Comparisons of cooling performance and flow characteristics of a combustor liner plate with compound angle and simple angle effusion holes

Abstract

The present investigation considers a unique compound angle arrangement, never previously considered, with α = 30°, β = ±30°, such that the compound angle of the effusion holes changes from β = +30° to β = −30°, as adjacent rows of effusion holes are encountered. Also provided are data for comparison from a simple angle configuration with α = 30°, β = 0°. Coolant is supplied to both effusion hole arrays using arrays of impingement cooling jets. The results of the numerical simulations are obtained using the ANSYS FLUENT V 21.1 numerical code, with a shear stress transport (SST) k–ω turbulence model. Data are provided for main flow Reynolds numbers from 142,000 to 155,000, impingement flow Reynolds numbers from 7900 to 18,000, effusion flow Reynolds numbers from 10,400 to 23,600, and overall blowing ratios from 3.3 to 7.4. When β is changed from 0° to ±30°, area-averaged film cooling effectiveness values and area-averaged heat transfer coefficient magnitudes increase overall by approximately 2.89% and 11.7%, respectively. This is because the use of compound angle arrangements often inhibits the formation of the horseshoe-shaped vortex, and the resulting counter-rotating vortex legs, that often promote lift off of significant film concentrations from the test surface. The skewed and non-symmetric character of the horseshoe-shaped vortex is also increased by the use of compound angle arrangement, which also sometimes provides local improvements in surface thermal protection.

Introduction

Combustion is a series of complex exothermic chemical reactions, where the oxidation of fuels releases large amounts of heat and produces new chemicals as reactants [1]. Owing to the combustion reaction within the combustor, the liner is one of the hottest parts of a gas turbine engine, with the shortest lifespan, due to the large thermal and fatigue stresses and stress gradients [2]. The highest possible flame temperatures are employed within combustor liners in order to reduce pollution and achieve eco-friendly power generation. An example of such an arrangement with zero carbon emissions is hydrogen co-fired combustors. Maintenance and longevity of associated combustor liner components are also important, and require acceptable metal temperatures and allowable metal temperature gradient magnitudes [3]. As a consequence, effective and durable cooling technologies for combustor liner components are needed. The present investigation is focused on surface heat transfer, thermal field, and flow field characteristics of such a cooling technology. Employed is a unique compound angle film cooling configuration, as coolant is supplied to the entrances of effusion holes using an array of impingement cooling jets.

Other recent investigations which employ the simultaneous use of full-coverage effusion cooling and impingement jet array cooling for thermal protection of the combustor liner components in gas turbine engines include Andrews et al. [4], Al Dabagh et al. [5], Andrews et al. [6], Andrews and Nazari [7], Cho and Rhee [8], Liu et al. [9], and Ahmed et al. [10]. Results from these investigations provide evidence that the combination of these cooling technologies provide consistently improved thermal protection, compared to utilization of either an impingement jet array alone, or an effusion film cooling arrangement alone. Also addressed within these studies is consideration of the number and placement of impingement jets, relative to the locations of effusion holes. Hong et al. [11] and Cho et al. [12] consider the influences of a variety of different types of fins as these are installed between the impingement cooling plate and the effusion cooling plate. According to Cho et al. [12], with fins utilized, staggered hole arrangements provide improved thermal protection levels, compared to in-line hole configurations. Shi et al. [13] indicate that the optimal thermal performance of a combined effusion/impingement cooling system, with a 6 by 6 array of impingement holes, is achieved with a blowing ratio of approximately 1.0. According to Miller et al. [14], compared to in-line configurations, staggered hole arrangements on the outflow side of the film cooled plate provide better thermal protection because of reduced jet interactions and enhancement of horizontal distributions of the coolant. El-Jummah et al. [15] consider impingement/effusion heat transfer characteristics using conjugate computational fluid dynamics predictions, including comparisons with experimental results. Rao et al. [16] investigate cooling arrangements with different pin fin geometries and different effusion hole configurations, and demonstrate that overall heat transfer rates with pin fins and effusion holes are up to 51% larger, compared to values on flat plates. Chen et al. [17] provide numerically predicted data, which further demonstrate improved thermal performance of impingement/effusion cooling systems, relative to the use of impingement cooling alone. Using numerical predictions, Liu et al. [9] consider a novel hexagonal array of effusion holes. Another innovative arrangement is investigated by Ahmed et al. [10] in the form of a reverse jet impingement technology, which gives increased internal surface area, enhanced surface heat transfer levels, and minimization of adverse cross-flow effects. He et al. [18] numerically investigate a staggered arrangement of film and impingement holes, both with 90° inclination angles, and show that thickening of the downstream film plate gives improved overall cooling efficiency at low blowing ratios.

The present investigation considers a unique compound angle arrangement, never previously considered, with α = 30°, β = ±30°, such that the compound angle of the effusion holes changes from β = +30° to β = −30°, as adjacent rows of effusion holes are encountered. Also provided are data for comparison from a simple angle configuration with α = 30°, β = 0°. Coolant is supplied to both effusion hole arrays using arrays of impingement cooling jets. The results of the numerical simulations are obtained using the ANSYS FLUENT V 21.1 numerical code, with a shear stress transport (SST) k–ω turbulence model. Data are provided for main flow Reynolds numbers from 142,000 to 155,000, impingement flow Reynolds numbers from 7900 to 18,000, effusion flow Reynolds numbers from 10,400 to 23,600, and overall blowing ratios from 3.3 to 7.4.

Included are numerically simulated distributions of local flow velocity, local secondary flow vectors, local spanwise vorticity, and local streamwise vorticity. Note that these numerically-predicted flow characteristics are difficult or impossible to measure experimentally. Also provided are numerically-predicted local and spatially-averaged distributions of surface adiabatic film cooling effectiveness, and local and spatially-averaged distributions of surface heat transfer coefficients. Other additional numerically predicted results are also presented and compared to newly-measured experimental measurements of flow field distributions of stagnation pressure and local flow film cooling effectiveness. Associated results from the present investigation are unique because no other effusion/impingement cooling investigation considers such a unique compound angle film arrangement.