Kathryn L. Kirsch

Heat Transfer and Pressure Loss Measurements in Additively Manufactured Wavy Microchannels

The role of additive manufacturing for the hot section components of gas turbine engines grows ever larger as progress in the industry continues. The opportunity for the heat transfer community is to exploit the use of additive manufacturing in developing nontraditional cooling schemes to be built directly into components. This study investigates the heat transfer and pressure loss performance of additively manufactured wavy channels. Three coupons, each containing channels of a specified wavelength (length of one wave period), were manufactured via direct metal laser sintering (DMLS) and tested at a range of Reynolds numbers. Results show that short wavelength channels yield high pressure losses, without corresponding increases in heat transfer, due to the flow structure promoted by the waves. Longer wavelength channels offer less of a penalty in pressure drop with good heat transfer performance. [DOI: 10.1115/1.4034342]

Effects of Geometry, Spacing, and Number of Pin Fins in Additively Manufactured Microchannel Pin Fin Arrays

The demand for higher efficiency is ever present in the gas turbine field and can be achieved through many different approaches. While additively manufactured parts have only recently been introduced into the hot section of a gas turbine engine, the manufacturing technology shows promise for more widespread implementation since the process allows a designer to push the limits on capabilities of traditional machining and potentially impact turbine efficiencies. Pin fins are conventionally used in turbine airfoils to remove heat from locations in which high thermal and mechanical stresses are present. This study employs the benefits of additive manufacturing to make uniquely shaped pin fins, with the goal of increased performance over conventional cylindrical pin fin arrays. Triangular, star, and spherical shaped pin fins placed in microchannel test coupons were manufactured using direct metal laser sintering (DMLS). These coupons were experimentally investigated for pressure loss and heat transfer at a range of Reynolds numbers. Spacing, number of pin fins in the array, and pin fin geometry were variables that changed pressure loss and heat transfer in this study. Results indicate that the additively manufactured triangles and cylinders outperform conventional pin fin arrays, while stars and dimpled spheres did not. [DOI: 10.1115/1.4038179]

Repeatability in Performance of Micro Cooling Geometries Manufactured with Laser Powder Bed Fusion

Stringent regulations on aircraft engine emissions introduce a series restrictions on weight, size, and durability of all engine components to increase efficiency. In the hot section of a gas turbine engine, for example, airfoil internal cooling schemes must provide more efficient cooling with minimal mass flow. Such a requirement drives the cooling channels’ size to the micro scale. One new tool currently being explored to achieve industry-required efficiencies can be found in advanced manufacturing techniques, such as laser powder bed fusion. However, as with all new technologies, the laser powder bed fusion process must be thoroughly investigated, fully understood, and achieve reliable and repeatable results before the process is widely implemented for gas turbine airfoils. This paper provides experimental results on the dimensions, as well as pressure loss and heat transfer performance, of microchannels manufactured using laser powder bed fusion; the microchannels mimic those suitable for airfoil internal cooling. Variability in the performance will be quantified for different builds, as well as for different materials.

Row Removal Heat Transfer Study for Pin Fin Arrays

Arrays of variably-spaced pin fins are used as a conventional means to conduct and convect heat from internal turbine surfaces. The most common pin shape for this purpose is a circular cylinder. Literature has shown that beyond the first few rows of pin fins, the heat transfer augmentation in the array levels off and slightly decreases. This paper provides experimental results from two studies seeking to understand the effects of gaps in pin spacing (row removals) and alternative pin geometries placed in these gaps. The alternative pin geometries included large cylindrical pins and oblong pins with different aspect ratios. Results from the row removal study at high Reynolds number showed that when rows four through eight were removed, the flow returned to a fully-developed channel flow in the gap between pin rows. When larger alternative geometries replaced the fourth row, heat transfer increased further downstream into the array.Copyright

Data Mining of General Corrosion of Most Commonly Used Iron-Based Alloys Using Kohonen Mapping

This study was developed to provide an innovative methodology for designing steel alloys. Information on the general corrosion of a wide number of steel alloys in various electrolytes and environments was obtained from the National Institute of Standards and Technology (NIST). Parameters such as pH and conductivity used in each experiment (alloy in contact with an environment), along with alloy composition (from UNS number), and corrosion rates, were all collected in a single data row, or vector. To cluster by similarities, a web-based, publicly available Kohonen mapping software was used to perform the clustering analysis; Kohonen maps work by clustering together similar vectors and separating those vectors that differ. A vector was formed for each experiment for which corrosion rates were recorded; 1521 experiments were performed and each of those vectors was used to train the Kohonen Map. Once the Kohonen map is trained, each one of the cells forming the two-dimension Kohonen map will form clusters of vectors. Vectors containing similar information will be clustered together while dissimilar vectors will be clustered separately on the Kohonen map. The cells of the Kohonen map will adopt a “prototype” vector to be the representative of that cell; the prototype vector adopts the average values of all stored vectors in that cell. After the Kohonen map is trained, new vectors containing fabricated metal alloy composition (steels) and environment information can be input into the map. These new vectors, even though they do not contain corrosion rates, can be classified by the Kohonen map and entered into a cluster on the map. This methodology can be use to explore “if-then” scenarios of a new alloy in a different environment as well as obtain an expected corrosion rate of that particular alloy in that particular environment. Preliminary results of the trained Kohonen map are shown and discussed. The map results are used to explore the effects of the experiment environments and alloy composition on the general corrosion of the stainless steels.Copyright

Data Mining of General Corrosion of Most Commonly Used Alloys Using Kohonen Mapping

This study was developed to provide an optimum method for designing metal alloys. Information on general corrosion of the most commonly used alloys, namely nickel-, iron-, aluminum-, stainless steel-, copper- and carbon-based alloys, was obtained from the National Institute of Standards and Technology (NIST). Parameters such as pH, temperature, conductivity, and composition of the electrolyte used in each experiment (alloy in contact with an environment), along with alloy composition (UNS) and corrosion rates, were collected. The parameters in the collected data were the electrolyte characteristics, the alloy composition, and the general corrosion rates. The data consisted of over 4000 samples. The next task was to cluster the data by similarities of the parameters. A web-based, publicly available Kohonen mapping software was used to perform the clustering analysis; the two dimensional Kohonen map was chosen. The map is composed of a number of cells on a plane of two dimensions and each cell stores a sample prototype representing that cell. Kohonen maps have the ability to preserve the topological properties of the data; i.e. samples with similar “high corrosion rates” will cluster together in a given cell of the map, while samples with “low corrosion rates” will cluster in a different cell, far apart from the cell storing the “high corrosion rates” samples. Once the Kohonen map is trained to cluster the samples by their corrosion rates, each one of the parameters of the samples (representing the electrolyte characteristics, the alloy composition and the general corrosion rates) is drawn as a function of the (X,Y) map position of the cell where the samples were stored. In this paper, we present the results obtained with nickel alloy data for which 1369 samples (or independent experiments) were collected.Copyright