[sahm]

Hi
Has any body ever tried to understand the source code of WaveTransmissive and Advective Boundary conditions?
I have studied the paper by Poinsot and Lele and its relative papers, But i don't understand how the code does the method in the paper, can any body describe the parts of the code to me? specifically I would like to know what are refValue() and valueFraction().
Yours.

[cosimobianchini]

That notation is consistent with the notation of the base class: mixedFvPatchField<Type>.
It is substantially a linear combination of a fixedValue and a fixedGradient with coefficient valueFraction.
The formula implemented on the boundary is:
VF*FV+(1-VF)*FG*delta=VF*refValue+(1-VF)*refGrad

VF=valueFraction
FV= fixedValue coeffs
FG= fixedGrad coeffs


Expanding all the terms for the advective and waveTransmissive you will obtain an equation of the form of the NSCE (Eq.9:13 in Poinsot and Lele, "Boundary conditions for direct simulations of compressible viscous flow", J. Computational Physics 101 (104-129), 1992) without transverse and diffusive terms recovering the LODI relations as expressed in Eq.24:28 of the same paper.
Furthermore a Linear Relaxation Method similar to Eq.40 is implemented exploiting lInf and fieldInf.
In case of inviscid one-dimensional behavior on the boundary you only have to select the correct advection speed for each of uknown you are solving.

Hope you find this information useful,
Cosimo

[giovanni10]

The goal in many wave-dominated flows, such as high Mach number flow, is to have boundary conditions that do not reflect waves. Walls are reflective, but inlets and outlets are generally not supposed to reflect waves.

The waveTransmissive BC attempts to reconstruct this kind of non-reflective scheme, but in a simpler fashion without full inter-field coupling. Here is an example of how it is used for a pressure outflow boundary.

outflow
{

type waveTransmissive; value uniform 80000; //important for correct I/O

field p; //the name of the field that we are working on

gamma 1.4; //the ratio of specific heats

phi phiv; //the name of the volumetric flux field ( or if you use the mass flux phi, it will be divided by rho)

rho rho; //the name of the density field

psi psi; //the name of the field that is the deriv. of density with respect to pressure

lInf 0.05; //a measure of how far away the far-field condition should be

fieldInf 80000; //the far-field value to be applied to p

}

[immortality]

is waveTransmissive same as pressure farfield in fluent?
Then how does advective BC work?
Whats the difference between these three BC's?