Dynamics and stability of lean-premixed swirl-stabilized combustion

Active noise control exploits the long wavelengths associated with low frequency sound. It works on the principle of destructive interference between the sound fields generated by the original primary sound source and that due to other secondary sources, acoustic outputs of which can be controlled. The acoustic objectives of different active noise control systems and the electrical control methodologies that are used to achieve these objectives are examined. The importance of having a clear understanding of the principles behind both the acoustics and the electrical control in order to appreciate the advantages and limitations of active noise control is emphasized. A brief discussion of the physical basis of active sound control that concentrates on three-dimensional sound fields is presented. >

Active noise control

A review of active control of combustion instabilities

Composites have been found to be the most promising and discerning material available in this century. Presently, composites reinforced with fibers of synthetic or natural materials are gaining more importance as demands for lightweight materials with high strength for specific applications are growing in the market. Fiber-reinforced polymer composite offers not only high strength to weight ratio, but also reveals exceptional properties such as high durability; stiffness; damping property; flexural strength; and resistance to corrosion, wear, impact, and fire. These wide ranges of diverse features have led composite materials to find applications in mechanical, construction, aerospace, automobile, biomedical, marine, and many other manufacturing industries. Performance of composite materials predominantly depends on their constituent elements and manufacturing techniques, therefore, functional properties of various fibers available worldwide, their classifications, and the manufacturing techniques used to fabricate the composite materials need to be studied in order to figure out the optimized characteristic of the material for the desired application. An overview of a diverse range of fibers, their properties, functionality, classification, and various fiber composite manufacturing techniques is presented to discover the optimized fiber-reinforced composite material for significant applications. Their exceptional performance in the numerous fields of applications have made fiber-reinforced composite materials a promising alternative over solitary metals or alloys.

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Fiber-Reinforced Polymer Composites: Manufacturing, Properties, and Applications.

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

It is shown in this article that adaptive control algorithms may be used to suppress combustion instabilities in turbulent combustors. In a typical configuration a signal delivered by a sensor monitoring the flame serves as input to a numerical adaptive filter which sends a control signal through an actuator into the combustion chamber. The controller coefficients are updated at the sampling rate using a global response signal. The controller automatically finds optimal coefficients to control the different unstable modes of oscillation. In addition it adapts to evolutions in operating conditions such as a continuous sweep of air flow rate and a shift in the global equivalence ratio. Under certain conditions a secondary mode appears when the control system is operating. While this oscillation occurs as a result of a destabilizing effect of the control loop its amplitude remains limited. The theoretical background is developed and used to explain typical implementation problems such as the filter ...

Adaptive Active Control of Combustion Instabilities

Surface impedance control for sound absorption: direct and hybrid passive/active strategies

In this article, rice hull (RH) was used in the moulding of polyurethane (PU) foam system. The article analyzed the participation of RH in the chemical reaction of PU synthesis with Attenuated Total Reflection-Fourier Transform Infrared spectroscopy method. Besides, the influence of RH on the formation of pore structure along with the acoustic performance such as sound impedance rate, acoustic reflection factor, sound absorption coefficient, and transmission loss of the products were studied with the Transfer Function Method. The results indicated that RH significantly influenced the uniformity of pore diameter in PU foam. As the content of RH increased, the sound absorption peak shifted toward lower frequency region. And the sound absorption coefficients increased till a threshold value of RH content. POLYM. COMPOS., 34:1847–1855, 2013. V C 2013 Society of Plastics Engineers

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Influences of rice hull in polyurethane foam on its sound absorption characteristics

https://acoustique.ec-lyon.fr/publi/galland_applacoust05.pdf

Hybrid passive/active absorbers for flow ducts

https://acoustique.ec-lyon.fr/publi/wang_cs14.pdf

Marie-Annick Galland

Papers

Adaptive Active Control of Combustion Instabilities

Surface impedance control for sound absorption: direct and hybrid passive/active strategies

Influences of rice hull in polyurethane foam on its sound absorption characteristics

Hybrid passive/active absorbers for flow ducts

Sound absorption of a new bionic multi-layer absorber