Robert Patrick Campbell

Quantitative Visualization of Full-Coverage Discrete-Hole Film Cooling

Water tunnel experiments were carried out to study full-coverage discrete-hole film cooling for geometries applicable to gas turbine combustor liners. The cooling holes were spaced at a pitch to diameter ratio of 6.5 and had an injection angle of 20° to the cooled surface. The mainstream flow direction was in line with the cooling holes. Blowing ratios from 0.5 to 5.7 were studied, which is a range typical of combustor liners.A unique multiple plane PLIF (planar laser-induced fluorescence) technique was used to measure time-averaged film cooling concentration at various heights above the surface to be cooled. Three-dimensional data sets were generated to quantitatively visualize cooling-jet film coverage, structure, and interaction. Film coverage as close as 0.25 mm (0.010 in.) from the surface was measured, thereby yielding data that approach adiabatic film effectiveness. Two sets of film cooling experiments were conducted. One set used a model with a relatively small array of 2.54 mm (0.100 in.) holes, meant to be a large-scale model of hole sizes encountered in combustor liners. The second set used a large array of 0.51 mm (0.020 in.) nominal diameter laser-drilled holes, manufactured in the same manner as combustor liner cooling holes.The results show that near-wall film coverage is minimum for blowing ratios from 1.7 to 3.3. At blowing ratios less than 1.7 and greater than 3.3, the film coverage was improved. Jet structure and interaction was also observed. In particular, jet separation behavior and coalescence were visualized, and both were generally a function of blowing ratio.Copyright

Applications of Advanced Liquid Crystal Video Thermography to Turbine Cooling Passage Heat Transfer Measurement

Over the past few years advances in thermochromic liquid crystal (TLC) thermography have improved its usefulness as a quantitative temperature measurement technique. Many of these improvements have been discussed in the literature but few have been directly applied to solving gas turbine heat transfer problems. The purpose of this work is to combine the best of these techniques into an advanced, easy to use, low cost system which can provide accurate, rapid and complete heat transfer data for advanced gas turbine development.The older, more common technique of using narrow band liquid crystals to map isotherm distributions has been updated to use wide temperature range crystals with full hue-temperature calibrations over their entire response range with accuracy as good or better than thermocouples. The system consists of an RGB video camera, a hue, saturation and intensity (HS1) framegrabber, on-axis lighting and a linear thermal gradient TLC calibrator. Algorithms have been developed for automated data validation, spatial transformations of data taken on non-planar surfaces and superposition of multiple data sets to construct full field data over surfaces with wide ranges of heat transfer coefficients (h). Instead of yielding mean h, h at a few thermocouple locations or h at individual isotherms, this system provides continuous distributions of h.These techniques have been used to map the heat transfer coefficient distributions in advanced power generation gas turbine internal cooling passages. These include serpentine passages with and without turbulators, leading edge passages and 180° rums. Results are presented in full field plots of heat transfer enhancement, Nu(x,y)/Nudb.Copyright

Measurements of Time-Varying Jet Isopleths Using Dual Light Sheet PLIF

Mass transfer analogies have long been used to experimentally determine the distribution of cooling fluid through pointwise sampling for turbine blade, nozzle or combustor film cooling. The behavior of a turbulent jet or plume flowing into its surroundings cannot be fully understood from point measurements alone, however. Full-field measurement of the instantaneous distribution of cooling fluid can reveal the structure and mechanisms governing cooling performance. This paper describes an improved dual light sheet PLIF (Planar Laser Induced Fluorescence) technique developed for full field concentration measurements. An analytical model of laser light sheet / fluorescent dye interaction was formulated and used to evaluate the light sheet attenuation corrections. With the more common single light sheet technique, these corrections lead to substantial concentration uncertainty which can be substantially reduced by using a dual light sheet. The dual light sheet technique was used to study the time-varying position and area of concentration isopleths for a round jet issuing into quiescent surroundings. Results show that, although concentrations at any point vary widely with time, the area within a given concentration isopleth remains virtually constant.Copyright