To reduce noise in ducts and piping, the SILDIS Module 1B software enables the sizing of reactive silencers as illustrated by a tutorial covering the case of a simple expansion chamber tuned to optimize noise reduction performance.
Applications include, in particular, noise control for pressurized fluid systems (e.g. those involving a compressor) and the reduction of exhaust noise from internal combustion engines.
In general, the SILDIS Module 1B software (in Excel format) allows for the modeling of acoustic and aerodynamic performance for noise attenuation devices used in air handling systems and pressurized fluid systems (operating at low or high temperatures), specifically enabling the calculation of:
- insertion loss / transmission loss (and also "noise reduction" in the sense of the decrease in sound pressure level at a specified location downstream of the silencer, respectively with and without the silencer)
- self-generated noise (due to flow)
- total pressure loss
Evaluations of these performance indicators are based on the transfer matrix method, involving the decomposition of a given silencer into a specific number of elements (as required) referenced in the software's dedicated library[1]. Their arrangement, i.e. their combination in a sequence from upstream to downstream to form a cascade, determines the configuration (pre-programmed in the software[2], yet allowing user-defined parameters for the fluid's dimensional and thermodynamic characteristics under operating conditions), which dictates the effectiveness of the noise-control equipment.
For reactive silencers without perforated tubes, calculations can be performed for axial or radial inlets and/or outlets, with a variable number of chambers ranging from 1 to 3 (12 combinations).
It is also possible to model silencers featuring perforated tubes and branch-Helmholtz resonators.
In many cases, a tuning feature allows for the optimization of acoustic performance, regarding both the level of noise attenuation and the frequency range of effectiveness.
While the task of modeling a reactive silencer - whether in an engineering or R&D context - may lack the artistic quality of tuning an organ (a truly noble pursuit!), both processes share some of the physical phenomena underlying actions to be conducted to carry them out succesfully. Just as the sound produced by an organ pipe depends on factors that are widely known (or easily discoverable via widely available information), the performance of a reactive silencer - especially one without perforated tubes - hinges on the geometry of the ducts/pipings through which a fluid flows (for silencers: not always the clean, dry air found in organs), of which dimensions (including those of expansion chambers) are determining for noise emissions (this includes accounting for famous "added lengths" i.e. end corrections, which compensate for the thermo-viscous phenomena occurring at the ducts extremities).
This plays a significant role in the distinctive sounds of certain iconic car engines play (the musical aspect being a matter of taste for enthusiasts of specific brands e.g. such as German or Italian ones - as far as Europe is concerned - who value the unique acoustic signature of these high-performance machines for the enjoyment of their passionate, and wealthy, clientele).
There is no better way to satisfy one's curiosity regarding easy, quick[3] and reliable[4] sizing calculations for reactive silencers using the SILDIS software than by following the tutorial linked below.
Tutorial (a quarter of one hour)
[1] cf. Elements for Module 1B of SILDIS software
[2] cf. Mountings for Module 1B of SILDIS software
[3] with Module 1B of the SILDIS software, there is no need to create complex geometry, perform tedious meshing, or wait for lengthy calculations to complete. The user simply enters input data (parameters) into an Excel spreadsheet, selects models from drop-down menus for various calculation stages - accounting for the recommendations provided in a manual - and instantly obtains the simulation results, as demonstrated in the tutorial
[4] in the context of the development and of the validation of the software (regularly certified as compliant with the ISO 9001 Quality Management standard), numerous comparisons were made with predictions obtained via other methods (e.g. the finite element method - FEM -) and with measurements, yielding conclusive results across the entire frequency range corresponding to plane wave propagation