燃气涡轮机英文文献和中文翻译

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ombustion processes have been a concern for decades due to their complex nature.This paper thus adopts an experimental approach to characterise large coherent structures in swirl burners under isothermal conditions so as to reveal the effects of swirl in a number of geometries and cold flow patterns that are relevant in combustion. Aided by techniques such as Hot Wire Anemometry, High Speed Photography and Particle Image Velocimetry, the recognition of several structures was achieved in a 100 kW swirl burner model.49001

Several varied, interacting, structures developed in the field as a consequence of the configurations used. New structures never observed before were identified, the results not only showing the existence of very well defined large structures, but also their dependency on geometrical and flow parameters. The PVC is confirmed to be a semi-helical structure, contrary to previous simulations performed on the system. The appearance of secondary recirculation zones and suppression of the vortical core as a consequence of geometrical constrictions are presented as a mechanism of flow control. The asymmetry of the Central Recirculation Zone in cold flows is observed in all the experiments, with its elongation dependent on Re and swirl number used.

1. Introduction

Lean premixed combustion using swirl flame stabilisation is widespread amongst gas turbine manufacturers. The use of swirl mixing and flame stabilisation is also prevalent in many other non-premixed systems. Problems that emerge include those due to flame stabilisation as a function of fuel type, combustor geometry and thermo-acoustic instabilities.

Noise arises from two factors, the fine turbulent scale structures and the large coherent structures which occur in the jet flow This also has important implications for flame stabilisation, dependent on whether or not the flames stabilise in and around the coherent structures or in other regions. Nevertheless, both the above phenomena are poorly understood. Numerical simulations have been used to try to explain the development of such structures; their extremely complex nature has become apparent as well as the lack of time dependent validation data for these models.

Low NOx and syngas burners are processes that are used to considerably reduce emissions and cope with new fuels and are used extensively in gas turbine technologies. Swirling flows and often lean premixing of fuel and air are at the core of these processes. These techniques are effective in emissions reduction programmes due to the more uniform temperature profiles generated by the very stable and lean combustion processes produced by swirling flows. However, localised non-homogeneities in air–fuel ratio are well known to be able to stimulate instabilities in the burning region via unbalanced combustion regimes, often coupled with system or combustor acoustic modes, fluid dynamic instability and stimulated by the Rayleigh criterion. The effectiveness of any premixing system is also clearly of importance here

Swirling flows have been studied extensively for numerous combustor/burner applications with special emphasis on their three-dimentional characteristics and methodology for flame holding . These flows are designed to create coherent recirculation zones capable of recycling hot chemically active reactants to enable excellent flame stability to be achieved. It has been found that the levels of swirl used in some combustors, coupled with the mode of fuel injection can induce the appearance of unwanted and undesirable regular fluid dynamic instabilities. These can couple with natural resonances, exciting large amplitude oscillations which can damage equipment, provoking partial or complete failure of the system . Combustion may also occur in and around these structures causing fundamental changes of flame stabilisation mechanisms owing to changes in length scales, turbulent flame speed, flame stretch and other related parameters. Simultaneously combustion may occur in flame fronts which engulf these coherent structures again giving rise to different flame stabilisation mechanisms . Combustion may also suppress some time dependent coherent structures, although evidence is that acoustic coupling may well re-introduce them .