Analysis of Thermo-Acoustic Properties of Combustors and Afterburners

2010 ◽  
Author(s):  
Guillaume Jourdain ◽  
Lars-Erik Eriksson
Keyword(s):  
Stability Analysis ◽  
Acoustic Waves ◽  
Structural Damage ◽  
Low Frequency ◽  
Acoustic Properties ◽  
Combustion Chambers ◽  
Energy Feedback ◽  
Useful Knowledge ◽  
Mode Stability ◽  
Acoustic Instabilities

Predicting thermo-acoustic instabilities in combustion chambers remains an important issue. These instabilities mainly contain hydrodynamic and acoustic waves and can lead to severe structural damage if the energy feedback due to combustion builds up high amplitudes. In order to predict their behavior, linearized flow solvers have been developed in combination with an Arnoldi extraction method to compute several of the least damped eigenmodes of combustor flows. This technique has been validated against an atmospheric combustor test rig, named Validation Rig I, in which both low frequency buzz and high frequency screech modes could be induced. Both types of modes have also been found computationally, by matching frequencies and modes shapes. A post-processing mode stability analysis procedure has also been developed with which any computed eigenmode may be analyzed with respect to the Rayleigh criterion. The results of the mode stability analysis are consistent with the corresponding unsteady RANS simulations, but not with the experimental data. Understanding the modes coupled with combustion can provide useful knowledge regarding the the possibility to suppress them.

scholarly journals Longitudinal acoustic instabilities in slender solid propellant rockets: linear analysis

2001 ◽  
Vol 437 ◽  
pp. 229-254 ◽  
Author(s):  
J. E. GARCÍA-SCHÄFER ◽  
A. LIÑÁN
Keyword(s):  
Acoustic Waves ◽  
Solid Propellant ◽  
Multiple Scale ◽  
Phase Reaction ◽  
Acoustic Oscillations ◽  
Mean Flow ◽  
Combustion Chambers ◽  
Cross Sectional ◽  
Longitudinal Acoustic ◽  
Acoustic Instabilities

To describe the acoustic instabilities in the combustion chambers of laterally burning solid propellant rockets the interaction of the mean flow with the acoustic waves is analysed, using multiple scale techniques, for realistic cases in which the combustion chamber is slender and the nozzle area is small compared with the cross-sectional area of the chamber. Associated with the longitudinal acoustic oscillations we find vorticity and entropy waves, with a wavelength typically small compared with the radius of the chamber, penetrating deeply into the chamber. We obtain a set of differential equations to calculate the radial and axial dependence of the amplitude of these waves. The boundary conditions are provided by the acoustic admittance of the propellant surface, given by an existing analysis of the thin gas-phase reaction layer adjacent to the solid–gas interface, and of the nozzle, accounting here for the possible effect of the vorticity and entropy waves. The equations are integrated in closed form and the results provide the growth rate of the disturbances, which we use to determine the conditions for instability of the longitudinal oscillations.

Review of piezoelectric impedance based structural health monitoring: Physics-based and data-driven methods

2021 ◽  
pp. 136943322110384
Author(s):  
Xingyu Fan ◽  
Jun Li ◽  
Hong Hao
Keyword(s):  
Structural Health Monitoring ◽  
Health Monitoring ◽  
Structural Damage ◽  
Low Frequency ◽  
Data Driven ◽  
Mode Shapes ◽  
Monitoring Methods ◽  
Destructive Testing ◽  
Electromechanical Impedance ◽  
Structural Health

Vibration based structural health monitoring methods are usually dependent on the first several orders of modal information, such as natural frequencies, mode shapes and the related derived features. These information are usually in a low frequency range. These global vibration characteristics may not be sufficiently sensitive to minor structural damage. The alternative non-destructive testing method using piezoelectric transducers, called as electromechanical impedance (EMI) technique, has been developed for more than two decades. Numerous studies on the EMI based structural health monitoring have been carried out based on representing impedance signatures in frequency domain by statistical indicators, which can be used for damage detection. On the other hand, damage quantification and localization remain a great challenge for EMI based methods. Physics-based EMI methods have been developed for quantifying the structural damage, by using the impedance responses and an accurate numerical model. This article provides a comprehensive review of the exciting researches and sorts out these approaches into two categories: data-driven based and physics-based EMI techniques. The merits and limitations of these methods are discussed. In addition, practical issues and research gaps for EMI based structural health monitoring methods are summarized.

Spatial Stability Analysis of a Flap Side Edge Vortex

2005 ◽  
Vol 4 (1-2) ◽  
pp. 37-47
Author(s):  
Jean-Philippe Brazier ◽  
Frédéric Moens ◽  
Philippe Bardoux
Keyword(s):  
Stability Analysis ◽  
Temporal Stability ◽  
Low Frequency ◽  
Aerodynamic Noise ◽  
Navier Stokes ◽  
Mean Flow ◽  
Side Edge ◽  
Amplification Rate ◽  
Edge Vortex ◽  
Flap Deflection

The flap side edge vortex is suspected to contribute to aerodynamic noise generation. Using a temporal stability analysis, Khorrami and Singer have shown that unstable modes could exist in this vortex. Due to the convective nature of this instability, a spatial analysis is more suitable. This is the subject of the present work. The mean flow past a 2D wing with a half-span flap has been computed with a steady 3D Navier-Stokes code. Then, local linear stability calculations are performed in several planes perpendicular to the vortex axis. The vortex is assumed axisymmetric and modelled with Batchelor's analytical vortex. Using Gaster's relation, the spatial amplification rate is calculated, giving by integration the relative amplitude of the fluctuations. Some low-frequency fluctuations are seen to be preferentially amplified by the vortex, but the amplifications remain small, so that this mechanism alone should not produce important noise in this particular configuration, where the flap deflection angle is moderate.

scholarly journals Low Frequency Noise Emission From a Natural Gas Compressor Station

1987 ◽  
Author(s):  
Manfred Sieminski ◽  
Manfred Schneider
Keyword(s):  
Natural Gas ◽  
Gas Turbines ◽  
Low Frequency ◽  
Frequency Noise ◽  
Compressor Station ◽  
Low Frequency Noise ◽  
Noise Emission ◽  
Combustion Chambers ◽  
The Subject ◽  
Remarkable Reduction

Low Frequency Noise at Gas Turbines A natural gas compressor station that was equipped with Hispano Suiza Turbines THM 1202 emitted high intensity noise between 20 Hz and 40 Hz, causing window vibrations and standing waves within the living rooms of a nearby residential area. Since additional sound attenuation by increasing the volume of the exhaust silencers was impossible, further investigations were carried out to explain the mechanism of this low frequency noise emission. By changing the flame pattern inside the combustion chambers of the turbines it was possible to achieve a remarkable reduction at 31.5 Hz amounting to 15 dB. The investigation procedure leading to the final results will be the subject of this presentation.

scholarly journals Effect of Variable Viscosity and Gravity Modulation on Linear and Non-Linear Rayleigh-Benard Convection in Viscoelastic Ferromagnetic Liquids

2020 ◽  
Vol 9 (3) ◽  
pp. 3482-3488
Keyword(s):  
Stability Analysis ◽  
Heat Transport ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Variable Viscosity ◽  
Low Frequency ◽  
Physical Parameters ◽  
Gravity Modulation ◽  
Non Linear ◽  
The Individual

The combined effect of various parameters of gravity modulation on the onset of ferroconvection is studied for both linear and non-linear stability. The effect of various parameters of ferroconvection is studied for linear stability analysis. The resulting seven-mode generalized Lorenz model obtained in non-linear stability analysis is solved using Runge -Kutta-Felberg 45 method to analyze the heat transfer. Consequently the individual effect of gravity modulation on heat transport has been investigated. Further, the effect of physical parameters on heat transport has been analyzed and depicted graphically. The low-frequency gravity modulation is observed to get an effective influence on the stability of the system. Therefore ferro convection can be advanced or delayed by controlling different governing parameters. It shows that the influence of gravity modulation stabilizes system.

Studies on the interaction of low‐frequency acoustic signals with the ocean bottom

Geophysics ◽  
1979 ◽  
Vol 44 (12) ◽  
pp. 1922-1940 ◽  
Author(s):  
Salvatore R. Santaniello ◽  
Frederick R. DiNapoli ◽  
Robert K. Dullea ◽  
Peter D. Herstein
Keyword(s):  
Acoustic Waves ◽  
Grazing Angle ◽  
Low Frequency ◽  
Propagation Loss ◽  
Ocean Bottom ◽  
Computer Technique ◽  
Quantitative Evidence ◽  
Ocean Sediment ◽  
Wave Models ◽  
Processing Techniques

Understanding the mechanisms by which the ocean sediment redirects impinging sound back into the ocean is necessary in developing propagation models for sonar performance prediction. The Naval Underwater Systems Center (NUSC) has (1) conducted controlled, self‐calibrating acoustic measurements where the ocean bottom interacted signal is isolated in time for analysis, (2) developed deconvolution processing techniques to aid in describing the impulse response of the ocean sediment, and (3) performed modeling to study the interaction of acoustic waves at the ocean bottom. This paper presents a synopsis of studies showing the necessity of considering the refraction of sound by the ocean sediment when predicting low‐frequency propagation loss. Constructive interference between nonplanar wave sediment refracted sound and sound reflected by the ocean‐sediment interface and subbottom layering can cause negative values of bottom loss when using plane‐wave models to interpret measured data. These models cannot account for all possible acoustic arrivals at a receiver. In addition, for a given frequency and constant ocean bottom grazing angle, bottom loss can be dependent upon both processing bandwidth and source/receiver depth. Deconvolution has aided in time resolution of signals that make up the bottom‐interacted signals. Resolution of these signals aids in interpreting results. A modeling effort utilizing the Fast Field Program (a computer technique for evaluating the field integral by the fast Fourier transform) provides quantitative evidence for the necessity of accounting for the refraction of sound by subocean sediments to interpret properly low‐frequency propagation loss measurements.

Sign in / Sign up

Export Citation Format

Share Document