The interactions between acoustic waves and a premixed combustion process can play an important role in the characteristicunsteadinessofcombustiondevices.Inparticular,theyareoftenresponsiblefortheoccurrenceofselfexcited, combustion-driven oscillations that are detrimental to combustor life and performance. A tutorial review is provided of current understanding of these interactions. First, the mutual interaction mechanisms between the combustion process and acoustic, vorticity, and entropy waves are described. Then, the acoustic‐ e ame interaction literatureisreviewed,primarily focusingon modeling issues.Thisliteratureisessentially organized into fourparts, depending on its treatment of 1) linear or 2) nonlinear analyses of 1) e amelets or 2) distributed reaction zones. A sizeable theoretical literature has accumulated to model the unsteady response of the laminar e ame structure, for example, the burning rate response to pressure perturbations. However, essentially no serious experimental effort has been performed to critically assess these predictions. As such, it is dife cult to determine the state of understanding in this area. On the other hand, good agreement has been achieved between well-coordinated experiments and theory describing the interactions between inherent e ame instabilities and acoustically induced e ow oscillations. Similarly, both the linear and nonlinear kinematic response of simple laminar e ames to acoustic velocity disturbances appear to be well understood, as evidenced by the agreement between surprisingly simple theory and experiment. Other than kinematic nonlinearities, additional potential mechanisms that introduce heat release‐ acoustic nonlinearities, such as e ame holding, or extinction, have been analyzed theoretically, but lack experimentalverie cation.Unsteadyreactormodelshavebeenusedextensivelytomodelcombustionprocessesinthe distributed reaction zone regimes. None of thesepredictionsappears to have been subjected to direct experimental scrutiny. Itisunlikelythatthismodeling approach willbeusefulforquantitativecombustion responsecalculations, due to their largely heuristic nature and the dife culty in rationally modeling the key interactions between reaction rate and the global characteristics of the combustion region, such as its volume. Several areas in need of work are particularly highlighted. These include e nite amplitude effects, modeling approaches for interactions outside of the e amelet regime, turbulent e ame wrinkling effects, and unsteady vortex‐ e ame interactions.

Modeling Premixed Combustion-Acoustic Wave Interactions: A Review

This paper presents recent progress in the field of thermoacoustic combustion instabilities in propulsion engines such as rockets or gas turbines. Combustion instabilities have been studied for more than a century in simple laminar configurations as well as in laboratory-scale turbulent flames. These instabilities are also encountered in real engines but new mechanisms appear in these systems because of obvious differences with academic burners: larger Reynolds numbers, higher pressures and power densities, multiple inlet systems, complex fuels. Other differences are more subtle: real engines often feature specific unstable modes such as azimuthal instabilities in gas turbines or transverse modes in rocket chambers. Hydrodynamic instability modes can also differ as well as the combustion regimes, which can require very different simulation models. The integration of chambers in real engines implies that compressor and turbine impedances control instabilities directly so that the determination of the impedances of turbomachinery elements becomes a key issue. Gathering experimental data on combustion instabilities is difficult in real engines and Large Eddy Simulation (LES) has become a major tool in this field. Recent examples, however, show that LES is not sufficient and that theory, even in these complex systems, plays a major role to understand both experimental and LES results and to identify mitigation techniques.

https://hal.archives-ouvertes.fr/hal-01502419/document

Prediction and control of combustion instabilities in real engines

Basic principles of aerodynamic noise generation

: This book has several purposes, including a broad historical summary of combustion instabilities in propulsion systems; a concise compilation of the main mechanisms for instabilities in liquid and solid fueled rockets, ramjets, thrust augmentors and gas turbines; development of a theoretical framework for investigating unsteady motions in combustion systems; and accessible surveys of the basic material required to understand the subject. Emphasis is placed throughout the book on observed behavior. For well-understood reasons, the best, and in many respects most useful quantitative data, have been obtained for solid propellant rockets. Hence that type of device occupies a special position in the subject. The book comprises nine chapters and eight annexes. Material in the annexes is not essential for reading and broadly understanding the main part of the book, but is likely interesting for those choosing to do research on the subject. The nine chapters divide into three parts.

Unsteady Motions in Combustion Chambers for Propulsion Systems

This article proposes a review of the state of knowledge in the field of combustion noise The survey comprises an initial discussion of indirect and direct noise sources and their general characteristics, a summary of expressions devised to estimate combustion noise from turbulent flames, a discussion of the fundamental equations describing sound emission from a reactive region and an evaluation of scaling methods for combustion noise An account is provided of a set of experiments on noise radiation from perturbed laminar flames Sources of intense radiation of sound are identified and theoretical expressions of the pressure field are compared with detailed measurements from well controlled experiments These experiments indicate that flame dynamics determine to a great extent the radiation of sound from flames This is further demonstrated with experiments dealing with effects of confinement Links between combustion noise and combustion instabilities are drawn on this basis These two aspects are usua

Flame Dynamics and Combustion Noise: Progress and Challenges

Upon review of past experimental results and theoretical efforts it is apparent that the mechanism by which combustion noise is generated is not well understood. A theory of combustion noise is developed in this paper which follows rigorously from the principles of fluid mechanics. Lighthill's approach, used in his studies of aerodynamic noise, is closely followed in the present work. The sound radiated from open, turbulent flames is found to depend strongly upon the structure of such flames; at present their structure is not well known. However, meaningful bounds and scaling rules for the sound power output and spectral content are derived based upon the present limited knowledge. A framework is developed which explains past experimental work and the origin of combustion noise.

W. Strahle

Papers

On combustion generated noise

Some results in combustion generated noise

Combustion generated noise

Combustion noise radiation by open turbulent flames

A review of combustion generated noise