fluent中多孔介质模型的设置 - 图文

(7.19-20)

and dividing by the plate thickness,

(7.19-21)

, we obtain

where is the superficial velocity (not the velocity in the holes).

Comparing with Equation 7.19-6 it is seen that, for the direction normal to the plate, the constant

(7.19-22)

can be calculated from

Using Tabulated Data to Derive Porous Media Inputs for Laminar Flow Through a Fibrous Mat

Consider the problem of laminar flow through a mat or filter pad which is made up of randomly-oriented fibers of glass wool. As an alternative to the Blake-Kozeny equation (Equation 7.19-16) we might choose to employ tabulated experimental data. Such data is available for many types of fiber [ 158].

volume dimensionless fraction of permeability solid of glass wool material 0.262 0.258 0.221 0.218 0.172

0.25 0.26 0.40 0.41 0.80 where and is the fiber diameter. , for use in

Equation 7.19-4, is easily computed for a given fiber diameter and volume fraction.

Deriving the Porous Coefficients Based on Experimental Pressure and Velocity Data

Experimental data that is available in the form of pressure drop against

velocity through the porous component, can be extrapolated to determine the coefficients for the porous media. To effect a pressure drop across a porous medium of thickness, , the coefficients of the porous media are determined in the manner described below. If the experimental data is:

Velocity (m/s) Pressure Drop (Pa) 20.0 50.0 80.0 110.0 78.0 487.0 1432.0 2964.0

then an curve can be plotted to create a trendline through these points yielding the following equation

(7.19-23)

where

is the pressure drop and is the velocity.

Note that a simplified version of the momentum equation, relating the pressure drop to the source term, can be expressed as

(7.19-24)

or

(7.19-25)

Hence, comparing Equation 7.19-23 to Equation 7.19-2, yields the following curve coefficients:

(7.19-26)

with

kg/m , and a porous media thickness,

, assumed to be .

1m in this example, the inertial resistance factor, Likewise,

(7.19-27)

with factor,

.

, the viscous inertial resistance

Note that this same technique can be applied to the porous jump boundary condition. Similar to the case of the porous media, you have to take into account the thickness of the medium . Your curve, yielding an experimental data can be plotted in an

equation that is equivalent to Equation 7.22-1. From there, you can determine the permeability and the pressure jump

coefficient

.

Using the Power-Law Model

If you choose to use the power-law approximation of the porous-media momentum source term (Equation 7.19-3), the only inputs required are the coefficients and. Under Power Law Model in the Fluid panel, enter the values for C0 and C1. Note that the power-law model can be used in conjunction with the Darcy and inertia models. C0 must be in SI units, consistent with the value of C1.

Defining Porosity

To define the porosity, scroll down below the resistance inputs in the Fluid panel, and set the Porosity under Fluid Porosity.