Hot-wire anemometry measurements of simulated film cooling are presented to document the influence of the free-stream turbulence intensity and film cooling hole length-to-diameter ratio on mean velocity and on turbulence intensity. Measurements are taken in the zone where the coolant and free-stream flows mix. Flow from one row of film cooling holes with a streamwise injection of 35 deg and no lateral injection and with a coolant-to-free-stream flow velocity ratio of 1.0 is investigated under free-stream turbulence levels of 0.5 and 12 percent. The coolant-to-free-stream density ratio is unity. Two length-to-diameter ratios for the film cooling holes, 2.3 and 7.0, are tested. The Measurements document that under low free-stream turbulence conditions pronounced differences exist in the flowfield between L/D= 7.0 and 2.3. The difference between L/D cases are less prominent at high free-stream turbulence intensities. Generally, Short-L/D injection results in “jetting” of the coolant farther into the free-stream flow and enhanced mixing. Other changes in the flowfield attributable to a rise in free-stream turbulence intensity to engine-representative conditions are documented.

An experimental investigation of transition in concave-curved boundary layers at two free-stream turbulence levels (0.6 and 8.6 percent) was performed. For the lower free-stream turbulence intensity case, Go¨rtler vortices were observed in both laminar and turbulent flows using liquid crystal visualization and spanwise velocity and temperature traverses. Transition is thought to occur via a vortex breakdown mode. The vortex locations were invariant with time but were nonuniform across the span in both the laminar and turbulent flows. The upwash regions between two vortices were more unstable than were the downwash regions, containing higher levels of u’ and u’ v’, and lower skin friction coefficients and shape factors. Turbulent Prandtl numbers, measured using a triple-wire probe, were near unity for all post-transitional profiles, indicating no gross violation of Reynolds analogy. No streamwise vortices were observed in the higher turbulence intensity case. This may be due to the high eddy viscosity, which reduces the turbulent Go¨rtler number to subcritical values, thus eliminating the vortices, or due to an unsteadiness of the vortex structure that could not be observed by the techniques used. Based upon these results, predictions that assume two-dimensional modeling of the flow over a concave wall with high free-stream turbulence levels, as on the pressure surface of a turbine blade, seem to be adequate—there is no time-average, three-dimensional structure to be resolved. High levels of free-stream turbulence superimposed on a free-stream velocity gradient (which occurs within curved channels) cause a cross-stream transport of momentum within the flow outside the boundary layer. The total pressure within this region can rise above the value measured at the inlet to the test section.

The JOURNAL OF HEAT TRANSFER (JHT) has, for some time, recognized the need to prepare a set of guidelines on estimating experimental uncertainty. This was warranted for two major reasons: to ensure uniformity of presenting experimental data, and to raise the authors' awareness regarding the importance of giving a more precise statement about their measurement uncertainties. The JHT Editorial Board has reached the consensus that the guidelines recently adopted by the Journal of Fluids Engineering (JFE) are sound and can be modified for use by the JHT authors and readers. The JFE guidelines can be found in its Vol. 113, September 1991, pp. 313-314. The JFE editors have discussed the subject thoroughly to reach an agreement on their guidelines. Much of the guideline material described below was adopted from the JFE guidelines with few modifications. The example, drawn from a simple heat transfer problem, is added. It is hoped that the guidelines and example will help the authors prepare their papers and the referees review the papers on a consistent basis. The example, suggested by H. W. Coleman, a principal author of the JFE statement on experimental uncertainties, is gratefully appreciated. Suggestions and comments by R. J. Moffat are also gratefully appreciated.

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Experimental hot-wire anemometry and thermocouple measurements are taken to document the sensitivity which film cooling performance has to the hole length and the geometry of the plenum which supplies cooling flow to the holes. This sensitivity is described in terms of the effects these geometric features have on hole-exit velocity and turbulence intensity distributions and on adiabatic effectiveness values on the surface downstream. These measurements were taken under high freestream turbulence intensity (12%) conditions, representative of operating gas turbine engines. Coolant is supplied to the film cooling holes by means of (1) an unrestricted plenum, (2) a plenum which restricts the flow approaching the holes, forcing it to flow co-current with the freestream, and (3) a plenum which forces the flow to approach the holes counter-current with the freestream. Short-hole (L/D = 2.3) and long-hole (L/D = 7.0) comparisons are made. The geometry has a single row of film cooling holes with 35°-inclined streamwise injection. The film cooling flow is supplied at the same temperature as that of the freestream for hole-exit measurements and 10°C above the freestream temperature for adiabatic effectiveness measurements, yielding density ratios in the range 0.96–1.0. Two coolant-to-freestream velocity ratios, 0.5 and 1.0, are investigated. The results document the effects of (1) supply plenum geometry, (2) velocity ratio, and (3) hole L/D.

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