# scalar-quadrangle-value in Gmsh's ASCII post-processing file

**Robert Jurjevic**
robert.jurjevic at bhead.co.uk

*Tue Mar 13 11:27:48 CET 2001*

Dear Mr Remacle and Geuzaine,
Thank you for developing Gmsh!
My name is Robert Jurjevic and some time ago I wrote a solver for a
classical fluid mechanics system of partial differential equations modelling
two-dimensional stationary incompressible Newtonian fluid flow.
I tried the solver on classical examples of driven cavity laminar flow,
laminar flow past a cylinder and a laminar flow past a symmetric NACA
airfoil.
I used 2D 8-node superparametric (pressure) and isoparametric (velocity)
quadrilateral finite elements.
Pre- and post-processing has been handled using I-DEAS Finite Element
Modelling software running on an HP UNIX workstation.
Now when there is a Gmsh, I thought that I could produce a coloured picture
of a NACA airfoil pressure field on my PC.
I kindly beg you if you could answer the following questions. Thank you.
QUESTIONS
1. Is there a scalar-quadrangle-value equivalent of the
scalar-triangle-value in the Gmsh ASCII post-processing file. The pressure
in my examples is calculated using 2D 8-node superparametric quadrilateral
finite elements, but approximation with 2D 4-node isoparametric
quadrilateral finite elements will do fine. I know that I can approximate a
2D 4-node isoparametric quadrangle finite element with two 2D 3-node
isoparametric triangular finite elements, but I would like to avoid that
(extra work and the error).
2. Do you intend to implement the support for 2D 8-node isoparametric finite
elements (for both pre- and post-processing)? If you introduce something
like vector-quadrilateral8-value I would be able to present the velocity
field (variable length arrows i presume).
If I manage to produce the colourful picture of pressure field for the flow
around the airfoil I will send it (the picture or the data to generate the
picture) to you.
In fact the sole purpose of producing the pressure picture is due to its
aesthetic value and I regard it as a peace of scientific art.
Yours sincerely,
Robert Jurjevic