On measurement of acoustic transfer properties of compact in-duct objects

Welcome to the MWL seminar on Friday, May 9, from 12:10 to 13:00 CEST. The seminar will be held in Munin (Teknikringen 8, KTH), and the online audience can join via Zoom: kth-se.zoom.us/j/69436706509 . Feel free to forward this invitation to colleagues interested in attending.

Speaker: Hans Bodén, MWL, KTH.

Abstract: At MWL we have over the last couple of years been involved in projects including measurement of plane wave two-port properties of acoustically compact samples in ducts. The starting point is in most cases measurement of the scattering matrix using the two-source method and we were for instance interested in: understanding the physics, comparing with models or developing new (at least empirical) models. In this talk we will not focus on these aspects of the individual research projects but rather on if simplified descriptions using a transfer impedance, or side-branch impedance, is sufficient to describe the acoustic properties of the object instead of a full scattering matrix or transfer matrix description. This is coupled to the question of if some quantity: particle velocity, mass flow, momentum, pressure, enthalpy etc., is conserved over the sample. The talk will discuss what the experimental data can tell us about these questions. Results will be presented for the following cases:
• Perforate plate for low level linear acoustic excitation without flow.
• Tube row for low level linear acoustic excitation without flow.
• Perforate plate for high level nonlinear acoustic excitation without flow.
• Tube row with through flow.
• Perforate plate covering a side-branch duct with grazing flow.