Thermoacoustic Analysis in a Combustion Chamber

Thermoacoustic Analysis in Combustion Chamber, CFD Simulation Tutorial

Description

This project, covering non-premixed combustion and acoustics together, investigates a thermoacoustic phenomenon within a combustion chamber using ANSYS Fluent. In thermoacoustic systems, heat is converted into sound waves, which can then be harnessed for tasks such as pumping heat or generating electricity. Since the process involves no moving parts, it offers a reliable, low-maintenance approach to energy conversion.

Methane and oxygen enter the domain through separate inlet boundaries at mass flow rates of 0.001 kg/s and 0.025 kg/s, respectively, mixing and combusting within the chamber. This simulation extracts both the Acoustic Power Level (dB) and Surface Acoustic Power Level (dB) using the steady-state acoustic model available in ANSYS Fluent — the former measuring total sound power, and the latter measuring sound power per unit surface area. The geometry was built in SpaceClaim, with the mesh generated in ANSYS Meshing.

Methodology

Combustion was modeled using the Non-Adiabatic, Non-Premixed Combustion model, which accounts for heat loss occurring during combustion — reflecting the reality that some generated heat escapes to the surroundings rather than remaining fully contained. This makes the model more representative of practical scenarios where such losses can't be neglected. Acoustic behavior was captured using the Broadband Noise Source model, which predicts the broadband noise generated by turbulent flow within the CFD simulation.

Conclusion

The extracted results include contours of several key parameters. The fuel's mass fraction shows it entering the domain from the center of the inlet plate, while air — defined with a 0.23 oxygen mass fraction and the remainder nitrogen — enters the surrounding zone around the fuel inlet. Mass fraction contours of the combustion reaction products are similarly visible throughout the domain.

Acoustic results include the Surface Acoustic Power Level across the chamber walls and the Acoustic Power Level across a plane defined at the chamber's center. The maximum Surface Acoustic Power Level reached 73.56 dB, while the corresponding Acoustic Power Level value was somewhat lower, at 62.93 dB — illustrating how combustion-driven sound generation varies between the chamber's bounding surfaces and its interior flow field.