In-Wall Network (Mesh) Cooling Augmentation of Gas Turbine Airfoils

Abstract

The present study investigates a new class of in-wall mesh cooling techniques intended to produce significant wetted surface area heat transfer enhancement products, hAAwetted, with low to moderate pressure losses. Cooling networks (meshes) are presented using round pins and rounded diamond shaped pins with H/Dp ratios of 0.2 and S/Dp ratios of 1.5, as well as less dense rounded diamond pins of smaller diameter with H/Dp of 0.3 and S/Dp of 2.14. These geometries differ substantially from conventional pin fin arrays in which H/Dp ≥ 1 and S/Dp ratios are typically about 2.5. The objective of mesh cooling is to provide highly effective cooling inside component walls while maintaining very thin outer protective skin thickness. Special attention is paid to the combination of techniques including pin meshes, turbulators, and concavity arrays that can provide multiple design solutions for heat transfer and pressure loss goals. Average channel wetted-area heat transfer capabilities exceeding 3 times that of smooth channels have been demonstrated using actual surface area enhancements of no more than 20%. This cooling capability increase is also realized with a large decrease in channel material solidity, up to 30%, compared to conventional pin fin arrays. Friction factor enhancements in the range of 15 to 25 times that of a smooth channel turbulent flow accompany this performance. This investigation represents the first of its kind to demonstrate feasible in-wall cooling methods that may be realized in practice for investment cast turbine blades.