Bends (elbows) (allowing guidance of a transported fluid with change of flow direction) 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 ...
The acoustic performance of bends must be accounted for the purpose of the design of equipments for which noise transmission either at extremities of the duct system or through duct walls of the components of the duct systems must be limited. Indeed, the presence of a bend (an elbow) causes a reduction in acoustic power, in particular at low frequency (depending on the cut-off frequency of the duct ), what is not without a practical interest  in many contexts.
ITS has integrated the prediction of the acoustic performance of bends to the simulation software SILDIS® (this is the subject of Module 6).
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 or with mixed cross section), the main input data taken into account for modeling the acoustic performance of bends (in fluid netwoks) being:
- the geometric characteristics of the duct (shape, transverse dimensions) potentially different upstream and downstream
- the parameters (depending on the thermodynamic conditions) and the flow rate of the transported fluid
- the radius of curvature
- the presence of turning vanes
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 bends with various geometries and dimensions.
The expected result of improvements to the acoustics calculation software SILDIS® (for the prediction of the acoustic performance of bends) 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.
 function of the dimensions of the cross section, the speed of sound, the Mach number
 obtaining insertion loss (reduction of sound power) at low frequencies by means of noise reduction devices such as dissipative silencers (whose performance is based on sound-absorbing material) is often complicated (even with resonators), requiring space (not always available) and involving substantial costs (always undesirable)