Elliptical pin fins as an alternative to circular pin fins for gas turbine blade cooling applications: Part I: Endwall heat transfer and total pressure loss characteristics

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.