Showing papers on "Rijke tube published in 2012"

Nonlinear Thermoacoustic Instability Dynamics in a Rijke Tube

Abstract: We present a data-driven nonlinear and chaos theory–based analysis of thermoacoustic instabilities in a simple Rijke tube. Thermoacoustic instability modes in this simple Rijke tube display very rich nonlinear behavior because of the interaction of acoustic modes and unsteady heat-release processes during combustion. This approach of analyzing thermoacoustic instabilities, their evolution, and interactions differs from traditional linear time-series–based approaches, such as the Fourier transform or the autocorrelation function. The objectives of this work are to address the limitations of conventional linear and model-based nonlinear analyses and to describe the potential of data-driven nonlinear and chaos theory–based analyses to gain a deeper understanding of thermoacoustic instability dynamics for reacting flows. The Rijke tube permits investigation of the nonlinear dynamics of thermoacoustic instabilities in a very systematic way by using picosecond time-resolved laser-induced fluorescence (PITLIF) o...

Obtaining Bifurcation Diagrams with a Thermoacoustic Network Model

Abstract: Proceedings of the ASME Turbo Expo 2012: Power for Land, Sea and AirJune 11-15, 2012, Copenhagen, DenmarkGT2012-68241AbstractLinear techniques can predict whether the non-oscillating (steady) state of a thermoa-coustic system is stable or unstable. With a suciently large impulse, however, a ther-moacoustic system can reach a stable oscillating state even when the steady state is alsostable. A nonlinear analysis is required to predict the existence of this oscillating state.Continuation methods are often used for this but they are computationally expensive.In this paper, an acoustic network code called LOTAN is used to obtain the steadyand the oscillating solutions for a horizontal Rijke tube. The heat release is modelledas a nonlinear function of the mass ow rate. Several test cases from the literature areanalysed in order to investigate the e ect of various nonlinear terms in the ame model.The results agree well with the literature, showing that LOTAN can be used to map thesteady and oscillating solutions as a function of the control parameters. Furthermore, thenature of the bifurcation between steady and oscillating states can be predicted directlyfrom the nonlinear terms inside the ame model.

Experimental Investigation of LMS Algorithm for Active Control of Combustion Instabilities: FIR or IIR

Abstract: Combustion instabilities are characterized by self-excited oscillations generated by the interaction between unsteady heat release and acoustic waves. To suppress combustion instabilities, the coupling between unsteady heat release and the pressure perturbation must somehow be interrupted. Active control techniques with a dynamic controller implemented can be used to achieve this. One of the most popular controllers is based on a finite (FIR) or infinite impulse response (IIR) filter, whose coefficients are optimized by using least mean square algorithm(LMS). In this work, we experimentally investigated and compared the performance of the LMS-based FIR and IIR control strategy on a laminar premixed flame, carried out with off-line system identification. It was found that there is a wide range for step size to be varied. When the step size is small, IIR filters performs better than FIR ones. However, with the step size increased, FIR and IIR filters behaves similarly. Approximately 45 dB sound reduction was achieved by applying either FIR or IIR filter, as long as the step size is properly selected. In order to improve the performance of conventional LMS-based filters, a time-varying step-size controller is developed and experimentally implemented on the Rijke tube. Finally, a thermoacoustic model of a Rijke tube with a Loudspeaker implemented as a tunable actuator is developed. By linearizing the model and recasting it into the classical N , the transfer function of the thermoacoustic system between the second sound source and the pressure measurement is calculated. Compared with the experimental measurements, good agreement is observed.

Robust Output Model Predictive Control of an Unstable Rijke Tube

Abstract: This work investigates the active control of an unstable Rijke tube using robust output model predictive control (RMPC). As internal model a polytopic linear system with constraints is assumed to account for uncertainties. For guaranteed stability, a linear state feedback controller is designed using linear matrix inequalities and used within a feedback formulation of the model predictive controller. For state estimation a robust gain-scheduled observer is developed. It is shown that the proposed RMPC ensures robust stability under constraints over the considered operating range.

Flame shape and spatially resolved Rayleigh criterion using proper orthogonal decomposition

Abstract: Chemiluminescence imaging was performed for premixed flames with natural thermoacoustic instabilities in a Rijke tube. The images were phase locked to the natural pressure oscillations in the tube. The use of proper orthogonal decomposition (POD) to identify phase-resolved flame fronts and flame surface area is reported. The flame front results compare favorably to an Abel transform for axisymmetric cases but also work well for cases with non-axisymmetric contributions. The flame area perturbations are compared to previous work using OH planar laser induced fluorescence. The relatively-simpler chemiluminescence approach finds the same flame surface area correlations versus pressure. Additionally, the modes from POD are used to compute local acoustic coupling via the space and time resolved Rayleigh index. It is found that one mode in the decomposition is spatially the same as the Rayleigh index and can be used to characterize the thermoacoustic coupling. This similarity is due to the mode's time constant ...

Heat transfer in a thermoacoustic process

Abstract: Thermoacoustic instability is defined as the excitation of acoustic modes in chambers with heat sources due to the coupling between acoustic perturbations and unsteady heat addition. The major objective of this paper is to achieve accurate theoretical results in a thermoacoustic heat transfer process. We carry out a detailed heat transfer analysis aimed at determining the stability?instability border of the thermoacoustic system. In this paper, we present a project type of physical examination and modelling task. We employed an electrically heated Rijke tube in our thermoacoustic project work. The aim of our project is to help our students enlarge their knowledge about thermodynamics, mainly about thermoacoustics, and develop their applied information technology and mathematical skills.

Modular system for studying tonal sound excitation in resonators with heat addition and mean flow

Abstract: An educational experimental system has been developed for studying tonal sound generation in acoustic resonators Tones are excited by either heat addition or vortex shedding in the presence of mean flow The system construction is straightforward and inexpensive Several test arrangements and experimental data are described in this paper The experimental setups include a modified Rijke tube, a standing-wave thermoacoustic engine, a baffled tube with mean flow, and an acoustic energy harvester with a piezoelement Simplified mathematical models for interpreting data are discussed, and references are provided to literature with more advanced analyses The developed system can assist both graduate and undergraduate students in understanding acoustic instabilities via conducting and analyzing interesting experiments

Modelling flame-generated noise in a partially premixed, bluff body stabilized model combustor

Abstract: Numerical simulation using Computational Fluid Dynamics (CFD) has become increasingly important as a tool to predict the potential occurrence of combustion instabilities in gas turbine combustors operating in lean premixed mode. Within the EU-funded Marie Curie project, LIMOUSINE (Limit cycles of thermo-acoustic oscillations in gas turbine combustors), a model test burner has been built in order to have reproducible experimental results for model validation. The burner consists of a Rijke tube of rectangular section having a flame-stabilizing wedge at about 1/4 of its length. Fuel and air supplies were carefully designed to give closed end acoustic inlet boundary conditions while the atmospheric outlet representing an acoustically open end. A transient CFD simulation of the turbulent, partially premixed, bluff body stabilized combusting flow has been carried out for the LIMOUSINE burner using ANSYS CFX commercial software. A 2-D section has been modelled by means of the scale resolving turbulence model, Scale-Adaptive Simulation (SAS), and a two-step Eddy Dissipation combustion model.Experiments were performed on the LIMOUSINE model burner to measure the dynamic variation of pressure and temperature. Results were obtained for several cases with power input ranging from 40 to 60 kW and air factors between 1.2 and 1.8.The CFD results are found to be in good agreement with experiments: the flame is predicted to stabilise on the bluff body in the fluid recirculation zone; resonance frequencies are found to change depending on power and air excess ratio and have a good agreement with experimental results and analytical values; pressure oscillations are consistent with pipe acoustic modes.Copyright © 2012 by ASME