Annular Combustion Chamber Research Articles

On the Optimum Distribution of Multiple Helmholtz Resonators for Annular Combustors

Abstract The combustors of many modern land-based gas turbines and aero-engines are annular. This kind of combustors often suffer from thermoacoustic oscillations, with the occurrence of mostly the circumferential first-order, second-order and third-order oscillation modes in the annular combustion chamber. To solve this problem, passive control methods are widely used adding passive acoustic dampers such as Helmholtz resonators (HRs). Depending on the type and number of HRs, and the possible positions over the circumference to install them, there could easily have millions, or even billions, of possible arrangment patterns. Finding a good design is the key to solve this problem. In this paper, we perform a theoretical and numerical study of an annular combustor installed with multiple types of HRs over the circumference. Firstly, a simple annular duct with arbitrary distributions of these HRs is studied analytically by solving the nonlinear eigenvalue problem of a 1D network model. Based on the results of the analytical method, the impact of the HRs on the acoustic modes of the combustion chamber is studied and the optimum arrangement of multiple resonators is obtained. This arrangement usually gives a null (or small) mode splitting strength and a good damping effect. Finally, we apply the optimum arrangement to damp the thermoacoustic modes that have been captured by numerical simulation for a real annular combustor. We use numerical simulations based on solving the 3D Helmholtz equation in COMSOL to verify the feasibility of the optimum arrangement.

Design and Numerical Analysis of an Annular Combustion Chamber

Designing a combustion chamber for gas turbines is considered both a science and an art. This study presents a comprehensive methodology for designing an annular combustion chamber tailored to the operating conditions of a CFM-56 engine, a widely used high bypass ratio turbofan engine. The design process involved calculating the basic criteria and dimensions for the casing, liner, diffuser, and swirl, followed by an analysis of the cooling sections of the liner. Numerical simulations using NUMECA software and the HEXPRESS meshing tool were conducted to predict the combustion chamber’s behavior and performance, employing the κ-ε turbulence model and the Flamelet combustion model. Methane was used as the fuel, and simulations were performed for three fuel injection angles: axial, 45°, and 60°. Results demonstrate that the combustion chamber is properly dimensioned and achieves complete combustion for all configurations. The pressure ratio is 0.96, exceeding the minimum design criteria. Additionally, the emissions of unburned hydrocarbons are zero, while nitrogen oxides and carbon monoxide levels are below regulatory limits. These findings validate the proposed design methodology, ensuring efficient and environmentally compliant combustion chamber performance.

Saturation of flames to multiple inputs at one frequency

Existing experimental results show that swirling flames in annular combustors respond with a different gain to acoustic azimuthal modes rotating in either the clockwise or anti-clockwise direction. The ratio $R$ of these two gains is introduced, with $R=1$ being the conventional case of flames responding the same to the two forcing directions. To allow a difference in response to the different directions ( $R\neq 1$ ), a multiple-input single-output azimuthal flame describing function is successfully implemented in a quaternion valued low-order model of an annular combustion chamber in the current work. Theoretical studies have explored this kind of symmetry breaking between the two acoustic wave directions in the past, but it has not been backed by experimental data. One of the main features of the new model proposed in this work is the potential difference in mode shapes between the acoustic and the heat release rate modes, which has recently been observed experimentally. This results in a gain-dependent equation for the nature of the mode, which has a significant influence on the fixed points of the system. For example, one of the spinning solutions and the standing solution can disappear through a saddle node bifurcation as the parameters are varied. The presence of only a single direction for the spinning solution matches experimental observations better than the conventional models, and the proposed model is shown to qualitatively describe experimental measurements well.

Experimental study on detonation characteristics of liquid kerosene/air rotating detonation engine

Thermal experiments were conducted to investigate the characteristics of rotating detonation waves in a Liquid Kerosene/Air Rotating Detonation Engine featuring gas-liquid two-phase non-premixed injection. The annular combustion chamber for the rotating detonation had inner and outer diameters of 206 mm and 144 mm, respectively. To mitigate pressure back-propagation of detonation waves, a 3 mm high annular gap structure was employed. The fuel injection system utilized an integrated structure for fuel atomization and mixing, which was designed by our research group based on high-speed shear flow and fuel injection principles. The experiment successfully initiated and sustained a single-wave mode rotating detonation wave with tangentially arranged kerosene/air pre-detonators. The frequency of detonation wave propagation ranged from 2.4 kHz to 2.5 kHz, with a detonation wave velocity of up to 1600 m/s. The initiation delay time of the detonation wave varied between 1600 ms and 400 ms. Within the experimental conditions, as the equivalence ratio increased, the detonation wave velocity increased while the stable establishment time of the detonation wave decreased. However, the overall stability of the detonation wave exhibited a decreasing trend. Additionally, a long-term test of the kerosene/air rotating detonation engine was conducted for 4 s, confirming the engine's ability to operate continuously over an extended period. The frequency of the rotating detonation wave obtained during the long-term test differed by only 0.2 % from the results of the short-term experiments, validating the accuracy and universality of the conclusions drawn from the short-term experiments.

Experimental study of mode control in rotating detonation combustor using Tesla valve mode control configuration fueled by kerosene

The detonation mode has a significant impact on the operational characteristics and propulsion performance of the rotating detonation combustor (RDC). Controlling the combustion mode effectively is advantageous for improving the propulsion performance of the pressure gain combustor. A Tesla valve mode control combustion chamber (TVMC) was used for experimental research in this study. An equal-width annular combustion chamber (EWA) was used as a control test, with room temperature kerosene as the fuel, and oxygen-enriched air as an oxidizer. The experiment successfully validated the feasibility of mode control in TVMC along with its operational characteristics. Monitoring the pressure pulsation of detonation and guide channels in TVMC led to the unfolding of possible mode control mechanism. The results indicated that the rotating detonation wave (RDW) propagates clockwise in TVMC. After RDW propagating counterclockwise enters the guide channel, the width limitation of guide channel causes RDW decoupling. It changes the propagation direction of the leading shock wave, resulting in mode control. Because of the presence of a guide channel, the RDW is unstable at low equivalence ratios, and the operation range is also narrower.

The Effect of Methane–Ammonia and Methane–Hydrogen Blends on Ignition and Light-Around in an Annular Combustor

Abstract The use of hydrogen and ammonia in gas turbines, either alone or blended with natural gas, poses various technical challenges for combustion systems, including ignition. Depending on the fuel composition, the laminar flame speed and the ratio of unburned to burned gas density (dilatation ratio) of hydrogen and ammonia flames can be well outside the range seen in natural gas flames. Previous studies in annular combustion chambers have provided evidence of the importance of these properties in determining the ignition dynamics including light-around times. So far, these studies have mostly considered hydrocarbon fuels, have been limited to only a few runs, and have not yet systematically investigated variations in the dilatation ratio and the flame speed but rather have considered them as a lumped parameter. To investigate these effects in more detail, experiments characterizing the light-around times were carried out on an atmospheric annular combustor in which the dilatation ratio and the laminar flame speed was independently varied. This was achieved by varying the equivalence ratio and employing a variety of different hydrocarbon fuels (ethylene, propane, and methane) and fuel blends of methane–ammonia and methane–hydrogen. Light-around times were evaluated from global chemiluminescence measurements obtained using an azimuthal array of photomultipliers placed round the combustor chamber as well as high speed imaging. To improve statistical certainty, more than 3000 ignition and light-around times were measured with 30 repetitions obtained for each operating condition. To provide some insight into the light-around dynamics in specific cases, 900 of the 3000 sets included high-speed OH* chemiluminescence images. Light-around times for premixed pure hydrocarbon flames showed a similar dependence on the laminar flame speed as reported in previous studies. For the range of ammonia fuel blends investigated, an increase in laminar flame speed leads to a predictable increase in the flame propagation speed, as in the case of hydrocarbon fuel. Furthermore, collapse of this dependence for all blends could be achieved when corrected for an effective Lewis number, noting that all Lewis numbers for these blends were above unity. However, for hydrogen fuel blends, a decrease in dilatation ratio was found to decrease the light-around time counter to existing experimental results on the ignition of hydrocarbon fuels for which we currently do not have an explanation.

Effect of Operating Conditions on the Emission Characteristics Of an Annular Combustor

Pollutant emissions from combustion processes have become of great public concern due to their impact on health and the environment. Recent growth in civil aviation and stationary gas turbines power plants is worsening the situation both at airport vicinity and in altitude. This has called for rapid changes both in the regulations and controlling gas turbine emissions and in the technologies used to meet these regulations. All these developments have been accompanied by continuous and increasing pressure on the combustion engineers to reduce pollutant emissions from all types of gas turbines while operating at very high levels of pressure and temperature. In this paper an effort is made to characterize an annular combustion chamber from emission point and effect of various operating conditions has been analyzed. The emission characteristics of combustor are very satisfied and are inline to that of contemporary combustors of same class. This study can lead to combustor modifications for bringing down the emission levels to meet the international regulations.

Research on Reconstruction Technology of Temperature Field in Engine Combustion Chamber Based on Image Thermometry

In order to make up for the defects of traditional temperature measurement methods, image temperature measurement technology is gradually applied to the measurement of temperature field of high-temperature objects. By analysing and demonstrating the feasibility of three-dimensional temperature field reconstruction in engine combustion chamber, the algorithm of temperature field reconstruction was put forward in this paper, the model between flame radiation energy and temperature field in engine combustion chamber was established, and the application of radiation imaging temperature measurement technology in aero engine annular combustion chamber test was preliminarily realized.

Experimental investigation for the different blend ratios of kerosene with diesel on the exergetic performance of a small-scale turbojet engine for UAV missions

The main purpose of this study is to experimentally analyze the exergetic performance of a small-scale turbojet engine that can be used in unmanned aerial vehicles (UAVs) when different blend ratios of kerosene with diesel are necessary, like in extraordinary situations. Comparative analysis was performed to understand the effects of the use of various diesel rates on the jet engine’s performance. To maintain air operations when refueling is required, easy-reachable fuels can help for short but important periods. In cases when there is a need for the use of a quick-reachable fuel in war conditions, diesel may be a suitable fuel. The UAV turbojet engine consists of a radial compressor, an annular combustion chamber, an axial turbine, and a propelling nozzle. The compressor, combustion chamber, turbine, and nozzle were evaluated by using the exergy analysis method. The performance parameters to evaluate the turbojet engine components were specific fuel consumption, thrust, overall exergy efficiency, and air-to-fuel ratio. The turbojet engine was operated at different throttle settings to monitor the changes in the performance parameters. As a result of using different kerosene and diesel fuel blends at different throttle settings, it was observed that the findings were consistent. Generally, the maximum exergy efficiencies took place in the turbine except for the full throttle settings. The minimum exergy efficiencies belonged to the nozzle. It was observed that irrespective of which fuel blend was used, thrust specific fuel consumption values decreased as the throttle setting increased. On the other hand, thrust values, overall exergy efficiencies, and air-to-fuel ratios had an increasing trend as the throttle setting was increased.

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.

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.

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.

Analytical solutions for the acoustic field in thin annular combustion chambers with linear gradients of cross-sectional area and mean temperature

Predictions of thermoacoustic instabilities in annular combustors are essential but difficult. Axial variations of flow and thermal parameters increase the cost of numerical simulations and restrict the application of analytical solutions. This work aims to find approximate analytical solutions for the acoustic field in annular ducts with linear gradients of axially non-uniform cross-sectional area and mean temperature. These solutions can be applied in low-order acoustic network models and enhance the ability of analytical methods to solve thermoacoustic instability problems in real annular chambers. A modified WKB method is used to solve the wave equation for the acoustic field, and an analytical solution with a wide range of applications is derived. The derivation of the equations requires assumptions such as low Mach number, high frequency and small non-uniformity. Cases with arbitrary distributions of cross-sectional surface area and mean temperature can be solved by the piecewise method as long as the assumptions are satisfied along the entire chamber.

A Comparative Performance Analysis of the Novel TurboAux Engine with a Turbojet Engine, and a Low-Bypass Ratio Turbofan Engine with an Afterburner

Presented herein is a comparative performance analysis of a novel turbofan engine with an auxiliary combustion chamber, nicknamed the TurboAux engine, against a turbojet engine, and a low bypass ratio turbofan engine with an afterburner is presented. The TurboAux engine is an adaption of the low-bypass ratio turbofan engine, but with secondary combustion in an auxiliary bypass annular combustion chamber for thrust augmentation. The TurboAux engine is envisioned with the desire to facilitate clean secondary burning of fuel at temperatures higher than in the main combustion chamber with air exiting the low-pressure compressor. The comparative study starts by analyzing the turbojet engine and its performance with and without an afterburner segment attached. In parallel, the conventional turbofan and its mixing counterpart are analyzed, also with and without an afterburner segment. A simple optimization analysis of a conventional turbofan is performed to identify optimal ‘fan’ pressure ratios for a series of low-bypass ratios (0.1 to 1.5). The optimal fan pressure ratios and their corresponding bypass ratios are adapted to demonstrate the comparative performance of the varying configurations of the TurboAux engine. The formulation and results are an attempt to make a case for charter aircrafts and efficient close-air-support aircrafts. The results yielded increased performance in thrust augmentation, but at the cost of a spike in fuel consumption. This trade-off requires more in-depth investigation to further ascertain the TurboAux’s utility.

Effect of the flame motion on azimuthal combustion instabilities

In the analysis of combustion instabilities in the annular combustors, especially for the azimuthal combustion modes, the flame motion is usually neglected and the flame is typically regarded as a discontinuity at rest. However, this simplicity may cause severe prediction errors for certain conditions. In this paper, the influence of the flame motion on the entropy, vortex, acoustic, and intrinsic modes in the annular combustion chamber is investigated by constructing an analytical model with the flame motion. Meantime, the influence of flame model parameters is also explored. The flame motion can affect both the frequency and growth rate of the entropy mode, but the growth rate is influenced more significantly. This effect can be damped or enlarged by the inlet Mach number depending on which parameter of flame model remains unchanged. The effect of the flame motion on vortex, acoustic, and intrinsic modes remains small when the inlet Mach number is very small. However, the increase of inlet Mach number can enlarge this effect.

Аналіз впливу способу подачі гарячих газів пристрою запалювача на запуск камери згоряння за допомогою тривимірного комп'ютерного моделювання

This paper presents the results of a numerical simulation of the gas flow in the flame tube of an annular combustion chamber of a gas turbine engine. Numerical simulation was performed in the ANSYS Fluent 2022 R1 computational complex, in which the numerical solution of the Reynolds-averaged Navier-Stokes equations (RANS) was implemented, the dissipation rates were determined using the Enhanced Wall Treatment near-wall function. For numerical simulation problems, a computational polyhedral mesh was built. The purpose of the calculations was to evaluate the effect of the method for supplying igniter hot gases to the start of the combustion chamber. The article does not address the operation of the igniter itself (its ignition, combustion, and the flow in it), but only its main task is the generation of a flame (gas) with a given temperature. All calculations were carried out for two gas temperatures, 800 and 1200 °C, at the outlet of the igniter nozzle, and a temperature of minus 20 °C at the inlet to the combustion chamber. In the calculation model, at the inlet to the igniter nozzle, the gas flow rate was set with a temperature taken from the experiment. When the chamber operates in the region of low temperatures, low velocities and pressures at the inlet, the degree of fuel evaporation and the mixing of its vapors with air have a significant effect. Therefore, with an increase in air flow through the chamber, the limits of flame blow-off expand. With a further increase in air flow, the processes of fuel evaporation and its burnout in the reverse current zone are completed, and flameout is mainly determined only by the temperature in the reverse current zone, and the boundaries of stable combustion narrow with increasing flow rate, which is typical for combusting a homogeneous mixture. The calculations found that the penetration and spread of heat when using igniter nozzles with a large diameter (12 mm) in the outlet section are higher than those in holes with a smaller diameter (8 mm). In the variants where the supply of hot gases is in the plane of the nozzle, a better distribution of heat in the zone of reverse currents is shown than where the supply of hot gases is carried out between the nozzles. Also, to analyze the results of the calculation, a criterion was proposed that shows the optimal conditions for the ignition of the mixture.

The effect of mean flow on the intrinsic thermoacoustic instabilities in the duct and annular combustion chambers

Thermoacoustic instability in the combustion chamber of gas turbines, aero and rocket engines has become a topic concern. In this paper, a new instability phenomenon in the field of the thermoacoustic instability - Intrinsic ThermoAcoustic instabilities (ITA) is studied. The classic thermoacoustic instability is caused by the coupling among acoustic disturbances, flow fluctuations and heat release pulsations. When the influence of acoustic disturbance is removed, there is still a thermoacoustic instability phenomenon in the combustion chamber, which is known as ITA. In the previous research on ITA, the scholars found that the ITA is mainly determined by the flame response, but many scholars neglected the influence of the mean flow and entropy waves. In this paper, the influence of the mean flow on the ITA mode in the duct and annular combustion chambers is studied by constructing a low-order acoustic network model. At the same time, it also explores the influence of other parameters on the ITA mode. The mean flow greatly affects the growth rate of the ITA mode, and has little effect on its frequency in the duct combustion chamber model. This is also the main reason for neglecting the effect of mean flow on the ITA mode in previous studies. In addition, the influence of other parameters on the ITA mode is also reflected in the growth rate. In the annular combustion chamber, a new ITA mode, which does not meet the −π criterion, is found. And the increase of Mach number makes all ITA modes more unstable. The circumferential mode number has a great influence on the high frequency ITA mode. In addition, the ITA mode has a significant effect on the thermoacoustic mode of the system in the annular combustion chamber.