Micro-perforation: hole diameter or slit width

The hole diameter (circular holes) or the slit width (slits) of a micro-perforated wall whose flow type is "Micro-perforated (laminar)". With an acoustic micro-perforate model the acoustic card's aperture is used instead (one input).

Last updated 2026-11-05

Theory

The aperture enters the linear flow term as $1/d^2$ (or $1/b^2$ ), so a small change of it changes the pressure drop much: 10 % smaller holes give 23 % more viscous loss Maa (1998) Kabral et al. (2014).

Equations

\Delta p = \left(\mu D + \tfrac12 \rho I |U|\right) U\,t, \qquad I\,t = \frac{2}{\sigma^2}

(1)

where	meaning	unit
$\Delta p$	Pressure jump across the wall	Pa
$U$	Velocity through the wall face	m/s
$t$	Wall thickness	m
$I$	Inertial coefficient	1/m

Default and rule

Default: 0.2 mm
Rule: 0.2 mm.
Source: Maa (1998) eq. 3a; Kabral et al. (2014) eq. 2; Allam and Abom (2011) eq. 23 (inertial term).

Valid range 0.05 - 1 mm (the micro-perforate models' range)

Sub-millimetre

Above about 1 mm the holes are no longer micro-perforations: use the perforated-tube or plate type.

Theory

Equations

Default and rule

Valid range 0.05 - 1 mm (the micro-perforate models' range)

Related 5

References 3