Determination of the impedance for lined ducts with grazing flow

A systematic uncertainty analysis for liner impedance eduction technology

“…which is consistent with results from the axial sound level and phase decay described in [7]. Here k zR and k zI are real and imaginary parts of axial wavenumber for the first mode k ð1Þ z , respectively, where mode number (1) has been omitted for brevity.…”

“…Here there is a risk for spurious errors in the pressure data interpolation [5]. The measured acoustic information can vary from the sound pressure [6] to the measured transmission coefficients [7,10], or velocity field [11]. For the simulation of sound propagation in the lined section and the connected hard walled ducts, different methods have been used, for instance analytical solutions combined with mode-matching method [3,4] or the finite difference method [6].…”

“…Both systematic acoustic prediction and liner optimization necessitates progress in impedance measurement methods by including the effect of the grazing flow. For this objective, impedance eduction techniques have been developed during the past three decades, e.g., [1][2][3][4][5][6][7]. The acoustical waves in the experimental duct are normally computed with potential flow, while both the effect of the boundary layer and the effect of the lined wall are taken into account as a boundary condition for the computation.…”

Numerical investigation of a honeycomb liner grazed by laminar and turbulent boundary layers

“…The popular two-microphone method for impedance eduction, such as used by Dean (1974), was used because of its simplicity and reliability, even when a grazing flow was present. Solving an associated inverse problem is an indirect way to educe the impedance and has been studied by several, including Jones et al (2002), Taktak et al (2010), Enghardt et al (2012) and Piot, Primus & Simon (2012). For full-scale engines, an insertion loss method can be used (Motsinger & Kraft 1995).…”

Comparison of Liner Impedance Derived From the Results of Measurements at Two Different Setups Using a Small Number of Microphones

“…Анализ зарубежных публикаций [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] показывает, что, несмотря на проведенные многочисленные экспериментальные и теоретические исследования, достаточно надежной методики по извлечению импе-данса по результатам измерений звукового поля еще не создано. Все предлагаемые методы определения импеданса находятся в стадии тес-тирования.…”