This paper discusses the use of novel porous sound absorbent ceramic tiles as heat shields in combustion chambers with respect to their sound absorption. For this purpose, a theory describing the bulk properties of a homogeneous porous absorber layer was combined with a transfer matrix approach to account for the temperature gradient within the absorber. By means of a high temperature scenario, the maximum absorption performance and the required microscale properties of the absorber are presented.

This paper discusses the use of novel porous sound absorbent ceramic tiles as heat shields in combustion chambers with respect to their sound absorption. For this purpose a theory describing the bulk properties of a homogeneous porous absorber layer was combined with a transfer matrix approach to account for the temperature gradient within the absorber. By means of a high temperature scenario, the maximum absorption performance and the required microscale properties of the absorber are presented.

This paper discusses the potential of using porous ceramic lining as insulating material in combustion chambers with respect to their sound absorbent ability to suppress thermoacoustic instabilities. For this purpose a combustion chamber test rig was developed and different types of ceramic linings were tested. The examined range of power was between 40 and 250 kW and the air-propane equivalence ratio was between 1.2 and 2.0. The overall sound pressure level and frequency domain of a lean premixed swirl stabilized and piloted burner are presented. The resonance frequencies and sound pressure levels are obtained and compared for the different combustion chamber linings. The results show a significant decrease in overall sound pressure level by up to 23.5 dB for sound absorbent lining in comparison to the common sound reflecting combustion chamber lining. In summary, sound absorbent ceramic combustion chamber lining can contribute to improve the stability of lean premixed gas turbines.

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Recently discussed sound absorption models for porous ceramic materials use porosity and flow resistance as variables. The prediction of the porosity and especially flow resistance of a porous ceramic is not trivial even though it was examined intensively. A particular issue is the use of porosity and flow resistance as variables without judging their likelihood, so that physically impossible combinations of porosity and flow resistance are calculated. To prevent this, a model is presented to predict the porosity and airflow resistance of a freeze cast ceramic with spherical pores provided by sacrificial templating. The model is validated by measurements of the flow resistance of ceramic samples with different porosity and pore–size distributions. An optimal sacrificial template diameter for the desired application is presented.