# waveTransmissive边界条件

• 这个无反射边界条件具体怎么用呢？看了OpenFOAMwiki也是一头雾水。有两个疑问：
这个Ilnf和fieldIlnf的值怎么选呢？
这个条件如果用到出口有反压的情况，是否可以？

• @Aeronastro
看过这个描述么？

Description
This boundary condition provides an advective outflow condition, based on
solving DDt(psi, U) = 0 at the boundary.

The standard (Euler, backward, CrankNicolson) time schemes are
supported.  Additionally an optional mechanism to relax the value at
the boundary to a specified far-field value is provided which is
switched on by specifying the relaxation length-scale \c lInf and the
far-field value \c fieldInf.

The flow/wave speed at the outlet is provided by the virtual function
advectionSpeed() the default implementation of which requires the name of
the flux field \c (phi) and optionally the density \c (rho) if the
mass-flux rather than the volumetric-flux is given.

The flow/wave speed at the outlet can be changed by deriving a specialised
BC from this class and over-riding advectionSpeed()  e.g. in
waveTransmissiveFvPatchField the advectionSpeed() calculates and returns
the flow-speed plus the acoustic wave speed creating an acoustic wave
transmissive boundary condition.

\table
Property     | Description             | Required    | Default value
phi          | flux field name         | no          | phi
rho          | density field name      | no          | rho
fieldInf     | value of field beyond patch | no      |
lInf         | distance beyond patch for \c fieldInf | no |
\endtable

Example of the boundary condition specification:
\verbatim
myPatch
{
phi             phi;
}
\endverbatim

Note
If \c lInf is specified, \c fieldInf will be required; \c rho is only
required in the case of a mass-based flux.

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