Straight ducts are components which are often present in duct systems such as those to be envisaged for air conditioning systems, ventilation systems for premises or for enclosures (in general: each time the installation of a fan is to be envisaged), exhaust lines for thermal engines or gas turbines, etc ... for which they are (among others) the basis for the construction of stacks.

The acoustic performance of straight ducts must be accounted for the purpose of the design of equipments for which noise transmission either at extremities of the duct system [1] or through duct walls of the components of the duct systems [2] must be limited (the noise attenuation due to straight ducts is rarely negligible, except in the case of ducts of very large cross section, or of very short length).

ITS has integrated the prediction of the acoustic performance of straight ducts to the simulation software SILDIS®.

Calculation routines have been implemented for the calculation of the insertion loss (attenuation) and of self noise of those equipments (with a rectangular or a circular cross section), the main input data taken into account for modeling the acoustic performance of ducts being as follows:

  • the geometric characteristics of the duct (shape, transverse dimensions, length)
  • the parameters (depending on the thermodynamic conditions) and the flow rate of the transported fluid
  • (in the case of a chimney, e.g. for the evacuation of burnt gases) the fouling

Following the modification operations of the software SILDIS®, the comparison of simulation results with bibliographic data (results of measurements, results of calculations by others ...) has shown a satisfactory agreement for the noise transmission of straight ducts with various geometries, constitutions and dimensions.

The expected result of improvements to the acoustics calculation software SILDIS® (for the prediction of the acoustic performance of straight ducts) is an improvement of the accuracy of the definition of the performance required for soundproofing equipments such as ventilation silencers and in general: of all industrial silencers (and of their connecting parts) which design is very demanding given the sound power levels of the considered noise sources (before soundproofing) and expected performance in terms of sound insulation in the context of protection of workers, or of preservation of environment, or of improvement of the acoustic comfort in buildings.

Computer Aided Design (CAD): SILDIS® calculation software for acoustics and aeraulics in the construction sector (in Excel format)

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[1] a correct evaluation of the reduction in the sound power level due to the (linear) attenuation of a duct makes it possible to optimize (sometimes expensive) noise reduction devices such as silencers

[2] the sizing, according to the standard practice, of the walls of a duct (either aeraulic or for the transport of a pressurized fluid), making it necessary, in some cases, to include an external lagging (which must be reduced to what is strictly necessary in terms of acoustic performance) of a pipe (for the purpose of limiting sound transmission) requires the consideration of the reduction, in relation to that of the inlet of the section considered, of the sound power level due to the attenuation (depending on the distance that the length is) of the duct