Yanji Xu

Effect of Maximum Camber Location on Aerodynamics Performance of Transonic Compressor Blades

It is well known that to increase rotational velocity is one of the effective measures to increase total pressure ratio. With increasing velocity, under the condition of transonic flow, the obvious effect of maximum camber location on aerodynamics performance of compressor blades especially in the supersonics zone can be found. In order to reduce the blade losses and to improve the blade design methodology it is necessary to study this complex flow mechanism. This paper describes only the influence of relative maximum camber location on aerodynamics performance, mainly adiabatic efficiency. As an example an axial fan was designed and calculated by the methodologies developed at the Institute of Engineering Thermophysics, Chinese Academy of Sciences.Copyright

An Effective Turbine Blade Parameterization and Aerodynamic Optimization Procedure Using an Improved Response Surface Method

This paper describes a procedure for a rapid and accurate 3D aerodynamic optimization of high performance turbine blades. This procedure has been developed to account for the complicated geometrical aspects and the complex nature of the associated fluid flow, while remaining simple, practical and demanding less computing power. The focus has been placed on the blade geometrical representation using a set of simple algebraic equations (blade parameterization) and on the aerodynamic optimization methodology based on the numerical computations by a N.S. solver. The turbine blade, including thickness distribution and camber line for each section of the blade span and radial stacking line, has been defined by polynomials, allowing investigation of the influence of any single-parameter change on blade performance. An improved response surface method, by incorporating a simulated annealing algorithm (RS-SAM), has been found to improve the accuracy and to strengthen the optimum-searching ability. A multi-objective response surface method (MORSM) has also been included for testing. One example is given here to demonstrate the effectiveness of the procedure.Copyright

Experimental Investigation of Thermoacoustic Oscillations in Syngas Premixed Multi-Swirler Model Combustors

This paper presents the experimental results of the thermoacoustic oscillations in several premixed syngas multi-swirler model combustors. Multi-swirler lean premixed combustion technology has been successfully applied to achieve an anticipative stability, lower noise and high efficiency in industrial gas turbines that burn natural gas or distillated oil. However, some critical operational issues, including combustion oscillations, flashback, blowout and autoignition, should be considered and balanced when burning the coal-derived syngas mainly composed of H2 and CO. In this paper several multi-swirler combustors are tested on an atmospheric-pressure downscaled test rig. Each multi-swirler combustor includes several elemental swirling nozzles with the equal Swirl Number and different array of port configurations. The dynamic pressure, dynamic heat release and critical flashback equivalence ratio are tested in these model combustors burning several kinds of simulated syngases with a similar low heat value. Firstly, the critical equivalence ratios of flashback are shown and compared with those in single-swirler combustors. Secondly, the paper presents the analysis of the temporal and spectral features of dynamic pressure oscillations using many data-processing methods. Thirdly, we describe the bifurcation and retardation phenomenon when the combustion transforms between stable and unstable operations. We also discuss how the equivalence ratio, the fuel composition and the combustor inlet velocity play important roles in determining the amplitudes, the frequencies, the bifurcation and retardation of the thermoacoustic oscillations. Finally, we use a wavelet transformation with a higher resolution in time domain than that with a PSD estimation by the AR model. The processes of amplitude “jump” and flashback are analyzed in details. The results in this paper could improve the current understanding of the nonlinear self-excited and combustion driven thermoacoustic oscillations in gas turbines and give us some references to the development of lean premixed syngas turbines for coal-based IGCC and co-generation systems.Copyright

Investigation of Coal Fueled Chemical Looping Combustion Using Fe3O4 as Oxygen Carrier

Chemical-looping combustion (CLC) is a novel combustion technique with CO2 separation. Magnetite (Fe3O4) was selected as the oxygen carrier and Shenhua coal (Inner Mongolia, China) as the fuel for this study. The influences of operation temperatures, and coal to Fe3O4 mass ratios on the reduction characteristics of the oxygen carrier were investigated using an atmosphere TGA. The sample, comprised of 2.25mg coal and 12.75mg Fe3O4, was heated to 1000°C. Experimental results show that the reaction between the coal volatile and Fe3O4 began at 700°C while the reaction between the coal char and Fe3O4 occurred at 800°C and reached a peak at 900°C. Fe3O4 was fully reduced into FeO, while some FeO was further reduced to Fe. As the operation temperature rises, the reduction conversion rate increases. At the temperatures of 850°C, 900°C, and 950°C, the reduction conversion rates were 37.1%, 46.5%, and 54.1% respectively. When the mass ratios of coal to Fe3O4 were 5/95, 10/90, 15/85, and 20/80, the reduction conversion rates were 29.5%,40.8%,46.5%, and 46.6% respectively. With the increase of coal to Fe3O4 mass ratio, the conversion rate increases first and then changes no more. There exists an optimal coal to Fe3O4 mass ratio.

Dynamic and Flashback Characteristics of the Syngas Premixed Swirling Combustors

Flashback and combustion thermoacoustic oscillation are two of the major problems in the lean premixed combustors of gas turbine, especially for hydrogen enriched syngas fuels. This paper introduced the experimental results regarding the characteristics research of thermoacoustic oscillation, dynamic heat release and flashback based on a premixed combustion experimental system. The critical flashback equivalence ratio and three dynamic parameters were tested in four types of combustor using eleven kinds of simulated syngas which have the same LHV. Partial flashback and full flashback are observed. With the increase of the hydrogen concentration, the critical equivalence ratio is decreasing and full flashback occurs more easily. The change of nozzle’s geometry structure has a consequent effect on the flashback characteristics. Flashback occurs more easily when the thermoacoustic oscillation is greater, and the corresponding critical equivalence ratio is smaller. Both flashback status and normal status are relative stable combustion within a certain range of equivalence ratio. As the generation and disappearance of the thermoacoustic oscillation and its amplitude-frequency characteristics somehow could be in some randomicity, the critical equivalence ratio is correspondingly not a constant. The dynamic chemiluminescence intensity which indicates the dynamic heat release has a good corresponding relationship in terms of amplitude and frequency characteristics with the dynamic pressure which indicates the thermoacoustic oscillation. Through power spectral density analysis, dynamic pressure and chemiluminescence intensity signals both reflect the dynamic characteristics of the combustor and can be applied in the research of the combustion instability, including the thermoacoustic oscillation characteristics, fluctuation of the chemical heat release rate and flashback characteristics and so on. The results and methods could give some reference to the development of hydrogen enriched gas turbines for future IGCC and poly-generation systems.Copyright