Hydraulic diameter

From CFD-Wiki

Revision as of 14:01, 24 March 2006 by Jola (Talk | contribs)

(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)

Jump to: navigation, search

The hydraulic diameter, $d_h$ , is commonly used when dealing with non-circular pipes, holes or ducts.

The definition of the hydraulic diamater is:

$d_h \equiv 4 \; \frac{\mbox{cross-sectional-area of duct}}{\mbox{wetted perimeter of duct}}$

Use of hydraulic diameter

=Estimating the turbulent length-scale

For fully-developed flow in non-circular ducts the turbulent length-scale can be estimated as $0.07 d_h$ . This is as usefull estimation for setting the turbulence boundary conditions for inlets that have fully developed flow.

Hydraulic diameters for different duct-geometries

Using the definition above the hydraulic diamater can easily be computed for any type of duct-geometry. Below follows a few examples.

Circular pipe

For a circular pipe or hole the hydraulic diamater is:

$d_h = 4 \; \frac{\frac{\pi d^2}{4}}{\pi d} = d$

Where d is the real diameter of the pipe. Hence, for circular pipes the hydraulic diameter is the same as the real diameter of the pipe.

Rectangular tube

For a rectangular tube or hole with the width $a$ and the height $b$ the hydraulic diamter is:

$d_h = 4 \; \frac{a b}{2 a + 2 b} = 2 \; \frac{a b}{a + b}$

Coaxial circular tube

For a coaxial circular tube with an inner diameter $d_i$ and an outer diameter $d_o$ the hydraulic diameter is:

$d_h = 4 \; \frac{\frac{\pi d_o^2}{4} - \frac{\pi d_i^2}{4}}{\pi d_o + \pi d_i} = d_o - d_i$

Hydraulic diameter

From CFD-Wiki

Contents

Use of hydraulic diameter

=Estimating the turbulent length-scale

Hydraulic diameters for different duct-geometries

Circular pipe

Rectangular tube

Coaxial circular tube

Views

My wiki

wiki navigation

wiki search

wiki toolbox