Aeroacoustic and Aerodynamic Performance of Silencer Units at Different Inflow Profiles

Application of Analytical, Computational and Experimental Methods

Silencer units are installed downstream of axial fans to reduce the noise emission. An inhomogeneous or swirling fan outflow profile, respectively inflow profile to the silencer unit, leads to increased aerodynamic losses. Additionally, the acoustic properties are impaired by the sound generation of areas with high flow velocity.
Experiments are carried out on a scaled test rig, which is based on a state of the art configuration. Total and static pressure measurements are conducted in the diffuser, the silencer and downstream the silencer. The results show that there is a strong dependence of the performance of the configuration on the diffuser inlet profile. The undisturbed or hubstrong inflow profile leads to the formation of a high velocity area in the center of the splitter silencer. The tipstrong inlet and swirl inflow profiles lead to the opposite behavior. There are high velocities close to the casing and low or negative velocities in the center. The loss coefficient of the silencer unit can increase up to 169 % depending on the inflow profile. The flow noise, which is generated at the outlet of the splitters, is investigated as well. Therefore two characteristic silencer flow profiles are reproduced. Additionally, a nearly homogeneous flow distribution in the silencer is investigated as a reference. The results show that the flow noise for the characteristic silencer flow profiles is up to 11 dB higher than for the reference flow profile.