Theory

Steady laminar flow through a circular hole of diameter $d$ loses $32\mu t U_h/d^2$ (Poiseuille), through a slit of width $b$ $12\mu t U_h/b^2$ ; with the hole velocity $U_h = U/\sigma$ these are the linear terms of the wall's pressure jump Maa (1998) Kabral et al. (2014). With acoustics on, the wall's impedance model is always a micro-perforate model, which already says holes (Maa) or slits: its shape is used and this choice is hidden. It is shown only in a flow-only case, where no impedance model is chosen.

Equations

D = \frac{32}{\sigma d^2} \ \text{(holes)}, \qquad D = \frac{12}{\sigma b^2} \ \text{(slits)}

(1)

where	meaning	unit
$D$	Darcy coefficient of the pressure jump	1/m^2
$\sigma$	Open-area ratio	-
$d, b$	Hole diameter, slit width	m

Default and rule

Default: circular holes
Rule: Circular holes.
Source: Maa (1998) eq. 3a (zero-frequency limit); Kabral et al. (2014) eq. 2 (zero-frequency limit).

Valid range circular holes | slits

Shape

Holes or slits; the aperture is entered next to it.

Micro-perforation: holes or slits

Theory

Equations

Default and rule

Valid range circular holes | slits

References 2

Theory

Equations

Default and rule

Valid range circular holes | slits

Related 5

References 2