Identification of High-Frequency Transverse Acoustic Modes in Multi-Nozzle Can Combustors

2020 ◽  
Author(s):  
J. Kim ◽  
W. Gillman ◽  
D. Wu ◽  
B. Emerson ◽  
V. Acharya ◽  
...  
Keyword(s):  
High Frequency ◽  
Gas Turbines ◽  
Least Squares Method ◽  
Flame Temperature ◽  
Three Dimensional ◽  
Transverse Mode ◽  
Nodal Line ◽  
Acoustic Mode ◽  
Mitigation Measures ◽  
Mode Shapes

Abstract High frequency thermoacoustic instabilities are problematic for lean-premixed gas turbines. Identifying which acoustic mode is being excited is important, in that it provides insight into potential mitigation measures and mechanical stress/life. However, the frequency spacing between modes becomes quite close for high frequency instabilities in a can combustor. This makes it difficult to distinguish between the modes (e.g., the first transverse mode vs. a higher order axial/mixed mode) based upon frequency calculations alone, which inevitably have uncertainties in boundary conditions, temperature profiles, and combustion response. This paper presents a methodology to simultaneously identify the acoustic mode shapes in the axial and azimuthal directions from acoustic pressure measurements. Multiple high temperature pressure transducers, located at distinct axial and azimuthal positions, are flush mounted in the combustor wall. The measured pressure oscillations from each sensor are then used to reconstruct the pressure distributions by using a least squares method in conjunction with a solution of a three dimensional wave equation. In order to validate the methodology, finite element method (FEM) calculations with estimated post-flame temperature is used to provide the candidate frequencies and corresponding mode shapes. The results demonstrate the reconstructed mode shapes and standing/spinning character of transverse waves, as well as the associated frequencies, both of which are consistent with the FEM predictions. Nodal line location was also extracted from the experimental data during the instabilities in the pressure data.

High-Frequency Acoustic Mode Identification of Unstable Combustors

2019 ◽  
Author(s):  
J. Kim ◽  
T. Lieuwen ◽  
B. Emerson ◽  
V. Acharya ◽  
D. Wu ◽  
...  
Keyword(s):  
High Frequency ◽  
Least Squares Method ◽  
Pressure Fluctuations ◽  
Acoustic Mode ◽  
Modal Identification ◽  
Mode Shapes ◽  
Similar Frequency ◽  
Pressure Transducers ◽  
Mode Identification ◽  
The Time Domain

Abstract High frequency thermoacoustic instabilities are becoming increasingly problematic in modern combustion systems. Understanding which acoustic mode is being excited is important for understanding potential mechanisms and control approaches — for example, influence of a helical shear layer mode on the flame has profoundly different effects on the first tangential acoustic mode, than a higher order axial mode of similar frequency. Nonetheless, the modal density increases with frequency and it becomes increasingly difficult to determine which acoustic mode is self-excited, based upon frequency calculations alone. Moreover, access issues and cost usually limit the number of pressure probes that can be distributed axially and azimuthally in the combustor. This paper presents a methodology for identifying the acoustic mode by using high temperature pressure transducers flush mounted in a combustion chamber. Modal identification is demonstrated with a siren under non-reacting conditions. The siren is mounted on the chamber to excite longitudinal and azimuthal waves. Five acoustic sensors at different axial and azimuthal locations measure the pressure fluctuations simultaneously. Given the forcing frequency and the speed of sound, the pressure distribution in the combustor is reconstructed in the time domain from the measured data by using a least squares method to determine its mode shapes. In addition, the finite element method (FEM) solver is used to provide the eigenfrequencies and corresponding mode shapes. The test results demonstrate that the mode shapes from the reconstructed data and corresponding frequencies are consistent with those predicted from the FEM, which validates the methodology in this study. In addition, the methodology is extended to practical reacting cases without the siren to determine the acoustic mode shapes of naturally occurring instabilities. In these cases, the modal features have strong stochastic features, such as what appear to be stochastic variations in overall amplitude and relative amplitudes of clockwise and counterclockwise waves.

Optimum Multi-Nozzle Configuration for Minimizing the Rayleigh Integral During High-Frequency Transverse Instabilities

2021 ◽  
Author(s):  
Vishal Acharya ◽  
Tim Lieuwen
Keyword(s):  
High Frequency ◽  
Transverse Mode ◽  
Acoustic Mode ◽  
Combustion Stability ◽  
Circular Distribution ◽  
Transverse Modes ◽  
Fixed Set ◽  
Circular Configuration ◽  
Swirling Strength ◽  
The Stability

Abstract This paper develops a formalism for optimizing nozzle location/configuration with respect to combustion stability of high-frequency transverse modes in a can combustor. The stability of these acoustically non-compact flames was assessed using the Rayleigh Integral (RI). Several key control parameters influence RI - flame angle, swirling strength, nozzle location, as well as nozzle location with respect to the acoustic mode shape. In this study, we consider a N-around-1 configuration such as typically used in a multi-nozzle can system and study the overall stability of this system for different natural transverse modes. Typically, such nozzles are distributed in a uniformly circular manner for which we study the overall RI and for cases where RI>0, we optimize the nozzle distribution that can reduce and minimize RI. For a fixed geometry such a circular configuration, the analysis shows how the flame's parameters must vary across the different nozzles, to result in a relatively stable system. Additionally, for a fixed set of flame parameters, the analysis also indicates the non-circular distribution of the N nozzles that minimizes RI. Overall, the analysis aims to provide insights on designing nozzle locations around the center nozzle for minimal amplification of a given transverse mode.

Combined Acoustic Damping-Cooling System for Operational Flexibility of GT26/GT24 Reheat Combustors

2015 ◽  
Author(s):  
Bruno Schuermans ◽  
Mirko Bothien ◽  
Michael Maurer ◽  
Birute Bunkute
Keyword(s):  
Gas Turbines ◽  
Cooling System ◽  
Acoustic Mode ◽  
Acoustic Properties ◽  
Front Panel ◽  
Mode Shapes ◽  
Front Face ◽  
Operational Flexibility ◽  
Fuel Gas ◽  
Near Wall

In the development process of gas turbine combustion chambers, finding countermeasures for thermoacoustically induced pressure pulsations is a major focus. This paper presents a novel system consisting of a multi-layered and multi-functional high frequency damping and cooling structure that is implemented on the sequential burner front panel of the GT26/GT24 gas turbines. The device features multiple single Helmholtz dampers and an advanced convective near wall cooling system to improve the cooling capability and to reduce the cooling mass flow and thereby reducing NOx emissions. The acoustic properties of the dampers and their placement have been defined as function of the identified acoustic mode shapes. The latter is very important since the dampers are designed to counteract screech tones that have acoustic wave lengths of the order of one burner front face width. In order to identify the acoustic mode shapes, multiple dynamics pressure measurements are applied in the full scale engine. The near-wall cooled damping front panel design represents a new technology which has been developed and successfully validated at engine level in fuel gas and oil operation. The restrictions of the stable operating range due to pulsations are completely eliminated resulting in an increase of operational flexibility and lifetime. In addition to a thorough treatment of the damper’s acoustic performance, information on the improved near wall cooling scheme is given in the paper, too.

Optimum Multi-Nozzle Configuration for Minimizing the Rayleigh Integral During High-Frequency Transverse Instabilities

2021 ◽  
Author(s):  
Vishal Acharya ◽  
Timothy Lieuwen
Keyword(s):  
High Frequency ◽  
Transverse Mode ◽  
Acoustic Mode ◽  
Combustion Stability ◽  
Circular Distribution ◽  
Transverse Modes ◽  
Fixed Set ◽  
Circular Configuration ◽  
Swirling Strength ◽  
The Stability

Abstract This paper develops a formalism for optimizing nozzle location/configuration with respect to combustion stability of high-frequency transverse modes in a can combustor. The stability of these acoustically non-compact flames was assessed using the Rayleigh Integral (RI). Several key control parameters influence RI – flame angle, swirling strength, nozzle location, as well as nozzle location with respect to the acoustic mode shape. In this study, we consider a N-around-1 configuration such as typically used in a multi-nozzle can system and study the overall stability of this system for different natural transverse modes. Typically, such nozzles are distributed in a uniformly circular manner for which we study the overall RI and for cases where RI > 0, we optimize the nozzle distribution that can reduce and minimize RI. For a fixed geometry such a circular configuration, the analysis shows how the flame’s parameters must vary across the different nozzles, to result in a relatively stable system. Additionally, for a fixed set of flame parameters, the analysis also indicates the non-circular distribution of the N nozzles that minimizes RI. Overall, the analysis aims to provide insights on designing nozzle locations around the center nozzle for minimal amplification of a given transverse mode.

Predicting the onset of high-frequency self-excited oscillations in elastic-walled tubes

2010 ◽  
Vol 466 (2124) ◽  
pp. 3635-3657 ◽  
Author(s):  
Robert J. Whittaker ◽  
Matthias Heil ◽  
Oliver E. Jensen ◽  
Sarah L. Waters
Keyword(s):  
High Frequency ◽  
Solid Mechanics ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Normal Modes ◽  
Theoretical Description ◽  
Elastic Tube ◽  
Mode Shapes ◽  
Navier Stokes ◽  
Navier Stokes Equations

We present a theoretical description of flow-induced self-excited oscillations in the Starling resistor—a pre-stretched thin-walled elastic tube that is mounted on two rigid tubes and enclosed in a pressure chamber. Assuming that the flow through the elastic tube is driven by imposing the flow rate at the downstream end, we study the development of small-amplitude long-wavelength high-frequency oscillations, combining the results of two previous studies in which we analysed the fluid and solid mechanics of the problem in isolation. We derive a one-dimensional eigenvalue problem for the frequencies and mode shapes of the oscillations, and determine the slow growth or decay of the normal modes by considering the system’s energy budget. We compare the theoretical predictions for the mode shapes, frequencies and growth rates with the results of direct numerical simulations, based on the solution of the three-dimensional Navier–Stokes equations, coupled to the equations of shell theory, and find good agreement between the results. Our results provide the first asymptotic predictions for the onset of self-excited oscillations in three-dimensional collapsible tube flows.

Effect of Combustor Inlet Geometry on Acoustic Signature and Flow Field Behavior of the Low Swirl Injector

2010 ◽  
Author(s):  
Peter L. Therkelsen ◽  
David Littlejohn ◽  
Robert K. Cheng ◽  
J. Enrique Portillo ◽  
Scott M. Martin
Keyword(s):  
Gas Turbines ◽  
Atmospheric Condition ◽  
Combustion Method ◽  
Acoustic Mode ◽  
Mode Shapes ◽  
Acoustic Oscillations ◽  
Lean Premixed Combustion ◽  
Acoustic Signature ◽  
Swirl Injector ◽  
Particle Imaging

Low Swirl Injector (LSI) technology is a lean premixed combustion method that is being developed for fuel-flexible gas turbines. The objective of this study is to characterize the fuel effects and influences of combustor geometry on the LSI’s overall acoustic signatures and flowfields. The experiments consist of 24 flames at atmospheric condition with bulk flows ranging between 10 and 18 m/s. The flames burn CH4 (at φ = 0.6 & 0.7) and a blend of 90% H2 - 10% CH4 by volume (at φ = 0.35 & 0.4). Two combustor configurations are used, consisting of a cylindrical chamber with and without a divergent quarl at the dump plane. The data consist of pressure spectral distributions at five positions within the system and 2D flowfield information measured by Particle Imaging Velocimetry (PIV). The results show that acoustic oscillations increase with U0 and φ. However, the levels in the 90% H2 flames are significantly higher than in the CH4 flames. For both fuels, the use of the quarl reduces the fluctuating pressures in the combustion chamber by up to a factor of 7. The PIV results suggest this to be a consequence of the quarl restricting the formation of large vortices in the outer shear layer. A Generalized Instability Model (GIM) was applied to analyze the acoustic response of baseline flames for each of the two fuels. The measured frequencies and the stability trends for these two cases are predicted and the triggered acoustic mode shapes identified.

Vehicle Miles Traveled in Multivehicle Households

2005 ◽  
Vol 1926 (1) ◽  
pp. 198-205
Author(s):  
Somchai Pathomsiri ◽  
Ali Haghani ◽  
Paul M. Schonfeld
Keyword(s):  
Least Squares Method ◽  
Substitution Effect ◽  
Mitigation Measures ◽  
Vehicle Miles Traveled ◽  
Emission Mitigation ◽  
Conservation Policies ◽  
Multiple Vehicles ◽  
Single Vehicle ◽  
Household Travel ◽  
Behavior Shift

Vehicle miles traveled (VMT) is an important factor in the development of transportation plans, emission mitigation measures, and energy conservation policies. Therefore, estimation of VMT is a crucial task supporting such plans and policies. This research addresses the estimation of VMT in households owning multiple vehicles. This sector is expected to use vehicles differently from single-vehicle households because usage of any vehicle may depend on usage of other vehicles. Previous studies concluded that there is a substitution effect between usages of two vehicles (i.e., greater usage of one vehicle lessens usage of the other). In view of more recent changes in sociodemographic structure, the problem was revisited with the 2001 National Household Travel Survey database. The proposed VMT model is a system of simultaneous equations. Each equation explains the VMT for one of the household's vehicles. The three-stage least-squares method was used to estimate the coefficients. A case study of two-vehicle households was investigated. The resulting model shows that VMT can be explained by variables such as the vehicle's newness, number of potential car users in a household, and household income. Surprisingly, the results show not a substitution effect but a spilling effect. The VMT of the first vehicle does not depend on how much the second vehicle is driven. However, increased use of the first vehicle tends to spill over and increase the use of the second one. Some explanation of this behavior shift is provided.

scholarly journals Identification of Mode Shapes of a Composite Cylinder Using Convolutional Neural Networks

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2801
Author(s):  
Bartosz Miller ◽  
Leonard Ziemiański
Keyword(s):  
Neural Networks ◽  
Convolutional Neural Networks ◽  
Composite Structures ◽  
Three Dimensional ◽  
Mode Shapes ◽  
Identification Algorithm ◽  
Material Degradation ◽  
Local Material ◽  
Noisy Input ◽  
Shape Vector

The aim of the following paper is to discuss a newly developed approach for the identification of vibration mode shapes of multilayer composite structures. To overcome the limitations of the approaches based on image analysis (two-dimensional structures, high spatial resolution of mode shapes description), convolutional neural networks (CNNs) are applied to create a three-dimensional mode shapes identification algorithm with a significantly reduced number of mode shape vector coordinates. The CNN-based procedure is accurate, effective, and robust to noisy input data. The appearance of local damage is not an obstacle. The change of the material and the occurrence of local material degradation do not affect the accuracy of the method. Moreover, the application of the proposed identification method allows identifying the material degradation occurrence.

Development and Validation of a Three-Dimensional Multiphase Flow CFD Analysis for Journal Bearings in Steam and Heavy Duty Gas Turbines

2012 ◽  
Author(s):  
Stephan Uhkoetter ◽  
Stefan aus der Wiesche ◽  
Michael Kursch ◽  
Christian Beck
Keyword(s):  
Experimental Data ◽  
Multiphase Flow ◽  
Gas Turbines ◽  
High Speed ◽  
Three Dimensional ◽  
Air Entrainment ◽  
Journal Bearings ◽  
Heavy Duty ◽  
Present Contribution ◽  
Two Phase

The traditional method for hydrodynamic journal bearing analysis usually applies the lubrication theory based on the Reynolds equation and suitable empirical modifications to cover turbulence, heat transfer, and cavitation. In cases of complex bearing geometries for steam and heavy-duty gas turbines this approach has its obvious restrictions in regard to detail flow recirculation, mixing, mass balance, and filling level phenomena. These limitations could be circumvented by applying a computational fluid dynamics (CFD) approach resting closer to the fundamental physical laws. The present contribution reports about the state of the art of such a fully three-dimensional multiphase-flow CFD approach including cavitation and air entrainment for high-speed turbo-machinery journal bearings. It has been developed and validated using experimental data. Due to the high ambient shear rates in bearings, the multiphase-flow model for journal bearings requires substantial modifications in comparison to common two-phase flow simulations. Based on experimental data, it is found, that particular cavitation phenomena are essential for the understanding of steam and heavy-duty type gas turbine journal bearings.

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