Hello,
The Reynolds number depends on the diffusion coefficient you are using (and on a typical length depending on every geometry), if it is a matter of issuing it in the results, read the following.
There is a procedure to create new outputs in the results file. First there is a key word for allocating new arrays : NUMBER OF PRIVATE RRAYS (NOMBRE DE TABLEAUX PRIVES). These arrays are in a block called PRIVE (see programming guide to know what is a block), double precision values of array 1 are in PRIVE%ADR(1)%P%R. Then you can write what you want in this array in subroutine PRERES_TELEMAC2d (which then must be in your FORTRAN FILE). Then you have to add N for array 1, O for array 2, R for array 3 and Z for array 4 in key-word : VARIABLES FOR GRAPHIC OUTPUTS.
HOWEVER, in your case, the Reynolds number, once you have chosen a typical length, is proportionnal to the scalar velocity which is already programmed (letter M to add in the VARIABLES fOR GRAPHIC PRINTOUTS), this is probably simpler.
With best regards,
Jean-Michel Hervouet