On the use of the periodicity condition in cross-flow tube Boumedienne Beladjine, Mohammed Aounallah, Mustapha Belkadi, Lahouari Aadjlout and Omar Imine EPJ Web of Conferences, 92 (2015) 02005 Published online: 06 May 2015 DOI: 10.1051/epjconf/20159202005