A Combustion noise CFD simulation is a powerful computer model used by engineers to understand and reduce the noise created by engines and burners. The burning of fuel is not a quiet process; it creates pressure waves that we hear as noise. Using a Combustion acoustic Fluent simulation with ANSYS Fluent, we can predict this noise before building expensive physical prototypes. This report details an Acoustic noise CFD analysis of a non-premixed combustion chamber. In this type of combustion, fuel and air mix and burn at the same time. The simulation uses the detailed GRI Combustion CFD chemical model to accurately represent the flame. It then uses the Broadband Noise model in Fluent to calculate the sound produced by the turbulent flow. This type of analysis is essential for designing quieter, more stable, and more efficient combustion systems.

Learn more about combustion CFD simulation tutorials and explore acoustic analysis resources for advanced studies.

Simulation Process: Non-Premixed Combustion and Acoustic Modeling

The simulation process for this Combustion noise CFD Simulation started with designing the chamber geometry and creating a high-quality computational mesh. The final mesh contains 5,630,442 tetrahedral elements, which provides the detail needed for an accurate analysis. Inside ANSYS Fluent, the Species Transport model was activated to track the different chemical gases involved in the reaction.

The combustion was modeled using a non-premixed combustion approach combined with the steady diffusion flamelet model. This is a smart and efficient method for complex flames. Instead of solving the full chemistry everywhere, this model pre-calculates the detailed chemical reactions from the GRI mechanism and stores the results in a table. The solver then uses this table to quickly and accurately find the temperature and species concentrations during the main simulation. For the Acoustic noise Fluent analysis, the Broadband Noise model was used.

Figure 1: The 3D geometry of the combustion chamber used as the computational domain for the Fluent CFD simulation.

Figure 2: A 3D plot of the mean temperature distribution within the chamber, calculated by the PDF flamelet model.

Post-processing: CFD Analysis of Noise Sources and Flame Structure

The simulation results provide a complete engineering analysis, successfully showing the direct cause-and-effect relationship between the intense combustion process and the acoustic noise it produces. The analysis begins with the effect: the noise. The acoustic power level contours in Figure 3 show that the noise is not the same everywhere. There are specific locations where the sound is loudest, reaching a peak of approximately 120 dB. The circular patterns show the pressure waves, or sound, moving outwards from these high-intensity zones. From an engineering viewpoint, these contours are like a map that pinpoints the exact source of the combustion noise.

Figure 3: Contours of the Acoustic Power Level on four cross-sectional planes, showing the intensity and pattern of sound generated by the combustion.

Now, we analyze the cause: the flame itself. The temperature contour in Figure 4 visualizes the combustion flame, showing a maximum temperature of 2051 K right where the fuel is injected and burned. When we compare this with the acoustic contour, we see a perfect match: the hottest part of the flame is in the exact same location as the loudest part of the noise. This is the critical connection. The rapid release of heat and the turbulent mixing of hot gases, shown by the velocity streamlines in Figure 5, are what generate the intense pressure fluctuations that we measure as sound. The strong temperature gradients, from the hot 2091 K flame to the cooler 600-900 K walls, also change the gas density, which affects how these sound waves travel through the chamber.

The most important achievement of this simulation is the successful correlation between the high-temperature combustion zone and the peak acoustic power levels. This proves that the GRI Combustion Fluent Simulation and the Broadband Noise model are working together correctly. This provides engineers with clear and actionable data: to reduce the noise in this chamber, design changes must focus on modifying the flame structure or the flow dynamics in that specific high-temperature, high-noise region.

Figure 4: Contours of the flame structure colored by temperature, visualizing the high-temperature reaction zone from the GRI Combustion Fluent Simulation.

Figure 5: Velocity streamlines showing the path of the fuel flow through the combustion chamber.