Numerical analysis of acoustic characteristics in gas turbine combustor with spatial non-homogeneity

Acoustic characteristics in an industrial gas-turbine combustor are numerically investigated by a linear acoustic analysis. Spatially non-homogeneous temperature field in the combustor is considered in the numerical calculation and the characteristics are analyzed in view of acoustic instability. Acoustic analyses are conducted in the combustors without and with acoustic resonator, which is one of the acoustic-damping devices or combustion stabilization devices. It has been reported that severe pressure fluctuation frequently occurs in the adopted combustor, and the measured signal of pressure oscillation is compared with the acoustic-pressure response from the numerical calculation. The numerical results are in good agreement with the measurement data. In this regard, the phenomenon of pressure fluctuation in the combustor could be caused by acoustic instability. From the numerical results for the combustor with present acoustic resonators installed, the acoustic effects of the resonators are analyzed in the viewpoints of both the frequency tuning and the damping capacity. It is found that the resonators with present specifications are not optimized and thus, the improved specification or design is required.     

Combustion instability mechanism of a lean premixed gas turbine combustor

Lean premixed combustion has been considered as one of the promising solutions for the reduction of NOx emissions from gas turbines. However, unstable combustion of lean premixed flow becomes a real challenge on the way to design a reliable, highly efficient dry low NOx gas turbine combustor. Contrary to a conventional diffusion type combustion system, characteristics of premixed combustion significantly depend on a premixing degree of combusting flow. Combustion behavior in terms of stability has been studied in a model gas turbine combustor burning natural gas and air. Incompleteness of premixing is identified as significant perturbation source for inducing unstable combustion. Application of a simple convection time lag theory can only predict instability modes but cannot determine whether instability occurs or not. Low frequency perturbations are observed at the onset of instability and believed to initiate the coupling between heat release rate and pressure fluctuations.     

某重型燃气轮机燃烧室燃烧流动的数值模拟

对某重型燃气轮机燃烧室燃烧天然气进行数值模拟,在模拟过程中采用了雷诺应力模型、EBU-Arrheniue湍流燃烧模型和六通量辐射模型来描述其燃烧流动过程,运用FLUENT软件求解了三维流场和温场分布.计算结果能够很好地反映该重型燃气轮机燃烧室燃烧流动特点,对预测燃烧室内的燃烧流动有一定参考价值.     

Experimental study on combustion instability and attenuation characteristics in the lab-scale gas turbine combustor with a sponge-like porous medium

The present study has experimentally investigated the combustion instability and its attenuation characteristics in the lab-scale swirlstabilized premixed combustor with a sponge-like porous medium. Unlike the conventional premixed burners, this model combustor has the unique features including a porous dump plane and an acoustic cavity, which was devised for attenuating the combustion instability. When replacing the dump plane with a non-porous medium, the burner becomes the conventional design. In order to evaluate the damping effects of the porous medium on the unstable flame dynamics, various acoustic and photonic measurements and flame visualization were made. Special emphasis is given to the effects of the acoustic cavity length on the stabilization characteristics. Results showed that the model combustor with the porous dump plane and the acoustic cavity exhibited dramatic attenuation of the pressure oscillation intensity by up to about 40 %. The attenuation was increased with increasing the acoustic cavity length. It was also found that the attenuation is effective not only for the fundamental resonance but also for its higher harmonics. Based on the experimental results, detailed discussions are made for the combustion instability and its attenuation characteristics in the model gas turbine combustor with porous and nonporous media.

     

Analysis of the combustion instability of a model gas turbine combustor by the transfer matrix method

Combustion instability is a major issue in design of gas turbine combustors for efficient operation with low emissions. A transfer matrix-based approach is developed in this work for the stability analysis of gas turbine combustors. By viewing the combustor cavity as a one-dimensional acoustic system with a side branch, the heat source located inside the cavity can be described as the input to the system. The combustion process is modeled as a closed-loop feedback system, which enables utilization of well-established classic control theories for the stability analysis. Due to the inherent advantage of the transfer matrix method and control system representation, modeling and analysis of the system becomes a straightforward task even for a combustor of the complex geometry. The approach is applied to the stability analysis of a simple combustion system to demonstrate its validity and effectiveness. This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon Dong Jin Cha received his B.S. and M.S. degrees from Hanyang University in Seoul, Korea, in 1981 and 1983, respectively. He then received his Ph.D. in ME from the University of Illinois at Chicago in 1992, and worked at the US DOE NETL for the next three years as a National Research Council (NRC) Associate. Dr. Cha is currently a Professor at the Department of Building Services Engineering at Hanbat National University in Daejeon, Korea. His research interests include combustion instability of gas turbine for power generation and fluid flows in building services engineering. Jay H. Kim received his BSME from Seoul National University in 1977, MSME from KAIST in 1979 and Ph.D. in ME from Purdue University in 1988. He has joined the Mechanical Engineering faculty of the University of Cincinnati in 1990, and is currently a Professor. Before joining the University of Cincinnati, he worked in industry for six years in Korea and US. His research interests have been in broad areas of acoustics, vibrations and applied mechanics with recent focuses on human/bioacoustics and vibration, gas pulsations and elastic stability. Yong-Jin Joo received his BSME and MSME from Sung Kyun Kwan University in Seoul, Korea, in 1990 and 1992, respectively. Mr. Joo is currently a Project Leader for IGCC Operation Technologies at KEPRI (Korea Electric Power Research Institute) which is the central R&D center of KEPCO (Korea Electric Power Corporation). His research interests include the development of operation and maintenance simulator for power plants including IGCC.     

In-situ measurement of reflection coefficient and its application to predicting combustion instability in a gas turbine combustor

Journal of Mechanical Science and Technology - Here, a procedure that uses in-situ data recorded by two microphones placed inside an operating gas turbine combustor to determine the reflection...     

Experimental study on flame structure and temperature characteristics in a lean premixed model gas turbine combustor

Experimental study was carried out in an atmospheric pressure, laboratory-scale dump combustor showing features of combustion instabilities. Flame structure and heat release rates were obtained from OH emission spectroscopy. Qualitative comparisons were made between line —integrated OH chemiluminescence image and Abel—transformed one. Local Rayleigh index distributions were also examined. Mean temperature, normalized standard deviation and temperature fluctuations were measured by coherent anti-Stokes Raman spectroscopy (CARS). To see the periodic behavior of oscillating flames, phase—resolved measurements were performed with respect to the pressure wave in the combustor. Results on system damping and driving characteristics were provided as a function of equivalence ratio. It also could be observed that phase resolved temperatures have been changed in a well—defined manner, while its difference between maximum and minimum reached up to 280K. These results would be expected to play an important role in better understanding of driving mechanisms and thermo-acoustic interactions.     

大气参数对燃气轮机进气冷却效果的影响

针对燃气轮机进气冷却的效果在不同大气参数下变化很大的问题,对燃气轮机进气冷却装置的热力过程、影响因素、经济效果等方面进行了研究。基于某电厂燃气轮机和燃气-蒸汽联合循环机组的运行数据,利用热平衡仿真软件Gate Cycle对两种发电机组系统进行模块化建模,并增加进气冷却装置,定量分析了两种发电机组进气被冷却后输出功率的增加量(即进气冷却效果)在不同大气参数(温度、相对湿度和压力)下的变化情况。研究结果表明,大气参数的变化,会对燃气轮机进气冷却的效果产生很大影响,两者之间呈现出一定的数值关系。     

基于CFD的氢气／空气当量比对微尺度燃烧室燃烧特性影响的分析

以美国麻省理工学院（MIT）研制的硅基六晶片微燃烧室为研究对象,提出利用二维CFD（计算流体动力学）数值模拟的方法,研究在保持微尺度燃烧室进口氢气／空气流量不变的情况下,改变氢气／空气当量比对燃烧室燃烧特性的影响。整个模拟计算主要包括氢气／空气的流动路径、微燃烧室的内部区域以及整个燃烧室的墙壁面;同时在计算过程中我们考虑了氢气／空气的流体动力学特性、传热学特性和详细的基元反应机理。结果表明,利用二维CFD数值模拟的方法研究微尺度燃烧室燃烧特性可行,与国外实际测量结果较为相似,为今后微型燃气轮机燃烧室的研制及改进提供了一定的参考依据。     

A study on 65 % potential efficiency of the gas turbine combined cycle

Journal of Mechanical Science and Technology - This study investigates the possibility of achieving 65 % efficiency in a gas turbine combined cycle. Several options to realize it were compared. A...     

A CFD study of wet gas metering over-reading model under high pressure

The venturi flow meter is increasingly being preferred in multiphase flow measurement because of its shorter upstream and downstream straight sections, less influenced by the flow pattern and relatively small pressure loss. However, when the venturi is used for wet gas measurement, the over-reading phenomenon occurs due to the presence of a small amount of liquid. Many scholars have established over-reading models to correct the measured values of wet gas. Regrettably, the applicability of these over-reading models under actual high pressure operating conditions has not been verified. Therefore, this review focuses on numerical simulation of the flow of wet gas in the venturi tube under high pressure conditions (11MPa/13MPa/15 MPa). The discrete phase model (DPM) and the standard k-ε model was employed in this review. The simulations results reveals the flow characteristics of wet gas in venturi tube, which includes the flow field distributions, droplet concentration distributions and wall pressure profile distributions, and indicates that the over-reading values increases with the increase of Lockhart-Martinelli parameters and gas volume flow rate, but decreases with the increase of pressure. Moreover, the ISO model has the best performance under high pressure conditions.     

A CFD study of low pressure wet gas metering using slotted orifice meters

Wet gas metering is becoming an increasingly important problem to many industries, in particular the oil and gas industry. Extensive studies have been done in the past on Venturi and standard orifice differential pressure (DP) flow meters to tackle wet gas flow problems. However in recent years, the slotted orifice flow meter has been developed in the attempt to improve the performance of the standard orifice meter. The novel flow meter is shown to be insensitive to the upstream flow profile with lower head loss and faster pressure recovery. This paper describes the numerical studies to establish the effect of different geometrical perforations on the performance of the slotted orifice. Three sets of slotted orifices with varying aspect ratios (1.5≤l/w≤3.0), of rectangular perforations and one slotted orifice with a circular perforation and a β ratio of 0.40 are simulated in a 1.6 m horizontal pipe using the k-ε turbulence model over a range of parameters, i.e. gas volume fraction (GVF) and gas mass flow rate. The commercial CFD code, FLUENT 6.3 was used to model the wet gas flow. Simulation results revealed that the shape of the perforation has no effect on the differential pressure, However, a marginally better pressure recovery was observed with rectangular perforations of l/w=3.0. The relatively higher over-reading values obtained in this work are consistent with the results of Geng et al. (2006) [1] that for a slotted orifice, a low β ratio is more sensitive to the liquid presence in the stream and hence is preferable for wet gas metering. Mass flow prediction by wet gas correlations showed that the homogeneous model, Steven’s and De Leeuw’s correlations had the best performance, with a calculated mean error of 4%-5%.     

A study on combustion characteristics of superadiabatic combustor in porous media

Because of the energy resource exhaustion, the aggravating environmental air pollution, the smoke phenomena and so on, the recent trends and targets in designing combustor are reduction of pollutant emissions and improvement of combustor efficiency. Therefore many combustion methods and emission control technologies have been proposed by many researchers through numerical and experimental analyses, One of the most available and effective combustion methods is the excess enthalpy combustion, so called, the superadiabatic combustion. In this study, the superadiabatic combustion with the reciprocating flow in a porous media has been investigated with the variation of equivalence ratio, flow velocity and reciprocating cycle time. In this system, the flow direction is reversed regularly by the solenoid valves. The results of this study show that the maximum gas temperature is remarkably higher than the theoretical adiabatic flame temperature and the emission characteristic is very excellent. The analyses reveal several attractive characteristics of the flame and the proposed idea is promising to burn mixtures of low heat content in a reciprocating type combustor. This combustor can be applied to the elimination of unburned compound, with more intensive and continuous study.     

基于PLC的燃气轮机进气冷却测控系统的研制

介绍了由PLC作为下位机的燃气轮机进气冷却测控系统,详细阐述了测控系统的设计方案以及PLC的功能实现.运行结果表明,该系统性能稳定可靠,自动化程度高,能够满足进气冷却的测控要求.     

A numerical study on extinction and NOx formation in nonpremixed flames with syngas fuel

The flame structure, extinction, and NO_x emission characteristics of syngas/air nonpremixed flames, have been investigated numerically. The extinction stretch rate increased with the increase in the hydrogen proportion in the syngas and with lower fuel dilution and higher initial temperature. It also increased with pressure, except for the case of highly diluted fuel at high pressure. The maximum temperature and the emission index of nitric oxides (EINO_x) also increased in aforementioned conditions. The EINO_x decreased with stretch rate in general, while the decreasing rate was found to be somewhat different between the cases of N₂ and CO₂ dilutions. The reaction paths of NO_x formation were analyzed and represented as NO reaction path diagram. The increase in N radical resulted in larger NO_x production at high initial temperature and pressure. As the pressure increases, EINO_x increases slower due to the third-body recombination. The thermal NO mechanism is weakened for high dilution cases and non-thermal mechanisms prevail. The combustion conditions achieving higher extinction stretch rate can be lead to more NO_x emission, therefore that the selection of optimum operation range is needed in syngas combustion.     

Investigation on the liquid water droplet instability in a simulated flow channel of PEM fuel cell

To investigate the characteristics of water droplets on the gas diffusion layer from both top-view and side-view of the flow channel, a rig test apparatus was designed and fabricated with prism attached plate. This experimental device was used to simulate the growth of a single liquid water droplet and its transport process with various air flow velocity and channel height. Not only dry condition but also fully humidified condition was also simulated by using a water absorbing sponge. The detachment height of the water droplet with dry and wet conditions was measured and analyzed. It was found that the droplet tends towards becoming unstable by decreased channel height, increased flow velocity or making a gas diffusion layer (GDL) dryer. Also, peculiar behavior of the water droplet in the channel was presented like attachment to hydrophilic wall or sudden breaking of droplet in case of fully hydrated condition. The simplified force balance model matches with experimental data as well.     

A study on separate learning algorithm using support vector machine for defect diagnostics of gas turbine engine

A separate learning algorithm with support vector machine (SVM) has been studied for the development of a defect-diagnostic algorithm applied to the gas turbine engine. The system using only an artificial neural network (ANN) falls in a local minima and its classification accuracy rate becomes low in case it is learning nonlinear data. To make up for this risk, a separate learning algorithm combining ANN with SVM has been proposed. In the separate learning algorithm, a sequential ANN learns selectively after classification of defect patterns and discrimination of defect position using SVM, resulting in higher classification accuracy rate as well as the rapid convergence by decreasing the nonlinearity of the input data. The results have shown this suggested method has reliable and suitable estimation accuracy of the defect cases of the turbo-shaft engine. This paper was recommended for publication in revised form by Associate Editor Dongsik Kim Tae-Seong Roh received his B.S. and M.S. degrees in Aeronautical Engineering from Seoul National University in 1984 and 1986. He then went on to receive his Ph.D. degree from Pennsylvania State University in 1995. Dr. Roh is currently a Professor at the department of Aerospace Engineering at Inha University in Incheon, Korea. His research interests are in the area of combustion instabilities, rocket and jet propulsions, interior ballistics, and gasturbine engine defect diagnostics. Dong-Whan Choi received his B.S. degree in Aeronautical Engineering from Seoul National University in 1974. He then went on to receive his M.S. and Ph.D. degrees from University of Washington in 1978 and 1983. Dr. Choi had served three years as a President of Korea Aerospace Research Institute since 1999. He is currently a Professor at the department of Aerospace Engineering at Inha University in Incheon, Korea. His research interests are in the area of turbulence, jet propulsions, and gasturbine defect diagnostics.     

A parametric study on oil/air lubrication of a high-speed spindle

The ball-bearing is widely used on many high-speed spindles due to its low starting friction and high load capacity. However, heat generation and dynamic loading caused by high-speed rotation have been obstacles for increasing the speed limit in many high-speed ball-bearing applications. Applying an appropriate lubrication and preload cannot be overemphasized. Recently, oil/air lubrication has been used on high-speed spindles because of its accuracy in oil quantity control and high cooling efficiency. However, an oil/air supply with inadequate parameters is undesirable. In this study, the performance of a high-speed spindle under different lubrication parameters and preloads was investigated. The Taguchi method was applied to study the effects of design parameters on the lubrication efficiency. This method can also be used to obtain the optimum lubrication conditions. The optimum operating conditions that create the smallest temperature increase were established. The effects of preload on the temperature increase, the thermal deformation and the static stiffness of an oil/air lubricated spindle were studied. The results provide a useful tool in designing a high-speed spindle with a small increase in temperature and sufficient static stiffness.     

Effect of swirling flow by normal injection of secondary air on the gas residence time and mixing characteristics in a lab-scale cold model combustor

The present study investigates gas residence time and mixing characteristics for various swirl numbers generated by injection of secondary air into a lab-scale cylindrical combustor. Fine dust particles and butane gas were injected into the test chamber to study the gas residence time and mixing characteristics, respectively. The mixing characteristics were evaluated by standard deviation value of trace gas concentration at different measurement points. The measurement points were located 25 mm above the secondary air injection position. The trace gas concentration was detected by a gas analyzer. The gas residence time was estimated by measuring the temporal pressure difference across a filter media where the particles were captured. The swirl number of 20 for secondary air injection angle of 5° gave the best condition: long gas residence time and good mixing performance. Numerical calculations were also carried out to study the physical meanings of the experimental results, which showed good agreement with numerical results.     

Experimental and CFD study on the mass flow-rate characteristic of gas through orifice-type restrictor in aerostatic bearings

This paper describes the experimental and CFD study on the mass flow-rate characteristic through an orifice-type restrictor in aerostatic bearings. In the conventional design of gas-lubricated aerostatic bearings, the mass flow-rate of gas through an orifice-type restrictor is generally derived from a well-known mathematical model, which is originally developed to describe the mass flow-rate property through an ideal nozzle. It is reasonable to doubt if there is any difference between the property of mass flow-rate through an orifice and that through a nozzle. In this paper, therefore, a series of simulations and experiments are carried out and the results show that the mass flow-rate characteristic through an orifice is different from that through a nozzle. Consequently, the conventional model to determine the mass flow-rate through an orifice-type restrictor in aerostatic bearings may have to be updated to the proposed new model for more precise design and modelling of the gas-lubricated aerostatic bearings.