Hole diameter

perforate.tube_hole_diameter Unit: mm (stored in m) Step 05 · Boundary Conditions

The diameter of the holes of a perforated tube, or of a perpendicular plate with the thick-plate formula. It selects the no-grazing discharge coefficient $C_{D0}$ (with the thickness) and the $l/d$ of the thick plate; in a flow + acoustics run it is also the hole diameter of the acoustic model.

Last updated 2026-11-03

Theory

For a perforated tube the hole diameter $d$ and wall thickness $t$ fix $C_{D0}$ by bilinear interpolation in Elnady's measured table (Discharge coefficient C_D0); $C_{D0}$ then gives the starting loss coefficient $K_0 = 1/(\sigma C_{D0})^2$ (Jet loss K0 (read-only)). The grazing correction is checked against the orifices Rogers and Hersh tested, $1 \le d \le 12.7$ mm and $0.12 \le t/d \le 2$ (Rogers and Hersh, 1975); outside, an advisory note is recorded with the K update.

For a thick perpendicular plate $d$ gives $l/d = t/d$ (Plate formula). When this card owns the hole diameter (a perforated tube, or a thick plate) the acoustic section of the card does not ask for it again (Hole diameter (acoustics)).

Equations

C_{D0} = C_{D0}^{table}(d,\,t), \qquad K_0 = \frac{1}{(\sigma\,C_{D0})^2}, \qquad \frac{l}{d} = \frac{t}{d}

(1)

where	meaning	unit
$d$	Hole diameter	m
$t$	Wall thickness	m
$C_{D0}$	No-grazing discharge coefficient	-
$\sigma$	Open-area ratio	-
$K_0$	Starting loss coefficient of the tube	-

Default and rule

Default: none stored; the card pre-fills 3 mm
Rule: None is stored for a new perforated wall; the card pre-fills 3 mm and saves what is shown. A perforated tube needs it unless a discharge coefficient is typed.
Source: Table: Elnady's doctoral thesis (KTH 2004, Paper III, Table 1; the related paper is (Elnady et al., 2010)). Grazing range: (Rogers and Hersh, 1975).

Valid range d > 0; discharge table 0.6-5 mm, measured 0.6-2.4 mm

Table range

The table spans 0.6-5 mm; outside it the edge value is used. Elnady measured 0.6-2.4 mm; larger holes are his extrapolation (above 2.5 mm $C_D$ depends on the thickness only). The card says when either applies.

Grazing data

Rogers and Hersh measured holes of 1-12.7 mm; a hole outside that range gets a note in the run's K-update log (logs/perforate_k.json).

Theory

Equations

Default and rule

Valid range d > 0; discharge table 0.6-5 mm, measured 0.6-2.4 mm

Related 5

References 2