Defined by (perforated plate)

For a perpendicular plate: whether the loss coefficient $K$ is typed directly (Resistance coefficient K) or computed from the open-area ratio (Open-area ratio) with Idelchik's thin- or thick-plate formula (Plate formula). Hidden for a perforated tube, whose $K$ always comes from the open-area ratio and the discharge coefficient.

Last updated 2026-11-03

Theory

The plate is a porous jump with $\Delta p = \tfrac12\rho K U_n^2$ (see Perforation type). A measured $K$ (or one from a manufacturer or a fine-mesh calculation of the holes) is the best input; when only the geometry is known, the program estimates $K$ from the open-area ratio $\sigma$ . The estimate is shown read-only on the card ("Estimated K") as soon as $\sigma$ (and, for the thick formula, the hole diameter and thickness) are entered.

Either way the solver receives the same two numbers: the inertial coefficient $I = K/t$ and the length $t$ (Plate / wall thickness), equation (1), with the Darcy coefficient (Darcy coefficient D) as a separate viscous term.

Equations

\Delta p = \left(\mu D + \tfrac12\rho\,I\,\lvert U_n\rvert\right) U_n\,t, \qquad I = \frac{K}{t}

(1)

K = K_{typed} \quad \text{(resistance coefficient)}, \qquad K = K_{Idelchik}(\sigma,\ t/d) \quad \text{(open-area ratio)}

(2)

where	meaning	unit
$\Delta p$	Pressure jump across the plate	Pa
$\mu$	Dynamic viscosity	Pa·s
$D$	Darcy coefficient	1/m²
$I$	Inertial coefficient of the jump	1/m
$t$	Plate thickness (the jump's length)	m
$U_n$	Velocity normal to the plate face	m/s
$\sigma$	Open-area ratio	-
$d$	Hole diameter	m

Default and rule

Default: open-area ratio (a new perforated wall); resistance coefficient K (a case file that stores no mode)
Rule: A new perforated wall is preset to the open-area ratio (the card then shows the estimated $K$ ). A case file that does not store the mode reads as "resistance coefficient" with its stored $K$ .
Source: The thin- and thick-plate formulas: (Idelchik, 2008), see Plate formula. The jump law is OpenFOAM's porousBafflePressure (OpenFOAM user guide, 2026). Validation on a straight two-body test pipe with a plate: 465 Pa against the 428 Pa the jump law predicts with the same $K$ (+8.7 %). The difference is the plate area left open by the boundary layers on the baffle, about 7 % below the cross-section.

Valid range open-area ratio | resistance coefficient K

Prefer a measured K

The open-area formulas assume sharp-edged holes at high Reynolds number ( $Re \ge 10^5$ ); burred, punched or very small holes deviate from them.

Plate only

For a perforated tube the mode is not used; $K = 1/(\sigma C_d)^2$ (Perforation type).

Theory

Equations

Default and rule

Valid range open-area ratio | resistance coefficient K

Related 6

References 2