Elliptical Pin Fins as an Alternative to Circular Pin Fins for Gas Turbine Blade Cooling Applications: Part 1 — Endwall Heat Transfer and Total Pressure Loss Characteristics

Abstract

Detailed experimental investigation of the wall heat transfer enhancement and total pressure loss characteristics for two alternative elliptical pin fin arrays is conducted and the results are compared to the conventional circular pin fin arrays. Two different elliptical pin fin geometries with different major axis lengths are tested, both having a minor axis length equal to the circular fin diameter and positioned at zero degrees angle of attack to the free stream flow. The major axis lengths for the two elliptical fins are 1.67 and 2.5 times the circular fin diameter, respectively. The pin fin arrays with H/D = 1.5 are positioned in a staggered 2 row configuration with 3 fins in the first row and 2 fins in the second row with S/D = X/D = 2. Endwall heat transfer and total pressure loss measurements are performed two diameter downstream of the pin fin arrays (X/D = 2) in a rectangular cross-section tunnel with an aspect ratio of 4.8 and for varying Reynolds numbers between 10000 and 47000 based on the inlet velocity and the fin diameter. Liquid Crystal Thermography is used for the measurement of convective heat transfer coefficient distributions on the endwall inside the wake. The results show that the wall heat transfer enhancement capability of the circular pin fin array is about 25–30% higher than the elliptical pin fin arrays in average. However in terms of total pressure loss, the circular pin fin arrays generate 100–200% more pressure loss than the elliptical pin fin arrays. This makes the elliptical fin arrays very promising cooling devices as an alternative to conventional circular pin fin arrays used in gas turbine blade cooling applications.

Experimental Investigation of Innovative Internal Trailing Edge Cooling Configurations with Pentagonal Arrangement and Elliptic Pin Fin

“…Looking at the graph, it is clearly visible that the streamwise-oriented pin fins experience lower heat transfer coefficients than the circular ones. Such result, as also described by other authors [23,24], is mainly due to the different wake behavior of the two devices: while circular pin fins produce a wake with two large counter-rotating vortexes, for the elliptic pin fin configurations, such vortexes usually are not present. Hence, streamwise elliptic pin fins produce less turbulence and then lower HTC values.…”

“…By means of the transient TLC technique, [5,6] studied the effects of the fillet radii on the endwall heat transfer, while [7][8][9] studied the effects of turning flow in a wedge-shaped duct with circular, elliptical, and diamond cross-section pin fins. It has been demonstrated by various authors [23,24] that cylinders with streamline-shaped crosssection have much less flow resistance than circular ones, while they have about the same behavior in terms of heat transfer. The work in [10] also investigated the partial length circular pin fin concept and found that both the array averaged-heat transfer and friction factor decrease with increasing gap distance.…”

Variable Property Nusselt Numbers in a Channel with Pin Fins

“…10 and 19 and the presentstudy are then in approximateagreement with values from Chyu 10 for circular-in-line, llet-cylinder-in-line,and llet-cylinder-staggeredtypes of pin ns, but are higher than elliptic pin-n data (N n and SEF) from Uzol and Camci. 19 Figure 17 also shows that N u=N u 0;cp data from the present study increase from 2.2 to 3.0 as the temperature ratio T 0i =T w decreases from 0.93 to 0.68. Because of the effects of variable properties,these data are located above the circular-staggeredpin-n data obtainedat different Reynolds numbers (and T 0i =T w near 1.0).…”

“…10 The Nusselt number data in Fig. 17 are plotted as dependent on this parameter because data from Chyu, 10 data from Uzol and Camci, 19 and the present Re d varying data for circular-staggeredpin ns collectin one continuous distribution. This not only illustrates the agreement and consistencyof these three differentsets of data, but also indicatesthe usefulness of this parameter in correlating heat transfer data from channels with pin ns.…”

Numerical investigation of pin-fin thermal performance for staggered and inline arrays at low Reynolds number

“…As the crosssection of the fins remain a dominant factor in deciding fin performance and efficiency experimentation on unorthodox cross-section of fins continue to extract maximum fin performance. Uzol and Camci [10] have experimented on elliptical fins as a substitute for circular fins for gas turbine cooling blade applications. They have been able to accurately describe the physics behind pressure loss and heat transfer enhancements by using Wake flow field measurements and Particle Image Velocimetry (PIV) to create visualizations insides the wakes of elliptical and circular fins.…”