How One Mechanical Engineering Graduate Mastered Flow-Induced Noise Modeling with COMSOL Multiphysics

Subwoofer ports on speakers regulate airflow to improve bass response. They take the forms of bass reflex ports or passive radiators, optimizing the enclosure for enhanced low-frequency performance.

These ports work by allowing air to move in and out of the speaker, which helps to tune the resonance of the enclosure to specific frequencies. This results in more efficient reproduction of deep bass tones, enriching the overall sound quality of the speaker system.

To further explore the intricacies of subwoofer port design, Mark Csikszentmihalyi, a mechanical engineering graduate from Budapest University of Technology and Economics, focused on modeling the flow-induced noise around these ports for the practical part of his thesis. The task required the simultaneous modeling of several different physical phenomena.

Due to the displacement of the membrane, structural calculation is necessary, and flow and acoustics effects must also be included in the model. These phenomena entail challenges even for experienced numerical simulation engineers.

Challenge

Flow-induced noise simulation is a complex and challenging task that involves modeling the interaction between fluid flow and acoustic waves. Some of the main challenges are:

• Capturing the turbulent structures of the flow and their acoustic sources in the flow field, which requires high-resolution numerical methods and large computational resources;
• Solving the acoustics field in complex geometries and boundary conditions, which may involve multiple scattering, reflection, and diffraction effects; and
• Multiphysics, computationally demanding, and time-dependent simulation are required.

Solution

Different techniques are used to address these challenges, such as acoustic analogy, hybrid method, and direct method. Each of these methods has its advantages and limitations, depending on the application and the desired accuracy.

Since there are no restrictions on the central processing unit (CPU) cores used for computing, coming up with a solution for large models is well supported. COMSOL Multiphysics helps us to understand the underlying physical properties by simply revealing the equation that is being used by the interface.

Adding a lumped speaker with Thiele/Small (TS) parameters to the model reduces model complexity and maintains accuracy, simultaneously. While different physical properties are addressed at the same time, in COMSOL Multiphysics the data format is the same, so no back-and-forth copy-pasting or conversion is necessary. 

The solution to such a complex model includes many steps, such as solving the Fluid-Structure-Interaction problem using a Large Eddy Simulation (LES) model to resolve the structure of the turbulence. This problem is solved on a mesh appropriate to the flow with apt time-stepping settings. This typically consists of several steps, for example, first solving a stationary RANS model to obtain a good initial parameter for the transient LES model.

Results

• Using a unified platform enabled us to work on various physical properties and eliminated the need to learn different workflows.
• The model set-up is faster since there is no need to use one tool for the CFD and another for the structural part.
• It was easy to try out different turbulent models and couple them to the structural deformation to model the fluid-structure interaction.
• With the multicore support of COMSOL being utilized, the model required significantly less effort.

Conclusion

COMSOL Multiphysics helped us to understand and investigate the effect of a reflex tube on the flow pattern inside a subwoofer. An easy-to-use tool, the equation view makes it clear that the right interface is being used. Creating these virtual prototypes helped us visualize and investigate the effects of various tube geometries on the flow and acoustics model.

Summary

Challenge

Simulating flow-induced noise entails capturing turbulent structures, modeling complex geometries, and validating results with sparse experimental data, demanding high-resolution methods and significant computational resources.

Solution

Utilizing various techniques such as acoustic analogy, hybrid, and direct methods, alongside a unified platform such as COMSOL Multiphysics, streamlines complex simulations. It enables the simultaneous solving of diverse physical properties, simplifies model management, and facilitates understanding of underlying equations.

Result

COMSOL integration speeds up setup, simplifies turbulent model testing, enhances fluid-structure interaction, and reduces computational effort via multicore support.

Products Used

All products mentioned are developed by COMSOL.

• COMSOL Multiphysics
• Structural Mechanics Module
• Acoustics Module
• CFD Module
• CAD Import Module

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