*Currently at the Naval Surface Warfare Center, Philadelphia, PA ROW REMOVAL HEAT TRANSFER STUDY FOR PIN FIN ARRAYS Kathryn L. Kirsch, Jason K. Ostanek* and Karen A. Thole Eleanor Kaufman Pennsylvania State University Pratt and Whitney Mechanical and Nuclear Engineering Department 400 Main Street University Park, PA 16802 East Hartford, CT 06108 ABSTRACT 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. INTRODUCTION In the hot section of a gas turbine engine, gas path temperatures far surpass each component’s melting temperature. Consequently, advanced cooling schemes are necessary to maintain the functional lifetime of the component and are integral in extending these lifetimes as engine designs progress. Cooling schemes are present on the exterior of components as well as in internal passages. Internal cooling can take numerous forms but in areas where structural support, in addition to high heat removal is necessary, pin fin arrays are commonly employed. Pin fins in this paper refer to pins that extend across the entire channel; note that many also refer to these features as pedestals. The addition of pin fins into the flow induces vortices at the pin base as well as increases the amount of surface area over which heat transfer can take place. The typical pin fin shape is a circular cylinder; much research has focused on the spacing variations of such pin fins and has reported on both row-averaged and overall array heat transfer. A consistent finding from these previous studies is that a peak in heat transfer augmentation is seen near the third row of pins [1–4], depending on the streamwise spacing of the pins. Beyond this peak, a leveling off or even a slow decay in heat transfer augmentation is reported. For these studies, a baseline configuration of sixteen rows of pin fins was studied at two different Reynolds numbers. This paper seeks to accomplish the following: understand changes in heat transfer when there is a gap in the pin fin array by removing a particular row; and understand the changes in augmentation when a row of alternatively-shaped pin fins is inserted into the gap. NOMENCLATURE A c pin cross sectional area A wet wetted area D pin diameter D h hydraulic diameter f Fanning friction factor f 0 fully developed, smooth passage Fanning friction factor, f 0 = (0.078)Re Dh -0.25 [5] h heat transfer coefficient H pin fin height k air thermal conductivity k p pin thermal conductivity L length of pin fin array, length of oblong pin m fin eigenvalue,        [6] N pins number of pins in array N rows number of pin rows Nu Dh duct Nusselt number, Nu Dh = hD h k -1 Nu 0 fully developed, smooth passage Nusselt number, Nu 0 = 0.023Re Dh 0.8 Pr 0.4 [7] p static pressure p 0 static pressure in unobstructed duct P perimeter of pin q in heat dissipated by foil heaters 1 Copyright © 2014 by ASME Proceedings of ASME Turbo Expo 2014: Turbine Technical Conference and Exposition GT2014 June 16 – 20, 2014, Düsseldorf, Germany GT2014-25348