Abstract

A new experimental study is presented for a combustor with a double-wall cooling design. The inner wall at the hot gas side features effusion cooling with 7-7-7 laidback fan-shaped holes, and the outer wall at the cold side features an impingement hole pattern with circular holes. Data have been acquired to assess the thermal and aerodynamic behavior of the setup using a new, scaled up, engine-similar test rig. Similarity includes Reynolds, Nusselt, and Biot numbers for hot gas and coolant flow. Different geometrical setups are studied by varying the cavity height between the two walls and the relative alignment of the two hole patterns at several different blowing ratios. This article focuses on the thermal performance of the setup. The temperature data are acquired using two infrared systems on either side of the effusion wall specimen. In addition to cooling effectiveness evaluations, finite element simulations are performed, yielding the locally resolved wall heat fluxes. Results are presented for three cavity heights and two longitudinal specimen alignments. The results show that the hot gas side total cooling effectiveness can achieve values as high as 90% and is mainly influenced by the effusion coverage. Impingement cooling has a small influence on overall effectiveness, and the area of influence is mainly located upstream where effusion cooling is not built up completely. The analyzed geometric variations show a major influence on cavity flow and impingement heat transfer. Small cavities lead to constrained flow and high local Nusselt numbers, while larger cavities show more equalized Nusselt number distributions. A present misalignment shows especially high influence at small cavity heights. The largest cavity height, in general, showed a decrease in heat transfer due to reduced jet momentum.

Highlights

  • The continuous development of aero-gas turbines leads to constant improvements that benefit air passengers and the environment

  • Using FE models, heat fluxes and heat transfer coefficients can be derived in addition to total cooling effectiveness data

  • The measurements are performed at engine-similar density ratios and blowing ratios

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Summary

Introduction

The continuous development of aero-gas turbines leads to constant improvements that benefit air passengers and the environment. The development of new combustor technologies and the improvement of existing concepts are key to reaching new target efficiencies. A commonly used combustion technology to reduce the formation of nitrogen oxides (NOx) is the Rich-Quench-Lean (RQL) combustor describing the three major combustion regions in an annular combustor. The air from the compressor is divided into two major flow paths. A small amount of the compressor air is used to create an air-assisted fuel spray, providing a minimal amount air for burning that fuel spray in a rich environment (red arrow). The remaining air is guided around the combustor liner and used for consecutive mixing and dilution and mainly for the cooling of the liner walls

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