As future land-based gas turbine engines are being designed to operate with inlet temperatures exceeding 1300°C (2370°F), efforts at NETL have been focused on developing advanced materials systems that are integrated with novel airfoil cooling architectures. Recent achievements in the areas of low cost diffusion bond coat systems applied to single- and poly-crystalline nickel-based superalloys, as well as development of thin nickel-based oxide dispersion strengthened layers are presented in this paper. Integration of these material systems with commercially cast, novel, pin-fin internal cooling airfoil arrays, tripod film cooling hole architectures, trailing edge cooling geometries, and near surface micro-channel concepts is also presented.

The current study focused on the effects of varying jet diameter and surface roughness on the target plate from jet impingement. A single row of five jets, plenum fed, expels air onto the flat target surface and the spent air is constrained to exit in only one direction, causing the jets to encounter maximum cross-flow. Baseline jet plates were equipped with pressure taps, one for each jet, to determine flow. The initial parameters, diameter D, height to diameter H/D, and jet spacing to diameter S/D is 9.53 mm (0.375 in), 2 and 4 respectively. Upon defining the optimum array of jet diameters, three test cases will be conducted using different surface features, 90 degree ribs, chevrons and X-shaped ribs on the target plate to further enhance the heat transfer performance of the jet impingement. The parameters, width W and height H, for the surface features will be set constant at 3.18 mm (0.125 in). The Reynolds number, Re, in this experimental study ranged from 50,000 to 80,000. A transient liquid crystal technique is employed in this study to determine the local and average heat transfer coefficient distribution on the target plate. The baseline tests revealed that the heat transfer is more predominate in the upstream jets impingement zones, however, by varying the diameters the heat transfer is more uniformly distributed downstream. The results also revealed that the rib-turbulators, especially X-shaped ribs, can further enhance heat transfer enhancement in the downstream jets where crossflow can affect impingement.

This paper describes a detailed experimental investigation of a narrow rectangular channel based on the double-wall cooling concept that can be applicable to a gas turbine airfoil. The channel has dimensions of 63.5 mm by 12.7 mm, corresponding to an aspect ratio of 5:1. A single pin-fin element, arranged in 9 rows is fitted into the channel. The pin diameter, D, is 12.7 mm, and the ratio of pin-height-to-diameter, H/D is 1. The pins are arranged based on the typical inter-pin spacing of 2.5D in both spanwise and streamwise directions. The Reynolds number, based on the hydraulic diameter of the pin fin and the mean bulk velocity, ranges from 6,000 to 15,000. The experiments employ a hybrid technique based on transient liquid crystal imaging to obtain the distributions of the local heat transfer coefficient over all of the participating surfaces, including the endwalls and all the pin elements. Commercially available CFD software, ANSYS CFX, is used to qualitatively correlate the experimental results and to provide detailed insights of the flow field created by the array.The heat transfer on both the endwall and pin-fin surfaces revealed similar pattern compared to the typical circular pin-fin array, which were conducted at higher Reynolds number. The total heat transfer enhancement of current pin-fin array is approximately five times higher than that of fully developed smooth channel with low pressure loss, which resulted in much higher thermal performance compared to other pin-fin array as reported in the literature.

The current detailed experimental study focuses on the optimization of heat transfer performance through jet impingement by varying the coolant flow rate to each individual jet. The test section consists of an array of jets, each jet individually fed and metered separately, that expel coolant into the channel and exit through one end. The diameter D, height-to-diameter H/D, and jet spacing-to-diameter S/D are all held constant at 9.53 mm, 2, and 4, respectively. Upon defining the optimum flow rate for each jet, varying diameter jet plates are designed and tested using a similar test setup with the addition of a plenum. Two test cases are conducted by varying the jet diameter within 10% compared to the benchmark jet diameter, 9.53 mm. The Reynolds number, which is based on hydraulic diameter of the channel and total mass flow rate entering the channel, ranges from approximately 52,000 up to 78,000. The transient liquid crystal technique is employed in this study to determine the local and average heat transfer coefficient distributions on the target plate. Commercially available computational fluid dynamics software, ansys cfx, is used to qualitatively correlate the experimental results and to fully understand the flow field distributions within the channel. The results revealed that varying the jet flow rates, total flow varied by approximately ±5% from that of the baseline case, the heat transfer enhancement on the target surface is enhanced up to approximately 35%. However, when transitioning to the varying diameter jet plate, this significant enhancement is suppressed due to the nature of flow distribution from the plenum, combined with the complicated crossflow effects.

The current detailed experimental study focuses on the optimization of heat transfer performance through jet impingement by varying the coolant flow rate to each individual jet. The test section consists of an array of five jets, which is individually fed and metered separately, and expels air through one exit. The jet diameter D, channel height to jet diameter H/D, and jet spacing to diameter S/D, are all held constant at 9.53 mm (0.375 in), 2 and 4 respectively. The Reynolds number, which is based on jet diameter and bulk mean velocity at each jet, ranges from 50,000 to 80,000. A transient liquid crystal technique is employed in this study to determine the local and overall-average heat transfer coefficient distribution on the target plate. Commercially available CFD software, ANSYS CFX, is used to qualitatively correlate the experimental results and to provide detailed insights of the flow field created by the array of jets. The results revealed higher heat transfer coefficients in the impingement area, while decreasing in the radial direction. The upstream region exhibited high heat transfer performance, which is ultimately driven by the jet impingement from the first jet to the third jet. Heat transfer performance decreases at the downstream region with the development of cross-flow. By varying the jet flow rates at approximately ±2%, local heat transfer at the downstream region is elevated and the total heat transfer enhancement on the target surface is enhanced up to 35% compared to the baseline case.