Heat Transfer and Pressure Drop in Combustor Cooling Channels With Combinations of Geometrical Elements

Abstract

An investigation was conducted to assess the thermal performance of 90° ribs, low and high W-shaped ribs, and combinations of low W-shaped ribs with high W-shaped ribs and with dimples in a rectangular channel with an aspect ratio (W/H) of 2:1. The blockage ratios (e/Dh) were 0.02 with the 90° ribs and the low W-shaped ribs and 0.06 with high W-shaped ribs. The rib pitch-to-height ratio (P/e) were 10 and 20. The channel height-to-dimple diameter (H/D) was 16.67; the dimple depth-to-dimple diameter (δ/D) was 0.3. The ribs and the dimples were located on one channel wall (side W). Furthermore, W-shaped ribs and 90° ribs with e/Dh = 0.027 and P/e = 10 were also individually investigated in a test channel with 1/4 of its cross section blocked. The Reynolds numbers investigated (Re > 100k) are typical for combustor liner cooling configurations in gas turbines. Local heat transfer coefficients using the transient thermochromic liquid crystal technique and overall pressure losses were measured. The different configurations were investigated numerically to visualize the flow pattern in the channel and to support the understanding of the experimental data. The results show that the highest heat transfer enhancement rates are obtained by a combination of W-shaped ribs with P/e = 10 and e/Dh = 0.06 and W-shaped ribs with P/e = 10 and e/Dh = 0.02. The best thermal performance is achieved by regularly spaced lower W-shaped ribs and by a compound roughness of regularly spaced W-shaped ribs and dimples at Re below and above 300,000, respectively.