Experimental evaluation of noise damping performance of in-duct perforated orifices with different geometric shapes

Abstract

In this work, 10 in-duct perforated plates are experimentally tested in a cold-flow pipe. These plates have the same porosities but different number N and geometric shaped orifices: 1) triangle, 2) square, 3) pentagon, 4) hexagon, and 5) star. The damping effect of these orifices is characterized by power absorption coefficient Δ and reflection one R from 100 to 1000 Hz. It is found that the orifice shape has little influence on Δ and R at lower frequency (ωa/2π≤700 Hz). However, as ωa is increased, star-shaped orifice is shown to be with much lower Δ in comparison with that of other shaped orifices. For the in-duct plates with the same shaped orifices, increasing N does not lead to an increase of Δ at lower frequency (ωa/2π≤900 Hz). However, the orifice with the same shape and porosity but larger N is found to be associated with 20% more power absorption at approximately 970 Hz. Δ max is approximately 85% around 190 Hz, as Ma≈0.29. The optimum Ma depends on the orifice shape. The present parametric measu...