Annular Combustor Research Articles

Fluid flow and heat transfer characteristics of three-dimensional slot film cooling in an annular combustor

Film cooling methodologies in air-breathing gas turbines have been evolving for many decades. In the present work, a combined experimental and numerical parametric study is conducted to investigate the three-dimensional slot film cooling of an annular combustor. The experimental investigation is conducted to understand the fluid flow and heat transfer phenomenon of the film cooling and to validate the numerical study under laboratory conditions (low temperature and pressure). Transient infrared thermography is used to estimate both adiabatic film-cooling effectiveness (ηad) and heat transfer coefficient (h) simultaneously using a semi-infinite approximation method. The blowing ratios considered in the study are in the range of 0.5 to 5. The experimental results showed that film-cooling effectiveness (ηad) enhanced with an increase in the blowing ratio from 0.5 to 2 and deteriorated beyond BR = 2 due to the adverse effects of turbulence. A parametric study is conducted numerically to understand the effect of flow and geometrical parameters under actual engine conditions (high temperature and pressure). The parameters considered are slot Reynolds number (Res), slot jet diameter (d), slot jet pitch (p), lip taper angle (α), lip length (L), and slot jet injection angle (β). For the considered parameters, numerical results showed that the slot jet diameter (d) = 2 mm, dimensionless slot jet pitch (p/d) = 2, slot jet injection angle (β)=20o and dimensionless lip length (L/d) = 5.9 outperformed the other configurations due to the low turbulence and entrainment. Finally, an Artificial Neural Network-based mathematical model is developed that correlates the ηlat as a function of flow and geometrical parameters.

Influence of Oxy-Fuel Lance Parameters on the Scrap Pre-Heating Temperature in the Hot Metal Ladle

As one of the vital ways to improve the converter heat balance and increase the scrap ratio, scrap pre-heating technology has attracted much attention from researchers. The aim of this paper is to reveal the effect of the oxy-fuel lance parameters on the temperature field, flow field, and scrap pre-heating temperature in the ladle by means of numerical simulations. For this, a three-dimensional mathematical model containing the turbulence model, the porous medium heat balance model, and other models has been developed. The research results show that the rational and correct choice of gas flow rate, lance position, and nozzle angle has an important influence on the temperature field and the average scrap temperature. When the gas flow rate increases, the internal annular combustion zone of the scrap gradually expands, the cold zone at the bottom of the scrap continues to decrease, and the average scrap temperature keeps increasing. When the gas flow rate is 5000 m3/h, and the average scrap temperature reaches 1197 K, the pre-heating time is 9.98 min. Lowering the oxy-fuel lance position helps to reduce the cold zone at the bottom of the scrap and increases the average temperature in the cold zone. Reasonable selection of the nozzle angle is conducive to improving the uniformity of the flow field. When the angle of the nozzle is 15°, the gas circulation zone is the largest, and the time to reach an average scrap temperature of 1197 K is the shortest.

Characteristics of ethylene–air continuous rotating detonation in the cavity-based annular combustor

Characteristics of continuous rotating detonation (CRD) in a cavity-based annular combustor are studied through three-dimensional simulations, which are solved in OpenFOAM with a skeletal chemical kinetics mechanism. The results show that the continuous rotating detonation wave (CRDW) attaches to the outer wall and detaches from the inner wall in the cavity-based annular combustor. A high-temperature recirculation zone is found in the cavity with reactive intermediate species in the cavity-based annular combustor. The cavity is identified as a high-temperature ignition source, which provides heat and active intermediate radicals enhancing the detonability of the combustible gases in front of the CRDW. Consequently, the propagation performance, the propulsive performance, and the detonation combustion intensity are promoted in the cavity-based annular combustor. The propagation mode of the CRDW transforms from an unstable mode to a single-wave mode with the application of cavity. As the cavity deepens from 0 to 15 mm, the propagation velocity significantly increases from 923.21 to 1662.81 m/s and the fuel-based specific impulse increases from 941.91 to 1044.48 s as the cavity depth varies from 0 to 15 mm. Furthermore, the detonation-dominant combustion fraction remarkably improves from 27.21% to 62.29%.

Experimental study on the rotating detonation engine based on a gas mixture

A direct connection test of a rotating detonation engine was conducted. The outer and inner diameters of the annular combustors were 206 and 166 mm, respectively. High enthalpy air was used as an oxidizer, and a mixture of hydrogen, carbon monoxide, and methane was used as fuel with a volume fraction of 5/4/1. The mixture was injected through small holes, and air was injected through annular slots. The effects of combustor length, width of annular slots, and the equivalent ratio on formation, development, propagation, and flameout of rotating detonation waves were analyzed, and several modes of rotating detonation were observed. It was found that when the width of the air annular slot was within the range of 3–5 mm, the pressure of the detonation wave was augmented with an increased slot width. As width increased, detonation waves became unstable. In study test conditions, an annular slot width of 6 mm was the critical condition for the formation of stable detonation. When the slot width was 4 mm and combustor length 160 mm, the phenomena of the conversion between single and double waves, double-wave collision, and conversion of the propagation direction occurred at different equivalent ratios. When the equivalent ratio was 1.2/1 and the slot width was within the range of 3–6 mm, the slot width was inversely related to the detonation wave velocity. When the slot width was 4 mm and the equivalent ratio was 1.0/1–1.2/1, the slot width was positively correlated with the detonation wave velocity. When the combustor length was shortened to 80 mm, the propagation mode of the detonation wave was changed to a single wave first and then to a double wave in the same direction, and the velocity reduced from 1130.69 to 1024.16 m/s. The injector used in the test inhibited the propagation of back pressure from the combustor.

Optimization the TIT profile in an annular combustion of a turbojet engine based on smart modeling and CFD simulation

In this research, the turbine inlet temperature (TIT) profile optimization of an annular combustion chamber in a turbojet engine is studied based on the computational fluid dynamic (CFD) simulation- artificial neural network (ANN)- genetic algorithm (GA). This loop is named smart modeling and CFD simulation. The pattern factor (PF) is the maximum deviation of the engine temperature profile in the worst conditions. The turbojet engine performance is estimated by mass parameter (MP) of 0.17 at the design point by changing the dilution holes in order to optimizing the turbine inlet temperature profile's uniformity. Two different optimized designs are presented based on the changing of dilution holes geometry to assess the TIT profile in the turbojet engine. Their position and geometry of the primary zone (PZ) and secondary zone (SZ) and holes at the dilution zone (DZ) assumed constant. There is a row of cooling holes with 0.6 mm diameter in DZ. Thus, the effect of changing the inner diameter of dilution holes was studied by proposing two optimized different designs with different equivalent dilution. Three-dimensional numerical simulation results show that the Max.TIT are 1816.80, 1650.46 and 1540.69 in the basic design (BD) and the first and the second optimized design (OPTD1, OPTD2) respectively. Based on the Max.TIT quantity, PF are equal 0.81, 0.60 and 0.45. The comparison of the numerical simulation and experimental investigation results show that the TIT for the OPTD2 in the design point is 1203.04 K and 1227 K, respectively. The error percentage is about 2.87%.

Experimental Investigations on the Propagation Characteristics of Rotating Detonations Utilizing the Ethylene-Air Mixture

ABSTRACT In order to realize stable propagation of the ethylene-air rotating detonation wave with less velocity deficit in the annular combustion chamber, a series of experiments have been carried out while changing the combustor width (i.e. 10 mm, 15 mm, 25 mm, and a hollow combustor), mass flow rate of air, and equivalence ratio. The air and ethylene are supplied into the combustor through a slot-orifice impinging injection scheme, where air is injected through a slot with a height of 0.5 mm and ethylene is supplied by 160 orifices with a diameter of 0.35 mm. Experimental results indicate that four propagation modes have been obtained, i.e. the single wave mode, the sawtooth wave mode, the periodic oscillation mode, and the deflagration mode. The sawtooth wave mode and the periodic oscillation mode are considered unstable modes. In the single wave mode, the average propagation velocity of rotating detonations in the annular combustion chamber with a combustor width of 15 mm is between 1121 and 1215 m/s. The minimum velocity deficit is 21.9%, and the relative standard deviation of the propagation velocity is less than 5%, which is much lower than the experimental results of other studies utilizing ethylene and air in the annular combustors. In addition, the reasons may lead to the failure of producing rotating detonations have been analyzed. The effects of the chemical reactivity on the generation of rotating detonation waves have been demonstrated by installing a convergent nozzle at the exit of the combustor.

Modeling analysis of combustion instability in an annular combustor equipped with circumferentially segmented perforated liner

Hazardous azimuthal thermoacoustic modes often occur in lean-premixed annular combustors. One practical control method is the application of perforated liners with bias flow. However, circumferentially uniform perforated liners are not competent to control them, because the perforated plate covered by a single azimuthally uniform backing cavity cannot provide sufficient acoustic pressure difference across the perforated plate to bring in adequate acoustic damping. In this work, we developed a three-dimensional thermoacoustic model to consider the effects of a novel passive control damper of the circumferentially segmented perforated liner. Emphasis is placed on the effects of the segmented liner on controlling the azimuthal modes. It is found that the azimuthal mode in the premixed annular combustor can be either plenum-dominant or combustor-dominant, with the frequency of the latter one larger than the former. The stabilities of the two kinds of modes behave differently with the change of time delay. The results of the lined combustor cases indicate that the circumferentially segmented perforated liner generally improves the control effectiveness compared with the circumferentially uniform perforated liner thanks to the rigid plates inserted in the backing cavity. At the locally inserted position, the rigid plate enforces a rigid boundary condition that changes the azimuthal pressure mode shape in the backing cavity. As a result, more acoustic damping through the pressure difference across the plate is produced. Symmetry-breaking effects are found if the segmentation is asymmetric or two-fold symmetric. The behavior of the splitting frequencies caused by the segmented liner is also studied, and the symmetric segmented liner turns out to be a better choice because the resulting azimuthal mode is degenerate with two equivalent suppressed growth rates. In order to further enhance the control effect, one significant effective measure is to increase the depth of the backing cavity.

Low-order network modelling of the effect of Helmholtz resonators on nonlinear thermoacoustic modes in annular combustors

Modern aero-engines and land-based gas turbines often use annular combustors where many burners are installed in the circumferential direction. These combustors are often operated under lean-premixed pre-vaporized (LPP) conditions in which the flames are more susceptible to acoustic perturbations than traditional combustion systems. The resulted thermoacoustic instabilities may involve mode patterns varying in both longitudinal and circumferential directions. When nonlinear flame models are considered, our previous work proved that a 2-D low-order network model can capture limit cycle oscillations involving uncoupled and nonlinearly coupled modes, including longitudinal, circumferentially spinning/standing, and slanted modes. This kind of low-order network modelling tool has been recognised as a computationally efficient way of analysing thermoacoustic instabilities in annular combustors. Helmholtz resonators (HRs) are widely used to damp acoustic oscillations. For thermoacoustic instabilities in annular combustors, the presence of the HRs causes modal coupling and mode shape change. For nonlinearly coupled thermoacoustic modes, it is difficult to predict the change of modality accurately. In this paper, HRs are incorporated into the aforementioned low-order network model. The effect of HRs on different nonlinear thermoacoustic mode patterns are studied in detail. This provides a powerful low-order network modelling tool for studying the damping performance of HRs on nonlinear thermoacoustic modes in annular combustors.

A 2D low-order thermoacoustic network model of annular combustor with baffles in the plenum

Experimental results showed that configuring different baffles (a regular flat, a single- or double-layer perforated plate and a Helmholtz resonator) in the plenum can well suppress the self-excited oscillation in annular combustor. In this paper, a 2D low-order network model is proposed to describe this phenomenon and predict the modal frequencies and growth rates of longitudinal and circumferential thermoacoustic modes for annular combustor with different baffles. In the plenum, only the circumferential acoustic propagation and the influence of baffles on it are accounted for as the longitudinal geometry size is much smaller than the acoustic wavelength of the longitudinal mode. Pure longitudinal acoustic propagation is considered in burners and both longitudinal and circumferential ones are accounted for in the combustion chamber. These three modules are connected by jump conditions. The numerical prediction matches the experimental results. Baffles using Helmholtz resonators feature the best damping performance. The circumferential mode is converted to two unfolded non-degenerate modes when configuring perforated plates baffles. Best damping effect for the configuration of the baffles in the plenum can be achieved based on the proposed model.

Nonlinear characterization of azimuthal combustion instability exhibiting flame transient phenomena

This article characterizes the nonlinear features observed in an annular combustor exhibiting self-excited azimuthal thermoacoustic instability. The annular combustor consists of 12 burners with flames stabilized by bluff bodies protruding into the combustion chamber. This burner configuration closely resembles the flame stabilization geometry and flame shape in ramjet and afterburners configurations. As a first step, two different bluff bodies stabilize the flame: 1) circular and 2) conical and associated instability dynamics are characterized. The combustor exhibits intermittent oscillation in pressure with dominant 1A-1L (first azimuthal - first longitudinal) acoustic mode at about 630 Hz. The duration of periodic oscillation in the intermittent pressure fluctuation varies non-monotonically with the airflow rate. Further, relatively large amplitude pressure fluctuations are observed for intermediate values of airflow rate in both flame stabilization. During these large-amplitude pressure fluctuations, localized flame extinction in certain burners is observed, leading to partial blow-off operation of the combustor. This localized flame extinction is subsequently followed by either successful or unsuccessful re-ignition, leading to introduction of slow time scale heat release rate modulation in the problem. Further, this slow time scale heat release rate modulation is stochastic, contributing to the appearance of intermittent oscillation in pressure.

Prediction of combustion instabilities based on the Green's function in a three-dimensional annular combustor with multiple flames

The prediction of combustion instabilities is essential for modern annular combustors fed by multiple flames. This paper develops a model based on Green's function to study the interaction of multiple flame responses with different types in a three-dimensional (3D) geometry. The flame responses are described by flame transfer functions and are recognized as monopole sources in 3D cavities. Then the dispersion relation equation in the form of matrix is performed with the condition of equality of pressure. Thermoacoustic complex frequencies, mode structure, as well as the stability behaviors in combustor can be obtained in this model and the analysis is accomplished using Rayleigh index. The results are compared to the values of existing theoretical models and a good agreement is achieved. Furthermore, the effects of non-identical flame responses on complicated slanted mode under the condition of asymmetric are studied. In addition, the combustion instabilities of radial mode can be predicted by this model when the radial position distributions of the heat sources move in the case of small ratio of inner wall to outer wall.

Deflagration-to-Detonation Transition in a Semi-Confined Slit Combustor Filled with Nitrogen Diluted Ethylene-Oxygen Mixture

The conditions for the mild initiation of the detonation of homogeneous stoichiometric ethylene-oxygen mixtures diluted with nitrogen up to ~40%vol. in a planar semi-confined slit-type combustor with a slit 5.0 ± 0.4 mm wide, simulating the annular combustor of a Rotating Detonation Engine (RDE), are determined experimentally using self-luminous high-speed video recording and pressure measurements. To ensure the mild detonation initiation, the fuel mixture in the RDE combustor must be ignited upon reaching a certain limiting (minimal) fill with the mixture and the arising flame must be transformed to a detonation via deflagration-to-detonation transition (DDT). Thus, for mild detonation initiation in a C2H4 + 3O2 mixture filling the slit, the height of the mixture layer must exceed the slit width by approximately 10 times (~50 mm), and for the C2H4 + 3(O2 + 2/5 N2) mixture, by approximately 60 times. The limiting height of the mixture layer required for DDT exhibits a sharp increase at a nitrogen-to-oxygen mole ratio above 0.25. Compared to the height of the detonation waves continuously rotating in the RDE combustor in the steady-state operation mode, for a mild start of the RDE, the fill of the combustor with the explosive mixture to a height of at least four times more is required.

Numerical investigation of azimuthal thermoacoustic instability in a gas turbine model combustor

Self-excited spinning mode azimuthal instability in an annular combustor with non-swirling flow is investigated using large eddy simulation (LES). Compressible Navier–Stokes equations are solved with a flamelet combustion model to describe the subgrid chemistry-turbulence interactions. Two flamelet models, with and without heat loss effects, are compared to elucidate the non-adiabatic wall effects on the thermoacoustic instability. The azimuthal modes are captured well by both models with only marginal differences in the computed frequencies and amplitudes. By comparing with the experimental measurements, the frequencies given by the LES are approximately 10% higher and the amplitudes are well predicted. Further analysis of the experimental and LES data shows a similar dominant anti-clockwise spinning mode, under which a good agreement is observed for the phase-averaged heat release rate fluctuations. Dynamic mode decomposition (DMD) is applied to shed more light on this spinning mode. The LES and experimental DMD modes reconstructed for their azimuthal mode frequencies agree very well for the heat release fluctuations. The DMD mode structure for the acoustic pressure from the LES shows a considerable non-zero profile at the combustor outlet, which could be essential for azimuthal modes to establish in this annular combustor. Finally, a low-order modelling study was conducted using an acoustic network combined with the flame transfer function extracted from LES. The results show that the dominant mode is associated with the plenum showing a first longitudinal and azimuthal mixed mode structure. By tuning the plenum length to match the effective volume, the predicted frequency becomes very close to the measured value.

Numerical study of pressure profiles in an annular combustor and a manifold during continuous spin detonation of nonstoichiometric hydrogen-air mixtures

A closed mathematical model of continuous spin detonation of nonstoichiometric hydrogen-air mixtures in a quasi-three-dimensional unsteady gas-dynamic formulation taking into account the reverse effect of the oscillation processes in the combustor on the mixture injection system is utilized in pressure profiles in the combustion chamber and in the manifold investigation. Numerical simulations are performed for the flow-type annular combustor 503 mm in diameter with an annular gap of width 18 mm and other geometric dimensions corresponding to experiments. Three-wave mode of continuous spin detonation is calculated and the flow structure is analyzed for the equivalence ratio of 0.6 and the specific hydrogen-air mixture flow rate of 390.6 kg/(s·m2). The static, the mean static and the mean total pressure distributions in the combustor are calculated. The results are validated against experimental data.

Experimental research on the performance of hollow and annular rotating detonation engines with nozzles

• The performance of hollow and annular RDEs with nozzles are compared. • The hollow RDE can reduce the injection pressure loss. • The hollow chamber brings a higher performance loss. Rotating detonation engines (RDEs), which are hoped to achieve significant performance improvements in propulsion systems, have received much attention in recent years. The annular RDE and hollow RDE are two of the major configurations of which the structure is very similar to each other. However, there has been a lack of experimental research discussing the differences in their performance. In the present study, experiments on hollow and annular RDEs are conducted. Four configurations in total are tested at ambient conditions: hollow and annular combustion chambers with two exit throat areas. The gaseous methane and gaseous oxygen are used as propellants. The results reveal that the c*-efficiency of the two hollow combustion chamber configurations is on average 0.7 and 0.79, which is lower than the 0.75 and 0.84 of annular chambers. However, it is exhibited that the hollow RDE can ensure high detonation efficiency at a lower injection pressure ratio. From this perspective, the hollow RDE can be considered a more promising configuration for practical application because it provides a new approach to reducing injection pressure loss. In addition, the analysis of nozzle indicates that the Laval nozzles overperform the aerospike nozzles, which goes against previous studies. The mechanism that accounts for this phenomenon needs further investigation.

Design optimization of the suspension unit of the liner in the combustion chamber housing

The design of the suspension unit of the flame tube in the housing of the annular combustion chamber of a ground-based gas turbine installation of a gas pumping unit is given for placing it in a device for fixing the flame tube in the combustion chamber housing, where automatic clearance selection is required arising between the contacting surfaces of the docking nodes of the combustion chamber and the nozzle apparatus of the turbine, when the combustion chamber is operating as part of the engine. The proposed design of the suspension unit of the flame tube in the annular combustion chamber housing makes it possible to increase the reliability and resource of the combustion chamber and, in general, the entire ground-based gas turbine installation by eliminating the jamming of the split rings in the cups of the suspension units and the misalignment of the pushers relative to the suspension units and split support rings.

환형연소기에서 불안정성에 따른 유동적인 대칭성파괴 효과 Part Ⅰ: 노즐 배치의 특성

환형연소기에서 불안정성에 따른 유동적인 대칭성파괴 효과 Part Ⅰ: 노즐 배치의 특성

Investigation of coupled radiation-conduction heat transfer in cylindrical systems by discontinuous spectral element method

Nowadays, in order to achieve higher efficiency in aero-engines, the increase of turbine inlet temperature in aero-engine is in urgent need. At present, the turbine inlet temperature is around 2,000 K, which means the radiation and coupled radiation-conduction heat transfer play more and more important roles in hot section of aero-engines. As we all konw, considering the cylindrical symmetry of aero-engines. It is convenient to adopt the cylindrical coordinate to simplify the description of these systems, such as annular combustor, exhaust nozzle, etc. In this paper, Discontinuous Spectral Element Method (DSEM) is extended to solve the radiation and coupled radiation-coduction heat transfer in cylindrical coordinate system. Both the spatial and angular computational domains of radiative transfer equation (RTE) are discretized and solved by DSEM. For coupled radiation-conduction heat transfer problem, Discontinuous Spectral Element Method-Spectral Element Method (DSEM-SEM) scheme is used to avoid using two sets of grid which would cause the increase of computational cost and the decrease of accuracy. Then, the effects of various geometric and thermal physical parameters are comprehensively investigated. Finally, these methods are further extended to 2D cylindrical system.

NUMERICAL AND EXPERIMENTAL INVESTIGATION OF A MICRO GAS TURBINE COMBUSTION CHAMBER

Micro gas - turbines (MGT) offer many advantages such as higher thermal efficiency and reduced noise, and are suitable sources for power generation due to their fuel flexibility, small sizes, and high efficiencies. In recent years, there has been an increase interest in developing MGT for transportation platforms such as Range Extender for Electric Vehicle (REEV), Unmanned Ground/Air Vehicles (UGV/UAV), Auxiliary Power Units (APU). For these applications, the MGT must meet essential requirements like reliability, reasonable price, ecological safety, low noise and vibration, multi-fuel, etc. This paper presents the numerical and experimental investigation of a newly designed annular type combustion chamber. This combustion chamber is part of a 40 daN micro gas turbine, destined to equip a small-scale multifunctional airplane. The combustion chamber is equipped with six innovative vaporizers, using Jet-A as fuel, patented by INCDT COMOTI. The experimental installation on which the combustion tests have been performed consists of: the fuel supply system, an air source, the combustion chamber assembly, a chimney for flue gas exhaust. During the combustion chamber testing campaign, the following parameters have been monitored and registered: air mass flow, air temperature, and pressure before the combustion chamber entrance, the temperature at the combustion chamber exit, the temperature before the pressure regulating valve placed on the exhaust pipe. After the testing campaign has been concluded the numerical simulations have been resumed. A three-dimensional RANS numerical integration of the Navier-Stokes equations has been carried out, using an Eddy Dissipation Combustion Model (EDM) and the k-ε turbulence model, implemented in a numerical simulation conducted using the commercial software ANSYS CFX. The computational domain has been modified in order to match the testing rig. Due to the complex geometry of the computational domain, an unstructured type computational grid has been used. The imposed boundary conditions have been changed in order to match the testing conditions and functioning regimes. A kerosene – air two steps reaction mechanism, with NO formation, has been used. The numerical simulation results have been compared with the parameters measured experimentally, thus validating the obtained results.

Разработка математической модели газотурбинной установки с малоэмиссионной камерой сгорания и особенности ее интеграции в среду SimInTech

The results of the development of a mathematical model of a gas turbine plant (GTP) SGT5-4000F with an annular low-emission combustion chamber are presented. This plant has a low NOx emission and a high coefficient of performance (COP). The obtained results of mathematical modeling are integrated into the domestic environment of dynamic modeling of technical systems "SimInTech". The obtained results were verified by comparing the model values with the trends of the real technological parameters of the gas turbine unit taken from the archive of the automated process control system of the power plant. According to the results of the experimental studies carried out on the model with changes in the electrical load from 280 to 160 MW, it is shown that the model allows you to control the combustion process in the combustion chamber, depending on the composition of the fuel, evaluate the change in NOx emissions and provide an analysis of the stability of the gas turbine compressor according to surging in conditions of changing temperature and humidity of the incoming air.