1、Copyright Free Field TechnologiesStudy of an Air FilterInfluence of an Air Filter on the Acoustic Behavior of an Air Cleaner using Actran 2Copyright Free Field TechnologiesObjectives Compute the acoustic transparency (Transmission loss) of an air cleaner using Actran. Study the influence of the air

2、filter on the transmission loss and the energy balance. The frequency range of computations is 10Hz; 3000HzInlet ductOutlet ductInterior acoustic fluid = airFilter 3Copyright Free Field TechnologiesAir Cleaner GeometryEntire geometryInlet ductAir cleaner boxinlet ductFilter4Copyright Free Field Tech

3、nologiesAir Filter The filter is made of a rubber sealing and an undulated paper sheet To model the filter within Actran, a foam layer will be placed at the filter position. This foam is modeled using the POROUS_RIGID (Biot model) formulation available in Actran with the following material propertie

4、s: Fluid density = 1.225 kg/m3 Porosity = 0.98 Flow resistivity = 100000 N.s/m4 Tortuosity = 1.2 Viscosity =1.821e-05 Ns/m2 A more complete POROUS_UP formulation is also available (see next slide) 5Copyright Free Field TechnologiesVolume Absorbent Material To model foam, rock wool, Porous elements :

5、 Biot model Material properties (frequency dependant): Foam skeleton : Young modulus, density, Fluid properties : fluid density, Foam properties : tortuosity, resistivity, porosity, Rigid porous elements : same as for POROUS materials except that skeleton is rigidExample of multi-layered panel alu f

6、oam septum6Copyright Free Field TechnologiesComputations A first computation is performed without the filter = the filter is replaced by standard air Plane mode is injected at the inlet side. Non reflective boundary conditions are used at the outlet side The injected power, reflected power and trans

7、mitted power are automatically outputted by Actran Then a second computation is performed with the air filter Model statitistics 11236 nodes, 48198 elements CPU time : 2 seconds per frequency on a standard Win XP PC RAM consumption : 100MB 7Copyright Free Field TechnologiesResults Transmission Loss

8、TL = 10*log10(Incident_Power/Transmitted_Power)8Copyright Free Field TechnologiesResults Power BalanceWithout FilterWith Filter9Copyright Free Field TechnologiesWithout Air FilterResults SPL MapsSPL dBWith Air FilterInlet ductOutlet ductFilter Inlet ductOutlet duct10Copyright Free Field TechnologiesConclusions The use of Actran to study the acoustic effect of air filter is demonstrated Actran includes the required porous material library to correctly account for this kind of components The air filter