Predicting the Amplitude of Thermoacoustic Instability Using Universal Scaling Behaviour

2021 ◽  
Author(s):  
Induja Pavithran ◽  
Vishnu Rajasekharan Unni ◽  
Abhishek Saha ◽  
Alan J. Varghese ◽  
Prof. R. I. Sujith ◽  
...  
Keyword(s):  
Amplitude Spectrum ◽  
High Amplitude ◽  
Dominant Mode ◽  
Turbine Engines ◽  
Stable Operation ◽  
Scaling Relation ◽  
Thermoacoustic Instability ◽  
Universal Scaling ◽  
Engine Components ◽  
Accuracy Of Prediction

Abstract The complex interaction between the turbulent flow, combustion and the acoustic field in gas turbine engines often results in thermoacoustic instability that produces ruinously high-amplitude pressure oscillations. These self-sustained periodic oscillations may result in a sudden failure of engine components and associated electronics, and increased thermal and vibrational loads. Estimating the amplitude of the limit cycle oscillations (LCO) that are expected during thermoacoustic instability helps in devising strategies to mitigate and to limit the possible damages due to thermoacoustic instability. We propose two methodologies to estimate the amplitude using only the pressure measurements acquired during stable operation. First, we use the universal scaling relation of the amplitude of the dominant mode of oscillations with the Hurst exponent to predict the amplitude of the LCO. We also present a methodology to estimate the amplitudes of different modes of oscillations separately using ''spectral measures' which quantify the sharpening of peaks in the amplitude spectrum. The scaling relation enables us to predict the peak amplitude at thermoacoustic instability, given the data during the safe operating condition. The accuracy of prediction is tested for both methods, using the data acquired from a laboratory-scale turbulent combustor. The estimates are in good agreement with the actual amplitudes.

Predicting the Amplitude of Thermoacoustic Instability Using Universal Scaling Behaviour

2021 ◽  
Author(s):  
Induja Pavithran ◽  
Vishnu R. Unni ◽  
Abhishek Saha ◽  
Alan J. Varghese ◽  
R. I. Sujith ◽  
...  
Keyword(s):  
Amplitude Spectrum ◽  
High Amplitude ◽  
Dominant Mode ◽  
Turbine Engines ◽  
Stable Operation ◽  
Scaling Relation ◽  
Thermoacoustic Instability ◽  
Universal Scaling ◽  
Engine Components ◽  
Accuracy Of Prediction

Abstract The complex interaction between the turbulent flow, combustion and the acoustic field in gas turbine engines often results in thermoacoustic instability that produces ruinously high-amplitude pressure oscillations. These self-sustained periodic oscillations may result in a sudden failure of engine components and associated electronics, and increased thermal and vibra-tional loads. Estimating the amplitude of the limit cycle oscillations (LCO) that are expected during thermoacoustic instability helps in devising strategies to mitigate and to limit the possible damages due to thermoacoustic instability. We propose two methodologies to estimate the amplitude using only the pressure measurements acquired during stable operation. First, we use the universal scaling relation of the amplitude of the dominant mode of oscillations with the Hurst exponent to predict the amplitude of the LCO. We also present a methodology to estimate the amplitudes of different modes of oscillations separately using ‘spectral measures’ which quantify the sharpening of peaks in the amplitude spectrum. The scaling relation enables us to predict the peak amplitude at thermoacoustic instability, given the data during the safe operating condition. The accuracy of prediction is tested for both methods, using the data acquired from a laboratory-scale turbulent combustor. The estimates are in good agreement with the actual amplitudes.

scholarly journals Experience With the TF40B Engine in the LCAC Fleet

1992 ◽  
Author(s):  
Edward M. House
Keyword(s):  
Gas Turbine ◽  
Hot Corrosion ◽  
Compressor Blade ◽  
Turbine Engines ◽  
Gas Turbine Engines ◽  
Improvement Program ◽  
Air Cushion ◽  
Engine Components ◽  
Carbon Erosion ◽  
The U.S

Four Textron Lycoming TF40B marine gas turbine engines are used to power the U.S. Navy’s Landing Craft Air Cushion (LCAC) vehicle. This is the first hovercraft of this configuration to be put in service for the Navy as a landing craft. The TF40B has experienced compressor blade pitting, carbon erosion of the first turbine blade and hot corrosion of the hot section. Many of these problems were reduced by changing the maintenance and operation of the LCAC. A Component Improvement Program (CIP) is currently investigating compressor and hot section coatings better suited for operation in a harsh marine environment. This program will also improve the performance of some engine components such as the bleed manifold and bearing seals.

scholarly journals Synchronization of Thermoacoustic Modes in Sequential Combustors

2018 ◽  
Author(s):  
Giacomo Bonciolini ◽  
Nicolas Noiray
Keyword(s):  
Gas Turbines ◽  
High Amplitude ◽  
Operating Conditions ◽  
Operational Flexibility ◽  
Order Model ◽  
Thermoacoustic Instabilities ◽  
Physical Mechanisms ◽  
Sustained Oscillations ◽  
Engine Components

Sequential combustion constitutes a major technological step-change for gas turbines applications. This design provides higher operational flexibility, lower emissions and higher efficiency compared to today’s conventional architectures. Like any constant pressure combustion system, sequential combustors can undergo thermoacoustic instabilities. These instabilities potentially lead to high-amplitude acoustic limit cycles, which shorten the engine components’ lifetime and therefore reduce their reliability and availability. In case of a sequential system, the two flames are mutually coupled via acoustic and entropy waves. This additional inter-stages interaction markedly complicates the already challenging problem of thermoacoustic instabilities. As a result, new and unexplored system dynamics are possible. In this work, experimental data from our generic sequential combustor are presented. The system exhibits many different distinctive dynamics, as function of the operation parameters and of the combustor arrangement. This paper investigates a particular bifurcation, where two thermoacoustic modes synchronize their self-sustained oscillations over a range of operating conditions. A low-order model of this thermoacoustic bifurcation is proposed. This consists of two coupled stochastically driven non-linear oscillators, and is able to reproduce the peculiar dynamics associated with this synchronization phenomenon. The model aids in understanding what the physical mechanisms that play a key role in the unsteady combustor physics are. In particular, it highlights the role of entropy waves, which are a significant driver of thermoacoustic instabilities in this sequential setup. This research helps to lay the foundations for understanding the thermoacoustic instabilities in sequential combustion systems.

On the Interaction of Swirling Flames in a Lean Premixed Combustor

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Gopakumar Ramachandran ◽  
Ankit Kumar Dutta ◽  
Harish Durairaj ◽  
Swetaprovo Chaudhuri
Keyword(s):  
Gas Turbine ◽  
Thermal Power ◽  
Stereoscopic Particle Image Velocimetry ◽  
Stable Operation ◽  
Flame Surface ◽  
Large Radius ◽  
Power Cost ◽  
Thermoacoustic Instability ◽  
Swirling Flames ◽  
Interaction Regions

Abstract Premixed or partially premixed swirling flames are widely used in gas turbine applications because of their compactness, high ignition efficiency, low NOx emissions and flame stability. A typical annular combustor consists of about twenty swirling flames, which interact (directly or indirectly) with their immediate neighbors even during stable operation. These interactions significantly alter the flow and flame topologies thereby bringing in some discrepancies between the single nozzle (SN) and multinozzle (MN), ignition, emission, pattern factor and flame transfer function (FTF) characteristics. For example, in MN configurations, application of a model based on SN FTF data could lead to erroneous conclusions. Due to the complexities involved in this problem in terms of size, thermal power, cost, optical accessibility etc., a limited amount of experimental studies has been reported, that too on scaled down models with reduced number of nozzles. Here, we present a detailed experimental study on the behavior of three interacting swirl premixed flames, arranged in-line in an optically accessible hollow cuboid test section, which closely resembles a three-cup sector of an annular gas turbine combustor with very large radius. Multiple configurations with various combinations of swirl levels between the adjacent nozzles and the associated flame and flow topologies have been studied. Spatio-temporal information of the heat release rate obtained from OH* chemiluminescence imaging is used along with the acoustic pressure signatures to compute the Rayleigh index (RI) so as to identify the regions within the flame that pumps energy into the self-excited thermoacoustic instability modes. It is found that the structure of the flame–flame interaction regions plays a dominant role in the resulting thermoacoustic instability. To resolve the flow and reactive species distributions in the interacting flames, two-dimensional (2D), three component stereoscopic particle image velocimetry (SPIV) and planar laser-induced fluorescence (PLIF) of hydroxyl radical is applied to all the test conditions. Significant differences in the flow structures among the different configurations were observed. Simultaneous OH-PLIF and SPIV techniques were also utilized to track the flame front, from which the curvature and stretch rates were computed. Flame surface density (FSD) which is defined as the mean surface area of the reaction zone per unit volume, is also computed for all the test cases. These measurements and analyses elucidate the structure of the interaction regions, their unique characteristics, and possible role in thermoacoustic instability.

On the Interaction of Swirling Flames in a Lean Premixed Combustor

2019 ◽  
Author(s):  
Gopakumar Ramachandran ◽  
Ankit Kumar Dutta ◽  
Harish Durairaj ◽  
Swetaprovo Chaudhuri
Keyword(s):  
Gas Turbine ◽  
Transfer Functions ◽  
Stereoscopic Particle Image Velocimetry ◽  
Stable Operation ◽  
Flame Surface ◽  
Large Radius ◽  
Power Cost ◽  
Thermoacoustic Instability ◽  
Swirling Flames ◽  
Interaction Regions

Abstract Premixed or partially premixed swirling flames are widely used in gas turbine applications because of their compactness, high ignition efficiency, low NOx emissions and flame stability. A typical annular combustor consists of about eighteen to twenty-two swirling flames which interact (directly or indirectly) with their immediate neighbors even during stable operation. These interactions significantly alter the flow and flame topologies thereby bringing in some discrepancies between the single nozzle (SN) and multi nozzle (MN), ignition, emission, pattern factor and Flame Transfer Functions (FTF) characteristics. For example, in MN configurations, application of a model based on SN FTF data could lead to erroneous conclusions. Due to the complexities involved in this problem in terms of size, thermal power, cost, optical accessibility etc., a limited amount of experimental studies has been reported, that too on scaled down models with reduced number of nozzles. Here, we present a detailed experimental study on the behavior of three interacting swirl premixed flames, arranged in-line in an optically accessible hollow cuboid test section, which closely resembles a three-cup sector of an annular gas turbine combustor with very large radius. Multiple configurations with various combinations of swirl levels between the adjacent nozzles and the associated flame and flow topologies have been studied. Spatio-temporal information of the heat release rate obtained from OH* chemiluminescence imaging was used along with the acoustic pressure signatures to compute the Rayleigh index so as to identify the regions within the flame that pumps energy into the self-excited thermoacoustic instability modes. It was found that the structure of the flame-flame interaction regions plays a dominant role in the resulting thermoacoustic instability. To resolve the flow and reactive species field distributions in the interacting flames, two-dimensional, three component Stereoscopic Particle Image Velocimetry (SPIV) and Planar Laser Induced Fluorescence (PLIF) of hydroxyl radical was applied to all the test conditions. Significant differences in the flow structures among the different configurations were observed. Simultaneous OH-PLIF and SPIV techniques were also utilized to track the flame front, from which the curvature and stretch rates were computed. Flame surface density which is defined as the mean surface area of the reaction zone per unit volume is also computed for all the test cases. These measurements and analyses elucidate the structure of the interaction regions, their unique characteristics and possible role in thermoacoustic instability.

Multifractal characteristics of combustor dynamics close to lean blowout

2015 ◽  
Vol 784 ◽  
pp. 30-50 ◽  
Author(s):  
Vishnu R. Unni ◽  
R. I. Sujith
Keyword(s):  
Stability Margin ◽  
Static Stability ◽  
Combustion Noise ◽  
Stable Operation ◽  
Nonlinear Behaviour ◽  
Classical Literature ◽  
Unified Framework ◽  
Simple Description ◽  
Thermoacoustic Instability ◽  
Lean Blowout

In classical literature, blowout is described as loss of static stability of the combustion system whereas thermoacoustic instability is seen as loss of dynamic stability of the system. At blowout, the system transitions from a stable reacting state to a non-reacting state, indicating loss of static stability of the reaction. However, this simple description of stability margin is inadequate since recent studies have shown that combustors exhibit complex nonlinear behaviour prior to blowout. Recently, it was shown that combustion noise that characterizes the regime of stable operation is itself dynamically complex and exhibits multifractal characteristics. Researchers have already described the transition from combustion noise to combustion instability as a loss of multifractality. In this work, we provide a multifractal description for lean blowout in combustors with turbulent flow and thus introduce a unified framework within which both thermoacoustic instability and blowout can be described. Further, we introduce a method for predicting blowout based on the multifractal description of blowout.

scholarly journals Stability and Limit Cycles of a Nonlinear Damper Acting on a Linearly Unstable Thermoacoustic Mode

2018 ◽  
Vol 141 (5) ◽  
Author(s):  
Claire Bourquard ◽  
Nicolas Noiray
Keyword(s):  
Growth Rate ◽  
Combustion Chamber ◽  
Limit Cycle ◽  
Nonlinear Effects ◽  
Coupled System ◽  
High Amplitude ◽  
Van Der Pol Oscillator ◽  
Mean Velocity ◽  
Thermoacoustic Instability ◽  
Numerical Predictions

The resonant coupling between flames and acoustics is a growing issue for gas turbine manufacturers, which can be reduced by adding acoustic dampers on the combustion chamber walls. Nonetheless, if the engine is operated out of the stable window, the damper is exposed to high-amplitude acoustic levels, which trigger unwanted nonlinear effects. This work provides an overview of the dynamics of this coupled system using a simple analytical model, where a perfectly tuned damper is coupled to the combustion chamber. The damper, crossed by a purge flow in order to prevent hot gas ingestion, is modeled as a nonlinearly damped harmonic oscillator. The combustion chamber featuring a linearly unstable thermoacoustic mode is modeled as a Van der Pol oscillator. Analyzing the averaged amplitude equations gives the limit cycle amplitudes as function of the growth rate of the unstable mode and the mean velocity through the damper neck. Experiments are also performed on a simple rectangular cavity, where the thermoacoustic instability is mimicked by an electro-acoustic instability. A feedback loop is built, through which the growth rate of the instability can be controlled. A Helmholtz damper is added to the cavity and tuned to the mode of interest. The stabilization capabilities of the damper and the amplitude of the limit cycle in the unstable cases are in good agreement between the experiments and the analytical and numerical predictions, underlining the potentially dangerous behavior of the system, which should be taken into account for real engine cases.

Ceramic Component Processing Development for Advanced Gas Turbine Engines

1993 ◽  
Vol 115 (1) ◽  
pp. 1-8 ◽  
Author(s):  
B. J. McEntire ◽  
R. R. Hengst ◽  
W. T. Collins ◽  
A. P. Taglialavore ◽  
R. L. Yeckley
Keyword(s):  
Injection Molding ◽  
Room Temperature ◽  
Slip Casting ◽  
Turbine Engines ◽  
Gas Turbine Engines ◽  
Processing Conditions ◽  
Technology Applications ◽  
Ceramic Components ◽  
Manufacturing Technologies ◽  
Engine Components

Norton/TRW Ceramics (NTC) is developing ceramic components as part of the DOE-sponsored Advanced Turbine Technology Applications Project (ATTAP). NTC’s work is directed at developing manufacturing technologies for rotors, stators, vane-seat platforms, and scrolls. The first three components are being produced from a HIPed Si3N4, designated NT154. Scrolls were prepared from a series of siliconized silicon-carbide (Si-SiC) materials designated NT235 and NT230. Efforts during the first three years of this five-year program are reported. Developmental work has been conducted on all aspects of the fabrication process using Taguchi experimental design techniques. Appropriate materials and processing conditions were selected for power beneficiation, densification, and heat-treatment operations. Component forming has been conducted using thermal-plastic-based injection molding (IM), pressure slip-casting (PSC), and Quick-Set™ injection molding.1 An assessment of material properties for various components from each material and process were made. For NT154, characteristic room-temperature strengths and Weibull Moduli were found to range between ≈920 MPa to ≈1 GPa and ≈10 to ≈19, respectively. Process-induced inclusions proved to be the dominant strength-limiting defect regardless of the chosen forming method. Correction of the lower observed values is being addressed through equipment changes and upgrades. For the NT230 and NT235 Si-SiC, characteristic room-temperature strengths and Weibull Moduli ranged from ≈240 to ≈420 MPa, and 8 to 10, respectively. At 1370°C, strength values for both the HIPed Si3N4 and the Si-SiC materials ranged from ≈480 MPa to ≈690 MPa. The durability of these materials as engine components is currently being evaluated.

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