[basecase]

Hi all - I'm an OpenFoam user but sadly, no coder

I currently use OpenFoam 7

I've used the fixedProfile inlet boundary condition with .csv files routinely without problem.

I am however stuck on the section in fixedProfileFvPatchField which refers to type as fixedProfile with profile assigned as - polynomial for the inlet BC.

I've researched fairly extensively and I apolgise if I missed a reference elsewhere that clarifies usage and might end my confusion. There are some references which refer to polynomials in profiles - but they don't seem to match my cases. The user guide alludes to polynomial functions in time dependent BCs - but those refs don't relieve my confusion.

I would be very grateful if some kind soul would explain in simple terms the numbers in the example quoted in fixedProfileFvPatchField documentation (below)-



inlet { type fixedProfile; profile polynomial ( ((1 0 0) (0 0 0)) ((-6200 0 0) (2 0 0)) ); direction (0 1 0); origin 0.0127; }


also U file from 0 folder for fully functioning pitzDaily version attached.


I have worked out some of the numbers - the max velocity of the function in the first set - and of course the direction and origin refs. I just can't quite get a handle on the remaining numbers - one looks like a coefficient for the profile function (in the above a parabola).

When I cut and paste the above into U in the 0 folder for pitzDaily the BC does indeed work well and deliver just what it says. Sadly that still hasn't brought enlightenment.
Attempts to plot the line function from the inlet (U @ t=0) in a spreadsheet have yielded little reward in terms of understanding - but a really nice parabola .

I have another less well defined question on this - the use of the term polynomial as in the attached (and above) implies the profile is flexible and not simply a parabolic profile function application. An understanding of the numbers will likely help me - but I would be grateful for any advice from those that have used this boundary condition to apply polynomials other than or in addition to parabolic functions as the inlet profile.

One last point - I'm not looking for alternative solutions to apply at this point - I'm on a mission of understanding that which I currently fail to grasp. And any advice of help would be very much appreciated.

Thanks

John Base

[bigphil]

I was also confused by this example.

I figured it out (with some help of my trusty LLM friend):

From PolynomialEntry.H, the header says:

PolynomialEntry container data entry for scalars. Items are stored in a
list of Tuple2's. Data is input in the form,
e.g. for an entry \<entryName\> that describes y = x^2 + 2x^3

Inline specification:
\verbatim
<entryName> polynomial
(
(1 2)
(2 3)
);
\endverbatim

For the pitzDaly inlet geometry, we can figure out that a parabola with a maximum velocity of 1 m/s has the equation Ux = - 6200 y^2 + 1, assuming y = 0 at the centre of the channel.

So, in this case, the entry is

profile polynomial
(
    ((1 0 0)        (0 0 0))  // Coefficient for x^0 = 1 (constant term)
    ((-6200 0 0)    (2 0 0))  // Coefficient for x^2 = -6200
);