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Transfer impedance of microperforated materials with tapered holes
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10.1121/1.4824968
/content/asa/journal/jasa/134/6/10.1121/1.4824968
http://aip.metastore.ingenta.com/content/asa/journal/jasa/134/6/10.1121/1.4824968

Figures

Image of FIG. 1.
FIG. 1.

(Color online) Sketch of the CFD geometry. The axis for this axisymmetric geometry is at the bottom of the sketch, and the upper boundaries are slip-surfaces (symmetry).

Image of FIG. 2.
FIG. 2.

Typical computational mesh in the region of the perforation.

Image of FIG. 3.
FIG. 3.

Inlet velocity as a function of time (a) and the corresponding Fourier spectrum as a function of frequency (b).

Image of FIG. 4.
FIG. 4.

(Color online) Straight hole steady-state CFD results: (a) pressure field, Pa, (b) velocity magnitude, mm/s, (c) shear rate, 1/s, and (d) energy loss rate, W/m3. In these images, the flow is from the bottom to the top.

Image of FIG. 5.
FIG. 5.

(Color online) Sketch of relevant geometry for understanding the taper angle terms in Eq. (16) . The ratio of the entrance (and exit) angle to 90° (i.e., π/2) enters into the equation.

Image of FIG. 6.
FIG. 6.

(Color online) Tapered hole steady-state CFD results: (a) pressure field, Pa, (b) velocity magnitude, mm/s, (c) shear rate, 1/s, and (d) energy loss rate, W/m3. In these images, the flow is from the bottom to the top.

Image of FIG. 7.
FIG. 7.

(Color online) Comparison of one hundred and forty steady-state CFD pressure drop results with the three formulas discussed in the text.

Image of FIG. 8.
FIG. 8.

(Color online) This series of images shows the shear rate (1/s) for the eight cases listed in Table II .

Image of FIG. 9.
FIG. 9.

(Color online) Inlet pressure from the CFD calculations for cases 2 (“straight”) and 5 (“tapered”) of Table II . The tapered hole was run with flow in both directions, and it can be seen that the two curves are practically on top of each other. The velocity is shown simply for timing reference.

Image of FIG. 10.
FIG. 10.

(Color online) Dynamic flow resistances for 4 cases with straight holes (a) and 4 cases with tapered holes (b). CFD results (solid) are compared with results from Eq. (23) (dashed).

Image of FIG. 11.
FIG. 11.

(Color online) For a straight case (#2 in Table II ) the velocity magnitude (m/s) is shown in the upper row and the corresponding shear rate (1/s) is shown in the lower row. The times from left to right are at 30, 50, 70, and 90 s.

Image of FIG. 12.
FIG. 12.

(Color online) Resistance (a) and reactance (b) plots for a straight case (#2 from Table II ). Corresponding formula results using Eq. (22) , Eq. (1) (Maa), and Eq. (6) (Guo) with  = 2 and  = 4 are shown as well.

Image of FIG. 13.
FIG. 13.

(Color online) For the tapered case (#5 in Table II ) the velocity field (m/s) is shown in the upper row and the corresponding shear rate (1/s) is shown in the lower row. The times from left to right are at 30, 50, 70, and 90 s.

Image of FIG. 14.
FIG. 14.

(Color online) Resistance (a) and reactance (b) plots for straight and tapered cases (#2 and #5 from Table). Corresponding formula results using Eq. (23) are shown as well. Only a slight difference between forward and reverse flow can be seen in the resistance plot.

Image of FIG. 15.
FIG. 15.

(Color online) Dynamic flow resistances for cases with equal static flow resistance, from Table II . Sketches of the eight hole designs, all on equal scales, are shown so the length and diameter of the holes can better be compared; additionally, the horizontal extent of the film (shown shaded) gives an indication of the hole density.

Image of FIG. 16.
FIG. 16.

(Color online) Absorption coefficients for cases with equal static flow resistance, from Table II , and a rigidly terminated air space of 25 mm. Graph (a) shows results using the impedance from the CFD calculations, and graph (b) shows the results using the impedance from Eq. (23) .

Tables

Generic image for table
TABLE I.

Parameters defining the steady-state cases.

Generic image for table
TABLE II.

Parameters defining eight cases expected to have equal static flow resistance.

Generic image for table
TABLE III.

Parameters defining the time-dependent cases.

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/content/asa/journal/jasa/134/6/10.1121/1.4824968
2013-12-01
2014-04-20
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Transfer impedance of microperforated materials with tapered holes
http://aip.metastore.ingenta.com/content/asa/journal/jasa/134/6/10.1121/1.4824968
10.1121/1.4824968
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