Analysis of the aeroacoustic behavior of flow duct systems using an active multi-port characterization

For the aeroacoustic design of flow duct systems such as automotive intake and exhaust systems and HVAC ducts both the convective noise propagation effects and the aerodynamic noise generation mechanisms should be taken into account. Often, a compromise has to be made between maximizing the total noise attenuation and minimizing the aerodynamic flow-noise generation. In this framework, an active two-port formulation is commonly used to describe an arbitrary type of duct element using both an acoustic transfer matrix, for the propagation characterization, and an active source vector, to investigate the aerodynamic noise generation mechanisms. Although this approach enables a straightforward evaluation of the aeroacoustics properties for the various subcomponents of the flow duct network, it is limited to the low-frequency range, i.e. below the cut-on frequency of the non-planar duct modes. In this paper, the effect of the high-order modes is included in a similar modelling strategy yielding an active multi-port (N-port) characterization. The active multi-port parameters can be obtained numerically or experimentally using an extension of the well-known two-port characterization techniques. Both the numerical and experimental multi-port characterization techniques are applied to the aeroacoustic analysis of a straight cylindrical duct and a butterfly valve configuration, representative for HVAC systems of engineering relevance.status: publishe