included are comparisons of impingement jet array cooling results with: (i) results associated with crossflow supply cooling with CR = 1 and CR = 4 and (ii) results associated with impingement supply cooling with CR = 1, when the mainstream pressure gradient is near zero. Overall, the present results show that, for the same main flow Reynolds number, approximate initial blowing ratio, and streamwise location, significantly increased thermal protection is generally provided when the effusion coolant is provided by an array of impingement cooling jets, compared to a crossflow coolant supply.
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